Tradeoffs between fisheries harvest and the resilience of coral reefs

Abstract

Many countries are legally obliged to embrace ecosystem-based approaches to fisheries management. Reductions in bycatch and physical habitat damage are now commonplace, but mitigating more sophisticated impacts associated with the ecological functions of target fisheries species are in their infancy. Here we model the impacts of a parrotfish fishery on the future state and resilience of Caribbean coral reefs, enabling us to view the tradeoff between harvest and ecosystem health. We find that the implementation of a simple and enforceable size restriction of >30 cm provides a win:win outcome in the short term, delivering both ecological and fisheries benefits and leading to increased yield and greater coral recovery rate for a given harvest rate. However, maintaining resilient coral reefs even until 2030 requires the addition of harvest limitations (<10% of virgin fishable biomass) to cope with a changing climate and induced coral disturbances, even in reefs that are relatively healthy today. Managing parrotfish is not a panacea for protecting coral reefs but can play a role in sustaining the health of reefs and highquality habitat for reef fisheries. M uch effort in ecosystem-based fishery management has been directed to reducing the detrimental impacts of fishing gear on the ecosystem, including bycatch and habitat damage (1, 2). A more complex consideration is maintaining the ecosystem function of the target species. A well-known example is the importance of forage fish and krill to the diet of large fish, sea birds, and marine mammals (3-5), which generates a tradeoff between human and nonhuman (natural) consumption of the stock. Measuring such direct trophic tradeoffs is challenging enough (6), but some ecosystem functions act through complex ecological interactions that might involve multiple trophic levels and result in nonlinear impacts on the ecosystem (7). Perhaps not surprisingly, there has been little progress in modifying fishing activity to take account of these compound ecological processes (8).The impacts of fishing are particularly severe in the most complex of marine ecosystems, coral reefs. In the Caribbean, parrotfish (Labridae, Scarinae) are the dominant herbivores on middepth (5-15 m) forereefs (9-11), helping keep large seaweeds in check and facilitating the recovery and growth of corals (12-14). However, parrotfish are an important fishery species (15), and their depletion can lead to a flip in coral population dynamics that locks reefs into a persistent degraded state (16). A shift to macroalgal dominance offers relatively little value to fisheries, because much of the primary production is lost to detrital pathways rather than fish-based consumption (17). Macroalgal dominance usually is associated with less complex coral habitats, which in turn are associated with lower biodiversity and fewer ecosystem functions (18). Although several countries [e.g., Belize, Bonaire, and Bermuda (19)] have implemented a ban on parrotfish harvest, most jurisdictions either have no fisheries restrictions ...

Identity of coral reef herbivores drives variation in ecological processes over multiple spatial scales

“…, Bozec et al. ). These studies have generally assumed that foraging behavior and diets of parrotfishes are strongly conserved phylogenetically.…”

“…In recognition of the importance of the ecological roles parrotfish play in coral reef resilience, previous work has sought to better understand the net ecological impacts of parrotfish herbivory on reef ecosystems (Mumby 2006, Perry et al 2013, Bozec et al 2016). These studies have generally assumed that foraging behavior and diets of parrotfishes are strongly conserved phylogenetically.…”

“…Importantly, parrotfishes are often the targets of fisheries throughout the Caribbean (Hawkins and Roberts 2004a, SERO-LAPP 2012, Vall es and Oxenford 2014, Bozec et al 2016. While these fisheries can be locally important both culturally and economically, fishery extraction may reduce the ecological impacts of targeted species by suppressing overall biomass and altering the species composition and size-structure of the parrotfish assemblage (Hawkins and Roberts 2004a).…”

Interactive Effects of Predator and Prey Harvest on Ecological Resilience of Rocky Reefs

“…The forward and reverse shifts between alternative stable states exhibit hysteresis, in that they occur at different levels of forcing (Scheffer et al 2001, Scheffer andCarpenter 2003), which can make a return to the alternative state difficult once a shift has occurred. While the existence of alternative stable states can be difficult to demonstrate empirically because of the long time scales required (Petraitis andDudgeon 2004, Schr€ oder et al 2005), mathematical models can reveal the potential for hysteretic behavior, provide evidence of mechanistic drivers of community shifts, and estimate threshold values of important ecosystem state variables and/or parameters (Scheffer and Carpenter 2003, Mumby et al 2007, Baskett and Salomon 2010, Bozec et al 2016. Systems that exhibit alternative stable states often have strong feedbacks both within and across trophic levels that act to maintain a given state, including recruitment facilitation (Mumby et al 2007, Baskett andSalomon 2010) and predatorprey role reversals (Barkai andMcQuaid 1988, Walters andKitchell 2001).…”

The Dynamics and Resilience of Coral Reefs

“…A suite of 33 potential drivers were explored including ecological variables such as turf, macroalgae Bozec et al 2016) and coral recruitment (Doropoulos et al 2015), stochastic abiotic stressors such as storms (Connell 1997) and floods (Devlin et al 2001), as well as chronic anthropogenic influences from land-based runoff such as sedimentation (Rogers 1990;Fabricius 2005) (Table S 4 Reconstructed Sea Surface Temperature (ERSST) were also extracted to represent regional temperature effects (Wolter & Timlin 1993;Wolter & Timlin 1998;Huang et al 2015;Huang et al 2016). The Wet Tropics NRM includes three catchments: Daintree, Johnstone and Tully.…”