Accumulation of Dissolved Carbon by the Solitary Coral Balanophyllia Elegans — an Alternative Nutritional Pathway?

Abstract

In classical treatments of their feeding biology, madreporarian corals are viewed as chiefly carnivorous (Hyman, 1940; Yonge, 1930). However, some recent studies indicate that hard corals may obtain their nutritional requirements by not one, but several means including autotrophy, particulate feeding and accumulation of dissolved organic material. For example, coral species which host endosymbiontic zooxanthellae accrue nutritional benefit in the form of soluble carbohydrates released by their algal guests (Lewis and Smith, 1971; Goreau, Goreau and Yonge, 1971). Sorokin (1972 and 1973) has confirmed that some scleractinian corals feed upon planktonic algae and bacteria. However, the nutritional role of dissolved organic matter in corals is less certain than autotrophy and particulate feeding. Studies by Stephens (1962) upon the hermatypic coral Fungia scutaria have demonstrated that under laboratory conditions, F. scutaria is capable of accumulating ¹⁴C-labelled glucose and amino acids from modest concentrations made available in seawater. Nonetheless, the significance of dissolved organic material in the nutrition of corals remains to be established because, to date, there have been no experiments in this regard carried out under natural field conditions. The experiments reported here were undertaken to determine whether the solitary coral Balanophyllia elegans Verrill will accumulate under in situ conditions, dissolved carbon exudated by the “large kelp” Macrocystis integrifolia.