Eco-engineering: a concrete solution to increasing biodiversity and monitoring microplastics.

As urban populations grow, coastal landscapes are becoming increasingly dominated by diverse forms of artificial coastal structures. This ‘Ocean sprawl’, the extension of artificial structures into the marine environment, poses significant threats to the health and functioning of both estuarine and marine ecosystems. More recently eco-engineered has focused on tackling the loss of biodiversity through creating novel habitats with features such as tide pools, pits, grooves, and towers that promote biodiversity within artificial environments.

Eco-engineered rock pools were installed in an artificial causeway in Galway, Ireland in 2013 (n=80) to monitor the increase in biodiversity. Sampling was based on a timeline reflective of ‘ecological succession by inhibition’ within tidal rockpools. Rockpool sampling occurred a) in 2014 (month 12) using non-destructive methods to confirm early colonisation by r-strategists and their potential to function as a rockpool habitat, b) in 2015 (month 24) using destructive sampling to determine taxonomic biodiversity and c) in 2023 (7.5 years later since the last destructive sampling) using destructive sampling to confirm the presence of a mature benthic community in addition to the rockpool water was collected and filtered for the presence of microplastics (MPs)

Results of modelling showed that the change in physical oceanography surrounding the causeway resulted in the establishment of two different habitats. The exposed rockpools were effective at maintaining biodiversity over long periods no overall significant increase in the species richness (t (23.09) = -0.37, p=0.72). In addition, the rockpools retained their functional diversity. However, the community composition of similar rockpools on the exposed western side the causeway, reflecting both the upper and lower shore height, when compared over time showed a significant difference (PERMANOVA Pseudo-F = 19.063; p=0.001). In contrast the sheltered rockpools hosted a sedimentary habitat with a much reduced faunal diversity similar to the adjacent shoreline.

MPs were recorded from all artificial pools on both the exposed and sheltered side. There were significantly more microplastics found per litre of water in the pools at the upper shore height than in the lower shore pools. The quantity per rockpool was highly variable, 14.7± 8.35 MPs recorded from the exposed rockpools and 10.7 ± 6.9 MP in the sheltered pools which had become inundated with sediments, thus failing to function as rock pools as intended. Furthermore, the rockpools recorded on average 19.6 ±15.3 MP L^-1 are deemed a hotspot for the bay with significantly higher numbers recorded than from the surface water in Galway Bay in previous studies.

The findings can be utilized to inform the architectural design requirements of future coastal engineering projects and planning policies around the world, thereby establishing guiding principles for the field of eco-engineering standards. Furthermore, this study suggests the possibility of real strategies for mitigating and monitoring maritime pollution through concrete solutions.