Can marine reserves buffer climate-phenology mismatches?

IMG_0785Assorted rockfishes, Sebastes spp. (photo by Sarah Wheeler)

Climate change is causing shifts in seasonal timing of climatic events and the population-dynamic consequences of these environmental changes is of great interest to applied ecologists. Some populations seem to be adapting by shifting the timing of their life-cycle events (their phenology) like flowering, leafing-out, and producing eggs or larvae. Other populations may not be able to adapt. For example, individuals may not be able to perceive the correct environmental cues (if they even exist) to track changes in the timing of climatic events. Thus, populations which do not track the climate changes may experience some reduction in survival or reproductive output due to mismatches between their phenology and seasonal changes in the environment. One aim of my work is to develop a framework for quantifying the effects of climate-phenology mismatches on population persistence and the yield returned from harvesting populations.

Along with my PhD advisors, Marissa Baskett and Louis Botsford, I applied this framework to a system in which climate change and natural resource use may have non-additive effects on population dynamics and asked which management techniques may mitigate this synergy. The spring transition is a critical seasonal climatic event in temperate marine systems, which initiates atmospheric conditions that drive the wind-driven upwelling of cold, nutrient-rich water that promotes primary and secondary productivity. The surge of productivity caused by the transition to upwelling provides forage (primarily zooplankton such as copepods) for the larvae of many marine organisms, including fishes. Therefore, changes in the timing of the spring transition may lead to reductions in larval mortality due to temporal mismatches between the timing of larval release and the upwelling-driven production of their prey. These mismatches are driven not only by climate change, but also by the act of harvesting. As in many species of birds and mammals, some fishes have maternal-age-dependent offspring traits, affecting the timing of reproduction and the amount of energy provisioned to each of their juveniles at birth. Harvesting a population truncates the age structure, thereby narrowing the distribution of offspring traits and potentially causing or exacerbating mismatches. We quantify the potential for spatial protection with no-take reserves to buffer the synergy between fishing and climate by ameliorating age truncation.

Copepod_MBaquariumFish food: Unidentified copepod (photo courtesy of Monterey Bay Aquarium)

IMG_1872 (2)

In an application to rockfishes (Sebastes spp.), we demonstrated that spring transition timing and maternal-age-dependent larval traits influence fishery harvest and population persistence. These results were due primarily to maternal influences on energy provisioning, as opposed to the influence on birth date. Compared to nonspatial (conventional) management, no-take reserves generally decreased total yield and increased persistence under fishing. Therefore, reserves may provide a buffer against the synergy of harvest and climate change. However, this buffering effect is diminished when environmental variability is included. For species that are not harvested, this result may provide support for alternative management actions that prevent or reduce other forces that disproportionately affect older individuals in species, such as habitat destruction, diseases, and parasites.

Barnett, LAK, Baskett, ML, & LW Botsford. 2015. Quantifying the potential for marine reserves or harvest reductions to buffer temporal mismatches caused by climate change. Canadian Journal of Fisheries and Aquatic Sciences 72(3):376–389.

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