UC Santa Barbara

Marine species are under mounting threat from stressors associated with climate change, such as ocean acidification and warming. Extreme events such as marine heatwaves (MHWs) are also forecasted to increase in frequency, intensity, and duration. The environment varies greatly with regard to the factors associated with these climatic stressors. Parameters of the physical environment are heterogeneous spatially across gradients associated with marine macrophytes such as kelp forests, and variable across time associated with regular cycles such as seasons, and events such as upwelling or MHWs. Therefore, in this dissertation, I investigated whether this physicochemical variability associated with kelp forest ecosystems or MHWs can drive transgenerational effects in marine invertebrate larvae exposed to stressors associated with climate change (temperature and pH). Early life history stages are believed to be particularly vulnerable to the stressors associated with global change, therefore I focused my investigations on the early larval stages of two marine invertebrate species of ecological and commercial importance: the purple urchin, Strongylocentrotus purpuratus and the green-lipped mussel, Perna canaliculus. First, I monitored the conditions inside and outside a kelp forest environment in the Santa Barbara Channel (SBC) and investigated the maternal effects of conditioning S. purpuratus inside and outside the kelp forest for 6 months spanning gametogenesis. pH and temperature were slightly elevated and more predictably variable inside the kelp forest as compared to outside. After acclimation, the urchins were spawned and their larvae were raised under high and low pCO2 conditions in lab to assess their physiological response to the maternal and developmental environments. Larvae from outside conditioned mothers were more resilient to an additional stressor in the form of an acute thermal tolerance trial, and tended to have more skeletal development than those from inside conditioned mothers. Two experiments were also conducted to explore the paternal effects of simulated MHWs, on P. canaliculus aquaculture in the Marlborough Sound region of New Zealand, which has suffered devastating MHW events in recent years. In the first experiment, I exposed male P. canaliculus to an acute 1-week exposure to MHW or ambient temperatures and then raised their larvae under warm of ambient temperatures to the veliger stage. Paternal and developmental heat exposure had a negative impact on successful development of the larvae, but veliger larvae from heat exposed fathers had the highest thermal tolerance in a lethal tolerance assay. In the final experiment, I conditioned P. canaliculus males from wildtype lineages and lineages selectively bred for heat tolerance to a chronic 1-month exposure to a slightly lower MHW temperature in order to investigate the interaction between selective breeding and paternal effects. Elevated paternal and larval temperatures had negative impacts on successful larval development and size for larvae from both selectively bred and wildtype lineages. Overall, the results of this dissertation indicate that heterogeneity in abiotic factors can have transgenerational effects through the maternal and paternal line with consequences for how key marine invertebrates respond to stressors associated with global change. It will be critical to consider the impact of natural gradients on plasticity and how transgenerational effects can be used to inform aquaculture practices to mitigate the effects of MHWs.