Hazel Farrell

Distribution of the genus Alexandrium (Halim) and paralytic shellfish toxins along the coastline of New South Wales, Australia.

Blooms of Alexandrium species, in particular the species Alexandrium catenella, accounted for more than 50% of algal related, shellfish aquaculture harvest zone closures in New South Wales (NSW) Australia since 2005. While there are indications that species of Alexandrium are more abundant than they were formerly, there is little data available on the spatial and temporal distribution and abundance of the genus in NSW. A six and a half year dataset comprising a total of 8649 fortnightly samples from 31 estuaries spread over 2000 km of NSW coastline was analysed. The greatest abundances of Alexandrium spp. were observed during the austral Spring and Summer, in estuaries in the mid and southern latitudes of the state. In identifying these high risk zones, we propose variables such as season, temperature, rainfall and estuarine flushing to be targeted in intensive site specific studies, to support the development of predictive tools for resource managers.

Molecular Detection of the Sxta Gene from Saxitoxin-Producing Alexandrium minutum in Commercial Oysters

ABSTRACT The production of toxic secondary metabolites by marine phytoplankton and their accumulation in molluscs and fish has ecosystem-wide and human health impacts. The potent neurotoxin saxitoxin and its analogs, which can cause paralytic shellfish poisoning, are produced by species of the dinoflagellate genus Alexandrium. These toxins can accumulate in filter-feeding molluscs, including commercially grown species of shellfish. A feeding experiment was designed to assess the use of quantitative polymerase chain reaction to detect a gene involved in saxitoxin biosynthesis (sxtA) in two commercial oyster stocks. Both diploid and triploid Crassostrea gigas were fed with toxic cultures of Alexandrium minutum over a period of 12 days to allow toxin accumulation. A barcoding gene specific to Alexandrium (ITS 5.8s rRNA) and the sxtA gene, domain 4, which is specific to the saxitoxin synthesis pathway, were assayed. Both targets were detected in oysters collected after 6 and 12 days feeding with A. minutum, and after 24 h of depuration during which the oysters were fed nontoxic microalgae only. The target genes were not detected in control oysters. These methods can be used as a relatively rapid and inexpensive screen that is indicative of the presence of saxitoxin-producing microalgae in shellfish.

Management of Ciguatoxin Risk in Eastern Australia

Between 2014 and 2016, five cases of ciguatera fish poisoning (CFP), involving twenty four individuals, were linked to Spanish Mackerel (Scomberomorus commerson) caught in the coastal waters of the state of New South Wales (NSW) on the east coast of Australia. Previously, documented cases of CFP in NSW were few, and primarily linked to fish imported from other regions. Since 2015, thirteen individuals were affected across four additional CFP cases in NSW, linked to fish imported from tropical locations. The apparent increase in CFP in NSW from locally sourced catch, combined with the risk of CFP from imported fish, has highlighted several considerations that should be incorporated into risk management strategies to minimize CFP exposure for seafood consumers.