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All over the world, coral health has been threatened by human activity. A new danger to algae is exploiting the already dangerous coral conditions in the Caribbean and making it more difficult for coral reef ecosystems to thrive.
A study recently published in Scientific reports describes how a hostile, golden brown, crust-like alga is rapidly invading shallow coral reefs, taking the place of coral broken by severe storms and aggravating damage from bleaching, pollution, disease and ocean acidification.
For the past four years, Bryan Wilson of Oxford University, Chen-Ming Fan of Carnegie Science, and Peter Edmunds of California State University Northridge have explored the biology and ecology of peyssonnelid, or PAC, algal crusting in the U.S. Virgin Islands, which are outpacing coral larvae competing for limited surface space and growing further on the current reef architecture, severely damaging these delicate ecosystems.
This seaweed appears to be something of an ecological winner in our changing world.
Bryan Wilson, lead author of the study, University of Oxford
Wilson said many other threats to coral communities make them more vulnerable to algal crusts.
Initially, Edmunds noticed invasive crust growth following Category 5 hurricanes Irma and Maria as they were rapidly occupying spaces that had been swept away by storms.
Corals are marine invertebrates that develop huge exoskeletons from which coral reefs are built. For the growth of new coral reef structures, it is essential that the small floating corals first successfully attach themselves to a stable surface. They choose to settle on the crunchy surface formed by a particular type of friendly seaweed that grows on local rocks.
Such crusted coral algae (CCA) act as guides for coral larvae, generating biochemical signals along with their related microbial community, which cause the small coral to attach itself.
The team was confused that both the destructive PAC and the useful CCA grow on the rocks and form a crust, but the PAC eliminates coral settlement and the CCA induces it. What causes this variation?
Researchers set out to find out how golden brown PAC affects coral reefs in the Caribbean. They identified that PAC favors a microbial community that differs from that associated with CCA, which is known to attract corals.
These PAC crusts have biochemical and structural defenses that they deploy to discourage grazing by fish and other marine creatures. It is possible that these same mechanisms, which allow them to invade marine bio-space, also discourage corals.
Fan Chen-Ming, Carnegie Science
More studies are needed to understand the enormous success of algal crusts in conquering Caribbean reef communities and to look for ways to reduce the threat they pose.
“There is a new genomic and evolutionary frontier to explore to help us understand the complexity of the interactions of organisms on the reef, both mutualistic and antagonistic“Fan added.
Coral and their ecosystem are as fragile as they are. They are attacked by environmental pollution and global warming. We have made their lives so fragile, yet they are in there. And now this is thrown into the mix. We don’t know if this is the straw that breaks the camel’s back, but we have to find out.
Peter Edmunds, of California State University Northridge
This study was financially supported by a long-term environmental biology research grant and a rapid response research grant from the US National Science Foundation.
The study was completed with permits offered by the Virgin Islands National Park.
Journal reference:
Wilson, B., et al. (2020) An unusual microbiome characterizes a spatially aggressive crusty alga that grows rapidly on shallow Caribbean coral reefs. Scientific reports. doi.org/10.1038/s41598-020-76204-0.
Source: https://carnegiescience.edu/
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