Photosynthetic responses of crustose coralline algae recruit from an upwelling area to light intensity, temperature and current flow rate in a mesocosm

The crustose coralline algae (CCA) play an important role building carbonate habitats and enhancing species diversity in rocky shores, rhodolith beds and coral-algal reefs. Though worldwide distributed some taxonomic groups were proved to show light and temperature boundaries. Nevertheless, little is known about the biological limits of CCA recruits and photosynthetic responses in a climate change environment. In this way, experimental studies are essential to identify their optimal conditions development. The aim of the study was to test ideal environmental conditions for CCA recruits from an upwelling area to verify Fv/Fm response patterns as an indicator of photosynthetic performance. Artificial disks were fixed on a rocky shore to provide substrate for CCA recruitments and then moved to be tested in a flow-through system. The CCA tested were species of the Genus Lithophyllum and experiments were performed with CCA exposed to different levels of light, temperature and current flow rates. The photosystem II function, measured by chlorophyll a fluorescence (Fv/Fm), was used as an indicator of potential photosynthetic electron transport. There was an interaction between light intensity, flow rate and temperature. Low light intensity, high temperature and fast flow rate (20 μmol m-2. s-1; 19 and 24 °C; 0.09 m s-1 respectively) provided optimal conditions for CCA recruits.