Human exploitation shapes productivity–biomass relationships on coral reefs

Abstract

Coral reef fisheries support the livelihoods of millions of people in tropical countries, despite large‐scale depletion of fish biomass. While human adaptability can help to explain the resistance of fisheries to biomass depletion, compensatory ecological mechanisms may also be involved. If this is the case, high productivity should coexist with low biomass under relatively high exploitation. Here we integrate large spatial scale empirical data analysis and a theory‐driven modelling approach to unveil the effects of human exploitation on reef fish productivity–biomass relationships. We show that differences in how productivity and biomass respond to overexploitation can decouple their relationship. As size‐selective exploitation depletes fish biomass, it triggers increased production per unit biomass, averting immediate productivity collapse in both the modelling and the empirical systems. This ‘buffering productivity’ exposes the danger of assuming resource production–biomass equivalence, but may help to explain why some biomass‐depleted fish assemblages still provide ecosystem goods under continued global fishing exploitation.

Production of mobile invertebrate communities on shallow reefs from temperate to tropical seas

“…Reef ecosystems are among the most productive and diverse on earth. The productivity of reefs is often quantified in terms of fish production [15], fisheries yield [16,17], or the primary productivity generated by phytoplankton or benthic algae [18]. A substantial proportion of reef secondary production, though, is generated by small mobile invertebrates (epifauna) that inhabit the surfaces of macroalgae, coral and other benthic structures [11,19].…”

Spatial subsidies drive sweet spots of tropical marine biomass production

“…Indeed, differences in α, β, and γ species diversities between the 3 locations were insufficient to explain distinctions in productivity ( S1 Text ). These disparities in productivity also appeared not to be determined by differential rates of human exploitation in the locations surveyed (e.g., [ 43 ]), as evidenced by similarities in fish size structure among locations. There was large variability and widespread overlap in quantile intervals between locations for both size-specific biomass and productivity, but the most productive region (Raja Ampat) had similar or higher productivity compared with the other locations in all size classes ( Fig 3B and 3C ).…”

Globally consistent reef size spectra integrating fishes and invertebrates

“…Integrative modelling, and empirical and mechanistic studies (e.g. Barneche et al ., 2014; Morais et al ., 2020a), are all needed to disentangle the combined and relative influences of multiple anthropogenic stressors when contrasted with natural ecological variation affecting size spectra. Advancing this research goal would assist the development of predictive modelling tools for mapping changes on reefs, giving us a better idea of baseline reef size spectra and thus helping improve marine biodiversity policy and management (Stuart‐Smith et al ., 2017).…”

“…This study provides improved understanding on the variability of reef size spectrum slopes globally, which is crucial for the development of size spectra as indicators for reef ecosystem health (e.g. Nash and Graham, 2016; Trebilco et al ., 2016; Zgliczynski and Sandin, 2017; Morais et al ., 2020a).…”