Underwater gardens boost coral diversity to stave off `biodiversity
meltdown'
Symbiotic relationship between Pacific Ocean coral species offers a
potential solution to restore climate-damaged reefs

Date:
October 13, 2021
Source:
Georgia Institute of Technology
Summary:
Researchers are building symbiotic 'underwater gardens' in the
Pacific Ocean to show how different species of coral can work
together to possibly restore degraded reefs.



FULL STORY ========================================================================== Corals are the foundation species of tropical reefs worldwide, but
stresses ranging from overfishing to pollution to warming oceans are
killing corals and degrading the critical ecosystem services they
provide. Because corals build structures that make living space for
many other species, scientists have known that losses of corals result
in losses of other reef species. But the importance of coral species
diversity for corals themselves was less understood.


==========================================================================
A new study from two researchers at the Georgia Institute of Technology provides both hope and a potentially grim future for damaged coral
reefs. In the study, published October 13 in Science Advances,
Cody Clements and Mark Hay found that increasing coral richness by 'outplanting' a diverse group of coral species together improves coral
growth and survivorship. This finding may be especially important in
the early stages of reef recovery following large-scale coral loss --
and in supporting healthy reefs that in turn support fisheries, tourism,
and coastal protection from storm surges.

The scientists also call 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 rapid and efficient recovery of degraded reefs.

But the ecological pendulum swings the other way, too. If more coral
species are lost, the synergistic effects could threaten other species
in what Clements and Hay term a "biodiversity meltdown." "Yes, corals
are the foundation species of these ecosystems -- providing habitat
and food for numerous other reef species," said Clements, a Teasley Postdoctoral Fellow in the School of Biological Sciences. "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 Hay
traveled to Mo'orea, French Polynesia, in the tropical Pacific Ocean,
where they planted coral gardens differing in coral species diversity
to evaluate the relative importance of mutualistic versus competitive interactions among corals as they grew and interacted through time.



========================================================================== "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," said Hay, Regents Professor and Teasley Chair in the School of
Biological Sciences.

Hay is also co-director of the Ocean Science and Engineering graduate
program at Georgia Tech. "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." Under the sea, in a coral-growing garden, in the
shade Coral reefs are under threat worldwide. Hay notes that according to
the EPA, the Caribbean has lost 80 to 90 percent of its coral cover. The Indo-Pacific region has lost half of all its corals over the last 30
years. During the bleaching event of 2015-2016 alone, nearly half of
the remaining corals along the Great Barrier Reef bleached and died.

"The frequency of these big bleaching and heating events that are killing
off corals has increased fairly dramatically over the last 20 to 30
years," he said. "There are hot spots here and there where coral reefs
are still good, but they're small and isolated in general." In their
coral gardens in French Polynesia, Hay and Clements manipulated the
diversity of the coral species that they planted on platforms resembling underwater chess tables, to try and see if species richness and density affected coral productivity and survival.

Hay noted many previous, similar experiments involved bringing corals
into a lab to "pit species against each other." But he points out,
"We do all of our experiments in the real world. We're not as interested
in whether it can happen, but whether it does happen." An experimental
setup suggested by Clements involving Coke bottles helped the scientists arrange their garden. The end tables "have Coca-Cola bottlecaps embedded
in the top of them," Hay said. "We can then cut off the necks of
Coke bottles, glue corals into the upside-down necks of these things,
and then screw them in and out of these plots. This allows us to not
only arrange what species we want where, but every couple of months
we can unscrew and weigh them so we can get accurate growth rates."
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." Clements said
their research demands more investigation. Why do corals perform better
in mixed species communities than single-species communities? Why does
this biodiversity effect diminish -- rather than continue increasing --
at the highest level of coral diversity? "We need a better mechanistic understanding of how diversity influences these processes to predict
how biodiversity loss will impact corals, as well as how we may be
able to harness biodiversity's positive influence to protect corals,"
said Clements.

========================================================================== Story Source: Materials provided by Georgia_Institute_of_Technology. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Cody S. Clements, Mark E. Hay. Biodiversity has a positive but
saturating
effect on imperiled coral reefs. Science Advances, 2021; 7 (42)
DOI: 10.1126/sciadv.abi8592 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211013152203.htm

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