Ecological succession within microhabitats (tidepools) created in riprap structures hosting climax communities: An economical strategy for mitigating the negative effects of coastal defence structure on marine biodiversity

Abstract

The substitution of natural habitats with artificial structures, such as coastal defence structures, has significantly detrimental effects on the marine biological community. In this context, the application of ecological engineering to marine ecosystems presents an opportunity to mitigate these environmental impacts and enhance ecosystem services. There are proposals aimed at mimicking structures found in the natural environment to increase topographic complexity in artificial substrates, thereby promoting biodiversity and hindering the establishment of invasive species. The present study focuses on assessing change in the biological community of intertidal pools constructed on existing coastal defence structures and their influence on a halo (5 cm) of humidity created around the pools. Using an inexpensive method, the tidepools were created at the beginning of 2014 using a pneumatic hammer (DeWalt brand D25902K), imitating the tidepools of the adjacent natural substrate. The coastal defence structures (riprap) which were selected for the study host climax communities since they were built >8 years ago. After 7.5 years of the creation of this microhabitat, the value of species richness in the tidepool was 64.2% higher than in the control, Shannon diversity 41.54% and functional diversity 6.27%. The study of the effect on a halo (5 cm) of humidity produced around the pool shows that Shannon diversity is higher than in the control treatment, demonstrating that the microhabitat created mitigates the harsh environmental (high temperature and desiccation) conditions of the intertidal zone beyond the interior of the tidepool. The results showed that the species richness in the tidepools was bigger in the high intertidal than the low, therefore it is more beneficial to create this microhabitat in high intertidal zone. The created microhabitats serve as shelter and breeding sites for animal species that were not previously observed in the studied artificial structure, as detected for species such as Pisania striata, Ocenebra edwarasii, Stramonita haemastoma, Meralarhaphe neritoides, Siphonaria pectinata, Paracentrotus lividus and Spirorbis sp., thus contribute to reducing the fragmentation of their populations. In terms of “ecological succession”, the current study demonstrated that typical species of a mature benthic biological community had colonised the created microhabitat 7.5 years later. These species included the Anthozoa Anemonia sulcata, Actinia equina and Exaiptasia diaphana or the endangered Mollusc Dendropoma lebeche.