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First record of Mercenaria mercenaria (Bivalvia: Veneridae) and Ensis directus (Bivalvia: pharidae) on Bay of Biscay, Iberian Peninsula.

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 dominant Ensis 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, sudden range extensions are often prompted by the humans. This may be 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 opportunities for species to colonize areas where, until recently, they were not able to survive. We report the establishment of two bivalves--Mercenaria mercenaria and Ensis directus--in the southwest Bay of Biscay. Bivalves M. mercenaria and E. directus are not the only nonnative bivalves in these waters. The Japanese carpet shell Ruditapes philippinarum (Adams & Reeve, 1850) and its hybrids R. philippinarum x Ruditapes decussatus (Urtado et al. 2010), the Japanese oyster Crassostrea gigas (Thunberg, 1793), and the Pacific semelid Theora lubrica Gould, 1861 have also been reported in the Bay of Biscay (Adarraga & Martinez 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 Veneridae family. These clams can reach a size of 150 mm, but usually measure 60-70 mm (Stanley & Dewitt 1983). The native distribution range of the species is from the Gulf of St. Lawrence in Canada through the northern Gulf of Mexico to Texas (Loosanoff 1946, Harte 2001). The bivalve M. mercenaria has been introduced to the west coast of the United States-British Columbia, 49[degrees]N, to California, 33.7[degrees]N, (Coan et al. 2000), Puerto Rico Island, the United 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 bivalve M. mercenaria is found in intertidal as well as subtidal habitats 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[degrees] N, 5.27[degrees] W; Asturias, northern Spain; Fig. 1). Twenty-four living specimens of M. mercenaria were collected in shallow waters. These specimens were deposited and preserved in the collection of the Department of Biology of Organisms and Systems at the University of Oviedo, Spain. After 33 y, in January 2011, near Video Cape in a sandy cove, M. mercenaria was found again.

The bivalve Ensis directus (Conrad, 1843), or American razor clam or American jack knife clam, is native to the western Atlantic Ocean from Labrador, 60[degrees]N, to South Carolina, 34[degrees]N (Coan et al. 2000). This species was discovered in Europe in the Elbe estuary in June 1978. Since 1982, E. directus has become common along the northern coast of Holland, Britain, and Denmark (von Cosel et al. 1982). By the end of the 1980s, E. directus was the dominant Ensis species along the Belgium shores and southern Norway. In June 1991, it was found in the French North Sea (Luczak et al. 1993). By 1999, E. directus had spread along the English Channel (Davoult et al. 1999). More recently, in 2005, this species was reported in the Baltic Sea (Streftaris et al. 2005) (Fig. 2B). The American razor clam lives in sand, muddy sand and gravel from the intertidal to the subtidal zones in bays and estuaries. Its adaptability to different substrates and depths allows this species to occupy higher intertidal habitats where native Ensis species do not five.

Data Collection and Analysis

Survey and sampling of M. mercenaria and E. directus were carried out taking advantage of 2011 equinoctial tides. The specimens were obtained from the intertidal and shallow subtidal sandy areas at low tide (Fig. 1). Both species were collected by excavating quadrats (50 x 50 cm, and 25 cm deep) and passing the sand through sieves of 0.5-mm mesh. Eighteen replicate quadrats were taken along 4 transects along the coastline at these localities. The total intertidal area of each sample location was Musel Port of Gijon (~480 [m.sup.2]), Video Cape cove (~600 [m.sup.2]), and Otur sandy beach (~540 [m.sup.2]); and a portion of the external basin (~320 [m.sup.2]) [m.sup.2]) in Villaviciosa estuary. All collected and central basin (~360 [m.sup.2]) in villaviciosa estuary. All collected specimens were measured and classified by size. We also estimated average density and substrate characteristics. Particle size analysis was conducted using the Wentworth scale, and determination of organic matter by loss of weight on ignition (Buchanan & Kain 1971).

