For many species, reproductive failure may occur if abundance drops below critical Allee* thresholds for successful breeding, in some cases impeding recovery. At the same time, extreme environmental events can cause catastrophic collapse in otherwise healthy populations.

Understanding what natural processes and management strategies may allow for persistence and recovery of natural populations is critical in the face of expected climate change scenarios of increased environmental variability.

This study used a spatially explicit continuous-size fishery model to investigate whether the establishment of a system of marine protected areas (MPAs) can prevent population collapse, compared with nonspatial management when populations are affected by mass mortality from environmental shocks and subject to Allee effects.

The authors found that MPA networks dramatically reduced the risk of collapse following catastrophic events, while populations often continued to decline in the absence of spatial protection. It was found as well that similar resilience could be achieved by closing the fishery immediately following mass mortalities but would necessitate long periods without catch and therefore economic income.

It is concluded that for species with Allee effects, the use of protected areas can ensure persistence following mass mortality events while maintaining ecosystem services during the recovery period.

*Lower breeding success at low densities. The most dramatic consequence of Allee effects is the negative per capita population growth when a population drops below a critical density threshold, further lowering abundance and growth in a negative feedback loop or “extinction vortex”.

Aalto et al. (2019) Catastrophic mortality, Allee effects, and Marine Protected Areas. American Naturalist 193:391-408.