A new study is attempting to develop early warning systems to identify the presence of dangerous algal blooms, writes Lorna Siggins, Marine Correspondent
Farmers get weather warnings about possible potato blight, but fin and shellfish farmers are rarely so lucky when it comes to marine algal blooms. Now scientists involved in a three-year State-funded research project have expressed optimism that an early-warning system can be developed.
A recent survey carried out on Killary fjord on the Galway-Mayo county border has yielded positive preliminary results, according to the scientists involved. The two-week survey was commissioned as part of the BOHAB project, a study of the biological oceanography of algal blooms on the west coast by the Marine Institute and NUI Galway.
Funded under the National Development Plan, the project drew on international expertise. Killary fjord was selected as the focus for work, due to persistent bloom problems experienced by mussel farmers along its southern shore over the last 10 years. Killary's shellfish production is worth over €1 million annually.
Some 130 bays, estuaries and sea areas under shellfish cultivation are regularly tested by the Marine Institute for toxins linked to a group of phytoplankton known as dinoflagellates. Whereas algal blooms on inland lakes are usually traced to man-made pollution, the particular bloom associated with marine closures - the Dinophysis group of toxin-producing phytoplankton - is naturally occurring. Although it is not harmful to the shellfish, the toxin can cause diarrhetic shellfish poisoning (DSP) in humans who have consumed the seafood.
Two vessels, the MV Lughnasa and RV Conamara, were chartered for a fortnight between July 19th and 30th to carry a French scientific team lead by Dr Patrick Gentien of the French marine research agency, Ifremer, and a US team led by Dr Percy Donaghay of the University of Rhode Island. Spanish scientist Dr Beatriz Reguera also participated in the research on the presence and life cycles of the Dinophysis group.
The French team employed a video camera to transmit "realtime feedback" to the ship, and also used a particle-size-analyser, a pump taking samples directly on to the boat, and instruments measuring high resolution temperature, depth and salinity. The team also towed a scanfish device behind the vessel to take profiles of temperature, salinity, chlorophyll fluoresence and turbidity from the water column at varying depths.
Three WetLabs AC-9 instruments, which are designed to detect the presence of thin "micro-layers" within the water column by measuring absorbance (the amount of light passing through the water), and attenuation (how the light is coloured by the water) were deployed by the US team. The AC-9 sends high-resolution real-time data back to the boat on nine different wavelengths.
Dr Donaghay of the University of Rhode Island has particular expertise in using the AC-9 to determine the presence of thin layers of potentially toxic phytoplankton.
Sometimes it is possible to fingerprint the species of phytoplankton present in these layers according to the spectral information. The Marine Institute has recently acquired an AC-9 for the national equipment pool.
Two species of toxic phytoplankton were identified in the water, Karenia mikimotoi (which is harmful to finfish and can cause the death of fish at salmon farms) and the Dinophysis. Their occurrence and the association with water density was examined during the survey.
As the scientists explain, warmer, less salty water appears near the surface in the summer and cooler, more salty water occurs near the seabed. A sharp density gradient may occur between these water masses, and thin layers of phytoplankton may develop.
Preliminary observations suggest that phytoplankton may come into the inner fjord in thin layers at depth rather than as a visible surface bloom, according to the research team led by Joe Silke of the Marine Institute and Dr Robin Raine of NUI, Galway under overall BOHAB project manager Dr Caroline Cusack.
"With this information, we can begin to develop monitoring methods to identify potentially toxic and fish killing algal events by targeted sampling before it arrives into an aquaculture production area," Silke says. It could allow producers to receive between a week and month's notice of a "toxic event".
Richie Flynn of the Irish Shellfish Association says that the project was initiated as a result of demands from producers, and the early results seem positive. "There are many more questions to be answered, and it does highlight the lack of knowledge and the need for far more research in this area."