Temporal changes in the sponge holobiont during the course of infection with Aplysina Red Band Syndrome

Diseases of marine organisms, including sponges on coral reefs, are being reported with increasing frequency worldwide. Aplysina Red Band Syndrome (ARBS) occurs across the Caribbean basin, predominantly affecting Aplysina cauliformis , one of the most common reef sponges in this region. Existing ARBS lesions and their effects on the sponge holobiont have been documented, yet little is known about the biochemical and microbial changes associated with the onset of infection. Due to the transmissible nature of ARBS, infection can be induced and monitored through sponge-to-sponge direct contact. Nine-day contact experiments with healthy-diseased and healthy-healthy sponge pairings were conducted in the Bahamas in January and July to compare individual sponges sampled initially and at one of three successive time points. Temporal changes in bacterial assemblages and photosymbiont abundance (via concentrations of chlorophyll a ), and concentrations of total protein, heat shock protein 70, and major secondary metabolites that may correspond with disease onset were characterized. All healthy sponges in contact with diseased sponges developed ARBS by day 9 in January and by day 6 in July, suggesting that observed changes in the holobiont corresponded with the development of ARBS. The concentrations of several major secondary metabolites, as well as heat shock protein 70 and chlorophyll a , changed significantly in samples of visibly healthy tissue from initially healthy sponges that became diseased. In contrast, the composition of the associated bacterial community changed in all attached sponges over time. These results suggest that infection with ARBS elicits rapid responses by the sponge holobiont, providing a model system in which to investigate immune responses in an early metazoan.