Seasonal Dynamics of Faunal Diversity and Population Ecology in an Estuarine Seagrass Bed

Abstract

Biodiversity is important for communities to be resilient to a changing world, but patterns of diversity fluctuate naturally over time. Understanding these shifts — and the species driving community dynamics — is crucial for informing future ecological research and conservation management plans. We investigated the impacts of seasonality, small-scale changes in seagrass cover, and small-scale spatial location on the epifaunal communities occupying a temperate seagrass bed in the South Island of New Zealand. By sampling epifaunal communities using a fine-mesh push net two to three times per season for 1 year, and using a combination of multivariate and hierarchical diversity analyses, we discovered that season, seagrass cover, and the location within the bay, and their interactions, explained 88.5% of the variation in community composition. Community composition and abundances, but not numbers, of species changed over seasons. The most common taxa were commercially important Caridean shrimp and juvenile flounder (Rhombosolea spp.), and both decreased in abundance in summer (shrimp: 1.40/m2 in winter to 0.80/m2 in summer; flounder: 0.15/m2 in winter to 0.01/m2 in summer). Other commercially important species were captured as juveniles, including blue cod (Parapercis colias), kahawai (Arripis trutta), and whitebait (Galaxias spp.). The only adult fish captured in the study were two pipefish species (Stigmatopora nigra and Leptonotus elevatus), which had distinctly seasonal breeding patterns, with reproductively active adults most likely to be found in the spring and fall. Our study highlights the importance of estimating biodiversity parameters based on sampling throughout the year, as some species will be overlooked. We demonstrate that the temperate estuarine seagrass-affiliated animal communities differ in response to season and fine-scale local environments, causing fluctuations in biodiversity throughout the year.