Characteristics Of Primary Producers Determine Their Distribution Across An

Ecological Gradient.

Marine Systems

SCIE2204

Group name: Fellowship of the Fish Members: Natalie Chai (21125447), Shannon Holt (21099061) , Amber Knapp-Wilson (21165232), Eileen Lee (21043284) , Elaine Lui (21003953), Amy Robey (21021544)

Abstract Cottesloe Reef and its associated Fish Habitat Protection Area (FHPA) is a dynamic ecosystem that holds important ecological significance due to their highly diverse flora and fauna. Students from the University of Western Australia survey this reef annually to determine species richness and abundance of marine life. We focused on the primary producers, arguably the most important set of organisms found at the reef as they support the complex trophic web. The four main categories of primary producers found in the area are seagrasses, brown algae (Phaeophyta), green algae (Chlorophyta) and red algae (Rhodophyta). Over 15 genera and many species fit into these categories. We investigated whether species composition would change over habitat type. Our hypothesis was that there would be a higher proportion of seagrasses growing in the lagoon where the substrate is sandy and a larger proportion of macroalgae species (seaweeds) growing in zones containing reef. Additionally, we expected that invertebrate abundance would correlate to the population of primary producers. By calculating the percentage cover over 12 quadrats in each of the three different habitat zones (lagoon, flat reef and broken reef). Then, cross-referencing the survey data for invertebrates, we hypothesised that a) seagrasses were more common in the lagoon, b) macroalgae were more common over reef habitat with the Phaeophyta genera being the most prominent and c) invertebrates were more common in areas that had higher primary producer abundance. We deduced that these abundance patterns were linked to the different nutrient acquisition methods of the different species.

Introduction

Primary producers are the most important organisms found in marine ecosystems as they are the foundation of a complex trophic web. Using energy captured from the sun, these autotrophs create organic compounds from aquatic carbon dioxide (CO2). These compounds provide nutrition for a wide range of herbivores which in turn provide nutrients for small and large predators. In oceanic systems, a vast proportion of photosynthesis is performed by algae while a smaller proportion is carried out by vascular plants and eubacteria (Mann 1973). Dominant primary producers in coastal ecosystems are Phaeophyta (brown algae), Chlorophyta (green algae), Rhodophyta (red algae) and seagrasses from the order Alismatales.

In investigating the community composition across an ecological gradient, we hypothesised that there would be a higher proportion of seagrasses growing in environments consisting of sandy substrate. This is because seagrasses have evolved from terrestrial plants and possess roots that not only anchor the plant into the substratum but also allow it to extract nutrients from the sediment (Kirkman 1997). Conversely, macroalgae (seaweeds) have never inhabited terrestrial ecosystems and neither do they possess the reproductive structures of true plants nor have specialised tissues that give rise to roots, leaves and stems. Instead they consist of holdfasts that anchor them to the substratum. This structure is not able to extract nutrients unlike the roots of true plants. Thus, nutrients are taken in from the surrounding water which provides an effectively inexhaustible nutrient supply (Mann 1973). We expected these macroalgae to grow in zones containing reef as the reef provides a solid, hard surface for the algae to attach to.

Previous studies have shown that diversity and abundance of animal species increases with the rise in seagrass biomass. The reason for this is (along with additional interacting factors) that seagrasses can provide favourable foraging areas, shelter, spawning habitat and nurseries for various marine organisms (Orth et al. 1984). Similarly, seaweeds such as Sargassum provide habitat for a diversity of marine life (Ross et al. 2001). Hence, we anticipated the number of invertebrate species to correlate directly with the abundance of primary producer.

Cottesloe Reef, lying off Perth, Western Australia, was declared a Fish Habitat Protection Area (FHPA) in 2001. This protective legislation was enforced to prohibit spearfishing, commercial fishing, and specimen collection, jet skiing and anchoring in the area. The legislation was made in acknowledgment that this valuable reef ecosystem is under increasing threat from human processes (Department of Fisheries 2001). Cottesloe Reef holds not only great social significance due to its proximity to densely populated urban areas, but also important ecological significance as marine biologists have identified the area as having characteristics unique to the Perth metropolitan coast (Department of Fisheries 2010). Cottesloe Reef encompasses a wide and unique range of habitats; extending from a sandy near shore lagoon to a limestone reef and sponge beds (Department of Fisheries 2010).

