The rate of current global warming is making it hard for fish (such as colourful anthias and damselfish, pictured here in a busy reef) to adapt, say researchers.

Credit: iStockphoto

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SYDNEY: As if life wasn’t tough enough for young fish, which battle to survive while dodging hungry predators, a new study reveals that climate change could be cooking them in their delicate hatchling stage.

In a find that could spell trouble for many marine species, Australian biologists have found that increasingly warm tropical waters are killing some embryos and shortening the lifespan of survivors.

To probe the effects of climate change on reef fish, experts at the Australian Research Council Centre of Excellence for Coral Reef Studies at James Cook University in Queensland, painstakingly studied populations of Ambon damselfish (Pomacentrus amboinensis) around Lizard Island, part of the Great Barrier Reef.

Damselfish in distress

Damselfish embryos are produced when eggs laid by a female are enveloped by the male’s sperm and fertilised. Tiny larvae develop which, if they manage to avoid being eaten – sometimes by their own dads – will grow into adults.

The team found that elevated water temperatures during development of the young fish have devastating consequences for their future survival. Summer breeding temperature currently vary between 25 and 31°C – but the top of the range is already affecting survival. In experiments up to 50 per cent of embryos died at 31°C.

"Survival of fish embryos was dramatically compromised at 31°C, which is [no longer] uncommon at this location during summer" said lead researcher Monica Gagliano.

"For the first time, we have been able to establish the fate of young fishes in their natural environment by following them through time, from leaving their parents up to months after settling back on the reef," she added.

Double-whammy

Furthermore, the researchers found that climate change may be having a double-whammy effect on reef fish survival, as climate change is affecting the scarcity of food resources too. Poorly fed damselfish mothers produced smaller eggs, which themselves were found to be more at risk of dying in warm waters than large eggs.

"There is no doubt that the quality of parents and the early environment experienced by fish as they develop have major effects on who will survive," said Gagliano.

The results are published in recent papers in the Journal of Animal Ecology and Oecologia.

The findings may well extend beyond damselfish, and have implications for many reef fish species, said the researchers. Increased temperatures on the Great Barrier Reef have resulted in mass coral die-offs of late, meaning that fish have less to eat. If this translates into poor quality eggs and hatchling death, fish populations could severely diminish, they said.

Sea temperatures on the Great Barrier Reef are predicted to rise by between a further one to three degrees by 2100 and “Impacts on reef biodiversity, fishing and tourism are very likely,” said Gagliano.

“This study, while only on one species and under lab conditions, suggests that even a slight increase in ambient water temperatures of 2°C could have profound negative effects on reef fish production,” commented David Booth, a marine ecologist from the University of Technology in Sydney, Australia.

Galgliano's team will now focus on determining whether or not environmental stress has implications for successive generations of fish. The level of environmental stress is significant because global warming-induced changes are happening so rapidly.

Although sea temperatures have fluctuated over history, scientists believe current climate change is happening at unusually rapid rate.

“This long period of time would [usually] give a chance for natural selection to get down to work,” said Gagliano. “The problem we face now is that temperature and other environmental changes are occurring too fast for species to adapt.”

Another recent study on frog declines suggested that it is the rate – rather than the magnitude – of current climate change that is dooming some species to extinction (See, Amphibians in losing race with climate, Cosmos Online).