A comparison of durability and recruitment for reef mimics constructed from marine concrete and CaCO₃-enriched concrete

Abstract

Coastal landscapes continue to be altered on a global scale by man-made infrastructure. Coastal and marine infrastructure, such as seawalls, breakwaters, have replaced natural intertidal, subtidal, and benthic habitats along many coastlines. Coastal infrastructure has a multitude of impacts on biodiversity and ecosystem functioning. The habitat provided by man-made coastal infrastructure typically supports ecological communities that are characterized by greater abundances of invasive species and lower overall biodiversity. New design approaches have emerged with the aim of mitigating the impacts of man-made coastal infrastructure, but few studies have investigated the role of CaCO₃ as a concrete additive in increasing biodiversity, species recruitment, material strength and durability, and ion leaching. Textured reef mimics in both standard marine concrete and CaCO₃-enriched concrete were studied constructed and deployed along the coast in Dorchester Bay, Massachusetts.

Reef mimics were compared with regard to performance in recruitment and durability at 90, 180, 330, and 420 days to evaluate effect of CaCO₃ and correlations with seasonal influences over a 420-day period. CaCO₃ had limited effect on community structure as a whole, but increased mussel recruitment, mussel size, and increased barnacle and common slipper shell recruitment on the innermost disc surface. Community structure varied more with submersion time than material type. Community structure varied in time with boom-bust cycles, where the invasive ascidians S. clava, A. aspersa, B. violaceous, and Didemnum sp. competed for surface coverage. CaCO₃ did not decrease the compressive strength or durability of concrete reef mimics. Submersion caused a decrease in compressive strength of both standard and enriched concretes, but after the initial decrease, compressive strength increased with submersion time in the field, but never recovered to its original strength.

Although CaCO₃-enriched concrete leached higher concentrations of calcium and carbonate ions, reef mimics of both material types demonstrated the ability to provide continued leaching of ions.