Nutrients make coral bleaching worse

Date:
August 21, 2020
Source:
ARC Centre of Excellence for Coral Reef Studies
Summary:
Nutrients can aggravate the already negative effects of climate
change on corals to trigger mass coral bleaching. A study suggests
ecosystem managers can reduce the impacts of coral bleaching by
implementing strategies to reduce nutrient stress in areas subject
to thermal stress.



FULL STORY ==========================================================================
A new study shows nutrients can aggravate the already negative effects
of climate change on corals to trigger mass coral bleaching.


========================================================================== Coral reef environments are typically low in naturally occurring nutrients
such as nitrogen and phosphorus compounds. But ocean currents passing
by can bring in a concentration of nutrients from elsewhere. Similarly, nutrients from human-made fertilisers and stormwater runoff enter reefs
from adjacent coastlines.

Lead author Dr Thomas DeCarlo from the King Abdullah University of
Science and Technology (KAUST) says corals are sensitive to high levels
of nutrients.

"As the climate warms, mass coral bleaching could occur as often as
annually within this century," Dr DeCarlo said. "In our study, we found
that already heat-stressed corals exposed to excess nutrient levels
were even more susceptible to bleaching." The study suggests ecosystem managers can reduce the impacts of coral bleaching by implementing
strategies to reduce nutrient stress in areas subject to thermal stress.

Co-author Professor John Pandolfi from the ARC Centre of Excellence for
Coral Reef Studies (Coral CoE) at The University of Queensland says this
and previous studies, including on the Great Barrier Reef, related coral bleaching to combinations of heat and nutrient stresses.



==========================================================================
"Our results provide a roadmap for coral reef conservation efforts to be
at their most effective," Prof Pandolfi said. "We suggest oceanographic processes should be included when deciding when and where to allocate
resources or protection." Using the skeletal cores of long-living corals,
the authors studied the past few decades worth of bleaching events in the
Red Sea. They found the reefs historically suffered severe bleaching only
when high sea surface temperatures were coupled with high nutrient levels.

The Red Sea was chosen as a study site as it is one of the only marine environments where the effects of summertime nutrients and heat stress
are independent of each other: only one area has a single major source
of nutrients in the summer, when a water mass brings nutrients to the
surface through a process called upwelling.

Previous field tests on the role of nutrients in coral bleaching were
otherwise difficult: nutrients and temperature often co-vary in the ocean, making it difficult to disentangle their effects. Nutrient loads are
also difficult to measure in the same way sea surface temperatures are,
via satellite.

"The fact that nutrients are more difficult to measure than temperature
may be restricting our recognition of their importance," Dr DeCarlo
said. "And we need greater longer-term monitoring efforts of nutrient
levels on coral reefs." "Incorporating nutrient-supplying ocean currents
into coral bleaching forecasts will enhance those predictions that are
based on temperatures alone," Prof Pandolfi said.

"Our research suggests that projections of coral reef futures should
move beyond solely temperature-based stress to incorporate the influence
of ocean current systems on coral reef nutrient enrichment, and thus susceptibility to bleaching," Dr DeCarlo said.


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


========================================================================== Journal Reference:
1. DeCarlo T, Gajdzik L, Ellis J, Coker D, Roberts M, Hammerman N,
Pandolfi
J, Monroe A, Berumen M. Nutrient-supplying ocean currents modulate
coral bleaching susceptibility. Science Advances, 2020 DOI:
10.1126/ sciadv.abc5493 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200821155749.htm

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