International Journal of Marine Science, 2024, Vol.14, No.1, 29-39 http://www.aquapublisher.com/index.php/ijms 36 marine habitats, sustainable fisheries practices, and the conservation of biodiversity. Overall, the positive influence of artificial reefs underscores their potential as valuable tools for marine conservation and resource management in the face of increasing anthropogenic pressures. While the results are promising, highlighting the potential of HCARs in marine restoration efforts, the call for extended monitoring underscores the complexity of artificial reef ecosystems and the need for cautious interpretation of short-term findings. Future research should aim to address the identified gaps, particularly regarding long-term ecological impacts, to better inform conservation and management practices. Future research should focus on long-term ecological outcomes, including potential changes in species composition, biodiversity, and the artificial reefs' physical and chemical impacts on the surrounding marine environment. 3 Materials and Methods The HCARs Parc is situated at a depth of 20 meters within the Marine Reserve Colls i Miralpeix, Costes del Garraf, located 4 km off the Garraf coast in Catalonia, Spain (Figure 3A; Figure 3B). The area saw the deployment of a series of HCARs, initiating a seasonal ecosystem study aimed at assessing biodiversity changes and enhancements. Geode construction employed polyester fibre moulds with external metal reinforcement, followed by the construction of 24 mass concrete pieces. To anchor the geode modules to the seabed of the port of Vallcarca (Garraf), professional divers utilized hydrostatic balloons of 10 000 litres inflated by an air compressor, with subsequent re-floating. Upon re-floatation, precise repositioning occurred utilizing a submetric GPS global radio positioning system and buoy fields as references, leading to the sinking of each module to its designated location – either on the seabed or at corresponding plant levels. The installation consisted of 24 geodes, including a central geodes area (CGA) comprising 10 modules – 5 at the lower and 5 at the upper level –alongside a first radial ring of 4 modules surrounding the central area and a second radial ring consisting of 10 modules encircling both the central and first ring areas (Figure 2A; Figure 2B; Figure 2C; Figure 2D). Figure 3 The western Mediterranean and the included Catalan Sea (A); Costes del Garraf MPA (B) Note: Area where the study was conducted (indicated by the red circle) in front of the coast of Sitges, and the Colls i Miralpeix This innovative HCAR model has not been previously attempted in the Mediterranean seabed for marine biodiversity restoration or elsewhere globally (to our knowledge). A specific image acquisition protocol was developed for fish species sampling within this heterogeneous environment. The study spanned three consecutive seasons – autumn, spring, and summer – selected for their distinct environmental conditions and biological activity. Fixed transects were established within the HCAR for underwater surveys during each season, conducting visual censuses to record marine species’ presence and abundance. Additionally, the Shannon-Weaver Diversity Index was calculated to assess species diversity within the reef ecosystem.
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