reef fish assemblage

Bonaire has long been considered to have amongst the healthiest reefs of the Caribbean. However, at the 2002 Annual Meeting of Pew Fellows for Marine Conservation in Bonaire, several scientists with a long history of research on Bonaire’s coral reefs, expressed concern over the future of the island’s reefs. Specifically, they identified the decline in large predatory fish such as groupers as a noticeable change during the past decade. They suspected that this change resulted from increased fishing pressure on Bonaire’s reefs. They also suggested the Bonaire authorities take action to protect the reef-fish stocks. In response to those concerns, officials of the Bonaire Marine Park consulted with scientists and fishermen on Bonaire to explore the possibility of establishing fish protected areas (FPAs), as a way to protect the reef fish stocks. If FPAs improve both fish stocks and the condition of the coral reef, all stakeholders will profit. If fish stocks increased significantly in FPAs, a “spill over” of these fish to adjacent fished areas would be expected. Also, fish that perform important ecological functions could improve the quality of the coral reef ecosystem. Therefore, areas protected from fishing should have healthier coral reefs, which would also improve the island’s valuable ecotourism businesses. The Pew Fellows program funded a research project designed to identify potential FPAs. The Bonaire Marine Park authority, in consultation with the local fishing community would determine the location and size of the FPAs. To monitor the effects of fish protection areas so fishing impacts can be isolated from other factors (such as natural changes, shore-based impacts or effects of scuba divers), an equal number of similar reef sites were selected for study, with half closed to fishing while half remaining open (as “control” reefs). This report reviews the status and recent trends of coral reefs in the Caribbean and Bonaire. It identifies the key features of healthy reefs and how Bonaire’s reefs compares with those elsewhere in the Caribbean. The seven chapters go into scientific detail on factors contributing to the condition of Bonaire’s reefs as of March and April 2003. Special focus will be on factors that threaten reef health or are critical to reef resilience such as seaweed overgrowth, nutrient inputs from land and the ecology of juvenile corals. The report concludes with chapters on the socioeconomic effects of Bonaire’s coral reefs on the fishing and diving industries that depend on them.
Summary Results 2003: The Biological Status of the Coral Reefs of Bonaire & Socioeconomic Implications
 In March and April of 2003, teams of researchers studied the coral reefs of Bonaire to establish the baseline conditions that currently exist and against which trends can be determined and future changes from fish protection areas be assessed. Six study sites were chosen with advice from the Bonaire Marine Park. They represent a range of comparable reefs minimally affected by the 1999 Hurricane Lenny. The sites selected for this study were: Windsock, Plaza, Forest on Klein Bonaire, Scientifico, Barcadera and Karpata (Fig. 0.4). When feasible, parallel studies were conducted at 5 and 10 m depths, however, only the latter depth had fully developed reefs at all sites. The study was designed to quantify the patterns of abundance of the dominant reef organisms as well as to study the processes that control their abundances or threaten their stability. This was done to establish a baseline and to determine if significant differences exist among any of the study sites that would make them a poor choice as a FPA. We also examined some socioeconomic factors related to fishing and scuba diving activities if FPAs are established in Bonaire.

Many environmental variables may influence fish assemblage structures in terms of abundance, biomass and mean size. The aim of this study is to provide a baseline survey on reef fish assemblages and shark presence covering the whole Saba bank (Dutch Caribbean). Hereby determining the influence of habitat, depth and fishing pressure on the structure of reef fish assemblages and shark presence. Baited Remote Underwater Video (BRUV) survey was used to describe reef fish assemblage structures on the Saba bank. Between 2012-2014, a total of 165 60 min BRUV deployments were conducted on locations varying in habitat complexity (0-4, Polunin and Roberts, 1993), depth (15-40m) and fisheries. The eleven most abundant fish species observed on the Saba bank represented eight families and accounted for nearly 50% of the total number of individual fish observed. Labridae was the most abundant fish family observed with a relative abundance of 22%. Most abundant fish species by number of individuals were Thalassoma bifasciatum (N=849 (9.8%)) Stegastus partitus (N=725 (8.4%)) and Acanthurus bahianus (N=430 (5.0%)).

Habitat complexity was positively correlated with species richness (Nsp), fish abundance (MaxN), and mean biomass, and negatively correlated with mean fish length. Strongly developed vertical relief habitats were found to support high numbers of fish species (N=19.1±0.6SE) of relatively low mean lengths (22.4cm±0.3SE), whereas less complex habitats were characterized by low numbers of species (N=8.3±0.8SE) with relatively high mean lengths (24.6cm ±0.81SE). Depth was negatively correlated with Nsp, MaxN and mean biomass and positively correlated with mean fish length. These relationships were all according to expectations based on earlier studies.

A minor part of the variability in the structure of reef fish assemblages was explained by differences in fisheries activity, indicating that no clear fisheries effect was observed in fish assemblages in this study. Furthermore, no significant differences in average size of target species were observed between areas with different fishing pressure. However, the general absence of piscivores such as large snappers and groupers was an indication of the indelible effects of past fisheries on the Saba bank.

A total of 85 shark observations were made with Ginglymostoma cirratum as most abundant species (N=41), followed by Carcharhinus perezii (N=36), Galeocerdo cuvier (N=5) and Carcharhinus limbatus (N=3). Relatively high shark abundances (0.20 sharks hour-1) were observed on the Saba bank compared with other Caribbean regions (The Bahamas: 0.14 sharks hour-1, Belize, 0.17 sharks hour-1). Shark abundance (CPUE) was positively correlated with habitat complexity, whereas depth exerted a negative influence on shark abundances. High shark numbers are a good sign for the health of the Saba Bank ecosystem, since sharks are apex predators, making them a prime indicator for ecosystem health.

Besides ‘traditional’ measures, ecomorphology was presented as an alternative measure in explaining variation in reef fish assemblages. For ecomorphological analysis insight in trophic morphology was obtained by using a Fish Food Model (FFM). The FFM in this study quantitatively related properties of 14 marine food types to morphological characterics of 15 common fish species on the Saba bank and predicted the capacity of utilizing these food types for each species. Strong differences in morphology and little overlap was observed for all different fish species in the FFM-analysis, which was mainly explained by two sets of variables involving predatory and herbivorous lifestyle. By multiplying each species’ capacity of using food types with its abundance an ecomorphological profile of each fish assemblage was calculated. On a functional level reef fish assemblages showed less variability than on species composition level, this possibly is an indication for high levels of robustness in niche differentiation in reef fish communities on the Saba bank.