Corals and coral reefs of the Pacific coast of Colombia
Fernando A. Zapataa and Bernardo Vargas-Ángelb
aDepartamento de Biología, Universidad del Valle. Apartado Aéreo 25360, Cali, Colombia bNational Coral Reef Institute, Nova Southeastern University, 8000 North Ocean Drive,
Dania Beach, Florida 33004 USA
ABSTRACT: Based on a literature review and our own research, we examine coral reef development on the Pacific coast of Colombia. Several. We provide a historical outline of the research, a summary of studies on coral community distribution, composition and ecological structure, a discussion on natural and anthropogenic impacts and effects, and finally, an overview of the current conservation and management status. Coral reef development in this area of the eastern Pacific is marginal, and communities are small, species poor (only 21 species of zooxanthellate corals), and discontinuously distributed. They occur in a variety of environmental settings ranging from coastal (Ensenada de Utría and Tebada), to continental insular (Gorgona Island), to oceanic (Malpelo Island). The largest (~10 ha), most developed (up to ~8 m thick), and species-rich coral reefs are located at Gorgona Island. These fringing reefs show a diffuse zonation pattern characterized by the dominance of pocilloporid corals on the shallow reef flat and the presence of massive colonies of Pavona and Gardineroseris on the deeper outer reef base. Coral and coral reef development on the Pacific of Colombia is limited due to suboptimal climatic and oceanographic conditions such as a narrow continental shelf, intense rainfall (which results in elevated terrestrial run-off and turbidity, and reduced light and salinity conditions), and extreme temperature fluctuations caused by sporadic upwelling and El Niño. Most important among these are El Niño warming events, which have caused coral bleaching and mortality since at least 1983. In addition to recurrent El Niño conditions, other natural disturbances affect the coral reefs in this region, including periodic sub-aerial exposure during extreme low tides, high sedimentation, seasonal upwelling, and tectonic activity. Most of the areas with coral reef development on the Colombian Pacific are legally protected. However, all are subject to sporadic anthropogenic impacts. Human disturbances are lowest on the remote Malpelo Island and highest on the northern coastal reefs. Corals reefs of the Colombian Pacific constitute a key marine biotope, and provide economic and social assets as habitats for artisanal fisheries, as well as recreation and educational activities. Further studies addressing basic questions and management and conservation issues are necessary.
1. INTRODUCTION
The first observations on coral formations from the Colombian Pacific coast were made by Crossland (1927), who reported results of the S.Y. St. George Expedition to the south Pacific, and by Durham and Barnard (1952), who reported results of the Velero III and IV cruises in the eastern Pacific. In 1968 the Stanford Oceanographic Expedition 18 aboard de RV Te Vega made short visits to Gorgona, Bahía Solano and
Bahía Cupica and briefly described subtidal stations and made limited observations on coral formations and associated fauna (Youngbluth 1968a, b). The first formal descrip-tion of a coral formation in the Colombian Pacific was made by Birkeland et al. (1975) for Malpelo Island. The late H. von Prahl and his co-workers made qualitative descrip-tions of coral reef structure at Gorgona Island and discussed diverse ecological aspects (Prahl et al. 1979). Their pioneering work was later complemented by quantitative studies on the distribution, zonation, and community structure of corals and corallivores (Glynn et al. 1982; Cantera 1983). The structure and species diversity of coral formations in the northern portion of the Colombian coast, particularly at Ensenada de Utría, was later described (Vargas-Ángel 1988, 1989, 1996). Species lists, illustrations, and accounts for identification purposes of Colombian Pacific corals were provided by Prahl (1985a, 1986b, 1987a) and Prahl and Erhardt (1985).
Other works on corals and coral reefs from the Colombian Pacific include studies on coral growth at several localities (Prahl 1986d; Prahl et al. 1987; Prahl and Vargas-Ángel 1990), coral growth forms and their implications for coral taxonomy and systematics (Cantera et al. 1989; Prahl and Estupiñán 1990), biogeographical studies (Prahl 1986c; Prahl et al. 1990a, b), effects of the 1982–83 El Niño event (Prahl 1983a, 1986e, 1987b; Prahl et al. 1989), and the contribution of sea urchins (Toro 1998) and parrot fishes (Jiménez 1999) to reef erosion. Taxonomic and ecological studies on animal communities associated with coral reefs in the Colombian Pacific include studies on symbiotic crustaceans associated with pocilloporids (Abele 1975; Castro 1982; Prahl 1982, 1983b, 1986f; Ríos 1986, 1987; Escobar and Barbosa 1992; Navas 1993; Barbosa 1994), molluscan assemblages (Cantera et al. 1979; Cosel 1986; Cantera and Contreras 1988; Ocampo and Cantera 1988; Cantera and Arnaud 1995), echinoderms (Neira and Prahl 1986; Pardo 1989) and fishes (McCosker and Rosenblatt 1975; Findley 1975; Zapata 1982, 1987; Rubio 1986, 1990; Rubio et al. 1987, 1992; Estupiñán et al. 1990; Guzmán and López 1991; Zapata and Morales 1997; Giraldo et al. 2001; Mora et al. 2001; Mora and Ospina 2001; Zapata and Herrón in press). Much of the early information had already been summarized (Prahl and Erhardt 1985; Prahl 1986b; UNEP/IUCN 1988).
This chapter provides a synthesis of current knowledge on the ecology of coral communities and coral reefs in the Colombian Pacific Ocean. Major emphasis is placed on the distribution of coral formations, the community structure of corals, and the effects of natural and anthropogenic disturbances on the reefs. 2. DESCRIPTION OF CORAL REEF AREAS 2.1. Distribution and community structure
The distribution of corals and coral reef communities in the Colombian Pacific Ocean is directly related to the presence of hard substrates and clear waters, away from the influence of major river discharge and mangrove forests. According to their geo-graphical location and following a nearshore-offshore gradient, coral formations in Colombian Pacific waters can be divided into three main groups (Fig. 1): 1) the northern, coastal reefs of the Gulf of Cupica and Ensenada de Utría; 2) the southern, continental-island reefs of Gorgona; and 3) the oceanic-island coral formations of Malpelo.
In general terms low species richness and strong dominance by one or two species characterize coral communities along the Pacific coast of Colombia and adjacent waters. A total of 21 coral species has been observed, with a minimum of 7 and a maximum of
Corals and coral reefs of the Pacific coast of Colombia 421
Fig. 1. Map of the Pacific coast of Colombia showing the location of major coral formations (Tebada, Ensenada de Utría, Gorgona Island and Malpelo Islands). Other reference points mentioned in the text are also shown. 18 species occurring at any one locality (Table 1). Although these estimates are based on the best available information, the state of knowledge on coral taxonomy and sys-tematic in the tropical eastern Pacific (TEP) is still inadequate. Despite the depauperate nature of the TEP coral fauna (Glynn and Ault 2000), new species are still being described (e.g., Glynn et al. 2001). A major revision of the genus Pocillopora is badly needed, and a revision of the genus Pavona is currently under way (J.L. Maté per. com.). Four new records have recently been added to the list of previously known coral species reported for the Colombian Pacific ocean (Table 1) and it is likely that a few other species will be added to the list as knowledge of coral taxonomy in the area improves.
Climatic and oceanographic conditions in the Colombian Pacific are thought to be suboptimal for coral reef development (Glynn et al. 1982). On the one hand, narrow and steep platforms restrict reef development. On the other hand, salinity and light levels are severely reduced due to high river input and high cloud cover in one of the rainiest regions of the world. Mean annual precipitation exceeds 5000 mm over most of the coast,
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TABLE 1 Known zooxanthellate scleractinian coral species from the Colombian Pacific Ocean. + = species present, ? = unconfirmed record. Numbers in parentheses indicate information sources as follows: 1 = Birkeland et al. (1975), 2 = Glynn et al. (1982), 3 = Cantera (1983), 4 = Prahl and Mejía (1985), 5 = Prahl and Erhardt (1985), 6 = Prahl (1986b), 7 = Prahl (1990), 8 = Guzmán and Cortés (1993), 9 = Vargas-Ángel (1996), 10 = J. Garzón-Ferreira, photographic record, 11 = Garzón-Ferreira and Pinzón, (1999), 12 = H.M. Guzmán, per. com., 13 = B. Vargas-Ángel, unpubl. data, 14 = F.A. Zapata, per. obs.
