Underwater Video
A submersible digital video camera is deployed at selected sites to ensure accurate echo-sounder habitat boundary definitions and obtain more detailed information on habitat modifiers, particularly the dominant seagrass and macroalgal species. Video sampling involves individual vertical drops and transects conducted at regular intervals perpendicular to the shore along the depth gradient.
A SONY TRV900 digital camera is used to record the video footage. The video camera frame contains around 40 kg of weight and is towed at a speed less than 1 knot to ensure that the camera is positioned as close to the GPS antenna as possible (this is often visible directly under the vessel in depths less than 20 m). The camera is suspended approximately 1 m from the sea floor giving a field of view (FOV) that varies between 1-2 m wide. Differential GPS location, time, date and water depth are overlayed onto the video from the GPS sounder using a genlock device and logged in a file on Seabed Mapper 4.0 for use in the analysis.
The video footage is reviewed in the labratory, and in conjuntion with the field notes, is used to estimate the percentage cover of each of the major visually dominant macroalgal species for reef habitat attibution. This information is correlated against depth and exposure to determine characteristic biotic community types for combinations of each of the physical variables or habitats.
A representative image is taken from a range of depths at each video transect site and archived. A selection of photographs or video can be viewed in the Photo Gallery or in the Video Gallery