Detailed Threats to Coastal Habitats
Physical Habitat Loss or Degradation
Water column, shell bottom, SAV, wetlands, soft bottom, hard bottom
Navigation channels, marinas, boat basins
- Dredging can directly remove SAV, shell bottom, wetlands, or shallow soft bottom features.
- Conversion of shallow water habitats to deep habitat results in loss of valuable nursery habitat and alters natural circulation patterns.
- Dredging can degrade SAV habitat, shell bottom, and hard bottom by increasing turbidity and sedimentation.
- Increased turbidity in the water column can deter successful recruitment of larvae, clog fish’s gills, reduce ability of visual foraging predators to catch prey, and make toxins in bottom sediments biologically available to fish.
Marinas, Docks, and Piers
Water column, shell bottom, SAV, wetlands, soft bottom
- Shading by boats and structures reduces light availability for SAV, and to a lesser extent wetlands. Reduced light can cause mortality of SAV or prevent its expansion in otherwise suitable areas.
- Dredging of marina basins reduces productivity of the soft bottom community.
- Dredged basins alter circulation patterns and can result in water quality degradation and low oxygen events, which stress or kill fish.
- Fuel, bottom paint, and other toxins found at marinas and docking facilities can impact recruitment and survival of oyster larvae and degrade water quality.
- Biological problems associated with docks and piers can be minor individually but can have significant cumulative impacts on coastal fish habitat.
Channelization / Ditching / Filling
Wetlands, water column, soft bottom
Flood control, agriculture, urban and suburban development, forestry
- Reduction in wetland habitat.
- Loss of wetlands or conversion to uplands reduces system's ability to filter pollutants and regulate water flows.
- Loss of riparian vegetation increases loading of non-point source pollutants.
- Filling and channelization reduces fish access to wetlands.
- Channelization increases erosion of stream banks and turbidity in the water.
- Waters adjacent to channelized streams and ditched wetlands support lower abundance and diversity of fish.
Flow Regulation / Obstruction
Dams, water withdrawals, road fill, and culverts
- Dams, road fill, and pipe culverts can obstruct passage of anadromous fish to historical upstream spawning grounds.
- Surface and ground water withdrawals can significantly alter currents, temperature, and oxygen levels to conditions that deter spawning and egg development of anadromous fish.
Bottom Disturbing Fishing Gear
Shell bottom, SAV, soft bottom, ocean hard bottom, water column
See Table above.
- Mobile bottom disturbing gears dig down into the bottom and uproot SAV.
- Hard bottom and shell bottom structure can be broken apart, killing organisms and reducing habitat value.
- The vertical profile of subtidal oyster reefs can be lowered, making the shell bottom community more susceptible to low oxygen events.
- Elevated turbidity can degrade water column, SAV, shell botttom, or hard bottom habitat, depending on the frequency and intensity.
- Disturbance of soft bottom habitat can alter productivity of benthic microalgae and reduce structural complexity of the bottom.
Water column, SAV, wetlands, soft bottom
Bulkheads, jetties, seawalls, groins
- Increased wave energy on shoreline due to hardened structures accelerates erosion of wetlands and leads to loss of intertidal soft bottom habitat.
- Increased turbidity in the water column.
- Deepening of nearshore habitat and elevated turbidity due to hardened structures deters future colonization of wetland or SAV plants.
- Reduced fish and invertebrate use of hardened shore due to decrease in habitat complexity and toxicity of wood preservatives.
- Prevents landward migration of wetlands (along estuarine shorelines) or barrier islands (along oceanfront).
Water column, soft bottom, ocean hard bottom
Nourishment projects on ocean-facing beaches
- Partial or complete burial of nearby hard bottom areas with redistributed sediment
- Increased turbidity in water column
- Physical disturbance to mining (“borrow”) sites
- Direct mortality of important food resources for fish and shorebirds, including mole crabs, coquina clams, amphipods
Water column, SAV, wetlands
Construction and operation of bridges, roads, culverts, sewage systems, pipelines, etc.
- Construction of new bridges may result in loss of SAV or wetlands, while also degrading nearby habitat with increased sediment loading.
- Fill, impervious surfaces, or culverts placed in wetlands for roadways alters the hydrology of the system, often impacting upstream wetlands, and the ability of fish to migrate upstream to spawning or nursery areas.
- Installation of submerged pipes or cables across SAV beds or ocean hard bottom can result in destruction of habitats that have long recovery periods.