Species Localities Malpelo Gorgona Ensenada de Utría Tebada
although it is lower in the south and greater in the north, reaching 7000 mm or more in some areas (West 1957; Eslava 1993). Intense rainfall during the rainy season increases the concentration of suspended particulate matter at sea, often leads to topsoil runoff, and even occasional landslides. Finally, coral reefs of the Pacific coast of Colombia are also subject to periodic, severe natural disturbances. Intense upwelling in the Gulf of Panama (Legeckis 1988) lowers sea surface temperatures (SST) down to as low as 16°C (Vargas-Ángel 1996), whereas occasional very-strong El Niño events increase SST causing thermal stress, bleaching and coral mortality (Prahl 1983a; Vargas-Ángel 1996 per. obs.). 2.1.1. Coastal reefs. Few true coral reefs occur along the Colombian Pacific coast. Except for the small reefs in Ensenada de Utría and the Gulf of Cupica (Tebada), only isolated coral colonies and small build-ups are sparsely distributed along the coast at localities such as Cabo Corrientes, Bahía Solano, and Punta Cruces (Prahl and Erhardt
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Fig. 2. Location of the northern, coastal reefs of the Pacific coast of Colombia. A) Ensenada de Utría with planar view of La Chola Reef. Other sites with coral reefs (triangles) or coral communities (circles) are also shown. B) Location of Tebada Reef. 1985; B. Vargas-Ángel per. obs.). Isolated colonies of Pocillopora spp. occur as far south as Isla de Palma (Bahía de Málaga: Escobar and Neira 1992; per. obs.).
Ensenada de Utría. Coral reefs at Ensenada de Utría National Park have developed on relatively shallow substrates in sheltered bays. Two main coral reefs occur in the Utría region: these are La Chola reef (following Prahl and Erhardt 1985) and Diego reef (Fig. 2a). La Chola reef, is the largest coral reef (ca. 10.5 ha), and is located on the east margin of Ensenada de Utría. According to Prahl (1986f), in 1981 La Chola reef was characterized by a lush and diverse coral assemblage, including several species of Pocillopora, as well as Psammocora stellata, Pavona clavus, Pavona gigantea and Porites spp. To date (Vargas-Ángel 1996, 2001), little or no evidence of the past occurrence of a complex and diverse coral community at La Chola reef has been found. Coral community surveys conducted in 1988–89 (Vargas-Ángel 1996) showed that La Chola reef was composed predominantly of thin-branched ecomorphs of Pocillopora
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damicornis (80% of colonies), and Psammocora stellata (16%). Other species present included Pocillopora capitata (approx. 4%), Pavona varians and Pavona gigantea (< 1%). Also, mean live-coral cover at La Chola reef was not greater than 33% and the spatial distribution of live corals was highly patchy. All areas where live cover exceeded 60% were associated with dense monospecific stands of Pocillopora damicornis. Lower coral cover (< 20%) occurred in areas where P. damicornis was less abundant or absent. In addition, diversity indices (Shannon-Wiener's H') were overall low (0-1.6), not only because of the reduced coral species richness, but also due to the overwhelming dominance of P. damicornis. Although mean percent cover at La Chola reef was greater along the northern sector (45.3%) than at the central and southern sectors (26.5% and 26.8%, respectively), differences were not significant. By contrast, coral cover was significantly lower on the seaward slope than on the reef flat and leeward zones. Live coral cover varied inversely with coral species diversity and richness, which were highest at the central and southern sectors of the reef. Only a weak coral zonation pattern was evident at La Chola reef, where coral cover decreased from north to south and from inshore to offshore (Vargas-Ángel 1996).
Coral community surveys conducted in 1995–96 (Vargas-Ángel 2001) showed that neither mean coral cover nor species relative abundance had changed substantially at La Chola reef since 1989. By contrast, shifts in community composition have occurred, including: 1) the spatial re-distribution of the dense monospecific stands of Pocillopora damicornis from the leeward area to the central reef flat, and 2) a notable increase in macro-algal cover (Vargas-Ángel 2001). Although La Chola reef seems to have suffered a long history of sedimentation and siltation stress (discussed below, but see Murphy 1939; Prahl and Vargas-Ángel 1990; Vargas-Ángel 1996, 2001), it is still premature to consider these recent changes in community structure as evidence of degradation. In fact, spatial and temporal heterogeneity in coral reef communities can result from adaptation and recovery to various stressors on numerous and complex scales (Connell 1978; Brown and Howard 1985; Grigg and Dollar 1990; Reice 1994; Grigg 1995).
Other coral communities at Utría include Diego reef, as well as sparse, small coral aggregations and build-ups at Punta Diego, Playa Blanca and Cocalito, which do not form true constructional reefs. In comparison to La Chola reef, Diego reef is a much smaller formation (ca. 1.5 ha). The reef flat starts at approximately 100 m offshore; it extends seaward for approximately 150 m at a depth of 2.0–2.5 m, and then slopes gradually to 6.0 to 8.0 m depth at the reef base. Diego reef is covered mainly by coral rubble and encrusting coralline algae. According to Vargas-Ángel (1996 and per. obs.) live cover does not exceed 2%; it consists mainly of Psammocora stellata, with very few sparsely scattered colonies of Pocillopora damicornis. No live or dead massive coral colonies have been found on Diego reef, yet large colonies of Pavona clavus, P. gigantea, and Porites lobata occur along the wave-exposed basaltic rocks of Punta Diego (Vargas-Ángel per. obs). In 1981, when Prahl visited the zone, he characterized Diego reef (referred to as Playa Blanca reef by Prahl and Erhardt 1985, p. 281, see Vargas-Ángel 1996) as having a mature structure dominated by Pocilloporids and Psammocora, with isolated colonies of Pavona gigantea, P. clavus, P. varians and Porites panamensis. Present day coral community composition and structure suggest that Diego reef has been severely disturbed, and community recovery to a pre-disturbance stage has not yet oc-curred. Severe bioerosion in excess of accretion (Vargas-Ángel in progress) seems to have been an important factor in reducing this reef structure to rubble and sediments.
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Trying to assess and characterize the causes of coral reef community deterioration at Utría (i.e., La Chola and Diego reefs) has been difficult due to the lack of data prior to 1989, when the first quantitative surveys were conducted. It has been suggested (Vargas-Ángel 1996) that natural and anthropogenic disturbances, including El Niño Southern Oscillation (ENSO), terrigenous siltation, dynamite fishing, recurrent low tides (discussed below) and bioerosion must have played pivotal roles in coral community deterioration and demise at Utría. Sclerochronological and sedimentary studies have provided evidence that ENSO events and chronic siltation are important stressors limiting coral growth and reef development at Utría (Vargas-Ángel 2001; see bellow).
