Biological pumps at the sediment-water interface: Mechanistic evaluation of the alpheid shrimp Alpheus mackayi and its irrigation pattern

Deep-burrowing crustaceans are common on all coasts. In a series of model experiments conducted at the Hawaii Institute of Marine Biology from March to October 1977, the effect of the alpheid shrimp Alpheus mackayi Banner and Banner, on material fluxes across the sediment-water interface has been determined. Viewed as a biological pump, the shrimp's irrigation pattern was not random, but intermittent, with a mean period of 6 min activity and 16 min resting. Plume velocities between 1 and 18 cm s^–1 were measured by seawater-resistant hot-wire anernometry at the apertures of active burrows. Based on 55 h of velocity data, mean hourly pumping rates of 0.35 liters h^–1 were calculated, with an average mechanical energy of 4000 erg h^–1 dissipated by burrow-wall friction and plume mixing. In microcosm experiments with 177 cm² sediment surface area and 120 cm² burrow-system surface, the pumping of one shrimp enhanced the release of silica from the pore water by an average factor of 5 compared to concentration gradient-driven flux across the sedimentwater interface in a control core with the same dimensions but without a shrimp. Our data suggest that real-world models of interfacial fluxes without inclusion of the macro-infauna as biological pumps will be unrealistic.