Increased temperatures impact the reproduction of localized estuarine kelp populations more than salinity or invasive species

ABSTRACT: Estuarine habitats regularly experience large variations in abiotic conditions such as temperature and salinity; however, under climate change and the increasing threat of invasive species, the pressure from both abiotic and biotic stresses has been increasing. Several studies have investigated the interactions of the adult stages of macroalgae; however, there is little understanding of how microscopic stages of Macrocystis pyrifera and Sargassum muticum interact or how climate change may influence this interaction. Our research considers the effects of climate-driven changes in temperature and salinity and their interactions with S. muticum on the growth and survival of M. pyrifera gametophytes from Tomales Bay, CA, USA. Using kelp culturing experiments, we tested (1) how different salinities and temperatures impact early life stages M. pyrifera from different sources within Tomales Bay, (2) how the presence of invasive S. muticum propagules affect M. pyrifera gametophyte development, and (3) how the combined effects of salinity, temperature, and S. muticum presence affect M. pyrifera early life stages. Our results suggest that M. pyrifera may be able to adapt to local conditions like salinity; however, higher temperatures from a changing climate and the presence of competitors from biological invasions act additively, but not interactively, to negatively impact the early life stages of kelp. By determining how foundation species respond to various abiotic and biotic stressors, we can better predict how these species will perform in a changing environment and how they will contribute to overall ecosystem resilience.