Tebada. Tebada reef, (ca. 6°32’N, 77°21’W) is located south of Bahía Cupica (Fig. 1), and not at the north of it as presented in Prahl and Erhardt (1985 p. 279). Tebada reef is separated from the mainland by a channel of ca. 500 m, and is protected from ocean surge by a chain of small islets and rocky outcrops (Fig. 2b). The reef is a shallow, gently-sloping platform of approximately 4.5 ha, which is not subaerially exposed during extreme low tides (mean depth close to 2.0 m). Although several species of reef corals are present, including Pavona varians, Pocillopora damicornis, and Pavona gigantea, Psammocora spp. are dominant, accounting for over 80% of the total live coral cover. Reef probings done in 1996 indicate that this reef has a vertical buildup of at least 4 m on the reef flat (B. Vargas-Ángel unpubl. data). 2.1.2. Insular reefs. There are two contrasting insular environments with significant coral formations within Colombian Pacific waters: Gorgona Island and Malpelo Island. Gorgona (2º59’N, 78º12’W) is a continental island located approximately 35 km off the nearest point on the Colombian Pacific coast (Fig. 1) within the area of influence of the Intertropical Convergence Zone (ITCZ). The periodical displacement of the ITCZ pro-duces a unimodal, biseasonal pattern of precipitation at Gorgona with a wetter season between May and October. Mean annual precipitation is about 6700 mm at Gorgona and 4900 mm at the mainland in front of it (Rangel and Rudas 1990). Even though sea surface temperatures around Gorgona (normally between 26–29°C) are within the range of temperatures for vigorous coral growth and reef development, salinity (between 30–33 ppt) and water clarity (< 5–25 m) are decreased by the freshwater input caused by the abundant rain. Therefore, the strong influence of the nearby continental estuarine envi-ronment most likely limits the development of coral reefs at Gorgona Island. In contrast, Malpelo (3°51'N, 81°35'W) is a small oceanic island of volcanic origin located approxi-mately 400 km west of the Pacific coast of Colombia (Fig. 1). It is the only emergent pinnacle of the Malpelo ridge (Chase 1968), separated from mainland Central and South America by depths greater than 3000 m (Graham 1975). Malpelo island is thus surrounded by clear oceanic waters which allow corals to be present as deep as 30 m, which is close to the maximum depth for the occurrence of corals in the Panamic Province (Graham 1975) and second only to Clipperton Island in the TEP, where corals occur as deep as 60 m (Glynn et al. 1996). SST at Malpelo normally ranges from 26–28ºC, but tem-peratures below 30 m depth are often below 20ºC. Salinity is relatively constant, varying between 32–33 ppt, although occasionally it drops down to 30 ppt (Stevenson et al. 1970).
Gorgona Island. Like most reefs in the tropical eastern Pacific, the coral reefs of Gorgona Island cover a small area, are patchily distributed and show modest develop-ment. Yet Gorgona's reefs are among the best developed within the region, similar to those in the Gulf of Chiriquí in Panama (Glynn and Wellington 1983; Guzmán and Cortés
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Fig. 3. Map of Gorgona Island showing distribution of coral formations, major topographic features and distribution of freshwater streams. Planar view of major coral formations are shown. Reefs with relatively high live coral cover are indicated in solid black, whereas former reef areas reduced to rubble or significantly deteriorated are indicated with a dashed pattern. Based on aerial photographs from Instituto Geográfico “Agustín Codazzi”, a map in Glynn et al. (1982), and personal observations. 1993; Cortés 1997). Additionally, Gorgona's reefs are unique in that they are located in a non-upwelling area of the TEP and are free of predation by a major corallivore, the crown-of-thorns starfish (Acanthaster planci: Glynn et al. 1982; Glynn and Wellington 1983). Coral formations around the island show varied degrees of development, includ-ing coral communities, incipient reefs, and well-developed fringing reefs. Some of these reefs are the most mature and best studied coral reefs of the Colombian Pacific (Prahl et al. 1979; Glynn et al. 1982; Prahl and Erhardt 1985; Prahl 1986b).
Except for one small reef, all coral formations at Gorgona are located on the eastern, leeward side of the island (Fig. 3). Prahl et al. (1979) speculated about the causes of this uneven distribution of coral formations around Gorgona and attributed it to: 1) low sa-linity stress due to an assumed greater number of freshwater streams discharging on the west side of the island; 2) lower and more variable water temperatures on the western
Corals and coral reefs of the Pacific coast of Colombia 427
side of Gorgona; 3) stronger wave action on the western shore causing resuspension of sediment, increased turbidity and decreased light penetration in addition to substrate fragmentation and instability; and 4) a smaller shelf area on the western side. However, except for the fact that the number of freshwater streams on either side of the island is almost identical (west = 12, east = 11) thus not lending support to the first hypothesis, there is a lack of detailed knowledge on the local oceanography and the physical envi-ronment around Gorgona necessary to test the above hypotheses (but see general oceanographic descriptions by Prahl et al. 1979; Glynn et al. 1982; Prahl 1986a). Addi-tionally, the relative inaccessibility of the western shore by both land and sea has made it difficult to study this side of the island.
Coral communities. Coral communities (i.e., characterized by the dominance of hermatypic corals but lacking a significant reef frame buildup) are common around Gorgona. Several coral communities, with up to 30% live coral cover, are patchily dis-tributed on rocky substrates from the northernmost tip of Gorgona and moving southward along the eastern coast (Fig. 3). These are briefly mentioned by most authors (Prahl et al. 1979; Glynn et al. 1982; Cantera 1983; Prahl and Erhardt 1985; Prahl 1986b), but remain largely undescribed except for limited observations (Glynn et al. 1982; López-Giraldo 1992). These communities are located at El Horno, El Remanso, Yundigua, and Playa Pizarro. These communities, but particularly those at El Remanso and Playa Pizarro appear to be the remains of former fringing reefs judging by the amount of coral rubble present in the area. Other coral formations previously reported at Gorgona (Glynn et al. 1982) but now reduced include those at La Gómez, La Ventana, and the Paso de Tasca area. Most likely, these reefs deteriorated significantly during the strong El Niño event of 1982–83 and unlike other reefs at Gorgona have not yet recovered.
Incipient reefs. At least four areas around Gorgona (Fig. 3) have incipient coral reef developments, which have been briefly described (Glynn et al. 1982; López-Giraldo 1992). At La Gómez there is a series of linear ridges formed by pocilloporids, similar in appearance to those at La Camaronera (see below). The linear ridges appear to be formed in response to prevailing wind and wave conditions. The shallow shelf in the areas of La Gómez and La Ventana support dense stands of Pocillopora spp. with a vertical buildup of approximately 1 m (Glynn et al. 1982). In the Paso de Tasca area, the strait between Gorgona and the islet of Gorgonilla, there is one small reef (ca. 200–250 m long) located at the northern tip of Gorgonilla and a few, small coral patches built mainly by pocil-loporids. This reef, also known as Los Farallones reef, has a vertical buildup of 1–2 m, and is similar in structure and zonation to La Azufrada and Playa Blanca reefs (Glynn et al. 1982; Prahl and Erhardt 1985; Prahl 1986b; López-Giraldo 1992). Much of the reef flat consists of a dead pocilloporid frame tightly bound by coralline algae, whereas the reef crest and upper slope are dominated by living pocilloporids (Glynn et al. 1982). The outer reef base consists of a sandy and bioclastic plain dominated by many large colonies of massive species, mainly Pavona gigantea, growing a few meters apart (F.A. Zapata per. obs.).
The main reef on the western side of the island, known as La Camaronera reef, is located on a rocky headland between the sandy beaches of La Camaronera and El Cocal. This area is characterized by strong wave action. Two kinds of coral formations in this area have been briefly described (Glynn et al. 1982): 1) a series of small, shallow reefs consisting of a reef flat formed by a tightly intermeshing framework of Pocillopora spp. lying on a basalt substrate, and sloping sharply to a sandy bottom at 4 m depth. 2) Several
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linear spurs located further offshore and oriented parallel to the prevailing wave direction, formed by pocilloporids and having a vertical buildup of 2–3 m. Some spurs lack any live coral and appear to be accumulations of coral rubble bound together by coralline algae. Along with these and further north, at the southern end of La Camaronera Beach, there are numerous hillocks of various sizes built also by pocilloporids. All of these formations lack any evident zonation. Crustose coralline algae binding the reef frame were more evident on these windward reefs than on those on the leeward side of the island (Glynn et al. 1982; F.A. Zapata per. obs.).
