Great Barrier Reef recovery through multiple interventions

Abstract

The decline of coral cover on Australia's Great Barrier Reef (GBR) has largely been attributed to the cumulative pressures of tropical cyclones, temperature-induced coral bleaching, and predation by crown-of-thorns starfish (CoTS). In such a complex system, the effectiveness of any management intervention will become apparent only over decadal time scales. Systems modeling approaches are therefore essential to formulating and testing alternative management strategies. For a network of reefs, we developed a metacommunity model that incorporated the cumulative pressures of tropical cyclones, coral bleaching, predation, and competition between corals. We then tested the response of coral cover to management interventions including catchment restoration to reduce discharge onto the reef during cyclone-induced flood events and enhanced protection of trophic networks supporting predation of CoTS. Model results showed good agreement with long-term monitoring of the GBR, including cyclical outbreaks of CoTS driven by predator-prey dynamics on the network of reefs. Testing of intervention strategies showed that catchment restoration would likely improve coral cover. However, strategies that combined catchment restoration with enhanced CoTS predation were far more effective than catchment restoration alone.

DNA-based identification of predators of the corallivorous Crown-of-Thorns Starfish (Acanthaster cf. solaris) from fish faeces and gut contents

“…Most of these records, however, comprise predation on injured and moribund or dead individuals under experimental conditions, with only a limited number of field observations of predation on early life stages and on healthy, un-injured adults 16 . Despite this lack of field observations of CoTS predation, several independent modelling studies have provided support for the 'predator removal' hypothesis [17][18][19] . Hence, a more comprehensive understanding of coral reef organisms that prey on live CoTS in the field, including on early life stages, is critical to inform active intervention in predation pressure to mitigate CoTS population outbreaks.…”

Split spawning increases robustness of coral larval supply and inter-reef connectivity

“…In conclusion, we found that split spawning events could increase the robustness of larval supply to coral reefs. Such considerations may increase in importance as the GBR faces an increasingly uncertain future of escalating intensity and severity of disturbances 6,43,56–59 . Allee effects may become more frequent as densities of coral populations decline, exacerbating potential reproductive costs of split spawning.…”

Where the Ecological Gaps Remain, a Modelers' Perspective

“…As we outline above, nested network approaches are also helping to link understanding of interactions and connectivity across processes, space, and time (Pilosof et al, 2017). As an example, to support management of the deleterious impacts of crown of thorns starfish on Australia's Great Barrier Reef coral communities, ecological models are being integrated across a range of scales accounting for finescale Allee effects (Rogers et al, 2017) through to embedding an ecological model in a meta-community reef network model incorporating large scale processes such as cyclone and terrestrial runoff from agriculture practices (Condie et al, 2018).…”