Health – SAMS
Turning the tide T
Researchers from the Scottish Association for Marine Science help guard against the risk of harmful algae by careful monitoring
here are claims from some scienti sts that a ‘global epidemic’ of harmful algal blooms (HABs) that poison farmed fi sh and potenti ally lead to toxins in shellfi sh
has been caused by human acti vity. But experts at the Scotti sh Associati on for Marine Science (SAMS), who have advised and tested for DEFRA and the Food Standards Agency (FSA), have found litt le evidence of anthropogenic nutrients (originati ng from hu- man acti vity) being the problem, instead citi ng wind-driven currents bringing phytoplankton from deeper water to the coast as the main driving mechanism in Scotland. Harmful (micro) algae are a component
of phytoplankton, the ocean’s equivalent of grass on land, and are known to naturally produce biotoxins. Their blooms occur when the harmful algae grow quickly in water. They can deplete the oxygen in the water and some harmful algae release toxins that are danger- ous to animals and humans. Worldwide there are approximately 4,000 species of marine phytoplankton, around 300 of which have properti es that make them harmful to humans or infl uence human use of the marine ecosystem (including fi sh farming). While there is no dispute that nutrients are
important for algal growth, the evidence that nutrients cause wide- spread HAB events is more limited and restricted to a relati vely few studies, says Professor Keith Davidson, principal investi gator in microbi- al ecology at SAMS. ‘When considering harmful phytoplankton, a disti ncti on needs to
be made between harm which results from high and low biomass ‘blooms’,’ he said. ‘Generally, but not exclusively, problems associated with shellfi sh poi-
soning are associated with low biomass blooms (approximately a few hundred or thousand cells per litre). ‘These cells probably don’t even dominate the surrounding biomass
but cause problems because fi lter feeding shellfi sh ingest the cells and concentrate the toxins in their fl esh but are not harmed. Human health is aff ected only when the shellfi sh is consumed. ‘High biomass blooms, however, require a source of nutrients and are
oft en not toxic. They are someti mes visible as ‘red ti des’ or as the cause of beach-covering foam.’ The harm related to high biomass blooms is oft en most keenly felt at
fi nfi sh aquaculture sites, as a result of competi ti on for oxygen, smoth- ering or abrasion of gills. The development of high biomass blooms requires a nutrient supply and this could be natural, for example when cold, mixed water meets warmer, layered water, or it can be of human origin. Prof Davidson and his colleagues have analysed internati onal records
and found no consensus regarding the role of anthropogenic nutrients in sti mulati ng the occurrence of HABs. The threat of HABs is, however, a very real one for a growing number of aquaculture sites around the UK. Toxins found in some shellfi sh can
related to high biomass blooms is oft en most keenly felt at fi nfi sh aquaculture sites
“The harm ”
Left: The dinofl agellate Karenia sp., a producer of brevetoxins Above: The diatom Pseudo-nitzschia, a producer of domoic acid, is known to form harmful algal blooms
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