Beware of blooms
Researchers from the Scottish Association for Marine Science help guard against the risk of harmful algae by careful monitoring
There are claims from some scientists that a global epidemic of harmful algal blooms (HABs) that poison farmed fish and potentially lead to toxins in shellfish has been caused by human activity.
But experts at the Sco sh Association for Marine Science (SAMS), who have advised and tested for DEFRA and the Food Standards Agency (FSA), have found little evidence of anthropogenic nutrients (originating from human activity) being the problem, instead citing 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 e uivalent of grass on land, and are known to naturally produce biotoxins. Their blooms occur when the harmful algae grow uickly in water. They can deplete the oxygen in the water and some harmful algae release toxins that are dangerous to animals and humans.
Worldwide there are approximately 4,000 species of marine phytoplankton, around 300 of which have properties that make them harmful to humans or in uence human use of the marine ecosystem (including fish farming).
While there is no dispute that nutrients are important for algal growth, the evidence that nutrients cause widespread HAB events is more limited and restricted to a relatively few studies, says Professor Keith Davidson, principal investigator in microbial ecology at SAMS.
When considering harmful phytoplankton, a distinction needs to be made between harm which results from high and low biomass blooms , he said.
Generally, but not exclusively, problems associated with shellfish poisoning 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 filter feeding shellfish ingest the cells and concentrate the toxins in their esh but are not harmed. Human health is a ected only when the shellfish is consumed.
High biomass blooms, however, re uire a source of nutrients and are o en not toxic. They are sometimes visible as red tides or as the cause of beach-covering foam.
The harm related to high biomass blooms is o en most keenly felt at finfish a uaculture sites, as a result of competition for oxygen, smothering or abrasion of gills. The development of high biomass blooms re uires 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 international records and found no consensus regarding the role of anthropogenic nutrients in stimulating the occurrence of HABs.
The threat of HABs is, however, a very real one for a growing number of a uaculture sites around the UK. Toxins found in some shellfish can
“The harm related to high biomass blooms is o en most keenly felt at finfish a uaculture sites”