Changes in the morphology of widgeon grass (Ruppia maritima) with the onset of reproduction and impacts on fish assemblages at the Chandeleur Islands, LA

Abstract

Seagrass beds are important submerged coastal habitats that support nearshore communities. Ruppia maritima (widgeon grass) is a widespread seagrass species that undergoes dramatic changes in morphology at the onset of reproduction. The goal of this study was to compare fish assemblages associated with reproductive and non-reproductive R. maritima, recognizing the morphological change undergone by the plant when flowering. During the peak reproductive season in August and September 2021, R. maritima meadows at the northern extent of the Chandeleur Islands, Louisiana were sampled to describe the spatial distribution and morphology of reproductive plants and investigate habitat use by fish assemblages. We assessed spatial trends in R. maritima presence and occurrence of reproductive plants and evaluated differences in shoot morphology. We calculated total fish density, Shannon diversity, and species richness to describe fish assemblages in reproductive and non-reproductive meadows. Additionally, general additive models were used to predict drivers of fish assemblage metrics. Results indicate that R. maritima was distributed along the entire length of the sampled area, but reproductive plants were only located in the central, protected portion of the island. Reproductive plants were more morphologically complex with longer shoots, greater surface area, and more leaves, but this did not impact fish assemblages. Rather, fish abundance was related to R. maritima biomass. This study provides information on patterns and drivers of habitat use by fish in R. maritima-dominated ecosystems that can be used to inform management and restoration.