With increasing stressors to coral reefs, defining tools that evaluate their dynamics and resilience is important to interpret system trajectories and direct conservation efforts. In this context, surveys must go beyond conven- tional monitoring approaches that focus on abundance and biomass of key groups and quantify metrics that better assess ecological processes and ecosystem trajectories. By measuring a variety of conventional (e.g. proportional cover of broad benthic groups, biomass of herbivorous fish) and complementary resilience-based metrics (e.g. algal turf height, coral recruitment rates, juvenile coral densities, herbivorous fish grazing rates), this study evaluated the ecosystem responses to community-based management in Fiji. The study was conducted across three paired tabu areas (periodically closed to fishing) and adjacent fished sites. Conventional metrics reflected no management effect on benthic or herbivorous fish assemblages. In contrast, the complementary metrics generally indicated positive effects of management, particularly within the benthos. Significant differ- ences were observed for turf height (33% lower), coral recruitment rate (159% higher) and juvenile coral density (42% higher) within areas closed to fishing compared to adjacent open reefs. In addition, turf height was in- versely related to coral recruitment and juvenile coral density, and longer turfs (≥5 mm) were more competitive in interaction with corals. These results emphasise that conventional metrics may overlook benefits of local management to inshore reefs, and that incorporating complementary resilience-based metrics such as turf height into reef survey protocols will strengthen their capacity to predict the plausible future condition of reefs and their responses to disturbances.
Coral reef management
The island of Bonaire in the lesser Antillean islands is economically dependent on the tourism industry. A majority of tourists who visit the island are scuba divers, drawn by Bonaire‘s coral reefs. Increased development, tourism, fishing, and pollution threaten Bonaire‘s marine resources. Survey questionnaires and oral interviews were conducted to determine the interactions between the inhabitants of Bonaire and marine resources, specifically the coral reefs. Four sub-cultures (fishermen, divers, researchers, and others) were identified through their use of marine resources. These subcultures were asked to identify major threats to the reefs and changes in the reefs over the past decade. Overall, 81% of Bonairean residents were able to identify changes to the reef over the past decade, and 77% of residents were able to identify at least one threat to the reef. The freelisted responses were analyzed to determine how sub-cultures interact with marine resources, and although the nature of interactions varied between sub-cultures, the threats listed were similar, identifying a shared communal knowledge of reef ecological importance. Through the advent of the Bonaire Marine Park and the increased access to scuba technology, the Bonairean culture has adapted to include the reefs as part of the cultural identity. Residents on Bonaire have a vested interest in the preservation of Bonaire‘s marine resources. Public education and increased access to research conducted on the island is suggested to promote community engagement with marine resource management.
This student research was retrieved from Physis: Journal of Marine Science XIII (Spring 2013)19: 23-32 from CIEE Bonaire.
Phototoxic polycyclic aromatic hydrocarbons (PAHs) have been welldocumented as major marine pollutants. While PAHs are known to have negative ecological effects, the spread of point-source PAHs into coral reefs is poorly understood. This study focuses on a potential source of marine PAH contamination from a drain into a coral reef in Bonaire, Dutch Caribbean. PAHs were believed to be detected outside of the drain between October and November 2013, providing incentive for continued monitoring of PAH presence. Insight from this investigation is important not only to the general understanding of point-source marine pollution pathways, but holds implications for drain management strategies. Water samples from sites of varying distances from the drain were analyzed for UV-reactive toxicity using two Artemia sp. bioassays. Results from the bioassays indicated that PAH presence was undetectable, and that there was no relationship between distance from the drain and UVreactive toxicity. It was concluded that sediment dispersion and marine organism bioaccumulation likely accounted for the apparent temporal discrepancy in PAH presence. Field observations displayed noticeable coral reef degradation, which was assumed to be largely caused by factors other than PAH pollution. Despite the lack of evidence for current PAH presence, observations of poor reef health outside of the drain suggest that further studies and management strategies be considered for the drain and cement trough.
The invasion of Pterois volitans (lionfish) is a serious concern for Caribbean coral reef health. The morphology and behavior of lionfish is novel to the reef in Bonaire, which allows lionfish to take advantage of resources at the expense of native reef fish. Cephalopholis cruentata (graysby) is a native grouper on a similar trophic level as lionfish. Other groupers show congeneric aggression, but documentation of graysby behavior is scarce. This study observed graysby behavior and investigated whether graysbys recognize lionfish as competitors. A model-bottle experiment was used to present lionfish to graysbys. Graysby responses, aggressive, neutral, and submissive, were observed. Behavior was quantified using a reactive index. No significant difference in the frequency distribution of behavior types was observed between treatments. A moderate correlation was observed between graysby size and reactive index, suggesting that graysby reactions may be size-dependent. Future studies should consider size when analyzing graysby behavior towards other species, native or invasive.