Fringing reefs. Old Pier reef. This small fringing reef (about 45 m long and covering an area of
about 0.16 ha) is located south of the remains of a large wooden pier destroyed in 1984. Although a total of 10 species of corals, including species of Psammocora, Porites and Pavona, have been previously observed on this reef (Cantera 1983), it is now made up almost entirely of pocilloporids, mainly Pocillopora damicornis (F.A. Zapata per. obs.). Total live coral cover varies from 20% in the backreef and lower slope to 85% on the reef front. Whereas species richness tends to be greater on the reef flat and crest, species diversity increases steadily from the backreef to the reef front (Cantera 1983). Despite its small size, the reef is similar in structure and zonation to other larger fringing reefs on the island (see below). It has a relatively extensive reef flat followed by a steep (ca. 60°) reef front, and at about 6 m depth, by a sand plain composed of bioclastic and car-bonate debris (Glynn et al. 1982; Cantera 1983; Prahl and Erhardt 1985; Prahl 1986b). The reef frame may have a vertical buildup of up to 6 m (Glynn et al. 1982).
La Azufrada reef. This is the largest, continuous coral reef of Gorgona Island, as well as the best studied (Prahl et al. 1979; Glynn et al. 1982; Prahl and Erhardt 1985; Prahl 1986b; see also Cantera and Arnaud 1995; Zapata and Morales 1997). Direct measurements made recently, however, indicate that it is slightly smaller (780 m long and 80–180 m wide) than previously reported (Glynn et al. 1982), covering about 11.2 ha (F.A. Zapata et al. unpubl. data). Glynn et al. (1982) observed 10 coral species on this reef; it is clearly dominated by pocilloporids, but also includes (in decreasing order of importance) species of Psammocora, Pavona, Porites, and Gardineroseris. Live coral cover varies from < 50% in the backreef up to > 80% on the reef crest and front (Glynn et al. 1982; Prahl 1986b; F.A. Zapata et al. unpubl. data). On the backreef and reef flat, the continuity of live coral is occasionally interrupted by relatively large patches of dead pocilloporid fragments, among which many small, live colonies of Psammocora are found covering a significant proportion of the substrate (ca. 40%). Species richness and diversity are variable but overall higher on the reef crest and upper slope than elsewhere. The reef has a coral framework buildup varying from 2 to 8.3 m (Glynn et al. 1982).
A unique feature of La Azufrada reef is the presence of a crater-like depression located on the northern portion of the reef near the crest. The depression is circular with a 40 m diameter and is completely surrounded by the thick coral growth typical of the reef crest. On the inner side of the rim coral cover decreases with increasing depth reaching a uniform soft-sediment bottom at approximately 10 m depth. A few very large colonies of Gardineroseris planulata, with a high proportion of their surface dead and covered by algae, are scattered around the inner edge of coral growth. Glynn et al. (1982) specu-lated that the origin of this depression was likely the result of coral growth around a small submarine valley. This depression appears to have been present on the reef for at least a few decades since it is visible on aerial photographs taken in 1957 and 1962. A second
Corals and coral reefs of the Pacific coast of Colombia 429
interesting feature of this reef is the unusually high abundance of Pocillopora eydouxi at the reef crest on the northernmost portion of the reef (F.A. Zapata per. obs.).
Playa Blanca reef. The reef at Playa Blanca consists of two patches separated by a channel approximately 60 m wide. The smaller, northernmost patch is ca. 240 m long and has a relatively uniform width of ca. 40 m due to the rapid increase in depth as one moves seaward. This patch exhibits a very diverse and "healthy" appearance, and has very dense coral growth. As on other reefs, pocilloporids dominate the shallow areas whereas massive corals, particularly Pavona varians and Gardineroseris planulata form large clusters at the outer reef base. Of particular interest at this site in early 1997 were 1) the high frequency of scars apparently caused by fish corallivores on massive species, 2) the frequent presence of dense patches of Pocillopora eydouxi, and 3) the presence of an as yet undentified species of Pavona, very similar to Pavona frondifera from the Indo-Pacific and previously unreported for Gorgona (F.A. Zapata per. obs.). Although Pavona frondifera has been previously reported for other localities in the TEP (Guzmán and Cortés 1993; Glynn 1997; Cortés and Guzmán 1998), there remains some doubt about the specific status of the specimens collected at these localities and it is plausible that they belong to a species as yet undescribed (J.L. Maté per. com.).
The second, southernmost reef patch at Playa Blanca is slightly longer (ca. 930 m) but more variable in width (ca. 60–230 m) than La Azufrada reef. Nonetheless, it is similar in areal coverage (9.9 ha; F.A. Zapata unpubl. data), general shape, structure and zonation to the reef at La Azufrada (Glynn et al. 1982; Prahl and Erhardt 1985). How-ever, the backreef zone is wider and closer to the beach, the reef crest is not as notice-able, the forereef has a steeper slope, and the bioclastic sandplain is shallower than at La Azufrada. This reef’s framework is also made up mostly of pocilloporids with large colonies of Pocillopora eydouxi abundant on the crest and forereef. Large colonies of Pavona clavus and P. gigantea are relatively abundant at the reef base (Glynn et al. 1982), but show a conspicuous patchy distribution. Patches of Gardineroseris planulata are occasionally found at the reef base as well.
Zonation of Gorgona’s fringing reefs. The coral reefs of Gorgona are in general characterized by their diffuse zonation pattern, although it is more defined on the larger than on the smaller coral formations. Nevertheless, published descriptions of zonation on the main reefs of Gorgona generally agree with the identification of major zones (Prahl et al. 1979; Glynn et al. 1982; Cantera 1983; Prahl and Erhardt 1985; Prahl 1986b; see also Zapata and Morales 1997). The following is a generalized zonation scheme from the beach seaward based on the latter works and our own observations (Fig. 4): 1) The reef is separated from the beach by a shallow, boat channel, 20–100 m-wide, characterized by fine-sediment substrate (partly derived from land runoff), and by the lack of coral growth. At Playa Blanca, a strip of coral rubble several meters wide and covered by algae follows the channel. 2) At La Azufrada, a few isolated coral colonies begin to appear at the boat channel-backreef interface, whereas at Playa Blanca the transition from coral rubble to denser live coral is more abrupt. The backreef is character-ized by a low and patchy distribution of live-coral cover, which increases seaward from < 10% to < 50% over a stretch of 20–30 m. Dominant species in this zone are in order of decreasing cover: Psammocora stellata (more abundant at La Azufrada), Pocillopora spp. (mostly P. damicornis) and very few, small Pavona varians. 3) Moving seaward, pocilloporids, particularly Pocillopora damicornis and P. elegans, dominate the reef flat, although colonies of Porites panamensis, Pavona varians and Psammocora stellata are
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Fig. 4. Depth profiles of three transects at La Azufrada Reef, Gorgona Island, showing the approximate width of five reef zones as follows: B = backreef, F = reef flat, C = reef crest, Fr = reef front, and S = upper reef slope. Inset shows planar view of the reef and adjacent coastline with approximate location of transects. found interspersed amongst the pocilloporids. P. stellata can be abundant, particularly within pockets of dead coral and consolidated calcareous rock. Total live coral cover varies both within and between reefs in this zone and may reach up to 70%, whereas the remaining substrate is composed of consolidated calcareous algae, sand, and coral rubble. 4) Like many fringing reefs, Gorgona's reefs lack a true reef crest. Nonetheless, the outer portion of the reef flat is slightly elevated, making it the shallowest portion of the reef, and thus a distinct zone frequently referred to as the crest. It is densely covered by Pocillopora spp., mainly P. damicornis, although notably large colonies of Pocillopora eydouxi, P. elegans and P. capitata are more abundant here than elsewhere on the reef. Total live coral cover can be as high as 80%–90% due to the close packing of colonies. The backreef, the reef flat, but particularly the crest, are occasionally exposed during extreme low tides. The effects of subaerial exposure create a mosaic of dead coral covered by algae patchily distributed over live coral, and contribute to the spatial heterogeneity of the reefs (see section “Natural disturbances, extreme low tides”). 5) In the reef front the bottom begins to slope steeply although live coral cover and species composition continue to be similar to those in the reef crest. The limit of the pocilloporid reef framework is located at the outermost portion of this zone. Relatively large blocks (up to 2 m long by 0.5 m wide) of the pocilloporid frame are often found torn off at this level. 6) On the upper reef slope, concomitant with a pronounced decrease in pocilloporid coral cover (to 20% or less) there is an increase in the amount of coral rubble and abundance of large (up to 2–3 m in diameter), massive colonies of Porites lobata, Pavona gigantea and Pavona clavus, or clusters of Pavona varians or Gardineroseris planulata, which produce high topographic complexity. Psammocora stellata becomes once again a dominant member of the community in terms of cover, whereas Pocillopora spp. occur as scattered, isolated colonies. 7) Finally, reefs may be followed by either a sand plain composed of bioclastic and carbonate debris (Old Pier reef and Playa Blanca) or by a lower slope largely
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composed of coral rubble and fine sediment, Psammocora stellata and a few and widely separated, small colonies of Pocillopora spp. and Pavona varians (La Azufrada reef).
