Harmless Invasion

A type of damsel fish from the other side of the world has invaded the Gulf of Mexico. But it doesn’t appear to be doing much harm to the fish that were already there—at least not so far.

The Regal Damselfish comes from the Indian and western Pacific oceans. It’s only about four inches long, and it lives on coral reefs, in shallow coastal waters.

The invader was first seen in the Gulf in 2013. It probably hitchhiked on an oil platform that was moved from the eastern hemisphere.

A recent study looked at how the fish spread across the Gulf through 2021. It also looked at how other types of fish fared—especially those that compete with the invaders for resources.

Researchers from the University of Texas Marine Science Institute and elsewhere counted the fish found in sections of five reef systems along the coast of Mexico. They then used mathematical models to estimate the total populations of the entire system.

The invading damsel fish spread across all the reefs in the study area. At the same time, the populations of its competitors dropped. But so did the populations of some of the other species of fish that don’t compete with the invaders. That suggests that the dip in the number of competing fish had some other cause.

One possibility is loss of habitat caused by human activities. One of the reefs in the study is near a busy port that’s growing bigger. So that might be damaging the reefs more than the invasion of the damsel fish.