Trophic dynamics of eight intertidal communities of the Sylt-Rømø Bight ecosystem, northern Wadden Sea

The intertidal area of the Sylt-Rømø Bight was divided into 8 benthic and 1 pelagic subsystems according to habitat nature and the unique biodiversity of each. A quantitative food web network was constructed for each of the subsystems. Each flow model consists of 56 living and 3 nonliving compartments and depicts the biomass of each, a balanced energy budget for each of the living components, and the flow of energy and material between all compartments. These models were analysed by means of network analysis that revealed a considerable amount of variability between them in terms of system properties such as total system throughput (TST), development capacity, ascendency and redundancy, and a number of dimensionless ratios used in comparative systems ecology. Mussel beds stood out as the most productive subsystem at 5095 mgC m–2d–1, with a high TST of 33 571 mgC m–2d–1. The amount of material recycled in each of the systems ranged from a high of 28% in the muddy sand flats to a low of 2.5% in the mussel beds, while the efficiency of energy transfer in the various systems fluctuated from a low of 3.3% in the sandy shoals to a high of 15% in the mussel beds. Mussel beds are highly specialized in terms of ascendancy and average mutual information in comparison with the other subsystems, but have less resilience. Most of the systems showed ratios between 0.8 and 1.4 for the 2 mutually exclusive system attributes of ascendency and redundancy. Relative redundancy indices calculated for the pelagic and mussel bed subsystems are low, indicating less organized systems with less resistance to disturbance.