Rising sea temperatures could result in a new menace - sea squirts.

In this shellfish farm in the Thau lagoon in Bouzigues, France, aquaculturist Jean-Christophe Cabrol checks the growth of oysters covered with sea squirts on the collector lines. Though they may look harmless, some of these soft-bodied marine animals, or tunicates, could spell trouble.

Research by the University of New Hampshire shows that with a water temperature increase of up to 2 deg C predicted in the coming decades, invasive sea squirt species would be able to double their reproduction. This could result in them taking up more space on natural and artificial places where organisms grow, crowding out native species and potentially creating more problems for the aquaculture and fishing industries.

For those who make their living on the water, this may come as no surprise. Oyster farmers sometimes have to use power sprayers to remove tunicates that grow on their oyster bags, costing them additional time and expense.

Marine biologist Franck Lagarde thinks it is important to watch the lagoons as they respond to rising temperatures. "They are like fragile mirrors of the future," he said. "What is happening in lagoons today is what will happen in coming years in other ecosystems."