Global baselines and benchmarks for fish biomass: comparing remote reefs and fisheries closures

Abstract

Baselines and benchmarks (B&Bs) are needed to evaluate the ecological status and fisheries potential of coral reefs. B&Bs may depend on habitat features and energetic limitations that constrain biomass within the natural variability of the environment and fish behaviors. To evaluate if broad B&Bs exist, we compiled data on the biomass of fishes in ~1000 reefs with no recent history of fishing in 19 ecoregions. These reefs spanned the full longitude and latitude of Indian and Pacific Ocean reefs and included older high-compliance fisheries closures (>15 yr closure) and remote reef areas (> 9 h travel time from fisheries markets). There was no significant change in biomass over the 15 to 48 yr closure period but closures had only ~40% of the biomass (740 kg ha −1 , lower confidence interval [LCI] = 660 kg ha −1 , upper confidence interval [UCI] = 810 kg ha −1 , n = 157) of remote tropical reefs (1870 [1730, 2000] kg ha −1 , n = 503). Remote subtropical reefs had lower biomass (950 [860, 1040] kg ha −1 , n = 329) than tropical reefs. Closures and remote reef fish biomass responded differently to environmental variables of coral cover, net primary productivity, and light, indicating that remote reefs are more limited by productivity and habitat than closures. Closures in fished seascapes are unlikely to achieve the biomass and community composition of remote reefs, which suggests fisheries benchmarks will differ substantially from wilderness baselines. A fishery benchmark (B 0 ) of ~1000 kg ha −1 adjusted for geography is suggested for fisheries purposes. For ecological purposes, a wilderness baseline of ~1900 kg ha −1 is appropriate for including large and mobile species not well protected by closures.KEY WORDS: Baselines · Coral reef fish · Fisheries and ecological indicators · Pristine or virgin biomass · Sustainability

Natural variation in coral reef trophic structure across environmental gradients

“…Presumably, primary consumers benefit from the higher rates of benthic primary production, as increased irradiance bolsters the base of the food web. Higher fisheries production in tropical coral reefs than in the subtropics is due in part to higher solar radiation (McClanahan et al 2019). As such, coral reef fisheries that target lower TLs may be more viable where energy into the base of the food web is higher and therefore where fish assemblages are more naturally bottom-heavy.…”

“…) and high irradiance is linked to increased fish biomass (McClanahan et al . ). How this affects consumers – and ultimately trophic structure – remains unknown.…”

“…Examples include remote Indo-Pacific coral reefs located several hundreds of kilometers from the nearest human population centers. Studies from these near-pristine ecosystems can inform fisheries management targets, help evaluate ecosystem status, and have shown, for example, that the fisheries potential of subtropical reefs is lower than that of tropical ones (McClanahan et al 2019). From microbes to top predators, natural gradients in wave energy, water temperature, and primary production are key determinants of coral reef structure and function (Williams et al 2019).…”

“…Primary production in the coastal ocean is limited in part by sunlight, which decreases with depth and latitude (Campbell and Aarup 1989). Light influences benthic primary producers on coral reefs (Gattuso et al 2006) and high irradiance is linked to increased fish biomass (McClanahan et al 2019). How this affects consumers -and ultimately trophic structure -remains unknown.…”

Oyster Reefs in Northern Gulf of Mexico Estuaries Harbor Diverse Fish and Decapod Crustacean Assemblages: A Meta-Synthesis

“…Benchmarks provide a tool to assess the status of natural, managed, or restored ecosystems (Angermeier and Karr, 1994;McClanahan et al, 2019). Ideally, benchmarks are set using baseline data derived from natural or pristine systems, which are defined by functional and evolutionary limits of the ecosystem (Pickett et al, 1992).…”