Simulation of hurricane-like disturbances on a Caribbean seagrass bed

We tested the hypothesis that hurricanes cause changes in the plant community structure of Caribbean seagrass beds by acting selectively on populations of rooted macrophytes, which include seagrasses and rhizophytic algae. We also tested the hypothesis that susceptibility to elimination of the rooted macrophytes by the disturbance depends on differences in their growth forms. Two commonly registered disturbances by hurricanes in shallow seagrass beds are burial and sediment removal, which were simulated in marked plots of 1.1 × 1.1 m, at two randomly selected stations in Puerto Morelos tropical reef lagoon. The treatments consisted of control (no disturbance), two levels of burial, and two levels of sediment removal, with four replicates per treatment per station. The experiment was initiated in July 2002 and, 2 months afterwards, the densities of the populations of macrophytes were measured in experimental units of 0.8 × 0.8 m within the plots. MDS analysis showed that both sediment removal and burial caused changes in the species composition of the seagrass community. At one station, burial had a greater impact than sediment removal, whereas at the other station, the degree of impact of both types of disturbance was similar. Some macrophytes were consistently removed more than others, supporting the selective elimination hypothesis. Populations of Thalassia testudinum Banks ex König, Halimeda spp., and spongy algae (Avrainvillea spp. and Cladocephalus spp.) were, in almost all cases, undamaged by experimental manipulations. The populations of Syringodium filiforme Kütz., brush-like algae (Penicillus spp. and Rhipocephalus spp.), and Udotea spp. were reduced by more than 70%, when averaged across all manipulations and stations. A comparative analysis of growth forms of the above-mentioned macrophytes suggested that a solid, deeply anchored root-rhizome or rhizoid system, combined with a flexible or modular above-ground structure, is an advantageous characteristic to resist perturbation by hurricanes or storms.