The effect of fishing on hysteresis in Caribbean coral reefs

Abstract

Coral resilience is important for withstanding ecological disturbances as well as anthropogenic changes to the environment. However, the last several decades have demonstrated a decline in resilience that has often resulted in phase shifts to a degraded coraldepleted state with high levels of algal abundance. A major defining issue in current research is to identify when and how it is possible to reverse these phase shifts allowing for the ecosystem to escape coral depletion and maintain coral-based ecosystem services. We extend an analytic model to focus on the effects of overharvesting of herbivorous reef fish in the Caribbean by explicitly including grazer dynamics which introduces feedbacks between habitat and grazer abundance posing constraints on management options excluded in previous studies. This allows us to develop ecosystembased management recommendations for two distinct scenarios of coral reef recovery: The first follows significant habitat damage in response to a large disturbance and the second maintains reef structure but has suffered from events such as coral bleaching. We identify critical fishing effort levels to allow for coral recovery and demonstrate that regions exhibiting severe damage to reef structure have little resilience implying that fishing reductions should be coupled with other restoration methods. Regions that are coraldepleted but maintain reef structure allow for recovery given sufficiently small levels of fishing mortality. However, we demonstrate the difference in recovery time in response to varying levels of control efforts on fishing.

The differential effects of increasing frequency and magnitude of extreme events on coral populations

“…We defined persistence as coral cover remaining above a fairly low cover value, 1%, but corals are no longer reefdominating structures at such low cover. In addition, the long transients in models of this time (Blackwood et al 2012) mean that some of the corals considered persistent at the end of our simulations might not persist under longer time scales. While these decisions were central to FIG.…”

Timescales and the management of ecological systems

“…However, this observation may still understate the nature of the problem if the control parameter is itself one that has inherent biological dynamics. Two particular systems (24,25), one marine and one terrestrial, that have been studied theoretically provide key insights into how temporal scales play an important role in thinking of management of systems that have tipping points and hysteresis.…”

“…However, grazing is a biological process and in the Caribbean is primarily due to feeding by parrotfish (26). In a more detailed study of the dynamics of coral-algal-grazer systems (24), the explicit dynamics of the grazer were included. Then the control (management option) is not an adjustment of grazing levels directly, but changes in fishing pressure, which leads to reductions in mortality for the grazer.…”

Simplifying complexity : reflections on ecosystems, psychiatric disorders and biogeochemical pathways

“…Previous work on alternative stable states on coral reefs includes more elaborate models examining hysteresis (e.g. Mumby et al 2007;Blackwood et al 2010), and the effect of multiple stressors (e.g. Blackwood et al 2011;Fung et al 2011).…”