Size-spectra analysis in the estuary: assessing fish nursery function across a habitat mosaic

Abstract

Estuaries act as nurseries for a wide variety of fish species, potentially providing vital foraging opportunities and refuge from predation for their juvenile residents. Yet, these dynamic environments are comprised of a mosaic of habitat types that span gradients of both salinity and physical habitat structure. Here, we present a novel use of size-spectra analysis to infer nursery habitat function across the estuary habitat mosaic. Interpreting slope and intercept values of abundance against body mass size-spectra regressions as indicators of predation risk and production, we constructed spectra for six distinct habitat types across the entire tidal influence of an unindustrialized estuary in coastal British Columbia. Based on catches of >200,000 individual fish representing 30 different species from April through September, the estuary rockweed mudflat habitat had the lowest size-spectra slope and highest intercept, consistent with lower predation risk and higher production. Size-spectra coefficients varied seasonally across the ecotone, indicating spatio-temporal variation in key nursery functions. Size-spectra can provide insight into key ecological processes of productivity and predation risk across dynamic aquatic habitats.