Artificial Reefs Research

Human intervention is required to preserve wild animals due to human-induced problems such as climate change and altered habitats. Marine animals are unaffected by the boundaries drawn by humans and freely cross them. Most marine life exists, moves, and evolves in unexplored waters, and it is reported that only ~5% and ~1% of the ocean and benthic ecosystems have been studied, respectively [1,2]. Moreover, marine organisms and fishery resources are dramatically affected by human intervention and environmental changes. Declining fish stocks in oceans and coastal areas have increased the importance of farmed fisheries, which now yield more fish than wild fishing activity. Therefore, artificial reefs are being installed in coastal waters around several countries to stabilize fishery resources. The installation of artificial reefs may require more careful consideration than the construction of artificial habitat enhancement structures in terrestrial areas (e.g., artificial waterholes in the Serengeti). Research should focus on the function of artificial reefs, the negative effects of improper installation, and the complexity of long-term monitoring. Because it is difficult to understand and improve the habitats of marine organisms, we should continue to research artificial reefs by adding to the six highly valuable articles published in this Special Issue.

The articles in this Special Issue discuss core issues in artificial reef research: artificial seaweed reefs for macroalgal forest formation; a monitoring method for artificial benthic reefs; engineering, ecological, and social monitoring of the world’s largest underwater structure; the correlations of hydraulic characteristics with fishery activities near an underwater structure; and the accumulation and dispersion of microplastics near artificial reefs. These articles report the construction materials, structure, hydraulic characteristics, monitoring strategies, and current state of artificial reefs that have been installed in the coastal waters of Australia, Malaysia, and South Korea.

Jung et al. [3] review artificial seaweed reefs that support submerged aquatic vegetation beds and facilitate ocean macroalgal afforestation. They answer four research questions through their review pertaining to why artificial seaweed reefs must be established, why marine forests are required, why macroalgal forest must be restored, and why seaweed matter is under threat. Ali et al. [4] present an observation method that utilizes side-scan sonar and scuba diving, along with the results of enhanced artificial benthic reef monitoring along the coast of Terengganu, Peninsular Malaysia. They emphasize that monitoring efforts should focus on pre-deployment aims, the location and condition of the reef structure, and the evaluation of artificial habitat performance. Smith et al. [5] perform multi-phase monitoring of the world’s largest underwater sculpture at John Brewer Reef, Australia. They discuss the engineering, ecological, and social monitoring of the target site and emphasize that the installation of the Coral Greenhouse and transplantation of coral fragments onto the structures have increased the abundance and diversity of the marine community. Jang et al. [6] use numerical analysis to determine the hydraulic characteristics (i.e., wake region, local upwelling, and flow velocity) of the Ieodo (or Socotra Rock) underwater reef near Jeju Island, South Korea. They relate these characteristics to fishery activities that were tracked using an automatic fishing vessel identification system. Fish attraction was assessed by synthesizing the results of numerical analysis and information from the automatic identification system. Park et al. [7] evaluate heavy metals eluted from artificial reef construction materials in South Korea. They discuss the effects of artificial reefs that comprise concrete, steel, and steel slag, and the concentrations of heavy metals (i.e., As, Cd, Cr⁶⁺, Cu, Hg, Ni, Pb, and Zn) in seawater and marine organisms over 1 year. Consequently, they show that the material effects on the marine environment are insignificant. Quyen and Choi [8] analyze the accumulation and dispersion of microplastics around artificial reefs using a numerical wave tank. They show that the fate of microplastics adjacent to artificial reefs in coastal areas depends on their physical properties and that submerged reefs that attract biomass can accelerate the consumption of microplastics by fish and small organisms.

The editor is delighted with the scientific exploration of artificial reefs described in these articles. However, artificial reefs can negatively affect marine habitats if improper design, installation, and post-installation management strategies are used. The scientific resolution of these issues will require collaborative interdisciplinary research. Given that only ~5% of the ocean has been studied, it will not be possible to resolve these issues quickly. Both large- and small-scale social and economic interventions are needed to improve marine habitats and manage fishery resources. Furthermore, we must improve our understanding of marine habitats using more sophisticated scientific approaches. We must also recognize that good marine science provides a basis for decision-making, although translating this into effective policy and action will require considerable effort. Using artificial reefs as renewable marine habitats and fishery resource management require rigorous oversight and strong collaboration between scientists and engineers, as exemplified in efforts toward artificial waterholes in the Serengeti.