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Saturday, June 15, 2019

Coles et al. (2018) -- Coral adapt to higher sea temperatures -- A 1970 experiment was repeated in 2017

Coles, S.L., Bahr, K.D., 
Rodgers, K.S., May, S.L., 
McGowan, A.E., Tsang, A., 
Bumgarner, J. and Han, J.H. 


"Evidence of acclimatization 
or adaptation in Hawaiian corals 
to higher ocean temperatures."

PeerJ 6: e5347, DOI: 10.7717/peerj.5347.

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 )

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), 

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. 

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 
L. scutaria was only 40%, 
P. damicornis 5% and 
M.capitata 0%.

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.