Percent Coral Coverage - Laura and Billy

One of the transect photos used to identify the percent cover of different bottom types.

During the 1980’s-90’s there was a dramatic increase of macroalgal cover on Caribbean reefs, specifically Discovery Bay, Jamaica. This shift from coral to algal cover has been attributed to top-down control due to the reduction of herbivory by both the continuous overfishing of grazers (Acanthurids and Scarids) and the mass die off of Diadema antillarum in 1983-84. Since the return of D. antillarum in the late 1990s, a trend of reduced macroalgae began. Our study looks at the current phase state of the Discovery Bay reefs by measuring percent cover of coral, macroalgae, turf algae and coralline algae. Three sites were selected in Discovery Bay where 20 meter transects were run multiple times per site at depths of both 9 m and 18 m to assess benthic cover and potential variation with depth. Video transects were taken along each transect as well as counts of D. antillarum within one meter of the transect line to determine the presence or absence of herbivores in each transect. Data analysis supports a continued dominance of an algal phase state. Percent coral cover was 3-6 % compared to algal cover of 46.6 – 57.7 %. The reduced presence of D. antillarum in the study sites below 9 m may support the idea that decreased herbivory results in higher algal percent coverage and therefore lower coral coverage.

 

Comments

[Gary Learned]

interesting