SOURCE: NOAA (2019a).

Exposed Rocky Banks (ESI 1A)

SOURCE: Daderot, CC0, via Wikimedia Commons.

• The intertidal zone is steep (>30° slope) and narrow with very little width.
• Regular exposure to high wave energy or tidal currents.
• Strong wave-reflection patterns are common.
• Substrate is impermeable (usually bedrock or cement) with no potential for subsurface penetration.
• Species density and diversity vary.
• Barnacles, snails, mussels, polychaetes, and macroalgae can be abundant.

• Oil is held offshore by waves reflecting off the steep, hard surfaces.
• Any oil that is deposited is rapidly removed from exposed faces.
• The most resistant oil would remain as a patchy band at or above the high tide line.
• Impacts to intertidal communities are expected to be short term.
• An exception would be where heavy concentrations of a light refined product came ashore very quickly.

SOURCE: NOAA (2019a).

• These are solid, man-made structures such as seawalls, groins, revetments, piers, and port facilities.
• They are built to protect the shore from erosion by waves, boat wakes, and currents, and thus are exposed to rapid natural removal processes.

SOURCE: NOAA (2019a).

• Natural formations that protect shore from erosion by waves, boat wakes, and currents.

SOURCE: NOAA (2019a).

Shelving Bedrock Shores (ESI 2A)

SOURCE: NOAA (2019a).

• These shores consist of a bedrock shelf or platform of variable width and very gentle slope.
• The surface of the platform is irregular; tide pools are common.
• Along headlands, they have only a small accumulation of sediments, mostly at the high tide line.
• They often co-occur with gravel beaches; the gravel beach can be either at the upper or the lower half of the intertidal zone, depending on the nature of the bedrock outcrop.
• Species density and diversity vary greatly, but barnacles, snails, mussels, and macroalgae are often abundant.

• Oil will not adhere to the wet rock surface but could penetrate crevices or sediment veneers.
• Oil persistence is usually short-term, except in wave shadows or where the oil was deposited high above normal wave activity.

SOURCE: NOAA (2019a).

Coarse-Grained

SOURCE: NOAA (2019a).

• These beaches are flat to moderately sloping and relatively hard-packed.
• There can be heavy accumulations of wrack.
• They can be important areas for nesting by birds and turtles. Upper beach fauna include ghost crabs and amphipods; lower beach fauna can be moderate, but highly variable.

• Light oil accumulations will be deposited as oily swashes or bands along the upper intertidal zone.
• Heavy oil accumulations will cover the entire beach surface; oil will be lifted off the lower beach with the rising tide.
• Maximum penetration of oil into fine- to medium-grained sand is about 10–15 cm, up to 25 cm in coarse-grained sand. Burial of oiled layers by clean sand can be rapid (within 1 day), and burial to depths as much as one meter is possible if the oil comes ashore at the beginning of a depositional period.
• Organisms living in the beach sediment may be killed by smothering or lethal oil concentrations in the interstitial water.
• Biological impacts include temporary declines in infauna, which can affect important shorebird foraging areas.

SOURCE: NOAA (2019a).

SOURCE: NOAA (2019a).

SOURCE: NOAA (2019a).

SOURCE: NOAA (2019a).

• These are erosional features with tundra vegetation overlying peat and exposed ground ice or permafrost.
• Cliff heights range from less than 1 meter to as much as 5–10 meters.
• There may be a narrow beach present or just a vertical scarp. As the cliffs erode at rates of 0.5–4 meters/year, the vegetation and peat accumulate as fragmented and irregular blocks at the base of the cliff until they are reworked by waves.
• The vegetation on the tundra is a living plant community that is sensitive to disturbances.
• Large numbers of migratory birds can use these shorelines during the summer months.

• Oil could be stranded onshore only during the ice-free summer season.
• Oil is not likely to adhere to exposed ground ice unless air temperatures are below freezing.
• Oil persistence on the vegetation and peat substrates would be short in most cases, due to natural cliff erosion, provided that the oil is not stranded at the onset of freeze-up.
• If the oil mixes with the peaty substrate or accumulated peat, it could create sheens until the oiled area erodes.
• Biological risks would be greatest to birds feeding along oiled cliffs in summer.

SOURCE: NOAA (2019a).

SOURCE: NOAA (2019a).

SOURCE: NOAA (2019a).

Mixed Sand and Gravel Bars and Gently Sloping Banks (ESI 5)

SOURCE: NOAA (2019a).

