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The Impact of Surface Currents on Sargassum Movement Causing Havoc to the Jamaican Coast

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The journey taken by passive, water-borne organisms, such as the marine plant Sargassum  recently causing havoc to the Jamaican coast and other Caribbean countries, is controlled mainly by offshore and onshore current flow as well as water quality changes over time. The dense proliferation ofSargassum in our coastal areas causes environmental problems for local marine ecosystems, as well as the livelihood of people relying on these resources. The sudden growth of these plants, for example, results in a change in water quality that may not be conducive for the survival of marine life, or may destroy the seascape for tourism and other industries – impacts which interfere with the revenue potential and economics of the area. A number of reasons are presented for the sudden growth in coastal areas, including climate change, shifting currents and even chemicals used in cleanup efforts for the BP oil spill in the Gulf of Mexico. For this particular seaweed proliferation event in the Caribbean, remotely sensed images from satellites show the seaweed path emanating from the Amazon and Orinoco Rivers southeast of the Caribbean that bring nutrient-rich water to the ocean.Sargassum seaweed thrives in eutrophic waters containing a high concentration of nutrients, especially nitrates and phosphates. As the algae die and decompose, high levels of organic matter and the decomposing organisms deplete the water of available oxygen, causing the death of other organisms, such as fish.

Given the damaging effects of Sargassum proliferation on our shorelines, it is important to understand the underlying hydrodynamics that drives their transport. The current system in most coastal areas (known as the “coastal current”) – driven by wind and density differences – is easily trapped towards the coast, particularly for the south coast of Jamaica when the current flows along-shore. Should this entrained water mass be invaded by Sargassum, as well as the optimum nutrient conditions exist that boost their growth, then an over-abundance of the plant occurs.  Typically, transport is from east to west – from the eastern regions of the Atlantic Sea through to large current systems such as the Caribbean Current and Gulf Stream, and then into coastal currents. Rarely, however, does it proliferate inshore. Large floating collections of the plant are typically found off-shore in open ocean. Sagassum seaweed is found abundantly in the Sargasso Sea, a floating ecosystem as large as two million square miles in the North Atlantic. Over the past year, many Caribbean shorelines have been impacted. Countries such Jamaica, Trinidad and Tobago, Grenada, St. Martin, St. Thomas, Barbados and Antigua have all reported invasions. The National Environment and Planning Agency (NEPA) reports several beaches that have been impacted in Jamaica so far, namely, Winnifred Beach and Innes Bay Beach in Portland, Robins Bay Beach and Pagee Beach in St. Mary, Portland Bight in Clarendon, Holland Bay in St. Thomas, Ironshore in St. James, Ocho Rios and Discovery Bay in St. Ann and Braco and Oyster Bay in Trelawny. These locations indicate the likely spread of the proliferation from east to west, as they are affected by surface currents that flow past Jamaica in this direction. Of the eleven beach areas impacted, eight of these (73%) scored low in durability profile. These are beaches that are considered particularly exposed and unprotected – lacking natural sources of physical and environmental shoreline protection from degradation. Now they face the additional threat of poor water quality from rotting seaweed debris.

Writers: Dr. Ava MaxamDr. Kioshi Mishiro & Luke Buchanan

Organization: Mona GeoInformatics Institute (MGI)


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