Malpelo Island. Because of its geographic location, both oceanic and continental currents influence Malpelo Island (Wyrtki 1965). However, despite the biogeographic importance of oceanic islands in the TEP as potential stepping stones for the invasion of Indo-Pacific species (Graham 1975; see also Glynn et al. 1996; Robertson and Allen 1996; Glynn and Ault 2000), Malpelo Island has been overlooked. Due to the remote location of this small island few studies have addressed the ecological aspects of Malpelo’s marine communities. After initial work by Birkeland et al. (1975), only three contributions have considered the coral formations at Malpelo (Prahl 1990; Brando et al. 1992; Garzón-Ferreira and Pinzón 1999).
Steep cliffs and vertical walls characterize the perimeter of Malpelo Island. Hermatypic corals occur mostly as a veneer, interspersed with other benthic invertebrates, especially barnacles (Balanus peninsularis) and octocorals (Anthozoa: Alcyonaria). In some cases corals occur as shingled overhanging masses on the vertical rocky walls (Birkeland et al. 1975). Rich coral aggregations and build-ups occur only on the gradually sloping substrates. These observations led Birkeland et al. (1975) to conclude that no true reefs occur at Malpelo. However, there is no information about the extent of coral build up at Malpelo and reef probings are needed to confirm such conclusion.
Of special interest is the coral formation found by Birkeland et al. (1975) in a small protected embayment on the east coast of the island. This is the largest and most developed coral formation at Malpelo and is known as “El Arrecife” (Fig. 5). Whereas Birkeland et al. (1975) reported that cover by hermatypic corals varied between 42% and 89% at El Arrecife in 1972, Garzón-Ferreira and Pinzón (1999) found values between 15% and 60% at the same reef in 1999. Here corals exhibit a clear zonation pattern (Birkeland et al. 1975). Colonies of Pocillopora capitata dominate (80–94% of live coral cover) between 9 and 12 m. In contrast, massive corals are more abundant on deeper substrates, also presenting specific depth preferences. Porites lobata and Pavona clavus are most abundant (80% and 54%, respectively) between 14 to 18 m. The deepest substrates (26–27 m) are dominated by Gardineroseris planulata (53%). These zonation results are in accordance with recent observations by Garzón-Ferreira and Pinzón (1999). Similar observations were made by B. Vargas-Ángel and F. Estupiñán (unpub. data), who visited the island in 1990 and found a small coral community (ca. 0.1 ha) on the west coast of the island at the site known as “El Mirador”. The shallow substrate between 5 and 10 m depth was dominated by low-profile colonies of Pocillopora capitata and Pocillopora eydouxi. Of special interest in these areas were the few colonies of P. eydouxi, which exhibited very broad and flattened branches. The second zone, between 10 and 20 m was densely covered (93–99%) by shingle-like colonies of Porites lobata. Below 20 m depth Pavona clavus and Pavona varians were abundant. Other smaller, undescribed, coral formations are located at two other sites known as “El Náufrago” and “Bajo de Junior” (Fig. 5; S. Bessudo per. com.).
The rich development of reef corals in the two coral formations described above sug-gests that conditions are favorable for coral growth at Malpelo (Birkeland et al. 1975). However, hermatypic coral growth is limited elsewhere around the island (~10%). Birkeland et al. (1975) suggested that two main factors limit reef development at Malpelo Island, namely sunlight and lack of a gently sloping shelf. Vertical surfaces are frequently shaded due to the sun angle and vertical irregularities of the walls. Moreover,
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Fig. 5. Map of Malpelo Island showing distribution of coral formations (black circles) and major topographic features. Names of sites are those commonly used by sport divers (S. Bessudo, per. com.). vertical walls provide little or no support at all on which corals can build and develop a reef. Low water temperatures may also limit the depth distribution of corals at Malpelo. The occurrence of temperatures as low as 19.5°C below 30 m depth are evidently cold enough to limit coral growth (Birkeland et al. 1975). Additionally, oceanic swells may have a profound impact on the development of coral formations at Malpelo. First, strong wave action is most likely the major cause of erosion of the island, causing frequent rockfalls (Stead 1975) that affect the development of coral buildups (Birkeland et al. 1975). Second, unusually strong wave action during occasional storms has long been known to disturb coral reefs (Brown 1997) and it is likely that it does at Malpelo as well. For instance, in June 1999 strong oceanic swells caused the breakage of many pocilloporid colonies, overturned many large colonies of massive species and caused severe perturbations to Malpelo’s main reef in just one night (Garzón-Ferreira and Pinzón 1999).
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3. NATURAL DISTURBANCES 3.1. EL Niño-Southern Oscillation
During 1982 and 1983 an increase in sea surface temperature (SST) occurred along the Colombian Pacific coast that lasted at least 16 months, causing bleaching and death of hermatypic corals. The bleaching event was preceded by increases of 1–2°C above the long-term norm over an 11-month period (June 1982 to April 1983: Prahl 1985b; Glynn 1990), while the greatest temperature deviation (3.5°C) occurred in March of 1983. However, one temperature reading of 31.5°C obtained from Gorgona Island in February 1983 (3.2°C above the mean), suggests that coral reefs in this location may have experienced even greater sea warming (Glynn 1990).
As at many other locations in the TEP, the first sign of coral thermal stress was the loss of endosymbiotic algae by corals. On the Pacific coast of Colombia, coral bleaching was only noticed in April 1983, although it may have begun as early as February. It reached widespread and catastrophic proportions by June 1983, when Prahl (1983a) reported coral bleaching in excess of ca. 85% in all the coral reefs of Gorgona Island. Massive corals along the reef base (> 6 m depth) showed bleached surfaces, while the bases of the colonies remained with normal coloration (Prahl 1983a). In addition, coral bleaching at Gorgona Island was accompanied also by decreased mucus release, mainly in pocilloporid corals, and a dramatic reduction of coral commensal symbionts (Prahl 1985b). In situ coral skeletal staining (Prahl 1986d) demonstrated not unexpectedly that bleached corals were incapable of calcification. By July 1983, most of the bleached coral colonies at La Azufrada reef were dead, and covered by macroalgae. However, Pocillopora eydouxi at La Azufrada and Playa Blanca reefs was the coral least affected by the warming event (Prahl 1983a).
Recovery of coral reefs at Gorgona Island since 1983 has been slow, not only because most live corals were severely reduced by the 1982–83 warming event, but also because of low coral growth and recruitment rates, and secondary environmental disturbances. In November 1984, Prahl visited the island and noticed a slight recovery in coral cover of ca. 15%, mainly due to regeneration of pocilloporid colonies; however, no signs of recovery by the massive coral G. planulata was observed (Prahl 1985b). In October 1985 B. Vargas-Ángel and C. Moreno (unpubl. data) still observed large extensions of dead coral at La Azufrada reef. In December 1987, reef corals, predominantly Psammocora stellata and Pocillopora damicornis, had recolonized most of the dead coral platform at the northern portion of La Azufrada reef (Prahl et al. 1988).