This student research was retrieved from Physis: Journal of Marine Science XIX (Spring 2016)19: 85-90 from CIEE Bonaire.
Unusually warm ocean temperatures surrounding Bonaire during the late summer and fall of 2010 caused 10 to 20 % of corals to bleach (Fig. 1). Bleaching persisted long enough to kill about 10 % of the corals within six months of the event (Steneck, Phillips and Jekielek Chapters 2A – C). That mortality event resulted in the first significant decline in live coral at sites monitored since 1999 (Fig. 2). Live coral declined from a consistent average of 48 % (from 1999 to 2009) to 38 % in 2011 (Steneck Chapter 1). This increase in non-coral substrate increased the area algae can colonize and the area parrotfish must keep cropped short (Mumby and Steneck 2008). For there to be no change in seaweed abundance would require herbivorous fish biomass and population densities to increase, but they have been steadily declining in recent years. This decline in parrotfish continues despite the establishment of no-take areas (called Fish Protection Areas – FPAs) and the recent law that completely bans the harvesting of parrotfish. The other major herbivore throughout the Caribbean is the black spined sea urchin, Diadema antillarum. However, since 2005 Diadema abundance has steadily declined. Damselfishes continue to increase in abundance (except in FPAs) and their aggressive territoriality reduces herbivory where they are present. These declines in herbivory resulted in a marked increase in macroalgae (Steneck Chapter 1). Although patchily distributed, algae on some of Bonaire’s reefs are approaching the Caribbean average (Kramer 2003). All research to date indicates that coral health and recruitment declines directly with increases in algal abundance (e.g., Arnold et al 2010).
On the bright side, predatory fishes are increasing in abundance in general but increasing most strongly in FPAs. Typically, responses to closed areas take 3 - 5 years to begin to manifest themselves. Predators of damselfishes have increased significantly in FPA sites and there, damselfish abundances are trending downward. These trends are the first signs of changes in the FPAs, and they are encouraging.
Overall, Bonaire’s coral reefs today are more seriously threatened with collapse than at any time since monitoring began in 1999.
The abundance of live coral at the monitoring sites has been remarkably constant since 1999. However, the bleaching related mortality event (Fig. 1) resulted in the first marked decline in live coral.
Seaweed abundance (“macroalgae”) increased sharply in 2011. While the greatest increase in algae occurred at the 18th Palm site where effluent could have increased nutrient levels, most of the other sites showed marked increases in algal abundance (see Steneck Chapter 1). Coralline algae, which has been shown to facilitate coral recruitment, remains at or near unprecedentedly low levels (Fig 2). Herbivory from parrotfishes and the grazing sea urchin Diadema antillarum remains at or near the lowest levels recorded since monitoring began in 1999 (Fig. 3 and see Cleaver Chapter 5). Herbivory from parrotfish is widely thought to be most important (e.g., Steneck and Mumby 2008) but territorial damselfishes can negate parrotfishes’ positive effects by attacking grazing herbivores and preventing them from effectively grazing (Arnold et al 2010). Damselfish abundances have trended upward in recent years (Fig. 3). However, there is a hint of a reversal to this trend in the FPAs (see Arnold Chapter 3). This reversal is consistent with the possibility that areas without fishing have elevated abundances of damselfish predators such as species of groupers and snappers (Randall 1965)
Predatory fishes including snappers, groupers, barracuda, grunts and others increased in abundance at our monitored sites (Fig. 4 and see DeBey Chapter 6a). Specific predators known to eat damselfishes (see Preziosi Chapter 6b) show variable population densities with only a hint of an increase in 2011.