• Because of the mixed sediment sizes on these moderately sloping beaches, there may be zones of pure sand, pebbles, or cobbles.
• There can be large-scale changes in the sediment distribution patterns depending on season, because of the transport of the sand fraction offshore during storms.
• Desiccation and sediment mobility on exposed beaches cause low densities of attached animals and plants.
• The presence of attached algae, mussels, and barnacles indicates beaches that are relatively sheltered, with the more stable substrate supporting a richer biota.

• During small spills, oil will be deposited along and above the high tide swash.
• Large spills will spread across the entire intertidal area.
• Oil penetration into the beach sediments may be up to 50 cm; however, the sand fraction can be quite mobile, and oil behavior is much like on a sand beach if the sand fraction exceeds about 40 percent.
• Burial of oil may be deep at and above the high tide line, where oil tends to persist, particularly where beaches are only intermittently exposed to waves.
• In sheltered pockets on the beach, pavements of asphalted sediments can form if oil accumulations are not removed, because most of the oil remains on the surface.

SOURCE: NOAA OR&R.

Gravel Beaches (Granules and Pebbles) (ESI 6A)

SOURCE: NOAA (2019a).

• Gravel beaches can be very steep, with multiple wave-built berms forming the upper beach.
• The degree of exposure to wave energy can be highly variable among gravel beaches.
• Density of animals and plants in the upper intertidal zone is low on exposed beaches but can be high on sheltered gravel beaches and on the lower intertidal zone of all beaches.

• Stranded oil is likely to penetrate deeply into gravel beaches because of their high permeability.
• Rapid burial can occur at the high tide and storm berms.
• Long-term persistence will be controlled by the depth of routine reworking by the waves.
• On exposed beaches, oil can be pushed over the high tide berms, pooling and persisting above the normal influence of wave washing.
• Along sheltered portions of the shorelines, chronic sheening and the formation of asphalt pavements is likely where accumulations are heavy.

SOURCE: NOAA (2019a).

SOURCE: NOAA (2019a).

SOURCE: NOAA (2019a).

• Riprap structures are composed of cobble- to boulder-sized blocks of granite, limestone, concrete, or other materials.
• Riprap structures are used as revetments and groins for shoreline protection, and as breakwaters and jetties around inlets and marinas.
• Attached biota are generally sparse at the upper intertidal zone, but more common in the lower intertidal zone.
• They are common in highly developed waterfront areas.
• 6c applies to estuarine shorelines only in Southeast Alaska

• Deep penetration of oil between the blocks is likely, with oiling of associated debris.
• Oil adheres readily to the rough surfaces of the blocks.
• Uncleaned oil and debris can cause chronic leaching until the oil hardens.

SOURCE: NOAA OR&R.

Boulder Rubble (ESI 6D)

SOURCE: NOAA (2019a).

SOURCE: NOAA (2019a).

SOURCE: NOAA (2019a).

• Exposed tidal flats are broad intertidal areas composed primarily of sand and minor amounts of gravel or mud.
• The presence of sand indicates that tidal currents and waves are strong enough to mobilize the sediments.
• They are usually associated with another shoreline type on the landward side of the flat, though they can occur as separate shoals; they are commonly associated with tidal inlets.
• The sediments are water saturated, with only the topographically higher ridges drying out during low tide.
• Biological use can be very high, with large numbers of infauna, heavy use by birds for roosting and foraging, and use by foraging fish.

• Oil does not usually adhere to the surface of exposed tidal flats, but rather moves across the flat and accumulates at the high tide line.
• Deposition of oil on the flat may occur on a falling tide if concentrations are heavy.
• Oil does not penetrate water-saturated sediments but may penetrate coarse-grained sand and coat gravel.
• Biological damage may be severe, primarily to infauna, thereby reducing food sources for birds and other predators.

SOURCE: NOAA (2019a).

SOURCE: NOAA (2019a).

SOURCE: NOAA (2019a).

• Sheltered rocky shores are characterized by a rocky substrate that can vary widely in permeability.
• Of particular concern are rocky shores that have a semi-permeable veneer of angular rubble overlying the bedrock.
• Sheltered clay scarps are characterized by a steep, usually vertical scarp in hard-packed and stiff clay. Vegetation usually occurs landward of the scarp.

• Oil will adhere readily to dry, rough, rocky surfaces, particularly at the high tide line, forming a distinct oil band.
• The lower intertidal zone of rocky shores is usually algae-covered and stays wet, preventing oil from adhering.
• Oil will not adhere to the wet clay sediment surface but could penetrate dry sediment.
• Stranded oil will persist because of the low-energy setting.
• Oil will adhere readily to the rough surface, particularly along the high tide line, forming a distinct oil band.
• The lower intertidal zone usually stays wet (particularly if algae covered), preventing oil from adhering to the surface.

