Underwater forests threatened by future climate change, new
study finds Australia’s two largest fisheries potentially at risk

Researchers at the University of Sydney (USYD) and the Sydney
Institute of Marine Science have found that climate change could lead to
declines of underwater kelp forests through impacts on their microbiome.

In humans, it has
been observed that changes in the microbes in the gut can result in poor
health. A similar process happens in kelp. Predicted ocean warming and
acidification can change microbes on the kelp surface, leading to disease and
potentially putting Australia’s two biggest fisheries – the lucrative rock
lobster and abalone markets – at risk. 

Climate change is affecting biodiversity
at a global scale. In the marine realm, ocean warming and acidification are
pushing dominant habitat-forming species, such as corals and large seaweeds,
into decline, affecting biodiversity. New research shows these two processes
can cause changes in the microbiome on the surface of large brown seaweed
leading to disease-like symptoms. Blistering, bleaching and eventually
degradation of the kelp’s surface is impacting the species’ ability to
photosynthesise and potentially survive. This could contribute to further
declines of the 8000km long kelp forests that dominate the bottom half of
Australia – known as the Great Southern Reef – potentially affecting all the
associated ecosystems, including many species of fish, shellfish, lobster and
abalone.

“If we lose the kelp forests, we also lose our two biggest fisheries,”
said Dr Ziggy Marzinelli, from the USYD.  The cooler water kelp forests
support a significant component of Australia’s fisheries and is estimated to be
worth over $10bn to the Australian economy. 

Published in the Proceedings of
The Royal Society B, the study tested the independent and interactive effects
of ocean warming and acidification on the associated microbiome and condition
of the dominant kelp Ecklonia, which is already in steep decline. 

“Our study
shows the effects of climate change can be complex, driven by changes in tiny
organisms – microbes – that cannot be seen,” Dr Marzinelli said. “Changes in
the microbiome impacts the life of the host. When you have disruption to the
microbiome in the human gut, it affects your health. It’s the same for seaweed.
One of the consequences you see is clusters of blisters on the surface of the kelp.”

The study has implications for the health and resilience of entire marine
ecosystems, said Professor Peter Steinberg, director of Sydney Institute of
Marine Science, who co-authored the study. “The impact of losing the kelp
forests would be the same as cutting down all the eucalypts on the land. All
the animals would be affected. It is the same in the oceans. If we lose the
physical structure of the habitat, we lose the ecosystems.”

One surprising
aspect of the research showed the microbiome reverted to a healthier state when
it was exposed to the most extreme scenarios. “When we tested under warming and
acidification conditions predicted in 50 years time, the microbiome reverted to
what it was at the start with healthy hosts,” said Professor Steinberg. “This
was a surprise. It means it is hard to predict what might happen in the most
extreme future ocean conditions.”