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.