Interaction between the thinly encrusting sponge Clathria venosa and the branched coral Acropora palmata

Acropora palmata is colonized by encrusting sponges, such as Clathria venosa, in the lower zones of coral branches, especially in areas devoid of living tissue. To analyze the responses of tissues involved in the areas of interaction, we investigated the advancement rates and the sponge growth and recovery rates after the removal of sponge tissue. To assess the advance or retreat rates of the sponge and coral, steel screws were placed at the limits of the sponge/coral interaction area (treatment 1), and the response of the coral and sponge tissues was recorded. In treatment 2, the sponge was removed by scraping and cleaning the area. In treatment 3, the sponge was removed, and the area occupied by the sponge was filled with epoxy putty. We found that the interaction was a standoff ( T 1) in 64.2% of cases, the sponge advanced in 7.1% of cases, and regression was observed in 28.7% of cases. Following its partial removal of the sponge ( T 2), C. venosa recovered the formerly occupied space in one month, whereas in T 3, growth and recovery required 3 months. Clathria venosa is a colonizing species of the lower parts of the bases and branches of A. palmata , which despite presenting a rapid regeneration rate, no evidence was found that in contact with the coral, the sponge generates tissue deterioration.