Predation of cockles (Cerastoderma edule) by the whelk (Buccinum undatum) under laboratory conditions

The feeding rate and behaviour of whelks (Buccinum undatum) offered cockles (Cerastoderma edule) in laboratory experiments were examined. When presented with cockles in a range of sizes (10–40 mm), 14 B. undatum (34.6–88.3 mm), held individually in aquaria, consumed a wide size range of cockles. Small whelks (\u3c40 \u3emm) consumed cockles (\u3c23 \u3emm), whereas large whelks, (\u3e60 mm) ate a greater number of larger cockles (\u3e30 mm) and a wider size range of cockles (12–40 mm) than smaller whelks. The majority (90%) of the shells of the predated cockles were undamaged and the few (B. undatum feeding on C. edule showed a method of attack that has not previously been reported and involved the use of the whelk\u27s foot to asphyxiate the cockle or to pull the shell valves apart. No filmed evidence was found for the previously reported shell ‘wedging’ technique for prising open the closed shell valves of C. edule, although 10% of the shells of consumed cockles in feeding experiments had damaged shell margins

Swimming rate and responses of larvae of three mactrid bivalves to salinity discontinuities

Straight-hinge, umbo and pediveliger larvae of the mactrid bivalves Spisula solidissima, Mulinia lateralis and Rangia cuneata were exposed to intense salinity discontinuities of 0, 5, 10 and 15 parts per thousand in vertically oriented swimming chambers. Larvae concentrated in the region of highest gradient, i.e. at the salinity discontinuity, regardless of species, stage of development or larval brood. S. solidisima larvae, initially swimming at 30 parts per thousand salinity, crossed discontinuities of both 5 and 10 parts per thousand but not of 15 parts per thousand. M. lateralis larvae, initially swimming at 25 parts per thousand salinity, also crossed a discontinuity of 5 parts per thousand but not of 10 or 15 parts per thousand. R. cuneata larvae, initially swimming at 10 parts per thousand salinity, generally preferred to remain at that salinity. Swimming and passive sinking velocities, defined as vertical distance traversed per unit time, were measured in different salinities under constant temperature and light. For all species, swimming rate changed with larval stage, highest velocity occurring at the umbo stage. Upward swimming rate of S. solidissima larvae ranged from 0.18 to 0.49 mm s-1 and increased with increasing salinity. Upward swimming rate of M. lateralis larvae ranged from 0.25 to 0.50 mm s-1, but was not consistently related to salinity. Upward swimming rate of R. cuneata larvae ranged from 0.18 to 0.53 mm s-1; swimming rate of pediveliger larvae increased consistently as salinity decreased. Downward swimming rates were similar to upward rates. No significant differences in downward swimming rate were detected in relation to salinity. Passive sinking was more frequent than active downward swimming in umbo and pediveliger larvae. Sinking rate increased with larval size of S. solidissima and M. lateralis larvae; however, R. cuneata straight-hinge larvae sank faster than umbo and pediveliger larvae. Species-specific differences in larval sinking and swimming are related to the different habitats occupied by adults. Larvae of S. solidissima, a marine stenohaline species, remained in high salinity water. Larvae of M. lateralis, a euryhaline species, use their preference for discontinuities or higher salinity water to assist retention in partially mixed estuaries. High sinking rate and short larval period of R. cuneata may offset the behavioural characteristic and aid in the retention of R. cuneata larvae in the low salinity zone of most partially mixed estuaries

Effects of oyster population restoration strategies on phytoplankton biomass in Chesapeake Bay: a flexible modeling approach

Cultural eutrophication in estuaries and other coastal systems has increased over the last 50 yr. Some recently proposed strategies to reverse this trend have included the restoration of bivalve suspension feeders as an ecological tool for reducing phytoplankton biomass. The ecological benefits accruing from such bivalve restoration will be dependent on the characteristics of the estuary, as well as how restoration is implemented. We developed a filtration model to estimate the effect of bivalve restoration on the rate of phytoplankton removal over a range of spatial and temporal scales and used it to compare alternate restoration strategies for the eastern oyster Crassostrea virginica in Chesapeake Bay, USA. Model results suggested that currently accepted restoration goals for oysters in the bay are unlikely to result in significant bay-wide reductions in phytoplankton biomass. This is partially due to low current biomass targets for oyster restoration, but also important are several spatial and temporal mismatches between oyster and phytoplankton biomass that may limit the ecological benefit of oyster restoration. Our model did predict important increases in phytoplankton removal by oysters at the tributary scale, and this effect was dependent on where oyster restoration was achieved and whether restoration and management plans affected the size distribution of oysters. Our findings suggest that the ecological benefit of restoring bivalve populations are variable, and a comparative model analysis of restoration plans in particular systems can be highly beneficial to maximizing the benefit-to-cost ratio of restoration efforts intended to reduce the negative effects of cultural eutrophication

Can artificial substrates enriched with crustose coralline algae enhance larval settlement and recruitment in the fluted giant clam (Tridacna squamosa)?

10.1007/s10750-008-9698-0Hydrobiologia625183-90HYDR