Why Mapping Matters

First Voyage: Gulf of Maine

Steve has been working with maps of the seafloor since 2012, when he was on an expedition in the Gulf of Maine that used paper sounding charts to plan  tow-sled  deployments in near-shore environments for recording video of the seafloor where corals might be present. “We were making our best guesses from ‘bumps’ on these sounding charts,” he recalled. However, since that first mission, multibeam bathymetric maps have been the basis of most of Steve’s work. 

Image: Annotated sounding map from Steve's expedition to the Gulf of Maine. Inset: Coral community photographed by the tow-sled. Image credit: Auster, P. J., et al (2014). Imaging surveys of select areas in the northern Gulf of Maine for deep-sea corals and sponges during 2013-2014. Report to the New England Fishery Management Council—1 December.

Cayman Rise

Steve’s first chance to use high resolution digital maps of the seafloor was on  an expedition to the Cayman Rise , south of Cuba, in 2013. This was his first time as a member of the Corps of Exploration on the Nautilus as an Ocean Science Intern. The area is home to a unique tectonic spreading center with  hydrothermal vents . The expedition obtained mapping data at night and deployed the remotely operated vehicles (ROVs) during the day. Despite the much higher resolution of bathymetric maps over paper sounding charts, Steve remembers being surprised at the additional level of detail obtained from the ROV dives. “The seafloor has a lot more texture than any surface mapping technique will show.”

Ho’oikaika Seamount

Since that first expedition as an ocean science intern, Steve has been a frequent member of the Corps of Exploration, serving as Science Manager, Supporting Scientist, and Lead Scientist. He highlights how maps are important before, during, and after an expedition. 

“Months in advance, the mapping team aggregates all available data for the expedition area. In remote areas, we might have just one or two passes of high quality bathymetry transits.” Expedition planners use the composite map to evaluate specific features to explore with ROV dives or areas where more mapping is needed. The team considers many factors, including depth, steepness, orientation within currents, transit times between dive targets, and more. 

Detailed bathymetric maps guide ROV dives during expeditions. In addition, existing mapping is expanded during transits and any time that ROVs are not in the water.

Image credit: OET / QPS Fledermaus

Ground-Truthing with ROVs

After the expedition, new data gathered during ROV dives, including biological samples, imagery, and centimeter-scale mapping data along the dive track are combined with the bathymetric maps. One of the big goals is to gather enough information to create predictive habitat maps that will allow scientists to target areas for future exploration and conservation. For example, the depth and steepness of seamount slopes have a great influence on what species we might find and how many of those organisms might be in an area. Most corals and sponges, for example, prefer hard substrates so that they can have firm attachment points and require currents carrying marine snow as their food source. Predictive models like this are so important because of the limited scope and scale of ROV exploration. “It’s not possible to survey every area, even on a single seamount.”

Image credit: OET / QPS Fledermaus

Pacific Remote Islands Marine National Monument

One of Steve’s favorite areas is the Pacific Remote Islands Marine National Monument (PRIMNM).  Expeditions near Jarvis Island, Howland and Baker Islands, Kingman Reef and Palmyra Atoll, and Johnston Atoll have given him the opportunity to explore this vast, remote region. “One of the greatest concentrations and diversities of seamounts in the world are in this region, and there are unique oceanographic processes that occur in equatorial seas that aren’t happening at more northerly or southerly areas of the Pacific.” 

For example, primary production and upwelling along the equator can result in higher animal density on the seafloor. Also, the equator is an overlap region of a lot of different regional and global water masses that have unique oceanographic properties, including temperature, salinity, and dissolved oxygen. The mixing of these water masses, which often have a unique collection of species, could result in higher diversity benthic communities on the seafloor as a result of range overlaps.

Image credit:  NOAA 

Jarvis Island

Another one of Steve’s most memorable  expeditions  was in and around Jarvis Island. “The diversity and abundance in this area was some of the highest I have ever seen.” 

Johnston Atoll Surprise

An  expedition to the Johnston Atoll area  in 2022 also made it into Steve’s list of top favorite locations for ROV dives. The team observed a Solumbellula sea pen, an organism that was previously only known to occur  in the Atlantic and Indian Oceans.  This sighting will require a major revision in the range map or even a new species description for this strange and wonderful organism.

More Work To Be Done

Less than 25% of the seafloor has high quality mapping data, so there are plenty of places to prioritize. Steve is especially interested in seamounts that are in the “high seas”, outside the jurisdictional waters of any country.  Not only does mapping coverage tend to be sparser in these areas, but since they are outside of any particular country’s Exclusive Economic Zone (EEZ), these areas are vulnerable to extractive practices like fishing, dredging, and seafloor mining. Mapping and exploring these areas is the first step towards making the case for conservation and protection.

Image: Areas mapped by Nautilus both inside and outside the yellow extended boundary of Papahānaumokuākea Marine National Monument. Areas inside the monument (which are also part of the United States EEZ) are protected and prioritized for mapping, while those outside are not.

Image credit: OET / QPS Fledermaus