SOURCE: NOAA (2019a).

SOURCE: NOAA (2019a).

Sheltered Riprap (ESI 8C)

SOURCE: NOAA (2019a).

• These are structures such as seawalls, groins, revetments, piers, and port facilities, constructed of concrete, wood, or metal.
• Most structures are designed to protect a single lot; thus, their composition, design, and condition are highly variable.
• Often there is no exposed beach at low tide, but multiple habitats may be present.
• There can be dense attachments of animal and plant life.
• They are common in developed waterfront areas.

SOURCE: NOAA (2019a).

Peat Shores (ESI 8E)

SOURCE: Gillham (1978).

• This shoreline type includes exposed peat scarps, eroded peat, and peat slurries.
• Exposed peat scarps occur where the peat is frozen.
• They are highly erosional (>1 meter/year), resulting from wave action, ice scour, and melting of the frozen peat.
• The intertidal zone is often very complex, with slumped peat blocks and a thin (and temporary) sand layer on the peat.
• Eroded peat occurs as a peat mat or veneer in a dewatered state, deposited on a sand or gravel beach; it is usually less than 20 cm thick and considered to be relatively transient.
• Peat slurries (which have the appearance of coffee grounds) are up to 50 cm thick and 10 meters wide.
• Peat slurries are found at the foot of eroding peat scarps and in depositional areas; they are relatively permanent features that move along the shore with the currents.
• Peat shorelines comprise about 70 percent of the Beaufort Sea coast of Alaska.
• The intertidal zone of this shoreline type is not particularly important as a biological habitat.
• Substrate can be highly variable, from smooth, vertical bedrock to rubble slopes.
• There can be dense attachments of animal and plant life.

• Oil could be stranded onshore only during the ice-free summer season.
• Oil penetration and persistence are expected to be very low in frozen peat scarps.
• Light oil can penetrate peat slurries, especially when the peat is dry.
• Peat resists penetration by heavy oils, even when dry.
• Peat slurry reacts with oil like loose granular sorbent and will partially contain and prevent the oil from spreading.

SOURCE: Chrisseufert (2008).

SOURCE: NOAA (2019a).

• Steep shorelines with a vegetated bluff face often covered by shrubs.

• Oil adheres readily to dry, rough surfaces, forming a distinct oil band.
• Stranded oil will persist at low-energy settings.

SOURCE: NOAA (2019a).

Sheltered Sand and Mud Flats (ESI 9A)

SOURCE: NOAA (2019a).

• Sheltered tidal flats are composed primarily of mud with minor amounts of sand and shell.
• They are usually present in calm-water habitats, sheltered from major wave activity, and frequently backed by marshes.
• The sediments are very soft and cannot support even light foot traffic in many areas.
• There can be large concentrations of bivalves, worms, and other invertebrates in the sediments.
• They are heavily used by birds for feeding.

• Oil does not usually adhere to the surface of sheltered tidal flats, but rather moves across the flat and accumulates at the high tide line.
• Deposition of oil on the flat may occur on a falling tide if concentrations are heavy.
• Oil will not penetrate the water-saturated sediments but could penetrate burrows and desiccation cracks or other crevices in muddy sediments.
• In areas of high suspended sediment concentrations, the oil and sediments could mix, resulting in the deposition of contaminated sediments on the flats.
• Biological impacts may be severe.

SOURCE: NOAA (2019a).

• Vegetated low banks are composed primarily of mud with minor amounts of sand and shell.
• They are usually present in calm-water habitats, sheltered from major wave activity, and frequently backed by marshes.
• They are heavily used by birds for feeding.

SOURCE: NOAA (2019a).

• Tidal flats are composed primarily of sand and shell.
• They are usually present in calm-water habitats, sheltered from major wave activity, and frequently backed by marshes.
• The sediments are water saturated, with only the topographically higher ridges drying out during low tide.

SOURCE: NOAA (2019a).

Freshwater Marshes (ESI 10B)

SOURCE: NOAA (2019a).

Swamps (ESI 10C)

SOURCE: NOAA (2019a).

Scrub and Shrub Wetlands (ESI 10D)

SOURCE: NOAA (2019a).

