Ecological assessment to detect imminent change in coral reefs of Admiral Cockburn Land and Sea National Park, Turks and Caicos Islands

Abstract

Coral reefs of the Turks and Caicos Islands (TCIs) (Caribbean Sea) constitute some of the few pristine coral reef systems in the world and play a crucial role in the islands' economy because they support rich fisheries catches and tourism development. Ambitious development plans involving increase in fishing and tourism pressures are about to bring changes in coastal zone resources of the TCIs associated with increased sediments and nutrients and reduced predation by herbivorous fish on coral reefs. Understanding change is critical when attempting to protect the resources that these coral reefs support and to adopt proper management strategies. Yet, an environmental assessment program to detect imminent human-induced changes on the surrounding reefs of the TCIs is lacking. Thus, (i) we obtained baseline data on benthic composition and coral community structure at seven reef sites of representative reefs of the TCIs within the Admiral Cockburn Land and Sea National Park (ACLSNP) of South Caicos Island and (ii) performed a priori statistical power analysis to calculate replication requirements for safely and confidently detecting small (delta = 0.1), medium (delta = 0.3), and large (delta = 0.5) effect sizes for a number of relevant to anticipated changes, univariate, benthic indices and for power beta = 0.95. The platforms of the margin reefs studied (9-12 m depth) appeared rather variable regarding benthic composition but quite homogeneous regarding hard coral community structure. Mean percent cover of algal functional groups was 0.1 +/- 0.3 (mean +/- sd) percent for coralline algae and Halimeda, 0.1 +/- 0.6 (mean +/- sd) percent for macroalgae, 21.7 +/- 33 (mean +/- sd) percent for turf algae and 4.8 +/- 4.0 (mean +/- sd) percent for hard coral cover. The dominant benthic component, however, was carbonate substrate (mean +/- sd = 30.4 +/- 34.3), thus indicating an accreting reef framework. Mean hard coral density, colony size and recruit density were 5.5 +/- 1.8 (mean +/- sd) corals per 20-m line transect, 13.0 +/- 2.3 (mean +/- sd) cm maximum colony diameter, and 1.3 +/- 1.4 (mean +/- sd) recruits per square foot, respectively. Due to high natural variance, hard coral colony size and density were practically the most sensitive indices in detecting even small size changes on benthos. Also, the geometric mean of log-transformed colony size-frequency distributions of the most abundant hard coral taxa, i.e. Montastrea annularis, Agaricia spp., Siderastrea spp. and Porites asteroides were practically sensitive for the same purpose. We hope that the study will optimize the spatial component of a necessary environmental impact assessment program on coral reefs of the TCIs once the natural spatial variability of the system has been assessed and sensitive, benthic, univariate indices have been identified for representative reference coral reef sites of the TCIs.