The Caribbean Sea is bordered by 36 nations, including continental countries, island nations, and dependent territories. Some of these nations have large populations and industries while others are sparsely populated. At present, the responsibility for the region’s marine resources is divided between these 36 nations. There is a need for regional cooperation in resource management, considering that many of the resources and the stresses that are impacting them are transboundary in nature. Increasingly, ecosystems in the Wider Caribbean region are under heavy stress from human activities, and a number of unique ecosystems and habitats have been destroyed, and species exterminated. In the last 150 years, eight species of vertebrates have become extinct in Jamaica alone. More than 100 plant species, which are indigenous to Trinidad and Tobago may be threatened by extinction.

Worldwide, human activities, directly and indirectly, are now the primary causes for changes in biodiversity. Approximately 50% of the human population lives in the coastal zone, and pressures exerted on the marine environment are increasing. Some of the main threats to biodiversity in the Wider Caribbean Region are habitat destruction due to coastal development and to the expansion in population and in tourism, pollution, overexploitation of living resources, including fisheries, sedimentation, and predation by introduced species. As a result, coral reefs, seagrasses and mangroves, among other coastal ecosystems, are under intense pressure, threatening biological diversity in the region.

Habitat destruction and alteration

Habitat destruction and alteration is one of the leading causes for the loss of biodiversity. Because organisms are adapted to certain physical conditions and environments, altering these conditions will result in a change in the biological community. Physical destruction or alteration of marine and coastal environments includes the clearance of mangroves, construction activities, dredging, mining, and anchoring. Changing the structure of the environment results in simplifying, fragmenting (the breaking up of continuous ecosystems into fragments surrounded by unsuitable habitat), and eliminating the habitats of certain species. As a result, the functioning of entire ecosystems can be affected.

The scale, intensity, duration, and timing of the physical alteration to the environment all determine its impact. Clearance of mangrove forests is a problem throughout the Wider Caribbean Region. Mangroves are cut down to for housing and tourism-related development, for the construction of roads and for the development of industry and mariculture. Clearing mangrove forests makes the coast more vulnerable to erosion, and destroys the habitat of many species. The nursery grounds of the juveniles of many commercially important fisheries species, such as lobster, will also be destroyed when mangroves are cut down. These species will, as adults, migrate to live on nearby coral reefs. Since mangroves buffer the nearshore marine environments from many land-based impacts, such as nutrients, pollution and sediments, the loss of these functions may result in a deteriorating quality of other nearby ecosystems.

Of concern in the Wider Caribbean Region are construction-related activities, such as alteration to the coastline, beach mining and renourishment, dredging, and filling. All of these activities have considerable environmental impact. Shoreline structures, including piers, jetties and breakwaters, alter the patterns of sediment transport, preventing the renourishment of beaches downstream of this river of sand. A disruption in sediment transport can lead to the erosion of beaches and marshes. Beach sand mining, a common practice in the region, causes sedimentation, which has a negative impact on coral reefs and other marine ecosystems. Similarly, dredging not only physically alters marine ecosystems, but also causes the re-suspension of large amounts of sediment. Suspended sediments decrease water clarity and thus affect photosynthesis, stress corals and other suspension-feeders by making them expend energy in ridding themselves of sediment, and, in the most severe cases, smother the organisms themselves. Biodiversity of corals, other invertebrates, fish, and algae is reduced as a result.

Other activities altering the physical environment and causing a reduction in biological diversity include trawling for shrimp, which disturbs the seabed and the associated benthic communities, resuspends sediments and causes turbidity currents. In areas that are heavily visited by recreational visitors and tourists, impact caused by divers, snorkellers and boat ancors can be considerable. Land based activities, such as logging, construction of roads and buildings, and agricultural practices not only have an impact at the site of the activity, but also in coastal and marine ecosystems some distance away. The increased siltation resulting from such activities can have serious effects on coral reefs, especially on those fringing the coastline. Siltation in general is one of the largest sources of coral reef degradation worldwide.

Overexploitation of living things

Overexploitation of living resources is a serious problem at the current time because there are more people than ever utilizing limited resources, while technological advances have made it easier to exploit wild populations of animals. The sustainable use of species means that no more are taken than the species themselves can replace through reproduction.

The Wider Caribbean Region includes a large number of countries of diverse social and economic status. Because of this, there are as wide a variety of fishing activities taking place (including industrial, artisanal and recreational) as there are approaches to management. Overexploitation, at its simplest, means that fish and other commercially valuable species are removed faster than they can reproduce. Main fisheries within the area are for small and large pelagic finfish, reef fishes, coastal demersal finfish, crustaceans and molluscs. Fisheries in the Wider Caribbean region are affected by fishing pressure. According to FAO’s 1994 assessment, just over 35% of stocks in the region were regarded as overexploited. This number includes stocks that were considered fully fished, overfished, depleted or recovering. The assessment does not include mollusc stocks, which may be significant considering the importance of conch for the fisheries of the region. Just under 60% of demersal stocks were overexploited and just under 70% of pelagic stocks. Crustacean stocks were not generally considered overexploited. However, these figures are only overall estimates, and the state of local stocks varies greatly. Generally, overexploiting the inshore reef fishery resources has led many countries to direct exploitation of offshore pelagic resources. These stocks tend to be highly migratory, and their management will in most cases require regional and international cooperation.

