PHOTOPHYSIOLOGY OF A TURF ALGAL COMMUNITY: INTEGRATED RESPONSES TO AMBIENT LIGHT AND STANDING BIOMASS

This study investigated the variation in the relationship between photosynthesis and ambient light (P-E curves) for turf algal communities on a temperate reef off the coast of South Australia, analyzing the integrated effects of ambient light and standing biomass. The photophysiology of turfs was studied in situ on a seasonal basis, examining algal communities growing on artificial substrate (plates) at depths of 4 m and 10 m. P-E curves and estimates for the photokinetic parameters (P-m, R-d, alpha, E-k, and E-c) were obtained through oxygen evolution methods, using an automated underwater respirometer. Photoacclimation responses to changes in ambient light were strongly affected by the biomass of the community. P-m showed an inverse relationship to standing biomass, irrespective of depth and season, which was considered to be a response to self-shading and boundary layer effects. Biomass effects imposed a high variance on estimates for all photosynthetic parameters, overshadowing differences observed for season and depth. Biomass also affected photoinhibition on turf communities, where significant afternoon depression of photosynthesis was observed in sparse turf patches when compared to denser patches. High areal productivity rates were maintained across all seasons with a significant decrease only being observed during winter.