Definition of an estuary: Where freshwater and saltwater meet.

Formation of Estuaries

• Often formed by a barrier bar caused by longshore currents.
• Some formed by drowned river mouth (coastal plain estuary).

• Not a common type in CA because coast is rising.
• Notable examples: Tomales Bay, San Francisco Bay.

• Deltas

Productivity

• Cordgrass alone has a 5-10 X higher net productivity than wheat.
• Species richness is low, but biomass is high.

Salinity variation

• Fresh water is lighter than saltwater and therefore flows over the top.
• Coriolis effect also causes freshwater to flow closer to the coast on the north side.
• A wedge of water where salinity changes rapidly from fresh to seawater (0% to 3.5% TDS) moves back and forth with the tide.

Response of Organisms to Salinity

• Motile organisms travel with the tide in the region that best suits them.
• Stationary organisms are subjected to drastic changes in salinity.
• A critical dividing line appears to be 0.05-0.08% TDS.
• Upstream are freshwater organisms, downstream are saltwater organisms.
• Very few species live in this boundary region.

The Four communities of the Tidal Estuary

1. Freshwater marsh
2. Salt marsh.
3. Mud flats.
4. Open water.

Salt Marsh

Vegetational Zonation

• Eel Grass (Zostera) grows from low tide level to depths of 20 ft.

1. Has air spaces in blades for buoyancy and oxygen.
2. Provides substrate and food for many organisms.

• Cord Grass (Spartina foliosa) grows from mean high tide mark to low tide mark.

1. Hollow, air-filled stem to transport oxygen to roots.
2. Salt glands.
3. C₄ photosynthesis.
4. Nitrogen fixing bacteria in roots.
5. Contributes indirectly to productivity of the community by trapping detritus and sediments in root systems.
6. Very few organisms are equipped to eat Cord Grass.

• Pickleweed (Salicornia spp) grow just above mean high tide where they are submerged during the highest tides.

1. Succulent, store seawater in stem thus allowing favorable flow of water into the plant.
2. Actually used as a pickle by people in some parts of the world.

• Salt Grass (Distichlis spicata) and Sea Blite (Suaeda californica) also grow in association with pickleweed. They excrete salt on their leaves.

Animal inhabitants (not numerous)

• Various arthropods, worms (tube worms, polychaete worms), and snails.
• Bay Pipefish (Syngnathus leptorhunchus) hides in Eel Grass and feeds on small crustaceans.
• Salt-Marsh Harvest Mouse.

1. Endemic (and endangered) to SF Bay.
2. Builds a nest in the vegetation much like a bird.
3. Is able to use saltwater as a water source.

Resident Birds

• Three of the five resident bird species are endangered.
• 3 subspecies of Clapper Rail are endangered
• In 1986 only 143 pairs of Light-footed Clapper Rails were believed to be left.

Feed on insects and other invertebrates.

• Sora Rail is not endangered (also lives in freshwater marshes).
• California Black Rail is endangered (also known from a few freshwater marshes).
• Belding's Savannah Sparrow, endangered

1. Commonly in the pickleweed habitat.
2. Can drink saltwater.
3. Eats seeds and some insects.

• Marsh Wren

Migratory Birds

• American Bittern, hide during day and may even sway with tules in wind

1. Mostly active at night
2. Eat snails, fish, frogs, and even small mammals

• Northern Harrier (formerly Marsh Hawk)

Mud flats

General characteristics

• When tide is in mud-dwelling creatures become active.
• When tide is out a number of different birds feed.

Productivity

• Primarily a detrital driven system.
• Algae may provide some productivity in spring and summer.
• Plankton and dissolved organic matter of secondary importance.
• Oxygen levels in the mud often very low.

Water Organisms

• Innkeeper (Urechis caupo)

1. Builds a burrow in mud with two exits separated by up to 3 feet.
2. Constructs a funnel shaped slime net inside to trap detritus and plankton.
3. Shares burrow with various other commensals: worms, crabs, fishes.
4. Best known commensal is the Arrow Goby (Clevelandia ios), up to 5 found in a single burrow.
5. Classified by some as Annelida (segmented worm) but by others as Echiuroidea (it's own phylum) because it is unsegmented as an adult.

• Ghost shrimp (Callianassa affinis) (Photo of similar spcies, Sponge Shrimp)

1. Pumps water through burrow and extract detritus and plankton
2. They help to overturn and oxygenate the mud.

• Sea pen (Stylatula elongata), a coelenterate

1. Opens up it's feather-like appendages which have nematocysts and catches plankton.
2. Can produce waves of light along body when disturbed.

• Clams of various kinds

1. All filter feeders
2. Concentrate toxins such as heavy metals.

• Cloudy Bubble Snail (Bulla gouldiana)

1. Predatory
2. Soft parts cover its thin, fragile shell
3. Mucous cover picks up particles and conceals it when the tide is out

• California Sea Hare (Navanax inermis)

1. Low intertidal, seldom seen at low tide.
2. Yellow and blue dots on a brown background.
3. Preys on snails.

Birds

• Shorebirds (Willets, Marbled Godwits, Western Sandpiper, etc.)

1. Probe for food in mud or shallow water

2. Most are migratory

• Gulls

1. Scavengers

2. Some resident, some migratory

Open water

Primarily Birds & Fish

• Wading birds (Heron, Avocets, Stilts, Dowitchers)

1. Herons feed on fish
2. Avocets & Stilts feed primarily on swimming invertebrates
3. Dowitchers probe the mud for invertebrates in shallower water

• Plunging birds (Terns, Pelicans, Osprey)
• Ducks

1. Diving ducks (Buffleheads, Scoters, Canvasbacks, Grebes)
2. Puddling ducks (Mallard, Widgeons, Shovelers)

Preservation of Saltwater Marshes

• Thought ugly and useless by most people, therefore often filled or degraded by dumping.
• DDT, heavy metals, and other toxins become biologically amplified.
• Reduction in freshwater inflows.
• Effects of logging.

  

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