Climate change is reshaping marine ecosystems by altering the abundance and composition of phytoplankton communities. Warming sea-surface temperatures are causing diatoms to decline in abundance, with these species often being replaced by less-carbon rich species. Such changes in phytoplankton community composition will have cascading effects on marine food chains, and disrupt the ocean’s capacity to sequester carbon. Despite the significance of the marine carbon pump, these impacts remain poorly understood.
In a series of laboratory experiments, I investigate how projected shifts from diatom to non-diatom dominated assemblages influence the feeding preferences and population dynamics of marine primary consumers, using a model Australian copepod. I fed experimental populations of copepods different diatom and non-diatom diets (in isolation and combination) and estimated how different phytoplankton diets alter demographic parameters such as intrinsic rates of increase, carrying capacity and size-structure. Feeding trials explored how copepod feeding rates and preferences may drive these observed changes in copepod demography.
Overall, I found that different phytoplankton species affected the demography and feeding behaviour of copepod populations, with implications for marine food webs and carbon cycling. By focussing on phytoplankton and copepod species established in Southern Australia, my research provides valuable regional insight into carbon cycling processes.