Role of Macrodetritivores — Detritus Trophic Relationships in Phosphorus Dynamics at the Marine Water-sediment Interface: Laboratory Experiments Using 32P
We investigated the combined effects on sediment 32P uptake of bioturbation and particulate detritus processing by macrodetritivores in laboratory microcosms. Sediment and sediment + detritus microcosms were set using sediment and vascular plant detritus sampled in northwestern Adriatic Sea. The effects of macrodetritivores at the water-sediment interface were tested by adding to microcosms individuals of the amphipod Gammarus insensibilis in different densities (541 and 1624 individuals m−2, respectively). In defaunated controls, plant detritus caused a significant positive variation in sediment 32P adsorption rates (ca. 40% increase). Under “sediment only” conditions, the presence of macrodetritivores stimulated both uptake and diffusion of the radiotracer in sediments. Furthermore, the analysis of water-amphipod concentration factors highlighted an effective inability of macrodetritivores to feed upon the finest organic particles constituting the bulk of sediment organic matter. Excluding any significant trophic interaction with the clayish matrix, amphipod bioturbation activity at the water-sediment interface resulted decisively in affecting 32P dynamics. On the other hand, under “sediment + detritus” conditions, amphipod processing of plant detritus determined a significant, animal densityrelated increase of dissolved 32P originally immobilised by detritus and/or sequestered by the microbial component.
Our experimental investigation highlighted a clear “short-circuiting” effect of the detritivores-detritus trophic interaction on benthic phosphorus dynamics, potentially significant also in natural environments. In this perspective, phosphorus regeneration in coastal systems, conventionally related to abiotic factors and microbial mineralization, might result strongly influenced also by macrodetritivores trophic exploitation of allochthonous detritus.
KeywordsPositive Variation Plant Detritus Microbial Mineralization Coastal Marine System Phosphorus Regeneration
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