Influence of seasonality and edge effect on seagrass-associated macrobenthic communities: A case study from the Andaman Islands, India

Abstract

Seagrass seasonality and community interactions within a meadow are local-scale ecological measures that inform management, especially in the wake of climate change. We investigated the collective influence of two ecological processes- seagrass seasonality, and edge effect, on the macrobenthic communities in the Andaman Islands, India. Thalassia hemprichii formed two mono-species intertidal meadows, while Enhalus acoroides dominated the mixed-species meadow. The study was carried out across winter (January), summer (April), and monsoon (August) in 2021 using quadrat sampling (0.5 ×0.5 m), where we surveyed the edges, center, and unvegetated micro-habitats within a meadow. Our findings suggest site-specific seasonality trends for T. hemprichii, as seasonality was governed more by the local environment than species. However, seagrass growth was the lowest in summer for both the investigated meadows. Further, we report a differential influence of seagrass seasonality on macrofaunal densities. Infaunal densities were the highest in low seagrass growth (summer), while epifaunal densities positively correlated with seagrass meadow attributes. For both investigated sites, the highest epifaunal densities were observed in winters [Site 1 = 116.8 ± 27.5 ind./m2; Site 2 = 187.8 ± 14.3 ind./m2). Lastly, we report no influence of edge effect on infauna but a little on epifauna, where for the latter, trends were site, season, and group-specific. Epifaunal holothuroids were the only group with a consistent negative edge across sites and seasons, and densities were concentrated in center > edge > unvegetated regions. In conclusion, we suggest that seagrass seasonality is a product of the local environment rather than the species type. Furthermore, seagrass seasonality substantially influenced macrofauna more than the edge effect. This study is the first attempt from the Indian waters to collectively study community responses towards seagrass seasonality and edge effect, filling a critical ecological gap in seagrass research and management in India.