Tiny Fish a Big Buffet for Coral Reef Dwellers

Spotted fringe-fin dwarfgoby. (https://www.izuzuki.com via Wikipedia)

(CN) – Why don’t big fish pick on someone their own size? Because little larvae are tasty and abundant. Research published in Science on Thursday highlights the enormous role tiny cryptobenthic fish and their larvae play in sustaining the coral reef food web.

“The world runs on tiny organisms,” noted Dr. Simon Brandl, a lead author and a postdoctoral research fellow at the Earth2Ocean group at Simon Fraser University in Vancouver, British Columbia.

Combining field data from Australia, Belize, and French Polynesia with a meta-analysis of data published in scientific literature over 50 years, the international team of researchers built population models studying cryptobenthic fishes’ contribution to coral reef nutrient cycles.

Sometimes referred to as the reef’s “hidden half” because lay observers don’t see them, most cryptobenthic fish are smaller than 2 inches and live hidden away in complex crevices or along the bottom of the reef. One species, the dwarfgoby, even holds the record of shortest vertebrate lifespan at 59 days.

Because they’re small both as individuals and in terms of overall population – Brandl estimated 20 fish per square meter is a fairly healthy population – many scientists had assumed cryptobenthic fish played a niche roll in the ecosystem. Yet their larvae can make up two-thirds of overall ichthyoplankton population in the near-reef pelagic zone. Before they mature into adulthood, however, nearly 60% of cryptobenthic larvae are eaten like candy by invertebrates and young predatory fish.

“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,” Brandl said.

Researchers describe these events as examples of the “dark productivity of coral reefs,” since it’s difficult to document a biomass-buffet that “is consumed almost as quickly as it is produced.”

Still, Brandl’s team found cryptobenthic fish “form the basis of a critical energy and nutrient pump that operates across the reef-pelagic interface and may help explain the enigmatic productivity of coral-reef ecosystems.”

Understanding how cryptobenthic fish contribute to the reef may also inform better conservation efforts as climate change contributes to the decline of many coral species and reef ecosystems.

“Especially with climate change, the reefs are changing a lot and the primary change that happens if the little environments change is the coral bleach and die. That of course fundamentally changes the area where these fish live,” Brandl said.

“The problem arises once the reef becomes more simple, once the reef erodes to a flatter topography, that’s when it becomes more troublesome,” Brandl said. “That’s when an attempt to artificially increase the complexity of the reef might be valuable to try to bring back some of these tiny little fish.”

Cryptobenthic fish largely survive on a diet of copepods, algae, coral mucus, and because even they can’t help themselves, other cryptobenthics.

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