Season-specific impacts of two projected climate scenarios on intertidal seaweed communities

Predictions regarding the ecological impacts of future climate change often lack nuance when they rely on studies that focus on a single species under one future scenario. The inclusion of factors such as seasonality, multiple projected climate scenarios, and community-level interactions, which can alter how climate related stressors affect a species, will lead to more holistic and well-informed predictions. Rockweeds, such as Silvetia compressa, whose canopies support diverse understory communities, can have strong responses to climate change when in conjunction with these other factors due to narrow tolerance thresholds and tightly coupled species interactions. Therefore, we chose to assess the impacts of climate change on Silvetia by subjecting simplified Silvetia assemblages to elevated temperature and pCO2 in a mesocosm environment. Due to the uncertainty of future climate trajectories and the potential interactions with seasonality, we tested these stressors under two IPCC projected climate scenarios (RCP 2.6 & 4.5) in both the summer and winter. This was coupled with a field experiment involving Silvetia removal to simulate the effect of climate mediated Silvetia loss on natural assemblages. We found that Silvetia abundance declined under RCP 4.5 in both seasons, and this loss of canopy led to shifts in the understory algal assemblage. In contrast, Silvetia increased under RCP 2.6 in the winter, which resulted in an understory assemblage comparable to those observed under ambient conditions. These results indicate that while most future scenarios will reduce present-day Silvetia communities, some scenarios may lead to their recovery. Given these varied results, future experimental climate change research on similarly structured communities should consider seasonality, multiple climate change scenarios, and species interactions in their designs.

Truong, A., 2023. Season-specific impacts of two projected climate scenarios on intertidal seaweed communities. MSc thesis, San Diego State University, 39 p. Thesis.

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