Interactions among Florida sponges. Ⅱ. Mangrove habitats

摘要

This study documents interference interactions between Florida sponge species. In a companion study, we conducted transect surveys to examine interspecific interactions between reef sponges in Key Largo, Florida, USA. Herein, we conducted similar transect surveys to assess interspecific interactions between mangrove sponges growing on the prop roots of the red mangrove Rhi-zophora mangle in Florida Bay. We surveyed 10 transect sites at 2 locations with mean densities of 2.6 ± 0.8 and 3.4 ± 1.2 sponges on each meter of prop root. Overall, 73.5% of all available root space was overgrown by a total of 1195 sponges comprising 10 species. Chondrilla nucula, Lissodendoryx isodictyalis, and Tedania ignis were the most abundant sponges and overgrew more available root space than any other species. We used a nearest-neighbor technique to determine the degree and frequency of interactions between all sponges. Overall, 31.1% of sponges occurred alone, 3.3% in proximity to, and 65.6% in contact with other sponge species. Among all sponges in contact interactions, 39.0% were epibionts, 24.3% were basibionts, and 36.7% occurred in 'equal' interactions in which it was not possible to determine the epi- from the basibiotic species. Differences in the frequencies of each interaction category were statistically tested for all species to determine the ability of 1 sponge to overgrow or resist overgrowth by other species. Among all sponges surveyed in this study, Dysidea etheria and Clathrina canariensis were never overgrown, while Geodia gibberosa and Halichondria sp. were frequently overgrown by other species. The overgrowth ability of a sponge species appeared to be dependent on growth rate or the production of allelochemicals.