Evaluating otolith microchemistry as a method to distinguish habitat-use patterns in marsh-resident fish

Cyprinodontiform fishes are dominant in marshes, but the patterns of habitat use can vary among species as well as life history stages. Therefore, when evaluating their potential as sentinel species, specifically responses to environmental stressors (e.g., oil spills), it is important to consider the temporal and spatial distribution of these highly localized fish within different marsh subhabitats (marsh edges, creeks, ponds, and depressions). Our recent work indicates the four most abundant cyprinodontiformes in Louisiana marshes are gulf killifish (Fundulus grandis), diamond killifish (Fundulus xenicus), sheepshead minnow (Cyprinodon variegatus), and sailfin molly (Poecilia latipinna). While the abundance of these fish in ponds and depressions is high, only a small portion (<1%) occur along the marsh edge. Fish in these subhabitats can be exposed to varying levels of temperature, salinity, and trace metal concentrations. These three factors control the uptake of trace elements into the otoliths of fish, an uptake that occurs in daily growth increments and provides a record of the fish’s chemical environment. Our objective was to determine if the otoliths of fish from different marsh subhabitats have distinguishing elemental signatures. The chemical compositions of 200 sagittal otoliths from the four fish species mentioned above were analyzed. Fish were collected across four subhabitats in marshes near Chauvin, Louisiana.