Environmental Engineering Reference
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that corals can recruit from local sources, especially in the
absence of human-caused disturbances, which slow down
r e c ove r y.
Scientists have found an early warning sign for corals that
may bleach—some proteins in the zooxanthellae respond
rapidly and dramatically to temperature stress. Before actual
bleaching, hemoglobin genes are expressed at a higher level.
Because of this sensitivity, hemoglobin production by the
algae may be able to be used as an early warning indicator of
stress. Scientists have also found some heat-resistance genes
that enable corals in some areas to avoid bleaching and to sur-
vive in conditions that kill other corals. This is an encouraging
finding.
What happens in polar regions?
Polar ecosystems are also very vulnerable to climate change.
Their temperatures are increasing more rapidly than else-
where (more than 5 times the global average). Warming ocean
currents have been speeding up the melting of the Arctic sea
ice sheet and the decline and breakup of Antarctic ice shelves.
The Arctic ice sheets have been shrinking, with the lowest
recorded level in the summer of 2012. It is predicted that the
Arctic will be totally ice-free during the summer in less than
30Â years. Greenland is losing about 100 billion tons of ice annu-
ally as a result of melting. Sea levels are now projected to rise
much faster than predicted by the Intergovernmental Panel
on Climate Change (IPCC) in 2007, because of this accelerated
melting, which further threatens coastal habitats. As the tem-
perature has risen, plankton blooms typical of the region have
decreased, and the phytoplankton community has shifted
from large species to smaller ones. This shift has affected the
zooplankton. Shrimp-like krill, which are inefficient at graz-
ing on small phytoplankton, are declining, while salps, which
are efficient, are increasing. Krill also depend on diminish-
ing sea ice for their reproduction. Furthermore, according to a
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