Tiny fish fuel coral reefs
23 May 2019| Contact: Valeriano PARRAVICINI | Science
Our image of coral reefs typically features clear water and a staggering number of colorful fishes that swim about the coral. But what supports this abundance of life, when coral reefs exist in regions with little available food?
This central question has puzzled scientists since Charles Darwin’s voyages and is now more pertinent than ever: as coral reefs are undergoing dramatic declines, the bustling fish communities that underpin reefs and their value to humanity may be in jeopardy.
In a paper published in Science today, Dr. Simon Brandl from Simon Fraser University in Canada and a team of researchers from France (CRIOBE, EPHE-Université PSL/CNRS/University of Perpignan Via Domitia), Australia, Canada, and the United States reveal that the iconic abundance of fishes on reefs is fueled by a group that is unlikely to feature in our images of coral reefs: tiny, bottom-dwelling, “cryptobenthic” reef fishes.
Dr. Brandl and colleagues show that these smallest of all vertebrates perform a critical function on coral reefs that permits large reef fishes to flourish.
“These fishes are like M&Ms,” says Dr. Brandl. “They are tiny, colorful bundles of energy that any coral reef organism that can get its teeth on will gobble down almost as soon as they arrive on the reef.” In fact, the vast majority of cryptobenthic fishes on reefs will be eaten within the first few weeks of their existence.
So how come these fishes aren’t disappearing from reefs like a bag of candy in the office break room? The researchers solved this paradox by examining the larvae of reef fishes, which normally undertake epic journeys across the open ocean that only few of them survive. Cryptobenthics, however, seem to have found a way to avoid this purgatory.
Remarkably, most cryptobenthic larvae might simply stay close to their parents’ reefs. “Cryptobenthic fish larvae absolutely dominate the larval communities near reefs,” Dr. Jordan Casey from the Ecole Pratique des Hautes Etudes (EPHE) states, which strongly contrasts with their limited egg-production. Dr. Valeriano Parravicini from EPHE adds: “our data show that cryptobenthics get a lot more out of every egg they spawn, because they avoid the death trap of the open ocean.” This, in turn, supplies adult cryptobenthic populations with a steady stream of babies that rapidly replace each fish that is eaten on the reef. “This crypto-pump supplies almost 60% of all consumed fish tissue on reefs, but we never see it because the fish get eaten much faster than we could ever count them. It’s essentially a bag of candy that magically replenishes every M&M that is eaten,” says Dr. Brandl.
While their unique larval strategy may make cryptobenthics much more vulnerable to extinction than previously assumed, the researchers have hope that their extreme diversity could make them a resilient cornerstone of coral reef productivity on rapidly changing reefs.
Brandl et al. (2019) Demographic dynamics of the smallest marine vertebrates fuel coral reef ecosystem functioning. Science, 23 May 2019. DOI: 10.1126/science.aav3384.
Simon J. Brand1,2*, Luke Tornabene3, Christopher H.R. Goatley4, Jordan M. Casey5,6,7, Renato A. Morais8,9*, Isabelle M. Côté1, Carole C. Baldwin10, Valeriano Parravicini55,6, Nina M.D. Schiettekatte5,6, and David R. Bellwood8,9
1 Department of Biological Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
2Tennenbaum Marine Observatories Network, Smithsonian Institution, Edgewater, MD 21037, USA
3School of Aquatic and Fishery Sciences, and the Burke Museum of Natural History and Culture, University of Washington, Seattle, WA 98105, USA
4Function, Evolution and Anatomy Research (FEAR) Lab and Palaeoscience Research Centre, School of Environmental and Rural Science, University of New England, Armidale, 2351, Australia
5EPHE-Université PSL-UPVD-CNRS, USR 3278 CRIOBE, Université de Perpignan, 66860 Perpignan, France
6Laboratoire d’Excellence “CORAIL,” Perpignan, France
7 Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
8ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, 4811, Australia
9College of Science and Engineering, James Cook University, Townsville, 4811, Australia
10 Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
Dr. Valeriano PARRAVICINI | CRIOBE, École Pratique des Hautes Études (EPHE)
Tel: +33 (0) 4 68 66 21 94 (France)
Dr. Simon Brandl | Department of Biological Sciences, Simon Fraser University
Tel: +1 (604) 348 6423 (Canada)