Species, which mature slowly and produce few young are particularly vulnerable to overexploitation. Sea turtles, sharks, whales, manatees and sea birds fall into this category. Sea turtles, for example, may, in some cases, take up to 50 years to reach sexual maturity. High mortality from natural causes combined with human exploitation and loss of nesting beaches has put six out of seven species of sea turtle in danger of extinction. Many of the slow maturing species are also highly migratory, passing through the territorial waters and coastal areas of many countries. International cooperation is required to conserve the populations of such species. Most marine fishes and invertebrates making up the main fisheries species in the Wider Caribbean region reproduce early and in sufficient numbers to make sustainable use possible. However, even many of these species are now overexploited.

According to FAO’s 1994 estimation, by-catches and discards worldwide total an estimated 18 to 40 million tonnes. This represented just over 25% of the annual estimated total catch. Shrimp fishing, an important fishery in the Wider Caribbean Region, produces the largest volume of discards, an estimated 9 million tonnes annually worldwide. FAO estimated that the Wider Caribbean Region has the highest percentage of discard of any of the major fishing areas, with nearly half of the catch believed to be discarded. Most of this is the by-catch of shrimp trawling, particularly in the Northern Gulf of Mexico. By-catches include marine mammals, sea turtles, seabirds, as well as finfishes and invertebrates. Dolphins are caught in pelagic drift nets, sea turtles in shrimp trawls, and diving seabirds in long-lines. Solutions to by-catches and discards include improving the selectivity of fishing gear and fishing methods. However, much of the research in by-catch elimination has been carried out in North America and Europe, and is not readily transferable to multi-species tropical fisheries. Tropical shrimp trawls still produce the highest rates of by-catch. Turtle excluder devices (TEDs) are now required by all countries exporting shrimp to the U.S. However, even with TEDs in place, the number of invertebrates and other by-catch is still high, and trawling has a serious impact on benthic habitats. Improved utilization of by-catch as a food source is a possibility, but the mortality of potentially threatened species and the capture of immature specimens remains a serious problem.

Pollution

Pollution damages productive fisheries and viable tourism areas, and leads to reduced biological diversity. By straining the ecosystem, pollution removes sensitive species. Some pollutants are toxic or radioactive, and may not only have a direct impact on an organism, but can also be passed along the food chain. Other pollutants, such as nutrients, stimulate plant growth, which in a tropical marine environment may cause algae to overgrow coral reefs and seagrass meadows. Solid waste, including plastics, glass, metal, and other debris can be harmful to marine life. Plastics are known to cause widespread mortality in marine species through entanglement and ingestion. Sea turtles, for example, are known to die from ingesting plastic bags floating in the sea. Pollution may have a considerable impact on the state of the fisheries in an area. It may also affect biodiversity indirectly, by altering or destroying the habitat of a particular species. The impact can be particularly devastating in the case of an endangered or a threatened species.

The Caribbean is one of the most heavily traversed seas worldwide, and pollution from transboundary and extra-regional activities is significant. These activities include the transport of oil through the region as well as shipping, which generate pollution in the form of bilge water and garbage dumped in the ocean. However, there is also a considerable amount of pollution that originates from within the region. Contaminants include sewage, solid waste leachate from landfills, industrial and agricultural run-off, and petroleum products. The article titled Land Based Sources of Marine Pollution in our Environmental Issues in the Caribbean section discusses pollution and its effects on the marine and coastal environments of the region in more detail.

Several international treaties and conventions are in place for the prevention of pollution. Pollution from ship-based sources is regulated by the International Convention for the Prevention of Pollution from Ships of 1973, which was superseded by the 1978 Protocol (Marpol 73/78). Marpol Annex IV regulates the discharge of sewage from ships, while Annex V includes requirements for ships to control and prevent dumping of garbage. Ports must provide facilities to receive such wastes. The Wider Caribbean Region was designated as a "special area" under the provisions of Annex V of Marpol 73/78. This means that ships of any size are prohibited from discharging any waste material except food waste, which may be discharged 12 nautical miles (3 nautical miles in the Wider Caribbean Region) from land. However, in order for the special area designation to become effective, waste reception facilities will have to be established in the ports of the region. In practice, the establishment of waste reception facilities creates a problem, especially for smaller nations. The Marpol Treaty Annex V provides a legal framework to deal with polluters. Unfortunately, many Caribbean countries are not signatories to the Marpol Treaty.

