Seminar: Monday, October 2, 2023

Climate Change Impacts on Reef Fish Spawning Aggregations: Bottlenecks, Tradeoffs, Climate Refugia, and Management Implications:

Most projections of how climate change affect species distributions and phenology are based on a species’ most conspicuous life stage. However, not all life stages are equally sensitive to temperature. Among fishes, spawning adults often have narrower thermal tolerances than other life stages and may constrain population responses to climate change. My collaborators and I explore this within the context of reef fish spawning aggregations formed by groupers (family Epinephelidae) and snappers (family Lutjanidae) in the Greater Caribbean. Many species in these families are of conservation interest since past fisheries exploitation has caused them to be classified as vulnerable, threatened, or endangered species. We show that the spawning habitat of eight representative species can be modeled with a combination of remotely sensed thermal and hydrodynamic variables. Next, we show that the spawning habitat of Nassau grouper (Epinephelus striatus), a critically endangered species, is more sensitive to climate change than habitats used outside its spawning season. By 2081–2100, spawning habitat for this species is projected to decline under high greenhouse gas emissions by up to 82%, whereas suitable habitat for non-spawning Nassau grouper decreased by 46%. Nassau grouper’s narrow thermal tolerance range when spawning indicates that this life stage may be a bottleneck constraining its future distribution. Comparing groupers and snappers, we identified trade-offs in how species reacted to climate change, reflecting differences in spawning phenology. Groupers were projected to be more sensitive to climate, exhibiting larger losses of spawning habitat and greater poleward shifts in distribution. Snappers reacted to changing conditions predominantly by shifting their phenology to spawn earlier. We are examining the implications of these results for ecosystem-based fisheries management strategies, such as marine protected areas (MPAs) and seasonal fishing closures. Many seasonal measures established to protect spawning aggregations may need to be adjusted to continue providing conservation benefits. In contrast, the current configuration of Caribbean no-take MPAs fared better under climate change than surrounding areas due to the presence of climate refugia. Future projections indicate that small, but widely dispersed, MPAs provide better protection of spawning habitat than large MPAs.