Due to the aforementioned characteristics of Cottesloe Reef, this area was chosen to be a suitable survey site to test our hypothesis. Furthermore, the data obtained would allow greater insight into the species richness and abundance of the FHPA. This additional knowledge can be used to contribute to future management decisions. Methods

Study site The study was conducted at the Cottesloe Reef Fish Habitat Protection Area (FHPA). This area is approximately 4.4 kilometres long- starting from a point 300 metres south of the artificial surfing reef at Cable Station to the southern boundary of North Street, Cottesloe, and westwards to 800 metres from the high watermark (Department of Fisheries 2001).

Figure 1. Schematic map of Cottesloe Reef FHPA (Department of Fisheries 2010). Our main study site was located at the Cable Station Artificial Reef section. Two main areas were identified at the study site- the North and South area (Figure 2). These areas were then

further divided into four major habitat zones- the lagoon, flat reef, broken reef and front reef; with each zone located further away from the coast respectively (Figure 3 and 4). The lagoon is a shallow water body separated from a larger water body (sea, ocean) by barrier islands or reefs that lie parallel to the coastline (Hill 2001). In our study site, the reef borders the lagoon. Due to its shallow nature, it is highly susceptible to precipitation and evaporation processes which results in variable water temperature and salinity (Hill 2001). Most coral reefs that grow optimally in water temperatures between 23°C and 29°C require high water salinity and highlight (restricted to euphotic zones) (Lalli and Parsons 1995). Hence, the number of species of corals decline towards deeper water. Flat reefs are located towards the lagoon, with widths ranging from 20 meters to a few thousand and depths from centimetres to metres deep. This area is also shallow and experiences the same conditions as the lagoon- varying water temperature and salinity. As the flat reef is on the sheltered side of the reef, it is protected from the extreme forces of breaking waves (NOAA’s Coral Reef 2012). This area consists of loose sand and loose rock with the greatest number of species in the reef ecosystem living here (Lalli and Parsons 1995, Sumich 1996). Broken reef is within the reef crest area (highest point of reef), which can be exposed during low tides (NOAA’s Coral Reef 2012). This area has a width of up to 50 meters and lies on the outer side of the reef. Therefore, it is subjected to the severe force of breaking waves, resulting in the erosion of coral reefs. The corals here tend to have stout branching and small invertebrates such as shrimps and small crabs inhabiting the labyrinth cavities within the reef crest (Lalli and Parsons 1995). The outermost section of the reef (towards the sea) is known as the front reef or fore reef, where buttresses grow out from the reef. This structure is important as it acts as a wave-buffering zone (dissipate the strong forces of wave), stabilizing the reef structure and is a drainage system (drains sediment and debris back into deeper waters) (Lalli and Parsons 1995, Sumich 1996). Corals and algae flourish here which in turns attract other fishes to inhabit the front reef.

Figure 2. The areas from North and South (Fraser 2013).

Figure 3. Four habitat zones: 1-Lagoon, 2-Flat reef, 3-Broken reef and 4-Front reef (Fraser 2013).

Figure 4. Coral reef zones (NOAA’s Coral Reef 2012). Experiment Design In our study, we covered both the North and South areas and the three habitat zones nearer to the coast, which were the lagoon, flat reef and broken reef (circled in Figures 2 and 3). We collected data on the percentage cover of various primary producers and number of species of invertebrates and fishes in different habitat zones. Depths within each habitat zone were within a consistent range and thus, we assumed that the depths were identical for each habitat zone. The data sampling was conducted over four different days, starting in the morning till noon (9am-12pm). We were split into different groups that were in charge of collecting data on primary producers, invertebrates and fishes respectively. Each group was given one slate or pencil and waterproof paper with our identification (ID) guides and data sheet printed on. In addition, we wore wetsuits and used proper snorkelling gear. For added safety precaution, we had to snorkel in pairs and participate in a diver’s assessment before starting the data sampling. Primary producer sampling Two 0.25m2 quadrats were placed randomly in 12 different areas (average of 6 areas for each quadrat) in each habitat zone. We assumed that the data sampling was random by throwing or dropping the quadrats into the water with no specific preferences or pattern. However, some bias may have been introduced while placing the quadrats (direction in which the quadrat was thrown and where it landed may have reduced the unbiased random pattern). The different species of primary producers were identified and the percentage cover of each species in each quadrat was then counted. These readings were rough estimations as the counting and species identifications were carried out by ‘naked-eye’ observation. Other unidentified species that were not listed in

