Physiological responses of marine bivalves in Southern China to harmful algae

There is a growing concern on the potential impacts of the harmful algal bloom (HAB) on the human society. The HAB incidents increase substantially in recent decades in many parts of the world, including southern China. The effects of HAB on the physiological responses of bivalves, which can accumulate high levels of toxins in their soft tissues, attract many attentions due to the potential loss in shellfishes industry. Paralytic shellfish poisoning (PSP) toxins are one of the dominant phycotoxins affecting the southern China area; death and illness of human had been recorded. In this study, the physiological responses of bivalves in southern China to harmful algal bloom were studied. Toxic dinoflagellate Alexandrium tamarense ATHK is the local PSP causative organism affecting the area. Experiments were carried out to determine whether toxic A. tamarense could impose any harmful effects on the physiology of bivalves after short term and long term exposure. Clam Ruditapes philippinarum, mussel Perna viridis and scallop Chlamys nobilis were chosen as the model bivalves as different toxin burdens had been found in these bivalves in the field measurements. Results on feeding rate and absorption efficiency indicated that toxic A. tamarense had no effect on the local bivalves within the short term exposure period. However, after long term exposure on toxic dinoflagellates, the clam R. philippinarum reduced their growth rate and scope for growth, due to the reduced clearance rate and absorption efficiency, and the increase in respiration rate. Significant mortality was also recorded for both mussel P. viridis and clam R. philippinarum. It is concluded that the PSP producing dinoflagellates in this area had potential harmful impacts on the physiology of the bivalves, leading to potential losses to mariculture industry in southern China