Autotrophy, Heterotrophy, and Resource Partitioning in Caribbean Reef Building Corals

Porter, James

Competition can be shown to occur between two species when the removal or thinning of one causes an increase in numbers of the other. This is due to an increase in availability of resources formerly used by both. Over evolutionary time, competition can lead to the extinction of one of the species or to specialization onto different resources by either or both species involved, that is, niche separation, with a concomitant reduction in the degree of competition. Resource partitioning often occurs by character displacement in feeding structures or in feeding behavior in animals or in plants by adaptation to different physical regimes (Schoener 1974). How scleractinian reef corals compete for space (Lang 1973) and how these competitive strategies affect the community structure of New World coral reefs (Porter 1974a) has been worked out in detail. This paper will examine the consequences of competition for energy resources within the Caribbean fauna. Reef-building (hermatypic) corals differ considerably from most animals in functioning at every trophic level of their ecosystem (Porter 1974b). They contain symbiotic algae and can in shallow water produce more oxygen than they consume, placing them among the reef's primary producers. The importance of this symbiosis lies in the tight chemical cycling it allows between plant and animal in response to the nutrient deficiency, particularly of nitrogen, in tropical waters (Lewis 1973). The importance of this symbiosis is also clearly reflected in the morphology of many species, a number of which are plantlike in their growth forms, maximizing their surface area and orienting the major axis of their growth plane toward the light (Goreau 1959; Roos 1967). Although incontrovertible evidence demonstrates the movement of photosynthetic products (primarily glycerol, and to a lesser extent glucose, alanine, and glycolic acid [Muscatine 1973]) from the associated symbiotic algae to the coral, the absolute value of this organic material has not been established. One of the principal theses of this paper will be that, arguing from morphological evidence alone, one can estimate the potential energetic contribution of the zooxanthellae relative to other means of energy procurement by each species.

Autotrophy, Heterotrophy, and Resource Partitioning in Caribbean Reef Building Corals

Series