They might be beautiful, but migrating tropical fish are consuming more than their fair share of kelp and seagrass.
A study by Australian researchers at the University of New South Wales (UNSW) has found evidence of the harmful impact of tropical fish migrating off the coast of the US, Japan, the eastern Mediterranean, and Australia.
As a result of the ocean warming, tropical fish including unicornfish, parrotfish and rabbitfish are moving to new temperate areas, where they overgraze on the kelp forests and seagrass meadows that line the ocean floor.
“The tropicalisation of temperate marine areas is a new phenomenon of global significance that has arisen because of climate change,” said marine ecologist and lead author of the study, Adriana Verges, in a press release. “Increases in the number of plant-eating tropical fish can profoundly alter ecosystems and lead to barren reefs, affecting the biodiversity of these regions, with significant economic and management impacts.”
The study has been published in the journal Proceedings of the Royal Society B.
The researchers discovered that hotspots are developing in particular ocean regions that move warm tropical waters towards the poles. In the East Australian Current, which moves warm water from the tropical Coral Sea down the east coast of Australia, the waters are warming at two to three times the global average. This means tropical fish have become common in Sydney Harbour during the summer months.
Similar effects have been seen in Japan, the east coast of the US, northern Brazil and south eastern Africa.
“In tropical regions, a wide diversity of plant-eating fish perform the vital role of keeping reefs free of large seaweeds, allowing corals to flourish. But when they intrude into temperate waters they pose a significant threat to these habitats. They can directly overgraze algal forests as well as prevent the recovery of algae that have been damaged for other reasons,” said Verges.