Behavioural patterns of the soft-shell clam Mya arenaria: Implications for benthic oxygen and nitrogen dynamics

Abstract

It is well established that benthic infauna alter sediment biogeochemistry, but the importance of their behavioural patterns in biogeochemical processes has only recently been fully appreciated. Using arrays of O2 microoptodes, siphon imaging, accelerometer loggers and different incubation approaches, we investigated the importance of behavioural patterns of the soft-shell clam Mya arenaria for benthic O2 and nitrogen dynamics. The investigations resolved a new behavioural component of buried M. arenaria: pedal water ejection (PWE). During PWE, the clams contracted their valves while briefly closing the siphon to expel oxic water previously accumulated within the mantle cavity through the pedal gape. Consequently, an upward-moving oxic plume embedded most of the shell, and oxia at the shell−sediment interface was observed for 15% of the total time of investigation. The buried clams displayed 2 additional behavioural stages: resting (R) and ventilation (V) that occurred for 57 and 28% of the time, respectively. During the V and PWE stages, the siphon of the clam was elongated above the sediment surface and surrounded by a dynamic oxic halo; both behavioural stages thus markedly increase the sediment oxygenation. The resolved irrigation patterns enhanced the benthic exchange of O2 and NH4+ as well as the benthic denitrification rate, presumably via increased benthic NO3− supply and production. Particularly, the extensive sediment irrigation induced by the PWE stage has important implications for benthic nutrient cycling as well as for sediment oxidation and biogeochemical function of coastal sediments.