UWB The CROW, 2016 75 EXAMINING THE EFFECTS OF DIFFERENT DIETS AND SALINITIES ON COPEPOD POPULATION GROWTH Martha Raymore 1,2 and Megan Dethier 1 1.Friday Harbor Laboratories, University of Washington, Friday Harbor, WA 98250 2 School of Interdisciplinary Arts and Sciences, University of Washington, Bothell, 98011 ABSTRACT: The coastal oceans are subject to climate impacts leading to sea level rise, increases in the frequency and intensity of storms, and increased precipitation. These events can lead to a rise in the amount of fresh water entering coastal ecosystems from runoff or rainfall, which cause decreases in ocean salinity. Understanding marine food web dynamics requires an understanding of how species interactions will respond to environmental changes of this kind. Sea urchins are key members of nearshore food webs and may help to link food availability between shallow and deep zones along coastal areas. Sea urchins posess a very ineffcient digestive system, which means that their feces may possess large amounts of available nutrients which other organisms can use as a viable food source. This research studied the population growth of T. californicus copepods in both low salinity and normal seawater environments, and with diets of either fresh Ulva or urchin fecal Ulva. The calorie content for these different diets was also examined. Results show that both diet and salinity signifcantly affected population growth, low salinity is the better environment, and fresh Ulva is the better diet. C limate change is affecting coastal environments in many ways, but one of the major concerns is its effects on ecosystems, as deterioration of marine community structure is increasing (Doney et al., 2012). Coastal ecosystems are sensitive to sea level rise, changes in the frequency and intensity of storms, and increased amounts of precipitation (Harley et al., 2006). In the coming years we may see heavier rainfall, which in turn can lead to increased amounts of runoff into the ocean, and decreases in ocean salinity (Curry & Mauritzen, 2005). In this rapidly changing marine environment, population-level shifts are occurring, which decrease stability and recovery potential and can lead to altered species interactions in coastal systems (Hallegraef, 2010; Worm et al., 2006). Within marine habitats, primary producers like benthic algae and phytoplankton are essential to the food web, as they constitute the base on which all other species rely for energy. The next trophic level contains consumer organisms like zooplankton, including copepods, which eat phytoplankton. Further up this web are a variety of fsh species that depend on zooplankton for their main food source (Richmond, Wethey, & Woodin, 2007). Food web dynamics are driven by the nature and abundance of primary food sources that are available to these higher trophic levels (Wallner-Han et al., 2015). Understanding these feeding dynamics requires an understanding of how species interactions will respond to environmental changes such as salinity (Norkko et al., 2007). Coastal ecosystems have particularly complicated food webs. There are two distinct sources of primary production: phytoplankton and benthic macroalgae. Much of the organic matter entering the benthic food web derives from this material sinking to the deep subtidal Research Paper