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Cruising the Clyde update

22 August 2016
Prof. Keith Davidson of SAMS gives an update on the Clyde sampling cruises.
The Shelleye "Cruise to the Clyde" of September 2015 coincided with an unusually large bloom of the harmful dinoflagellate genera Dinophysis. This organism is common is UK waters and can result in diarrhetic shellfish poisoning, should the toxins it produces be accumulated in the flesh of filter feeding bivalves, such as mussels, that are subsequently consumed by humans. 

Dinophysis spp. is regularly recorded at densities with the potential to cause problems between March and October, and is generally most abundant between June and August. Dense blooms are not required to generate shellfish toxicity, but infrequent high-density events can be particularly problematic.

In Scottish waters in recent years Dinophysis blooms have most often been of the species Dinophysis acuminata. However, in the Clyde in 2015 the dominant species of Dinophysis was D. acuta with cell densities in our sampling reaching nearly 3000 cells L-1, 30 times the regulatory threshold of concern of 100 cells L-1.

Different species of Dinophysis produce somewhat different suites of toxins, with D. acuta being responsible for the production of dinophysistoxin-2 (DTX-2). The presence of DTX-2 in shellfish has implications for the accuracy of results obtained by harvesters using commercially-produced field kits to carry out end product testing, as some are known to have poor reactivity with DTX-2. Better understanding of the environmental factors governing blooms of Dinophysis, and of D. acuta in particular, would therefore be valuable in safeguarding humans from shellfish toxicity events.

Results from the Shelleye cruise showed significant spatial differences in the distribution of different species of Dinophysis in the Clyde Sea and the adjacent Loch Fyne and hence, environmental factors were influencing the species distribution. 

As well as enumerating Dinophysis we made measurements of other phytoplankton, water column structure and composition (temperature, salinity, fluorescence) and are utilising information relating to other potential environmental drivers of phytoplankton blooms, such as wind speed and direction. Using these combined sources of information we are currently attempting to evaluate those factors that were important in the 2015 bloom and hence, which might be of use in providing early warning of future events.