Mapping Underwater Habitats at Northeast Coastal Parks

Mapping the seafloor at a northeast coastal park. NPS / Sarah Gulick.

By Minh Phan.

Coastal communities live with the sea — harvesting clams and oysters, swimming, boating past sand flats, seagrass meadows and shellfish beds. Yet until recently, little was known about these shallow underwater habitats. Studies at northeast coastal parks after Hurricane Sandy set out to change that.

Why the seafloor matters

• Seagrass: tall, slender seagrass draws diversity, sheltering young fish such as striped bass and shellfish from predators. Without it, many fish important to recreational fishing and food would be threatened.
• Bathymetry: whether the bottom is rocky or sandy, steep or flat — its depth and shape — affects how it weathers storms and erosion.

Learning what lies beneath

Research teams mapped shallow waters from the Chesapeake region to New England, laying a much-needed foundation of information:

• Aerial photography from small planes covers large areas where water is shallow and clear.
• Acoustic sonar, the same idea ships use to detect objects, images the bottom with sound where photos don't work.
• Seafloor samples show sediment and biological communities in detail and check the aerial and sonar interpretations.

Before 2014, Cape Cod and Fire Island National Seashores and Gateway National Recreation Area knew very little about their submerged habitats, though submerged lands make up at least 40% of each park. Assateague Island National Seashore had offshore habitat maps from 2011; mapping again showed how storms like Sandy reshape the sand and sediment below.

Snapshots that help protect sea life

• Moving sediment, moving life: when waves and currents shift the seafloor, species that prefer certain sediments move, while sessile ones, fixed in place, may not cope — changing fish migration, seagrass growth, and shellfish beds.
• Fire Island's breach: habitat studies after Sandy informed a plan on whether a breach in the seashore's wilderness area should stay open. It increased exchange between the Atlantic and Great South Bay, improving water quality and clarity nearby. "There has been more clarity in the waters close to the breach, which allows more sunlight to penetrate through the water," said park biologist Jordan Raphael, which has helped eelgrass regrow and boosted biodiversity.
• A common language: parks classify habitats with the Coastal and Marine Ecological Classification Standard (CMECS), so findings can be combined to reveal regional patterns — the effects of tropical cyclones, warming ocean temperatures and sea-level rise.

These baselines will let researchers track trends over time and help managers support coastal resilience. The NPS is committed to continuing research into submerged habitats.

Sources

Based on "Mapping Underwater Habitats," by Minh Phan, National Park Service; a work of the United States government in the public domain.