The University of the West Indies Organization of American States PROFESSIONAL DEVELOPMENT PROGRAMME: COASTAL INFRASTRUCTURE DESIGN, CONSTRUCTION AND MAINTENANCE A COURSE IN COASTAL ZONE/ISLAND SYSTEMS MANAGEMENT CHAPTER 7 MARINE BIOLOGICAL ISSUES By JUDITH GOBIN, PhD Part-time Lecturer, Faculty of Engineering University of the West Indies St. Augustine Campus Trinidad, West Indies Organized by Department of Civil Engineering, The University of the West Indies, in conjunction with Old Dominion University, Norfolk, VA, USA and Coastal Engineering Research Centre, US Army, Corps of Engineers, Vicksburg, MS , USA. Antigua, West Indies, June 18-22, 2001 Marine Biological Issues 7-1 By Judith Gobin Coastal Zone/Island Systems Management CDCM Professional Development Training, 2001 This lecture is adapted from the paper “The Lesser Antilles, Trinidad and Tobago” by John B.R. Agard and Judith F. Gobin in Seas at the Millennium: An Environmental Evaluation (Ed. C. Sheppard) 2000 Elsevier Science Ltd. 1.0 INTRODUCTION All the islands of the Lesser Antilles have coasts that border on both the tropical western Atlantic and the Caribbean Sea. Major sills in the passages between these islands are the controllers of water flow into the Caribbean Sea from the Atlantic Ocean. Horizontal motion below the average sill depth of the Antillean Arc (1200m) is almost stagnant. These islands are probably the most important physiographic features of the Caribbean Sea as they act as the gatekeepers to the integrity of the Caribbean marine environment. The coastal marine environments around the islands are generally oases of high production associated with shallow waters, coral reefs, mangrove swamps, estuaries and coastal lagoons surrounded by deep oligotrophic seas. The oceanography of the southern Lesser Antilles is strongly influenced by the outflow of two of the world’s largest river systems, the Amazon and the Orinoco. Superimposed on this regime are the periodic passage of large eddies of Amazon water from the Guyana Current. The marine production of offshore waters is generally low due to the relatively stable thermocline, which in the absence of significant upwelling prevents the mixing of nutrient rich deep waters with surface waters. The main seasonal variation of the islands is due to rainfall. Hurricanes are another periodic event that occasionally has significant impacts on the marine biota of these islands. Penaeid shrimp dependent on estuarine conditions and muddy bottoms are the most valuable fishery resource harvested on the continental shelf between Trinidad and Venezuela. Pelagic fishes offshore (e.g. flyingfish, kingfish, dolphinfish, tuna, swordfish, sharks) and inshore (e.g. kingfish, jacks, herrings and anchovies) are the main commercial fisheries resource exploited among the islands in the area of mixed water stretching from the north coast of Trinidad to St Vincent. In the clear blue oligotrophic waters from St Marine Biological Issues 7-2 By Judith Gobin Coastal Zone/Island Systems Management CDCM Professional Development Training, 2001 Lucia to the Virgin Islands the only significant fisheries are for lobsters and conchs inshore, and for tuna offshore. Only Trinidad and Tobago and the French islands of Martinique and Guadeloupe show any noticeable increase in fish catches from 1990-95. Large commercial fishing vessels from several nations not indigenous to the sub-region frequently exploit the limited fish stocks within the Exclusive Economic Zone of these islands. In many cases, these vessels operate without the knowledge and consent of island governments. All of the islands have fisheries legislation but a shortage of trained personnel and the high cost of effective fisheries patrols in offshore as well as inshore waters and marine parks hinder their effective enforcement. In these islands human impacts on the marine environment are significant because population density is high ranging from 83 km-2 in Anguilla to 614 km-2 in Barbados. Ongoing deforestation is a serious problem affecting the coastal zone in Trinidad and Tobago, Guadeloupe, Martinique, St Lucia and the British Virgin Islands. Artisanal fishing methods such as trawling for shrimp, cutting mangrove roots to harvest oysters, over harvesting of edible sea urchins, lobsters and conch, also damage marine habitats. Beach sand mining is the major human induced cause of coastal erosion in the Eastern Caribbean. Marine pollution from inadequately treated sewage effluents is a problem on every island because of the lack of adequately maintained centralised sewage treatment facilities. The annual number of tourist arrivals in individual islands is substantially greater than their resident population in 12 out of 14 instances excluding only Dominica and