Gulf of Alaska | Ecosystem Perspectives
Food for thought: Bottom-up consequences of climate change at high latitudes Presenter: Lily Westphal , lily.westphal@gmail.com, University of California Santa Cruz
Lauren Bell , laebell@ucsc.edu, University of California Santa Cruz Kristy Kroeker , kkroeker@ucsc.edu, University of California Santa Cruz
In the North Pacific, little is known of how seasonal environmental variability may overlap with environmental change to affect species interactions. Changing environmental conditions associated with anthropogenic CO2 emissions may alter seaweed productivity, nutritional quality, and chemical defenses. We investigated whether seasonal scenarios of future ocean pH and temperature affect the palatability of high latitude seaweeds by measuring their relative rates of consumption and excretion by a common grazer. First, we grew two prevalent subtidal kelp species ( Neoagarum fmbriatum and Hedophyllum nigripes ) in two experiments simulating current seasonal conditions in Sitka Sound (7°C and pHT 7.7 in winter; 14°C and pHT 7.9 in summer) and future projected conditions (+4°C and -0.4 pHT offsets from current conditions). Then, we conducted a series of no-choice feeding assays by feeding these seaweed to a common kelp forest grazer, Strongylocentrotus droebachiensis (green urchin), in non-treatment conditions (~7 °C, ~8.0 pH). The relative consumption of seaweeds grown under different treatments was determined based on urchins’ consumption of gels made from homogenized algal tissue. To assess how relative excretion varied by algal treatment, we quantified total urchin fecal matter in the 24 hrs post-feeding. We found that urchins consumed 30% more of H. nigripes tissue grown in future summer temperature and pH conditions than in current summer conditions. Additionally, relative excretion of H. nigripes tissue grown in winter conditions was over 16% more than tissue grown in summer conditions. We did not observe an effect of any treatment on the trophic interaction between N.fimbriatum and its consumer. The increase in urchins’ consumption of H. nigripes tissue, when grown in future summer ocean conditions, could indicate a decrease in secondary metabolites, causing the algae to be more susceptible to grazing. Further research is needed to understand the underlying difference in excretion by season. The findings of this study demonstrate that climate change stressors may indirectly affect the coastal marine food web through changes in basal resource quality, and that these effects may be seasonally specific.
Alaska Marine Science Symposium 2023 156
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