Quantitative comparison of clamworm (Perinereis aibuhitensis) and crab (Macrophthalmus japonicus) burrowing effects on nitrogen and phosphorus dynamics at the sediment–water interface

Abstract

Exploring nitrogen and phosphorus dynamics in estuarine ecosystems is of great significance for understanding the nutrient cycle in terrestrial and marine ecosystems. However, the ecological functions of common species remain unclear because there is a dearth of observational data. To quantitatively compare the bioturbation effects of the clamworm Perinereis aibuhitensis and crab Macrophthalmus japonicus on the migration of nitrogen and phosphorus in the sediment–pore water–overlying water interfaces, an indoor experiment was carried out using microcosms containing substrate, water, and living specimens collected from the Dagu Estuary, China. The physical structure of the sediments was greatly altered by both clamworms and crabs, and the amount of suspended particulate matter in the overlying water was in the order: crab > clamworm > control groups. Sediments, especially the 0–2 cm layer, were continuously mineralized under bioturbation, releasing NH3-N, NO2−-N, NO3−-N, and dissolved total phosphorus. During the experiment, the release rate of NH3-N (2.45 mg L−1 to 10.23 mg L−1), NO2−-N (0.25 mg L−1 to 7.34 mg L−1), NO3−-N (0.02 mg L−1 to 6.03 mg L−1), and dissolved total phosphorus (0.07 mg L−1 to 0.16 mg L−1) in the crab group was higher than that in the clamworm group (NH3-N, 0.93 mg L−1 to 6.11 mg L−1; NO2−-N, 0.51 mg L−1 to 6.18 mg L−1; NO3−-N, 0.01 mg L−1 to 5.24 mg L−1, and dissolved total P, 0.04 mg L−1 to 0.08 mg L−1). Our findings indicate that crabs might play a more important role in promoting nitrogen and phosphorus migration than clamworms because of their stronger bioturbation strategies in sediments. Bioturbation by both clamworms and crabs reduced nitrogen and phosphorus accumulation in surface sediments and accelerated organic matter mineralization in the sediments, which may promote nutrient recycling in estuarine ecosystems.