Resource partitioning by Menidia menidia and Menidia beryllina (Osteichthyes: Atherinidae)

Resource overlap values were calculated for habitat and food utilization by Menidia menidia and M. beryllina in 2 Rhode Island estuaries (USA). Habitat overlap was nearly complete during spring, but declined during summer and fall. Food overlap varied greatly throughout the year. The 2 species coexist because they: (a) overlap strongly in both food and habitat utilization only when food is abundant, and (b) have evolved different spawning times and different growth rates. M. menidia grows to a larger body size than M. beryllina and can utilize different habitats and foods when zoopla.nkton becomes scarce. Time of hatching of each species in the upper estuary was related to cycles of zooplankton abundance M. menidia larvae probably have a substantial predatory impact on zooplankton In the upper estuary during June of each year.