An Assessment of Computational Fluid Dynamics as a Tool to Aid the Design of the HCMR-Artificial-ReefsTM Diving Oasis in the Underwater Biotechnological Park of Crete

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.

Movements of Hatchery-Reared Dusky Groupers Released in a Northeast Atlantic Coastal Marine Protected Area

“…According to prior evaluation, in the case of the releasing areas with carrying capacity deficit, habitat enrichment by means of artificial reefs or other appropriate structures may be considered [78,79]; as it has already been demonstrated that the use of artificial habitats can attract juvenile and adult dusky groupers and host a high density of juveniles [80][81][82].…”

Early Succession Patterns of Benthic Assemblages on Artificial Reefs in the Oligotrophic Eastern Mediterranean Basin

“…hcmr.gr/, accessed on 11 April 2022). It comprises a seafloor area of 2.5 ha at a depth increasing from 18 to 22 m along the south-north direction (Figure 1) [12,22]. The seawater temperature at the area of the UBPC ranges from 14 to 28 • C over the year, while the salinity is relatively stable at 39 PSU, except for occasional dropdowns during the rainy season (November-April); the main current has a west to east direction due to prevailing NNW winds [11].…”

“…The Cretan Sea (NE Mediterranean), as part of the South Aegean ecoregion, has been characterized as strongly oligotrophic with limited primary productivity [8,9], high salinity (often exceeding 39 PSU), and temperatures ranging from 14 to 28 • C throughout the year [10,11]. Artificial habitats with several heterogenous microhabitats and structural refugia can attract various benthic and benthopelagic organisms [12].…”

Wake Region Estimates of Artificial Reefs in Vietnam: Effects of Tropical Seawater Temperatures and Seasonal Water Flow Variation

“…Wake regions have been characterized in terms of wake length (WL) [49], wake area (WA) [34], and flow velocity profile in a certain plane [50][51][52][53]. However, the determination of WL and WA depends on how the wake plane was chosen and, accordingly, these measures cannot account for a wake region with one figure.…”