Investigating the effects of climate co-stressors on surf smelt energy demands

Surf smelt (Hypomesus pretiosus) are ecologically and economically important to the Pacific Northwest. They play a critical role in the food web and support numerous commercially important species and are an economically important baitfish. Surf smelt interact closely with the nearshore environment, utilizing approximately 10% of Puget Sound coastlines for spawning throughout the year. Surf smelt spawn at high tide and adhere fertilized eggs to beach sediment, causing their embryos to be exposed to air and seawater throughout embryonic development. Because of this unique life history, surf smelt may be susceptible to anthropogenic stressors including coastal development and climate change. However, very few studies have attempted to test the tolerance of surf smelt to climate change, including elevated temperature and ocean acidification. The purpose of this study was to examine the interactive effects of climate co-stressors ocean acidification and seawater warming on the energy demands of developing surf smelt. Surf smelt embryos and larvae were collected and placed into experimental basins under three temperature treatments (12 degreesC, 15 degreesC, and 18 degreesC) and two total carbon treatments (ambient and elevated) for a period of 14 days for the embryos, and 4 days for the larvae. Increased temperature significantly decreased yolk size in developing surf smelt embryos and larvae. During this time, embryo yolk sacs in the high temperature treatment were on average 10.2% smaller than embryo yolk sacs in ambient temperature water. Larval yolk and oil globules mirrored this trend with larvae in the high temperature treatment having on average 32.5% smaller yolk sacs and 20.0% smaller oil globules compared to larvae in ambient temperature. While no effect of acidification as a singular stressor was observed, the interaction with temperature significantly increased surf smelt embryo heart rates by 5% above ambient conditions. These results indicate that near-future climate change scenarios are going to impact the energy demands of developing surf smelt, a result that may have a variety of potential impacts including altered hatch times, larval deformities, and increased mortality, all of which will increase interannual variability in adult recruitment. The results of this study highlight the need to increase focus on studying surf smelt in the context of ecological and climate change research.