Although substantial coral regeneration has occurred since 1983, full recovery of the coral community to a pre-disturbance stage has apparently not occurred yet any of the reefs in flat Gorgona Island. However, comparisons of coral community structure at La Azufrada between 1979 (Glynn et al. 1982) and 1993, 1995 and 1996 showed that 1) live coral cover was similar across all years in all zones except the backreef (which was lower in 1979 due to high sedimentation); 2) species richness and diversity (H') did not differ significantly among years although they tended to be higher in the reef crest and front in 1979; and 3) evenness (J') was significantly greater in the reef flat and reef front in 1979 (C.E. Bárcenas et al. unpubl. data). Although massive corals, including species of Pavona, poritids and Gardineroseris planulata, are still present in all reef zones (but particularly on the upper reef slope), they occur only in relatively low abundance (Prahl et al. 1988; Guzmán and López 1991; per. obs. by the authors). Post-disturbance coral
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growth rates (23.6 mm yr−1 for P. damicornis) were low compared to those reported by Glynn and Stewart (1973) for Panama and were ascribed by Prahl (1985b) to slow coral regeneration after the 1982–83 warming event. However, reports of reduced coral growth rates during 1985–86 could have been the result of two non-mutually exclusive factors: 1) stained colonies were unattached to the bottom and free to wander on the reef, (E.J. Peña per. com.), and 2) other disturbances after the ENSO event, such as the strong upwelling in the Gulf of Panama of 1985 (Legeckis 1988; Guzmán et al. 1990), or extreme low tides, may have affected coral growth.
Although the 1982–83 El Niño warming lasted between 10 and 20 months (depending on location; see Glynn 1990), still little is known about long-term ecological changes affecting corals and coral reefs on the Pacific coast of Colombia. Glynn (1990) implicitly proposed that the 1982-83 El Niño event was responsible for the extinction of Acropora valida at Gorgona Island, hence the eastern Pacific. However, the colonies of A. valida at Gorgona had a normal appearance when they were found in September of 1983, at the end of the warming episode (Prahl and Mejía 1985). Nonetheless, the occurrence of A. valida at Gorgona or elsewhere in the TEP was never confirmed. It is thus unclear whether the 1982–83 El Niño event drove A. valida to extinction in the TEP.
Comparisons of maps of coral reef distribution around Gorgona made before the 1982–83 El Niño (Prahl et al. 1979; Glynn et al. 1982) with maps made after (Prahl and Erhardt 1985; Prahl 1986b; López-Giraldo 1992), in addition to our own observations, suggest that some reefs at Gorgona were more affected than others. Whereas the larger reefs of La Azufrada and Playa Blanca appear today almost as large and with similar live coral cover and species richness as before 1982, the smaller reefs at El Remanso, Yundigua, Playa Pizarro, El Muelle, La Gómez, La Ventana and Paso de Tasca are much smaller and show little coral buildup. Lack of detailed descriptions of most of these reefs prior to 1983, however, make it difficult to establish whether these changes were the result of the 1982–83 El Niño event.
Between May 1997 and June 1998 the second strongest ENSO event of the century occurred. A particular feature of this event was the occurrence of two intensity peaks, one in August 1997 and another in May 1998. Satellite-obtained data images indicate that in the Pacific coast of Colombia SST increased up to 2°C above the long term mean between May-September 1997, and more than 3°C between April-June 1998. In coinci-dence with the occurrence of this event there was widespread coral bleaching in tropical reefs around the world (ISRS 1998, Strong et al. 1998). In the Pacific coast of Colombia moderate to severe coral bleaching and mortality were observed at Utría, Gorgona, and Malpelo (Vargas-Ángel et al. 2001). The first unequivocal signs of bleaching were observed at Gorgona in September 1997, when patches of Pocillopora at various depths showed bleaching on the distal portion of branches. At this time, the extent of bleaching on massive species (mainly Pavona spp.) was much greater than on branching species, with a high proportion of the upper surface of colonies bleached. The extent of bleaching at the scale of the reefs was, however, low (ca. 1%). By December 1997 bleaching was evident reaching on average 21% by April 1998 and 25% by June 1998 at Playa Blanca reef. Similarly, at La Azufrada reef, coral bleaching was low during October 1997 (< 1%) but had reached 21% by May 1998 (Vargas-Ángel et al. 2001). At Playa Blanca reef the extent of coral bleaching was not uniformly distributed among reef zones. In June of 1998 bleaching had reached 17% on the reef slope and 30% on the reef crest.
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Evidently the extent of bleaching and mortality during the 1997–98 ENSO event did not reach the catastrophic proportions of the 1982–83 event. Casual observations made in August 1998 on Gorgona’s main reefs revealed that, although coral mortality inevita-bly occurred, much of the coral previously bleached had recovered its normal colora-tion. Massive corals, however, were less capable of recovery than branching corals and thus suffered the greatest mortality. This differential mortality of corals as a result of sea warming and bleaching provides yet another reason to explain the high dominance of pocilloporids on TEP coral reefs (Vargas-Ángel et al. 2001).
Meanwhile, the effects of El Niño events for locations such as Malpelo Island, Tebada, and Utría still remain to be studied. Sclerochronological evidence indicates that corals at Utría and Tebada were also severely impacted by the 1982–83 El Niño warming event. During this disturbance, skeletal growth in massive corals was halted across the region, and regeneration of tissues over dead coral surfaces required as long as 2–3 years (Vargas-Ángel et al. 2001). In some cases, corals never recovered and eventually died. Interestingly, the skeletal growth interruption associated to the 1982–83 El Niño was more prevalent and conspicuous in corals from Gorgona Island than from Utría and Tebada, suggesting that the impacts of the disturbance may have been greater at Gorgona than farther north (Vargas-Ángel et al. 2001). Nonetheless, growth records of massive reef corals can only provide evidence for individual colonies, and therefore inferences on ENSO effects at the community level can only be speculative. Because our knowledge about coral reef community structure at Utría, Tebada and Malpelo prior to the 1982–83 warming event is limited or nonexistent, a full understanding of the pre-disturbance/post-disturbance dynamics for those reefs is still precluded. A study of the possible synergistic effects of El Niño with other anthropogenic or natural disturbances such as upwelling, sedimentation, and aerial exposure should provide a more complete understanding of the interplay among the varied disturbance regimes and their effects on reef dynamics.
3.2. Extreme low tides
Aerial exposure of coral reefs during extreme low tides is an abiotic factor potentially important for population regulation and community organization of coral species in the TEP (Glynn 1976). Based on knowledge of the tidal regime and on the observation of large tracts of dead coral on the shallowest portions of a coral reef, Glynn et al. (1982) suggested the occurrence of tide-related mortality of corals at Gorgona Island. Indeed, anecdotal accounts indicate that aerial exposures of reef corals at Gorgona have long been known, and verified events have occurred regularly at least since 1993 when one of us (F.A.Z.) began to study this phenomenon. Aerial exposure of corals at La Azufrada reef occurs when the tidal level drops to − 0.4 m relative to MLLW, which is the relative position of the shallowest corals. The frequency of occurrence and duration of potential, diurnal, aerial exposure events at La Azufrada has been examined based on tidal predic-tions for the period 1966–1996. For this purpose, one aerial exposure event was defined as the emersion of corals on one or more consecutive days during a single spring-tide series. This analysis revealed that aerial exposure events occur on average every 90 d, although intervals between two consecutive events range between 25 and 441 d. On average, reefs are exposed more than twice during one spring tide series and occasion-ally up to five times. Exposure events occur only between January and April and between August and December (F.A. Zapata et al. unpubl. data). Because this analysis was based
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on tidal predictions, it is only indicative of the importance of aerial exposures as an agent of disturbance. In fact, aerial exposure of reefs may be more or less dramatic depending on local climatic conditions (e.g., atmospheric pressure, winds) during spring tides, and on large scale climatic and oceanographic conditions. For instance, under con-ditions of an El Niño event, when sea level is higher, aerial exposures may be reduced both in frequency and magnitude, while the converse may occur during La Niña, when sea level is depressed. Nocturnal emersions do occur as well, but may be less impacting than diurnal ones.
