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Marine Nearshore & Offshore

Nearshore marine habitat is found in ocean, bay, and river waters that are shallow enough to support photosynthesis, but deep enough to remain submerged at low tide. Offshore marine habitat extends from the edge of the photosynthetic zone to the outer edge of the MA Coastal Zone Boundary.

This habitat has been identified in the Massachusetts State Wildlife Action Plan because it supports a variety of plants and wildlife.

marine offshore
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Habitat description

Nearshore marine habitat is found in ocean, bay, and river habitats and includes eelgrass beds, rocky reefs, kelp forests and other marine habitats that are in water shallow enough to support plant or algal growth (photosynthesis), but deep enough to remain submerged at low tide (subtidal). Offshore marine habitat extends seaward from the edge of the photosynthetic zone (±200m water depth) to the outer edge of the Massachusetts Coastal Zone Boundary.  

Characteristic natural communities

The Massachusetts nearshore and offshore marine environments span both the Gulf of Maine and Southern New England ecoregions and supports a diversity of natural communities. Nearshore eelgrass beds are the basis of a complex ecosystem that provides nursery grounds for many species of fish, shellfish, and other invertebrates. Dense beds or reefs of oyster and other shellfish shape portions of the nearshore environment, and bivalve larvae provide a critical food source for many fish and bird species. Eelgrass bed and shellfish reef communities occur in both shallow nearshore (subtidal) habitats as well as in tidal wetlands. Artificial, man-made reefs may also provide important habitat. Kelp “forests” or algal beds are an important element of the Massachusetts nearshore environment, particularly north of Cape Cod. In the nearshore and deeper offshore environments habitats can also be defined by sediment type and slope. Although there is much important variation, an important distinction can be made between sandy and gravelly hard bottoms and silty or muddy, soft bottoms. 
 

Natural communities are given state rarity/imperilment ranks ranging from S1-S5 (S1: rarest/most imperiled).

Characteristic plants and animals

Nearshore and offshore habitats provide critically important habitat for diadromous and marine fish, seabirds and waterfowl, bivalves and other molluscs, sea turtles, and marine mammals including whales. These highly productive waters support commercial fisheries of great economic importance and are mapped as Essential Fish Habitat by NOAA.  Many SGCN depend on Nearshore and offshore marine habitats, including sturgeon (2 species), herring (2 species), shad, and American eel; green, leatherback, and Kemp’s ridley sea turtles; roseate and common terns, long-tailed duck and common eider, loons (2 species), Northern gannet, shearwater (3 species); and Northern Atlantic right whale.  Deeper offshore habitats support unique communities that include coldwater corals and brittle stars. 

View a complete list of Species of Greatest Conservation Need associated with this habitat.

Associated habitats

Located along the coastline, marine nearshore and offshore habitats are often associated with tidal wetlands, coastal beaches and dunes, and large rivers. Seagrass communities and shellfish beds can be found in both tidal wetlands and marine nearshore habitat. 

Ecological processes

These marine habitats are shaped by currents and tides that transport sediment and plankton and affect water temperature, salinity, and sunlight penetration.  Water chemistry also influences marine natural communities. 

Threats

  • Pollution: Nutrient enrichment and other pollution resulting from coastal development, agriculture, and other land uses is one of the biggest threats to marine habitats.  Nutrient enrichment and associated algal blooms can harm shellfish, fish, birds, and other wildlife, and result in the loss of eelgrass beds.  In some cases, algal blooms can cause a human health hazard.
  • Fishing (biological resource use) has the potential to impact fish populations directly, and fish and other wildlife populations indirectly through bycatch or damage to habitat (e.g. trawling impacts on substrate and submerged vegetation).
  • Invasive species and emerging diseases: Unfortunately, a variety of invasive organisms have become established along the Massachusetts coast.  These include seaweeds, tunicates (sea squirts), bryozoans, and crabs that occur in both marine and intertidal habitats, and can sometimes outcompete native species (MIMIC).
  • Other threats include dredging (natural systems modification), entrainment and impingement at power plants (energy production), and boat collisions.
  • Climate change can have significant impacts on marine habitat, primarily through increasing water temperatures, sea level rise, and increased carbon dioxide storage leading to ocean acidification.  These changes may result in significant shifts in the abundance and distribution of fish and other marine species, including economically important species such as lobster and cod.  Climate change may also affect marine environments in ways that may not at first seem obvious, such as increasing frequency and severity of storms, resulting in increased pollution through storm runoff. A combination of warming waters and increased nutrient runoff can lead to algal blooms, oxygen depletion, and “dead zones.” Ultimately, warmer temperatures and ocean acidification may affect ocean currents and primary production and may substantially alter marine food chains. 

Conservation actions

  • Proactive habitat protection. Protecting land in watersheds of sensitive estuaries and bays can help to maintain and improve water quality.
  • Habitat restoration and management.  See recommendations below
  • Law and policy. Regulate and limit the impacts of development, pollutants, harvest, and bycatch Innovative approaches to incentivizing compatible development and commercial activities in the marine environment should be considered where applicable.
  • Conservation planning. Include marine habitats and associated coastal area in conservation planning efforts at multiple spatial scales.  (See MA Ocean Management Plan as an example.)
  • Monitoring and research.  Monitor the health and trends of SGCN populations, other fisheries resources, and other marine organisms.  Monitor the effectiveness of habitat restoration efforts and conduct targeted research to improve habitat and population management.
  • Public outreach: Include information about the role marine habitats play in biodiversity conservation and climate resiliency as part of broader communication strategies. 

Restoration & management recommendations

A variety of techniques can be used to restore habitat in the marine environment.  In addition, restoration activities in coastal freshwater wetlands, tidal areas, and uplands can improve water quality and reduce stormwater runoff in marine habitats.

Artificial reefs: The introduction of these intentionally placed structures can improve habitat for invertebrates and fish leading to increased fishery production and recreational fishing opportunities. 

Eelgrass restoration: Replanting eelgrass and restoring eelgrass beds can provide significant benefits to a diversity of marine animals, including fish.

Oyster restoration: The seeding and restoration of oyster beds can improve habitat for other species as well as water quality.  

Invasive species: The MA office of Coastal Zone Management works to monitor and reduce the spread of invasive marine species. 

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