Habitat selection and adult-larvae interactions in settling larvae of soft-shell clam Mya arenaria

Abstract

Like many benthc taxa, the soft-shell clam Mya arenaria L. is patduly distributed in nature. Near Halifax, Canada (Eastern Passage), M. arenaria and several other species (Polydora cornuta, Pygospio elegans, Gemma gemma. Hydrobia sp.) occur in higher densities at a sheltered site than at an exposed site -300 m away with similar grain size but different sediment organic texture. Total fauna1 densities at the exposed site were comparatively low. To evaluate whether larval settlement plays a role in establishing M, arenaria patterns, laboratory flume experiments were conducted with competent M. arenaria larvae Natural cores from the sheltered and exposed sites with resident infauna intact, as well as cores from the same sites that had been defaunated by freezing, were inserted flush with the flume bottom. Highest settlement was observed in faunated cores from the sheltered site where M. arenaria are more common. Significantly lower settlement was observed in other treatments, including defaunated cores from the sheltered site. For corresponding treatments, settlement in sediment from the exposed site was less than that at the sheltered site. Of the abundant taxa in intact flume cores, Gemma gemma densities were a sign~ficant, albeit weak pred~ctor of M. arenaria settlement. We propose that G. gemma influence interface sediment characteristics which, in turn, result in differential larval response. Settlement patterns contradict a previous study (Emerson & Grant 1991; Limnol Oceanogr 36:1288-1300) that reported an absence of recently settled M. arenaria spat at the sheltered site, despite high numbers at the nearby exposed site. The contrast in results likely reflects our focus on settlement and their focus on spat abundance, and these results considered in tandem suggest that both pre-and post-settlement processes likely determine soft-shell clam distributions at Eastern Passage.

Settlement and Recruitment Patterns of the Soft-Shell Clam, Mya arenaria, on the Northern Shore of the Bay of Fundy, Canada

“…Cardoso et al (2006) suggest that differences in bivalve settler abundance between sites may be due to sediment grain size. M. arenaria are known to be broadly distributed in shallow northern boreal waters and are capable of burrowing into a wide range of sediment types from silt and mud to coarse sand (Alexander et al 1993;Snelgrove 1999). Cardoso et al (2006) results suggest that successful settlement might only be possible when settlement size is similar to or larger than that of sediment grain size.…”

Spatially structured genetic variation in a broadcast spawning bivalve: quantitative vs. molecular traits

“…body density for buoyancy, mucus strands for increased drag, and delayed metamorphosis (for a review see Young, 1995). Experimental evidence also suggests that pelagic larvae actively select substrate type for settlement (Ahn et al, 1993;Snelgrove et al, 1999). In M. balthica, shell dimensions have a strong impact during secondary migration, which it undertakes with the use of a mucoid thread in its first winter, taking it away from its high intertidal nursery areas into the entire range of habitats they will inhabit as adults (Beukema, 1993).…”

Facies Architecture and Ichnology of Recent Salt-Marsh Deposits: Waterside Marsh, New Brunswick, Canada

“…These bivalves easily tolerate extreme salinity fluctuations and salinities as low as 5 ppt (Gosner 1978) and are well adapted to colonize the brackish tidal creeks. Furthermore, M. arenaria larvae settle preferentially in sheltered sites (Snelgrove et al 1999). The low-energy environment of the tidal creeks, as a result of upstream dissipation of tidal energy and no direct wave assault is thus favorable for M. arenaria colonization.…”