Introduction of alien species

Alien species are organisms that have been transported by human activity into regions where they have not historically been found. Sometimes the introduction of an alien species is intentional, as is the case in activities such as agriculture and mariculture. Introductions may also be accidental, for example when organisms are carried from one port to another on ships. New organisms have arrived on many islands of the Caribbean either as stowaways onboard ships or in ship hulls. It is also common for organisms to move around in the ballast water carried in ship’s tanks to provide stability. Introduced species are responsible for many recorded species extinctions, especially on islands. In an isolated environment, an introduced species, having left behind its native predators, can rapidly outcompete the native species, which did not co-evolve with the newcomer.

A number of alien species have been introduced to the Wider Caribbean region as a result of aquaculture projects, with negative impact to the native Caribbean biota. Although mariculture operations are usually viewed as having positive social and economic impacts, there is always the chance of accidental introduction of diseases and pathogens and the potential escape of the maricultured species into the wild. In most cases, there have been no experimental studies to verify the exact impacts caused by the introduced alien species. However, it has been documented that invasions can lead to fundamental changes in natural communities.

One of the most significant impacts of introductions worldwide has been the increase of toxic phytoplankton blooms in coastal waters. Toxic dinoflagellate species or their cysts can be transported in ships ballast tanks from one nation to another. Toxic plankton blooms can have severe economic, social and human health impacts, often resulting in the closure of shellfishery operations.

Despite the potential threats posed by introductions of alien species on natural communities, there are many advantages for initiating mariculture operations in order to create supplemental fisheries. Additionally, the release of large numbers of marine organisms by ballast water continues in most regions. There is a need for effective national and international measures and policies in order to mitigate and prevent the negative consequences of alien introductions. One such iniative, the UNCLOS framework, requires states to take measures to control the accidental or intentional introduction of exotic species.

Global climate change

Oceans serve an important role as stabilizers of the global climate. They also function as sinks of atmospheric carbon dioxide (CO₂). The living oceans control the atmospheric concentration of carbon dioxide and serve as biological pumps transporting the atmospheric carbon dioxide to the depths of the oceans. Tiny oceanic plants, the phytoplankton, take up dissolved carbon from the water column during photosynthesis. This CO₂ originated in the atmosphere and was dissolved into the surface layer of the oceans. The phytoplankton will eventually either die or get eaten by animal plankton, the zooplankton. The dead remains will sink down from the surface waters. The carbon dioxide, which is incorporated into the tissues of the phytoplankton as carbon, will be removed to deeper waters or to the ocean floor in this manner. The processes of photosynthesis and decay pump carbon from the surface to the deep ocean. Any threat to the phytoplankton, such as climatically induced changes in ocean circulation patterns or increases in UV-B radiation at the sea surface, could dramatically reduce the efficiency of the biological carbon pump, and over time raise atmospheric Co₂ levels, while reducing the productivity of the oceans.

Sea level rise, which is a predicted effect of global warming is of special concern to low lying coastal areas and island nations. Water, when heated, expands causing a rise in sea levels. At the same time, the glaciers will be subjected to increased melting, another cause of rising seas. For the past century, sea levels have risen at a rate of 1 to 2 mm per year. Estimates of the rates of sea level rise under global warming vary according to the WMO-UNEP Intergovernmental Panel on Climate Change from a low estimate of 3 cm/decade to a high estimate of 10 cm/decade. The rates of sea level rise are not uniform and there are large localized variations. Coastal wetlands are likely to suffer the most impact from the predicted sea level rise. Coastal wetlands act as sediment traps stabilizing coastlines, storm protection, and as nursery grounds for many commercially important fisheries species. It has been debated whether coral growth can keep up with the predicted rates of sea level rise. If coral growth is not fast enough, large scale reef drowning may result. Rising seas will also put a stress on coastal ecosystems, threatening the habitats of the flora and fauna found there, causing an impact on both the biodiversity and the economy of the effected region.

Coral bleaching has been increasingly observed in the tropical seas of the world, and could bring about massive ecological changes for coral reefs and other marine ecosystems. With the predicted rise in sea water temperatures caused by global warming, the incidences of coral bleaching would likely increase. Corals bleach when they lose the symbiotic algae living inside the tissues of the coral animal. These algae give coral colonies their characteristic yellowish or brownish color. When algae leave, the bleached corals appear white. Prolonged intervals at one to two degrees above normal summer temperatures can cause bleaching. Bleached coral colonies are alive, but not actively growing or reproducing. Bleached corals can recover if the sea water temperatures fall back to normal limits. However, if temperatures rise for even a few days to up to four degrees over normal limits, or if bleaching continues for long time periods, death of the coral colonies may result.