Dynamic modelling of phycotoxin kinetics in the blue mussel, Mytilus edulis, with implications for other marine invertebrates WmL, Silver% and A.D, Cembella Abstract: Modelling the uptake and detoxification kinetics of phycotsxins in marine filter-feeding bivalve molluscs is discussed and illustrated by a case study involving blue mussels (Mytilus edukis) in the lower St. Lawrence estuary in eastern Canada. A dynamic model was fit to empirical data acquired on differential responses of mussels transplanted from sites characterized by differing history of exposure to toxigenic blooms responsible for paralytic shellfish poisoning (PSP). Although it is difficult to collect sufficient data to calibrate complicated models, it appears that one- and two- compartment models are fully adequate for this type of modelling. Measuring phycotoxin levels in shellfish can be a useful and cost-effective adjunct to direct monitoring of phytoplankton toxicity in the water column, because ongoing filtration by shellfish provides an integrated estimate of the toxin to which they are exposed. R$surn$ : Nous examinons la modClisation de la cynCtique de lbbssrption et de 1'Climination des phycotoxines chez des mollusques bivalves filtreurs, et nous l'illustrons par une Ctude de cas portant sur la moule bleue (~itilus edulis) du bas estuaire du saint-Laurint, dans l'est du Canada. Un mod8le dynamique a CtC ajustC aux donnCes empiriques recueillies sur diffbrentes reactions de rnoules provenant de sites car~ctCrisCs par des hi~t~ires-diffdrentes d9expositionaux efflorescences toxiques responsables de l'empoisonnement par la toxine paralytique (PSP). Bien qu'il soit difficile de recueillir suffisamment de donnCes pour Ctalonner des modkles compliquCs, il semble que les modeles ii un et i?i deux compartiments sont parfaitement satisfaisants pour ce type de modClisation. La mesure des concentrations de phycotoxines dans les coquillages peut constituer un moyen utile et rentable pour complCter la surveillance dfrecte de la toxicite du phytoplancton dans la colonne d'eau, car la filtration en continu de l'eau par les coquillages permet d'obtenir une estimation intCgrCe de la quantitC de toxine i?i laquelle ils sont exposCs. [Traduit par la R&Iaction] Accumulation of phyeotoxins in marine invertebrates, including molluscs and crustaceans, is a major public health concern in coastal zones throughout the world (Shumway 1990). In regions where toxigenic blooms are frequent events, such as in northern Europe, Japan, and the Pacific and Atlantic coasts of North America, both recreational and commercial exploitation of shellfish resources is severely restricted (Shumway and Cembella 1993). Shell- fish vary widely in their capacity to ingest toxigenic micro&- gae and to sequester phycotoxins in various anatomical Received June 28,1994. Accepted August 25, 1994. 512453 WeL. Silvert. Habitat Ecology Division, Bedford Institute of Oceanography, Department of Fisheries and Oceans, Dartmouth, NS B2Y 4A2, Canada. A.B. Cernbella. Institute for Marine Biosciences, National Research Council of Canada, Halifax, NS B3H3Z1, Canada. compartments (Lassus et al. 1989; Bricelj et al. 1990, 1991; Bricelj and Cembella 1995). Bivalve molluscs typ- ically acquire phycotoxins through direct filter-feeding upon toxic microalgae from pelagic and benthic sources (Shumway et al. 1987), whereas accumulation in crus- taceans and gastropods is most often the result of sec- ondary transfer through the food chain (Shumway 1995). Among the major phycotoxin syndromes, paralytic shell- fish poisoning (PSP) has the longest recorded history and has accounted for the majority of human fatalities. As a consequence, many countries have implemented toxin mon- itoring strategies yielding several decades of comprehensive PSP toxicity data from a variety of species collected from fixed stations (Quayle 1969; Ridcash et al. 197 1; Shumway et al. 8988). More recently, toxicity data has been sup- plemented by routine monitoring of toxic phytoplankton blooms in an effort to acquire baseline time-series data on bloom dynamics and to provide an early warning of impending deleterious environmental effects (ICES 199%). Experiments on toxin kinetics in controlled laboratory sys- tems that have utilized sophisticated analytical methods Can. J. Fish. Aquat. Sci. 52: 521-531 (1995). Printed in Canada / Imamprim6 au Canada