New research led by James Cook University shows huge differences in fish biomass and fish productivity between Caribbean and Indo-Pacific coral reefs, driven by the consumption of jelly-like gelatinous plankton.
Published in the journal Nature Ecology and Evolution, the JCU-led team of Australian scientists analysed two and half million plankton-eating fish observations, revealing fundamental differences in fish size, quantity and growth between the two reef realms.
Researchers found that plankton eating fish in the Caribbean were substantially smaller than their Indo-Pacific counterparts, leading to much larger fish biomass (6.6 times larger) and fish productivity (3.4 times larger) on Indo-Pacific reefs.
"What fish eat has far reaching consequences for the entire food chain, influencing the total biomass of fish as well as fish productivity," said the papers first author, James Gahan.
"Higher productivity means the reef can generate more food for people who are dependent on these ecosystems. The more productive fish communities grow quicker and can be harvested more."
Plankton can be shrimp-like (non-gelatinous) or jelly-like (gelatinous); washing into coral reefs where the nutrients they contain get eaten by planktivorous fishes.
"Gelatinous planktivores, like the Yellowtail Fusilier, hang out just off the reef edge feasting on all the jellies that come in," Mr Gahan said.
Plankton eating fish are very dominant on reefs, accounting for as much as 90 per cent of all surveyed fish on Indo-Pacific reefs.
While jelly-eating fish in the Indo-Pacific represented only four percent of total individuals, researchers discovered they accounted for over 30 percent of the total biomass of all plankton eating fish, illustrating their oversized contribution to fish biomass and fish productivity.
"We found that the gelatinous planktivore fish community in the Indo-Pacific was almost six times more productive than the non-gelatinous planktivores," said Mr Gahan.
Researchers found a remarkable absence of fish that ate the jelly-like plankton on Caribbean reefs, leading to biomass and fish productivity levels that were 15 to 20 percent of those estimated for the Indo-Pacific.
"The jelly-like food source has similar nutritional content to the non-gelatinous plankton, but is larger and potentially easier for fish to see, with higher water content. This may facilitate faster digestion and promote increased appetite," Mr Gahan said
"This research begins to merge our understanding of major oceanic energetic pathways that bring food onto reefs, with our knowledge of reef ecology and reef productivity.
"It highlights that not all coral reefs are the same. There are fundamental differences in how food flows through different reef ecosystems, with real consequences for fish productivity and resource availability."
