Worrying news has come from a recent study by Hooidank et al,
which suggests that coral bleaching is the greatest threat to coral reefs, and
that by the end of the century, the majority of corals will unfortunately have
gone past the ASB- Annual Severe Bleaching condition. This is where change is a
certainty and recovery is not certain whatsoever.
The corals are bleached when temperature stresses get to too
high a level. When this stress occurs, the zooxanthellae will leave the coral. If
the temperature stresses continue, the coral will die. How long the coral can
survive in this state will depend on the severity of the temperature stress,
and the resilience of the genus of the coral. If the water conditions return to
acceptable levels, then the coral may survive. Worldwide there has been an
ocean bleaching event that began in 2014, and may continue further into 2017.
Anthropogenic activity is the main driver behind the temperature
stress felt by the corals. Things are not looking good for the corals, with 99%
of reefs experiencing annual severe bleaching. The average projected year for
this event is 2043, so just 26 years into the future. There is just over a
quarter of a century to make changes, however the damage may already be done.
Above is a link to the figure used in the report. No one
ocean basin stands out as having particularly healthy or unhealthy reefs. However
specific countries are in danger. For example, Papa New Guinea has a high
proportion of their reefs that are likely to experience ASB events within the
next 15 years (as early as 2030). This is very troubling as Papa New Guinea is
not a wealthy nation, with a GDP per capita of just $2800, and so they may
struggle to tackle issues such as coral reef preservation. The Northern area of
the Great Barrier Reef is fairing slightly better, with the vast majority not
likely to experience an ASB event until at least 2050. However, this only
leaves 35 years or so to try and prolong the existence of corals in the ocean.
This is all very worrying, especially seeing as we have
known about the decline in coral reef health for decades, and the problem is
getting more severe and widespread. One strategy to prolong the lifespan of
coral reefs is to manage the ‘weak of the strong’. This is the idea that
attention and money be diverted to the healthiest coral reefs, while the
unhealthiest in the oceans is left to die. This would ensure the future of at
least some corals, preventing them from becoming extinct. The sad reality is
that this may be the best we can do, with worldwide coral reefs a thing of the
past.
The UN Framework on Climate Change Convention have met to
try and prevent irreversible anthropogenic damage to the environment. They have
195 members, and have the goal of keeping warming below 2 degrees. This may be
extremely problematic, but if global warming can be kept to 2 degrees, then
there may be some hope for corals yet.
The growing acidity in the oceans is a problem also. It prevents corals from calcifying, which means they are not protected against the environment, as the calcification enabled them to have a protective layer.
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| Calcification Rates across the Great Barrier Reef |
As we can see from the figure, calcification has decreased by 0.2 g/cm2/yr. over the last 100 years. This means that corals are now even more vulnerable than before. The most alarming conclusion that we can draw from this graph the rate of decline in the past 10 years. tTis shows that action is required now.
At this point I would like to speak about an example of
corals becoming healthier, to counter the earlier part of the blog. Unfortunately
I could find nothing along these lines. The only thing I could come across is
information of how the rate at which corals are being destroyed is slowing
down. This is as good as it gets. This was published in December 2016, so is
extremely relevant, and just highlights the struggles faced by corals in the
coming years.
Sources
- http://www.nature.com/articles/srep39666
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