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First Record of Mercenaria mercenaria (Bivalvia: Veneridae) and Ensis directus(Bivalvia: Pharidae) on Bay of Biscay, Iberian PeninsulaAuthor(s): Andrés Arias and Nuria AnadónSource: Journal of Shellfish Research, 31(1):57-60. 2012.Published By: National Shellfisheries AssociationDOI: http://dx.doi.org/10.2983/035.031.0107URL: http://www.bioone.org/doi/full/10.2983/035.031.0107

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FIRST RECORD OF MERCENARIA MERCENARIA (BIVALVIA: VENERIDAE) AND ENSIS

DIRECTUS (BIVALVIA: PHARIDAE) ON BAY OF BISCAY, IBERIAN PENINSULA

ANDRES ARIAS* AND NURIA ANADON

Department of Biology of Organisms and Systems (Zoology), University of Oviedo, Oviedo 33071, Spain

ABSTRACT We present the first record of two nonnative Bivalvia species originally from North America, Mercenaria

mercenaria and Ensis directus, in the waters of the Iberian Peninsula (southwest of the Bay of Biscay). This constitutes the

southernmost distribution for these species in the northeast Atlantic to date. We provide notes on the relative abundance, depth

range, and substrate preferences of the species in their new habitat. The bivalve E. directus has became the dominantEnsis species

along the Cantabric sandy shores it has colonized.

KEY WORDS: Mercenaria, Ensis directus, alien species, Bay of Biscay, aquaculture, ballast water

INTRODUCTION

Although species distribution changes over time, suddenrange extensions are often prompted by the humans. This maybe direct by introduction of a new species for a defined purpose

(e.g., aquaculture), or indirect (e.g., ballast water) (Padilla et al.2011). In addition, global warming could provide opportunitiesfor species to colonize areas where, until recently, they were notable to survive. We report the establishment of two bivalves—

Mercenaria mercenaria and Ensis directus—in the southwestBay of Biscay. Bivalves M. mercenaria and E. directus are notthe only nonnative bivalves in these waters. The Japanese carpet

shell Ruditapes philippinarum (Adams & Reeve, 1850) and itshybrids R. philippinarum3Ruditapes decussatus (Urtado et al.2010), the Japanese oyster Crassostrea gigas (Thunberg, 1793),

and the Pacific semelid Theora lubrica Gould, 1861 have alsobeen reported in the Bay of Biscay (Adarraga &Martınez 2011).

MATERIALS AND METHODS

Study Organisms and Site

The bivalve Mercenaria mercenaria (Linnaeus, 1758), or

hard clam or quahog, is a mollusc that belongs to the Veneridaefamily. These clams can reach a size of 150 mm, but usually mea-sure 60–70 mm (Stanley & Dewitt 1983). The native distribution

range of the species is from the Gulf of St. Lawrence in Canadathrough the northernGulf ofMexico to Texas (Loosanoff 1946,Harte 2001). The bivalveM. mercenaria has been introduced to

the west coast of the United States–British Columbia, 49�N, toCalifornia, 33.7�N, (Coan et al. 2000), Puerto Rico Island, theUnited Kingdom, France, Holland, Belgium, and the North

Adriatic in Europe (Chew 2001, Savini et al. 2002) see Fig. 2A,Taiwan and Wenzhou and Yantai in China (FAO 2004–2011).The bivalveM. mercenaria is found in intertidal as well as subtidalhabitats in a variety of substrates. It is often most abundant in

coarse substrates (Stanley &Dewitt 1983), but in their native areas,the hard clam is typically most abundant in sandy mud with shells(Kraeuter & Castagna 2001). The first collection of this species

in the Bay of Biscay occurred in January 1978 in Video Cape(43.13�N, 5.27�W;Asturias, northern Spain; Fig. 1). Twenty-fourliving specimens ofM.mercenariawere collected in shallowwaters.

These specimens were deposited and preserved in the collectionof the Department of Biology of Organisms and Systems at the

University of Oviedo, Spain. After 33 y, in January 2011, nearVideo Cape in a sandy cove, M. mercenaria was found again.

