2009 Steneck Et Al Status and Trends Of
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Status and Trends of 2009 Bonaire’s Coral Reefs, 2009 & Need for Action 2007 2004 Project Directors: Robert S. Steneck ([email protected]) Suzanne N. Arnold ([email protected]) University of Maine, School of Marine Sciences, Darling Marine Center, Walpole, ME 04573 Status and Trends of Bonaire’s Coral Reefs, 2009 & Need for Action Project Directors: Robert S. Steneck1 [email protected] Suzanne N. Arnold1 [email protected] 1University of Maine, School of Marine Sciences, Darling Marine Center, Walpole, ME 04573 USA Table of Contents and Contributing Authors Page Executive Summary- Status and Trends of Bonaire’s Reefs & Need for Immediate Action Robert S. Steneck and Suzanne N. Arnold 1-6 Monitoring and Baseline Studies for Bonaire: Chapter 1: Patterns of abundance in corals, seaweeds, sea urchins and juvenile corals in Fish Protection Areas and Controls: baseline data for monitoring Robert S. Steneck and Suzanne N. Arnold 6-12 Chapter 2: Herbivorous fishes: Patterns of distribution, abundance, body size and trends over time in Bonaire Sherri A. Eldridge 13-24 Chapter 3: Herbivory on Bonaire’s reefs: Spatial and temporal trends in species and group specific grazing frequencies Mahima Jaini 25-38 Chapter 4: Patterns of distribution, abundance and size structure of Bonaire’s predatory reef fish Henry S DeBey, and Robert S. Steneck 39-51 Chapter 5: The abundance of the seas urchins Diadema antillarum, Echinometra lucunter, Echinometra viridis, and Tripneustes ventricosus in shallow reef zones of Bonaire Kelly Prendiville 52-57 Chapter 6: Abundance of initial stage and juvenile parrotfish in shore habitats of Bonaire reef Rodolfo Chang 58-65 Chapter 7: Non-indigenous and nuisance species in Bonaire National Marine Park Felipe Paredes 66-74 Chapter 8: A comparison of 1998 bleaching events in Bonaire and Belize Danielle Brezinski 75-88 Other Topical Coral Reef Reports: Chapter 9: Overfishing and coral reefs David Kazyak 89-95 Chapter 10: Factors affecting macroalgal abundance on coral reefs: A global review Ashley Kling 96-111 Chapter 11: Ocean acidification and the future of coral reefs Keri Lindberg 112-128 Chapter 12: Creating a balance between tourism and coral reef sustainability: The effects of SCUBA diving on coral reef ecosystems worldwide Amber Bratcher 129-136 Chapter 13: Valuing Coral Reef Ecosystems and Their Ecological Services: An Ecological Economics Approach Derek Olson 137-163 Appendices: Appendix A: Average density, fork length, and biomass of herbivorous fish A1-A9 Appendix B: Density and fork length of initial and terminal phase Scarids B1-B3 Appendix C: Biomass of initial and terminal phase Scarids C1-C3 Appendix D. Average biomass and density of predatory reef fish D1-D10 Acknowledgements: Thanks to Ms. Elsmarie Beukenboom, Ramon de Leon, Dean Domacasse and Bonaire National Marine Park Rangers (STINAPA). Funding came in part from STINAPA, the Pew Fellows for Marine Conservation, and the University of Maine’s School of Marine Sciences. Additional support and help came from Toucan Dive operations, Captain Don’s Habitat, and STINAPA volunteers. To all we are grateful. Executive Summary: Status and Trends of Bonaire’s Reefs & Need for Immediate Action Bob Steneck1 and Suzanne Arnold1 1University of Maine, School of Marine Sciences Overview and conclusion In 2005 STINAPA requested we provide advice on how to monitor Bonaire’s coral reefs (Steneck and McClanahan 2005). Our advice was 1) keep it simple and 2) keep it focused on known drivers and indicators of coral reef health. We emphasized four key drivers, coral cover, algal abundance, herbivory and coral recruitment, as the best combination for monitoring the health and resilience of coral reefs (i.e., Hughes et al 2005, Mumby and Steneck 2008). Further, we suggested that the current status of any variable is less important than its trend over time. We applied our trend analysis for five time intervals (1999, 2003, 2005, 2007, and 2009) at six monitoring sites (Windsock, 18th Palm, Forest, Reef Scientifico, Barcadera and Karpata). We found negative trends in three of the four key variables (underlined in Fig 1), and additional negative trends in five other variables. In total, eight of the nine monitored variables (we did not monitor nutrients) showed negative trends (listed in Fig. 1). We detected no positive trends. The increase in algal abundance is most troubling. These results suggest that the risk of collapse of Bonaire’s reefs is increasing and warrants increasing protection of herbivorous fishes and reducing nutrient discharge. Fig. 1. List of variables to monitor to detect positive (left arrows) and negative (right arrows) trends. Key variables are underlined. Drivers for most variables are listed below those variables. (from Steneck and McClanahan 2005) 1 Monitoring Rationale and Results Of the 10 variables proposed for monitoring coral reefs (Fig. 1, Steneck and McClanahan 2005), four are “key variables” that either drive or indicate the health of coral reefs. Coral cover defines the physical and ecological structure