Aarhus Universitets segl

No. 255: Biological studies at Taarbæk Rev

Dahl, K., Stæhr, P.A.U., Buur, H. & Göke, C. 2022. Biologiske undersøgelser på Taarbæk Rev. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 42 s. - Teknisk rapport nr. 255. http://dce2.au.dk/pub/TR255.pdf

Summary

The report describes the results of a visual verification of the acoustic mapping carried out by a consultant prior to this project. The verification showed that the interpretation of the results from the acoustic survey has very likely led to a significant overestimation of hard substrate (gravel and boulders) in the area.

The visual examination was conducted with 11 ROV transects and 12 dives, supplemented with 7 Haps sediment core samples distributed over three sites. The conclusion was that the majority of what was interpreted as stone in the acoustic survey consisted of large quantities of blue mussels. However, there were still large boulders in the area and there was a coincidence between mapped dense boulder formations in smaller areas and observations of the same.

Filamentous algae growing on both mussels, pebbles and larger stones dominated the entire area studied. The filamentous algae made it difficult from ROV studies to assess how many pebbles there were on the seabed within the area. Presence of gravel could only be observed in the smaller areas that were examined by a diver. The large boulders clearly stood out despite the vegetation. There was coarse gravel and pebbles in the sieve residue from the 7 core samples.

Apart from the filamentous algae, scattered smaller individuals of sugar kelp (Sacharina latisima) and the red algae Deleseria sanguinea were also found. Both species were primarily associated with mussels and are expected to have only a short lifespan before being torn off with the mussel and carried out into deeper water. On the larger boulders, other perennial red algae were observed that usually form an understory on boulders in the seaweed zone.

Eelgrass was also observed in the area on quite a few parts of the studied transects. The coverage of eelgrass varied considerably but could reach a coverage of 15%, where it was most well developed. The depth was about 6-7 meters in the study areas.

Based on the observations and confirmed information on dense boulder fields   from the acoustic mapping report, DCE has proposed 8 possible areas where reef restoration is proposed to take place. The specific areas have been proposed with a view to link the existing few boulder fields with the new layouts in order to promote the biological "coherence" of the future restored Taarbæk Rev.