This is why the sea in Bournemouth is brown at the moment

BEACHGOERS have been told not to be concerned by the off-putting colour and smell of the sea as a spring plankton bloom is the cause.

Visitors to Bournemouth beach recently will have noticed the water has turned a rusty brown with layers of scum on the surface.

But while some have feared the cause is an oil spillage or sewage leak, it is in fact a harmless algae known as phaeocystis.

Phaoecystis close-up, sampled by a plankton net. It grows as colonies of thousands of cells within a jelly-like matrix. When a bloom dies the dead colonies can be whipped-up by wind and waves into a surface foam that is called spume. pic.twitter.com/89sMBYY77A

— Dr Richard Kirby (@PlanktonPundit) June 2, 2018

John Hourston, a volunteer for the Blue Planet Society, said the outbreak of the phytoplankton was “relatively uncommon” in Bournemouth, with the last bloom seen in 2016.

“Lots of people are worried about it as the sea is currently the colour of… chocolate,” he said. “Most people are automatically concerned it is sewage, but it’s nothing that unpleasant.

“We last had a phaeocystis phytoplankton bloom in 2016 after the beach sand replenishment, and that was the first one I had seen in Bournemouth since 2010. This one is very strong but not as strong as the one in 2016.”

John explained that a number of factors can lead to a spring plankton bloom, including sunlight, nutrients, and temperature.

“This particular phaeocystis plankton plant often blooms when you get a period of strong sunlight and warm weather, together with nutrients building up in the sea.

“They happen this time every year somewhere around the coast. It’s a completely natural event, although it doesn’t look very nice.

“It will clear up within the next week or ten days at most once it has died off, at which point it will sink to the sea bed.”

He added the oily patterns left on the sea’s surface were the result of dead phytoplankton.

“It’s nothing to worry about, but you wouldn’t really want to swim in it. When it gets a bit windier, it will froth up and create spume. It’s completely natural, but it does give off a slightly unpleasant smell,” he said.

The Environment Agency encourages people to report algal blooms, but says toxic algae is rare in English coastal waters.

On its website, the agency says: “Some non-toxic blooms can be mistaken for sewage pollution. One of the most common bloom-forming algae in English coastal waters forms a brown, frothy scum. This is often blown onto the shore where it breaks down into an unpleasant brown slime that smells like sewage. This soon breaks down and disappears.”

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