Fish

Reefs of the windward Netherlands Antilles (Saba, Saba Bank, St. Eustatius, St. Maarten) were assessed at 24 sites in the late 1999. The Atlantic and Gulf Rapid Reef Assessment (AGGRA) protocol was used with modifications to detect recent hurricane impacts. Live coral cover averaged 18%. The assemblage of >10 cm stony corals was primarily composed of small-sized colonies (mean diameter = 37 cm) of which the Montastraea annularis complex was the most abundant (30% of colonies). Overall, =1% of the individually surveyed colonies had been physically damaged by Hurricane Lenny but injury levels were higher in Saba (2.6%). Bleaching was noted in 23% of colonies at the time of the assessment with the greatest percentage occurring on St. Maarten (44%) and the lowest on Saba Bank (9%). Total (recent + old) partial mortality of reef-building corals averaged less than 18% although levels were higher (26%) in Colpophyllia natans. Coral recruitment densities were relatively consistent (mean = 5 recruits/m2) across sites. Commercially significant fish species (i.e. serranids, lutjanids, haemulids >5 cm) were present with mean densities of 4.5 individuals/100 m2. High biomass (mean = 5.8 kg/100 m2) of grazing, herbivorous fishes (acanthurids, scarids >5 cm, Microspathodon chrysurus) partially explains the relatively low macroalgal cover (mean = 7%) throughout this area. Saba’s fish community had a greater total biomass than those in the other three geographic areas (mean = 11 kg/100 m2 versus 7 kg/100 m2). While the coral reefs of St. Maarten show signs of disturbance (i.e., increased bleaching and sedimentation), those of Saba, Saba Bank, and southern St. Eustatius have been relatively little disturbed by coastal development and remain potential sources of marine life. Nevertheless, reef development in the windward Netherlands Antilles is limited by frequent hurricanes.

The invasion of lionfish in the Caribbean is causing grave concern because of its deleterious impacts on coral reef food-webs. We have used an Ecopath-with-Ecosim model to predict the impacts of lionfish invasion on a coral reef community based on pre-invasion fish community data. Forty-six groups were defined, and an initial Ecopath model was balanced with a near-zero biomass of lionfish. In Ecosim, the near-zero biomass was eradicated by applying a very high fishing pressure in the first year of simulation. We subsequently (re-)introduced lionfish with a very low biomass, and allowed them to increase to very high abundance. With a near-zero lionfish biomass, the great majority of mesocarnivorous/omnivorous coral reef fish were predicted to be dominant while sharks were predicted to be the apex predators. Different management scenarios were established in the ecosystem to explore the eradication and resilience of lionfish. The management scenarios showed that if all adult lionfish were exploitable it will in theory be possible to fish the lionfish to a very low level, but the fishing pressure will have to be maintained, or the lionfish will recover. If the largest individuals are unexploitable it will be much more difficult to control the lionfish population

Abstract:

The Atlantic and Gulf Rapid Reef Assessment (AGRRA) sampling strategy is designed to collect both descriptive and quantitative information for a large number of reef vitality indicators over large spatial scales. AGRRA assessments conducted between 1998 and 2000 across a spectrum of western Atlantic reefs with different histories of disturbance, environmental conditions, and fishing pressure were examined to reveal means and variances for 15 indicators. Twenty surveys were compiled into a database containing a total of 302 benthic sites (249 deep, 53 shallow), 2,337 benthic transects, 14,000 quadrats, 22,553 stony corals. Seventeen surveys contained comparable fish data for a total of 247 fish sites (206 deep, 41 shallow), 2,488 fish transects, and 71,102 fishes. Shallow (≤ 5 m) reefs were dominated by A. palmata, a good proportion of which was standing dead, while deep (>5m) reefs were nearly always dominated by the Montastraea annularis species complex. Fish communities were dominated by acanthurids and scarids with seranids making up less than 1% of the fish seen on shallow reefs and 4% on deep reefs.

AGRRA benthic and fish indicators on deep reefs showed the highest variation at the smallest spatial scale (~<0.1 km), with recent mortality and macroalgal canopy height displaying the largest area and subregional scale (~1-100 km) variation. A mean live coral cover of 26% for the 20 survey areas was determined for the deep sites. Significant bleaching and disease-induced mortality of stony corals associated with the 1998 (El Niño-Southern Oscillation) ENSO event were most apparent in the western Caribbean and Bahamas subregions and the Montastraea annularis complex was the most heavily impacted.

The overall low number of sightings for larger-bodied groupers and snappers (~< 1/100 m2) as a whole suggest that the entire region is overfished for many of these more heavily targeted species. More remote reefs showed as much evidence of reef degradation as reefs more proximal to human coastal development. Characterizing present-day reef condition across the region is a complex problem since there are likely multiple sources of stress operating over several spatial and temporal scales. Not withstanding the many limitations of this analysis, the value of making multiple observations across multiple spatial scales that can approximate the “normal” state for the region today is still very high.