Primary Studies On Filter-feeding Physiology Of Three Important Marine Bivalves On Two Red Tide Dinoflagellates

Based on the research of feeding pressure of marine bivalves on phytoplankton, this paper focuses on the progress of biological control of red tide, and the prevention and control of harmful red tide. General methods are used to study the feeding pressure and metabolism of three commercially important bivalves (Crassotrea gigas, Mytilus edulis, Chlamys ferreri) on two harmful red tide dinoflagellates (Alexandrium tamarense, Gymrodinium sp.), and the metabolism physiology of the animals after the consumption of these poisonous microalgae.The experiment was carried out between March 2002 and November 2003, into 3 stages. During the first stage (pre-experiment phase), literatures on methods and instruments for the experiment were consulted, feeding physiology of the bivalves was observed, and clones of red tide dinoflagellates were introduced and cultured in the laboratory. Based on the results of the pre-experiment phase, feeding rates of the three bivalves on two red tide dinoflagellates under different temperatures were studied for the second phase, and the effects of feeding on Dicrateia zhanjiangnsis Hu. var, sp. (an ordinary feed microalgae) after the ingestion of dinoflagellates were investigated. During the last phase, further study was carried out on ingestions of Alexandrium tamarense during 3 d continuous feeding experiment. Direct ingestion of log-phase dinoflagellates and metabolism physiology was studied for the bivalves; and the effects of different rearing density on feeding rate were compared.During the second phase (2002/9~2003/4), ingestion of three bivalves on two dinoflagellates under different temperatures was studied respectively. The results indicate that ingestion rate of Crassotrea gigas, Mytilus edulis, Chlamys ferreri on two above mentioned dinoflagellates is relatively high: ingestion rate on 10 000cells/ml Gymrodinium sp. is up to 107cells/h, whereas 1 000 cells/ml Alexandrium tamarense is up to 106cells/h. To some extent, the increase of ingestion rate correlates with the increase of temperature. Maximum feeding rate of Crassotreagigas and Mytilus eduli is occurred between 17and 22 and for Chlamys ferreri it is about 22.The IR of Chlamys ferreri on A. tamarense at the controlled temperatures is smaller than the other two bivalves, while Crassotrea gigas enjoys the highest 1R on the two dinoflagellates at any of the temperature controls. However, M. edulis alone exceeds in both CR and IR per unit dry weight. No significant effect was found for dinoflagellates on the afterwards ingestion of D. zhanjiangnsis for the bivalves (P>0.05).The CR (Clearance rate) of three bivalves on toxic dinoflagellate Alexandrium tamarense were continuously measured at 17 in laboratory conditions in April 2003. Each species was fed with A. a reference algal Dicrateia zhanjiangnsis Hu. var. sp., B. mixture of D. zhan-jiangsis and 1.5L cell-free A. tamarense cultural medium and , C. mixture of A. tamarense cells and D. zhan-jiangsis. The results indicated that (1) the cell-free medium of A. tamarense culture had no significant effect on the CR of the above bivalves 0.05), (2) All bivalves showed remarkable decline of CRa in contrast with the control (P<0.01) when fed with A. tamarense plus D. zhan-jiangsis cells, whereas RE and IR of A. tamarense did not change significantly during the 3 days. CRa of the three bivalves changed with time, and the order was oyster>mussel>scallop. whereas RE and IR of A. tamarense in the mixture had no evident variety during the 3 days. (3) Provided with the evidence from this study, esp. ingestion rate, mussel might be a potential candidate for controlling the A. tamarense red tide.30L Alexandrium tamarense and Gymrodinium sp. were cultured at 16and 22 in laboratory in May 2003. Feeding pressure of Crassotrea gigas & Mytilus edulis on the two red tide dinoflagellates and subsequent physiological response of the animals were studied. In Oct, 2003, further experiment was carried out on the two bivalves, in order to find the optimal culture density of bivalves, which can ach...