Coral Reef Fish Are Now Moving Into Temperate Kelp Forests, With Dire Consequences

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These rabbitfish can now be found in kelp forests, far from their coral reef homes. John Turnbull [CC BY-SA 2.0]/Flickr

If you're a diver who enjoys exploring coastal kelp forests, you might have noticed a recent shift in the biota inhabiting these lush marine habitats. Researchers have reported a sharp increase in some unusual visitors to the world's kelp forests: tropical coral reef fish, reports

Kelp forests are found in temperate oceans, so the presence of tropical fish swimming amongst their swaying stem-like stipes is alarming. It's an ominous reminder of the rapid rate at which our climate is changing and our ocean waters are warming.

Research recently published in Proceedings of the Royal Society B: Biological Sciences documents how species from the tropics are moving to higher latitudes around the world, settling within new temperate ecosystems in a process known as tropicalization. One such species is the tropical herbivore rabbitfish, Siganus fuscescens, which is currently invading kelp forests in Western Australia. These fish are not just being driven from their preferred coral reef habitat due to rising ocean temperatures, but they are entering kelp forests with a voracious appetite for canopy-forming seaweeds.

As a result, these fish threaten to consume the very seaweeds that are the scaffolding that make life in these majestic habitats possible.

"Our research provided important evidence about how ecologically important tropical fish species moving south can impact the functioning of temperate reefs," said Salvador Zarco Perello, from University of Western Australia's School of Biological Sciences and Oceans Institute.

It's not just the kelp that is getting mowed down, but as these fish chomp on the kelp, it changes the landscape and thus changes the types of animals that can survive there as well. It's a runaway domino-like process whereby the entire habitat is transforming at a pace that might be too rapid for many species to adapt to.

This process isn't an expansion of coral reef ecosystems. Rather, it's a result of the disappearance of coral reef ecosystems around the world, and the migration of creatures that inhabit coral reefs fleeing for greener pastures. The fear is that as coral reefs disappear and kelp forests get shredded, that we'll eventually be left with marine deserts rather than just a redistribution of ecosystem zones.

"The monitoring and understanding of the acceleration of this process due to tropicalization is critical for future management strategies, since kelp is a fundamental seaweed that provides shelter and food to multiple animal species of ecological and commercial importance," said Zarco Perello.

In just the last few decades alone, half of the world's coral reefs have disappeared due to bleaching and rising levels of ocean acidity, a direct result of increased carbon dioxide absorption from fossil fuel emissions. Coral reefs harbor a huge percentage of the planet's marine biodiversity, and those organisms are migrating north or south in a last ditch effort to find a replacement for the homes they've lost.

The best way to save our kelp forests from this invasion is to conserve our coral reefs; that's where these invading tropical fish would prefer to live. It's another reminder of the unpredictable ways that rapid climate change is transforming our planet, with dire consequences.