Secondary production of intertidal communities of Königshafen

The macrofaunal biomass increases from the upper high tide line towards the low water line, with mussel beds having more than a twentifold biomass compared with other faunal assemblages (Fig 1).  In a sand bottom communitys the lugworm Arenicola marina and the cockle Cerastoderma edule were the dominant macrofaunal species, whereas in seagrass beds Hydrobia ulvae and in mussel beds Mytilus edulis surpassed other species in biomass.

Secondary production of macrobenthic fauna in Königshafen ranged between  10 and 275 g C m^-2 a^-1. The secondary production of macrofauna showed the same pattern as the mean annual biomass. Low secondary production characterised the assemblage living close to the high tide line, whereas mussel beds near the low water mark had a secondary production more than 10 times higher than that found for other intertidal assemblages (Fig. 2). At the upper tidal levels, the main part of the production was due to Hydrobia ulvae.  In the seagrass bed and in the high tide line assemblage the production of this species constitutes 85% and 80% respectively, whereas in the Arenicola flat this percentage was lower and lugworm formed an important part of 30%. In the mussel bed secondary production was dominated by Mytilus edulis with more than 90 % of the total annual production.
Only a small part of the benthic primary production was transferred to the next trophic level. The benthic primary production utilised by grazers increased with inundation time and water depth during immersion. In contrast to this, the production of the suspension feeder group in mussel beds was much higher than the autochthonous primary production of the pelagic subsystem.
Biomass  and secondary production of suspension feeders were higher than those of other trophic groups, as we consider the average biomass and secondary production of macrofauna of the total tidal flats of Königshafen, taking into account the different shares of macrofaunal assemblages on the total area of Königshafen. The dominance of the suspension feeding  group reveales a high dependence of the total community on the pelagic subsystem of the tidal flat ecosystem. Total autochthonous primary production of phytoplankton is in the same range as total secondary production of suspension feeders, but the demand for energy requirements are distinctly higher. Therefore food has to be imported during every tidal cycle to sustain not only the richness of biomass and production of macrofauna, but also the energy requirements in this ecosystem. This food will originate from the North Sea and deeper parts of the Wadden Sea outside the Königshafen Bay.