Marine reserves stabilize fish populations and fisheries yields in disturbed coral reef systems

Abstract

Marine reserve networks are increasingly implemented to conserve biodiversity and enhance the persistence and resilience of exploited species and ecosystems. However, the efficacy of marine reserve networks in frequently disturbed systems, such as coral reefs, has rarely been evaluated. Here we analyze a well‐mixed larval pool model and a spatially explicit model based on a well‐documented coral trout (Plectropomus spp.) metapopulation in the Great Barrier Reef Marine Park, Australia, to determine the effects of marine reserve coverage and placement (in relation to larval connectivity and disturbance heterogeneity) on the temporal stability of fisheries yields and population biomass in environmentally disturbed systems. We show that marine reserves can contribute to stabilizing fishery yield while increasing metapopulation persistence, irrespective of whether reserves enhance or diminish average fishery yields. However, reserve placement and the level of larval connectivity among subpopulations were important factors affecting the stability and sustainability of fisheries and fish metapopulations. Protecting a mix of disturbed and non‐disturbed reefs, rather than focusing on the least‐disturbed habitats, was the most consistently beneficial approach across a range of dispersal and reserve coverage scenarios. Placing reserves only in non‐disturbed areas was the most beneficial for biomass enhancement, but had variable results for fisheries and could potentially destabilize yields in systems with well‐mixed larval or those that are moderately fished. We also found that focusing protection on highly disturbed areas could actually increase variability in yields and biomass, especially when degraded reef reserves were distant and poorly connected to the meta‐population. Our findings have implications for the design and implementation of reserve networks in the presence of stochastic, patchy environmental disturbances.

Changing role of coral reef marine reserves in a warming climate

“…Indeed, herbivorous fish have sustained reef-associated trap fisheries landings in Seychelles following the 1998 coral bleaching event 27 . The role of marine reserves in exporting herbivorous fish to fisheries through adult spillover or larval export is likely to be substantial, and could play a key role in continued food security as coral reefs degrade through climatic impacts 38 .…”

Direct and indirect effects of heatwaves on a coral reef fishery

“…While the predominant research focus has been on impacts of habitat loss on coral reef fish assemblage composition and productivity (e.g. Hopf et al, 2019; Robinson et al, 2019), our study adds to the evidence that temperature‐driven changes in catchability are important to consider in reef fishery management (Bacheler & Shertzer, 2020). We suggested here that changes in catchability are heavily influenced by mechanisms stemming from physiological responses to warming, but we recommend further experimental studies to explore ecological mechanisms that may independently involve changes in prey or habitat.…”

“…The management regime of the reef line fishery is likely robust to infrequent changes in catchability of the magnitude we observed because catches are well below the maximum sustainable yield (Campbell et al, 2019). The existing management regime that mixes marine parks and catch quotas is also robust to regional variation in ecological dynamics (Bode et al, 2016), overfishing (Hopf et al, 2016; Little et al, 2011) and climatic change (Hopf et al, 2019). A stock assessment conducted in 2014, which utilized UVC and CPUE data, did not find any effects of coral bleaching events on stock productivity, and environmental change was found to have limited impact on the fishery (Leigh et al, 2014).…”

Life histories decide reserve benefits in transient yields and bycatch persistence

“…Thus, the total number of larvae produced inside the marine reserve is the dot product of adult density and fecundity multiplied by the reserve size. Based on the “well-mixed” assumption as suggested in previous research (Hastings & Botsford 1999; Hart 2006; Hopf et al 2019), the larvae density both inside and outside the marine reserve is which equals the total number because the total marine system size is scaled as 1. Therefore, the density of larvae that survive to adults will be where f (·) is the Beverton–Holt growth function.…”