| Summary: | Climate change represents a threat to coastal marine ecosystems through variable effects on community structure and function due to increasing mean sea-surface temperatures (SST), marine heatwaves, variation in salinity, and ocean acidification. Among the most at risk species are California kelps, which have already experienced significant die-offs over the past several years as a result of elevated SST and urchin grazing. However, the effects of these stresses on the very sensitive microscopic kelp life stage (gametophyte) are much less understood. Gametophytes are generally less resilient to changes in abiotic conditions, so global environmental change could result in drastic changes in kelp forest community structure and composition via impacts on this life stage. My dissertation research used manipulative laboratory experiments to investigate the interacting role of abiotic stressors on kelp reproduction and community compositions, specifically, the growth and survival of early kelp life stages. My first chapter focused on the effects of climate-driven temperature increases and ocean acidification on bull kelp (Nereocystis luetkeana) gametophytes from Point Arena, CA (Korabik et al. 2023). From 2014 to 2016, the largest marine heatwave in history appeared off the coast of California resulting in large kelp die off events. In this chapter, I asked how increased temperature and lowered pH impact the survival of bull kelp gametophytes and the production of juvenile bull kelp sporophytes. My results showed that increased temperature resulted in a significant decrease in the survival of gametophytes and a lower number of juveniles produced, whereas lowered pH only had a significant effect on the production of juveniles, slowing their rate of development. These results indicate that the predicted increase of marine heatwaves could have devastating effects on the persistence of bull kelp forest ecosystems. My second chapter considered the interacting effects of climate driven changes in temperature and salinity and ...
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