Estuaries

An estuary is a semi-enclosed body of water that has a free connection with the sea

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Estuaries have more food for organisms, but the organisms usually have to deal with large temperature and salinity changes, high silt content and pollution.

Hint How does this organism get its food?

Estuaries are regions of transition and sharp gradients.

Estuaries support fauna recruited mostly from the sea

For those organisms that can survive the problems of the estuary, there is a great deal of food.

These organisms tend to be in large numbers.

The Chesapeake Bay is a drowned river valley. This is the most common type of estuary. It was formed during the last ice age some 12,000 – 18,000 years ago.

106 ft. 56 ft 32 ft. 21 ft. 14ft. 9ft.

21 feet is the correct answer. The deepest spot in the bay is 174 feet near Annapolis Md.

Can you name the 6 states that make up the watershed of the Chesapeake Bay?

Virginia Maryland West Virginia Delaware New York Pennsylvania

From South to North

James York Rappahannoc

k Potomac Susquehanna

The Susquehanna River provides about 50% of the fresh water coming into the Bay.

The river empties an average of 19 million gallons of water per minute.

About 50,000 commercial vessels enter the Bay each year.

All these people and activities put a strain on the Bay ecology.

The Bay is home to over 3600 living organisms!

Marsh dwellers are located in and around marshes. They include small fish, birds, and marsh grasses.

Submerged Aquatic Vegetation Communities are important for many reasons. They include ducks, crabs, and eelgrass.

The plankton community includes the drifters of the Bay.

It includes phytoplankton, bacteria, and zooplankton.

Benthic refers to the bottom of the Bay. Benthic organisms include oysters, clams, barnacles, and mud crabs.

Nekton refers to the swimmers of the Bay.

Croaker, Spot, and menhaden use shallow water in the Bay as a nursery

Formation of an estuary embayments—coastal areas where

portions of the ocean are partially cut off from the rest of the sea

rivers and streams carry freshwater runoff from land into some embayments

estuary forms where fresh and salt water are mixed

all estuaries are partially isolated from the sea by land, and diluted by fresh water

Coastal plain estuary—forms between glacial periods when melting glaciers raise the sea level and flood coastal plains found along the Gulf of Mexico and

eastern Atlantic coasts Drowned river valley estuary—forms when

melting glaciers raise the sea level and flood low-lying rivers e.g. Chesapeake Bay, Long Island Sound

Tectonic estuary—forms when an earthquake causes the land to sink, allowing seawater to cover it e.g. San Francisco Bay

Fjord—estuary formed when a deep valley cut into the coast by retreating glaciers fills with water found in Alaska and Scandinavia

Tidal flats—deltas formed in the upper part of a river mouth by accumulated sediments, which divide and shorten an estuary

Bar-built estuary—estuary in which deposited sediments form a barrier between the fresh water from rivers and salt water from the oceane.g. Cape Hatteras region of North

Carolina, Texas/Florida Gulf Coasts, etc.

Salinity varies horizontally salinity increases from the mouth of the river

toward the sea Salinity varies vertically

uniform salinity results when currents are strong enough to thoroughly mix salt and fresh water from top to bottom

layered salinity may occur, with the layers moving at different rates

Mixing patterns tidal overmixing—seawater at the surface moves

upstream more quickly; denser seawater at the surface sinks as lighter freshwater beneath it rises, creating a mixing action

Water circulation patterns positive estuary

influx of fresh water from the river more than replaces the amount of water lost to evaporation

surface water is less dense and flows out to sea denser salt water from the ocean flows into the

estuary along the bottom most estuaries are positive estuaries

Water circulation patterns (continued) negative estuary

occur in hot, arid regions lose more water through evaporation than the river

is able to replace surface water flows toward the river; its salinity is

increased by evaporation water along the bottom moves out to sea usually low in productivity e.g. Laguna Madre estuary in Texas

Salt-wedge estuary occur in the mouths of rivers that are flowing

into seawater freshwater flows rapidly out to sea at the surface denser saltwater flows upstream along the river

bottom rapid flow of the river prevents saltwater from

entering and produces an angled boundary between the freshwater moving downstream and the seawater moving upstream called a salt wedge

Well-mixed estuary river flow is low and tidal currents play a major

role in water circulation seaward flow of water and uniform salinity at all

depths lines of constant salinity move back and forth

with the tides

Partially-mixed estuary strong surface flow of freshwater and a strong

influx of seawater tidal currents force seawater upward to mix with

surface water rapid exchange of surface water between the

estuary and ocean

Shallowness of estuaries allows temperatures to fluctuate dramatically

Warmth comes from solar energy and warm tidal currents

In some estuaries, winter turnover results when cooler surface water sinks and warmer deep water rises circulates nutrients vertically between water and

bottom sediments

Nutrients in fresh and saltwater complement one another freshwater contains nitrogen, phosphorus and

silica surface seawater has less nitrogen and silica but

more phosphorus Silt and clay dumped by rivers hold, then

release excess nutrients Filter feeders consume more plankton than

they can absorb, producing pseudofeces which provide food for bottom feeders

Many are species are generalists, and can feed on a variety of foods depending on what is available

Species that tolerate temperature and salinity changes can exploit estuaries and grow large populations

