Climate Change And Its Impact On Marine & Coastal Ecosystems

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Coral reefs are extremely important in protecting shorelines and minimising the impact of high energy waves, but are faced with the threat of Global Climate Change (GCC).

These threats, noted Marine Biologist at the Coastal Zone Management Unit, Angelique Brathwaite, include an increase in the intensity of storms and hurricanes, sea level rise and ocean acidification, among others.

She explained that GCC was a term used to describe the phenomenon of increasing average global temperatures, as a result of elevated levels of greenhouse gases, which include carbon dioxide, methane, nitrous oxide and hydrofluorocarbons.

"The warmer temperatures affect [the] climate, which, in turn, affects the weather, and these atmospheric upheavals produce a number of undesirable impacts, especially for Small Island Developing States which are dependent on their marine and coastal systems," she said.

She added that beaches, sea grass beds, mangrove swamps and coral reefs were the most vulnerable to changes resulting from GCC, and often suffered the impacts of coral bleaching, increases in infectious diseases and agricultural output declines.

Ms. Brathwaite explained that bleaching was a response to stressors which could include unusually high temperatures. "High temperatures, just one or two degrees Celsius above the summer maximum can cause bleaching. During the process corals lose their symbiotic, photosynthetic zooxanthellae, which provides approximately 80 per cent of the nutritional requirements of the coral animal," she pointed out.

The Marine Biologist warned that if the stress remained for an inordinate length of time, the coral would die. "In recent times, unusually high temperatures have been occurring with increasing frequency. Mass bleaching events were first observed globally in the years 1997 to 1998 as a result of the El Nino and La Nina phenomena, followed by 2005 and 2010 events in the Caribbean," she said.

She added that predictions by the World Resources Institute suggest that approximately half of the global coral reefs would experience bleaching, and this percentage should rise to over 95 per cent by 2050. "In Barbados, corals experienced up to 26 per cent mortality as a result of bleaching episodes in 2005," she noted.

However, Ms. Brathwaite cautioned that concerns of sea level rise had serious implications, particularly for low lying countries.

In explaining this phenomenon, the Marine Biologist stated: "Water expands when heated and high temperatures melt the polar caps. Both of these have resulted in rising sea levels, which has already created problems for small low lying islands such as Kiribati and Tuvalu."

She warned that in addition to flooding and the reduction of land space and livelihoods, sea level rise was also capable of destroying some corals. "Corals rely on their zooxanthellae for nutrition, and these plants in turn rely on sunlight and photosynthesis. Hard corals are, therefore, restricted to relatively shallow waters (less than 200 feet). Many deep corals already exist at their lowest limit. So, even a small increase in sea levels can cause them to essentially ???drown’," she said.

Meanwhile, coral could also be exposed to ocean acidification as atmospheric carbon dioxide dissolves in sea water, thereby generating carbonic acid which is acidic. "This disrupts the ability of corals to generate their calcium carbonate skeletons and also dissolves the shells of other calcareous organisms. The present rate of acidification of the ocean is considered unparalleled in the past 300 million years," Ms. Brathwaite noted.

However, corals are also being affected by disease at an alarming rate with the Caribbean being listed as a "disease hot spot" due to the virulence and fast spread of disease on coral reefs over the past decade. "Pathogens are more virulent in hotter temperatures," she said.

She further pointed out that scientists were also predicting an increase in the intensity and frequency of hurricanes and storms, and longer spells of dry seasons leading to droughts.

julia.rawlins-bentham@barbados.gov.bb

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