In situ optical assessment of fish abundance and diversity in complex habitats by 3D imaging.
The temporal and spatial differentiation of (micro-)habitat use are central mechanisms in species coexistence and resource partitioning in any ecosystem. Compared to terrestrial or avian communities, where patterns of habitat use are normally assessed by counting organisms, this is not possible in aquatic communities. Even though echo-sounding provides a highly valuable method for direct abundance estimates e.g. for fish stocks, this method is mostly restricted to open water habitats and often fails in complex shallow water areas which are, however, most important especially for juveniles.
Besides the often rough and destructive abundance estimations by net catches, in situ optic systems have gained increasing attention over the last years especially for remote habitats like the deep sea as well as in clear water ecosystems like oligotrophic lakes and coral reefs.
In my group we use high-end digital underwater stereo-photography to estimate species abundance, size-class distribution and fish behaviour in complex habitats. For this we have developed the low-cost underwater observatory "RemOs1" from 1999 to 2006 at University Konstanz and now operate this system successfully also at Helgoland island in the North Sea in a variety of different research projects.
The observatory can easily be deployed from small ships, is cable connected (about 400 m) with a land control site and accessible from the Limnological Institute via consumer WLAN-technology for maintenance and data download. The observatory can be equipped with additional probes for temperature, light etc. etc. by underwater connector with RS232 compatibility and provides 12V power supply for additional instruments.
Have a look under water at Helgoland - a glance through the WebCam of our Underwater Observatory Remos1 off Helgoland.
Investigations on subtidal benthic macrofauna communities on artificial hard substratum
Diploma Thesis Björn Nadarzinski
Compared to intertidal benthic communities only very little is known about subtidal benthic macrofauna communities on hard substratum off Helgoland. Artificial concrete structures, especially Tetrapods, haven`t yet been focused in biological investigations at all.
Scratch-samples are taken monthly in order to characterize the macrofauna found on Tetrapods and its biodiversity. Natural substratum off Helgoland and old concrete structures in the harbour show high species richness and it is a very interesting question if a comparable richness can be found on tetrapods. In addition, measurements with gypsum-balls may show if an influence of water-motion, as the intermediate disturbance hypothesis describes, can be found. The results of this investigation will give an insight into the ecological meaning of tetrapods off Helgoland and due to climatic changes maybe some neobiota can be found as a side effect.
The importance of Tetrapods as refuge and settlement area for fish and crustacea.
PhD Thesis Stephanie Hayen
Using the strongly modified coastline of Helgoland island, I investigate the role of Tetrapods (Fig. 1) as artificial structure and hard bottom substratum for the benthic fish and crustacea community. In an experimental set-up in the southern North-Sea, six Tetrapods fields in two depth strata (5 – 7 m and 10 – 12 m) were installed in February 2010 in the subtidal zone in about 400 m distance to Helgoland.
In this underwater experimental area, I investigate the temporal and spatial distribution of the mobile fauna both, on the Tetrapods itself and in the adjacent area. The experiments are designed to address:
- The seasonal dynamics and colonisation patterns on Tetrapode hard bottom substrates.
- The mobile community composition on Tetrapods in the two different depths strata.
- The importance of Tetrapods as refuge and settlement area.
- The importance of Tetrapods for endangered species.
The since 2009 ongoing monthly sampling program in the area reveals a unique dataset on the temporal and spatial dynamic of the fish and crab community around Tetrapods with strong seasonal influence. Furthermore, a strong circadian in the Tetrapode community is expected. The intense line transect sampling program is mainly conducted by scientific diving allowing a non-destructive assessment of the community over the entire season.
Temporal dynamics on hard bottom communities in the North Sea
Matthias Wehkamp (PhD studen)
