Japanese vs French Artificial Reefs: High Technology vs Design to Enhance Ecological Services

摘要

Artificial reefs (ARs) worldwide are mostly used for fish production or recreational purposes. In Japan, fishermen have known this concept since the Middle Ages. Historically, fishermen used artisanal structures hand-made with traditional and natural materials to improve coastal fisheries. Nowadays, high technology assemblages optimize the operational effectiveness of artificial reefs. In France, artificial reefs are not used at the same scale as in Japan (200:1) and have been deployed since 1968 with the main objective of enhancing coastal artisanal fishing. More than half of the ARs in France have been constructed over the last 15 years. With the deployment in 2007 / 2008 of more than 400 ARs within a 200 ha zone of the Bay of Marseille (Mediterranean, France), RECIF PRADO represents the largest AR system in the French Mediterranean Sea (27 300m~2). Over the last few years, in France, it has been public policy to promote the research and deployment of small ARs for environmental restoration. Generally, the enhancement of species or ecological functions is targeted with the aim of offsetting environmental degradation. For example, the earliest benthic larval stages, fish recruitment and algal assemblages could benefit from AR-based systems. As an illustration, we may consider the example of the increase in the recruitment of juveniles on artificial reefs at Marseille from 2011 to the end of 2015, using artificial and biological systems. Artificial systems consisted of floating ropes arranged on the top of the ARs. Biological systems involved the transplantation on ARs of living specimens of Cystoseira zosteroides C. Agardh (Phaeophyceae, Fucales), an ecosystem engineer species currently in decline in the Mediterranean Sea. A four-year in situ monitoring survey was carried out on and around these systems through censuses of fish juveniles and the study of the fate of C. zosteroides transplants using SCUBA diving. The recruitment of fish juveniles was multiplied by 4 to10 on both systems, compared to non-equipped ARs. The fish family most concerned was the Labridae. Cystoseira zosteroides transplants survived, grew and produced fertile receptacles. The efficacy of the artificial system decreased over time because of the fouling that altered the habitat availability for the juveniles. In contrast, the biological system remained effective and even increased in efficacy over time, due to the recruitment on the ARs of offspring born of the transplanted C. zosteroides. During 2014, ten different species of juveniles of fishes were observed on the AR equipped with biological systems. Improved efficacy of ARs in terms of fish stock is therefore possible through the addition of special systems designed to increase the fish recruitment. Biological systems would appear to be preferable to artificial ones, especially since they are more in phase with sustainable management as they are long-lasting and do not require maintenance.