The bivalve Ensis directus (Conrad, 1843), or American razorclam orAmerican jack knife clam, is native to the western Atlantic

Ocean fromLabrador, 60�N, to SouthCarolina, 34�N (Coan et al.2000). This species was discovered in Europe in the Elbe estuary inJune 1978. Since 1982, E. directus has become common along the

northern coast of Holland, Britain, andDenmark (von Cosel et al.1982). By the end of the 1980s, E. directus was the dominant Ensisspecies along the Belgium shores and southern Norway. In June

1991, it was found in theFrenchNorth Sea (Luczak et al. 1993). By1999, E. directus had spread along the English Channel (Davoultet al. 1999).More recently, in 2005, this species was reported in theBaltic Sea (Streftaris et al. 2005) (Fig. 2B). The American razor

clam lives in sand, muddy sand and gravel from the intertidal tothe subtidal zones in bays and estuaries. Its adaptability todifferent substrates and depths allows this species to occupy higher

intertidal habitats where native Ensis species do not live.

Data Collection and Analysis

Survey and sampling of M. mercenaria and E. directus werecarried out taking advantage of 2011 equinoctial tides. Thespecimens were obtained from the intertidal and shallow subtidal

sandy areas at low tide (Fig. 1). Both species were collected by ex-cavating quadrats (503 50 cm, and 25 cm deep) and passing thesand through sieves of 0.5-mm mesh. Eighteen replicate quadratswere taken along 4 transects along the coastline at these localities.

The total intertidal area of each sample location wasMusel Port ofGijon (;480 m2), Video Cape cove (;600 m2), and Otur sandybeach (;540 m2); and a portion of the external basin (;320 m2)

and central basin (;360 m2) in Villaviciosa estuary. All collectedspecimens were measured and classified by size. We also estimatedaverage density and substrate characteristics. Particle size analysis

was conducted using the Wentworth scale, and determination oforganicmatterby loss ofweighton ignition (Buchanan&Kain1971).

RESULTS AND DISCUSSION

Mercenaria mercenaria (Linnaeus, 1758)

Examination of the specimens from the collection showed

they ranged from 51–63 mm in length, with a mean length of*Corresponding author. E-mail: ariasandres.uo@uniovi.es

DOI: 10.2983/035.031.0107

Journal of Shellfish Research, Vol. 31, No. 1, 57–60, 2012.

57

59 mm (n ¼ 25, SD ¼ 2.55). The hard clams reach sexualmaturity at a size of about 35 mm in shell length (Eversole 2001,MacKenzie et al. 2002); therefore, all specimens found in VideoCape were mature.

The specimens found in January 2011 in the same localityhad an average density of 2.17 specimens/m2 (n ¼ 36, SD ¼3.81), and an average shell size of 33 mm (n ¼ 20, SD ¼ 2.22).

Specimens ranged from 30–39 mm, and only 2 individualsexceeded 35 mm, indicating thatM. mercenaria has reproducedin the Bay of Biscay and has become part of the local benthic

fauna. The hard clams were found in an intertidal–shallow

subtidal (depth, 2 m) community. The sedimentary type wasmedium sand (median grain size, Md, �x ¼ 0.30 mm; SD ¼ 0.06)and with organic matter (�x ¼ 1.59%; SD ¼ 0.28) content. Thissandy cove was characterized by low bivalve biodiversity. The

only other bivalves found were the cockle Cerastoderma edule(Linnaeus, 1758) and the coquina clam Donax (Serrula) truncu-lus Linnaeus, 1758. Another Veneridae, Chamelea striatula (da

Costa, 1778), which was very common at this locality during theearly 1970s (Ortea 1974) was absent.

At least a portion of the M. mercenaria introduction comes

from aquaculture. Near Video Cape, there is a shellfish farm

Figure 2. (A) Northeast Atlantic distribution ofMercenaria mercenaria. (B) Northeast Atlantic distribution and range expansion (in decades) of Ensis

directus.

Figure 1. Locations of the sampling stations at northern Spain coast (Bay of Biscay). Source: PNOA (Plan Nacional de Ortofotografıa Aerea)

(National Plan of Aerial Orthophotography), National Geographical Institute of Spain.

