The effect of mussel size, temperature, seston volume, food quality and volume-specific toxin concentration on the uptake rate of PSP toxins by mussels (Mytilus galloprovincialis Lmk)

The accumulation of paralytic shellfish poisoning (PSP) toxins by bivalves is a serious threat to public health all over the world. However, very litt le is known about the uptake kinetics of these toxins and the environmental factors that may modify this process. We have studied the effect of mussel size, temperature, seston volume, food quality, and volume-specific toxin concentration (VOSTOC), on the uptake rate of paralytic shellfish poisoning (PSP) toxins by mussels (Mytilus galloprovincialis), by means of a second order factorial experiment. Over a 3-day period, the mussels were fed artif icial diets containing Alexandrium minutum AL1V (a PSP toxin producer), Tet raselmis suecica, Ensiculifera spl and silt, to the levels required by each treatment. Mussel size, seston volume and VOSTOC were found to be statisti cally significant when the total toxin accumulated per weight of wet tissue was considered. Mussel size affected the uptake negatively and latter two positively. The interactions, mussel size-VOSTOC and mussel size-food quali ty were also significant. The response was not linear as shown by the signi ficance of the quadratic term of mussel size. Notwithstanding, when the PSP toxins accumulation per mussel was analysed, only one factor, the VOSTOC a nd the interactions, food quality-mussel size and food quality-seston volum e, were found to be significant. VOSTOC was the most important factor in th e accumulation of toxins, in our opinion, probably due to toxin assimilatio n being mainly regulated by the probability of contact between the toxins a nd the cellular walls of the digestive system. The size of the bivalve is a lso especially important because toxin concentration is usually calculated per weight of bivalve tissue and because the weight-specific ingestion incr eases with mussel size. The food quality, which was directly related to the assimilation of organic matter, had an inverse effect on toxin assimilatio n. In our opinion, this is probably due to the effect of inorganic particle s in enhancing the disruption of Alexandrium cells. Temperature had no effe ct on the uptake rate except for the accumulation of the gonyautoxin GTX1. (C) 2001 Elsevier Science B.V. All rights reserved.