The origin and distribution of shallow water gammaridean amphipoda in the Gulf of Mexico and Caribbean Sea with notes on their ecology.

The present study details the occurrence, distribution and origins of shallow water marine gammarideans in the Gulf of Mexico and the Caribbean Sea. One hundred and forty species are diagnosed or discussed and keys to the families, genera and species are provided to further distinguish them. Twenty three new species are described and fully illustrated. They include species of the following genera: Amphilochus (2 species), Ampithoe, Atylus, Ceradocus, Corophium, Eriopisa, Eusiroides, Gammaropsis, Gitanopsis, Liljeborgia, Listriella (3 species), Maera, Megaluropus, Netamelita, Parametopella, Photis (2 species), Platyischnopus, Polycheria, and Seba. One emphasis of study was the ecological grouping of epiphytic amphipods generally associated with either of two series of habitats (biotopes): 1) general soft bottom areas dominated by the physical substrate, or 2) special habitats dominated by a complex biological community on hard substrate or biological substrate. The first series included: bays, lagoons, intertidal zones, and subtidal areas. The second series included: coral, serpulid and oyster reefs, tropical and temperate grass flats, submerged offshore banks, and offshore artificial substrates. Amphipods found these habitats are listed and discussed. Dispersal and colonization mechanisms of the amphipods in these habitats are also discussed. Rafting was found to be the chief means of dispersal between these habitats. Colonization followed a predictable pattern based on substrate utilization and composition. Areographic analysis of the Gulf-Caribbean fauna is presented. Tropical species extend far into the temperate nearshore areas of the Gulf by utilizing the offshore banks as a refuge from which recruitment occures during favorable conditions. Many widely distribution cosmopolitan species were found in the study area. More than half were known to be tropical or tropico-temperate species. Forty three endemic species were found which resulted in a level of endemism of 15%. The ecological distributions of these species are detailed and figured. The relatively new biogeographic method of generalized tracks was used to analyze the origin of the Gulf-Caribbean amphipod fauna. The method utilizes cladistic analysis and plate tectonics to relate modern distributions to their ancestoral biotas. It was discovered, by this method that the fauna of the two regions is closely related to that of the western Atlantic (particularly the east coast of North America) and secondarily to that of the eastern Pacific. Relationships with the faunas of the eastern Atlantic (Africa) and the Meditteranean (tethys) are distant and generally of generic level or higher. The analysis of the fauna by the means of generalized tracks also revealed some aspects of evolution within the Gulf-Caribbean region. The family Bateidae evolved to its present composition within the Gulf-Caribbean region in response to tectonically created (and rmoved) geographical barriers. Other species have been similarly affected by the opening and closing of the Central American Seaway and the submergence and emergence cycle of the Florida Peninsula as well as numerous other geological events.