Fisheries productivity under progressive coral reef degradation

Abstract

In response to multiple stressors, coral reef health has declined in recent decades, with reefs exhibiting reduced living coral and structural complexity, and a concomitant rise in the dominance of algal resources. Reef degradation alters food availability and reduces the diversity and density of refuges for prey. These changes affect predator–prey interactions and can have cascading impacts on food webs and fisheries productivity. We use a size‐based ecosystem model of coral reefs that incorporates the influence of structural complexity, benthic primary production and detrital recycling to explore how predator–prey interactions and fisheries productivity respond to a gradient of reef degradation. We show that fisheries productivity overall may be robust to initial stages of reef degradation because the benefits of increased resources outweigh the costs of moderate refuge decline. However, the assemblage composition and size structure of reef fish will differ on degraded reefs, with herbivores and invertivores contributing relatively more to productivity. More significant losses of refuges associated with the erosion of structural complexity correspond to fisheries productivity losses of at least 35% compared to healthy reefs. Synthesis and applications. Our model provides fisheries managers with quantitative predictions about how fisheries productivity may change in response to the ongoing degradation of coral reefs. We predict an initial increase in productivity at intermediate reef degradation, followed by a drastic decline when structural complexity is lost. We also capture subtle changes to potential catch composition and fish size, including increases in smaller herbivorous and invertivorous fish from degraded reefs, which will undoubtedly impact fisheries value. On the one hand, our results reassure for continued productivity in the short term, but on the other, we warn against complacency. Management must change to capture any potential benefits to fisheries, and long‐term sustainability still depends on the maintenance of complex coral reef habitats.

Form and function of tropical macroalgal reefs in the Anthropocene

“…Similarly, a number of herbivorous fishes such as Leptoscarus vaigiensis , Siganus sutor and Naso unicornis have evolved to target the high net primary production of canopy‐forming macroalgae (Choat, Robbins, & Clements, ; Hoey, Brandl, & Bellwood, ; Lim et al, ). These browsing herbivores may exhibit some of the highest known rates of secondary production (i.e., somatic growth) in tropical reef fishes (Morais & Bellwood, ), which can underpin important tropical fisheries (Hicks & McClanahan, ; Robinson et al, ; Rogers, Blanchard, & Mumby, ). We note emerging evidence that suggests microalgae, endolithic algae and bacteria are targeted by some reef fishes (Clements et al, 2017), which further quantitative data may ultimately reveal as a highly productive resource alongside macroscopic autotrophs such as macroalgae and corals.…”

Coral reef ecosystem services in the Anthropocene

“…For example, declines in the structural complexity of reef habitat are often linked to changes in fish communities, with likely impacts on fishery services (Pratchett, Hoey, & Wilson, 2014). However, recent modelling and empirical research suggests that increases in herbivorous fish are able to maintain fishery yields under certain conditions (Robinson et al, 2019;Rogers, Blanchard, Mumby, & Arlinghaus, 2018). The links between ecological change and services may therefore be more complex than originally suggested (Daw et al, 2016).…”

Coral Reef Degradation Differentially Alters Feeding Ecology of Co-occurring Congeneric Spiny Lobsters

“…Reef degradation and its associated loss of complexity may also eventually affect these lobsters in other ways by decreasing available refuge or reproduction sites (Wynne and Côté, 2007;Lozano-Álvarez et al, 2017). Precisely because of these issues, productivity of reef fisheries is expected to decline with increasing coral reef degradation (Rogers et al, 2018). However, this might not necessarily be the case for P. argus given the greater movement ranges and colonization abilities of this species that allow it to use various habitats in addition to coral reefs Briones-Fourzán, 2014).…”