Northern Wadden Sea Research Articles

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

In three intertidal sand bottom communities of the “Konigshafen” (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 molluscHydrobia ulvae. Benthic diatoms are the major constituents of plant biomass in theArenicola-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 theNereis-Corophium-belt, only microphytobenthos is important for biomass and primary productivity (gross: 152 g C m−2 a−1). Annual production of macrofauna proved to be similar in theArenicola-flat (30 g C m−2 a−1) to that in the seagrass-bed (29 g C m−2 a−1). Only one third of this amount is produced in theNereis-Corophium-belt (10 g C m−2 a−1). The main part of secondary production and animal respiration is contributed by grazingH. ulvae. In the seagrass-bed, 83 % of the energy used for production is obtained from the grazing food chain. In theArenicola-flat and theNereis-Corophium-belt, the importance of non-grazing species is greater. A synchrony of seasonal development of plant biomass and monthly secondary production was observed. In theArenicola-flat 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 theNereis-Corophium-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−1 in theArenicola-flat, 85 g C m−2 a−1 in the seagrass-bed and 35 g C m−2 a−1 in theNereis-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-flat), 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.

Feeding of calanoid copepods in relation to Phaeocystis pouchetii blooms in the German Wadden Sea area off Sylt

Population dynamics of the dominant calanoid copepods Acartia spp. and Tempora longicornis were followed during a dense spring bloom of Phaeocystis pouchetii in the northern Wadden Sea off Sylt. Positive correlations between algal concentration and abundance of the copepod species suggest that P. pouchetii constitutes an important food organism for the copepods in spring and early summer. In laboratory experiments, feeding and ingestion rates of A. clausi and T. longicornis were determined when P. pouchetii colonies were offered as food. Maximum food intake reached 48% of body carbon per day in A. clausi and 87% in T. longicornis, respectively.

Biology of the plankton of the Königshafen (northern Wadden Sea of Sylt)

Biology of the plankton of the Königshafen (northern Wadden Sea of Sylt)

On the biology of the plankton of the Königshafen (northern Wadden Sea of Sylt)

From May 1979 on, the following parameters were measured at a station in the inlet of Königshafen near List (Island of Sylt): temperature, salinity, mesozooplankton (>76 µm), chlorophyll-a, seston dry weight, oxygen and phytoplankton-nutrients (NH4-N, NO2-N, NO3-N, PO4-P, SiO3-Si). A multiple regression analysis showed the interrelationships between the parameters measured. Tidal influences on zooplankton and seston dry weight could be observed. At low tide, the amount of zooplankton (not counting the harpacticoid copepods) declines and the number of harpacticoid copepods rises as does the seston dry weight too. The chlorophyll-a content is a function of the phytoplankton-nutrients. An increase in chlorophyll-a leads to a decrease in nitrogen and silicate concentrations. Phosphate, due possibly to a sewage inlet into the Königshafen, is not a limiting factor. The availability of nutrients is influenced by temperature, salinity and the tidal cycle. The amount of oxygen is dependent on water temperature and seston dry weight. High water temperatures and a high seston content lead to a decrease in oxygen concentrations.

Beiträge zum Mesozooplankton des Nordsylter Wattenmeers

Contributions to the mesozooplankton of the northern Wadden Sea of Sylt. From June 1975 to June 1976 temperature, salinity, mesozooplankton (>76 µm), phytoplankton and seston (dry weight, particulate organic carbon and nitrogen) were measured at different stations in the northern Wadden Sea of Sylt (German Bight, North Sea). Maxima of the planktonic copepods, which form the biggest part of the zooplankton, occurred in the summer months from June to September. Larval development from nauplii to adults was observed inAcartia clausi, Acartia discaudata, Centropages hamatus andTemora longicornis; generation times ranged from 3 (Temora longicornis) to 7 1/2 weeks (Centropages hamatus) at ca. 20 °C. Organic carbon produced by zooplankton was about 0.4 g C m−3 year−1 and zooplanktonic carbon decomposed in the area studied amounted to about 1.4 g C m−3 year−1. Meroplanktonic larvae made up ca. 60 % of the organic carbon produced by zooplankton, indicating great influence of the benthos on the water column in this very shallow part of the German Bight.