EstuariesChapter 12

Estuary

•Semi-enclosed area where freshwater meets and mixes with salt water

•Chesapeake Bay, Galveston Bay, Hudson River Estuary, Bodega Bay

Physical Characteristics:

Salinity•Varies between 35 ppt and 0 ppt

•Lower salinity farther upriver, higher salinity closer to ocean

•Higher salinity deeper

•Salt wedge

•Moves with the tide

Physical Characteristics: Water Movement

•Tides create dramatic currents

•Exposes parts of the estuary regularly

•Tidal bores (video)

Physical Characteristics:

Nutrients•High nutrient

load from runoff

•Eutrophication: Blooms of algae because of too many nutrients

Physical Characteristics:

Substrate• Rivers carry lots of substrate

• Fine particulates of sand and mud

• Sediments mostly anoxic (no oxygen)

• Bacteria use up oxygen

• Not a lot of water in sediment to replenish

• Produce hydrogen sulfide that anaerobic bacteria can live in.

Physical Characteristics:

Temperature

•Temperature can fluctuate rapidly

•Salinity can change drastically because of heat-induced evaporation

Adaptations Needed

•Salinity

•Temperature

•Desiccation

•Currents

•Sediment instability

Tolerating Low Salinities

•Most are marine organisms that have adapted to low saline environments

•Euryhaline = organisms that can tolerate wide ranges of salinity

•Stenohaline = organisms that can only tolerate a narrow range of salinity

Changes in Salinity

•Organisms can:

•Swim or move away

•Close their shell

•Regulate their salinity

Regulating Salinity•Osmoconformers = organisms that

allow their body salinity to change with the water

•Osmoregulators = organisms that keep the salinity in their body relatively constant

•Need to use active transport or osmosis depending on water salinity

Plants and Salinity•Some plants have very high

tolerances to salinity

•Some have special pores to excrete salt

•Some take up extra water to dilute the salts (pickleweed and other succulents)

Changes in Temperature

•Live in the mud

•Move

•Heat shock proteins

Dessication

•Close shells

•Move

•Burrow deeper

Currents

•Burrow

•Locate areas downstream of jetties

•Byssal threads

•Glue

Mud is sticky•Organisms can burrow into it

•Move very slowly

•Changes in salinity are less in the substrate

•Can pump water through burrow to oxygenate or have hemoglobin to store oxygen better

•Plant roots can stabilize

Estuary Communities

•Open Water

•Mudflats

•Salt Marshes

•Seagrasses

•Oyster Beds

•Mangroves