The Ecosystem-Altering Invasion of Tropical Fish

Written by on July 23, 2014 in Fish, Marine Life, Physical Oceanography

A new study reveals the harmful impact that tropical fish have on the temperate areas they invade. As waters warm these migrating tropical fish are overgrazing on kelp forests and sea grass meadows, disrupting the balance of entire ecosystems.

Seagrass. Photo credit: NOAA.

Seagrass. Photo credit: NOAA.

“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. But when they intrude into temperate waters they pose a significant threat to these habitats,” lead author Dr. Adriana Verges of the University of New South Wales (UNSW) School of Biological, Earth and Environmental Sciences explained in a news release. “They can directly overgraze algal forests as well as prevent the recovery of algae that have been damaged for other reasons.”

As the oceans warm, hotspots have begun to develop in regions where the currents that transport warm waters to the poles are strengthening. Tropical fish, such as unicornfish, parrotfish, and rabbitfish, have started expanding their ranges, which is threatening temperate areas around the globe, particularly in southern Japanese waters and the eastern Mediterranean.

In southern Japan, more than 40 percent of kelp and algal beds have disappeared since the 1990s. In Japan, this phenomenon is known as isoyake.

In the eastern Mediterranean, tropical fish started moving in from the Red Sea after the opening of the Suez Canal, resulting in an increase in deforested areas and a 40 percent decrease in the variety of marine species.

Coral reefs benefit from having more parrotfish around.

Coral reefs benefit from having more parrotfish around. Photo credit: Nataraj Metz via photopin cc.

In the U.S., there has been a more than 20-fold increase in the number of parrotfish in the Gulf of Mexico, in addition to an increase in the number of herbivorous green turtles and manatees.

In western Australia, researchers believe an increase in tropical fish is preventing the recovery of a kelp forest damaged in 2011, while in eastern Australia, kelp has disappeared from several reefs in just the past five years.

“The tropicalisation of temperate marine areas is a new phenomenon of global significance that has arisen because of climate change,” Dr. Verges said.

“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.”

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Copyright © 2014 by Marine Science Today, a publication of Marine Science Today LLC.

About the Author

About the Author: Emily Tripp is the Publisher and Editor of She holds marine science and biology degrees from the University of Miami's Rosenstiel School of Marine and Atmospheric Science and a Master of Advanced Studies degree in Marine Biodiversity and Conservation from Scripps Institution of Oceanography. When she's not writing about marine science, she's probably running around outside or playing with her dog. .


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