Detection of decreased quantities of actively spawning female Fundulus heteroclitus in tidally restricted marshes relative to restored and reference sites

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Hydrologic restriction of salt marshes and subsequent invasion by Phragmites australis could influence the reproductive success of Fundulus heteroclitus, a common salt marsh resident that forages and spawns on the marsh surface at flood tide. Previous research in our laboratory using data from 2010 to 2011 examined the proportion of actively spawning F. heteroclitus residing in altered New England salt marshes as part of a larger experiment to examine the physiological condition of fish in restricted and restored marshes relative to paired unrestricted (reference) sites. We detected a significant decrease in the proportion of actively spawning fish in restricted relative to paired unrestricted marshes, but no difference between restored and paired unrestricted marsh fish. In this manuscript, we conduct a re-analysis of a portion of that data (July 2011) to explore potential mechanisms behind previous results. Using forward stepwise selection and generalized linear mixed models, we determined that the reduction in actively spawning restricted marsh fish was due to a single predictor (lipid mass); there were no effects of water temperature, body size, parasite prevalence, parasite density, and growth rate on the response. Previous results indicate healthy restricted marsh fish already have reduced energy reserves. Since investment in oocytes is energetically costly (this analysis), the effect could manifest at the population level as a reduction in actively spawning fish. In addition, oocyte quality is reduced in restricted marshes (as measured by % lipid; 13.9 ± 1.6 % SD) relative to paired unrestricted marshes (15.9 ± 2.3 % SD). Although these data are preliminary and represent a single lunar cycle, additional studies are warranted to explore relationships between P. australis invasion, restoration, and effects on the fecundity of this ubiquitous salt marsh fish.

Publication Title, e.g., Journal

Biological Invasions