Matthias Brenner

The role of iceberg scours in niche separation within the Antarctic fish genus Trematomus

Abstract. Species of the Antarctic fish genus Trematomus occupy different trophic niches. It is not clear, however, whether small-scale variability in benthic community structure affects niche separation. Therefore abundance and biomass of fish were determined and stomach content and food composition were compared in areas affected by iceberg scours and unaffected areas in the Weddell Sea. Trematomus eulepidotus, T. lepidorhinus and T. scotti dominate undisturbed areas, whereas T. nicolai and especially T. pennellii dominate disturbed areas. Total stomach content and number of prey taxa per fish are higher in preferred than in non-preferred areas. These findings indicate that small-scale horizontal patterns caused by iceberg scours play a distinct role in Trematomus niche separation.

Multi-biomarker approach using the blue mussel (Mytilus edulis L.) to assess the quality of marine environments: season and habitat-related impacts.

Using a comprehensive approach, intertidal, near- and offshore sites in the German Bight were analysed for their environmental quality by assessing the health of blue mussels (Mytilus edulis). During a ten month sampling period mussels were studied with a set of biomarkers comprising lysosomal membrane stability and accumulation of lipofuscin, supplemented by biomarkers indicating nutritional status such as neutral lipids and glycogen in the cells of the digestive gland. Data were analysed in relation to sex, gonadal status, condition index and for the presence of parasites, to determine the overall health status of mussels at the respective sites. Mussels from all sites showed clear signs of stress, indicating an inferior environmental quality throughout the southern German Bight. Further, habitat characteristics such as inundation time and growing on- or off-bottom, as well as seasonal factors, can clearly influence the response of biomarkers in mussels exposed to similar levels of chemical environmental stress.

Effect of air exposure on lysosomal tissues of Mytilus edulis L. from natural intertidal wild beds and submerged culture ropes.

Blue mussels collected from suspended culture ropes and from three natural intertidal wild beds from different areas of the German Bight were tested for their ability to cope with hypoxic conditions. During the experiment mussels were exposed to air from 0 to 72h. Mussels from all sampling sites displayed high tolerance to aerial exposure with moderate levels of mortality after 12 to 48h of exposure. Lysosomal membrane stability (LMS), a biomarker of general stress, changed notably between minimum values after 12h and maximum values after 24h of aerial exposure in intertidal mussels. In contrast, labilization times of mussels from the hanging culture increased continuously up to 48h of exposure. Intertidal mussels from the island of Heligoland exhibited significantly decreased membrane stability after 72h of air exposure, correlating to higher mortality rates. Intertidal mussels, although adapted to daily aerial exposure in their natural environment, showed a similar pattern of mortality and lower LMS values during the experiment than mussels from the suspended culture site. The increase of LMS values of mussels under hypoxic conditions at the beginning of the experiment at all sites was tested for the influence of macro-autophagic processes using immune labelling techniques. With this approach it could be demonstrated that high LMS values significantly correlate with low autophagic activity. However, hypoxic conditions do not enhance autophagic processes during the early periods of aerial exposure. Only at the end of the experiment, high values for autophagy were measured in mussels from an intertidal site accompanied with high mortalities. The results indicate that autophagic processes are not involved in the early adaptive processes that enable the mussel to cope with periods of aerial exposure.