Oceans cover about 71% of the Earth’s surface and contain more than 97% of the planet’s water. An estimated 80% of the world’s population lives within 100 km of the coast, and fish provide the bulk of the protein consumed by humans. But the marine ecosystem impacts of global warming on the biodiversity of ocean waters are difficult to determine.
Increasing concentrations of atmospheric carbon dioxide – the result of activities such as burning fossil fuels and deforestation – are acidifying and warming the world’s oceans.
One of the most widely documented effects of warming, according to Dr Adriana Vergés, senior lecturer in marine biology at the University of New South Wales, is the widening distribution of tropical fish as they move away from equatorial waters towards the poles, resulting in increasing numbers of tropical species appearing in temperate waters.
The marine ecosystem impacts from this warming has profound implications for the underwater environment and marine life.
“Species have three options in response to changing conditions – they die, adapt or move,” explains Vergés. “We are seeing a lot of movement. And because the rate of change is so fast, the question is: will species be able to keep up?”
The intrusion of tropical fish to temperate waters, referred to as tropicalisation, could have far-reaching repercussions for the health of these waters, their biodiversity and the industries that rely on them.
“When the tropical fish arrive, they overgraze on the seaweed and the whole system begins to shift,” says Vergés. “And we’re starting to see this in oceanic waters around northern NSW, where algal forests are disappearing.”
“In Australia, the two largest fisheries are abalone and rock lobster, whose preferred habitats are algal forests and seagrass meadows. If you lose algal forests, the abalone industry will collapse, with significant consequences for the fishing industry and the economy.”
The Abalone Council Australia Ltd estimates about 4500 tonnes of wild abalone were harvested in Australian waters last year, worth around $180 million. And according to Southern Rock Lobster Ltd, in 2011–12 rock lobster fishing produced around 3000 tonnes, worth nearly $175 million.
Vergés, however, is working to reverse some of the damage to the algal forests that threaten this industry.
Together with a number of volunteers, she is involved in Operation Crayweed, a project that aims to re-introduce crayweed – a vital habitat for lobsters, abalone and crayfish – to the waters around Sydney.
“The project is looking to bring crayweed back to the whole of Sydney. We’ve re-planted crayweed, and it has started to come back – we’re now on to our third generation. It’s a really good news environmental story, and we hope the fisheries will benefit too,” she says.
As well as helping to save the fisheries industry and reduce the marine ecosystem impacts in temperate waters around Sydney, Vergés is also involved in the Scientists in Schools national program, where she sparks enthusiasm for the wonders of the underwater world in seven and eight-year-olds.
“It’s so rewarding – children are natural scientists and they ask all the right questions. Speaking to a group of them is the closest I’ve felt to being a rock star. And they love absolutely anything to do with the sea. They are the best audience without a doubt,” says Vergés.
– Carl Williams