The importance of grazing food chain for energy flow and production in three intertidal sand bottom communities of the northern Wadden Sea

Abstract

In three intertidal sand bottom communities of the "K6nigshafen" (Island of Sylt, North Sea), the biomass production and respiration of phytobenthos, phytoplankton, macrozoobenthos, and in situ community metabolism were measured monthly during 1980. The study sites were characterized by different communities (Nereis-Corophium-belt, seagrass-bed, Arenicola-flat) and by a high abundance of the mollusc Hydrobia ulvae. Benthic diatoms are the major constituents of plant biomass in the Arenicola-flat. In this community, gross primary productivity amounts to 148 g C m-2 a-1.82 % of this productivity is caused by microbenthos, whereas phytoplankton constitutes only 18 %. In the seagrass-bed, gross primary productivity amounts to 473 g C m -2 a -1. 79 % of this is generated by seagrass and its epiphytes, whereas microphytobenthos contributes 19 %. In the Nereis-Corophium-belt, only microphytobenthos is important for hiomass and primary productivity (gross: 152 g C m -2 a-l). Annual production of macrofauna proved to be similar in the A_renicola-flat (30 g C m -2 a -1) to that in the seagrass-bed (29 g C m -2 a-l). Only one third of this amount is produced in the Nereis-Corophium-belt (10 g C m -2 a-l). The main part of secondary production and animal respiration is contributed by grazing H. ulvae. In the seagrass-bed, 83 % of the energy used for production is obtained from the grazing food chain. In the Arenicola-flat and the NereisCorophium-belt, the importance of non-grazing species is greater. A synchrony of seasonal development of plant biomass and monthly secondary production was observed. In the Arenicolaflat and the seagrass-bed, where density and production of macrofauna are high, a conspicuous decrease in biomass of microbenthos occurs during the warmer season, whereas in the NereisCorophium-belt primary production causes an increase in microphytobenthic biomass in summer and autumn. Energy flow through the macrofauna amounts to 69 g C m -2 a -~ in the Arenicola-flat, 85 g C m -~ a -1 in the seagrass-bed and 35 g C m -2 a -1 in the Nereis-Corophium-belt. Based on the assumption that sources of food are used in proportion to their availability, 49 g C m -2 a -1 (Arenicola-fiat), 72 g C m -2 a -1 (seagrass-bed) and 26 g C m -2 a -1 (Nereis-Corophium-belt) are estimated as taken up by the grazing food chain. All three subsystems are able to support the energy requirements from their own primary production and are not dependent on energy import from adjacent ecosystems.

Temporal variations in microbenthic metabolism and inorganic nitrogen fluxes in sandy and muddy sediments of a tidally dominated bay in the northern Wadden Sea

“…5). A similar seasonal pattern of GPP has previously been observed at the same two locations (Asmus & Asmus, 1985). Temperature appeared to be a significant controlling factor for GPP at the muddy site (Table 3), while overall control at the two sandy sites seems more complex clue to simultaneous influence of biotic (e.g.…”

“…Grant, 1986), where incubations are carried out at prevailing temperature and light conditions. Although differences between fluxes obtained by the latter approaches in the Wadden Sea and our laboratory core experiments occur, the general pattern and flux rates of 02 and DIN are of similar and comparable magnitude (van Es, 1982;Hargrave et al, 1983;Henriksen et al, 1984;Asmus & Asmus, 1985;Therkildsen & Lomstein, 1993). However, flux rates obtained by the use of large-scale flumes and similar constructions, which enclose entire sub-systems under the influence of all prevailing physical and chemical factors, may differ considerably (Asmus et al, in prep).…”

“…Similar impact of Hydrobia spp. and other benthic grazers has previously been reported (Connor et al, 1982;Hargrave et al, 1983;Asmus & Asmus, 1985;Kristensen, 1993). It is generally accepted that at low grazing pressures there is a positive feedback on microalgal biomass, while a negative feedback occurs above a certain threshold (Hargrave et al, 1983;Andersen & Kristensen, 1988).…”

The microphytobenthos of Königshafen—spatial and seasonal distribution on a sandy tidal flat

“…Data of the microalgal composition of the Arenicola-flat are already given in Asmus (1982), and the annual course of total microalgal biomass in the three communities has been described in Asmus & Asmus (1985). Here we present annual courses of cell numbers, size spectra, species composition of benthic microalgae in the seagrass-bed and in the Nereis-Corophium-belt, cluster analyses and dendrograms.…”

A fine-grained sediment budget for the Sylt-Rømø tidal basin

“…Cad6e & Hegeman (1974) found values of 100 (+ 40) g C/m2/year for the benthic primary production -a value that is supported by results from the Dollard estuary presented by van Es (1977), who estimated a benthic primary production of 116 g C/m2/year. Asmus & Asmus (1985) found values of 150 g C/m2/year for the benthic primary production in K6nigshafen, and Bruns et al (1995) found a mean value of 111 (+ 35) g C/m2/year computed for the whole of Sylt-Romo tidal basin. Furthermore, van Es (1977) found a pelagic primary production of 7.5 g C/m2/year.…”