Not all aerial exposure events affect corals, but after repeated and prolonged exposures, exposed tissues (usually at the distal portions of branches) are bleached and later die. Filamentous algae rapidly colonize dead portions and eventually grow to cover the entire colony. As a result, abundant algal patches of varied sizes are typically formed on the most elevated portions of the reef crest and reef flat. This effect appears to be widespread at Gorgona since it is readily visible on most reefs around the island one to three months after the occurrence of an emersion event.
Comparisons of algal cover and coral richness and diversity on the reef crest of La Azufrada reef at Gorgona Island following the occurrence of one or more verified exposure events for two pairs of consecutive years (1992–93 and 1995–96) indicate that filamentous algal cover increased from almost 0% in previous years to a maximum of 24% following aerial exposure. Whereas coral species richness and diversity were not affected in 1993 when compared to 1992, both decreased in 1996 relative to 1995 levels (F.A. Zapata et al. unpubl. data). At la Chola reef (Ensenada de Utría), extreme low tides are also potentially deleterious to reef corals. For example, in October 1988 severe and widespread bleaching was observed resulting from a prolonged sub-aerial tidal exposure (-0.4 m), which coincided with elevated mid-morning air temperatures (29–30ºC). Unexpectedly, this event did not cause coral mortality and corals recovered their normal pigmentation within two weeks (Vargas-Ángel 1996).
Not only are corals affected by the aerial exposure of reefs, but their associated fauna can be severely affected as well. Anecdotal accounts (R. Franke per. com.) indicate the occurrence of high mortality in a broad variety of reef associated organisms during extreme low tides. This mortality appears to be related to increased water temperature, and to oxygen depletion in the pools formed during the exposure of reefs. These pools act also as traps for many species, particularly fish. In addition, stressed corals appear to release great amounts of mucus that accumulates on the water surface and may contribute to the deterioration of water conditions.
At present we have only observed the short-term effects of aerial exposure of reefs. Following the succession of algal patches, particularly focusing on their use by reef herbivores and measuring any potential bioerosion caused by them, will allow a better evaluation of the long-term effects of aerial exposures on coral community structure and reef development. Furthermore, a more detailed assessment of the impact of aerial exposures on the reef-associated fauna is needed.
3.3. Sedimentation
Terrigenous sediment influx in coral reef ecosystems can lead to coral bleaching, as well as coral tissue necrosis and colony death (Cortés and Risk 1985; Hubbard 1986; Cortés 1990). On the Pacific coast of Colombia, coral reefs have not been exempt from this kind of disturbance. From 1960 to 1983, Gorgona Island was the site of Colombia's
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top-security prison. During this time extensive forest clearing occurred as well as large-scale enterprises, including the construction of the penal facility to accommodate about 2000 people, a pier, a road and several trails, and a landing strip for small aircraft. According to Prahl et al. (1979) extensive coral death was observed on the backreef at La Azufrada as a consequence of sediment accumulation, mainly caused by the runoff of unstable top soils due to indiscriminate excavation for the construction of the landing strip. Even after >15 years of natural reforestation, corals at the boat channel-backreef interface in front of the landing strip at La Azufrada reef are still covered with fine sediment.
In addition, recent concern has arisen about the possibility of siltation stress to the marine fauna of Gorgona Island due to the Naranjo channel. The Naranjo channel is a major engineering pitfall of the early 1970's, responsible for the diversion of more than 80% of the waters and the formation of a new delta for the Patía river, on the Colom-bian mainland about 50 km south of Gorgona Island. Possible impacts of this disturbance to the marine communities of the island were never considered at the time of construction. Recent satellite imagery suggests that the sediment plume discharged from the new delta of the Patía River may have been reaching Gorgona during the last twenty years (C. Monge per. com.). Preliminary measurements of sedimentation rates made in 1996 at La Azufrada reef (L.H. Chasqui and G. Morales unpubl. data) suggest that these are greater on the reef slope (7.9 g m−2 d−1) than in the backreef (2.7 g m−2 d−1). This result is contrary to what one would expect if sediments were primarily derived from Gorgona itself, and compatible with the idea that sediments arrive from the mainland. However, estimates obtained between November 1999 and March 2000 reveled greater overall sedimentation rates and a more complex spatial patterns (Lozano et al. unpubl. data). Sedimentation rates on the slope of La Azufrada and Playa Blanca were lower (34 and 47 gm-2 d-1, respectively) than on the back reef at both sites (95 and 293 gm-2 d-1, respectively), suggesting that terrestrial run-off from the island is impor-tant. Nonetheless, because surrounding currents generally flow in a north-eastern direc-tion, the greater rates of sedimentation at Playa Blanca than at La Azufrada are still compatible with the idea that continentally derives sediments may be reaching Gorgona, but more comprehensive studies are clearly needed.
Prahl and Vargas-Ángel (1990) proposed that suboptimal environmental conditions in association with high rates of sedimentation were causative factors for reduced growth rates (12.7 mm yr−1) of the main reef builder, Pocillopora damicornis at La Chola reef, Ensenada de Utría. Moreover, the fact that La Chola reef is dominated by finely branching ecomorphs of Pocillopora damicornis can be considered as supplementary evidence in support for coral sedimentation and turbidity stress at Utría (Prahl and Erhardt 1985; Prahl and Estupiñán 1990). In addition, Vargas-Ángel (2001) observed an increase in macroalgal biomass cover at La Chola reef and severe coastal erosion, in contrast to earlier observations in 1988 (Vargas-Ángel 1996). It is possible that elevated sediment loads, turbidity levels and concomitant nutrient loading have led to coral stress, fostering the proliferation of macroalgal patches at La Chola reef. Macroalgal cover may have also increased, however, due to the effects of aerial exposures during extreme low tides. Sediment stratigraphic studies by Vargas-Ángel (2001) offer evidence of chronic siltation stress at La Chola reef during part of its Holocene growth history. The development of a relatively vital calcifying community under environmentally “poor” conditions is thought to occur due to the interplay of physical and biological factors,
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including climate, water circulation, the presence of mangrove forest and coral colony morphology.
3.4. Strong upwelling
Seasonal upwelling along the coast of Central America is most apparent from Decem-ber to March. The main driving force for these events is the intermittent arrival of high atmospheric pressures from Canada to the Caribbean and Central America. Under these conditions, coastal surface waters can be rapidly blown offshore, coastal level is de-pressed, and coastal upwelling can reduce surface water temperatures by nearly 10°C in less than a day (Legeckis 1988). During March 1985, unusually persistent upwelling off the Gulfs of Panama and Papagayo caused red tides severely affecting corals and coral reefs in Central America (Guzmán et al. 1990). According to Legeckis (1988) this phenomenon depressed SST by 6 to 10°C relative to the surrounding waters, and cooler waters extended southwest off Panama reaching the Galapagos Islands. There are no reports, however, of the effects of this event on the corals of the Pacific coast of Colombia. Nonetheless, corals at Utría and Gorgona may have been affected, both by long-term exposure to low water temperature, as well as to toxicity, oxygen depletion and reduced light penetration caused by the dinoflagellate bloom (see Guzmán et al. 1990). In February 1989, low SST (16–18°C) in association with red tides resulted in widespread coral bleaching at La Chola reef, Ensenada de Utría (Vargas-Ángel 1996). On this occasion, blooms of Gymnodynium sp. were responsible for the red tides (B. Vargas-Ángel and F. Estupiñán unpubl. data). Bleaching of corals was observed only at Utría, where corals regained their normal pigmentation in about a week. In contrast, although SSTs as low as 18°C also were recorded for Gorgona Island at this time (F. Estupiñán unpubl. data), no red tides or coral bleaching were observed.
