Estuaries

LECTURE NOTES    MARINE BIOLOGY (MARSC 180)                       L. SNYDER

Ch. 7:  Estuaries

Estuaries:  Semi-enclosed embayment where freshwater rivers (riparian) meet the ocean

• Vegetation can tolerate salt (Halophytes)
• 1/3 of Americans live w/in an estuarine watershed

Estuaries:  Rivers ®estuaries ®oceans

• Rivers bring nutrients/minerals from land to sea
• Highly productive
• Comparable to coral reefs & tropical rain forests
• Unappreciated
• Most have been filled in or polluted:
• Development, harbors, power plants, agriculture, roads
• California:  greatest wetland losses
• 90% total wetlands, 75% salt marsh

Value of Estuaries:

• High Primary Productivity
• Food web support
• Oxygen
• Fish & Wildlife habitat
• Flood Protection
• Water quality improvement
• Filter pollutants
• Shoreline stabilization & bank protection
• Groundwater recharge
• Recreation & aesthetics

Types of Estuaries:

• Coastal Plains (drowned river mouths): When sea level rises, lower portion floods
• Fjords: glaciers melt, sea level rises & glacial valleys flood (Alaska, Scandinavia)
• Coastal-plains (Atlantic, Pacific Northwest)
• Bar-built (S. Atlantic & Gulf of Mexico), Lagoons: little or no freshwater input (San Diego)
• Fjords (Alaska, British Columbia, Scandinavia)

Estuarine Circulation

• Salinity & water temp. change with daily tidal cycle & season
• Salinity ­ w/ depth & distance from river
• Seawater is more dense = incoming tides move along estuarine floor
• Freshwater exits at surface

Tidal Flushing

• Time for total volume of water in estuary to be replaced
• Range: days to years
• Shape of embayment, tidal regime, river flow, human alteration
• Influences transport of nutrients & residence time of pollutants

Salinity Adaptations

• Osmoconformers: Can’t regulate salinity in body fluids when subject to low salinity
• Avoid salinity fluctuations:  stay near mouth (ocean) or travel in & out w/ tides
• Slow moving invertebrates
• Osmoregulators: regulate H2O & solutes w/in body fluids in all conditions
• Excrete excess H2O, gills take up ions
• Vertebrates, fast moving inverts.

MUDFLATS

• Covered w/ fine silt, clay                  
• Exposed at low tide
• Primary producers: seagrasses, diatoms, algae (form mats)
• Grazed & contribute to detrital food web
• Bacteria (decomposers)
• Gastropods, polychaetes, crustaceans (amphipods)
• Shorebird feeding area

SALT MARSHES: Salt tolerant plants (halophytes)

• Submerged at high tide
• Vegetation eaten by herbivores

            OR

• Decomposed by bacteria
• Enter food web as detritus & nutrients            

CHANNELS:  Primarily marine

• Always filled w/ water
• Link mudflats
• Habitat for plankton, invertebrates, fish
• Spawning & nursery areas
• Including many pelagic species                       
• BRACKISH: Where Salt & freshwater meet (Salinity 1‰ - 29‰)
• RIPARIAN:  Freshwater creek or river
• UPLAND:  Slopes & bluffs (Coastal Sage Scrub & Dunes)

Estuaries are Fish Nurseries:  Provide shelter, food, protection

Birds inhabit local estuaries (some year-round, others are seasonal)

Pacific Flyway

• Many birds migrate from northern (summer) breeding grounds TO Southern, winter grounds
• Rest & winter in estuaries

Zooplankton
Holoplankton (Permanent Plankton)

Meroplankton (Temporary plankton)

Invertebrates

Environmental Pollutants

• Estuaries receive freshwater from rivers (& storm drains) that drain vast watersheds
• Pollutants carried to estuaries, then  trapped & accumulate

Dioxins: (chlorine)  bleaching paper products
Bioaccumulate in fish®humans

Toxins Bioaccumulate in Food Web

• Animals feeding higher in food chain consume large quantities of toxins
• Concentrate in fatty tissue

Synthetic Organic Chemicals

• DDT:  Widely used pesticide
• Brown pelicans, ospreys, bald eagle, peregrine falcon produce thin egg shells
• Banned worldwide (1970’s), still used in developing countries (malaria)
• PCB: Cool & insulate electrical devices, strengthen wood & concrete
• ↓ Reproductive fertility, weakens immune             systems
• Dolphin (nearshore): 6,900 ppm
• EPA: 5ppm (human), 50ppm (non-human animals)

Fertilizers, Sewage & Eutrophication

• Nutrients (animal waste & Fertilizer) enter estuaries as runoff
• Sewage effluent, farms, ranches, homes, golf courses
• ↑ Growth of marine autotrophs

Eutrophication:           ↑ Nutrients = ↑ algae & plankton = ↑ bacteria (use oxygen to decompose algae) = ↓ oxygen =         ↓ animals (fish kills)

U.S. Gulf Coast Dead Zone

• At mouth of Mississippi River
• Caused by agricultural runoff upstream
• Anoxic water to 60 m deep
• Worst in Spring & Summer
• Mobile species leave
• Immobile die

California’s Coastal Wetlands

• 91% lost since state’s settlement
• 75% on south. California coast
• Dense population
• Dredged & filled
• Housing, agriculture, harbors
• Remaining salt marshes
• Dissected by roadways
• Surrounded by development 

Estuarine Destruction
~60% lost in lower 48 states
75% lost in Southern California

• Batiquitos Lagoon (Carlsbad) – restored in 1997

• Talbert Marsh (Huntington Beach) – tiny remnant restored at mouth of Santa Ana River
• Still Disturbed by PCH, Powerplant, OC sanitation treatment plant

 

• Upper Newport Bay: 1,401 acres
• Portion is Protected as UNB Ecological Reserve: 730 acres
• Historic area:  2800 acres
• Lost nearly half of its historic area to housing, golf courses & Newport harbor construction

Coastal Wetland Restoration

• Recognize value of marshes
• Goal of restoration:
• Return degraded marsh to former conditions
• Many major projects in Southern California:
• Batiquitos Lagoon, Bolsa Chica, Ballona Wetlands
• Possible projects:  San Diegito, San Elijo, Los Cerritos
• Ongoing UNB Restoration Projects:
• Occasional dredging to remove excess sediments
• Former Drain area (15 mi2)
• Now (118 mi2)
• San Diego Creek Watershed:  154 square miles of Orange County drains daily, rain or shine into Newport Bay!
• Remove invasive plants (exotic)
• Re-plant native species
• Research & habitat creation for endangered species

 

• Bolsa Chica Restoration Project:
• 1,247 acres (largest wetland restoration in S. Calif. History)
• Historic area 2,298 acres
• $65 million project
• Completed in 2007
• Full tidal basin (387 acres), managed tidal (178 ac.), new nesting areas (20 ac.), dune restoration (19 ac.), Cleanup of pollutants, New Tidal inlet (2 Bridges over for PCH)

           
Estuaries continue to face problems:
Adjacent land use (development, resorts, golf courses, sanitation treatment plant, roads; urban & suburban runoff; exotic, invasive plants; non-native predators (house cats)