Intense Mediterranean Sea heatwave raises fears for marine life - July 2025
Warmer water at the seaside might sound nice for your holiday dip, but recent ocean heat in the Mediterranean Sea has been so intense that scientists fear potentially devastating consequences for marine life.
The temperature of the sea surface regularly passed 30C off the coast of Majorca and elsewhere in late June and early July, in places six or seven degrees above usual.
That's probably warmer than your local leisure centre swimming pool.
It has been the western Med's most extreme marine heatwave ever recorded for the time of year, affecting large areas of the sea for weeks on end.
The heat appears to be cooling off, but some species simply struggle to cope with such prolonged and intense warmth, with potential knock-on effects for fish stocks.
To give you some idea of these temperatures, most leisure centre swimming pools are heated to roughly 28C. Competitive swimming pools are slightly cooler at 25-28C, World Aquatics says.
Children's pools are a bit warmer, recommended at 29-31C or 30-32C for babies, according to the Swimming Teachers' Association.
Such balmy temperatures might sound attractive, but they can pose hidden threats. Harmful bacteria and algae can often spread more easily in warmer seawater, which isn't treated with cleaning chemicals like your local pool.
Massive coral bleaching killing Australia's Great Barrier Reef - 2016
Fish swim amid bleached coral near Lizard Island, Australia, Great Barrier ReefCoral - 4 stages of coral - healthy, bleached, algal growth voer bleached dead coralClose-up of four staes of coral bleaching dying coral great barrier reef australiaheavy algal overgrowth over bleached dying coral - Great Barrier Reef Australia
The massive bleaching hitting the Great Barrier Reef off the coast of Australia is likely that country's "biggest ever environmental disaster," says Dr. Justin Marshall, who has studied the reef for three decades.
Only 7 percent of the reef has escaped bleaching, according to researchers at the ARC Center of Excellence. Marshall, a professor at the University of Queensland, says the destructive phenomenon is happening in an area the size of Scotland.
"Before this mass bleaching started, we already were at the point of losing 50% of the coral cover on the Great Barrier Reef. This, I think, will probably take another 50% off what was left," Marshall says.
Over the course of the last six months, Marshall and his colleagues with the citizen science project Coral Watch have documented the degradation of reef structures near Lizard Island, one of the worst-hit areas.
They photographed the same formations of coral multiple times, showing clearly the pace of the destruction.
Reef in Bermuda.
Healthy coral reefs have declined by about 50% in the past 40 years
Many of the Caribbean's coral reefs could vanish in the next 20 years, according to a report published by the International Union for the Conservation of Nature (IUCN).
Data from more than 35,000 surveys suggests that habitats have declined by more than 50% since the 1970s.
The report's authors believe that over-fishing and disease is mainly to blame.
They say the trend could continue if nothing is done, but with protection the reefs could bounce back.
Carl Gustaf Lundin, director of IUCN's Global Marine and Polar Programme, said the findings were alarming.
"The reefs support a number of different countries and populations," he said.
"Tourism is one of the biggest industries, and the health of the reef is essential to the well-being of many of the people living there. And of course they are immensely beautiful and wonderful places as well."
Reef overrun with algae The reefs are becoming over-run with algae, which suffocates the coral.
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