Tiny fish live fast, die young

James Cook University’s Professor David Bellwood was part of a team searching for answers to the longstanding puzzle of ‘Darwin’s paradox’.

“Charles Darwin wondered how fish on coral reefs manage to thrive in isolated areas where there are very low levels of nutrients for them to use. We thought the answer may lie in the tiny fish that live in the gaps in the coral structure,” he said.

Professor Bellwood and PhD student Renato Morais were part of an international team led by former JCU student Dr Simon Brandl from Simon Fraser University in Canada that surveyed reefs around the globe and records of larval abundance.

“These tiny fish are less than 5 centimetres long and are known as ‘cryptobenthics’. They include gobies, blennies, cardinalfish, and several other families,” Professor Bellwood said.

The scientists discovered that cryptobenthics and their larvae make up nearly 60% of all fish flesh eaten on the reef. “Because of their size and tendency to hide, these little fish are commonly overlooked,” lead-author Simon Brandl said, “but their unique demographics make them a cornerstone of the ecosystem.”

“Their populations are completely renewed 7 times a year, with individuals in some species living only a few days before they are eaten. The only way they can sustain this is by a spectacular supply of local larvae,” said Mr Morais.

Professor Bellwood said almost anything capable of eating cryptobenthics does so, including juvenile fish and invertebrates such as mantis shrimps, which then became food for other creatures.

“These factors have made it hard for researchers in the past to realise the importance of cryptobenthics and discover the food supply that the ‘crypto-pump’ supplies.

Professor Bellwood said that the cryptobenthics have finally emerged from the shadows. “Their extraordinary larval dynamics, rapid growth, and extreme mortality underpins their newly discovered role as a critical functional group on coral reefs.”

Link to paper here.

Link to images here. Please credit as marked.