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

The specimens found in January 2011 in the same locality had an average density of 2.17 specimens/[m.sup.2] (n = 36, SD = 3.81), and an average shell size of 33 mm (n = 20, SD = 2.22). Specimens ranged from 30-39 mm, and only 2 individuals exceeded 35 mm, indicating that M. mercenaria has reproduced in 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 was medium sand (median grain size, Md, [bar.x] = 0.30 mm; SD = 0.06) and with organic matter ([bar.x] = 1.59%; SD = 0.28) content. This sandy 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) trunculus Linnaeus, 1758. Another Veneridae, Chamelea striatula (da Costa, 1778), which was very common at this locality during the early 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 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 farm activities or from unknown sources. Therefore, we believe that the introduction of M. mercenaria took place in one or very few episodes 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[degrees]C per decade during the past 30 y (IPCC 2001). In Video Cape, in 2011 the mean annual water temperature was 12.9 [+ or -] 1.03[degrees]C, with highs of 19.8[degrees]C in the summer, and a winter minimum of 7.7[degrees]C. These temperatures could favor the growth and reproduction of hard clams in this area.

Ensis direetus (Conrad, 1843)

Live specimens of E. directus were found at three northern Spain localities--Otur sandy beach (43.16[degrees] N, 2.15[degrees] W), Musel Port of Gijon (43.32[degrees] N, 5.42[degrees] W), and Villaviciosa estuary (43.31[degrees] N, 5.23[degrees] W)--in shallow waters (Fig. 1). In the Villaviciosa estuary (in the central basin), E. directus occurs sympatrically with Solen rotundatus Spengler, 1794 (syn. Solen marginatus Pulteney, 1799; see Huber (2010)) and other important natural resources of this estuary, including tubeworm Diopatra species, which are highly appreciated as fishing bait (Arias et al. 2010). Here, E. directus was found in an intertidal fine to medium sand (Md, [bar.x] = 0.27; SD = 0.05) with a mean organic matter content of 1.68% (SD = 0.27). In this Tellina tenuis community, E. directus reached densities of 5.6 individuals/ [m.sup.2] (n = 36, SD = 7.08). The size range varied from 105 149 mm, and the average size was 125 mm (n = 31, SD = 4.12). On the outer basin of Villaviciosa estuary, E. directus was the only Solenaceae that could be found, but in the past, the native species Ensis 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 Organisms and Systems, we have preserved specimens of E. arcuatus from the early 1980s to late 1990s from the outer basin of Villaviciosa estuary. These specimens range from 42-112 mm (n = 18, SD = 4.87) (Anadon et al. 1997), indicating this area recruited E. arcuatus. At this locality, the absence of E. arcuatus during 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 Ensis species like E. arcuatus in the Villaviciosa estuary. The American razor clam population in the Villaviciosa estuary has become large enough that local fishermen are beginning to harvest large specimens of E. directus for human consumption and small specimens for fishing bait (surf casting). Here, the recent harvesting of this species by the use of handheld digging tools, contrasts with mechanical harvesting with equipment such as scuba and hydraulic harvesters like those described for the St. Lawrence River 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 were released from ballast water off the Elbe estuary (von Cosel et al. 1982). Since the early 1990s, the Spanish Musel Port of Gijon has had regular routes to the port of Rotterdam in the Netherlands and the ports of Hamburg, Luebeck, Bremen, and Duisburg in Germany. In 2000, 24 different merchant ships from Rotterdam and 10 from Germany (mainly from the port of Hamburg) landed at Gijon. These included 4 weekly shipping lines (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 is probably a result of larvae drifting with water currents.

ACKNOWLEDGMENTS

We thank Dr. Markus Huber for assistance with the text of an earlier draft of the manuscript and Dr. John Kraeuter for helpful comments and suggestions that improved the final manuscript substantially.

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ANDRES ARIAS * AND NURIA ANADON

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

* Corresponding author. E-mail: ariasandres.uo@uniovi.es

DOI: 10.2983/035.031.0107
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Author:Arias, Andres; Anadon, Nuria
Publication:Journal of Shellfish Research
Article Type:Report
Geographic Code:4EUSP
Date:Apr 1, 2012
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