Seagrass Habitat Survey

Mapping and monitoring of shallow coastal seagrass habitats tend to be under-sampled globally, and as a result significant knowledge gaps in morphology, ecology and biodiversity remain in these important ecosystems. These environments tend to be too shallow for AUV platforms, and vegetation fouling of props and rudders render other types of ASVs largely ineffective.

As a novel approach, researchers in Norway adapted the Jetyak to use an even less expensive optical imagery method. A Jetyak fitted with GoPro Hero 4 was deployed in a shallow seagrass habitat in a semi-enclosed lagoon in Hopavågen, Norway. The nadir-mounted camera was was carried on an unstabilized mount below the hull and 1080p HD video was captured at a vessel forward speed of 3 kt in a manual (joystick) control mode.

Acquired video imagery was extracted in post-processing and combined into a photo mosaic to enable estimates of seagrass distribution within the study area using image analysis, and this manual unstabilized method was able to discriminate seagrass from bottom. Future refinements planned include improved image illumination, different lens / camera combinations to improve image quality, and greater variable control during mission planning.

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Hydrodynamics Over Seagrass

The hydrodynamics within an estuary control transport, erosion and deposition of sediment in the bottom boundary layer. Seagrasses, with their substantial root systems can offer coastal protection due to their ability to stabilize sediments in shallow coastal environments by altering hydrodynamics. The monitoring of seagrass flows could benefit coastal communities and provide alternatives to augment traditional structural mitigation strategies for coastal protection. However a deeper understanding of how seagrass interacts with complex estuarine flow patterns is essential before viable eco-engineering alternatives can be fully developed.

Acquiring flow data in the heavily vegetated, tidal current shallow water typical of seagrass habitats have traditionally been a challenge. The Jetyak platform, with its shallow draft and jet drive is able to overcome these obstacles. A Jetyak fitted with a Nortek Signature1000 ADCP, RBR Concerto CTD, a Lowrance HDS7 200 kHz echosounder and a Leica GS18T GNSS was used to collect data in the Tauranga estuary in New Zealand. The Jetyak was able to safely navigate through very shallow waterways to measure flows in seagrass canopies and was easier to set-up, launch and clean-up that alternative RVs.

Future consideration will be given to optimizing Jetyak parameters specific to the study area to obtaining higher resolution data and support the analysis of seagrass patch fragmentation and further analyze changes in near bed flow velocities and sedimentation patterns due to seagrass. In addition to flow monitoring, Jetyak can be used to assess seagrass coverage, quantifying growth, retreat and health which provides an indication of overall water quality.

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