Tropical species are taking over the Mediterranean Sea

Divers in the eastern Mediterranean are finding warm, clear water and an explosion of newcomers. Predators from tropical seas are settling in, while native fish are vanishing. 

What was once exceptional heat is now the new normal, and the sea’s ecology is changing fast.

Warmer depths, new arrivals

“We were at a depth of 30 meters (100 feet) this morning and the water was 29C,” said Murat Draman, a scuba instructor off Antalya in southern Turkey. 

Draman remembers August months in the early 2000s when the sea was closer to 25C. Now surface waters near Antalya are pushing nearly 32C, and the warmth reaches deep. 

Warmer water has flung open a biological gateway. Hundreds of Red Sea species are crossing the Suez Canal and finding a home in the eastern basin.

Scientists say the Mediterranean is among the fastest-warming seas on the planet. This year brought its hottest June and July on record, according to figures from Mercator Ocean International. 

As temperatures climb, tropical and subtropical species can survive – and thrive – farther north and west than before.

A surge of lionfish

“About a decade ago, we saw one or two of them. Now we’re talking about 15 or 20 per dive – even more than when we go to the Red Sea,” Draman said. 

He is referring to lionfish, the striking but highly venomous species Pterois miles, armed with long, spotted fins and a voracious appetite. In Antalya’s coves and reefs, they are now common.

“They are big predators. Small fish like gobies suffer a lot, we hardly see them anymore,” he added. 

The small, bottom-dwelling fish once dotted the rocks. Now they are at risk of being eaten out of sight. Warmer water is part of the story. So is the sudden arrival of skilled hunters that the local food web is not built to resist.

A warning from the east

“The invasion started almost immediately after the opening of the Suez Canal in 1869,” said Gil Rilov, a professor at Israel’s Oceanographic and Limnological Research Institute (IOLR). But the pace has recently quickened.

“But now it’s getting warmer, and also (in 2015), the canals got deeper and wider, so more and more new species move in every year.” 

Some newcomers may help fill niches as native species struggle with heat. Many others displace or outcompete what was there before.

What Rilov sees off Turkey, Lebanon, and Israel is spreading west. Rabbitfish, for example, have reached Malta – more than 1,700 kilometers from the canal.

Rilov calls the eastern basin “a warning,” pointing to two drivers behind native losses: relentless heat and fierce competition. “What is happening here will happen in five, 10 or 20 years in the north and west of the Mediterranean.”

Tropical species in a warmer Mediterranean 

Mercator’s latest analysis showed the Mediterranean posted its warmest July on record with an average surface temperature of 26.68C. That number hides local extremes and the vertical reach of heat. 

As heat soaks downward, species that once found cool refuge at depth now face thermal stress throughout the water column. 

The sea is not just warmer at the top. It is warmer everywhere that matters to fish, invertebrates, and algae.

The “tropicalization” is not limited to the Suez pipeline either. A 2024 study suggests the Strait of Gibraltar could deliver more warm-water species from West Africa into the western Mediterranean by mid-century. 

In a pessimistic scenario, researchers warn the basin could be entirely tropicalized by 2100. That would mean a wholesale turnover of communities, food webs, and the services people rely on.

Absence of Mediterranean predators

Local food webs can blunt an invader’s impact – if they have the right hunters. In the eastern Mediterranean, many apex predators are missing or depleted. That leaves lionfish and other arrivals with little to fear.

Draman sees the imbalance daily. He argues for keeping invasive species out of protected areas to shield what biodiversity remains. Without checks and balances, populations grow fast. 

“It is clear that with the absence of Mediterranean predators, species such as lionfish are very comfortable here and their population is increasing year on year,” said Draman.

In their native range, lionfish do not rule the reefs. “In the Red Sea, lionfish have predators. There are sharks and barracudas. Here, we have none of that.”

What can be done now

Managers face two timelines. One is immediate: reduce local pressures that make ecosystems fragile – overfishing, habitat loss, and pollution – and limit the spread of high-impact invaders near sensitive habitats. 

The other timeline is generational: curb greenhouse gas emissions to slow the ocean’s march toward tropical conditions. Neither is easy. Both are necessary.

The message from Antalya’s reefs is simple. The Mediterranean is warming fast. Tropical species are already here and native fish are losing ground. And what is unfolding in the east is a warning for the rest of the basin. 

The sooner that warning is heeded, the better chance there is to keep familiar seas from becoming something unrecognizable.

The study is published in the journal Proceedings of the National Academy of Sciences.

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