Toxic algae blooms linked to rise in sea temperature

Algae blooms

The Scottish Association of Marine Sciences are working on a project that brings together the expertise of five countries in developing a protocol to accurately forecast harmful algae blooms so that Scottish shellfish farmers can ensure their produce is toxin-free.

While the algae is vital to a healthy eco-system, they have the potential to produce toxins in shellfish that, while fleeting, can pose a risk to human health if not detected.

Dr Callum Whyte, of the Scottish Association of Marine Science (SAMS), told the Herald: “There are around 80 species of algae around the globe and they have the potential to produce toxins.

“[The algae] are vitally important for shellfish. They eat these things but if toxins get in they can bioaccumulate inside the shellfish and when we eat the shellfish, they don’t get broken down by heat so cooking doesn’t get rid of them.”

Harmful algal bloom (HAB) can spread over a square kilometre of ocean or be concentrated in a tiny area of a sea loch, appearing for a few days, or a week, before currents move it on or it dies from lack of nutrients.

Rise in sea temperature

The cause of the blooms are in debate but the rise in sea temperatures are recognised to be a contributory factor.

Dr Whyte said: “There’s a bit of controversy around that [if there are more instances of HAB]. We’ve got more farms now around the world than ever before and our techniques are getting better and we’re getting better at finding things in the water so that could be why we seem to find more of them occurring but we are aware they are spreading into areas they never have before.

“Most of the toxins are in dinoflaggelates that favour water that’s stratified so when the water heats up and has a nice warm top layer, they live there quite happily. Because of global warming sea temperatures have been rising so we get these stratified layers lasting for longer, they’re more persistent and widespread and they favour the dinoflaggelates who have longer to live up there and breed so they have more effect on the shellfish.”

The Predicting Risk and Impact of Harmful Events on the Aquaculture Sector (PRIMROSE) project is now in its second year of three, and builds on the already established Harmful Algal Bloom and Biotoxin Monitoring (HAB) reports run by SAMS that is used by Scottish shellfish farmers to monitor sea conditions.

Shellfish farmers carry out rigorous testing on their stock to ensure any toxins are detected, using equipment on site and sending samples to be checked to a monitoring programme run by Food Standards Scotland. Via that service, SAMS check around 40 samples from active shellfish sites in Scotland weekly.

Forecasting algae blooms

The HAB forecast sends out information and alerts to farmers and Food Standards Scotland who will check the shellfish coming off those farms if there is a bloom nearby.

The report, which can be accessed online, also produces a bulletin for the community of Shetland shellfish farmers who requested a specific risk assessment notice that includes what phytoplanktons are present, wind current and sea surface temperatures.

If the samples pass the limits, they’ll go ahead for sale and if not, the shellfish farms will be closed down for two weeks to allow the toxins to die out.

If shellfish are affected they “just keep on eating what’s coming through and recover and excrete the poisonous stuff so after a few weeks they’re usually healthy,” said Dr Whyte

The UK, Ireland, Spain and Portugal are working on the €2 million PRIMROSE model which will alert countries to blooms in their seas and nearby. Sharing bulletins, expertise and technologies will lead to better monitoring and forecasting and prevention of stock losses.

A portal will collect data from satellite analysis, samples and shellfish farmers as well as other sources to predict the blooms.

If farmers were due to harvest when a bloom is near, they would test the product and may send it away for further testing, harvesting only if safe. If there is any doubt, says Dr Whyte, farmers leave their stock in the water.

Dr Whyte said: “The idea is to try and push forward the forecasts as far forward as we can.

“We are using oceanographic models to try and predict when blooms would occur, why and how severe they might be.”

This article was originally published as Rise in sea temperature linked to harmful algae blooms at The Herald Scotland on 18/02/2020.

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