Mapping Underwater Habitats

A woman leans over the edge of a boat with an underwater mapping tool.
Scientists mapped the seafloor at coastal parks in the Northeast to help protect submerged habitats and the sea life which depend on them.

NPS Photo/Sarah Gulick

By Minh Phan

Whether it’s harvesting clams and oysters or going for a swim on a beautiful summer day, coastal communities are strongly connected to and influenced by the sea. Boaters often know coastal habitats like the back of their hand, expertly navigating through sand flats, seagrass meadows, and shellfish beds. Until recently, little information was available on these underwater habitats that are home to countless important plants and animals. With recent post-Hurricane Sandy studies at coastal national parks in the northeast, researchers are working to uncover more of the world that lies just beneath these shallow waters.

Imagine a young striped bass gliding through the sea. As marine creatures swim from open water towards the protected bayside of the barrier island, they happen upon patches of tall slender seagrass. This type of vegetation cover found in shallow waters is a magnet for diversity, providing a safe haven by shielding fish and shellfish from potential predators. Without seagrass, the livelihoods of many fish we rely on for recreational fishing and for food would be threatened.

Moving closer to the bottom of these marine habitats, tiny holes in the sand made by small fiddler crabs can be seen. What do you notice about the seafloor? Is it rocky or sandy? Is the slope of the terrain steep or flat? These are some of the elements studied in coastal bathymetry; the nooks and crannies that give the seafloor its depth and shape. The profile of the seafloor can determine how it weathers strong storms and other natural events, like erosion.

Learning What Lies Beneath

With so much value and diversity in this underwater patchwork of habitats and sea life, it’s no wonder the National Park Service (NPS) invested in a multi-park effort to map the relatively uncharted shallow waters in and around coastal national parks. Several research teams surveyed waters stretching from the coastlines of the Chesapeake region up to New England. These maps established a new, much-needed foundation of information on the complex shallow-water habitats that lie just off the coast.

Researchers use various types of instruments to map the mosaic of underwater habitats within each park and gather a wealth of information on the types of underwater sediment, animals, and vegetation. Aerial photography, for example, uses cameras mounted on small planes and are great for taking snapshots of large areas when the water is shallow and clear. In areas where aerial photography is not as reliable, acoustic sonar is used. Sonars use sound to create an image of what the seafloor looks like. This is the similar to the technology that ships use to detect other ships and objects. To complement aerial and acoustic data, physical samples of the seafloor are collected to examine sediment composition and biological communities in more detail. These samples also help researchers confirm their interpretations of the aerial and acoustic data.

Prior to 2014, Cape Cod National Seashore, Fire Island National Seashore, and Gateway National Recreational Area had very little information on submerged habitats, despite the fact that submerged lands make up at least 40% of the total area of each park. However, at Assateague Island National Seashore, maps of offshore aquatic habitats were developed in 2011 and repeating the mapping presented the unique opportunity for researchers to see how storms like Hurricane Sandy impact sand and sediment beneath the ocean surface.

Snapshots of the Seafloor Help Managers Protect Sea Life

When strong waves and currents cause shifts in underwater sediment along the seafloor, there can be dramatic changes that impact the homes of many aquatic animals and plants. Many species are attracted to specific types of sediment and will move to where they are most comfortable. Other species are sessile, meaning they stay in one place and are then unable to cope with new environmental conditions. Because habitat for sea life is tightly connected to the seafloor, any change to the texture or type of sediment in this region can result in ecosystem changes, including the migration of fish, the growth of seagrasses, and the extent and density of shellfish beds.

At Fire Island, analyses of submerged habitats since Sandy informed the development of a management plan to determine whether a breach that formed in the seashore’s wilderness area should remain open or be closed mechanically. Studies indicated that the breach allowed for increased exchange of water between the Atlantic Ocean and Great South Bay, improving water quality and clarity in the area of the bay near the breach.

“There has been more clarity in the waters close to the breach, which allows more sunlight to penetrate through the water. This in turn promotes the regeneration of eelgrass which has enhanced biodiversity in the vicinity of the breach” explains Jordan Raphael, a park biologist at Fire Island. Stability and balance are important for long term success and resilience, and changes in submerged habitats, both on large and small scales, often indicate underlying issues that may threaten the many coastal resources we rely on every day.

To understand these issues and bring together information on both local and regional levels, researchers at different parks compare information on submerged habitats by using the Coastal and Marine Ecological Classification Standard, called CMECS. This recently developed mapping framework for organizing information helps improve data use and sharing, by providing a consistent system for categorizing different types of underwater areas. Researchers can incorporate findings from multiple parks, allowing them to see the bigger picture and uncover large scale regional patterns and impacts relating to such things as tropical cyclone impacts, ocean temperature increases, and sea-level rise.

This systematic research provides northeast coastal parks with an organizational foundation that allows parks to establish data that can be used in future studies. This will help researchers establish trends over time that resource managers can use to guide decisions on how to best support coastal resilience and protect the many benefits of these systems now and into the future.

Preserving the mysterious and wonderful world beneath our shimmering seas is a priority. The National Park Service is committed to continuing research into submerged habitats to further understand the value these environments hold for coastal communities.

Assateague Island National Seashore, Cape Cod National Seashore, Fire Island National Seashore, Gateway National Recreation Area

Last updated: April 9, 2023