So, estuaries contain abundant individuals from relatively few species

Maintaining osmotic balance osmoconformers—animals with tissues and cells

that tolerate dilution e.g. tunicates, jellyfishes, sea anemones

Maintaining osmotic balance osmoregulators—animals that maintain an

optimal salt concentration in their tissues, regardless of the salt content of the environment concentrate or excrete salts, or shield themselves

from their environment

Remaining stationary in a changing environment natural selection favors benthic organisms

because of the difficulty in staying still to feed in constantly-moving water

non-benthic animals (e.g. crustaceans, fishes) maintain position by actively swimming or by moving back and forth with the movement of the tides

Estuaries as nurseries high level of nutrients + few predators makes a

great habitat for juveniles juveniles live in the estuary until they grow large

enough to be successful in the open sea e.g. striped bass, shad, bluefish, blue crabs,

white shrimp

Many hardy organisms are euryhaline—species that can tolerate a broad range of salinity

Oyster reefs reefs form from numerous oysters growing on

the shells of dead oysters provide a habitat for many organisms, which

may depend on oysters for food, protection, and a surface for attachment

oyster drill snails prey on oysters

Mud flats contain rich deposits of organic material + small

inorganic sediment grains bacteria and other microbes thrive in the mud,

producing sulfur-containing gases mud provides mechanical support for organisms cohesiveness permits construction of a

permanent burrow

Mud flats (continued) mud flat food webs

main energy base = organic matter consisting of decaying remains and material deposited during high tides

bacterial decomposition channels organic matter to other organisms, and recycles nitrogen and phosphate back to the sea floor

deposit feeders prey on bacteria larger organisms eat secondary consumers of

bacteria, and so forth

Mud flats (continued) animals of the mud flats

most are burrowers living just below surface closely-packed silt prevents good water circulation,

so many animals have a “snorkel” soft-shelled clams use a siphon to filter feed and

obtain oxygenated water, then metabolize anaerobically during low tide

lugworms are common mud flat residents innkeeper worms house many other organisms in

their burrows, as do ghost shrimp

Seagrass meadows seagrass productivity

depends on the ability of seagrasses to extract nutrients from the sediments

depends on activity of symbiotic, nitrogen-fixing bacteria

also depends on productivity of algae that grow on and among seagrasses

nutrients from drawn from sediments are released into the water by seagrasses, for use by algae

Seagrass meadows (continued) seagrass food webs

seagrasses are tough, and seldom consumed directly by herbivores

seagrasses are a food source to many animals as detritus, when their dead leaves are eaten by bacteria, crabs, sea stars, worms, etc.

organisms from other communities feed in seagrass meadows during high tide, exporting nutrients to other communities

Seagrass meadows (continued) seagrass meadows as habitat

epiphytes and epifauna attach to seagrasses filter feeders live in the sand among blades rhizoids and root complexes provide more

permanent attachment sites, and protect inhabitants from predators

larvae and juveniles of many species live here, protected from predators by changing salinity, plentiful hiding places, and shallow water

Salt marsh communities distribution of salt marsh plants

low marsh—region covered by tidal water much of the day and typically flushed twice each day by the tides

high marsh—region covered briefly by saltwater each day and only flushed by the spring tides

cordgrass dominates the low marsh short, fine grasses dominate the high marsh

Salt marsh communities (continued) salt marsh productivity

tides bring in replenishing supplies of nutrients most primary production supports detrital food

chains bacteria eat decaying plant material deposit feeders eat bacteria some salt marshes export large amounts of detritus

to nearby communities; in others, resident organisms consume most of the detritus

Salt marsh communities (continued) animals of the salt marsh

permanent residents include periwinkles, tidal marsh snails, ribbed mussels, purple marsh crabs, fiddler crabs, amphipods, grass shrimp

burrowing animals play an important role in bringing nutrient-rich mud from deeper down to the surface, while oxygenating deeper sediments

tidal visitors that come to the salt marsh to feed include predatory birds, herbivorous animals from land, fishes and blue crabs

Salt marsh communities (continued) succession in salt marshes

salt marshes can be the first stage in a succession process that produces more land

roots of marsh plants trap sediments until the area becomes built up with sand/silt that combine with organic material to make mud

mud islands appear and merge, and high tide covers less and less of them

tall cordgrass is replaced by short cordgrass, which is replaced by rushes and then land plants

Mangrove communities distribution of mangrove plants

red mangroves are usually pioneering species, and grow close to the water where the amount of tidal flooding is greatest

black mangroves occupy areas that experience only shallow flooding during high tide

white mangroves and buttonwoods (not true mangroves) live closest to land, but can tolerate flooding during high tide and saline soil

Mangrove communities (continued) mangrove root systems

shallow, widely spread root systems anchor the plants and provide oxygen for parts buried in the mud

red mangroves have prop roots, and black mangroves have many pneumatophores

prop roots and pneumatophores slow water movement, causing suspended materials to sink to the bottom

eventually, this sediment build-up can transform the estuary into a terrestrial habitat

Mangrove communities (continued) mangal productivity

primary producers (mangroves, algae and diatoms) support a productive detrital food web; burrowing/climbing crabs eat the leaves

Mangrove communities (continued) mangroves as habitat

many animals live on prop roots and pneumatophores, such as bivalves and snails

roots provide habitat for many organisms found in salt marshes and mud flats

sheltered waters provide a nursery as well