NCCOS developed benthic habitat maps for shallow (<30 m) areas around the Main Hawaiian Islands to help local managers and researchers develop reef fish management strategies, optimize biological monitoring sampling design, and develop place-based action strategies to address key issues and remedy specific threats to coral reefs.

WHY WE CARE

Shallow-water (< 30 m) coral reef ecosystems in the surrounding waters of the Main Hawaii Islands are unique natural resources that must be preserved. The mosaic of habitats, including hard and soft corals, are home to a diversity of marine organisms, which provide important ecosystem services to the community of Hawaii, including fishing, tourism and shoreline protection. However, coral reef ecosystems throughout the US Pacific are under increasing pressure from environmental and anthropogenic stressors. Mitigating these threats requires that resource managers first understand the spatial distribution of these resources, making benthic habitat mapping an integral component to ecosystem-based approaches to management.

WHAT WE DID

We mapped 1,310 km2 of shallow-water habitats around the Main Hawaiian Islands, supported by funding from NOAA’s Coral Reef Conservation Program.

In 2007, more contemporary and complete benthic habitat products were produced using commercial satellite imagery. This effort provided more detailed and up-to-date mapping product than those produced in 2003 using aerial photography. In tandem, this products provide a useful time series of habitat change. Both 2007 and 2003 maps and products are available through the data collections links below.

WHAT WE FOUND

In 2007, we mapped thirty-two distinct benthic habitat types using visual interpretation of satellite imagery. The cover types: coral, seagrass, macroalgae, coralline algae, turf algae, emergent vegetation, uncolonized, and unknown, are combined with a density modifier representing the percentage of the predominate cover type (10%-<50% sparse, 50%-<90% patchy, 90%-100% continuous).

Results are as follows:

1. Approximately 70% of the geomorphic structure was classified as coral reef and hardbottom.  For the detailed structure category, the coral reef and hardbottom class consisted mostly of pavement (~33%), sand (25%), rock/boulder habitat (22%), with aggregate coral reef and spur habitat at 5% and coral groove habitat at 3%.
2. In general, turf algae (30%) and macroalgae (23%) were fairly dominant cover types in the Main Hawaiian Island coral reefs.
3. Approximately 30% of the geomorphic structure was classified as unconsolidated sediment (sand and/or mud), including 25% sand and 5% mud classes.

The thematic accuracy of the maps was assessed by an independent team of scientists. The maps were also reviewed and edited by local experts prior to being published. The final deliverables for this project included the benthic habitat maps, source imagery and georeferenced underwater videos and photos.

These map products were used to evaluate the efficacy of existing marine protected areas, coastal development projects under consideration, and evaluating local-level management decisions.