Ecological studies of the alga, Acanthophora spicifera (Vahl) Børg. (Ceramiales: Rhodophyta): Vegetative fragmentation

Abstract

The propagation of Acanthophora spicifera (Vahl) Børg. was studied on a fringing-reef platform at Galeta Point, Caribbean Panama. Manipulative experiments and detailed descriptive data indicated that fragmentation accounted for this alga's standing crop and distribution. Fragments were broken off by turbulence in the fore reef, transported by currents across a seagrass meadow, snagged, and attached or entangled in the back reef. Accumulations of ≈66 g (dry wt.)·m −2 occurred. A. spicifera was a major contributor to drift biomass, and, depending on prevailing current velocities, fragments entering the back reef had a 49 to 93% chance of recruiting. Higher current velocities (≈0.24m·s −1) decreased the ability of free-floating fragments to snag by decreasing the frequency of fragment-substratum contacts. 25% of the snagged fragments remained > 3 days, and fragments required < 2 days to attach to Laurencia papillosa (Forsk.) Grev. or to another frond of Acanthophora spicifera. Fragments were unable to recruit into plots of Thalassia testudinum Bank ex König and Sims. Tetrasporic plants were common, comprising as much as 96% of fore-reef and 80% of the back-reef populations. In October, 3% of the fore-reef population had cystocarps; otherwise, no other gametophytes were found. The percentage of spore-bearing tetrasporophytes was significantly greater in the Laurencia zone than in the fragment-derived Acanthophora zone. Vegetative fragmentation was demonstrated as an effective means of propagation, while the ecological significance of tetraspores was unclear.