Coral Reef Morphodynamics

Many hermatypic corals are broadcast spawners. Little is known about the dispersal potential of their planktonic larvae. Settlement can begin 2-3 days post-fertilization, but competency may last for a month or more. Hydrographic models can be use d to estimate larval dispersal, but they require information about the swimming behavior of the larvae during transport, including buoyancy and vertical swimming behavior. Coral eggs are positively buoyant when released, but embryos and larvae with time become less buoyant and acquire the ability to swim downwards. The time-course of such developmental changes is needed to couple with hydrographic data to model dispersal curves. Such data are presented here for the major Caribbean hermatype, Montastraea faveolata. Larval buoyancy was measured as ascent rate in a volumetric pipette, and measured every 6 hours for 3.25 hours post-fertilization. V ertical swimming behavior was measured as vertical distribution of the larvae within 2 L graduated cylinders, placed on an orbital shaker table, measured every 6 hours from 40 hours to 8.5 days post-fertilization. Newly fertilized eggs (non-swimming) had an ascent rate of 1.82 mm s-1, and this decreased linearly to 1.04 mm s-1 over the following 2.3 days, by which time many larvae were swimming. Over 80 % of the larvae remained within the top 4 cm of the 40 cm-tall cylinder over the first 2.5 days postfertilization. Diel vertical migration became apparent after ca. 3 daysdownwards in dark, upwards in light), and became more pronounced over time. However, even 8 days post-fertilization, less than 20 % of the larvae were at the bottom of the cylinder at the end of the dark period. These results show that while some larvae of this species can settle within a few days, most do not develop strong bottom seeking behavior until much later, and could be dispersed far from their site of o rigin.

Coral-grounds are reef communities that colonize rocky substratum but do not form framework or three-dimensional reef structures. To investigate why, we used video transects and underwater photography to determine the composition, structure and status of a coral-ground community located on the edge of a rocky terrace in front of a tourist park, Xcaret, in the northern Mesoamerican Reef tract, Mexico. The community has a relatively low coral, gorgonian and sponge cover (10%) and high algal cover (40%). We recorded 23 species of Scleractinia, 14 species of Gorgonacea and 30 species of Porifera. The coral community is diverse but lacks large coral colonies, being dominated instead by small, sediment-tolerant, and brooding species. In these small colonies, the abundance of potentially lethal interactions and partial mortality is high but decreases when colonies are larger than 40 cm. Such characteristics are consistent with an environment control whereby storm waves periodically remove larger colonies and elevate sediment flux. The community only survives these storm conditions due to its slope-break location, which ensures lack of burial and continued local recruitment. A comparison with similar coral-ground communities in adjacent areas suggests that the narrow width of the rock terrace hinders sediment stabilization, thereby ensuring that communities cannot escape bottom effects and develop into three- dimensional reef structures on geological time scales.

Coral-grounds are reef communities that colonize rocky substratum but do not form framework or three-dimensional reef structures. To investigate why, we used video transects and underwater photography to determine the composition, structure and status of a coral-ground community located on the edge of a rocky terrace in front of a tourist park, Xcaret, in the northern Mesoamerican Reef tract, Mexico. The community has a relatively low coral, gorgonian and sponge cover (10%) and high algal cover (40%). We recorded 23 species of Scleractinia, 14 species of Gorgonacea and 30 species of Porifera. The coral community is diverse but lacks large coral colonies, being dominated instead by small, sediment-tolerant, and brooding species. In these small colonies, the abundance of potentially lethal interactions and partial mortality is high but decreases when colonies are larger than 40 cm. Such characteristics are consistent with an environment control whereby storm waves periodically remove ...

Coral-grounds are reef communities that colonize rocky substratum but do not form framework or three-dimensional reef structures. To investigate why, we used video transects and underwater photography to determine the composition, structure and status of a coral-ground community located on the edge of a rocky terrace in front of a tourist park, Xcaret, in the northern Mesoamerican Reef tract, Mexico. The community has a relatively low coral, gorgonian and sponge cover (10%) and high algal cover (40%). We recorded 23 species of Scleractinia, 14 species of Gorgonacea and 30 species of Porifera. The coral community is diverse but lacks large coral colonies, being dominated instead by small, sediment-tolerant, and brooding species. In these small colonies, the abundance of potentially lethal interactions and partial mortality is high but decreases when colonies are larger than 40 cm. Such characteristics are consistent with an environment control whereby storm waves periodically remove ...