The seagrass leaves carry epiphytic algae and animals, which are grazed by invertebrates and fish. The seagrass blades enhance sedimentation and reduce erosion by slowing down waves and currents, while the roots and rhizomes bind and stabilize the sediment surface. Seagrass beds are very important in the marine food chain as a result of the high rate at which they convert carbon dioxide dissolved in the water into organic matter, through the process of photosynthesis (high net productivity). This rate, approximately 1 kg of carbon for each square meter in the course of a year (1kgCm-2year-1) is significant because about half of this material is exported as detritus, which contributes food to offshore ecosystems. Seagrass habitats act as a nursery for the young of many commercial species of fish, crustaceans, and molluscs, while reef-based carnivores venture off into nearby seagrass beds in search of food. The wide variety of epiphytes which live in the seagrasses become the food of many bottom-dwelling fish species which feed off detritus. Organisms in seagrass beds with calcium-based external skeletons (for example, molluscs, echinoderms, crustaceans, calcareous algae, and some protozoa) also help to form beach sand.” 19 33. According to the report on the Caribbean Sea prepared in the context of the Millennium Ecosystem Assessment sponsored by the United Nations, each of these three habitats forms one large interdependent marine ecosystem with shared biodiversity. Consequently, degradation of one type of habitat can have far-reaching impacts on the services that another habitat provides to the inhabitants of the coasts and islands of the Caribbean. For example, damage to sea grass beds could affect income from fisheries and also speed up erosion of nearby beaches, which might reduce the appeal of a particular tourist resort and, therefore, damage local livelihoods. 20 34. As is well known, each of these formations that compose the ecosystem of the Caribbean Sea already shows signs of significant damage as a result of human activity. As has been demonstrated, in most cases this damage is irreparable. For example, it has been shown that recovery of coral has been both rare and, when present, slow. 21 Today, a large percentage of the habitats – corals, mangroves and sea grass beds – that support fishing and tourism in the Caribbean have been lost, while another significant proportion is severely threatened. 35. To illustrate this point, a map appears below showing the location of the reefs where there is limited threat (in blue), those where there is a medium threat (in yellow), and those where there is a high or very high threat (in orange). 22 19 Ibid. p. 13. 20 Ibid. p. 17. 21 Ibid. p. 15. 22 Annex III, L. Burke and J. Maidens, Arrecifes En Peligro en el Caribe, World Resources Institute, 2005, p. 38. 21