In his 1842 book, The Structure and Distribution of Coral Reefs, Charles Darwin remarked that coral reefs were like an “oasis in the desert” – they were flush with life despite being surrounded by nutrient-poor seawater. This is a mystery that scientists have continued to grapple with, ascribing the diversity of reefs to the close relationships between the sea life within the reefs. Essentially, all food and waste produced within reefs is rapidly taken up, leaving only a few remnants in the seawater. However, a new study shows that tiny “cryptobenthic” reef fish – so called because they easily camouflage with the seafloor – may help make up the nutrient gap in coral reefs.
Because cryptobenthic fish are incredibly small and reclusive, they can be difficult to study, so their role in ocean ecosystems is still being understood.
“We still don’t know the true diversity of cryptobenthic reef fishes on a global scale,” says Dr. Carole Baldwin, a co-author of this study and curator of fishes at the Smithsonian’s National Museum of Natural History, ”Most of the new reef-fish species discovered and described over at least the past few decades are cryptobenthics.”
Traditionally, when fish hatch from their eggs, they travel offshore to develop further before returning to their reefs closer to home. However, cryptobenthic reef fish stay closer to their parents’ reefs than other fishes do, which increases their survival and allows them to exist in such high quantities that they provide sufficient nutrition to larger fishes in the absence of other nutrients. The fish that survive their encounters with predators grow quickly and eventually become adults.
“The key to the role of the cryptobenthic fish larvae is that they don’t seem to be going anywhere,” says lead author Dr. Simon Brandl, who worked with the Smithsonian’s Tennenbaum Marine Observatories Network when this research was conducted, ”Basically, by foregoing the dangerous journey through the open ocean, the cryptobenthics form an (almost) endless cycle of life and death that provides a critical food source to larger fishes.”
Examples of cryptobenthic fish include gobies, blennies, and cardinalfishes, but also many fishes that will never be more than 1 inch in size. These fish are primarily fish food during the first few weeks of their lives and they exist in massive quantities during this time period, making up nearly 60 percent of the food that coral reef fishes consume.
“We are quick to recognize the importance of what we often call “forage fish” or “bait fish,” which have important roles for many important open-ocean fisheries species,” says Dr. Brandl, “My guess is that cryptobenthics fill a similar role to forage fish on the world’s shallow coastlines, but we have yet to fully discover this role.”
