Effects of the sea urchin<i>Echinocardium cordatum</i>on oxygen uptake and sulfate reduction in experimental benthic systems under increasing organic loading

Abstract

Abstract The effects of the presence of the sea urchin species Echinocardium cordatum on benthic oxygen uptake rates, oxygen penetration depths and sulfate reduction rates were studied in benthic boxcosms (volume ca. 25 1). Boxcosms were enriched by adding a single dose of organic material, collected during a natural spring bloom of Phaeocystis sp. to the sediment surface. Three series of boxcosms without E. cordatum and three series with E. cordatum were enriched with respectively 20, 40 and 60 gC/m2, to study the effect of increasing organic loading. Starved boxcosms (no organic matter supply) were used as a control. All experiments showed a steep peak in oxygen uptake one or two days after organic matter supply. Thereafter, oxygen uptake rates remained relatively constant, at significantly higher rates in the presence of E. cordatum. Increasing the organic load enhanced benthic oxygen uptake. However, under the highest loading, in the absence of E. cordatum, oxygen uptake did not further increase. Oxygen penetration depths showed little variation between different experiments. Sulfate reduction was positively correlated with organic load. Overall sulfate reduction rates were not enhanced by E. cordatum. It was concluded that E. cordatum augments benthic oxygen uptake. Under increasing organic loading, E. cordatum probably has a stimulating effect on both aerobic microbial respiration and reoxidation of reduced inorganic compounds.