Solent oyster enhancement reef concrete colonisation trials

Abstract

The Interreg funded project RECIF (2012-2015) developed waste shell concrete formulations specifically for artificial reefs. Its successor MARINEFF continues these evaluating further formulations to maximise both physical performance and endurance with biological attractiveness. Four formulations were produced by ESITC Caen for trials based on combinations of two cement types (CEM II and CEM IV) with either coarse aggregate or crushed oyster shells replacing 20% of the aggregate. The most extensive colonisation trials were carried out with 5x5x2cm blocks by both UK and French partners. These test blocks also had smooth and rough faces. This paper describes the results of Southampton biological colonisation trials. Four blocks, one of each formulation along with an oyster shell cut to the same area were secured in a framework and pairs of these were suspended vertically at 6 fully saline sites around the Solent region (Calshot, Beaulieu River, Hamble River, Itchen River, Portsmouth and Langstone Harbours) from May to August 2019. On recovery these were analysed for Total Biomass, Algae (PAM & %cover), Anemones (n), Ascidians (%cover), Barnacles (n & % cover), Bryozoans (%cover), Hydroids (%cover), Mytilus edulis (n), Pomatoceros sp. (n), Sponges (%), Spirorbis sp (n). There were considerable differences in colonisation between the sites which are described in detail, but overall in terms of overall biomass the formulation using CEM V and 20% oyster shell performed as well as the oyster shell. Given that it is accepted that oysters are attracted to natural shell substrate, this concrete was promising for the choice mix of the final oyster reef modules deployed at Calshot, September 2020.