Morphological variation and differential susceptibility to herbivory in the tropical brown alga Lobophora variegate

Abstract

Listen

Translate article

tropical brown alga Lobophora variegata (Lamouroux) Womersley has 3 distinct morphological forms (ruffled, decumbent and encrusting) along the Belizean barrier reef. These forms are commonly associated with habitats that differ in environmental characteristics and herbivore abundance. Previous research into among-habitat variation in plant susceptibility to herbivores has focused on interspecific comparisons; here we emphasize intraspecific variation. Field (fish) and laboratory (crab) experiments compared grazlng on L. vanegata forms with 2 other frondose algae of the same family (Dictyotaceae), the highly palatable Padina boergesenii and the unpalatable Stypopodium zonale. Transplant feeding studies were conducted in several reef habitats to determine if these forms differed in their susceptibility to fish herbivory. Significantly different susceptibilities to grazing among L. variegata forms for both fishes and crabs were observed. Preferences of fish and crabs were similar (from most to least preferred): Padina = ruffled Lobophora = encrusting Lobophora S decumbent Lobophora = Stypopodium. The distribution of ruffled and decumbent forms appears to be related to the intensity of fish grazing normally encountered in their habitats and their differential susceptibility to herbivory. The encrusting form is common in areas with high fish and sea urchin herbivory, despite being susceptible to fish grazing when removed from the substrate. The presence of this form in areas of intense grazing pressure is probably related to its encrusting habit. We suggest that the distributions of these forms, their growth morphologies and potential defenses are in some measure related to differential grazing intensities among habitats. Form variation and habit may represent an important evolutionary strategy for tropical algae when herbivory is locally intense but patchy.