. The Canadian field-naturalist. Natural history. 2003 Gagnon and Haedrich: European Giant File Clam in NW Atlantic 441. Figure 1. Collection sites of the Giant File Clam, Acesta excavata, (filled circles) in Bay d'Espoir, Newfoundland. 40 degrees and there are frequent overhangs (Figure 2). In areas where slopes are not as steep, the bottom is mostly made up of silty sediments. Benthic biomass in this basin appears to be important and primarily dominated by suspension and filter feeders such as sponges, several species of anemones, sea pens, the stalked cirriped Arcoscalpellum mitchellotianum
. The Canadian field-naturalist. Natural history. 2003 Gagnon and Haedrich: European Giant File Clam in NW Atlantic 441. Figure 1. Collection sites of the Giant File Clam, Acesta excavata, (filled circles) in Bay d'Espoir, Newfoundland. 40 degrees and there are frequent overhangs (Figure 2). In areas where slopes are not as steep, the bottom is mostly made up of silty sediments. Benthic biomass in this basin appears to be important and primarily dominated by suspension and filter feeders such as sponges, several species of anemones, sea pens, the stalked cirriped Arcoscalpellum mitchellotianum, and Giant File Clam (Acesta). This rich invertebrate fauna is supported by a high zooplanktonic biomass (Haedrich and Gagnon 1991), although no estimates of surface primary production are available for this area. The water column in the outer basin is divided in four distinct layers on the basis of temperature and salinity (Haedrich and Gagnon 1991; Figure 2). Below 250 m, which corresponds approximately to the sill depth at the entrance of the fjord, benthic communities are exposed to a uniformly warm ( to °C), saline () and stable water mass derived from the con- tinental slope water. Above, a cold water layer (40- 160 m, to °C) associated with the less saline Labrador Current and a transition layer (160-220 m, to °C) maintain the deep isolated layer; only limited exchanges occur with the Laurentian Modified Slope Water from the outside (Hay and deYoung 1983; Richard and Haedrich 1987). Materials and Methods The first specimens of Acesta were collected dur- ing a benthic sampling program conducted in the outer deep basin of Bay d'Espoir, Newfoundland, Canada, on 10 December 1984. During that sampling, one large, complete valve and fragments of smaller valves were found in the anoxic, muddy sub-surface sediment of a van Veen grab sample from a site to the southeast of Goblin Head, at approximate- ly 600-700 m depth (Figure 1; circa station
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