Division of Aquatic Resources

By West Hawaiʻi DAR/HCRI staff

Hawaiʻi Division of Aquatic Resources staff have been monitoring trends in fishes and coral reefs across the state for decades. This information allows us to track changes in coral reef health over time which helps to inform management decisions. A critical component of what makes a coral reef ecosystem healthy and functional is the condition and structure of the reef itself. Coral species in Hawaiʻi come in various forms from large mounding colonies to highly intricate branching structures and many shapes in between. In addition to living coral, basalt also plays a role in creating complex reef structure in the form of large boulders, underwater arches, spurs, and grooves. The structure of the reef is what makes it habitable for the fish and marine invertebrates that we appreciate and rely on as resources.

SCUBA diver collecting imagery for photogrammetry

Unfortunately, accurately tracking the complexity of coral reefs has long been a difficult task. Divers would often spend painstaking hours with small chains and measuring tapes on the seafloor trying to gain simple measures of rugosity (seafloor complexity). Marine researchers also rely on standard photography to capture individual images of the corals, algae, invertebrates and other organisms that occupy the reef. This, however, comes with its own challenges as each photo is limited to a two-dimensional view of a relatively small patch of reef. Lastly, remote sensing systems like LiDAR and sonar can cover large areas, but they lack the resolution to examine the fine structure of coral reefs. Luckily, a newer technology called photogrammetry has given us an opportunity to obtain multiple measures of structural complexity over relatively large portions of the seafloor while also documenting what organisms are living on the reef.

The process of photogrammetry involves taking a series of overlapping photos of a survey plot and using computer software to stitch them together into a high resolution 3-dimensional model of the reef habitat (see embedded videos). This gives us an unprecedented ability to effectively bring the reef back home with us and gather a much wider range of data than ever before. This 3-D model can be analyzed for key parameters that are important for providing habitat to fishes and invertebrates. The model can also act as a single, gigantic image of the reef to provide useful estimates of coral and algal cover and potentially detect problems like invasive algae and coral disease.

DAR staff across the state have been learning rapidly about photogrammetry techniques and all the ways we can apply them to help better monitor and manage coral reefs. The National Oceanic and Atmospheric Administration (NOAA) and the Scripps Institute of Oceanography helped to kick off our understanding of this technology over the past few years. More recently, the MEGA (Multiscale Environmental Geographical Analysis) Lab at the University of Hawaiʻi at Hilo has been providing hands-on training for DAR staff to tailor photogrammetry protocols to our specific needs. As of now, DAR has already integrated this technology in a number of ways including long-term reef monitoring in West Hawaiʻi and assessments of coral damage from vessel groundings and anchor damage incidents. We’re excited to continue applying this technique to additional projects in the future including tracking coral disease, monitoring invasive species, and measuring coral growth.

3D model of a small cauliflower coral (Pocillopora meandrina) colony off West Hawai’i