the ID guide were also recorded and identified later on. The readings were recorded on the data sheet and the total percentage cover area must be equivalent to 100%. Invertebrate sampling Two 1m2 quadrats were placed randomly in 12 different areas in each habitat zone by throwing or dropping the quadrats into the water. We identified the species and counted the number of species present in the quadrat. These observations were again done using the ‘naked eye’ and human errors may arise due to severe wave action and inaccurate counting. Other invertebrate species that were not listed in the ID guide were recorded on the data sheet as well. The final numbers were then tallied for each invertebrate family. Fish sampling A transect area of 10 X 5 meters were measured using a tape measure and placed at 4 intervals across each habitat zone. Then, two people swam along each transect (starting from opposite ends), identifying and counting the fish species in each transect. This was a ‘naked eye’ observation as well. The readings were recorded on the data sheet and any unidentified fish species were noted and identified later on. Data Analysis All data collected were assumed to be accurate representations of the percentage cover of primary producers and population of invertebrates and fishes in each habitat zone. Therefore, these readings can be used to reflect the whole Cottesloe Reef area. However, in reality, the data may be affected by human errors due to weather conditions and visibility in the water. The data were analysed using pivot tables in the Excel spreadsheet. For primary producers, calculations done were based on the total percentage cover of each macroalgae species and seagrass in each habitat zone while for invertebrate and fish species, the calculations were done using the total number of species present in each habitat zone. With these calculations, a comparison can be made between these three variables (primary producers, invertebrates and fish) and how they would relate to one another. In our paper, we looked at the relationship between primary producers and the abundance of invertebrates. Results

Figure 5. Average percentage coverage of seagrasses per quadrant across three habitat zones- lagoon, flat reef and broken reef. The distribution of seagrass across different habitat zones showed the highest coverage in the lagoon than either of the reefs- 14.75% in the lagoon compared to 0.42% and 0.92% for the broken reef and flat reef respectively. The average percentage (%) coverage was based on the data collected for 60 quadrants in each of the zones.

Figure 6. Average percentage coverage of seagrass, brown algae, green algae and red algae in the lagoon. Seagrass had the greatest coverage (14.75% on average), with brown algae coming in second (10.3%). Green and red algae cover in the lagoon was negligible (0.25% and 1% respectively).

Figure 7. Average percentage coverage of seagrass, brown algae, green algae and red algae in each of the three habitat zones-lagoon, flat reef and broken reef. Brown algae had the two highest cover percentages, in the broken and flat reefs (41.2% and 42.7%). Brown algae cover is notably less in the lagoon (10.3) but in comparison to the other classes, it still has significant coverage. There is variation in both green and red algae across the zones- this will be looked at in more detail in subsequent figures. The seagrass shows insignificant cover (0.42% and 0.92%) in both the reefs, and is only notable in the lagoon as seen in Figure 5.

Figure 8A. Average percentage coverage of red algae, green algae and brown algae in broken reef zone. Brown algae in the broken reef has significantly higher cover (41.1%) than the red algae (3.1%) and green algae (2.3%)

Figure 8B. Average percentage of red algae and green algae in broken reef. The percentage coverage of red and green algae (3.1% and 2.3% respectively) is shown more clearly here.

Figure 9A. Average percentage coverage of red, green and brown algae in the flat reef zone. Brown algae has the highest average cover recorded (42.7%) and is significantly higher in comparison to the other classes of algae-red and green (0.75% and 2.5% respectively).

Figure 9B. Average percentage coverage of red and green algae in flat reef. The differences between the red and green algae are emphasised (0.75% and 2.5% respectively) and there is a larger margin between the two when compared to that seen in the broken reef (Figure 8B).

