Habitat modification mediated by motile surface stirrers versus semi-motile burrowers: potential for a positive feedback mechanism in a eutrophied ecosystem

• Published in: Marine ecology. Progress series (Halstenbek) 2009-02, Vol.376, p.21-32
• Main Authors: Viitasalo-Frösén, Satu, Laine, Ari O., Lehtiniemi, Maiju
• Format: Article
• Language: English
• Subjects: Animals; Density; Fauna; Marine ecosystems; Moisture content; Nutrients; Sea water; Sediments; Taxa; Turbidity
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps07788

We performed a 4 wk laboratory experiment with the semi-motile burrowersMacoma balthicaandMarenzelleriaspp. and the motile surface sediment stirrersMonoporeia affinisandMysis mixtato study their effects on the transport of tracer particles (mean diameter [Ø] 1 μm) in the sediment, sediment parameters (depth of the oxidized layer, water content, organic matter content), water turbidity, and nutrient fluxes across the sediment-water interface (PO₄3–, NO₂⁻ + NO₃⁻, NH₄⁺; measured weekly). Two densities were included for each taxon, representing a low and a high field density.M. balthicasignificantly increased particle mixing, the rates being 59.6 and 61.9 × 10–3cm² d–1. While all taxa increased turbidity in the overlying water, the strongest effects were caused byM. affinisandM. mixta, resulting in 112- and 45-fold increases, respectively. In addition, these 2 motile species increased oxidation of the sediment surface layers. A distinctive difference in the nutrient fluxes was observed between the semi-motile (M. balthica, Marenzelleriaspp.) and the motile taxa (M. affinis, M. mixta). The former increased the efflux of both PO₄3–and NH₄⁺, while the latter suppressed the efflux of NH₄⁺ and decreased the sediment uptake of NOₓ, indicating enhanced N removal. Higher nutrient exchange rates were observed at the higher animal densities. We conclude that a shift in the benthic communities from the 2 motile to the 2 semi-motile taxa, observed throughout the northern Baltic Sea, may notably alter the regime of benthic nutrient cycling and thereby the performance of the entire ecosystem.