Home Science Tiny fishes fuel life on coral reefs

Tiny fishes fuel life on coral reefs

Coral reefs typically evoke clear, turquoise waters and a staggering number of colorful fishes. But what supports such an abundance of life?

How coral reefs survive as oases of life in low-productivity oceans has puzzled scientists for centuries. The answer may lie in internal nutrient cycling and/or input from the pelagic zone.

In a new study by a team of international researchers from Simon Fraser University, University of Washington and other institutions, scientists have uncovered that the iconic wealth of fishes on reefs is filled by an unlikely source: tiny, bottom-dwelling reef fishes. These small vertebrates perform a critical function on coral reefs that permit large reef fishes to flourish.

Most bottom-dwelling fish try to avoid predation through hiding or camouflage. This colorful bluebelly blenny fish scans its surroundings with its head sticking out of its hole.Tane Sinclair-Taylor
Most bottom-dwelling fish try to avoid predation through hiding or camouflage. This colorful bluebelly blenny fish scans its surroundings with its head sticking out of its hole.Tane Sinclair-Taylor

Lead author Simon Brandl, a Banting postdoctoral research fellow at Simon Fraser University in British Columbia said, “These fish are like candy. They are no more than 2 to 3 centimeters in length. They are tiny, colorful bundles of energy that get eaten almost immediately by any coral reef organism that can bite, grab or slurp them up.”

Co-author Luke Tornabene, an assistant professor at the UW School of Aquatic and Fishery Sciences said, “We were all truly excited to see how entire reef communities were being fueled by some of the smallest vertebrates on earth — including some species that live for an average of just 65 days.”

Gobies and blennies, like this redstreaked blenny, underpin coral reef productivity at a great cost: most of these tiny fishes get eaten within several weeks or months, but they are almost immediately replenished by the next generation.Tane Sinclair-Taylor
Gobies and blennies, like this redstreaked blenny, underpin coral reef productivity at a great cost: most of these tiny fishes get eaten within several weeks or months, but they are almost immediately replenished by the next generation.Tane Sinclair-Taylor

So why these fishes are not disappearing from reefs? Scientists found an answer, suggesting the larvae of reef fishes, which normally undertake epic journeys across the open ocean to find a home. Few of them survive.

In addition, the fishes avoid migration altogether. Most of the larvae appear to simply stay close to their parents’ reefs.

Redeye gobies hover in small groups above coral heads, on which they rely for shelter.Tane Sinclair-Taylor
Redeye gobies hover in small groups above coral heads, on which they rely for shelter.Tane Sinclair-Taylor

Brandl said, “Our data shows that these fish get a lot more bang for their buck with every egg they spawn, probably because they avoid the death trap of the open ocean.”

“This, in turn, supplies adult tiny fish populations with a steady stream of babies that rapidly replace each adult that is eaten on the reef. In total, these fish represent almost 60 percent of all fish tissue consumed on reefs.”

A Great Barrier Reef blenny looks out warily. It is these little fishes that supply over half the fish flesh eaten on coral reefs.Tane Sinclair-Taylor
A Great Barrier Reef blenny looks out warily. It is these little fishes that supply over half the fish flesh eaten on coral reefs.Tane Sinclair-Taylor

According to scientists, this pattern takes place on coral reefs everywhere around the world. As these fishes have a short lifespan, they also are good indicators of how healthy a reef environment is. Scientists noted, if the habitat starts to degrade, the fish populations will also take an almost immediate hit.

Tornabene said, “In many ways, these miniature fishes are more than just a conveyer belt of nutrients. If we keep a watchful eye on these tiny communities, they may serve as sentinels of the reef, warning us of big impending changes in the entire ecosystem.”

The study is published today in the journal Science.

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