Figure 10. Comparison of average percentage coverage of primary producers and invertebrates in three habitat zones- lagoon, flat reef and broken reef. When comparing the average invertebrate numbers against average primary producer percentage cover (per quadrant for each zone), the two reefs have similarly high values for primary producer coverage (54.1% and 51.6%) and higher values for invertebrate numbers compared to the percentage in the lagoon. However, the invertebrate numbers in the flat reef (15.4) are significantly higher than in the broken reef (10). The lagoon shows the lowest values for the primary producers and the invertebrates, 26.9% and 2.2 respectively. The change in invertebrate numbers is not proportional to the differences in primary producer coverage, as seen more directly in Table 1.

Table 1. Ratios of invertebrate numbers to primary producer coverage in each habitat zone based on the average values per quadrant. The flat reef has the highest number of invertebrates (15.4) while the broken reef has the highest percentage coverage of primary producers (47%). The lagoon has the lowest number of invertebrates and percentage coverage of primary producers (2.2 and 27.2% respectively).

Zone Average Invertebrates per quadrant

Average % coverage of Primary Producers per quadrant

Invertebrate to primary producer ratio

Broken Reef 10.0 47.0 0.21

Flat Reef 15.4 46.9 0.33

Lagoon 2.2 27.2 0.08

Discussion The results for the distribution of seagrass indicate that they prefer to grow in sandy sediment (Figure 6). As stated earlier, seagrasses evolved from terrestrial plants and therefore have true roots (Kirkman 1997). These roots can penetrate sandy sediment without any difficulty and can effectively make use of the nutrients available in the sediment (Duarte & Hemminga 2000, Huang et al. 2006). This is important because a majority of other marine primary producers such as algae are unable to do this. The different surfaces on the floor of the lagoon and the reef habitats (sandy sediment compared to rocky reef) is one of the factors contributing to the more prominent growth of seagrasses in the lagoon and their non-existence in the reef habitats. Seagrasses prefer to grow in lagoons or in-shore areas, where there are slow currents and the water is shallow. There is higher light availability in shallow waters; therefore the depths of the area in which seagrasses grow often reflect their intense light requirement. Seagrasses are restricted to growing in areas where more than 10% of the surface irradiance light levels can reach while some macroalgae are capable of growing at depths where only 1% of the light is able to penetrate (Alberte et al. 1997). The lagoon has the shallowest depth (approximately 2m) out of all the habitats and seagrass had a higher density than the brown, green and red algae (Figure 7). The next highest density was observed in the flat reef and then the broken reef which had depths of 4m and 5m respectively. These differences in density may be related to the light requirements. Seagrass is less dense in deeper water, where less light can penetrate to the bottom. Therefore, the high light requirement of seagrasses may have influenced their tendency to grow closer to shore where the water is shallow.

