International Journal of Marine Science, 2024, Vol.14, No.1, 29-39 http://www.aquapublisher.com/index.php/ijms 30 scales. Additionally, digital imaging systems play a crucial role in faunal exploration and monitoring despite encountering biological hazards (Zenetos et al., 2010; Condal et al., 2012; 2020; Nalmpanti et al., 2023). One of the most promising tools for marine restoration is the concept of High-Complexity Artificial Reefs (HCARs), intended to emulate the intricate nature of natural reefs, providing diverse habitats and shelter for a wide array of marine species (Willis et al., 2000; Harmelin-Vivien et al., 2008; Condal et al., 2012; 2020). While HCARs hold the potential to enhance species’habitat, serving as refuges from fishing pressures, and augmenting targeted species’ biomass, challenges such as potential overfishing, construction and maintenance costs, and susceptibility to climate change and ocean acidification necessitate careful consideration (Willis et al., 2000; Harmelin-Vivien et al., 2008; Condal et al., 2012; 2020; Hylkema et al., 2020). This study represents an unprecedented attempt at seasonal fish community monitoring within HCARs on the Mediterranean seafloor. We conducted seasonal samplings in an HCAR within a western Mediterranean marine reserve to delineate ecosystem succession and observe new fish species colonization, potentially influencing estimated biodiversity levels. Integrating research on HCARs, seasonal fish abundances, and ecosystem succession offers insights into the role of these artificial structures in fostering marine restoration and biodiversity conservation (Le Diréach et al., 2015). This knowledge significantly contributes to the effective management of marine protected areas and the sustainable deployment of AR structures. In conclusion, while HCARs hold promise as tools for restoring marine ecosystems due to their ability to mimic natural reef complexity and provide diverse habitats, meticulous attention to their limitations and long-term effectiveness is imperative. Continuous research and monitoring efforts are indispensable to fully unleash the potential of HCARs and ensure the preservation and restoration of marine ecosystems for future generations. 1 Results and Analysis A total of 960 seconds of video footage (equivalent to 16 minutes) underwent thorough analysis (Table 1), with a notable majority (98%, amounting to 944 seconds) recorded under optimal visibility conditions. However, it is essential to note the absence of winter video imagery due to adverse water visibility conditions. Specific time intervals were meticulously identified to facilitate analytical precision across each season: autumn (168 seconds), spring (415 seconds), and summer (377 seconds). Within the scrutinized video footage, 2684 fish images were meticulously classified at the species level. Regrettably, certain distant images posed challenges for species classification, leading to their exclusion from the analysis. The catalogued fish species encompassed 19 distinct types, spanning 12 different families, including Congridae, Gobiidae, Haemulidae, Labridae, Molidae, Mullidae, Pomacentridae, Sciaenidae, Scorpaenidae, Serranidae, Sparidae, and Trachinnidae (Table 2). Alongside the fish species, other intriguing or invasive species were observed during the study. For instance, the persistent presence of Caulerpa racemosa seabed throughout all sampling seasons and other filamentous algae common in polluted seawater was noted a year after HCAR depletion. The total count of fish per species, along with their corresponding occurrence percentages within the entire video-frame set (Table 2). Among the identified fish, three species – Bastard grunt (Pomadasys incisus Bowdich, 1825), Damselfish (Chromis chromis Linnaeus, 1758), and Two-banded seabream (Diplodus Vulgaris Geoffroy Saint-Hilaire, 1817) – comprised a substantial 91.6% of all identified fish species. Notably, these species occasionally formed large schools, some instances comprising 20 or more individuals. However, the remaining species were less prevalent in the video frames. Most species exhibited variations in occurrence patterns across the seasons (Figure 1D; Figure 1E; Figure 1F), showing a discernible temporal trend.
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