Herbivorous fish

The island of Bonaire has significant contamination from anthropogenic sources such as sewage and landfills, which can cause excess nutrients in groundwater that will eventually enter the ocean. Nutrients have been suggested to increase macroalgal growth. The amount of nutrients and abundance of herbivores play a key role in maintaining a healthy coral dominated reef system. The major objective of this study was to determine the health of Bonaire's reefs by assessing various bioindicators, evaluating bioacummulation of macroalgae, assessing the biocontrol mechanisms, and determining the presence of phase shifts. This study looked at the relationship of herbivorous fish, nitrogen content and abundance of macroalgae to make inferences regarding the overall health of the reef. Two study sites, Kas di Arte and Something Special, were chosen for research over the course of four weeks. Data collection included abundance of herbivorous fish, substrate composition and nutrient level in water and algae samples. No inferences could be determined from the nutrient tests due to the varying concentrations found in both water and macroalgae. The herbivorous fish abundance and macroalgae were found to be inversely proportional. This study is important to determine whether herbivorous fish or nutrient input control phase shifts on Bonaire's reefs and can aid in identifying similar issues in reefs all over the Caribbean.

This student research was retrieved from Physis: Journal of Marine Science XV (Spring 2014)19: 58-65 from CIEE Bonaire.

Coral reefs harbor a vast amount of global diversity relative to their size, and are an important economic resource to coastal communities. Over the past few decades, many coral reefs have undergone a phase shift from a substrate dominated by coral to one dominated by algae, largely due to anthropogenic stress. Herbivorous fishes play a major role in topdown control of algal growth and composition; however, depletion of biomass due to overfishing and habitat degradation has threatened the top-down control of fish herbivory on algal composition. This experiment compared endolithic turf algae (TA) composition on coralline rubble under complete fish exclusion, large fish exclusion (>13 cm), and no fish exclusion treatments. There was a significant increase in growth, richness, and percent cover of TA in response to reduced herbivory. The greatest compositional shift occurred in complete fish exclusion treatments. Crustose coralline algae (CCA), important in coral recruitment and growth, significantly increased in cover under every treatment except complete fish exclusion. This illustrates the importance of large-bodied herbivorous fish in controlling TA growth and maintaining bare substrate to facilitate coral recruitment and growth. This study provided insight into how Caribbean reefs go through initial stages of a phase shift from a coral dominated benthos to one dominated by taller, denser algae. Finally, it illustrates how Bonaire’s reef, currently regarded as one of the most intact in the Caribbean, could change in composition if large herbivorous fish are removed from the ecosystem.

This student research was retrieved from Physis: Journal of Marine Science XVI (Fall 2014)19: 55-65 from CIEE Bonaire.

Mimetic behavior signifies organisms evolving to share behaviors and a common resemblance despite different phylogeny. Relationships in mimicry rely on the characteristics of mimics and models: appearance and size, vertical and geographical distribution, mimic to model abundance, behavioral shifts of the mimic and observed benefits. Using these criteria, species from the Hypoplectrus genus (hamlets) were analyzed as potential aggressive mimics. Using a visual census, the distribution of each mimic and model were surveyed and behaviors of individuals within the mimetic pairs were video recorded. There was 80-94% difference between the population densities of two potential mimetic pairs: Hypoplectrus nigricans (black hamlet) and Stegastes adustus, (dusky damselfish) and Hypoplectrus unicolor (butter hamlet) and Chaetodon capistratus (foureye butterflyfish). Data collected for the potential mimetic pair, Hypoplectrus chlorurus (yellowtail hamlet) and Microspathodon chyrsurus (yellowtail damselfish) does not support the hypothesis because the population density of the supposed mimic was higher than that of the potential model. In addition, for all studied pairs, no notable behavioral shifts were observed, and therefore whether the studied pairs are cases of mimicry is still a question.

This student research was retrieved from Physis: Journal of Marine Science XVII (Spring 2015)19: 43-50 from CIEE Bonaire.

Diseases, pathogens, and parasites in marine ecosystems are difficult to research and understand. Tracking the health of ecosystems, such as tropical coral reefs, is important for protecting these sensitive ecological areas. On the coral reefs surrounding Bonaire and other Caribbean islands, a dark spot ailment has been observed on ocean surgeonfish, Acanthurus tractus. This condition has been found to be a parasite, although its exact taxonomic identity is still unknown. The study of this parasite has become the point of interest for many researchers because dark spots have now been observed on other herbivorous fish in this region. The current frequency of the parasite on ocean surgeonfish and other species of surgeonfish is not known. These herbivorous fish are crucial to a healthy and sustainable coral reef ecosystem; a large change to the health of the population of these fishes could potentially affect the entire system. The purpose of this research was to find the prevalence of this parasite in species of surgeonfish through repetitive transects of counting infected individuals on the reefs of Bonaire. Additionally, collection and excision of parasites from their hosts allowed for a hypothesized genus of the infecting organism. The proportion of the density of ocean surgeonfish infected with this black spot causing parasite was 63% and it was found that the proportion of density for the degree of infection for ocean surgeonfish differed significantly among the population. Furthermore, through individual samplings of ocean surgeonfish, the lowest possible taxonomic description of this parasite was found to be the genus Paravortex.

