Phylogenetic relationships among the filamentous cyanobacterial symbionts of Caribbean sponges and a comparison of photosynthetic production between sponges hosting filamentous and unicellular cyanobacteria

Abstract

We investigated the filamentous cyanobacteria associated with two newly described species from the Caribbean coast of Panamá, Haliclona walentinae and Xestospongia bocatorensis. In addition to sequencing cyanobacterial 16S ribosomal RNA genes from Hyrtios violaceus, H. walentinae and X. bocatorensis, we measured the chlorophyll a content of H. walentinae and X. bocatorensis as an index of symbiont abundance. The photosynthetic and respiration rates of these two associations were compared to those of two sympatric sponges that host unicellular cyanobacteria, Aplysina fulva and Neopetrosia subtriangularis. A phylogeny of 16S ribosomal RNA genes reveals that the symbionts of H. violaceus, H. walentinae and X. bocatorensis are part of the O. spongeliae clade and that each sponge hosts a unique ribotype of this cyanobacterium. H. walentinae yielded the highest chlorophyll a concentrations, while X. bocatorensis, A. fulva, and N. subtriangularis were not significantly different. All sponges measured showed gross productivity to respiration (P:R) ratios greater than 1.5, indicating that cyanobacterial photosynthesis can compensate for host sponge respiration, and that all four species can be considered phototrophic. X. bocatorensis yielded the highest P:R ratios, while those of H. walentinae, A. fulva, and N. subtriangularis were not significantly different. Specialized associations with filamentous cyanobacteria may provide a valuable source of carbon to host sponges. These associations occur over a broader phylogenetic range of hosts than previously described, including representatives of the orders Dictyoceratida and Haplosclerida.