Productivity and growth rates of Coral Reef Bacteria on hard Calcareous Substrates and in Sandy Sediments in Summer

Abstract

The growth rates and productivity of bacteria in the communities living on hard limestone substrate and sand were determined from the rates of incorporation of tritiated thymidine into DNA. Two reefs in the southern Great Barrier Reef, around Heron Island and One Tree Island, were studied during summer (January 1986). The specific growth rates varied on a diel cycle, being slowest at night, in both sand and hard substrate. They ranged from 0.005 h,^-1 at night to 0.025 h^-1 during the day in sand and from 0.002 to 0.01 h^-1 in hard substrate. Productivity was also greater during the day than at night, ranging from 1 mg C m^-2 h^-1 at night to 5.5 mg C m^-2 h^-1 during the day in sand and from 0.5 to 2 mg C m^-2 h^-1 in hard substrate. Values were similar for both islands. The increase of four- to five-fold in bacterial growth rates in the sand and hard substrate on Heron Island during the daytime indicates that the heterotrophic bacteria rely mostly on organic matter exuded from the algae with which they are associated.