Paralytic Shellfish Poisoning Toxin and Shell Valve Movements Response of Mussel Mytilus edulis Exposed to Toxic Dinoflagellates, Alexandrium catenella (Group Ⅰ) and A. pacificum (Group Ⅳ)

Abstract

In Korea, paralytic shellfish poisoning (PSP) caused by Alexandrium catenella and A. pacificum is gradually expanding from the Busan coast and Jinhae Bay to the southern coast. Moreover, the shipment of farmed bivalves is prohibited according to the PSP regulatory limit (less than 80 μg/100 g of tissue) in the spring of every year. Moreover, the early detection of shellfish toxins has been gradually accelerated with increasing of water temperature, and the occurring area is also expanding. Mytilus edulis among bivalves cultivated in coastal waters in Korea is considered useful marine biological resources due to their high production and high commercial value, so more thorough management is required. M. edulis is known to be a filter feeding species, which is easily poisoned than other bivalves. Moreover this species showed high bioaccumulation of toxic and contaminant substances in the same environmental conditions due to its high adaptability. Thus, to the provide basic information about PSP forecasting, change in PSP toxin of M. edulis exposed by two toxic dinoflagellates A. catenella and A. pacificum and effects of two toxic dinoflagellates on the shell valve movements (SVMs) were investigated. Toxification experiment of M. edulis after exposing the toxic dinoflagellates A. catenella and A. pacificum was conducted by one-time exposure as well as continuous exposure (10, 100, and 1,000 cells/ml) under experimental tank in the laboratory. The detoxification experiment was conducted by experimental tank in the laboratory as well as field experiments. In the toxification of M. edulis following one time exposure of two toxic dinoflagellates, PSP toxins of M. edulis were detected with the exposure of toxic dinoflagellates, and toxin amounts and toxicities of M. edulis exposure by A. catenella were increasing faster than those of A. pacificum. The maximum toxin amount of M. edulis exposure by A. catenella was above 2 times higher than that of A. catenella. In the toxification M. edulis following continuous exposure of two toxic dinoflagellates, the toxin amount and toxicity in M. edulis was increasing with increasing cell density of two toxic dinoflagellates. Toxicity of M. edulis exposed by A. catenella (maximum 7.40 MU/g) was higher than that of A. pacificum (maximum 3.15 MU/g) such as one-time exposure. In the detoxification experiment, the PSP toxins of M. edulis rapidly decreased under PSP regulatory limit within 24 hours both the experimental tank using filtered seawater and the field experiment. Detoxification under detection limit of PSP toxin (0.00) was required the elapsed time over 20 days. In addition, N-sulfocarbamoyl toxin as C1+2 was detected as a major component in A. catenella, and A. pacificum swimming cells, although carbamate toxin as gonyautoxin 1+4 was detected to be the main component in M. edulis. This is expected to quickly poison the bivalves in a short time when toxic dinoflagellates appear in the actual marine environment. On the other hand, it is thought that even if poisoned shellfish are not continuously exposed to toxic dinoflagellates, it will take a relatively long time for poisoned shellfish to be completely detoxified. In addition, if shellfish continuously feed on toxic dinoflagellates, the toxicity of bivalves may rapidly increase due to biotransformation, so caution is required. To investigate the early detection of the toxic dinoflagellates A. catenella and A. pacificum, effects of toxic dinoflagellates and non toxic algae Isochrysis galbana and Akashiwo sanguinea on the SVMs of M. edulis and Crassostrea gigas were examined under experimental tank using a Hall element sensor. SVMs of M. edulis and C. gigas exposed by I. galbana and A. sanguinea was no significant change during experiment. However, SVMs of M. edulis and C. gigas exposed by A. catenella and A. pacificum increased for 12 hours after exposure, and then it was changed to normal pattern over time. C. gigas showed a higher average level of SVMs than M. edulis to toxic dinoflagellates. Therefore, C. gigas has a relatively high sensitivity compared to M. edulis, so it is considered more suitable for bio-monitoring system (BMS) using SVMs. On the other hand, M. edulis is relatively insensitive and its SVMs are not active, but it has fast adaptability and is easily poisoned by toxic dinoflagellates. Therefore, it is considered suitable as an indicator organism that can confirm the poisoning of bivalves. In this study, shellfishes were poisoned in a short time following the appearance of toxic dinoflagellates, but continuous monitoring for a long period of time (more than 20 days) is considered necessary for complete detoxification. Shellfish are poisoned in a short time, so it is thought very important to detect toxic dinoflagellates at an early stage of their appearance. In this study, the SVMs of bivalves increased rapidly following exposure to toxic dinoflagellates. Since this phenomenon appeared quickly within an hour, it is expected that it will be a good way to minimize damage to fishermen by preventing the maximum poisoning of shellfish in advance.