#### Body mass index does not decline during winter for the sedentary marine gastropod Crepidula fornicata Authors: Amanda M. Franklin, Alberto Rivera, Justin Robbins, Jan A. Pechenik File: **data_BMI.csv** Description: Length and weight data used to calculate BMI Column headers: * Shell Length mm: shell length in mm * Dry tissue weight mg: dry tissue weight in mg * Location: location that Crepidula fornicata were collected * Date: date that Crepidula fornicata were collected File: **data_envvar.csv** Description: Environmental data for each collection location and date Column headers: * Date: date that Crepidula fornicata were collected * Location: location that Crepidula fornicata were collected * total measured: number of C. fornicata measured * OISST_daily: daily sea surface temperature in degrees celsius * WebpageSST: source for daily sea surface temperature * Chlorophyll_monthly: monthly chlorophyll a concentration in mg per L * Webpage_Chlorophyll: source for monthly chlorophyll a concentration * SST_Monthly: monthly sea surface temperature in degrees celsius * Webpage_monthlySST: source for monthly sea surface temperature * AirT_MonthlyAvg: monthly average air temperature in degrees celsius * AirT_website: source for monthly average air temperature File: **data_starvation.csv** Description: Data for the starvation experiment conducted in the laboratory Column headers: * Exp: Date experiment was conducted * Treatment: treatment group for individual C. fornicata. Either fielddata (measured immediately upon collection), no food * for 3 weeks or food for 3 weeks. * Shell Length mm: shell length in mm * Dry weight mg: dry tissue weight in mg * Location: location that Crepidula fornicata were collected

Seasonal extremes in environmental conditions can substantially limit the growth and reproduction of animals. Sedentary marine animals are particularly susceptible to winter food limitation since they cannot relocate to more favorable conditions. In several temperate-zone bivalve species, substantial winter tissue mass declines have been documented; however, no comparable studies have been conducted on intertidal gastropods. Here, we investigate whether the suspension-feeding intertidal gastropod Crepidula fornicata also loses substantial tissue mass during the winter. We calculated body mass index (BMI) for individuals collected in New England at different times of year for seven years to determine whether BMI declines through winter or varies seasonally. Remarkably, C. fornicata body mass did not decline significantly during winter months; indeed, a relatively poorer body condition was associated with higher seawater temperature, higher air temperature and higher chlorophyll concentration. In a laboratory experiment, we found that C. fornicata adults that were not fed for three weeks at 6 °C (local winter seawater temperature) showed no detectable declines in BMI compared to field collected individuals. Future studies should document energy budgets of C. fornicata and other sedentary marine animals at low winter seawater temperatures, and the impact of short-term elevated temperatures on those energy budgets.