Description: The Wadden Sea at the western coasts of Germany, Denmark and the Netherlands is one of the globally most important foraging areas for breeding and migrating birds which act at the same time as indicators for the ecological condition of the ecosystem. However, little is known about how the intense predation pressure of birds influences the Wadden Sea food web. The aim of the interdisciplinary project STopP (From Sediment to Top Predator) is to determine the food web structure in different Wadden Sea habitat types in terms of the interaction between the basis of the food web and birds as top predators. Studied habitat types included the most important foraging areas of birds; mussel banks, cockle beds, sand flats, mud flats, seagrass meadows and beds of the immigrant razor clam Ensis directus a recently preferred prey item of several bird species. Data were analysed using the Ecological Network Analysis (ENA) that reflects trophic structures within the systems and reveals direct and indirect relations between the lower and the upper trophic levels. Preliminary results show that bird predation increases the complexity of the food web due to an increase in connections and a higher total system throughput. On the other hand the predation has also a destabilizing effect due to a high demand of system’s carbon stocks and increased exports out of the tidal system. In addition, analyses show considerable indirect dependencies of birds to lower trophic levels such as sediment POC and phytoplankton. Future scenarios modelled with ENA shall show how changes within the lower trophic levels would affect foraging birds due to anthropogenic or natural impacts. Further analysis will focus on the importance of special habitat types for different bird species and the influence of changes in the biomass of key species for the whole ecosystem food web.

Description: The Wadden Sea at the western coasts of Germany, Denmark and the Netherlands is one of the globally most important foraging areas for breeding and migrating birds acting as indicators for the ecological condition of the ecosystem. However, little is known about how the intense predation pressure of birds influences the Wadden Sea food web. The aim of the interdisciplinary project STopP is to determine the food web structure in terms of the interaction between the basis of the food web and birds as top predators. Studied habitat types included the most important foraging areas of birds; mussel banks, cockle beds, sand flats, mud flats, seagrass meadows and beds of the immigrant razor clam Ensis directus a recently preferred prey item of several bird species. Data were analysed using the Ecological Network Analysis (ENA) that reflects trophic structures within the systems and reveals direct and indirect relations between the lower and the upper trophic levels. Preliminary results show that bird predation increases the complexity of the food web due to an increase in connections and a higher total system throughput. On the other hand the predation has also a destabilizing effect due to a high demand of system’s carbon stocks and increased exports out of the tidal system. Furthermore, analyses show considerable indirect dependencies of birds to lower trophic levels such as sediment POC and phytoplankton. Future scenarios modelled with ENA shall show how changes within the lower trophic levels would affect foraging birds due to anthropogenic or natural impacts.

Description: In the context of present global changes, interest in understanding how systems respond to anthropogenic environmental pressures and stress has increased. Indices that characterize ecosystem state are helpful tools for the interpretation of ecosystem responses. The central question is how to link these responses to ecosystem structure and functioning and to quantify ecosystem persistence, resistance or resilience. Quantification and characterization of trophic networks by ecological network analysis (ENA) indices is proceeding rapidly, especially in the field of coastal ecology. In this contribution, we review several theories that relate ecosystem structure and function to stability. The structure and functioning of ecosystems change during the maturation of ecosystems. In the first section, the maturation of ecosystems is described using thermodynamics. In the second and third parts of this paper, we define some concepts for analysing structure and functioning of food webs and discuss their relation to stability. In the last section, we describe three ENA indices and their link to stability. We demonstrate that ENA provides powerful tools for describing local stability, combining quantitative and qualitative concepts. However, it remains incomplete for describing real conservation cases that combine local and global stability.

Description: It has been postulated that mound-building callianassid shrimp and seagrass have mutually negative effects on each other. On reef flats in the Spermonde Archipelago, Indonesia, sediment mounds of callianassid shrimp are rare in wave exposed seagrass meadows, occur frequently in sheltered seagrass meadows, and reach their highest densities (4.2 mounds m− 2) in unvegetated subtidal areas. There sediment turnover is high at an estimated 3408 g DW m− 2 ∗ d− 1. Based on collected specimens and burrow casts, the most important bioturbators are Glypturus armatus within seagrass beds and Neocallichirus vigilax in unvegetated subtidal areas. Six shrimp exclusion, six control and six zero treatment plots were set up in an unvegetated subtidal N. vigilax bed. Half of the plots for each treatment were ca. 1.5 m (“shallow”) and the other half ca. 2 m or slightly more (“deep”) below spring low tide level. The survival of transplanted shoots of the six seagrass species Enhalus acoroides, Thalassia hemprichii, Cymodocea rotundata, Halodule uninervis, Syringodium isoetifolium and Halophila ovalis was monitored over 27 months. At the end, E. acoroides had survived in about half of the plots with no obvious relation to either treatment or water depth. C. rotundata and H. uninervis had successfully established themselves on the shallowest exclusion plot only, and had disappeared from all other plots. T. hemprichii and S. isoetifolium had disappeared from all plots. H. ovalis expanded rapidly in the dry seasons, but wet seasons caused a temporary decline in shoot numbers. At the end, the highest shoot numbers were counted in shallow exclusion plots, some shoots survived in deep exclusion plots and the species disappeared from all deep control and zero treatment plots. H. ovalis shoot numbers were significantly influenced by water depth (ANOVA p 〈 0.01) and, to a lesser extent, by treatment (ANOVA p 〈 0.05) but there was no interaction between the two factors. It is concluded that seagrasses are only controlled by shrimp bioturbation at the lower limit of their distribution in sheltered subtidal areas. Here they are already under considerable stress from a combination of factors such as light limitation and sedimentation. However, the distribution pattern of seagrasses vs. shrimp elsewhere on the islands suggests that seagrasses are equal competitors in sheltered intertidal areas, where they may even profit from the abundant small tidal pools between mounds created by the shrimp, and dominant competitors in exposed intertidal and subtidal areas.