Historical data on density and biomass of the meiofauna in sandy beaches of the Belgian coast as a baseline for future research

Abstract

Climate change and other anthropogenic pressures increasingly affect coastal systems worlwide. Much of the biodiversity in these areas is found at microscopic scales, within meiofaunal com- munities inhabiting the sediment. These small, benthic organisms play key roles in i.a. nutrient cycling, organic matter decomposition, and energy transfer–and have even been proposed as promising bio-indicators. However, little is known about how these communities are structured, or respond to environmental change. Here, we present a unique historical dataset of meiofaunal communities at the Belgian coast. Six beaches (Het Zwin, Knokke, Oostende, Bredene, Mariakerke, Heist), were monitored bi-monthly from 1984 to 1985. Diversity, densities and biomasses of all major meiofaunal groups were recorded, including soft-bodied taxa often missed in surveys. Meiofaunal densities varied across seasons and across localities, concurring with differences in sand granulometry. Generally, a vertical zonation was observed in the distribution of meiofaunal organisms, with specific taxa in deeper, reduced layers, and seasonal downward migrations in winter. Individual dry weights also differed between localities, with nematodes generally contributing most to total biomass, followed by turbellarians, harpacticoids, and gastrotrichs. Turbellarian flatworms, while often understudied, made up an important component of all inter- stitial meiofaunal communities, with acoels and proseriate flatworms dominating exposed beaches, and kalyptorhynchs thriving in the more sheltered areas. Overall, this study provides a new reference for Belgian beach meiofauna. We are optimistic it can serve as a baseline for much-needed beach health assessments in this area, and pave the way for meiofauna-based monitoring efforts.