The algae species had greater coverage in the two reef habitats than the lagoon, shown in Figure 7. Seaweeds do not have true roots and have to attach to a hard substrate (usually rock or reef) with their holdfast. Thus, for seaweeds to be able to thrive in sandy or muddy sediments, they must attach to a rock or shell and compete with other organisms for the same resources (Fredericq n.d). Brown algae dominated the littoral zone which was reflected in the results by the greater species richness and abundance of brown algae in comparison to green and red algae (Figure 8A and 9A) (Rost et al. 2006). Red algae were lower in species richness than green algae; suggesting that the studied environment may be better suited to green algae growth. This was seen in the flat reef but in the broken reef, the density coverage of red algae was greater than green algae (Figure 8B and 9B). A likely reason for this is the different depths of the two habitats- the flat reef was 4m deep and the broken reef was 5m deep. The availability of light and its quality varies at different depths; all light in the red wavelength is absorbed in the top layers of water while the blue-green wavelength is able to penetrate the deeper layers (Rost et al. 2006). Red algae contain accessory pigments called phycobilins which can capture the blue-green light and this light energy is then passed on to chlorophyll (Rost et al. 2006). Light in the blue-green spectrum is the most effective wavelength for photosynthesis in red algae while the red wavelength is the most significant in green algae (Rost et al. 2006). The different wavelengths utilized by red and green algae can affect their distribution - red algae were more densely populated in the broken reef (deepest depth). In Figure 10, the overall trend was an increase in the density of invertebrates as the total coverage of primary producers increased and Table 1 shows the ratio of the invertebrates to primary producers increasing with the percentage coverage as well. However, the increases were not directly proportional to each other, with the values obtained from the flat reef. Primary producers provide both shelter and food for herbivores. Therefore, a higher primary producer density could support a larger invertebrate population. Previous studies conducted by Orth et al. and Bates & DeWreede suggested a similar invertebrate to primary producer correlation. The study carried out by Orth et al. was on seagrasses while Bates & DeWreede focused on seaweeds; regardless of the different primary producer specimens, both studies concluded similar outcomes. These ideas stated that plant canopy and structural complexity were the most significant factors influencing the abundance and diversity of invertebrates (Bates & DeWreede 2007, Orth et al. 1984). The different structures of algae and seaweeds may be an important factor affecting the large difference in invertebrate population between the rocky reef zones and the lagoon. Brown algae had the greatest increase in average percentage cover from the lagoon to the reef zones compared to the other macroalgae. The most abundant species of brown algae observed was the Sargassum spp. and when compared to the dominant seagrasses observed (Halophila ovalis and Amphibolis antarctica), the Sargassum spp. had a denser canopy with many intertwining branches, making it

more favourable as habitat dwellings for small invertebrates or fishes and as well as a refuge from potential predators. In contrast, seagrasses had sparse foliage and dominated the lagoon. This difference in foliage could affect the survival of various invertebrates in the lagoon and the reef habitats. Hence, the total coverage of primary producers and the unique structure or morphology of seagrass and algae may have accounted for the large differences in invertebrates numbers seen across the lagoon to the reef zones.

Press Release The Cottesloe Reef ecosystem contains a diverse range of marine habitats supporting different species of aquatic plants and animals, and is considered to have attributes unique to the Perth metropolitan area. Primary producers including seagrasses, were the focus of this research project, provide a habitat for various rare organisms. Due to its proximity to the city and high population density residing nearby, the reef is vulnerable to human impacts. The surveyed area was under the Cottesloe Fish Habitat Protection Area established in 2001 to “promote and encourage protection of the Cottesloe Reef aquatic habitat”. The past groups of students from the University of Western Australia (UWA) had collected data in 2008, 2009, 2011 and 2012 and results, contributing to the ongoing monitoring program. For the study in 2013, measurements of primary producers (seagrasses and 3 different types of algae) distribution and percentage cover were measured. A total of 36 samples were collected randomly in 3 different sub-habitats within the Cottesloe Fish Habitat Protection Area. Primary producers play an important part in the food web, providing both shelter and nutrition for invertebrates. An attempt was made to correlate primary producer cover to the substrate in the area. Seagrass was the most dominant aquatic plant in the area closest to the shore (lagoon) as the substrate was more suited for the uptake of nutrients. Further research showed that seagrasses prefer areas with slow currents, shallow water and higher light penetration, conditions that were observed in the lagoon. These conditions facilitate photosynthesis, the basis of the food web. It was also noted that red algae were lower in species richness than green algae in the flat reef, but the opposite was noted in the broken reef. This was attributed to the depth of water and varying availability and quality of light. The report noted that red and green algae required different wavelengths of light to flourish. A comparison was made with invertebrate data, showing that the density of invertebrates increased as the total cover of aquatic plants increased. Primary producers provide shelter and nutrients for essential for invertebrates. A comparison of results highlighted the differences in the number of invertebrates between the rocky reef zone and the lagoon, which was attributed to the differences in physical structure between algae and seagrasses. The data collected can be compared with that of previous years to track changes in percentage cover and species richness over a period of time. The research will help in the study of flora and fauna in the area and influences the decision making for the future in the protected area. Cottesloe beach is considered one of the city’s most popular spots for swimming, snorkelling and surfing and has been featured in various tourist information guides. A sudden loss of seagrasses

would negatively impact the invertebrate population in the area, reducing the attractiveness of the area for both tourists and locals alike.

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