ALBERT

Description: Large-scale spatial heterogeneity in fisheries production is predominantly controlled by the availability of zooplankton and benthic organisms, which have a complex relationship with primary production. To investigate how cross-ecosystem differences in these drivers determine fish assemblages and productivity, we constructed a spatially explicit mechanistic model of three fish functional types: forage, large pelagic, and demersal fishes. The model is based on allometric scaling principles, includes basic life cycle transitions, and has trophic interactions between the fishes and with their pelagic and benthic food resources. The model was applied to the global ocean, with plankton food web estimates and ocean conditions from a high-resolution earth system model. Further, a simple representation of fishing was included, and led to moderate matches with total, large pelagic, and demersal catches, including re-creation of observed variations in fish catch spanning two orders of magnitude. Our results highlight several ecologically meaningful model sensitivities. First, coexistence between forage and large pelagic fish in productive regions occurred when forage fish survival is promoted via both favorable metabolic allometry and enhanced predator avoidance in adult forage fish. Second, the prominence of demersal fish is highly sensitive to the efficiency of energy transfer to benthic invertebrates. Third, the latitudinal distribution of the total catch is modulated by the temperature dependence of metabolic rates, with increased sensitivity pushing fish biomass toward the poles. Fourth, forage fish biomass is suppressed by strong top-down controls on temperate and subpolar shelves, where mixed assemblages of large pelagic and demersal fishes exerted high predation rates. Last, spatial differences in the dominance of large pelagics vs. demersals is strongly related to the ratio of pelagic zooplankton production to benthic production. We discuss the potential linkages between model misfits and unresolved processes including movement, spawning phenology, seabird and marine mammal predators, and socioeconomically driven fishing pressure, which are identified as priorities for future model development. Ultimately, the model and analyses herein are intended as a baseline for a robust, mechanistic tool to understand, quantify, and predict global fish biomass and yield, now and in a future dominated by climate change and improved fishing technology.

Description: Clay-rich salt marshes of mesotidal Wadden Sea coasts and of estuaries have been established mainly within artificial sedimentation fields in front of embankments. Natural salt marsh formation and natural range expansion outside artificial structures were rare. In the last three decades of this century natural marshes along the southern Wadden Sea coast of Schleswig-Holstein, Germany, started to grow outside groyne fields and extended on tidal mudflats. This growth happened without direct human influence and naturally structured marshes of considerable spatial dimension evolved. Due to a spread in recent decades, natural grown marshes in our study area – southern Schleswig-Holstein Wadden Sea coast - are younger than man-made marshes. Vegetation developed rapidly in response to fine-scaled geomorphological conditions. Meandering creeks and different surface elevation ranges of the developing natural salt marsh are special features. The naturally grown marshes show a high proportion of pioneer vegetation with Spartina anglica and Salicornia europaea. Succession proceeds fast and elevated parts of the marsh were rapidly colonised with marsh vegetation of Puccinellia maritima and Aster tripolium in the lower marsh to late successional stages, like Halimione portulacoides and Elymus athericus, on the higher elevated parts. Strikingly, median elevations of the vegetation zones in the natural marsh were several centimetres lower than those of the man-made marsh. The largest difference between both marsh types was the characteristic and the extent of drainage systems. Naturally grown marshes have a natural developed, fine-branched and four times shorter drainage system than man-made marshes with a dense drainage structure.