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ESTUARIES Estuaries - partially enclosed, coastal and transition areas where fresh water from rivers mixes with seawater (called brackish)

U.S. has nearly 900 estuaries, many of which were formed at the end of the last glacial period by rising sea level

Estuaries rank high among the environments most affected by humans

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Productivity and biomass are extremely high

Diversity is directly related to fluctuations in the characteristics of estuaries.

Primary producers are sea grasses that need good light and low sediment.

http://www.youtube.com/watch?v=jeyOA0mwBhc

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NEW JERSEY ESTUARIES

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TYPES OF ESTUARIES 1. Drowned River Valleys or Coastal Plain Estuaries

Formed when sea level rose due to melting ice at the end of the last ice age

Most common type

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Examples – Chesapeake Bay, Delaware Bay, Newark Bay

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TYPES OF ESTUARIES

2. Bar-Built Estuary

Form when sediments accumulate along the coast as sand bars and barrier islands that act as a wall between the ocean and fresh water from rivers

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Examples – Outer Banks, NC, Texas Coast, Long Beach Island, NJ

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TYPES OF ESTUARIES

3. Tectonic Estuaries

Formed when land sank or subsided due to movements in the crust

Example - San Francisco Bay

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TYPES OF ESTUARIES

4. Fjords

Formed when advancing glaciers cut deep valleys along a coast and then the valleys were submerged when seal level rose

Examples - Norway, Alaska, New Zealand, Puget Sound, WA

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PHYSICAL CHARACTERISTICS OF ESTUARIES

1. Salinity – fluctuates from place to place & time to time- organisms that stay in one place faced with dramatic changes in salinity

Salt wedge of seawater forms under river runoff when the tide comes in. This layers the salinity.

Salty seawater is more dense and stays on the bottom

More euryhaline organisms in the 0 - 30% salinity range than stenohaline organisms (30 - 32 % range).

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SALT WEDGE – high river flow, low tide - nutrients & sediments from river enter estuary

WELL-MIXED – low river flow, moderate tide – tidal turbulence mixes waters together

PARTIALLY-MIXED – low river flow, moderate tide – similar to well-mixed with deeper channel

FJORD – small surface area, high river flow, little tidal mixing

REVERSE – little river inflow, high evaporation

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PHYSICAL CHARACTERISTICS OF ESTUARIES

2. Temperature – varies due to shallow depths and large surface areas

– organisms exposed at low tide face even more drastic daily and seasonal temperature changes

3. Turbidity - large amounts of suspended sediments reduce water clarity - very little light penetrates water column - particulate matter clogs filter feeders

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PHYSICAL CHARACTERISTICS OF ESTUARIES

4. Substrate – type of bottom – mostly sand & soft mud - rivers carry large amount of sediment, organic matter AND

pollutants into estuaries - infauna have a more stable environment than epifauna

because mud traps the salt

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5. Oxygen - depletion can occur in the mud or in the water column due to bacterial respiration (ANOXIA)

6. Nutrients - come from river runoff and provides for a detritus-based food chain, inverted energy pyramid increases productivity

7. Water Depth - zones are determined by the tides, shallow water restricts large predators

8. Tides and currents - tidal ebb with river runoff cause net flushing. Tides transport larvae and nutrients into the ocean.

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Types of estuarine communities: - typically few species, with many individuals

1. Open Water - enter and leave with the tide- vary with currents, salinity & temperature

Murky water may limit primary productivity of phytoplankton in rest of estuary

Fishes & shrimps use as nurseries- take advantage of abundant food and safety from predators

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2. Sea Grass Communities -

primarily subtidal zones where sea grasses can stabilize the substrate

Leaves of grass slow currents, provide a place of attachment to prevent smothering in sediments, for hiding places, and for food

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3. Mud Flats - or oyster reefs - found in lower intertidal and subtidal zones - bottoms of estuaries exposed at low tide (organisms experience desiccation, wide temperature changes, predation, salinity changes)

- primary producers are diatoms & bacteria

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• Infauna live on detritus brought in by tides and rivers

• Deposit (mud) or suspension feeders (sandy)

Organisms include:• Bivalves• Burrowing shrimps

• oxygenate sediment• Fiddler crabs• Predators (snails, worms,

crabs)

MOST IMPORTANT PREDATORS IN MUDFLATS – FISHES and BIRDS• Fishes invade at high tide, birds invade at low tide

Figure 12.10

Wading shore birds most significant predator• Varying lengths of bills may represent specialization in prey

Example of RESOURCE PARTIONING – sharing of a resource by two or more species to avoid competition

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4. Salt Marshes - also called tidal marshes, wetlands, swamps or mangrove communities- develop when muddy sediments

allowed to accumulate-waves minimal

- muddy bottom held together by roots

Producers are Spartina (cordgrass) found mostly in intertidal water

Bacteria in the mud decompose dead plant material and contribute a large portion of the detritus in the estuary

Salt excreting leaves provide food and habitat. Air tubes from the leaves to the roots help oxygenate plants living in anaerobic mud.

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Estuaries very productive ecosystems – WHY???

1. Nutrients brought in by tides and rivers

2. Nutrients released by nitrogen-fixing organisms

3. Decomposition of detritus most animals feed on dead organic matter more energy from decomposers than from

producers

4. Excess detritus exported to the open ocean by outwelling

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LIVING IN AN ESTUARY – COPING WITH CHANGING SALINITY (ADAPTATIONS)

Euryhaline – tolerate wide range of salinities (most)

Stenohaline – tolerate narrow range of salinities (few)- limited to upper or lower ends of estuary

Maintaining salt and water balance is challenging: - change behavior (hide, close shell, move or swim away) - develop high salt tolerances (salt-marsh plants), excrete salt,

accumulate water - osmoconformers –salinity of body fluids vary with the water - osmoregulators – keep salt concentration of body fluids

constant

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LIVING IN AN ESTUARY – ADAPTING TO THE MUD

Disadvantages- nothing to hold onto- low oxygen caused by decay of

organic mater in mudAdvantage- salinity fluctuations less drastic

Difficult to move through mud –- Organisms stay put or move slowly- Clams use siphons

Low oxygen- some burrowers pump oxygen-rich water into burrow- some have hemoglobin – high affinity for oxygen- some can survive for days without oxygen

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Estuaries are usually the first dumping site for pollution and have been severely damaged by dredge and fill operations.

Estuaries are important because they support a large commercial seafood industry, prevent coastal erosion, provide recreation .

Estuaries are the sea’s nursery.

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