Decadal shifts in traits of reef fish communities in marine reserves

Abstract

Marine reserves are known to impact the biomass, biodiversity, and functions of coral reef fish communities, but the effect of protective management on fish traits is less explored. We used a time-series modelling approach to simultaneously evaluate the abundance, biomass, and traits of eight fish families over a chronosequence spanning 44 years of protection. We constructed a multivariate functional space based on six traits known to respond to management or disturbance and affect ecosystem processes: size, diet, position in the water column, gregariousness, reef association, and length at maturity. We show that biomass increased with a log-linear trend over the time-series, but abundance only increased after 20 years of closure, and with more variation among reserves. This difference is attributed to recovery rates being dependent on body sizes. Abundance-weighted traits and the associated multivariate space of the community change is driven by increased proportions over time of the trait categories: 7–15 cm body size; planktivorous; species low in the water column; medium-large schools; and species with high levels of reef association. These findings suggest that the trait compositions emerging after the cessation of fishing are novel and dynamic.

Linking key human-environment theories to inform the sustainability of coral reefs

“…Indeed, parrotfish scraping potential was the least sensitive to all drivers in our model, and herbivorous fish have been shown to continue to support reef fisheries and nutrient yields on heavily disturbed reefs 75 . As expected marine reserves had a positive effect on most of the metrics, but was weak for trait diversity where traits may respond differentially to protection, highlighting the importance of uncovering how individual traits respond to marine reserves 76 . While the presence of top predators, fish biomass, and fish trait diversity peak at intermediate HDI values, parrotfish scraping potential declines gradually with increasing HDI, suggesting this important ecological function has greatest potential in lower developmental settings.…”

Piscine predation rates vary relative to habitat, but not protected status, in an island chain with an established marine reserve

“…A deeper quantification of the fish community could reveal changes in predation within the MPA especially at the higher trophic levels likely to have the most benefit from a harvest ban. It took decades for an effect of protection to emerge in a traitbased analysis of small to medium sized fish like those that dominated our experiment (Hadj-Hammou et al, 2021). However, other work suggested an increase in similar size classes as a weak compensatory response from decreased predation as larger fish are harvested over shorter timescales (Dulvy et al, 2004).…”

“…As no-take MPAs increase the biomass and diversity of marine life, they can cause trophic cascades as predator populations recover from outside fishing pressure. Top-down control is a primary driver in reef fish community structure (Terborgh and Estes, 2013), MPAs protect exploited higher-level predators, and the functional traits and trophic level of an ecosystem can track recovery better than abundance trends (Coleman et al, 2015;Hadj-Hammou et al, 2021). In areas with long-term overharvest of piscine predators, MPAs are more likely to have higher levels of predation and maintain top-down control of the ecosystem (Boada et al, 2015).…”