Healthy snack or junk food? Examining the nutritional quality of a marsh prey subsidy to a freshwater and estuarine mesoconsumer in the Southwest Everglades.

In the Southwest Everglades, the movements of fishes are largely dictated by seasonal rainfall patterns. When rain subsides at the onset of the dry season, freshwater marsh floodplains begin to desiccate. This causes marsh aquatic inhabitants to seek out the deepest habitats in the landscape; including first and second order oligohaline creeks. Fish species include both smaller bodied secondary consumers such as dollar sunfishes, bluefin killifish and palemoid shrimp as well as larger bodied fishes like bass (Micropterus salmoides). At the same time an estuarine consumer species, snook (Centropomus undecimalis), triples in abundance presumably to capitalize on marsh prey. When this marsh dry down occurs, these two predators are entirely dependent upon marsh prey (snook primarily consume sunfishes while bass consume cyprinodontoids; both consume invertebrates once fish populations are depleted.) and largely exclude estuarine prey. This reason however, is largely unknown. Consumers may preferentially select prey that maximizes their energetic intake to meet nutritional demands. Thus, the aim of our study was to understand the nutritional quality of estuarine and marsh prey using a stoichiometric approach in order to determine if marsh prey are more energetically/nutritionally valuable than estuarine prey. Defining quality in terms of carbon: nitrogen and carbon: phosphorus ratios, we hypothesize that freshwater prey will have higher C: N and C: P ratios than estuarine prey. Because consumers are preferentially selecting freshwater prey over estuarine prey, we believe that freshwater prey offer some fitness gain that can be linked to energetics or nutrition. A total of 26 species, prey and predator, were sampled to determine their carbon: nitrogen: phosphorus stoichiometric ratios as well as their caloric content. Prey samples were sacrificed while muscle plugs were taken from a subset of predators caught. Our findings may suggest that marsh dry down results in abundant and high quality prey resources for both estuarine and freshwater consumers.