Water column, soft bottom, wetlands
As of October 2004, no mining (other than for beach nourishment) occurs in North Carolina estuarine and nearshore ocean waters. However, the potential for mining projects exists in phosphate-rich areas in nearshore ocean waters in Onslow Bay as well as the Pamlico River. In addition, sand mining is common throughout eastern North Carolina, and occasionally mines are dewatered into wetlands or coastal streams.
- Extraction of minerals could have bottom-disturbing effects similar to that of dredging, such as increased turbidity, and mortality of benthic organisms
- Underwater mining activities could lead to the unintentional release of “phosphate mining byproducts” into the water column, including radioactive substances, florides, and other chemicals.
- Water from sand mines entering wetlands and coastal streams can increase turbidity.
Water Quality Degradation
Nutrient Enrichment and Oxygen Depletion
Water column, shell bottom, SAV, wetlands, soft bottom, ocean hard bottom
Wastewater discharges, nonpoint runoff from agriculture, urban areas, animal operations, and air emissions
- Excess nutrients fuel phytoplankton blooms in the water column, which can contribute to low oxygen events in the water column and bottom sediments, causing fish kills and mortality of fish and non-mobile invertebrates in the water column, soft bottom, or shell bottom communities.
- Reduced light availability in the water column from plankton blooms and excessive epiphytic growth impacts the ability of SAV plants to survive and grow.
- High levels of nitrogen can cause mortality of eelgrass.
- Excess nutrient loading can result in toxic blooms such as red tide or Pfiesteria outbreaks.
Toxic Chemical Contamination
Water column, shell bottom, SAV, soft bottom, ocean hard bottom
Herbicides, pesticides, and other toxic chemicals from agriculture, golf courses, urban development, marinas, fuels, automobile transportation, boating activity, and industrial emissions
- Heavy metals, petroleum products, and other toxins can kill sensitive shellfish larvae, or lower reproductive success and growth, impacting shell bottom habitat.
- Toxins can accumulate in soft bottom, resulting in mortality or poor recruitment of benthic invertebrates or bio-accumulate in the tissue of top predators.
- SAV can be intentionally or unintentionally killed by spraying for aquatic nuisance plant control. See Introduced and Nuisance species for related information.
Turbidity and Sedimentation
Water column, shell bottom, SAV, soft bottom, ocean hard bottom
Construction sites, runoff from agriculture, forestry, roads, mining, resuspension from dredging, and bottom disturbing fishing activities
- Elevated turbidity impacts the ability of SAV plants to survive and grow.
- Suspended sediment in the water column can clog fish gills, deter successful recruitment of invertebrates onto shell bottom or ocean hard bottom, reduce feeding success of visually oriented predators.
- Excess sedimentation can cover shell bottom and ocean hard bottom, and fill in shallow creeks and rivers.
- Suspended sediments transport bacteria and toxins through coastal waters, making them available to aquatic organisms in the water column.
Water column, shell bottom
Stormwater runoff, failing septic systems, overloaded sewage systems
- Public health risks leading to restrictions on swimming, shellfish consumption
- Permanent or temporary closures of shellfish harvesting waters
- Water-borne illness
SEA LEVEL CHANGE
Natural event accelerated by global warming
- As sea level rises, wetlands erode and “drown”, especially along steeply sloping shorelines or where inland migration of wetlands is restricted.
- Rising sea level increases salinity upstream and alters distribution and composition of fish populations
Wetlands, water column, shell bottom
Natural events, but negative effects are worse where pollutant sources occur on adjacent lands.
- The combination of storm events and sea level rise causes erosion of wetlands at a rate of about 800 acres/yr in North Carolina.
- Non-point runoff from storms can result in excessive loading of sediment and nutrients into the water column.
- Sediment runoff can silt over oyster beds.
- High nutrient loading from storm runoff can lower oxygen levels in the water, killing oysters and benthic organisms.
- SAV can be physically damaged by boat propellers (recurrent damage and long recovery period), anchors, jet skis.
Water column, ocean hard bottom
Storm drains, accidental and intentional littering
Fish, reptiles, birds and mammals can become entangled in debris, leading to:
- loss of mobility
- increased mortality
- greater risk of infection
Introduced or Nuisance Species
Water column, shell bottom, SAV, wetlands
- Introduced species can compete with natives for space, light, and nutrients, and displace natives with species of lower value to native fish utilization. For example, Eurasian watermilfoil competes with native low salinity SAV plants in some areas of the coast.
- Unintended effect of nuisance species control on nontarget species.
Shell bottom, SAV
- Past occurrence of seagrass wasting disease caused extensive losses of SAV habitat.
- Increased occurrence of oyster diseases has contributed to decline of shell bottom habitat and its lack of recovery.