3.5. Tectonism
Tectonic activity is common along the Pacific coast of Colombia, and strong earth-quakes are not infrequent in this area (Oppenheim 1952; Case et al. 1971; Wilches-Chaux et al. 1993). Tectonic subsidence is the main process occurring along coastal southwest-ern Colombia (Herd et al. 1981). During the great Tumaco earthquake of December 12, 1979 (magnitude 7.9-8.1), which occurred 80 km southwest of the town of Tumaco and 200 km southwest of Gorgona, the sea floor at the Strait of Tasca (which separates Gorgona Island from the islet of Gorgonilla) reportedly subsided by 0.8 m (Herd et al. 1981). Neither substrate collapse and subsidence nor the accompanying tsunami were reported to have caused negative impacts to the corals and coral reefs at Gorgona Island. Nonetheless, episodic events of this nature can, not only seriously affect reef corals (see Woesik 1996), but also exacerbate the effects of other natural disturbances (Cortés et al. 1992). However, moderate subsidence of the magnitude recorded at Gorgona in 1979 could, at least temporarily, reduce the negative impacts of tidal-caused emersion.
In contrast with Colombia’s southwestern coast, tectonic uplift is more prevalent farther north along the coast of Chocó. Although several major earthquakes have shaken this region (e.g., at Bahía Solano in 1970: Ramírez 1971a, b), there are no reports on the effects that these occurrences might have had on the coral communities in the area. However, earthquake-caused landslides, such as the one that occurred on the coastal Panamanian-Colombian border in 1976 (Garwood et al. 1979), could cause serious dam-age to coral reefs in this region (see also Cortés et al. 1992).
Corals and coral reefs of the Pacific coast of Colombia 439
4. ANTHROPOGENIC IMPACTS, PROTECTION AND MANAGEMENT Most coral formations in the Colombian Pacific region are within legally protected
areas. These were originally under the supervision and management of the Park Division of the Institute of Natural Renewable Resources (INDERENA, Spanish acronym). Law 99 of 1993 (known locally as the Law of the Environment) created the Ministry of the Environment, under which INDERENA’s Park Division became the Special Adminis-trative Unit of the System of National Natural Parks (UAESPNN, Spanish acronym), now in charge of protected and special management areas in Colombia. The first coral reef area in the Colombian Pacific to be protected was Gorgona Island, which was declared as National Natural Park in November 1983 and became fully operative as such in July 1984, once the prison had been removed. The park encompasses the entire islands of Gorgona and Gorgonilla, and adjacent waters covering 61,000 ha. The Utría National Natural Park was created in December 1986 becoming functional in October 1987. This park covers approximately 54,200 ha, including portions of the continental and marine areas of Ensenada de Utría. Since 1987, it has been managed under a joint program between a private environmental NGO (Fundación Natura), and the UAESPNN. Manage-ment activities for the coral areas of the park have included: 1) demarcation and de-limitation of La Chola reef using buoys to prevent boat traffic, and 2) the implementa-tion of a coral replenishment experiment and monitoring program. Malpelo Island was designated as a Sanctuary of Flora and Fauna in October 1995, and is under the care of the Colombian Navy, which maintains a small post on this remote island.
All areas have been subject to some degree of anthropogenic impact, although as one would expect, impact has varied inversely with ease of access. Thus, while Malpelo is perhaps the least disturbed area, Ensenada de Utría seems to be the most disturbed. Alvarado (1992) listed 13 types of anthropogenic impacts likely to occur on Colombian coral reefs. Of these only two occur at Malpelo (direct contact by divers and fishing). At Gorgona, anchoring, sailing activities, direct contact by divers, and fishing were common during the years of the prison and first years after becoming a park. During the 1960’s and 1970’s some coral was regularly used as primary material for craft making by prison inmates. Most trails on the island used to be covered with coral rubble, which mixed with cement and sand was also used for the construction of some of the buildings’ floors. It is most likely, however, that this coral rubble was collected on the beaches rather than extracted from the reefs. Today, except for one site (Yundigua), the coral reefs of Gorgona Island are closed to visitors, although they remain open to researchers. This has reduced significantly the amount of damage caused by careless divers and boat anchoring, which used to be perhaps the major sources of human disturbance on these otherwise well-preserved reefs. At Ensenada de Utría, landslides, coastal erosion, siltation, dynamite blasting, and coral collecting and plundering have been reported as significant anthropo-genic impacts (Vargas-Ángel 1996).
Despite being protected, coral formations of the Pacific coast of Colombia are not totally exempt from human induced perturbations. For instance, fishing still occurs in all areas and is a major source of conflict between local fishermen and park authorities, although coral reef fishes are not preferred target species. Nonetheless, some species are used as bait for larger fish caught outside coral reef areas. At Malpelo it is not unusual to see foreign fishing boats exploiting the abundant fish populations. Some coral collect-ing still occurs on probably all coral reef areas of the Colombian Pacific, but particu-
F.A. Zapata & B. Vargas-Ángel 440
larly at Utría. Pocilloporids are used for making crafts, which are commonly sold in Buenaventura and other coastal towns. In 1998, 800 kg of coral collected at Gorgona were confiscated by park authorities in Buenaventura showing that protection efforts are still insufficient to prevent coral collecting and trading. Evidently, park authorities lack sufficient resources for effectively enforcing conservation and management policies.
Although rare, oil spills are another source of human disturbance to coral reefs in the Pacific coast of Colombia. Since 1996 at least two crude oil spills have reached Gorgona Island, apparently transported from Ecuador by northward moving currents. During the latest event, in March of 1998, an oil spill passed about 8 km southeast of Gorgona. Although it not directly hit Gorgona, about 2000 kg of tar were collected from the beaches by park personnel. No significant mortality of marine organisms was observed, however.
Few studies have been conducted with the aim of providing scientific knowledge that will serve as the basis for sound conservation and management policies of the coral reef areas of the Colombian Pacific coast. Fundación Natura, under agreement with park authorities, carried out a study to provide a basic cartography of habitat types and an ecological zonation scheme at Ensenada de Utría (Vieira 1992). Similarly, López-Giraldo (1992) did a relatively detailed characterization of community types and provided a zonation scheme for the management of the marine area around Gorgona Island. Under contract with park authorities, Villa (1999) did a preliminary evaluation of the artisanal fisheries resources at Gorgona to provide information on which to base management decisions to ease the conflict between fishermen and park authorities. Park authorities have recently tried to get scientists to increase their contribution to the solution of specific conservation and management problems within protected areas. However, a weakly developed marine scientific community and an overall insufficiency of financial resources for both research and management make this a challenging problem for all.
ACKNOWLEDGMENTS
We thank Jorge Cortés for his invitation to write this chapter, and P.W. Glynn, J. Cortés, and H.M. Guzmán for their comments and suggestions on an earlier version of the manuscript. The Unidad Administrativa Especial del Sistema de Parques Nacionales Naturales del Ministerio del Medio Ambiente (UAESPNN) has granted permits and provided logistic support for our continuing work at Gorgona, Utría, and Malpelo. We thank the park’s chief officers, particularly C. Acevedo and G. Mayor. F.A.Z. gratefully acknowledges the help and motivation of his students, particularly, Y.A. Morales, C.E. Bárcenas, J.M. Jiménez, P.A. Herrón, V. Francisco, S. Lozano, C. Mora, L.A. Serrano, and A.F. Ospina. F.A.Z. also thanks J.L. Maté and H.M. Guzmán for sharing their knowledge about TEP corals, D. Fenner for help in obtaining literature on Pavona frondifera, and S. Bessudo for sharing her knowledge of Malpelo. Universidad del Valle, Fundación para la Promoción de la Investigación y la Tecnología del Banco de la República, and the Instituto Colombiano para el Desarrollo de la Ciencia y la Tecnología (Colciencias) have provided financial support for F.A.Z.'s work. B.V.A. wishes to thank F. Estupiñán, C. Moreno, A. Salinas and F. Ortega for their valuable collaboration with the field work. Financial support for B.V.A.'s work at Tebada, Utría and Gorgona has been provided by a doctoral scholarship from Colciencias and the Reitmeister fellowship from the University of Miami. Most of the original work by
Corals and coral reefs of the Pacific coast of Colombia 441
B.V.A. mentioned here is part of his Ph.D. dissertation at the University of Miami and will be presented in greater detail elsewhere.
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