It's the little things that count: Meiofaunal density and production in the sediment of two headwater streams

Abstract

The distribution of biomass production and its allocation across populations under environmental constraints draw a picture of community dynamics and energy flows in ecosystems. However, microscopic benthic invertebrates (meiofauna) are often overlooked in stream production budgets. We monitored the meiofauna dwelling in the sediment at two headwater stream sites (Ems and Furlbach, NW Germany) during 1 year. The two streams were similar in their granulometries and temperature regimes, but they differed in their flow velocities and nutrient balances, which allowed investigations of the effects of these factors on the density and production of different taxonomic groups of meiofauna. Meiofaunal production in the top 10-cm sediment at Ems and Furlbach was 2.58 and 5.46 gC m−2 yr−1, respectively; these values are among the highest reported so far for a streambed. Allocation of density and production across taxonomic groups differed between the two streams. Tardigrades, rotifers, oligochaetes, and gastrotrichs thrived in the phosphate-rich, slow-flowing waters of the Ems, whereas nematodes, micro-turbellarians, and harpacticoid copepods were better adapted to the nitrate-rich, fast-flowing waters of the Furlbach. Body-size distribution varied across site and depth and was mostly multi-modal, with important contributions of minute individuals weighing between 0.01 and 0.1 μgC. Our study shows that, despite their small size, meiofauna can produce substantial amounts of biomass and should thus be better considered in budgets and models of stream ecosystems.