of this ecosystem. Macroalgae drives and indicates reef health. No algal dominated coral reef has ever been described as healthy. The two primary factors driving macroalgal abundance are herbivores and ambient nutrients. Evidence is strongest that herbivores play the greatest role in driving algal abundance (reviewed in Mumby and Steneck 2008). While overall coral abundance remains stable on Bonaire, macroalgae (harmful to reefs) and coralline algae (helpful to reefs) are increasing and decreasing in abundance respectively (Fig. 2). Macroalgae, and dense filamentous turf algae, inhibit coral settlement and can kill corals, whereas some species of coralline algae have been shown to facilitate the settlement and recruitment of reef corals (Harrington et al 2004). Fig. 2. Monitoring results 1999 – 2009 for coral, macroalgae and coralline algae (from Steneck and Arnold 2009, Ch. 1). Significant trends are indicated by the up arrows (i.e., increasing) and down arrows (i.e., decreasing). We did not monitor nutrient levels in Bonaire. However, recent studies indicate that nutrient levels are dangerously high in some areas (Ramon de Leon personal communication). Few 2 studies have shown a clear relationship between nutrient levels and algal abundance. This is most likely due to the countervailing effects of herbivory on most of the world’s coral reefs (Diaz-Pulido and McCook 2003). However, declining herbivory is clearly evident among herbivorous fishes (Fig. 3, Jaini 2009, Ch. 3). Specifically, the population density of scarid parrotfishes and their bite rates are both declining (Fig. 3). Additionally, populations of the herbivorous sea urchin, Diadema, that had increased from 1999 to 2005 have since declined to very low abundance (Steneck and Arnold 2009, Ch. 1). Although the recent Diadema decline could have been the result of Tropical Storm Omar, even when this species was at its recent peak abundance (2004), its population density was still too low to be effective in reducing seaweed. Fig. 3. Trends in herbivory. Parrotfish abundance, bite rate and Diadema abundance all scale positively with herbivory. Damselfish scale negatively. Arrows indicate trend. Data from Chapters 1 (Steneck and Arnold 2009), 2 (Eldridge 2009), 3 (Jaini 2009), and 4 (DeBey and Steneck 2009). To exacerbate the decline in effective herbivory is the rise in damselfish populations. Territorial damselfishes can interfere with the grazing activity of tangs and parrotfishes (Jaini 2009, Ch 3). 3 Therefore, the increasing abundance of damselfish (Fig. 3) is a negative trend for the health of Bonaire’s reefs. One of the strongest suspected links is the role of predatory fishes in controlling the abundance of territorial damselfish. For example, McClanahan 2005 studied how coral reefs changed in Belize following the establishment of no-take reserves. The strongest positive effect was among fish predators and the strongest negative effect was among damselfishes. That decline in damselfishes as predator abundance increased corresponds well with several other studies showing predator control of damselfish abundance (e.g., Almany 2004). Predatory fish that eat other fish (especially preying on damselfish) and were found in fish surveys in Bonaire include: trumpetfish, bar jack, schoolmaster snapper, tiger grouper, graysby, coney, cubera snapper, mahogany snapper, black grouper and barracuda. Their population densities dropped in half from 2003 and 2009 (Fig. 4). Fig. 4. Trends in predatory fishes that are known to or suspected to eat damselfishes. Data from AGRRA 1999, Bonaire Reports 2003, 2005 and 2009). Population densities of coral recruits (corals less than 4 cm in diameter) (Ch. 1; Steneck and Arnold 2009). Coral recruitment in 2009 was significantly lower than what was recorded in 2003 and 2005. 2007 data are lacking for coral recruitment, so it’s possible that the 2009 decline could have resulted from unusual destruction caused by Tropical Storm Omar in October, 2008. By applying the trend results (i.e., the arrows in Figs. 2 – 4) together with the predictions in the suggested approach to monitoring coral reefs (Fig. 1; Steneck and McClanahan 2005), we see that the preponderance of trends are negative for Bonaire’s coral reefs (Fig. 5). 4 Fig. 5. The interpreted monitoring protocol. Where clear trends were found (Figs. 2 – 4 and Eldridge 2009), they were surrounded by a red box. Note that no significant positive trends were found. No data were presented for nutrients or other herbivorous fishes. Only coral cover shows no trend all. Conclusion Coral reefs are complex biological systems prone to sudden change (Scheffer et al 2001). Given the clear trends in dangerous directions, immediate management actions should be taken. We suggest the greatest effort be placed in fisheries management. All herbivorous fishes (parrotfishes and tangs) should be protected. A moratorium on all other fishing on the reefs until the current threat stabilizes should also be considered. 5 Literature Cited Almany, G. R. 2004. Does increased habitat complexity reduce predation and competition in coral reef fish assemblages? Oikos 106: 275-284.