Mapping of seagrass and seaweed beds using hydro-acoustic methods

Mapping of seagrass and seaweed beds is very important for management and conservation of sound littoral ecosystems and sustainable fisheries in the coastal waters. The methods to map spatial distribution of seagrass and seaweed beds are reviewed. They are classified into two categories. One is a direct method by visual observation and the other is an indirect method using a remote sensing apparatus. Indirect methods are divided into optical or hydro-acoustic methods. Indirect methods require sea truth by direct methods. Optical methods are image analysis of aerial photography or satellite imagery. They are effective for mapping broad areas but limited to shallow waters due to light attenuation in waters. Hydro-acoustic methods such as an echosounder and a side scan sonar have no limitation of turbidity The echosounder is practical to map vertically density and height distributions of seagrass and seaweed beds. The side scan sonar is appropriate for mapping broad horizontal distributions. Coupling of several indirect mapping methods is more useful than using only one method.