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.
The coastal ocean is one of the most important environments on our planet, home to some of the most bio-diverse and productive ecosystems and providing key input to the livelihood of the majority of human society. It is also a highly dynamic and sensitive environment, particularly susceptible to damage from anthropogenic influences such as pollution and over-exploitation as well as the effects of climate change. These have the added potential to exacerbate other anthropogenic effects and the recent change in sea temperature can be considered as the most pervasive and severe cause of impact in coastal ecosystems worldwide. In addition to open ocean measurements, satellite observations of sea surface temperature (SST) have the potential to provide accurate synoptic coverage of this essential climate variable for the near-shore coastal ocean. However, this potential has not been fully realized, mainly because of a lack of reliable in situ validation data, and the contamination of near-shore measurements by the land. The underwater biotechnological park of Crete (UBPC) has been taking near surface temperature readings autonomously since 2014. Therefore, this study investigated the potential for this infrastructure to be used to validate SST measurements of the near-shore coastal ocean. A comparison between in situ data and Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Terra SST data is presented for a four year (2014–2018) in situ time series recorded from the UBPC. For matchups between in situ and satellite SST data, only nighttime in situ extrapolated to the sea surface (SSTskin) data within ±1 h from the satellite’s overpass are selected and averaged. A close correlation between the in situ data and the MODIS SST was found (squared Pearson correlation coefficient-r2 > 0.9689, mean absolute error-Δ < 0.51 both for Aqua and Terra products). Moreover, close correlation was found between the satellite data and their adjacent satellite pixel’s data further from the shore (r2 > 0.9945, Δ < 0.23 for both Aqua and Terra products, daytime and nighttime satellite SST). However, there was also a consistent positive systematic difference in the satellite against satellite mean biases indicating a thermal adjacency effect from the land (e.g., mean bias between daytime Aqua satellite SST from the UBPC cell minus the respective adjacent cell’s data is δ = 0.02). Nevertheless, if improvements are made in the in situ sensors and their calibration and uncertainty evaluation, these initial results indicate that near-shore autonomous coastal underwater temperature arrays, such as the one at UBPC, could in the future provide valuable in situ data for the validation of satellite coastal SST measurements.
There is growing interest about marine bivalve aquaculture globally, not only for the market value of the goods produced, but also for the socio-economic and environmental services that this activity can provide. Arca noae is an endemic Mediterranean bivalve of commercial value, whose previously undescribed population in Elounda Bay we studied in terms of its structure and reproduction, while constructing a timeseries of the basic environmental parameters of the bay, thus, gaining fundamental knowledge for the potential future exploitation of the species in the area. We found a variable spatial distribution of arks in the study area, with local high peaks in the population density, consisting of smaller size individuals, in comparison to other areas. Because of protandry of the species, human pressure on this population could have a strong negative effect, by targeting the limited numbers of large females in the study area. The reproduction pattern was similar to the reports from other Mediterranean locations. The abiotic conditions in Elounda Bay differed from those in the adjacent coastal zone, confirming that the Bay is a unique semi-enclosed marine area in the island of Crete.
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