Disturbing the peace

Marine biologist Vanessa Messmer finds that the iconic coral trout may be reaching the limits of its tolerance to the warming oceans.

To the well-heeled gourmet traveller, Lizard Island Resort is a luxury oasis, its wooded slopes gently descending to the white sandy beaches and waters of the Great Barrier Reef.

‘It’s easy to be lulled into the deep peace that comes with being in your own beautiful world’, claims the resort’s website. The resort is one of only two developments on this remote island, a national park situated 270 kilometres north of Cairns.

A three-kilometre stroll from the resort lies a very different development: the recently refurbished Australian Museum Lizard Island Research Station. Since 1973, many hundreds of barefoot scientists have made their way to the research station from all over the world to conduct research on the reef ecosystem. And for these visitors, there is trouble in paradise.

Living coral

‘Climate change is increasingly a threat to coral-reef ecosystems and their associated reef-dwelling animals’, said Dr Vanessa Messmer, a marine biologist from the ARC Centre of Excellence for Coral Reef Studies at James Cook University in Townsville.

Research on the Great Barrier Reef by Eureka prize-winner Professor Ove Hoegh-Guldberg from the University of Queensland has already shown that rising sea surface temperatures lead to the loss of living coral. ‘Coral bleaching is affecting coral reefs worldwide, with obvious consequences for reef-dwelling organisms’, Vanessa said. ‘As the oceans continue to warm, it’s only going to get worse.’

Vanessa is part of a larger research team looking at the effects of climate change on Common Coral Trout, Plectropomus leopardus.‘Climate change is affecting coral reefs in many ways. We want to know how it affects this species both indirectly – by bleaching and degrading the reef habitat – and directly by increasing water temperatures.’

Fishery

Little is known about the habitat preferences of coral trout at the crucial settlement stage. This large predatory fish grows to 75 centimetres and sustains the largest finfish fishery on the Great Barrier Reef, yielding an annual catch of around 1000 tonnes.

‘We know that the coral trout spawns into the water column and its buoyant eggs then drift with ocean currents, hatching and developing into larval fish (which by the way are active swimmers). After around 30 days, the fish larvae locate and swim towards nearby reefs where they can settle and grow’, said Vanessa.

‘But we don’t know what kind of habitat these larvae need to settle on and to what degree they depend on live coral. We also want to know how the fish is directly affected by temperature increases at different stages during its life.’

Warming

Vanessa and colleagues visited the research station throughout 2012 to capture juvenile and adult fish and keep them in temperature-controlled tanks.

‘People have studied smaller reef fish but each species will respond differently to ocean warming. Basically, we were able to measure the metabolic rate of larger coral trout at different temperatures. We are still analysing the data, but the main result seems to be that the coral trout is already beginning to struggle at 30 degrees’, she said.

‘Its resting metabolic rate increases at higher water temperatures, which means it needs more energy just to stay alive and maintain basic body functions, such as respiration. This can leave less energy available for other activities, such as feeding, avoiding predators and reproduction.

‘This may already be a challenge in the northern part of the fish’s range where water temperatures can exceed 30 degrees and it becomes a problem if these higher temperatures are experienced over longer periods.

‘We are concerned that coral trout may not be able to adapt to the kinds of increases being predicted for the Great Barrier Reef – up to 3 degrees this century.’

Research Fellowship

Vanessa’s work at Lizard Island is supported by the Isobel Bennett Marine Biology Fellowship, one of several research fellowships offered each year by the Australian Museum and funded by the Lizard Island Reef Research Foundation.

‘The fellowship has allowed me to explore some of these questions further especially the habitat component, to see whether they settle on living or dead coral. We’ll be going back to the island in March to look at this question more closely.

‘I’m curious and in awe about the natural world’, said Vanessa, ‘and am interested in applying knowledge towards a sustainable world.

‘Our work shows how climate change will likely affect this iconic reef fish. Any action to slow the rate of global warming can’t come soon enough for this and probably many other species.’

Now there’s a message to disturb the deep peace of any gourmet traveller.

Brendan Atkins Editor, Explore magazine

This story first appeared in Explore 35(1) pp14-15, 2013.

Applications for fellowships to conduct research at Lizard Island close in August or September each year. Find out more at Lizard Island Fellowships.

Donations to the Lizard Island Reef Research Foundation are tax deductible. Visit Lizard Island Reef Research Foundation for further information.