Recruitment variability and the Marine Protected Area Effect: Considering multiple life stages in the evaluation of protected areas

Background/Question/Methods

Both ecological theory and empirical data demonstrate that recruitment of marine species is highly variable in space and time as complex biological and oceanographic factors influence the transport and survival of larvae and recruits. The mosaic of recruitment patterns that occur along a coast can provide a particular challenge for evaluating the effect of marine protected areas (MPAs) on the marine communities they are established to protect. For example, if a particularly strong year class recruits to a protected site and associate reference area, this recruitment effect may in fact swamp any ecological effects of setting aside an area from extractive use. Using a decade-long time series of fish recruitment and adult densities in the MPAs of the Channel Islands National Marine Sanctuary (CINMS) and their fished reference areas, our goals were to 1) evaluate the spatial and temporal variability in recruitment of fishes to the MPAs and reference areas, 2) compare these to the observed MPA effect in species response ratios across the diverse sites protected in the CINMS, and 3) use these data to determine the statistical benefit of considering recruitment when evaluating the effect of protection on fish populations in the Channel Island MPAs.

Results/Conclusions

Over the course of the study period, annual variability in recruitment reflected differences in species settling to MPAs and non-protected areas. However, while an additive MPA effect was detected when evaluating the population responses after ten years of protection, adult response ratios varied annually based on lagged recruitment. Our results indicate that the inclusion of recruitment data in the evaluation of MPAs can contribute significantly to the detection of a true MPA effect. Overall, these data underscore the need for long-term monitoring to ensure that MPAs are meeting their intended goal to preserve populations of marine species across year classes.