Meeting Abstract
A number of common and ecologically important marine invertebrates including the sea urchin Lytechinus variegatus inhabit enclosed shallow bays at the northern end of their biogeographic distribution in the Gulf of Mexico. Seasonal high temperature events in these enclosed bays are already capable of inducing physiological stress, and geography prevents this sea urchin from gaining a thermal refuge by migrating northward. Accordingly, it is important to evaluate whether predicted near-future seawater temperatures may induce sub-lethal impacts on feeding and growth that may ultimately reduce the fitness of L. variegatus. Sea urchins were chronically exposed in the laboratory to two temperature treatments, a current ambient temperature (26°C) and a predicted near-future temperature (30°C) (n=12 per temperature treatment) for a total period of 60 days. Sea urchins were fed an ad libitum diet composed of field-collected blades of the seagrass Thalassia testidium every other day. Feeding and fecal production rates of sea urchins were measured every other day and averaged over 10 day periods. In addition, organismal growth was evaluated by recording wet weights for all individuals every 30 days. During the first 60 days of the temperature exposure experiment, there were no significant differences in feeding rates, fecal production rates, or growth of sea urchins held at either 26 or 30°C. However, there was a modest trend that suggested that individuals exposed to 30°C were beginning to lose weight by day 60. Accordingly, the experiment was prolonged and the results of continued exposure will be presented. The findings so far indicate that L. variegatus is able to feed efficiently and sustain growth in the face of chronic near-future elevated seawater temperature for a period of at least two months.
