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Hurricanes, pollution, disease, bleaching and the effects of an ever-warming planet all have a negative impact on the health of coral reefs around the world. However, those in the Caribbean are facing a new threat: an aggressive, golden-brown, crust-like algae that is rapidly invading shallow coral reefs.
Algae, known as peyssonnelid algal crusts (PACs), are invading coral reefs at such an aggressive rate that it interferes with the coral larvae’s ability to find places to settle on reefs and interfere with the coral reef’s natural ecosystem.
Marine biologists from Oxford University, California State University at Northridge, and the Carnegie Institution for Science have studied the biology and ecology of this alga on these coral reefs for the past four years. Today in Scientific Reports they describe this new threat and what it could mean for coral reefs already on the brink of collapse.
Dr Bryan Wilson of Oxford University’s Department of Zoology said: “This alga appears to be a kind of ecological winner in our changing world; it aggressively occupies any free space on coral reefs, grows rapidly and kills animals. live corals, prevents free-swimming coral larvae from settling on the benthos and becoming adult colonies, and is insensitive to the regular destructive hurricanes that pass through the area.
It is also apparently resistant to grazing by fish and, as far as we know, is only fed by a single creature, the black spiny hedgehog (Diadema antillarum), once ubiquitous and abundant in the Caribbean, but which has actually been wiped out over the years. 80 from a mysterious disease.
Professor Edmunds, who has studied these reefs for over three decades, first spotted the alga five years ago while studying the impact of two consecutive Category 5 hurricanes – Irma and Maria – on coral reefs near the island. John’s Caribbean in the US Virgin Islands. He was amazed at how quickly the seaweed began to dominate the reef.
Together, researchers have since been able to document how the PAC is aggressively conquering such large swaths of space on some of St. John’s shallow reefs. The PAC is taking up so much of the benthos that it is discouraging larval corals and other marine life, including sea urchins, from returning to the reef, which, in turn, undermines the persistence of the community itself.
Dr Bryan Wilson, of Oxford University’s Department of Zoology, said: “ On an ongoing mission to try to understand why this golden crusted alga is suddenly spreading over Caribbean reefs, our research initially looked at the microbiology of the PAC and compared it to that of close relatives (crusted coral algae, or CCAs) which are known to stimulate the recruitment of coral larvae into coral reefs.
“Our key finding was that PAC somehow inhibits the growth of beneficial marine bacteria that otherwise, in association with CCA, produce chemical compounds – almost like pheromones – that invite and attract coral larvae to the sea floor. . And therefore the coral reef areas detected by the PAC are unlikely to host corals again. “
Scientists have noticed that the PAC, with its dark brown and dirty orange coating, stands out among the white sands and light greens, pinks, yellows and other colors that make up the reef.
It is unclear whether the PAC consists of one or more species of algae, nor is it known what is causing the acceleration of algae spread across the region in recent years.
Professor Edmunds said: ‘What we do know is that this is an alarming trend and we need to know more about it.’ 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.
The next step in this research is to unravel the complex physiological mechanisms of the seaweed for this ecological success – and Dr. Wilson is currently delving into the recently obtained seaweed genome, which will hopefully illuminate them further.
Eventually the researchers hope to find ways to mitigate this new threat.
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