Domoic acid accumulation in Mytilus galloprovincialis: laboratory experiments with Pseudo-nitzschia multiseries

Domoic acid (DA) accumulation was studied in Mytilus galloprovincialis collected from rafts in Ría de Vigo, Spain, during short-term lab experiments. Mussels were fed Pseudo-nitzschia multiseries cultures (1900, 3800, 6000 cells/ml) and P. multiseries blooming in a phosphorus limited mesocosm. Toxin concentration in mussel whole tissue was proportional to toxin offered in food except for the lowest Pseudo-nitzschia concentration (1900 cells/ml). In that experiment, no toxin was detected in mussel whole tissue while food quantity, measured as chlorophyll a, was below minimum requirements for mussels to save energy for maintenance at limited ingestion. Domoic acid in fecal material was higher than in mussel whole tissue in all experiments. A large % of missing DA from the toxin offered to mussels by food was assumed to be due to toxin metabolism within the mussel body, to symbiotic DA-utilizing bacteria and/or to dissolved DA released in seawater as a result of food processing by the mussels. Introduction Domoic acid (DA) is a water-soluble neurotoxic amino acid, produced by the marine diatom Pseudo-nitzschia. Domoic acid intoxications of suspension-feeding bivalves occur primarily via ingestion of toxic diatoms during feeding activity rather than from the dissolved fraction. Mussels, due to their ability to remove large amounts of particulate matter, can transfer algal toxins to higher trophic levels acting as effective DA vectors (Vale & Sampayo, 2001). Mussels have flexible feeding behavior (filtration, ingestion ,assimilation) which allows them to maintain a positive energy balance, even from nutritionally poor and/or concentrated suspensions (Kreeger et al, 1995). The aim of the present study was to examine DA accumulation in bivalves exposed to low levels of toxin under different quantity and quality of food. The exposure of Mytilus galloprovincialis to toxic Pseudo-nitzschia multiseries cells was investigated in shortterm bioaccumulation experiments. Materials and methods Cultured mussels M. galloprovincialis were collected from Ría de Vigo mussel rafts (Galicia NWSpain) during July 2003. Before the experiments, pooled mussels were examined for background toxin in their whole tissue. Individuals, from the same population with shell length 5-6cm, were kept for acclimation to lab conditions in natural seawater without supplementary food. Three different food concentrations with P. multiseries from monocultures (1900, 3800. 6000 cells/ml) and water from P. multiseries blooming in a phosphorus (P) limited mesocosm were tested to simulate field conditions under potential phosphorus limitation (Table 1). Production of DA is