We review historical and recent information on the distribution, status, and habitat associations of the West Indian manatee, Trichechus manatus, summarize threats to its continued survival, and discuss some biogeographical patterns of trichechids. Historical accounts indicate that manatees were once more common and that hunting has been responsible for declining numbers throughout much of their range. Small numbers occur throughout the Greater Antilles, where opportunistic taking by fishermen is a major source of mortality. Populations in Haiti, the Dominican Republic, and Jamaica are particularly vulnerable. Manatees have not been documented to occur in the Lesser Antilles since the 18th century, except for rare sightings in the Virgin Islands. Manatee sightings in the Bahamas are also rare; however, a recent dispersal from the northwest coast of Florida to the Bahamas has been documented. Manatees are relatively abundant in Belize compared with other countries of Central America. They persist in some of the large river systems of South America: the Río Magdalena in Colombia, Río Orinoco in Venezuela, and probably the Río Mearim in Brazil. They are absent or scarce along most of the South American coast, except in the extensive coastal wetlands of Guyana and Suriname. At present, there are only three regions in Mexico where manatees are still commonly found. Manatees are widely distributed on both coasts of Florida, and some venture westward along the Gulf coast and northward along the Atlantic coast of the southeastern United States, primarily during the warm season. Heated industrial effluents along both coasts have influenced manatee distribution and migratory patterns in the United States. Illegal killing continues to threaten the survival of manatees in many countries. Despite protective measures to regulate boating activity, collision with boats is still the major cause of human-related manatee mortality in Florida. Habitat alteration is a growing concern in all countries.Manatees in the Greater Antilles and Central and South America belong to the same subspecies, T. manatus manatus. However, results of recent genetic analysis indicate greater similarity between the Florida manatee, T. manatus latirostris, and manatees in the Dominican Republic and Puerto Rico, than between the latter and manatees in South America. The highest genetic diversity is found along the northern coast of South America, at the core of the species' range; marginal populations (in Florida, Mexico, and Brazil) were each found to be monomorphic (only one haplotype apiece) although distinct from one another. Salinity, temperature, water depth, currents, shelter from wave action, and availability of vegetation are important determining factors of manatee distribution. The association of T. manatus with freshwater sources is a highly consistent pattern. Throughout most of their range, manatees appear to prefer rivers and estuaries to marine habitats. The Amazonian species, T. inunguis, may be restricted to the Amazon River because of in...

The Indian River Lagoon on the Atlantic coast of Florida, USA, and the east coast of Puerto Rico provide contrasting environments in which the endangered West Indian Manatee Trichechus manatus experiences different thermal regimes and seagrass communities. We compare Manatee feeding behaviour in these two regions, examine the ecological effects of Manatee grazing on a seagrass community in the Indian River Lagoon, describe the utility of aerial surveys, radio tracking, and seagrass mapping to study Manatee feeding patterns, and develop hypotheses on sirenian feeding strategies in temperate and tropical seagrass communities. In both the Indian River Lagoon and Puerto Rico, Manatees were typically observed grazing in water depths = 2.0 m and more frequently on the most abundant seagrasses present in the community: Halodule wrightii in the Indian River Lagoon and Thalassia testudinum in eastern Puerto Rico. Where both H. wrightii and Syringodium filiforme were consumed in the Indian River Lagoon, Manatees tended to remove more S. filiforme than H. wrightii rhizome + root biomass. Even though 80 to 95% of the short-shoot biomass and 50 to 67% of the rhizome + root biomass were removed, grazed patches of H. wrightii and S. filiforme recovered significantly between February and August. H. wrightii may be both more resistant and resilient than S. filiforme to the impacts of Manatee grazing. Despite the significantly greater abundance of T. testudinum in Puerto Rico, Manatees exhibited selective feeding by returning to specific sites with abundant H. wrightii. They also appeared to feed selectively on T. testudinum shoots associated with clumps of the calcareous alga Halimeda opuntia. We hypothesize that Florida Manatees are less specialized seagrass grazers than Manatees in tropical regions like Puerto Rico. Continued research on Manatee grazing ecology in temperate to tropical seagrass communities will enable better protection and management of these vital and unique marine resources.

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