Trinidad. Airport and marina construction to provide facilities for tourists have resulted in the filling in of coastal mangroves and increasing sedimentation in coral reef and seagrass areas. The development of heavy industry in the coastal zones of the various territories is very limited except for the island of Trinidad. Dense petrochemical related shipping Marine Biological Issues 7-3 By Judith Gobin Coastal Zone/Island Systems Management CDCM Professional Development Training, 2001 traffic passing through narrow straits around Trinidad and Tobago make this area a high- risk zone for marine pollution from shipping accidents. The Lesser Antillean countries are signatories to several important international conventions and programs, which are geared to protect the marine and coastal environment. However, the record of implementing the provisions of these conventions is very poor. Further, there are few significant ongoing marine investigations in the sub- region except for those undertaken through the Caribbean Coastal Marine Productivity (CARICOMP) network of Marine Laboratories, Parks and Reserves. The islands will have to significantly increase their environmental protection efforts if they are to stem the tide of pollution and natural resource depletion. 2.0 THE DEFINED REGION This review covers the Lesser Antillean arc of islands in the Eastern Caribbean, as well as the islands of Trinidad and Tobago, which are geologically parts of the South American continent. The sub-region includes the following countries: Anguilla, Antigua and Barbuda, Barbados, British Virgin Islands, Dominica, Grenada, Guadeloupe, Martinique, Montserrat, Netherlands Antilles (Saba and St. Eustatius), St. Kitts (St. Christopher) - Nevis, St. Vincent and the Grenadines, St. Lucia, Trinidad and Tobago, U.S.Virgin Islands (Fig. 1). All the islands of the archipelago have coasts that border on both the tropical southwest Atlantic and the Caribbean Sea. Major sills in the passages between these islands are the controllers of water flow into the Caribbean Sea from the Atlantic Ocean (Fig. 1). Horizontal motion below the average sill depth of the Antillean Arc (1200m) is almost stagnant. These islands are probably the most important physiographic features of the Caribbean Sea as they act as the gatekeepers to the integrity of the Caribbean marine environment from the Atlantic Ocean. The water forcing its way in the Marine Biological Issues 7-4 By Judith Gobin Coastal Zone/Island Systems Management CDCM Professional Development Training, 2001 upper layer of the sea, through the narrow channels between the islands creates jet currents as well as large turbulent wakes and eddies. These currents may concentrate marine organisms as well as nutrients and pollutants in the wake of islands. The coastal marine environments around the islands are generally oases of high production associated with shallow waters, coral reefs, mangrove swamps, estuaries and coastal lagoons surrounded by deep oligotrophic seas. The well being of these small islands is therefore intimately associated with the protection of their coastal ecosystems. The area seems amenable to the large marine ecosystem (LME) approach to managing marine resources. However, since this LME includes the territorial waters of 15 countries, the effectiveness of this management tool is dependent on the co-operation of all the bordering countries. 3.0 SEASONALITY,CURRENTS, NATURAL ENVIRONMENTAL VARIABLES Ocean surface temperatures are about 27 oC with seasonal fluctuations of no more than 3 oC and a decrease of 10-15 oC within the upper 200m, beyond which there is little change. The main seasonal variation of the islands is due to rainfall. The seasons are caused by the annual displacement of the Inter-tropical Conversion Zone (ICTZ) northward during April to September and it’s return southward during January to March. The climate year is divided into a dry season lasting from about January to May and a wet season from June to December. There are differences in precipitation between the islands with rainfall being highest among the central islands of the Antillean arc from Anguilla to Dominica. The effect of local rainfall on the marine biota is generally insignificant in comparison with the dominant hydrographic regime. The oceanography of the southern Lesser Antilles is strongly influenced by the outflow of two of the world’s largest river systems, the Amazon and the Orinoco. Together they account for about 20 % of fresh water discharges into the world’s oceans. During Marine Biological Issues 7-5 By Judith Gobin Coastal Zone/Island Systems Management CDCM Professional Development Training, 2001 February to May, the Guyana Current advects water of high primary productivity and sediment concentration