Growth and abundance of Fundulus heteroclitus and Menidia menidia in estuaries of Waquoit Bay, Massachusetts exposed to different rates of nitrogen loading

To assess the effect of land-derived nitrogen loads on fish populations, we estimated the abundance and growth rate of Fundulus heteroclitus and Menidia menidia, the most common fish species found in estuaries of Waquoit Bay, from June through September in 1996, 1997 and 1998 in six estuaries subject to different rates of nitrogen loading. Abundance of F. heteroclitus was greater in estuaries with greater nitrogen loading rates, but growth rates of F. heteroclitus obtained from growth rings on scales and otoliths did not vary among estuaries. Abundance and growth rates of M. menidia did not change with increased nitrogen loading rates. Increased nitrogen load may increase abundance of some fish species within an assemblage but not others. Such bottom up controls are effective at producer trophic levels, but appear to be less pervasive with secondary consumers. Higher trophic levels, therefore, may only be loosely coupled to nutrient supply rates.