• Intertidal wetlands contain emergent, herbaceous vegetation, including both tidal and muted tidal marshes.
• Depending on location and interannual variations in rainfall and runoff, associated vegetation may include species tolerant or adapted to salt, brackish, or even tidal freshwater conditions.
• The marsh width may vary from a narrow fringe to extensive areas.
• Sediments are composed of organic muds except where sand is abundant on the margins of exposed areas.
• Exposed areas are located along bays with wide fetches and along heavily trafficked waterways.
• Sheltered areas are not exposed to significant wave or boat wake activity.
• Abundant resident flora and fauna with numerous species and high use by birds, fish, and shellfish.

• Oil adheres readily to intertidal vegetation.
• The band of coating will vary widely, depending on the water level at the time of oiling.
• Large slicks will persist through multiple tidal cycles and will coat the entire stem from the high tide line to the base.
• Heavy oil coating will be restricted to the outer fringe of thick vegetation, although lighter oils can penetrate deeper, to the limit of tidal influence.
• Medium to heavy oils do not readily adhere to or penetrate the fine sediments but can pool on the surface or in animal burrows and root cavities.
• Light oils can penetrate the top few centimeters of sediment; under some circumstances oil can penetrate burrows and cracks up to one meter.

SOURCE: Strang (2013).

• This shoreline type occurs where very low-lying sections of the Arctic shoreline have been recently flooded by the sea, due to subsidence.
• Also includes areas that are not normally in the intertidal zone but can be frequently inundated by salt water during spring tides or wind induced surges.
• They have complex and convoluted shorelines comprised of tundra, vegetated flats, riverbanks, peat mats, brackish lagoons, and small streams.
• These shorelines have high ice content; the surface material is mostly peat with little mineral sediments.
• Where present, the vegetation is salt-tolerant and may be more adapted to drier conditions than the salt marshes.
• The tundra is a living plant community and provides important feeding areas for migrating birds in the summer.

• Oil could be stranded onshore only during the ice-free summer season.
• During storm surges, spilled oil could strand hundreds of meters inland.
• During the summer months, the surface sediments/peat deposits are usually water-saturated, so stranded oil is likely to remain on the surface.
• Physical removal rates of medium to heavy oils will be slow.

SOURCE: NOAA (2019a).

• The roots and trunks are intertidal, with only the lowest leaves inundated by high tide.
• The width of the forest can range from one tree to many kilometers.
• The substrate can be sand, mud, leaf litter, or peat, often as a veneer over bedrock.
• Wrack accumulations can be very heavy.
• They are highly productive, serve as nursery habitat, and support a great diversity and abundance of animal and plant species.

• Oil can wash through mangroves if oil comes ashore at high tide.
• If there is a berm or shoreline present, oil tends to concentrate and penetrate into the berm sediments or accumulated wrack/litter.
• Heavy and emulsified oil can be trapped in thickets of red mangrove prop roots or dense young trees.
• Oil readily adheres to prop roots, tree trunks, and pneumatophores.
• Re-oiling from resuspended or released oil residues may cause additional injury over time.
• Oiled trees start to show evidence of effects (leaf yellowing) weeks after oiling; tree mortality may take months, especially for heavy oils.

SOURCE: Wise Hok Wai Lum, CC BY-SA 4.0, via Wikimedia Commons.

• Coral reefs are structures created and maintained by the establishment and growth of populations of stony coral and coralline algae.
• Coral reefs are mostly subtidal in nature, although the shallowest portions of some reefs can be exposed during very low tides.
• Broad, pavement-like platforms formed by reefs when they reach sea level are a special concern.
• Many coral species spawn simultaneously over a very short time period (days), a behavior that makes the entire recruitment class very vulnerable.

• Coral reefs vary widely in sensitivity to spilled oil, depending on the water depth, oil type, and duration of exposure.
• There are three primary exposure pathways: direct contact with floating oil; exposure to dissolved and dispersed oil in the water column; and contamination of the substrate by oil deposited on the seafloor.
• Reef-associated community of fishes, crustaceans, sea urchins, etc. can experience significant mortality.

SOURCE: NOAA.

• Seagrasses are highly productive habitats that occur on intertidal flats and in shallow coastal waters worldwide from arctic to tropical climates.
• Water temperature, light penetration, sediment type, salinity, and wave or current energy control seagrass distribution.
• Seagrasses provide a food source for green turtles, manatees, and waterfowl, who graze on seagrasses.
• Seagrasses are used by fish and shellfish as nursery areas.

• Oil will usually pass over subtidal seagrass beds, with no direct contamination.
• Oil that is heavier than seawater can become trapped in the beds, coating the leaves and sediments.
• Oil readily adheres to the vegetation, and the oiled blades are quickly defoliated when intertidal beds are oiled.
• Floating oil stranded on adjacent beaches can pick up sediment and then get eroded and deposited in adjacent beds.