ARIAS AND ANADON58

that, during the 1970s, experimented with M. mercenaria.Several hard clams or their progeny may have escaped. The

origin of those found in 1978 may have been from other farmactivities or from unknown sources. Therefore, we believe thatthe introduction ofM. mercenaria took place in one or very fewepisodes during the late 1970s and early 1980s. Since the 1980s,

the shellfish farm stopped hard clam culture.Global warming of the waters of the Bay of Biscay during

recent decades has increased temperatures by 0.6–0.8�C per

decade during the past 30 y (IPCC 2001). In VideoCape, in 2011the mean annual water temperature was 12.9 ± 1.03�C, withhighs of 19.8�C in the summer, and a winter minimum of 7.7�C.These temperatures could favor the growth and reproduction ofhard clams in this area.

Ensis directus (Conrad, 1843)

Live specimens of E. directus were found at three northernSpain localities—Otur sandy beach (43.16� N, 2.15�W), MuselPort of Gijon (43.32� N, 5.42� W), and Villaviciosa estuary

(43.31� N, 5.23� W)—in shallow waters (Fig. 1). In theVillaviciosa estuary (in the central basin), E. directus occurssympatrically with Solen rotundatus Spengler, 1794 (syn. Solen

marginatus Pulteney, 1799; see Huber (2010)) and other impor-tant natural resources of this estuary, including tubewormDiopatra species, which are highly appreciated as fishing bait

(Arias et al. 2010). Here, E. directus was found in an intertidalfine to medium sand (Md, �x ¼ 0.27; SD ¼ 0.05) with a meanorganic matter content of 1.68% (SD ¼ 0.27). In this Tellinatenuis community,E. directus reached densities of 5.6 individuals/

m2 (n¼ 36, SD¼ 7.08). The size range varied from 105–149mm,and the average size was 125 mm (n ¼ 31, SD ¼ 4.12). On theouter basin of Villaviciosa estuary, E. directus was the only

Solenaceae that could be found, but in the past, the nativespeciesEnsis arcuatus (Jeffreys, 1865) and Ensis siliqua (Linnaeus,1758) were commonly found (Ortea 1974, Anadon et al. 1997).

In the collections of the Department of Biology of Organ-isms and Systems, we have preserved specimens of E. arcuatus

from the early 1980s to late 1990s from the outer basin ofVillaviciosa estuary. These specimens range from 42–112 mm

(n ¼ 18, SD ¼ 4.87) (Anadon et al. 1997), indicating this arearecruited E. arcuatus. At this locality, the absence of E. arcuatusduring early 2000 corresponds to the first record of E. directus.It is possible that if the E. directus population were to become

very large it could compete with and/or displace other Ensisspecies like E. arcuatus in the Villaviciosa estuary. The Americanrazor clam population in the Villaviciosa estuary has become

large enough that local fishermen are beginning to harvest largespecimens of E. directus for human consumption and smallspecimens for fishing bait (surf casting). Here, the recent harvest-

ing of this species by the use of handheld digging tools, contrastswith mechanical harvesting with equipment such as scuba andhydraulic harvesters like those described for the St. LawrenceRiver shores in Quebec (Kenchington et al. 1998) or the special

harvesting ships being used on the North Sea.The most probable means of introduction of E. directus to

the coasts of northern Spain is from ballast water. Currently, it

is assumed that free-swimming larvae of this species werereleased from ballast water off the Elbe estuary (von Coselet al. 1982). Since the early 1990s, the Spanish Musel Port of

Gijon has had regular routes to the port of Rotterdam in theNetherlands and the ports of Hamburg, Luebeck, Bremen, andDuisburg in Germany. In 2000, 24 different merchant ships

from Rotterdam and 10 from Germany (mainly from the portof Hamburg) landed at Gijon. These included 4 weekly shippinglines (Gijon–Rotterdam–Gijon) and 2 biweekly lines (Gijon–Hamburg–Gijon and Gijon–Bremen–Gijon). The subsequent

spread of E. directus along the coasts of the Bay of Biscay isprobably a result of larvae drifting with water currents.

ACKNOWLEDGMENTS

We thank Dr. Markus Huber for assistance with the text ofan earlier draft of the manuscript and Dr. John Kraeuter for

helpful comments and suggestions that improved the finalmanuscript substantially.

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