Artificial reefs and, more recently, ecoengineering are frequently advocated as possible tools to counteract the loss of tropical coral reefs worldwide. Despite increasing availability of novel materials, there is limited understanding of how different materials and their physical and chemical properties can influence coral recruitment success and early benthic community development. This study investigated the efficacy of several innovative materials as recruitment substrates for corals and other sessile benthic communities. Stacks of vertically oriented tiles made of eight innovative materials and two common (control) materials were deployed for 6 months during major coral spawning events on the forereef of Mo'orea, French Polynesia. Tiles were separated from their neighbors by 15 mm to mimic cryptic habitats that are sheltered from predation and typically favored by coral recruits. Six innovative materials, including 3D printed concrete, polyvinyl chloride (PVC) with chitosan coating, fiberglass polymer, and flax-based polylactic acid, produced similar coral recruitment to control materials (Portland concrete and PVC). Two materials (porous concrete and ceramic foam) produced lower recruitment. Porous concrete was characterized by a high abundance of non-coralline encrusting red algae, which negatively correlated with coral recruitment, while ceramic foam was prone to erosion. The results suggest the structural micro-complexity and durability of an artificial material and the composition of the benthic communities colonizing it can strongly influence coral recruitment. This study highlights several innovative materials as suitable recruitment substrates for coral restoration and provides a better understanding of the properties of artificial materials that are critical for coral recruitment success.
Photoluminescent silicon nanocrystals are very attractive for biomedical and electronic applications. Here a new process is presented to synthesize photoluminescent silicon nanocrystals with diameters smaller than 6 nm from a porous silicon template. These nanoparticles are formed using a pore-wall thinning approach, where the as-etched porous silicon layer is partially oxidized to silica, which is dissolved by a hydrofluoric acid solution, decreasing the pore-wall thickness. This decrease in pore-wall thickness leads to a corresponding decrease in the size of the nanocrystals that make up the pore walls, resulting in the formation of smaller nanoparticles during sonication of the porous silicon. Particle diameters were measured using dynamic light scattering, and these values were compared with the nanocrystallite size within the pore wall as determined from X-ray diffraction. Additionally, an increase in the quantum confinement effect is observed for these particles through an increase in the photoluminescence intensity of the nanoparticles compared with the as-etched nanoparticles, without the need for a further activation step by oxidation after synthesis.
Limited research effort in the Central Mediterranean deep sea has reported a lower species diversity in this area than in adjacent regions. With the recent advent of remotely operated underwater vehicles (ROVs), the deep sea has become more accessible to surveys, especially rocky benthic areas such as canyons and escarpments. The aim of the present study was to assess diversity, spatial and bathymetric distribution, density, habitat, and microhabitat associations of echinoderms in deep waters around the Maltese Islands. Video data were acquired through ROV surveys as part of the LIFE BaĦAR for N2K project, at depths of 216 to 1031 m. In total, 25 echinoderm taxa were recorded, including the first Central Mediterranean records of the sea stars Marginaster capreensis (Gasco, 1876) and Sclerasterias neglecta (Perrier, 1891), and the first record of the holothuroid Mesothuria intestinalis (Ascanius, 1805) from Maltese waters. Six species were observed deeper than their currently accepted depth range in the Mediterranean. The most abundant species were the crinoids Antedon mediterranea (Lamarck, 1816) and Leptometra phalangium (Müller, 1841), which formed very dense aggregations of up to 2900 individuals/1000 m 2 in a small area to the south of Malta. This area also supports the only known Mediterranean population of the Atlantic sea star Coronaster briareus (Verrill, 1882). Bathymetric distribution varied for each species, and the overall echinoderm diversity seemed stable across the surveyed depths. Since previous deep-sea studies in the area were based on trawling surveys, many deep-sea echinoderm species are reported in the literature as occurring on sedimentary bottoms. However, the present study revealed that several occur more often on rocky substrata, corals, or anthropogenic objects than on sediments. Our study based on video footage also provided insights into the microhabitat of many deep-sea species, yielding information that is not obtainable through remote sampling.
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