Predatory fishes increased in abundance in both biomass (most striking) and population densities (Fig. 5). While biomass of predators in FPA and control sites is identical, the population density of predators is slightly greater at FPA sites
Coral recruitment remained lower than recorded in 2003 and 2005 (Fig. 6). However, the abundance of juvenile corals was higher in 2011 than was quantified in 2009
This report characterizes the state of Bonaire’s reefs as of March 2005. We pay particular attention to structural and functional attributes of reefs that have changed in so many other Caribbean reefs. We characterize coral reefs by their resident organisms and the forces regulating their distribution and abundance. Thus, corals, algae and fish define the “structure” of coral reefs but climate changes, diseases, hurricanes, overfishing, sedimentation and excess nutrients may affect how they “function”. Recent unfavorable changes in the structural and functional attributes of reefs have caused “the coral reef crisis” (Bellwood et al. 2004). In Caribbean coral reefs the most alarming changes have been the declines in the abundance of corals, sea urchins and reef fishes and the accompanying increases in large harmful seaweeds (called “macroalgae”). The decline in coral and increase in macroalgae, called a “phase shift”, represents a significant change in the structure of coral reef ecosystems that could lower its resilience.
In March of 2005, a team of graduate students from the University of Maine revisited six study reefs on Bonaire to determine the status of those reefs and to detect if any change has occurred since March of 2003 when the last such survey was conducted. The study sites established in 2003 from north to south are: Karpata, Barcadera, Reef Scientifico, Forest on Klein Bonaire, Plaza and Windsock. Bonaire’s shallow (10 m) reefs remain in good condition. Coral cover averaged 47% in 2005 compared to 46% in 2003 (no change). Turf algae have increased and coralline algae have declined slightly over the past two years. Harmful seaweed “macroalgae” abundance remains low (2% in 2005 and 5% in 2003; see Steneck in this report) at the 10 m depth we studied. At depths below 20 m, macroalgae are now and have been (for at least the past 30 years) much more abundant (e.g. Van den Hoek et al. 1975) The absence of macroalgae in Bonaire most likely relates to the abundance of seaweedeating species or “herbivores”. Caribbean-wide, harmful macroalgal seaweed abundance corresponds inversely with the abundance of grazing fish such as parrotfish and tangs (Fig. 1). No comparable plot exists for seaweed abundance and any other measured factor on reefs.
Changes over the past two decades
Comparisons between the status of reefs over a few years tell us little about long-term changes. For example, today there is a distinct demarcation between where Bonaire’s fringing reefs begin at 5 to 10 m depth and the shore. This region today is largely coralfree and dominated by rubble and sediment laden turf algae. However, this may not have always been the case. Prior to whiteband disease that killed nearly 90% of the elkhorn and staghorn corals in the Caribbean (i.e. Acropora palmata and A. cervicornis) (Aronson et al. 1998, Aronson and Precht 2001), most of the near shore zone was coral-dominated.
Coral cover in the near shore zone surrounding Bonaire has declined dramatically and is now dominated by dead coral rubble where once elkhorn and staghorn corals had formed near monocultures prior to white band disease. Five of our six study sites have changed dramatically over the past 20 years except for Karpata. The decline of the Acropora species may have allowed competitively inferior species such as lettuce, pencil, finger and fire corals (Agaricia spp, Madracis spp, Porites porities and Millepora complanata) to expand since all have increased in abundance since the Van Duyl study (1985). Corals are not the only group to have changed dramatically since the 1980s. Diadema antillarum, the dominant grazing sea urchins was abundant in the near shore zone until it succumbed to the mass mortality of the mid 1980s. Today, more than 20 years later it remains below detectable levels at most of the sites we studied (Smith and Malek this report, Steneck this report). These changes, along with the significant declines in large predator finfish (see Bonaire Report 2003) indicate that several key players for the resilience of coral reefs (e.g. Fig. 3) have declined in abundance.
Fishers and divers are the major resource users of Caribbean coral reefs. On Curaçao and Bonaire, reef condition is good relative to the Caribbean average, but fishes and corals have greatly declined over the last few decades. We interviewed 177 fishers and 211 professional SCUBA divers to assess their views on the extent and causes of degradation. Fishers know fish stocks are severely depleted and declining, whereas divers were aware of declines but had “shifted baselines” and consider the reefs healthy. Fishers and divers differ in perceptions of the causes and appropriate remedies for decline. Fishers generally blame external factors such as changes in climate, currents, or industrial fishing offshore, whereas divers primarily blame overfishing and coastal development. Nevertheless, the great majority of both fishers and divers support more management of both fishing and diving. Thus the social climate is ripe for balanced and strong restrictions on both groups for reef recovery and sustainable use. Exclusion of both fishers and divers from protected areas of significant size around the islands would be a major step forward towards the long-term conservation of reef resources.