Meltdown in Algae Town: Implications of Warming Oceans on San Juan Island Ulva

Abstract

The green alga, Ulva spp., represents a widely distributed and ecologically influential genus of macroalgae that occurs in subtidal and intertidal habitats worldwide. A majority of Ulva spp. have high nutrient uptake rates and rapid growth in nutrient-rich habitats, forming prolific algal blooms known as green tides. The increasing frequency and severity of green tide events has been attributed to coastal anthropogenic eutrophication, particularly as it relates to nitrogen. Previous studies have indicated that high-temperature conditions may affect nitrogen metabolism in Ulva, but further research is needed to understand the impacts and associations between temperature and eutrophication on Ulva growth. The aim of this study was to gain insight into the implications of climate change and consequent increasing ocean temperatures on the proliferation of Ulva and potential for harmful green tide events. Effects of temperature on Ulva were investigated by selecting one individual alga at each of three San Juan Island locations (Eagle Cove, False Bay, and Friday Harbor Laboratories). A total of 9 Ulva discs (314 mm2) were taken from each individual representative to place into three temperature treatments (12ºC- 14ºC, 17ºC-19ºC, and 23ºC-25ºC). Growth of discs was recorded three times during the experimental period. No significant difference in temperature-dependent growth was found based on site. However, the high temperature treatment was found to result in negative growth independent of site. Future experiments should include a larger sample size, investigation of additional abiotic factors and a longer experimental timeframe.