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

Abstract

Primary decon~position of intertidally stranded kelp Ecklonia maxima in a mixed substrate microcosm is effected by bacteria rather than by fungi, which are generally reported to be responsible for the initial decomposition phases of debris in other habitats. Initial colonisation by cocci along the junctions of epidermal cell walls leads to lysis and release of cell contents. Lysed cells are then colonised by bacterial rods. High concentrations of leachates, reaching 5640 mg carbon 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. This relationship occurs despite wide variations in direct consumption by grazers, since much of the consumed material is returned to the microcosm as faeces. 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 and that this is capable of supporting a bacterial production of 444.9 g carbon m-' of beach per 8 d cycle; this accords well with recent observations on the biomass of bacteria in the beach itself. The residual 73-77 % of kelp carbon which is not incorporated ~n t o bacteria is mineralised by the sand beach microbes within 8 d. The microbial community thus occupies a central role in the rapid regeneration of inorganic materials necessary to support the characteristically high primary production of the kelp bed.

Annual cycle of wrack supply to sandy beaches: effect of the physical environment

“…Low wave energy on the beach front causes a reduction in flow, which creates more favourable conditions for stranding wrack material. The wide spatial variability in wrack biomass in this study is consistent with the extremely diverse data published on algae and seagrasses stranded on beaches: in South Africa, 2179 kg m -1 yr -1 (StentonDozey & Griffiths 1983), 1200 to 1800 kg m -1 yr -1 (Koop et al 1982) and 2920 kg m -1 yr -1 (McLachlan & McGwynne 1986) have been reported; 1000 to 2000 kg m -1 yr -1 have been reported in islands in the Gulf of California (Polis et al 1997); 473 kg m -1 yr -1 in southern California, (Hayes 1974); 60 kg m -1 yr -1 in Canada (Wildish 1988); 0.7 kg m -1 yr -1 in Kenya (Ochieng & Erftemeijer 1999); and in Australia, from 360 to 2900 kg m -1 yr -1 for macroalgae and from 900 to 1800 kg m -1 yr -1 for seagrass (Hansen 1984). Besides the inherent geographical variability and the fre- quency of resuspension and redeposition, which may complicate deposition rate estimates (Orr et al 2005), we suggest that other factors such as wave exposure or the L:A ratio may help explain this variability.…”

Variability and abundance of the epiphytic bacterial community associated with a green marine Ulvacean alga

“…This observation has also been made for kelp species of the genera Laminaria and Ecklonia (Linley et al, 1981;Koop et al, 1982;Corre and Prieur, 1990) and is thought to be related to the accumulation of nutrients in the depressions between cells on the algal surface. The intercellular spaces of an unclassified Ulva sp.…”

Energy Balance and Significance of Microorganisms in a Kelp Bed Community

“…There is also information on microbial carbon conversion of kelp debris in non-enriched local seawater Lucas et al, 1981;Newell, 1982;Newell and Lucas, 1981;Stuart et al, 1981Stuart et al, , 1982. Comparable results have been obtained in the field in a microcosm experiment (Koop et al, 1982).…”