The effects of environmental stressors on intertidal foundation species and their associated communities

As environmental stress increases due to climate change, species and the ecological communities that they comprise will be impacted, in many cases according to species’ abiotic tolerances. Ecological theory predicts that foundation species may become increasingly important for mitigating this environmental stress for the species that associate with them. However, it is often unclear how foundation species will be affected by climate change and if, and how, their ability to facilitate associated species may be altered. Here, I addressed questions stemming from this knowledge gap using field studies of intertidal, sessile invertebrate foundation species using natural and manipulated environmental stressors, primarily within coastal British Columbia, Canada. First, how are foundation species affected by realistic combinations of environmental stressors in situ? I found that an introduced oyster grew more quickly with increasing temperature and — though its survival was reduced by acutely high temperatures — it was not vulnerable to other environmental stressors, possibly because there was no temporal overlap between these and high temperatures. Second, how do foundation species and their associated community respond to extreme events? I found that a heatwave caused substantial mortality of a mid-intertidal barnacle where solar irradiance, and thus substratum temperature, was high and resulted in composition and diversity shifts in barnacle- associated communities. Third, do the impacts of environmental stress on foundation species persist through time? Within a high intertidal barnacle bed, I found that elevated temperatures in one summer had legacy effects on communities during the subsequent summer, likely mediated by differences in barnacle density. Finally, can introduced foundation species have positive effects in their introduced range on species with which they did not co-evolve? I found that high intertidal acorn barnacles, likely due to the generalist nature of their facilitation, can have positive effects in both their native and introduced ranges. Foundation species, while they are able to benefit associated species by buffering environmental stress, are often themselves vulnerable to that stress. By exploring these nuances, my work helps elucidate the importance of considering foundation species when predicting the ecological impacts of global change.Science, Faculty ofZoology, Department ofGraduat