Photoacclimation to light-limitation in a clionaid sponge; implications for understanding sponge bioerosion on turbid reefs

Watershed-based pollution is a common form of coral reef degradation. Affected reefs are often highly turbid, where light-limitation confines the distribution of photosynthetic benthic taxa and the capacity for photo acclimation is important for survival. We investigated low light photoacclimation in a Symbiodinium-hosting bioeroding sponge using in situ PAM fluorometry. Cliona aff. viridis was artificially shaded (70 & 95% ambient light reduction) on a low turbidity Indonesian reef for 25 days, with a subsequent 14-day recovery period. Significant changes in rETR(max), and qP, and a non-significant but observable decline in E-k, demonstrated that C. aff. viridis is able to photoacclimate to conditions of extreme light reduction and recover within a relatively short period of time. The sponge is therefore unlikely to be light limited on even the most turbid reefs. However, other aspects of watershed-pollution such as sedimentation may still limit their distribution in affected coastal waters.