Influence of winter and spring/summer algal communities on the growth and physiology of adjacent scleractinian corals

The influence of winter and spring/summer mixed algal communities from the low intertidal zone on the growth and physiology of four associated species of scleractinian corals was studied in outdoor culture. Experimental algae and corals came from the fringing reef of Sesoko Island, Okinawa, Japan, where fragments of the corals Acropora hyacinthus, Acropora sp., Porites cylindrica and Pavona divaricata were collected and exposed in aquaria 0.5–1.0 cm above mixed algal associations (AA), consisting of more than 100 species. A 30-day exposure did not show negative influence on algal growth, photosynthesis and respiration for the 4 coral species investigated, in spite of the fact that the AA included algae that are known to be toxic to corals. Moreover, the presence of the spring/winter AA in the aquaria actually stimulated the growth of coral fragments two- to four-fold. The results suggest that even though algal occupancy of the substratum on the fringing reef of Sesoko Island is 90%, it has no negative impact on the growth and physiological state of corals living near the algae. Possible mechanisms of a positive influence of algal communities near, but not in contact with, are organic uptake or enhanced planktonic prey.