Biodegradation and Carbon Flow Based on Kelp (Ecklonia maxima) Debris in a Sandy Beach Microcosm

Abstract

Primary decomposition of intertidally stranded kelp Ecklonia maxima in a mixed substrate microcosm is effected by bacteria rather than by fungi. Initial colonisation by cocci to lysis and release of cell contents. Lysed cells are then colonised by bacterial rods. High concentrations of leachates, reaching 5,640 mg carbon1 super(-1) subsequently appear beneath the decomposing kelp. Over 90% of the carbon in these leachates is utilised by bacteria during drainage through a strip of sand 1 m long, 50 cm wide and 12 cm deep, although on an open beach other organisms, e. g. nematodes, may be capable of direct absorption of such organic matter. Calculation of carbon flow via grazing invertebrates and through bacteria shows that 23-27% of the carbon in kelp is converted to bacterial carbon. Estimates of the bacterial carbon in equilibrium with the kelp cast up on the strandline suggest that 1648 g of kelp carbon is deposited per metre of strandline each 8 d.