Rhythmical changes in the division and degradation of symbiotic algae in hermatypic corals

Abstract

Three types of rhythmical changes in division and degradation (digestion) have been found and described in the symbiotic zooxanthellae of the scleractinian coral Seriatopora caliendrum and in the colonial hydroid Myllepora intricata collected at the reef of Sesoko Island (Okinawa, Japan). The first type of changes reported for S. caliendrum is daily variation of the intensity of these two processes peaking at night. The second type of rhythm changes described in S. caliendrum and M. intricata is opposing variations of cell division and degradation levels with a period of three days. The rhythm is disturbed by sudden weather changes or by variations in light. Rhythmical alterations of zooxanthella proliferation and degradation of the third type found in S. caliendrum have a period of 5–6 days and are connected with oppositely directed changes as well as with alterations of the second type. The rhythm of such alterations is not disturbed by abrupt weather changes. All three types of rhythmical changes in zooxanthellae division and digestion observed in hermatypic coral are supposed to be directed to the regulation of the population density of zooxanthellae in organism tissues.