Dipl. Biol. Matthias Brenner
Former investigations conducted by the AWI showed that the basic biotic conditions in many parts of the German North Sea are given for the cultivation of various candidates under offshore conditions, such as seaweeds, oysters and blue mussels.
In a new project “MytiFit” (Health of offshore cultivated blue mussels), financed by the Ministry of Construction, Environment and Transport of Bremen and the AWI in Bremerhaven, the culture potential and the response of the blue mussel (Mytilus edulis) (see Fig. 1a & 1b) growing under offshore conditions will be investigated in detail. The focus of this project will be the overall health of the candidate, regarding the loads of micro and macro parasites (analysis in cooperation with LAVES), the shell stability, the attachment strength of mussels using different artificial substrates and its lysosome membrane stability of the digestive gland cells as an indicator of the overall energy status of the mussel (analysis in cooperation with the International University of Bremen IUB).
In a testing area near Nordergründe, 17 nautical miles off the coast from the city of Bremerhaven, three test moorings with large buoyancy (see Figure 2) will be deployed to test the described parameters in different water depths. Collectors of different style and surface material will be fixed to ferrules around the body of the buoy to develop an optimized mussel collector for the rough hydrodynamic conditions in the German Bight. This will be realized in cooperation with the local fishing gear producer Engel-Netze.
Former analysis conducted by the AWI showed that farmed or wild mussels from the intertidal areas in the Wadden Sea suffer under high infestations of macro parasites such as copepods (see Fig. 3), trematods (see Fig. 4) and polychaets species. Some macro parasites are using the blue mussel only as an alternate host (e.g. Metacercarias of trematods) during their complicated life cycle.
In offshore areas alternate and final host animals are rare or missing completely, leading to an uncompleted life cycle of the parasites and minimum infestation rates of mussels. This dilution effect may occur also in case of micro parasites (see Fig. 5 & 6).
The offshore areas are far away from urban sewage and estuarine runoffs, which results in a continuous supply of clean water with good O2-conditions. Furthermore, the concentration of pollutants, pesticides and near-surface agents can be considered as minimal. One can assume that organisms living under good water conditions have a less stressed immune system, lower rates of parasites and accumulate fewer toxins in their bodies. Therefore, mussels grown under offshore conditions should have a better health status as mussels grown in near- and inshore areas. Additionally, the good health status of offshore cultured mussels should result in higher growth rates and yield to a qualitatively better product for human consumption.
The aim of the project is to inform all interested parties about best conditions for cultivating mussels within the planed offshore wind farms. The prediction of most rapid growth, best product quality and information about optimal culture techniques should compensate higher investment costs - compared to traditional bottom culture techniques - for the culture systems and help to install a functioning offshore mariculture system in the German Bight.
Dipl. Biol. Matthias Brenner