Shifting Distributions of Marine Sponges and the Ecology of an Endemic Species

The Florida Gulf of Mexico coast extends over both tropical and subtropical zones resulting in an intermingling of fauna typical to both zones. Cold winter water temperatures historically limited the distribution of many tropical species and allowed sub-tropical species to thrive. In the past 60 years, average winter sea surface temperatures have increased 2-3°C in the Northern Gulf of Mexico (NOAA OSPS), potentially allowing range expansion of tropical species and local extinction of subtropical species. While poleward range expansion is possible for species along the Atlantic coast, species in the Gulf of Mexico face land barriers that prevent northward movement. Distribution patterns of sponges in the Northeastern Gulf of Mexico have changed since previous studies in the 1950’s and 1960’s. A little over half of the common species (56%) are still widespread throughout the Northeastern Gulf of Mexico. Eleven species (44%) previously reported as widespread are either missing entirely or are no longer widespread throughout the region. Two species are newly reported in the Northeastern Gulf of Mexico (Niphates erecta and Haliclona curacaoensis) and eight other species are more widespread than before. Caribbean species make up most of the common species composition of the Northeastern Gulf of Mexico (de Laubenfels 1953, Little 1963, Storr 1976, current study). Due to the limited latitudinal range of the Northeastern Gulf of Mexico it is necessary to look at a wider scale to determine species’ northern range limits. When compared to the wide-scale Caribbean fauna, it appears that only a handful of Caribbean species occure in the Gulf of Mexico and the North West Atlantic. Of 90 common Caribbean species only 27% (24 species) were found in the Northeastern Gulf of Mexico and 38% (34 species) at Gray’s Reef in Georgia U.S.A. while 53% (48 species) were not found in either the Northeastern Gulf of Mexico or Gray’s Reef (Hopkinson et al. 1983, Freeman et al. 2007). While the species composition of Caribbean sponges at Gray’s Reef and in the Northeastern Gulf of Mexico is similar, each contain unique species that are not found at the other location. This may be due to a combination of biotic and abiotic factors that differ between the Atlantic and Gulf coasts of Florida, aiding the migration of some sponge species while hindering others. One species commonly found in the Northeastern Gulf of Mexico is endemic to the region. Halichondria corrugata Diaz, van Soest & Pomponi, 1993 is the most abundant sponge in shallow seagrass beds and on dockside fouling communities in the Northeastern Gulf of Mexico. The variation in abiotic conditions between these habitats and H. corrugata’s ubiquity make it an interesting system to test what aspects of ecology allow it to be so successful. H. corrugata utilizes different ecological strategies in seagrass and dock habitats. H. corrugata is flexible in its reproductive strategy, utilizes predator avoidance techniques when needed, and seems to be resilient to light variation despite being reliant on photosynthetic symbionts for supplemental nutrition.