Beautiful Tropical Fish May Destroy Kelp Forests as Oceans Warm

Tropical fish may be beautiful as they glide beneath ocean waters, but they can also destroy natural ecosystems. Scientists have found that the migration of tropical fish as a result of ocean warming poses a serious threat to temperature areas, including kelp forests and seagrass meadows.

"The tropicalization of temperate marine areas is a new phenomenon of global significance that has arisen because of climate change," said Adriana Verges, the lead author of the new study, in a news release. "Increases in the number of plant-eating tropical fish can profoundly alter ecosystems and lead to barren reefs, affecting the biodiversity of these regions, with significant economic and management impacts."

Scientists have found that hotspots have developed in regions where currents that transport tropical waters toward the poles are strengthening. For example, increased flow of the East Australian Current has meant that waters southeast of the continent are warming at two to three times the global average. This means that tropical fish are now common in Sydney Harbor during the summer months.

Yet these tropical fish may be playing havoc in temperate regions. The fish, used to keeping corals free from algae, are consuming more than their share of vegetation in temperate regions. In fact, researchers found that more than 40 percent of the kelp and algal beds in southern Japan have disappeared since the 1990s. Largely to blame are tropical rabbitfish and parrotfish.

"In tropical regions, a wide diversity of plant-eating fish perform the vital role of keeping reefs free of large seaweeds, allowing corals to flourish," said Verges. "But when they intrude into temperate waters they pose a significant threat to these habitats. They can directly overgraze algal forests as well as prevent the recovery of algae that have been damaged for other reasons."

The findings reveal that tropical fish could have a major impact in temperate regions as waters continue to warm. They also show that these areas may need protection in the future in order to recover from increased stresses from fish.

The findings are published in the journal Proceedings of the Royal Society B.