Abstract
Since recreational diving activities have increased in recent decades, resulting in additional environmental pressure on the coastal zone, the deployment of artificial reefs as a conservation strategy to divert mass ecotourism from fragile natural reefs has been proposed and realized in many areas of the world. Twelve units of a patented naturoid artificial reef technology developed by the Hellenic Centre for Marine Research (HCMR) were deployed in 2015 in the Underwater Biotechnological Park of Crete (UBPC) in order to create an experimental diving oasis and investigate the potential of achieving this aim for the over-exploited coastal ecosystems of this part of the Eastern Mediterranean. Assessment of the degree of establishment of artificial reefs and their ability to mimic natural ecosystems is often monitored through biological surveys and sampling. The measurement of the chemical, physical, and hydrodynamic characteristics of the water mass surrounding artificial reefs is also essential to fully understand their comparison to natural reefs. In particular, the flow field around reefs has been shown to be one of the most important physical factors in determining suitable conditions for the establishment of a number of key species on reef habitats. However, the combination of biological establishment monitoring and realistic flow-field simulation using computational fluid dynamics as a tool to aid in the design improvement of already existing reef installations has not been fully investigated in previous work. They are often reported separately as either ecological or engineering studies. Therefore, this study examined a full-scale numerical simulation of the field flow around individual already installed naturoid reef shapes, and part of their present arrangement on the sea bottom of the UPBC combined with the field-testing of the functionality of the installed artificial reefs concerning fish species aggregation. The results show that the simulated flow characteristics around the HCMR diving oasis artificial reefs were in good general agreement with the results of former studies, both for flows around a single deployed unit and for flows around a cluster of more than one unit. The results also gave good indications of the performance of individual reef units concerning key desirable characteristics such as downstream shadowing and sediment/nutrient upwelling and resuspension. In particular, they confirmed extended low flow levels (less than 0.3 m/s) and in some cases double vortexes on the downstream side of reef units where observed colonization and habitation of some key fish species had taken place. They also showed how the present distribution of units could be optimized to perform better as an integrated reef cluster. The use of computational fluid dynamics, with field survey data, is therefore suggested as a useful design improvement tool for installed reef structures and their deployment arrangement for recreational diving oases that can aid the sustainable development of the coastal zone.
Highlights
According to the World Tourism Organisation, coastal tourism is by far the most significant in terms of tourist flows and generation of income [1]
As part of this evaluation, this study was an assessment of a numerical simulation tool that employs computational fluid dynamics to calculate the flow around the naturoid artificial reefs (ARs) already deployed as the Hellenic Centre for Marine Research (HCMR) experimental diving oasis in the Underwater Biotechnological Park of Crete (UBPC)
The AR design of the HCMR diving oasis aimed at (a) diver-attractiveness, (b) mimicking the natural environment, and (c) fish aggregation, defined geometry shapes were excluded while the parameterization in our studies included various other inputs
Summary
According to the World Tourism Organisation, coastal tourism is by far the most significant in terms of tourist flows and generation of income [1]. The exploitation of the coastal zone’s resources should be governed by multidisciplinary principles of integrated management plans that are in good agreement with sustainable perspectives and actions. This exploitation should be from a holistic point of view that takes into account both physical and social impacts, especially when it comes to tourism and the interactions it provokes [6]. Having in mind the definition of ecological engineering as “the design of sustainable ecosystems that integrate human society with its natural environment for the benefit of both” [7], the deployment of artificial reefs (ARs) is a vivid example of an application that should be carefully implemented in such a harsh and demanding environment as the coastal zone. The United Nations Environment Program defines the artificial reef as a submerged structure deliberately constructed or placed on the seabed to emulate some functions of a natural reef such as protecting, regenerating, concentrating, and/or enhancing populations of living marine resources; objectives of an AR may include the protection, restoration, and regeneration of aquatic habitats, and the promotion of research, recreational opportunities, and educational use of the area [8]
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