Uptake kinetics of paralytic shellfish toxins from the dinoflagellate Alexandrium fundyense in the mussel Mytilus edulis

A laboratory study investigated cell ingestion, absorption of organic matter, and paralytic shellfish poisoning (PSP) toxin incorporation by Mytilus edulis exposed to a high-toxicity isolate of the red tide dinoflagellate Alexandrium fundyense (strain GtCA29, toxicity = 66 pg saxitoxin equivalents (STXeq) cell⁻¹). Maximum ingestion rate was achieved at 150 to 250 cells ml⁻¹. Clearance rates on A. fundyense were about 48 % lower than those for a non-toxic control diet of the diatom. Thalassiosira weissflogii. Mussels with no prior history of exposure to PSP maintained a constant ingestion rate over 17 d of exposure to a A. fundyense (at 256 cells ml⁻¹), and absorbed ca 62% of the organic matter ingested. They experienced no mortality or sublethal adverse effects during intoxication. Maximum (saturation) toxin levels of 4.5 × 10⁴ μg STXeq 100g⁻¹ were attained after 12 to 13 d, a value comparable to maximum toxicities reported during major toxic bloom events. Mussels could exceed the quarantine toxin level (80 μg STXeq 100g⁻¹) in < 1 h of exposure to high densities of this isolate. At saturation, they incorporated 79% of the toxin ingested, primarily in the viscera. This provides the first estimate of toxin incorporation efficiency in a bivalve under steady state conditions. Dinoflagellate toxins, determined by HPLC, were dominated by carbamate derivatives. The muscle, mantle/gill and foot of M. edulis showed significant enrichment in STX and reduction in the gonyautoxins GTX₂₊₃ and neoSTX relative to ingested cells. The toxin composition of the viscera more closely resembled that of ingested cells, reflecting the presence of numerous intact cells in gut contents. Through its pitential use of A. findyense as a sole food source, M. edulis is thus capable of remarkably efficient toxin accumulation at environmentally realistic dinoflagellate cell densities.