Can pumping up cold water from deep within the ocean halt coral
bleaching?
New research shows that pulses of cooler deep water reduced heat stress responses in corals

Date:
September 16, 2020
Source:
Bermuda Institute of Ocean Sciences
Summary:
Rising ocean temperatures cause marine heat waves, which place
stress on living coral animals, as well as the photosynthetic algae
on which they depend for energy. A new study is showing potential
for the use of artificial upwelling (AU)-- or the application of
cooler, deep water - - as a way to mitigate the thermal stress
on corals.



FULL STORY ==========================================================================
The risk of severe coral bleaching -- a condition in which corals lose
their symbiotic algae, called zooxanthellae -- is five times more frequent today than it was forty years ago. Coral bleaching is a direct result of
global warming, where rising temperatures cause marine heat waves, which
place stress on the living coral animals, as well as the photosynthetic
algae on which they depend for energy. This heat stress causes the algae
to malfunction, at which point they are expelled by the corals, causing
the organisms to lose their color and appear white (thus the term coral "bleaching").


==========================================================================
Due to the increasing pressure of global warming on highly valuable coral
reef ecosystems, scientists are now seeking novel ways to decrease heat
stress on corals. A new study led by Yvonne Sawall, assistant scientist
at the Bermuda Institute of Ocean Sciences (BIOS), is showing potential
for the use of artificial upwelling (AU) -- or the application of cooler,
deep water -- as a way to mitigate the thermal stress on corals.

Upwelling is a natural oceanographic process in which winds push surfaces waters away from a region, such as a coastline, allowing the uplift of
deep, cold waters to the surface. These waters are typically rich in
nutrients and form the basis of productive marine ecosystems which, in
turn, support many of the world's most important commercial fisheries. AU
is a geoengineering method that uses pumps to bring deep-ocean water to
the surface. Originally designed to fertilize surface waters to increase
fish stocks or carbon dioxide (CO2) sequestration, AU may also be used
to cool surface waters during heat waves, if the depth and intensity of
AU is chosen wisely.

"Ocean warming and the occurrence of heat waves will increase in frequency
and intensity over the coming decades and we need to consider rather unconventional solutions to protect and sustain coral reefs," Sawall said.

With funding from the German Research Foundation (DFG, with principal investigator Yuming Feng, doctoral student at the GEOMAR Helmholtz Center
for Ocean Research in Kiel, Germany), Sawall and her co-authors studied
three shallow water reef building coral species in Bermuda: Montastrea cavernosa (great star coral), Porites astreoides (mustard hill coral),
and Pseododiploria strigosa (symmetrical brain coral).

After collecting fragments from living corals on Sea Venture Shoals,
Bermuda, at a depth of 15 feet (5 meters), the research team placed
the colonies in aquaria at BIOS to test the effects of deep cold-water
pulses (AU) during thermal stress. Fragments were treated with various temperatures conditions, including an average summer temperature (28DEGC);
a heat stress treatment known to cause bleaching (31DEGC); a heat stress treatment with daily pulses of cooler deep water from a depth of 164
feet (50 m, 24DEGC); and a heat stress treatment with daily pulses of
cooler deep water from a depth of 300 feet (100 m, 20DEGC). The deep
water used for the experiment was collected aboard the BIOS-operated
research vessel (R/V) Atlantic Explorer approximately 2 miles (3 km)
off the Bermuda Platform.

The results of the study showed that even short intrusions of cooler
deep water (less than two hours per day) can mitigate thermal stress in
corals. This was evident in higher levels of zooxanthellae performance
in corals exposed to heat stress and AU compared to corals that were
exposed to heat stress only, and this effect seemed stronger in the
simulations with water from deeper depths.

"Our study shows the potential benefits of pulsed AU during heat
waves. The next steps now are to find suitable AU settings to maximize
the benefits, while minimizing potential harmful side effects of AU for
corals and the ecosystem they support," Sawall said.


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


========================================================================== Journal Reference:
1. Yvonne Sawall, Moronke Harris, Mario Lebrato, Marlene Wall,
Ellias Yuming
Feng. Discrete Pulses of Cooler Deep Water Can Decelerate Coral
Bleaching During Thermal Stress: Implications for Artificial
Upwelling During Heat Stress Events. Frontiers in Marine Science,
2020; 7 DOI: 10.3389/ fmars.2020.00720 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200916113411.htm

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