Gulf of Alaska | Lower Trophic Levels DOCTORATE ORAL PRESENTATION Seaweeds’ seasonal sweet spots: current production and future responses of kelps within high latitude Macrocystis beds
Presenter: Lauren Bell , laebell@ucsc.edu, University of California Santa Cruz Kristy Kroeker , kkroeker@ucsc.edu, University of California Santa Cruz
Environmental change in high latitude oceans will overlay onto the distinct seasonality of these environments. Our knowledge of how such environmental variability and change will interact to affect kelp productivity in these regions is limited. This is a concerning knowledge gap given the importance of macroalgae as an energy source in Alaska’s coastal ecosystems. The lack of data is particularly evident for the macroalgal communities associated with the globally abundant giant kelp Macrocystis pyrifera , which has been studied extensively at lower latitudes but rarely considered at the polar edges of its range. To assess the relative production potential of giant kelp forests at their high latitude fringe, we conducted a multi-year field study of the growth and turnover dynamics of M. pyrifera and co-occurring understory kelps Hedophyllum nigripes and Neoagarum fimbriatum in Sitka Sound, Alaska. We then grew these kelps in the lab within seasonally relevant scenarios of light and nutrient availability under current vs. end-of-century projections for temperature and pCO2. We found that Macrocystis beds in Southeast Alaska produce an estimated ~150 g C · m-2 · yr-1 and turnover an estimated 2.1 times per year. These are substantially lower rates than have been observed at lower latitudes. Based on manipulative experiments, carbon production of high latitude giant kelp was unaffected by end-of- century temperature and pCO2 conditions regardless of season. In contrast, the more poleward-occurring understory kelps exhibited reduced growth and nutritional content under elevated future summer temperatures. This research represents the most rigorous consideration of year-round kelp production in Southeast Alaska to date, providing a valuable quantification of kelp carbon cycling potential in this highly seasonal environment. Moreover, our results indicate that the relative production and quality of different co-occurring kelp species are likely to shift in the future. Such changes could have ‘bottom-up’ trophic consequences for many marine species that rely on diverse macroalgal communities to meet their metabolic needs across seasons. Further, our findings have notable implications for aquatic resource managers and the burgeoning seaweed mariculture industry as they anticipate the effects of environmental change on kelp productivity in this region.
Alaska Marine Science Symposium 2023 11
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