MEIOFAUNA AND SOLUTE TRANSPORT IN MARINE MUDS

Meiofauna typically inhabit sedimentary zones having substantial concentration gradients in biogeochemically important solutes such as O2. Diffusion experiments with the conservative tracers Cl- and Br- demonstrate that natural populations of meiofauna (approximately 30-100 cm-3) can increase transport rates of these solutes by factors of approximately 1.7-2.3 x (for T > 10-degrees-C) compared with uninhabited sediments. The effect varies seasonally, directly with temperature and probably with faunal composition. About 20-40% of the increase in transport is due to increased porosity (decreased tortuosity) caused by meiofaunal activities and would be accounted for in most estimates of diffusion. The remaining, larger portion, is apparently due more directly to biologically induced fluid motion and three-dimensional diffusion. Transport coefficients can be resolved into two components with apparent activation energies of approximately 3 and approximately 10 kcal mol-1 (Q10 approximately 1.2 and 1.8, T = 10-degrees-20-degrees-C), consistent with control by physical and metabolic processes. Measurements following addition of particular meiofaunal groups to otherwise natural populations suggest that nematodes, juvenile bivalves, and polychaetes have the greatest effect. Transport activities of meiofauna must stimulate solute fluxes and reaction rates, particularly aerobic decomposition and associated processes such as nitrification in the oxic zones of marine sediments. In contrast, macrofauna commonly enhance solute transport to a greater extent (2-10 x) than do meiofauna and, while stimulating aerobic reactions, also dramatically promote anaerobic processes in organic-rich deposits.