Coral gardens could hold off ‘biodiversity meltdown’
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A new study suggests that the symbiotic relationship between Pacific Ocean coral species could offer a potential solution for restoring precious coral reefs damaged by environmental stresses.
From global warming to overfishing, coral reefs are under an onslaught of stresses which degrade these critical ecosystems. Because corals build structures that create habitats for many other species, scientists have long recognised that coral loss results in the collapse of other species that depend on reefs. However, the significance of coral species diversity for corals themselves is less understood.
The Georgia Institute of Technology study found that increasing coral richness by “outplanting” a diverse group of coral species together can improve coral growth and survivorship overall. This finding may be especially important in the early stages of reef recovery following large-scale coral loss, as well as in supporting healthy reefs that in support fisheries, tourism, and protect coasts from extreme weather events.
They warn that, conversely, if more coral species are lost, this could precipitate a “biodiversity meltdown”.
“Corals are the foundation species of these ecosystems, providing habitat and food for numerous other reef species,” said Dr Cody Clements, one of the authors of the paper. “Negative effects on corals often have cascading impacts on other species that call coral reefs home. If biodiversity is important for coral performance and resilience, then a “biodiversity meltdown” could exacerbate the decline of reef ecosystems that we’re observing worldwide.”
Clements and his colleague Professor Mark Hay travelled to Mo’orea, French Polynesia, where they planted coral gardens differing in species diversity and richness to evaluate the relative importance of mutualistic versus competitive interactions among corals as they grew and interacted. This involved setting up various chessboard-like platforms with Coca-Cola bottlecaps embedded inside, and corals glued inside, for easy rearrangement and measurement.
The researchers found that corals benefitted from increased biodiversity, “but only up to a point,” Clements noted. “Corals planted in gardens with an intermediate number of species — three to six species in most cases — performed better than gardens with low, or one, species, or high, as in nine, species. However, we still do not fully understand the processes that contributed to these observations.”
“We’ve done the manipulations, and the corals should be competing with each other, but in fact they do better together than they do on their own,” explained Hay. “We are still investigating the mechanisms causing this surprising result, but our experiments consistently demonstrate that the positive interactions are overwhelming negative interactions in the reef settings where we conduct these experiments.”
“That means when you take species out of the system, you’re taking out some of those positive interactions, and if you take out critical ones, it may make a big difference.”
The scientists are calling for additional research to better understand and harness the mechanisms producing these positive species interactions, with dual aims to improve reef conservation and promote more efficient recovery of degraded reefs.
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