Experimental approach toward understanding the role of meiofauna in a detritus based marine food web

The rate of detrital degradation was measured in three model systems maintained in chemostats. Each 1 l reaction vessel contained natural sediment carefully removed from the surface of a salt marsh at low tide. Alternate freezing and thawing killed indigenous organisms in the substrate. At the beginning of each experiment 14C labeled Zostera detritus and filtered (<8μm) microflora dislodged from the surface detritus in a marsh were added to each reaction vessel. Some reaction vessels received additional inocula of Capitella capitata or C. capitata and a mixture of meiofauna. Flow rate was adjusted so that the seawater was replaced daily. Aeration was vigorous. Radioactivity was measured daily in the effluent from the chemostat and in the standing crop at harvest. In all 3 types of microcosms detritus mineralization was initially very rapid and then slowed to an almost steady state. In the reaction vessels with microflora alone, a typical sulfide biome with a redox potential discontinuity layer developed. The vessels with Capitella alone, or with Capitella and meiofauna, were well mixed and aerated. Bioturbation of sediments was greatest in the vessels with meiofauna. Radioactivity during the early phase of detritus mineralization appeared mainly in the particulate fraction of the effluent when approximately 1.5 to 2.0 percent of the original detritus was being mineralized per day. The rate of mineralization was slower (0.1 percent) after the early phase and was twice as great in the vessels with meiofauna than in vessels with microflora alone. The half-life of detritus in the experimental systems was slightly less than 1 yr. Feeding experiments using 32P as a tracer indicated that 2 of the 3 meiofaunal species and their food were not consumed or assimilated in sufficient quantity to be major constituents of the diet of Capitella