They are the glimmering jewels in the depths of our oceans, but plant-eating tropical fish are beginning to threaten Australia's forests under the sea.
Climate-driven changes are causing the fish to extend their range into temperate regions, threatening kelp forests and seagrass meadows, a study from the University of NSW has found.
Ecologist and lead author of the study Adriana Verges said the migration of plant-eating tropical fish can drastically alter ecosystems and lead to barren reefs.
''Most research until now has been about the direct effects of temperature on certain species, whereas this is more about the effects of temperature on the way different species interact,'' she said.
In reefs where coral are the main species that form the habitat, herbivorous fish that eat algae or seaweed play a critical role in cleaning the reef, however in more temperate waters the seaweed that forms underwater trees is the foundation species.
The study suggests that once herbivorous species like rabbitifsh, unicornfish and parrotfish migrate to these areas, they can overgraze underwater forests, leading to a complete shift in the ecosystem.
''A species that was tropical entering a temperate system for the first time can have traumatic cascading consequences. In Australia there is emerging evidence deforestation is already happening in the east and west,” she said.
Grazing by warm-water herbivorous fish has had the greatest impact in the Mediterranean and southern Japan, but evidence is growing here at home, where increased flow of the East Australian Current has meant waters south-east of the continent are warming at two to three times the global average.
''In terms of when we can expect this to get worse, it's sooner than we think,'' Dr Verges said. ''For fully tropical conditions you need winter water temperatures above 18 degrees, which is expected around 2020-2030.''
Dr Verges’ research suggests intense grazing by tropical fish has contributed to the disappearance of kelp from several reefs in the past five years.
She said the biggest challenge now is tackling climate change.
''We need to try and stop the world getting warmer. Once these underwater trees go, everything else goes with it,'' she said.