Coles, S.L., Bahr, K.D.,
Rodgers, K.S., May, S.L.,
McGowan, A.E., Tsang, A.,
Bumgarner, J. and Han, J.H.
2018
"Evidence of acclimatization
or adaptation in Hawaiian corals
to higher ocean temperatures."
PeerJ 6: e5347, DOI: 10.7717/peerj.5347.
NOTES:
Are the so-called
"rainforests of the sea"
destined for disaster
because of climate change?
Coles et al. (2018)
write in the Abstract
of their new paper that
"predicted projections
for the state of reefs
do not take into account
the rates of adaptation or
acclimatization of corals
as these have not as yet
been fully documented."
By not including the ability
of living organisms to acclimate,
acclimatize or adapt to changes
in their environment), many
scientists have projected
that future climate change
will lead to the collapse
of coral reefs within
the next few decades
(see, for example:
Hoegh-Guldberg, 1999;
Hoegh-Guldberg et al., 2007;
Veron et al., 2009;
Frieler et al., 2013).
( see REFERENCES below )
SUMMARY:
A 1970 coral experiment
was repeated in 2017.
There were
"significant differences
in coral bleaching, calcification,
survivorship, and mortality"
between the two experiments.
With respect to bleaching,
Coles et al. note that
it was observed
"much sooner in 1970
compared to 2017
at similar temperatures,"
adding that
"in 1970, onset of bleaching
occurred in half the number
of days (3 days) than in 2017 (6 days)
in P. damicornis and M. capitata
and three days sooner
in L. scutaria (5 days vs. 8 days),
respectively)."
Calcification rates were reduced
by high temperatures in both the
1970 and 2017 experiments,
but the authors report that
"reductions in 2017
were not as severe as those
documented in 1970."
In fact, comparison of calcification
rates between the two periods
revealed that they
"were 70-90% higher in 2017".
Coles et al. state that the corals
"were able to withstand
elevated temperatures (31.4 °C)
for a longer period of time
in the current 2017 experiment"
compared to the 1970 study.
They conclude that their results
"indicate a shift in the temperature
threshold tolerance of these corals
to a 31-day exposure to 31.4 °C,"
which findings
"provide the first evidence
of coral acclimatization or adaptation
to increasing ocean temperatures."
If ocean temperatures
rise in the future,
as living organisms,
corals can adapt.
DETAILS:
Coles et al. set out to
"assess possible changes
in thermal tolerances"
of three coral species
(Lobactis scutaria,
Montipora capitata and
Pocillopora damicornis).
Back in 1970, samples
of these corals were collected
from the Moku o Lo'e reef
in Kane'ohe Bay, O'ahu,
Hawaii, USA, and subjected
to one month's duration
of elevated temperature (31 °C),
following which temperatures
were returned to normal (26.4 °C).
During the one-month
of elevated temperatures,
and for one month after
temperatures were returned
to normal the authors conducted
a series of measurements
pertaining to the corals' growth
and survival.
In 2017, nearly five decades later,
the original experiment was repeated
using present-day coral samples
and "identical methodology,
location, seawater system,
and observer."
Finding that the baseline ambient
sea surface temperature
had risen +2.2°C since 1970,
the current experiment
provided an opportunity
to assess the corals' ability
to acclimate or adapt
to the warming trend.
Coles et al. report that
"coral survivorship
at elevated temperature (~31.4 °C)
was higher in 2017 across species:
L. scutaria (92%),
M. capitata (83%), and
P. damicornis (60%)."
In contrast, in 1970,
survivorship of
survivorship of
L. scutaria was only 40%,
P. damicornis 5% and
M.capitata 0%.
REFERENCES:
Frieler, K., Meinshausen, M., Golly, A., Mengel, M., Lebek, K., Donner, S.D. and Hoegh-Guldberg, O. 2013. Limiting global warming to 2°C is unlikely to save most coral reefs. Nature Climate Change 3: 165-170.
Hoegh-Guldberg, O. 1999. Climate change, coral bleaching and the future of the world's coral reefs. Marine and Freshwater Research 50: 839-866.
Hoegh-Guldberg, O., Mumby, P.J., Hooten, A.J., Steneck, R.S., Greenfield, P., Gomez, E., Harvell, C.D., Sale, P.F., Edwards, A.J., Caldeira, K., Knowlton, N., Eakin, C.M., Iglesias-Prieto, R., Muthiga, N., Bradbury, R.H., Dubi, A. and Hatziods, M.E. 2007. Coral reefs under rapid climate change and ocean acidification. Science 318: 1737-1742.