Dinophysis blooms in Greek coastal waters (Thermaikos Gulf, NW Aegean Sea)

Abstract

The first documented Dinophysis bloom from Greek coastal waters associated with a diarrhetic shellfish toxins outbreak was recorded in January 2000 during the HAB monitoring program in Thermaikos Gulf. A species with morphological features similar to D. acuminata Claparède and Lachmann dominated this bloom. Maximum D. cf. acuminata abundance (85.4 × 103 cells L-1) appeared in February 2000. In 2001, high numbers of D. cf. acuminata (5 × 103 cells L-1) were recorded in April under conditions of weak thermal stratification, while in 2002 maximum numbers (37 × 103 cells L-1) of the same species were found in February under low temperature levels (11.5-12.5°C). All Dinophysis blooms persisted for no more than 4 months. In addition to cells resembling typical D. cf. acuminata, cells of similar shape but smaller in size were observed at different stages of the blooms. Other observations include couplets of large and small-sized cells, and also a larger robust form with a dense granular cytoplasm. The D. cf. acuminata population always presented a stratified vertical distribution with vertical peaks positioned in or just above the pycnocline. Among the physico-chemical parameters, water temperature appears to be the most important factor influencing the distribution of Dinophysis abundance.