Are mussels and oysters capable of reducing the abundances of Picochlorum sp., responsible for a massive green algae bloom in Thau lagoon, France?

After an exceptional hydroclimatic year, a “massive green algae bloom”, dominated by the autotrophic picoeukaryote Picochlorum sp, was observed in 2018–2019 Thau lagoon. Oyster farmers informed decision-makers and scientists about alarming halt to growth, loss of flesh weight abnormal mortality commercial size oysters, whereas mussel no adverse effects. Two hypotheses were tested. First, Mediterranean mussels are capable filtering spp. Pacific flat oysters not. Second, picophytoplankton filtration rates vary with oyster, spats having greater ability than juveniles oysters. A series experiments conducted February 2019 using beakers containing (i) three different types solutions (1 L): water from lagoon at rate 45.2 million cells.L−1 (P) or diluted 20.7 cells. L−1 (D) solution Isochrysis galbana 9.4 L−1; (ii) absence presence five bivalves: sizes (spat, juvenile size), size. Four separate samples taken during 40-min incubation period measure fluctuations nanophytoplankton abundances flow cytometry. Retention efficiency (%) compared according species In contrast average 21.4 g, able drastically reduce depleted nearly one cells per minute 11.4 °C. These results suggest that 1228 t died 2018 before bloom could have helped limit if they had survived heat anoxia.