The Accumulation Of Amnesic Shellfish Toxins (AST) In King Scallop Pecten Maximus And Its Impact

Research developments on amnesic shellfish toxins (AST) and its marine diatom producer Pseudo-nitzschia sp. is reviewed; laboratory experiments were carried out to investigate the accumulation of the toxic agent - domoic acid (DA), in larval, juvenile and adult King scallop Pecten maximus, and it's impact on these animals; a behavioral study was done to examine the possible predator counteraction in juvenile scallops because of DA incorporation. Results of these studies are detailed as follows:1. A general overview is given on the latest developments of study on the origin, distribution, and toxicology of domoic acid. The physiological and ecological aspects of DA producing Pseudo-nitzschia sp. are presented. The interactions between DA and marine organisms are suggested, and the advance of analysis and monitoring methods of AST are followed. The importance of AST research in China is suggested and future work on Pseudo-nitzschia biotoxin is discussed.2. Domoic acid (DA) is a highly toxic phycotoxin produced by bloom forming marine diatoms Pseudo-nitzschia sp. It was found that bivalves can accumulate this toxin to a high level through their feeding activities, and thus cause illness or death in consumers. In this study, larvae of king scallop Pecten maximus, were exposed to dissolved domoic acid (DA) for 25 d, and the toxin accumulation and effects of harbouring this toxin were investigated. Scallop larvae incorporated DA continuously during the larval culture period and accumulated a maximum DA level of 5.21pg individual-1 when exposed to a solution of 50ng ml-1 dissolved DA. As a result of the DA treatment, larval growth, measured in terms of shell length and the appearance of the eye-spot, and larval survival were significantly compromised. This is the first study on DA incorporation dynamics in P. maximus larvae, signifying the potential of using shellfish larvae for the study on mechanisms of phycotoxin accumulation. The negative effect of DA exposure suggests that this toxin could possibly influence natural recruitment in P. maximus, and it may be necessary to protect hatchery-cultured scallop larvae from DA during toxic Pseudo-nitzschia blooms.3. Juvenile king scallop Pecten maximus were exposed to domoic acid (DA) and the toxin accumulation and effects of bearing this toxin were investigated. The juvenile scallops incorporated a relatively low DA burden of 15.9ng g-1 through feeding on DA spiked feed, which was similar to those being exposed to 10 and 50ng ml-1 dissolved DA. The maximum DA accumulation, 302.5ng g-1 whole tissue, was achieved by scallops being maintained in 100ng ml-1 dissolved DA. No significant effect of exposure to DA was observed in terms of feeding rate (on microalgae), shell valve activity (shell clatter), righting response, or the secretion of bysus. However, long term negative impacts on growth rate and survivorship were found for scallops exposed to DA spiked feed. This is the first study on DA accumulation in juvenile P. maximus and on the negative effect of DA on this life history stage.4. A simple method of spiking formulated feed with domoic acid was developed in this study. DA feed was prepared by mixing 0.15ml dissolved domoic acid at a concentration of 100μg ml-1 with 0.1g formulated feed, and drying the mixture under room temperature for 2h. The prepared DA feed contained domoic acid at 0.19pg per particle and 46.72% of added domoic acid was retained in the feed. Relatively high DA retention (50%±) was recorded up to 2h after the DA feed being soaked in the water. Exposure to DA feed for 7d did not increase the tissue DA level of adult Pecten maximus significantly up to 60d after the exposure, and the increase of their gonad index was not significantly different from the control. No significant change in DA level was found for sperm tissue, ovary or fertilized eggs as a result of DA exposure. These results indicate that DA excretion may be more efficient than DA accumulation under the current experimental conditions, and the mechanism of domoic acid incorporation in P. maximus may involve intracellular biotransformation. 5. Predation of juvenile king scallop Pecten maximus (shell height around 1.2 cm) by common shore crab Carcinus maenas (Linnaeus) (carapace width 5.5 cm) and sea star Marthasterias glacialis (Linnaeus) (arm length 10.5 cm) was examined in this study. One group of the scallops was exposed to domoic acid (DA) and accumulated this toxin at a concentration of 15.9 ng g-1 before the experiment. Scallops in the other group were DA free. The longer time both predators stayed near the DA free scallops may reflect their choice for these scallops. There was possibly a DA recognition mechanism in both predators, as more DA free scallops were consumed by both predators during the second 48h feeding experiment. The'avoiding'behaviour of DA contaminated prey was more evident in the sea star's movement during the second 48h. This was only a preliminary study on possible'predator counteraction effect'of bearing DA in juvenile scallops.