Using Thermal Performance Curves to assess the effects of temperature on metabolic and feeding rates of Balanus glandula

With the increase in global temperatures and anthropomorphic effects of climate change, it is important to understand how organisms will react to the thermal stress. Thermal performance curves (TPCs) can be useful models to predict how ectotherms might respond to extreme temperatures and calculate their thermal optimum (Topt), where performance peaks. However, most of these are generated in laboratory settings and the constant temperatures may not reflect natural conditions, thus, TPCs require more research to determine how accurately they represent performance in stressful conditions. It is largely unknown how Topts will differ when measuring different performance traits. Additionally, more research should be conducted to see if organisms are adapting their physiological rates to extreme local temperatures. This study focuses on the acorn barnacle, Balanus glandula, which lives in the intertidal range and is exposed to both air and water temperatures due to variations in ocean tides. Because of this unique exposure, barnacles are important organisms to see how terrestrial and aquatic animals may be affected by extreme environments. TPCs can vary based on air and water temperatures as well as the latitudes of the site. This study focused on three sites of varying latitudes and air/water temperatures: Friday Harbor Lab (FHL) in Washington, Bodega Bay (BB) in Northern California, and Los Angeles Harbor (LAH) in Southern California. Previous measurements of metabolic rate and feeding rate of barnacles were used to calculate TPCs and Topts. The Topts were compared across the three sites and two intertidal zones and the time spent over Topt was calculated using 97%ile daily temperature measurements over a twelve month period. I hypothesized that the time over Topt would be significantly different across the three sites, between the performance measured, and across intertidal zones. I predicted that LAH and Upper barnacles would spend more time over their Topt because of the differences in latitudes and exposure to warmer air temperatures. I expected the barnacles would be adapted to their local air temperatures and would have different Topts but still spend a significantly different amount of time over their Topt. As predicted, LAH spent the most time over Topt, and the Upper zone had more days over Topt than the Middle zone. The MR Topts were significantly higher than the FR Topts, which shows how easily TPCs can vary given the measured performance. The results showed the barnacles are locally adapted because the Topts across the sites were different, but each site spent a significantly different amount of time over their Topts. This study suggests that lower latitudes, like LAH, are already experiencing disrupted physiological rates even with their local adaptation, so measures must be taken to reduce their vulnerability to climate change. TPCs are valuable tools to predict thermal sensitivities, but more physiological rates should be tested and compared to determine which measure of performance most accurately models thermal tolerance. This study shows that TPCs can vary based on the air/water temperatures and latitudes of the sites chosen. More research should be conducted across more distant latitudes to further understand the variation of TPCs