Veligers from different populations of sea scallop Placopecten magellanicus have different vertical migration patterns

Abstract

ABSTRACT. Veligers spawned by adults collected from 3 different populations (Georges Bank, Passamaquoddy Bay and Mahone Bay, all on the northeastern coast of North America) of giant scallops Placopecten nlagellanicus were maintained for 2 mo in replicated, 9.5 m deep, polyethylene mesocosms with a 1.5"C thermal gradient at mid-depth and a 12/12 photoperiod. The populations came from varied hydrographic regimes that might require vel~gers to have different vertical migration patterns if they are to be in an appropriate area for settlement when they reach competency. Veligers from all population~ were found in shallower depths at night than during the day, developed strong bio-convective cells when numbers were high at the surface and were seldom found below the thermocline until about 21 d after spawning. Under similar conditions, veligers from the 3 populations exhibited significantly different vertical migration patterns and depth distributions. These patterns of vertical distribution are unlikely to be due to differences in buoyancy, growth rate, food density, settlement preference or mesocosm effect, and they differ substantially from patterns of mussel veligers raised according to the same protocol. Such differences may reflect selection for different behaviors in different populations, arguing for an active and genetically controlled component to vertical movements of scallop veligers. The observed patterns of vertical distribution could produce marked differences in horizontal transport in the various physical regimes; increased self-recruitment seems the most likely explanation for the intense selection required to fix such behavior in populat~ons.

Effect of thermoclines and turbulence on depth of larval settlement and spat recruitment of the giant scallop Placopecten magellanicus in 9.5 m deep laboratory mesocosms

“…Giant scallop larvae have been shown to undertake die1 vertical migrations both in laboratory mesocosms (Silva-Serra & O'Dor 1988, Silva-Serra 1995, Gallager et al 1996, Manuel et al 1996b) and in the field (Trem- . .…”

“…Larvae from Georges Bank, Passamaquoddy Bay (New Brunswick), and Mahone Bay (Nova Scotia) show dissimilarities in their vertical migration behaviour in laboratory mesocosms (Manuel et al 1996b) which may be Linked to genetic differences (Manuel et al 1996a). While larvae from these 3 populations show similar settlement depth distributions in 9.5 m deep mesocosms with a 1.5"C thermocline established at a depth of 4 to 5 m (i.e.…”

“…Species from a wide variety of taxonomic groups including polychaetes, gastropods, bivalves, cirripedes, decapods, bryozoans, and echinoderms produce larvae whose vertical position in the water column has been shown to be influenced by vertical discontinuities in salinity and/or temperature (e.g. Harder 1968, Oshurkov et al 1982, Scrope-Howe & Jones 1986, Boudreau et al 1991, 1992, Thiebaut et al 1992, Raby et al 1994, Gallager et al 1996, Manuel et al 1996b. Although the scientific literature on the vertical distribution of invertebrate planktonic larvae in the water column in relation to vertical boundaries and water column mixing is substantial, very little work has been conducted to examine how these factors influence settlement of larvae [but see Boudreau et al (1992) who found that laboratory thermoclines significantly reduced the number of post-larval lobster Homarus amencanus settling in comparison with control columns of water with no temperature discontinuities].…”

Colonization of artificial substrata by teredinid larvae released from a previously infested focus at Ilha Grande Bay, RJ

“…Different studies have established that larval settlement is affected by current velocity, there existing a critical range for the effectiveness of this event. Although, recently, no study could be found referring to processes involving teredinids, some investigations have focused on the importance of currents to other marine invertebrates (Hunt & Scheibling, 1996, * Author for correspondence on the recruitment of Mytilus trossolus and M. edulis; Manuel et al, 1996, on the migration of Placopecten magellanicus; and Judge & Craig, 1997, on the recruitment of Balanus eburneus). Besides the action of water currents, teredinids may guarantee their long distance dispersion through the infestation of wooden craft hulls or driftwood.…”

Temporal variability and vertical structure in larval abundance : the potential roles of biological and physical processes

“…Yet, the applicability of these diel vertical migration studies to populations separated in time (daily or seasonally) and space remains unknown (e.g., Banse 1964Banse , 1986. Moreover, Manuel et al (1996) presented evidence that larvae from different populations of the same species display different vertical migration patterns.…”