Utilisation of the sinking spring diatom bloom by the benthos and benthic boundary layer zooplankton: R. Thompson, D. Deibel, C. Parrish.
A suite of biomarkers is being used to determine energy flow from the sinking spring phytoplankton bloom to the benthos and hyperbenthos, including phytoplankton pigments, fatty acids and sterols. Since the sinking bloom is the largest annual input of organic material to the benthos of Newfoundland bays, and because commercially important fish and shellfish feed demersally in these bays, this fundamental research programme is of considerable applied significance. Observations from the field and from laboratory experiments demonstrate that the deposit-feeding protobranch bivalve Yoldia hyperborea responds to an influx of organic matter and that the water column and benthos may be tightly coupled. Deep-living hyperbenthic predator populations, such as the chaetognath Parasagitta elegans, appear to be closely coupled to a productive food web resulting from sinking phytodetritus from the spring diatom bloom. Adults of these deep chaetognath populations seem to quickly consume near-bottom copepods that feed on sinking phytodetritus and incorporate this energy into a massive production of eggs. This burst in biological activity is very interesting, since the bottom water in Conception Bay is 0°C year round.

Physiological genetics of the mussels Mytilus edulis and M. trossulus: R. Thompson, D. Innes (Biology).
The two species of mussels occur sympatrically in Newfoundland and produce hybrids. The viability of hybrids and the mechanisms by which the hybrid zone is maintained are being examined. Both pre- and post- zygotic mechanisms are being investigated. A combination of nuclear and allozyme markers is being used. At most sites M. trossulus dominates the larval and juvenile stages, while M. edulis is dominant in the adults. There is a partial separation in the timing of the reproductive cycles, permitting some interbreeding between the species and accounting partially for the presence of hybrids. Preliminary work suggests that there may be partial blocks to fertilisation between the species. Laboratory studies are in progress to compare fertilisation rates for F1 x F1 crosses and backcrosses from F1s to the each parent species, as well as the growth and survival rates of the resulting larvae and spat. This work is relevant to the mussel aquaculture industry in Atlantic Canada, because both species and their hybrids occur at mussel farms, and there is evidence that in some sites M. trossulus is a less desirable product than M. edulis.

Lipid nutrition of commercially important bivalves: R. Thompson, C. Parrish, F. Shahidi (Biochemistry), M. Bricelj (NRC, Halifax).
The fatty acid and sterol requirements of selected cold-water bivalves are being investigated. All species studied are rich in long-chain PUFAs. The lipid composition of one bivalve, the mussel Mytilus edulis, is being compared with that of the phytoplankton at farms from which mussel samples are obtained. Emphasis is being placed on larval and juvenile stages, especially in the sea scallop Placopecten magellanicus, as relatively little is known about these stages, and metamorphosis represents a critical phase in the life-history of the organism during which there is considerable structural and metabolic reorganisation, often leading to high mortalities in hatcheries. In one case an important functional role has been identified for a specific PUFA in regulating membrane fluidity in scallop membranes at low temperature.

Environmental effects of mussel aquaculture: R. Thompson, D. Deibel, R. Rivkin, M.R. Anderson (DFO).
A multidisciplinary approach is being taken to investigate the environmental effects of mussel aquaculture at two sites in northeast Newfoundland. The study focuses on the effects of excretion and particle removal by mussels on the composition and production of the plankton community (including microorganisms) and the benthos. The emphasis is on nitrogen cycling.