PARENT SESSION
Poster Session # 20: Predator - Prey / Mutualism - Parasitism Ecology.
Thursday, August 7 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Manipulations of sponge-cyanobacterial symbioses: Effects of shading on sponges with specialist and generalist symbionts.
Thacker, Robert*,1, Erwin, Patrick1, Bevis, Kevin1, Paul, Valerie2, 1 University of Alabama at Birmingham, Birmingham, AL2 Smithsonian Marine Station, Fort Pierce, FL
ABSTRACT- The marine sponge Dysidea herbacea hosts large populations of the host-specific, symbiotic, filamentous cyanobacterium Oscillatoria spongeliae. Cyanobacteria may benefit their host sponges by fixing carbon or nitrogen that is subsequently acquired by the host sponge. To determine whether cyanobacteria significantly contribute to sponge metabolism through photosynthesis, we manipulated light availability in the field. Sponges were held in plastic cages to remove the effects of fish predation. Light cages were constructed with transparent tops, while shaded cages had opaque tops. Sponges were distributed among the treatments in a randomized block design, blocked by source sponge colony. After 16 days, we terminated the experiment due to the dramatic mass loss of sponges in the shaded treatment. Sponges in the light cages lost 3.8% of their wet mass, an amount that was not significantly different from zero loss. Sponges in the shaded cages lost 28.5% of their wet mass, a significantly larger loss than the light cages (ANOVA, P = 0.002), despite a significant amount of variation among sponge colonies (P = 0.01). These results suggest that D. herbacea obtains more nutrition from light-harvesting symbionts than by feeding from the water column. Shading of sponges containing generalist symbionts (e.g. Xestospongia spp. that host Synechococcus spp.) does not have a measurable impact on sponge growth. The degree of physiological dependence on cyanobacterial photosynthesis may influence the degree of evolutionary specialization observed between sponges and their cyanobacterial symbionts.
Key words: cyanobacteria, symbiosis, porifera, mutualism