SOURCE: NOAA.

• Kelps are very large brown algae that grow on hard subtidal substrates in cold temperate regions.
• Because kelps require constant water motion to provide nutrients, they are located in relatively high-energy settings.
• Kelp forests support a diverse animal community of fish, invertebrates, and marine mammals as well as important algal communities.

• Kelp has a mucous coating that prevents oil from adhering directly to the vegetation on the water surface.
• Oil can be trapped in the dense surface canopy, increasing the persistence of oil within the kelp environment.
• Oil persistence in kelp increases the risks of exposure to organisms concentrated in kelp forest habitats.

SOURCE: USGS.

• Soft-bottom, subtidal habitats consist of various percentages of sand, silt, and clay, occurring in sheltered bays and estuaries, and deeper offshore areas.
• The presence of fine-grained sediments indicates that the substrate is not exposed to significant wave or tidal energy.
• Biological resources associated with this habitat include shrimp, crabs, clams, fish, and the pelagic and benthic communities that support them (e.g., plankton, worms, amphipods, isopods).

• This habitat is not often exposed to spilled oil.
• The greatest risk of exposure is from the sinking oil or the sorption of dispersed oil onto suspended sediments that are then deposited on the bottom.
• Significant natural dispersion of oil and sediments into the water column occurs only during large storms and nearshore oil spills.
• Shoreline cleanup can suspend oil and fine-grained sediments, causing deposition of oily sediments in nearshore habitats.

SOURCE: NOAA.

• This habitat consists of subtidal substrates composed of rock, boulders, or cobbles, though there can be patches of sand veneer covering a hard bottom.
• There may be rich, diverse communities of attached and associated algae and animals; often there is little open space.
• Some of these habitats form a relief (reef or bank) several meters high that attracts a diversity of fish.

• Mixed and hard-bottom habitats are usually considered to have low risk of exposure to oil spills.
• Oil in the water column seldom reaches toxic levels and benthic organisms have little exposure.
• There is little risk of deposition of oil or oiled sediments in these habitats.
• There could be a short-term exposure as oiled sediments are transported through the habitat into deeper areas.
• Concerns about seafood contamination from dispersed oil or oiled sediments can become a significant issue.
• Real, potential, or fear of contamination can close seafood harvesting activities.

SOURCE: Sandkvist (n.d.).

SOURCE: USCG photo by Petty Officer 1st Class Sara Francis, Public domain, via Wikimedia Commons.

• Ice forms on the sea surface during winter in cold climates and can persist for several months.
• Most sea surface ice is floating but can be frozen to the bottom or stranded in intertidal areas during low tide.
• Accessible ice can safely support the personnel and equipment suitable for response to a particular oil spill on, in, under, or adjacent to solid ice.
• Inaccessible ice cannot safely support response personnel and response equipment.

• Ice along the shoreline or in the adjacent nearshore water can act as a natural barrier, reducing the amount of oil that might otherwise make contact with the shoreline substrate.
• During the ice growth phase, oil in or under the ice can become encapsulated within the ice.
• During a thaw, or if the surface of the ice is melting and wet, oil is unlikely to adhere to the ice surface and will tend to remain on the water surface or in leads.
• In the spring, before the ice becomes inaccessible, oil in or below sea ice will often migrate through brine channels to the surface.

SOURCE: NOAA OR&R.

• Offshore waters are those where the water depth is >30 feet (10 meters) with no surrounding land.
• Evaluation of environmental impacts to open water habitats is focused on water column organisms and those which inhabit or use the sea surface.
• Animals include marine mammals, sea turtles, pelagic birds, and many commercially and recreationally important fish and pelagic invertebrates.
• Organism densities in this habitat are low on average.
• Localized high densities can occur in areas such as convergence zones and upwelling areas.
• Pelagic birds are at greatest risk when large numbers are concentrated for feeding, migration, overwintering, or breeding.
• Biological resources in the water column are less vulnerable to spills than those at the water surface.
• The sea surface microlayer is important for biochemical processes; the organisms most vulnerable to exposure are poor or passive swimmers (planktonic forms).

• Spilled oil transport is controlled primarily by wind and ocean currents than by tides and mixing with freshwater outflows.
• Most of the soluble and toxic components of the spilled oil are lost through weathering within hours and days.
• Dissolved or dispersed oil concentrations are likely to be greatest in the top few meters.