October 3, 2014, by Tim Radford
Tropical rabbitfish have devastated algal forests in the eastern Mediterranean Sea
Image: Zafer Kizilkaya
Warming seas are extending the range of tropical rabbitfish, whose voracious appetite for seaweed and other marine vegetation is turning areas of the Mediterranean Sea into rocky barrens. LONDON, 3 October, 2014 − Scientists in Australia, Europe and the US have identified a new menace in the Mediterranean. The tropical rabbitfish has arrived in the eastern Mediterranean Sea and − wherever the waters are warm enough − threatens to do to the marine vegetation what the terrestrial rabbit did to Australia’s tender grasses: eat the lot. A team of researchers led by Adriana Vergés, a marine ecologist at the University of New South Wales in Sydney, Australia, and Fiona Tomas, assistant professor at the Mediterranean Institute for Advanced Studies in Mallorca, Spain, report in the Journal of Ecology that they surveyed 1,000 kilometres of coastline around Turkey and Greece.
They found that two species of rabbitfish have become dominant in the region, and they think the invader is likely to claim more territory as the world’s climate changes and the waters warm. The range expansion of the rabbitfish, which first entered the Mediterranean basin from the Red Sea via the Suez Canal, provides a good example of how tropical herbivorous fish can impact on the structure of rocky bottoms in temperate seas. “The study identified two clearly distinct areas − warmer regions with abundant rabbitfish, and colder regions where they are rare or absent,” Dr Vergés said. ”The regions with abundant rabbitfish had become rocky barrens. There was a 65% reduction in large seaweeds, a 60% reduction in other algae and invertebrates, and a 40% reduction in the overall number of species present.” The hungry herbivores were first reported in the eastern Mediterranean in 1927, and have recently been found off the coast of Croatia and even the south of France. The invaders are a threat to ecosystems because seaweed forests − like terrestrial forests − provide food and shelter for hundreds of species.
The researchers recorded fish feeding behaviour and noted that the rabbitfish were not noticeably more greedy than the natives. But whereas the native temperate herbivores grazed only on adult algae, the two species of rabbitfish consumed both the adult and the juvenile seaweeds. The consequence is that the full-grown species were not replaced. In the long run, such seaweed clearance could be a threat not just to Mediterranean ecosystems but also to the Mediterranean diet, because these ecosystems ultimately support the shoals of sardines, anchovies, red mullet, sea bass, bream, tuna and other specialties of the tables of Spain, Greece and Italy. “This research highlights the need to work out how the interactions between different species will change in a warming world,” Dr Vergés said. − Climate News Network
Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.