This student research was retrieved from Physis: Journal of Marine Science XVII (Spring 2015)19: 1-9 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.
 
Monitoring Results
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.

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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.

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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.
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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.

Bonaire’s reefs remain among the best in the Caribbean. However, our monitoring has revealed some potentially troubling trends that may require management action. In 2005, we reported to the Bonaire Marine National Park on the status of Bonaire’s coral reefs, and we suggested a strategy for monitoring trends among four key reef attributes we believe track the health and resilience of Bonaire’s reefs (Steneck and McClanahan 2005). Here we report the results of monitoring studies conducted 2003, 2005 and now 2007 at each site. Where appropriate, we drew from Bonaire’s first AGRRA assessment conducted in February 1999 (Kramer and Bischof 2003) to extend temporal trends over a period of eight years. 
Troubling trends
We see three troubling trends of increased macroalgae, declining herbivory from parrotfish, and increases in damselfish populations. Of these, the first two are most serious (see Chapters 1, 2 and 3). Secondary trends of concern, increases in damselfish populations (Chapter 4) and declines in coralline algae (Chapter 1), could lead to reduced recruitment of reef corals (Chapter 7), but to date this is not evident (Chapter 7). Importantly, coral cover remains relatively high (Chapter 1). The monitored group of carnivorous fishes, the lutjanid snappers, are holding constant but we remain concerned about the past (Steneck and McClanahan 2003) and continued loss of other larger bodied reef carnivores such as groupers and barracuda. The positive ecological role of parrotfish is well documented (e.g. Mumby et al. 2006) so their decline is troubling. It is unclear exactly why their population densities are declining. While parrotfish are not currently a widely sought group of reef fish (Chapter 8), fishing pressure on them is growing. It is possible they are vulnerable to even modest fishing pressure, particularly from fish traps. Accordingly, we recommend that the capture and killing of parrotfish be stopped because of their key ecological role on Bonaire’s coral reefs. Further, other groups of grazing herbivores such as the longspined sea urchin (Diadema antillarum) are increasing but too slowly to effectively replace the functional role of parrotfish (Chapter 1). We suggest continued monitoring of key drivers of reef health (coral cover, algal abundance, herbivory and coral recruitment). Some standard protocols such as the Atlantic and Gulf Rapid Reef Assessment (AGRRA) are entirely commensurable with the data presented in our reports in 2003, 2005 and 2007 (this report). A streamlined monitoring protocol is likely to be most useful to managers to alert them as a potential problem is growing and, perhaps more importantly, to show improvement when it occurs.
 
 

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.

Bonaire’s coral reefs remain among the healthiest in the Caribbean. Although the island’s reefs have suffered bleaching disturbances similar to those plaguing reefs throughout the Caribbean, they uniquely show signs of recovery. Here we highlight key findings from our March 2015 biennial coral reef monitoring expedition. We put the findings in the context of both the trends recorded since 2003 when we began our regular monitoring and the most recent research related to the factors controlling the structure and functioning of healthy coral reef ecosystems. 

Abstract:

On coral reefs, herbivorous fishes consume benthic primary producers and regulate competition between fleshy algae and reef-building corals. Many of these species are also important fishery targets, yet little is known about their global status. Using a large-scale synthesis of peer-reviewed and unpub- lished data, we examine variability in abundance and biomass of herbivorous reef fishes and explore evidence for fishing impacts globally and within regions. We show that biomass is more than twice as high in locations not accessible to fisheries relative to fisheries-accessible locations. Although there are large biogeographic differences in total biomass, the effects of fishing are consistent in nearly all regions. We also show that exposure to fishing alters the structure of the herbivore community by disproportionately reducing bio- mass of large-bodied functional groups (scraper/excavators, browsers, grazer/ detritivores), while increasing biomass and abundance of territorial algal- farming damselfishes (Pomacentridae). The browser functional group that consumes macroalgae and can help to prevent coral–macroalgal phase shifts appears to be most susceptible to fishing. This fishing down the herbivore guild probably alters the effectiveness of these fishes in regulating algal abun- dance on reefs. Finally, data from remote and unfished locations provide important baselines for setting management and conservation targets for this important group of fishes.