IOS Proposal: RUI: Exploring range limits in the fiddler crab Uca pugnax using the Dynamic Energy Budget approach

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Marine intertidal invertebrates contend with daily cycles of submergence and exposure. As the planet warms, increases in both sea water and air temperature will impact the fitness of these fringe dwellers. This investigation uses Dynamic Energy Budget (DEB) modelling to investigate the impact of food availability and body temperature in both air and water on the energy budget of the mud fiddler crab, Uca pugnax, an abundant and impactful ecosystem engineer. In 2014 mud fiddler crabs appeared for the first time in the salt marshes of New Hampshire, 80 km north of its previous northern range limit, and it is expected to continue to spread north as the north Atlantic warms. This species will have a large impact on the ecosystems it invades because it forms dense colonies that often exceed 100 individuals/m2 and is an intense bioturbator and generalist consumer of infaunal prey. A model will be developed to predict the energetic trade-offs made by mud fiddler crabs under different food and body temperature conditions, which in turn impacts where it can survive and reproduce. This model will be useful for predicting future species ranges for mud fiddler crabs and other intertidal species under different warming scenarios.In the first year of this study, field and laboratory investigations will be conducted across the current species range to determine standard DEB budget parameters, including the shape coefficient, Arrhenias temperatures in air and water, ingestion and assimilation rates, maintenance costs, energy reserves, structural energy content, and the costs of growth. The model will be modified for bimodal breathing, a trait shared by thousands of species living at the sea-land interface, as well as some freshwater species, like lungfish and amphibians. Furthermore, a thermoregulatory correction factor will be developed for the model to explore the energetic costs caused by interruptions in feeding on very hot days when crabs retreat to burrows to avoid overheating. In the second and third years, the DEB model will be developed, tested and applied to questions about energetic constraints and tradeoffs under different environmental conditions and the implications of bimodal breathing for thermal tolerance. This grant will fund academic year and summer research opportunities, as well as, training in mathematical biology for 6-8 undergraduates for each year of the grant from Mount Holyoke College, a primarily undergraduate institution serving women.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.