Differential okadaic acid accumulation and detoxification by oysters and mussels during natural and simulated Dinophysis blooms

A bloom of D. acuminata complex was detected in early March 2008 in the shellfish farming area of Baia Sul, southern Brazil. Cell density reached up to 4.7 x 10(4) cells/L at the surface by March 31st, quickly decreasing (< 4.0 x 10(3) cells/L) 1-2 weeks later as salinity increased (> 32) in all sampling stations. On average, commercial-sized mussels, Perna perna, accumulated 11-fold higher okadaic acid (OA) levels in the digestive glands (DG) (maximum 2422 ng/g) compared to those of oysters, Crassostrea gigas (maximum 271 ng/g). Moreover, 50 % of the mussel DG extracts tested (n = 42) produced acute toxic effects as assessed by mouse bioassay, whereas all oyster samples produced negative results (n = 17). In parallel, juvenile oysters, Crassostrea brasiliana and C. gigas, and juvenile mussels, P. perna, exposed to a laboratory-simulated D. acuminata complex bloom (1350-13,750 cells/L) accumulated 7.5, 23.4, and 51.1 ng OA/g in whole bodies (22.7, 66.1, and 183.3 ng OA/g in visceral tissues), respectively. Toxin levels in the whole bodies dropped to similarly low average levels in all bivalve species (3.6, 3.7, and 1.3 ng/g, respectively) after 168 h of depuration. Mussels, therefore, detoxified OA at faster rates (0.023/h) than oysters C. gigas (0.010/h) and C. brasiliana (0.004/h).