Hawaiian corals show surprising resilience to warming oceans
22-month study provides realistic conditions, scientists say
Date:
March 10, 2022
Source:
Ohio State University
Summary:
A long-term study of Hawaiian coral species provides a surprisingly
optimistic view of how they might survive warmer and more acidic
oceans resulting from climate change.
FULL STORY ==========================================================================
A long-term study of Hawaiian coral species provides a surprisingly
optimistic view of how they might survive warmer and more acidic oceans resulting from climate change.
========================================================================== Researchers found that the three coral species studied did experience significant mortality under conditions simulated to approximate ocean temperatures and acidity expected in the future -- up to about half of
some of the species died.
But the fact that none of them completely died off -- and some actually
were thriving by the end of the study -- provides hope for the future
of corals, said Rowan McLachlan, who led the study as a doctoral student
in earth sciences at The Ohio State University.
"We found surprisingly positive outcomes in our study. We don't get a
lot of that in the coral research field when it comes to the effects of
warming oceans," said McLachlan, who is now a postdoctoral researcher
at Oregon State University.
While the findings are optimistic, they are also more realistic than
previous studies, said study senior author Andre'a Grottoli, distinguished professor of earth sciences at Ohio State.
The study lasted 22 months, which is much longer than most similar
research, which often spans days to up to five months, Grottoli said.
========================================================================== "There are aspects of coral biology that take a long time to adjust. There
can be a dip when they are faced with stressors, but after enough time
corals can recalibrate and return to a normal state," Grottoli said.
"A study that lasts five months is only seeing part of the arc of the response." The research was published today (March 10, 2022) in the
journal Scientific Reports.
Rising levels of carbon dioxide in the atmosphere have led to warmer
oceans and about a quarter of the carbon dioxide in the air dissolves
into the ocean, causing it to become more acidic. Both rising acidity
and temperatures threaten coral, Grottoli said.
In this study, the researchers collected samples of the three most
common coral species in Hawaii: Montipora capitata, Porites compressa
and Porites lobata.
==========================================================================
The samples were placed in tanks with four different conditions: a control
tank with current ocean conditions; an ocean acidification condition
(-0.2 pH units); an ocean warming condition (+2 degrees Celsius); and
a condition that combined warming and acidification.
Results showed that warming oceans will hurt coral species: 61% of corals exposed to the warming conditions survived, compared to 92% exposed to
current ocean temperatures.
The two Porites species were more resilient than M. capitata in the
combined warming and acidification condition. Over the course of the
study, survival rates were 71% for P. compressa, 56% for P. lobata and
46% for M. capitata.
"Of the coral that survived, especially the Porites species, they were
coping well, even thriving," McLachlan said. "They were able to adapt to
the above- average temperature and acidity." For example, the surviving
Porites were able to maintain normal growth and metabolism.
Grottoli said M. capitata may fare better in the real world than they
did in this study. The species relies heavily on zooplankton as a food
source when under stress, and they may not have had as much available
in the study conditions as they would in the ocean.
"We may have underestimated their capacity for resilience in this
study. It may be higher on the reefs," Grottoli said.
In most ways, though, this study did better than most at creating
real-life conditions, the researchers said.
The corals were put in outside tanks designed to mimic ocean reefs by
including sand, rocks, starfish, urchins, crabs and fish. These tanks also allowed natural variability in temperature and pH levels over the course
of each day and over the seasons, as corals would have in the ocean.
"When you're trying to make predictions of the long-term effects of
climate change, it is important to mimic the real-world conditions,
and our study does that," Grottoli said.
"We feel strongly that this makes our findings very robust." The findings regarding the two Porites species may offer particular hope for corals
around the world. The Porites are part of a genus of coral that is
common across the world and that has a key role in reef building, so
their resilience in this study is a good sign, Grottoli said.
While this study does lead to reasons for optimism, it does not mean
that corals face no threat under climate change.
"We don't know how corals will fare if changes in temperature and acidity
are more drastic than what we used in this study," McLachlan said. "Our
results do offer some hope but the approximately 50% mortality we saw
in some species in this study is not a small thing." The study also
didn't include local stressors like pollution and overfishing that may
have additional negative impacts on corals in some areas, according
to Grottoli.
Other co-authors were James Price, Agusti' Mun~oz?Garcia and
Noah Weisleder of Ohio State; Stephen Levas of the University of Wisconsin-Whitwater; and Christopher Jury and Robert Toonen of the
University of Hawaii at M?noa.
About 30 Ohio State undergraduate students also worked on the study,
some through Ohio State's Second-Year Transformational Experience Program.
Funding for the research was provided to Grottoli from the National
Science Foundation and the HW Hoover Foundation and to Jury and Toonen
from NSF.
========================================================================== Story Source: Materials provided by Ohio_State_University. Original
written by Jeff Grabmeier. Note: Content may be edited for style and
length.
========================================================================== Related Multimedia:
* View_of_the_test_tank_after_22_months ========================================================================== Journal Reference:
1. McLachlan, R.H., Price, J.T., Mun~oz-Garcia, A. et al. Physiological
acclimatization in Hawaiian corals following a 22-month shift in
baseline seawater temperature and pH. Scientific Reports, 2022 DOI:
10.1038/ s41598-022-06896-z ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/03/220310115150.htm
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