Diversity of attached marine life in different types of artificial timber reefs

Abstract

Artificial reefs (ARs) have been implemented as a tool to increase fish catch by gathering fish and creating new habitat. In Japan, fisheries production has been decreasing in the last several decades. Research on ARs to date has mainly focused on fish biomass and community structure. The present study describes the community structure of marine organisms attached to the ARs deployed in Mitsu Bay, Hiroshima, Japan. We compare those communities on three types of ARs, which are made of timbers (ATRs), ATRs with oyster shells (ATRsOS) and ATRs with leaves and branches (ATRsLB). Attached organisms were collected seasonally from 2016 to 2018. Overall, 272 taxa were identified from two deployment sites. Arthropods were the dominant group identified, followed by molluscs and annelids. Seasonal variation of individuals collected was observed, with numbers being high in summer and low in winter. The number of individuals was high in the first year after deployment of ATRs, decreasing in the second year and beyond, suggesting the animal community may have matured by balancing the growth and feeding by fish. All three types of ATRs were commonly large in individual number and small in species number, characterized by a low diversity index. The highest individual number and highest species number were observed in ATRsLB and ATRsOS, respectively. More specifically, the diversity index for simple ATRs was lower than those for ATRsOS and ATRsLB. This result suggests that ATRs with additional materials can provide a wide range of feed animals which may attract more fish. The deployment of ATRs made of materials like timbers and oyster shells is also good practice for promoting a recycling-oriented society.