Mapping and distribution of seagrass habitat using hydroacoustic technique, coastal region, South Sea of Korea

Abstract

Presence or absence of seagrass habitats is one of the important indexes for reproductive activity at coastal marine ecosystems. Like other countries, the habitats in Korea were rapidly decreasing in the natural condition because of polluted water or improper coastal development. Recently, studies on the restoration of the damaged seagrass habitat are carried out in Korea. Most important thing in the restoration is to assess present condition of the habitat. Generally, the studies for assessment of the seagrass have been depended on the directed sampling using scuba diving. The methods have some limitations for survey area, depth and efficiency. As an alternative method, an application with hydroacoustic technique was applied to know vertical and spatial distribution of seagrass bed. The field surveys were conduced around coastal regions, on the South Sea of Korea, in September 2005, February and July 2006. Acoustic data were collected using high frequency transducer (420 kHz split-beam), which was installed with a towed body system. Simultaneously, in situ underwater camera data and directly sampling data with quadrate were collected. The number of acoustic transect was 23, 34 and 66 for September 2005, February and July 2006, respectively. Then, survey speed was approximately 3-4 knots. Results indicated that the seagrass beds were strongly limited to bathymetry and region. Conside