The Nature of Macroalgae and Their Interactions on Reefs

What was known about tropical reef algae prior to the use of scuba came largely from dredging studies or drift collections, which usually resulted in highly mutilated specimens and questionable habitat data. Scuba allows a precise determination of ecological conditions and permits in situ photography, two techniques our group has relied on during the past three decades for quantitative studies and field guide production. A goal of this review is to familiarize the scientific diving community with the kinds and roles of algae on tropical reefs, with the hope that seaweeds will be utilized more fully as tools for addressing important ecological questions. Because of the rapid degradation of tropical reefs worldwide, it is imperative that the role and diversity of macroalgae be studied in a timely, efficient, and scientifically verifiable manner. It is of paramount importance to characterize the world’s coral reef environments and to understand the responses of foundation species. The fleshy macroalgal forms are the food of herbivores, and only become abundant when their production rate exceeds the capacity of herbivores to consume them. On healthy oligotrophic coral reefs, even very low nutrient increases may shift relative dominance from corals (Cnidaria) to macroalgae by both stimulating macroalgal production and inhibiting corals. As a result, frondose macroalgae are generally recognized as harmful to the longevity of coral reefs due to the link between excessive blooms and coastal eutrophication. Reef plant complexity has evolved along very different evolutionary lines. The range of sizes, shapes, life histories, pigments, and biochemical and physiological pathways is remarkable. The biodiversity of coral reef plant life is unequalled. Macroalgae from four evolutionary lines dominate and, in conjunction with coelenterate corals, are the primary producers and builders of coral reef habitats and carbonate architecture. Previously, marine plants were understudied on coral reefs; however, new scubabased field guides are alleviating this problem. Their rapid growth and short generation time make them ideal subjects for experimental studies.