Context dependency of climate responses in marine communities

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Copyright: Ledet, Janine
Global climate change is predicted to affect ecosystem functions and alter crucial interactions among species. While extensive research has been done on individual species across a range of stressors, less is known on how community responses to climate stressors are context dependent and vary across timescales. Responses may alter among individuals, by effects on interactions with other species, or with recent exposure to stress in an organism’s lifetime or that of previous generations. In this thesis, I measured the response of marine invertebrate assemblages associated with macroalgae to climate stressors, focusing on factors that may alter the magnitude or direction of climate effects. Subtidal macroalgae provide habitat for diverse communities and dominate temperate reefs worldwide. These habitats are some of the most vulnerable to climate stress, with the invertebrates associated with macroalgae critical to ecosystem function. Initially, I measured the combined effects of temperature and diet quality over two generations of the marine amphipod, Sunamphitoe parmerong. When provided their preferred diet, S. parmerong had greater survival at increasing temperatures that contributed to a larger potential population size, an effect not found on other alternate diets. Next, I considered effects of extreme temperatures on the survival of species within the epifaunal assemblage of the brown alga Sargassum across two seasons. Taxa were tolerant to extreme temperatures within the range of a heatwave, however, shifts in species composition between seasons suggests that the timing of stress is crucial. Using S. parmerong as a model, I determined whether trans- and multigenerational effects of prolonged temperature stress could influence individual traits and population survival. The fecundity of offspring from heat-stressed mothers was reduced, with no improvement of brood sizes found after three generations of increased temperatures. While thermal tolerance was greater in heat-stressed populations, further tolerance was not gained over multiple generations. Lastly, I measured how short-term acidification stress altered community composition and abundance. The most abundant taxonomic groups were tolerant to short-term acidification. Overall, factors relevant to ecological context altered assemblage-level outcomes under future climate conditions, emphasizing the need to incorporate these factors in climate research.
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Ledet, Janine
Poore, Alistair
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PhD Doctorate
UNSW Faculty
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