Uptake, retention and elimination of cysts of the toxic dinoflagellate Alexandrium spp. by the blue mussel, Mytilus edulis

Harper, Fiona Morag (1997) Uptake, retention and elimination of cysts of the toxic dinoflagellate Alexandrium spp. by the blue mussel, Mytilus edulis. Masters thesis, Memorial University of Newfoundland.

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Abstract

Cysts of the toxic dinoflagellate Aiexandriam spp. have been implicated in incidents of paralytic shellfish poisoning. There is a paucity of data concerning the possible effects the benthic resting cyst may have upon bivalve biology, although the effects of motile, vegetative Alexandrium cells on bivalve physiology have been extensively studied. The research presented in this thesis examines the role mussels may play in recirculating dinoflagellate cysts within an aquaculture site, the impact of passage through the bivalve gut on the viability of cysts, and the retention time of the cysts within the bivalve digestive tract. -- Mussels from the top and bottom of mussel socks were similarly contaminated with cysts of several dinoflagellate species (Scrippsiella sp., A. fundyense, putative A. ostenfeldii) as there was active sediment resuspension within the site. Scrippsiella sp. cysts dominated the dinoflagellate cyst population of the sediment, however fewer cysts of this species were egested. The composition of the faecal material collected from mussels contaminated in the field and in the laboratory suggests putative A. ostenfeldii cysts were not digested since intact cells of this species were dominant in the faeces. The estimated 8% daily replenishment rate of the bottom sediment A ostenfeldii hypnozygotes by faecal pellet deposition is a considerable contribution to the maintenance of dinoflagellate cyst populations. As well, putative A. ostenfeldii cysts were viable following passage through the acidic bivalve gut. The thick-walled dinoflagellate cysts egested in faeces were of similar viability as cysts found in sediments, germinating in about 10-14 days. The estimated gut retention time of these cysts was 9 h. -- The egestion of viable cysts from mussels could have serious implications for current aquaculture practice. The transport of contaminated bivalves among sites may result in the transfer of viable cysts, capable of germinating and seeding a toxic dinoflagellate bloom in a previously uncontaminated area.

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