Higher trophic levels in the Southern North Sea
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The TROPHOS project formed a continuation of the SPSD-I research project. The causal factors responsible for the observed trends in the benthic communities (and their parasites) and the avifauna (as they were described in Cattrijsse & Vincx, 2001) are still far from understood. TROPHOS will mainly focus on the structure that is present in the higher trophical levels.

The different research topics that were studied in Trophos project are:

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Processes occurring at the sediment-water interface: benthic pelagic coupling

The benthic-pelagic coupling can be considered as one of the most important processes occurring in a marine ecosystem: after a phytoplankton bloom, dead cells sink to the seafloor where they are remineralised. As a result of this process, nutrients are released again to the pelagic phase, where they fuel the next phytoplankton bloom.

The trophos results clearly show that at the BCS strongly different benthic ecosystems were present. Both processes,diversity and densities of bacterial, meiobenthic and macrobenthic communities were strongly related to the sedimentation and hence availability of labile organic matter from the water column.
    In the fine sanded sediments, mainly present in the coastal zone, sediment remineralisation of organic matter is rather intense, but delayed with respect to the major sedimentation event in spring. Here, oxygen consumption (as a proxy for remineralisation processes) is a function of temperature and macrobenthic activities.
    The more offshore permeable sediments show a fast response both in terms of densities and diversity of benthic organisms and mineralization processes. This is due to the prevailing lateral advective currents through the sediment, providing the deeper sediment layers with oxygen and removing toxic byproducts of the mineralization processes.
It is very important not to carry out activities which disturb the benthic processes when these are acting at their maximum rates. In the coastal zone, the fine sediments are most vulnerable during summer, while the more offshore coarser sediments show the largest activity in April-May.
Given the fact that the majority of the sediments at the Belgian Continental Shelf consists of these coarser sediments, the ecological value of these sediments for the functioning of the marine ecosystem should not be underestimated.

Dispersal of selected invertebrates, fish species and their parasites

Almost all marine organisms have expanded or stabilized their populations in response to processes such as climate cycling and sea level stand.The current populations of marine organisms integrate this history together with the ongoing postglacial equilibrium between hydrodynamics, habitat availability, ecological niche and anthropogenic factors such as fisheries, pollution and climate change. Trophos investigated the historical and current patterns of two invertebrate taxa (mysid shrimps and Gyrodactylus flukes) and two vertebrate taxa (Pomatoschistus gobies and common sole). We also initiated a modeling analysis of their patterns in the North Sea and English Channel

Link between breeding success of seabirds and the availability of their prey items

The tern colony at Zeebrugge is of high international importance and has recently been designated as a Special Protected Area under the Bird Directive. Scientific knowledge as has been gathered during the THROPHOS project is crucial for the preservation of these species and to develop a proper management plan for the breeding site. The study reveals that protecting the two tern species requires both local management (Common tern) as well as international and cross-North Sea management(Sandwich Tern). The two species are closely related and breed in close proximity, but exhibit very different life-history traits.

    Common Terns are largely self-supporting although there is some exchange of individuals with nearby colonies in the Dutch Delta-area. At present, the young Common Tern colony (first settlement in 1987) is highly productive. However, breeding output will probably decrease in future as carrying capacity of the area will be reached.
    In contrast, Sandwich Terns already experienced several years of poor breeding success in combination with strong fluctuations in breeding numbers and exchange of individual with colonies over a much larger distance than Common Terns.

Sandwich Tern

Common Tern

Both species may serve as indicators for the state of the marine environment. The fledging success and relative population growth of Common Terns prove to be good candidates to serve as a proxy for the condition of small pelagic fish in the surroundings of Zeebrugge.