Coral reef ecosystem functioning: eight core processes and the role of biodiversity

Abstract

Coral reefs are in global decline. Reversing this trend is a primary management objective but doing so depends on understanding what keeps reefs in desirable states (ie “functional”). Although there is evidence that coral reefs thrive under certain conditions (eg moderate water temperatures, limited fishing pressure), the dynamic processes that promote ecosystem functioning and its internal drivers (ie community structure) are poorly defined and explored. Specifically, despite decades of research suggesting a positive relationship between biodiversity and ecosystem functioning across biomes, few studies have explored this relationship in coral reef systems. We propose a practical definition of coral reef functioning, centered on eight complementary ecological processes: calcium carbonate production and bioerosion, primary production and herbivory, secondary production and predation, and nutrient uptake and release. Connecting research on species niches, functional diversity of communities, and rates of the eight key processes can provide a novel, quantitative understanding of reef functioning and its dependence on coral reef communities that will chart the transition of coral reefs in the Anthropocene. This will contribute urgently needed guidance for the management of these important ecosystems.

Synchronous biological feedbacks in parrotfishes associated with pantropical coral bleaching

“…The recent decline of coral reef ecosystems has brought the role of ecosystem functioning to the forefront (Bellwood, Hughes, Folke, & Nyström, ). Bellwood, Streit, Brandl, and Tebbett () defined “function” as the movement or storage of energy or material, which implies that the key to understanding functions is through rate‐based ecological processes (Brandl et al, ). However, many long‐established functional classifications commonly used in the context of coral reefs were derived from observations of “pre‐bleaching, 20th‐century reefs” (Bellwood et al, ).…”

Seasonal variability of calcium carbonate precipitation and dissolution in shallow coral reef sediments

“…While we do not know how the contribution of sediment precipitation/dissolution to total reef accretion might change in future, increasing sediment dissolution will add to total reef dissolution thereby tipping the balance closer to a net erosional reef. If a reef becomes net erosional, it loses its structural complexity that is imperative for a healthy functional ecosystem and may limit its capacity to keep up with future sea level rise (Brandl et al ). To provide an estimate of the sediments' contribution to the overall reef metabolism, we have compared our sediment dissolution/precipitation rates to reef NEC rates from the literature carried out within the same general area as our study (McMahon et al ).…”

A spatially explicit and mechanistic model for exploring coral reef dynamics

“…Most coral models have been developed to describe the effect of external drivers (mainly disturbances) on the state of the coral community (usually total cover) (e.g., Melbourne-Thomas et al 2011a, Madin et al 2012b, Bozec and Mumby 2015, Kubicek and Reuter 2016). In contrast, few models exist that assess the influences of aspects of diversity on community or ecosystem dynamics (e.g., Tam and Ang 2012, Ortiz et al 2014, Fabina et al 2015), but these have represented diversity with limited detail, and consequently have little capacity to evaluate the effects of identity and diversity on ecosystem functioning (Brandl et al, 2019), or the effects of functional redundancy and response diversity on ecosystem resilience (Mcleod et al, 2019). In contrast, our model represents diversity in detail — we considered eleven functional traits and included their influence over eight ecological processes applied to 798 functionally realistic species.…”

“…Our model is the first to implement six functional groups, which accommodated additional ecological details such as grazing preferences and coral-algae interactions (Appendix S2: §2.1 and §6.3, respectively). To date, trait-based research on tropical reef algae is modest compared to fishes and corals (Brandl et al, 2019) and an algal-traits database has not yet been created.…”

“…Disentangling the identity effect (effects of individual species on processes) from the diversity effect (shared effects of a collection of species on processes) is necessary to define which species, functional groups, or aspects of diversity are essential for maintaining ecological processes (Bellwood et al, 2019; Brandl et al, 2019). While the effect of such essential species on ecosystem function and the consequences of their loss has been widely reported (e.g., Hughes 1994, Alvarez-Filip et al 2009, Bellwood et al 2009), the relationship between species richness or functional diversity and ecosystem functioning is still poorly understood.…”