ESTUARIES Estuaries are semi-enclosed, transition areas where fresh water mixes with salt water (called brackish). U.S. has nearly 900 estuaries. Most were formed at the end of the last glacial period by rising sea level. Seawater flooded the land and was trapped by barrier island bays, river deltas and earthquakes. NOAA Marine Biology and Oceanography© by Carol Matthews Published by Teaching Point

Estuaries should have: lower salinity with more euryhaline organisms than stenohaline organisms 2. good light and low suspended solids (silt) that allows the primary producers (sea grasses) to grow 3. nutrients that come from river runoff and provide for a detritus- based food chain; the inverted energy pyramid increases productivity Marine Biology and Oceanography© by Carol Matthews Published by Teaching Point

Productivity and biomass are extremely high Productivity and biomass are extremely high. Specie diversity is directly related to fluctuations in salinity, temperature, oxygen, nutrients and light. Salt wedges of seawater form under river runoff when the tide comes in. This layers the salinity. Marine Biology and Oceanography© by Carol Matthews Published by Teaching Point

The shallow water restricts large predators. Tidal ebb with river runoff causes a net flushing of estuaries and the tides transport larvae and nutrients back into the ocean. Marine Biology and Oceanography© by Carol Matthews Published by Teaching Point

The three most common estuarine environments are: 1. Salt marshes - also called wetlands, swamps or mangrove communities. Producers like Spartina (marsh hay and cord grass) are found mostly in intertidal water. During the summer, grasses die and provide nutrients for crabs, isopods, snails, and worms. However as warm weather increases productivity, oxygen depletion can occur. NOAA Marine Biology and Oceanography© by Carol Matthews Published by Teaching Point

2. Mud Flats - or oyster reefs found in lower intertidal and subtidal zones; primarily composed of bacteria and fungi that carry out anaerobic metabolism. NOAA Infauna have a more stable environment than the epifauna because mud traps the salt. Marine Biology and Oceanography© by Carol Matthews Published by Teaching Point

3. Sea Grass Communities - primarily subtidal zones where animals find food and hiding places. Sea grasses stabilize the substrate and air tubes from the leaves to the roots help oxygenate plants living in anaerobic mud. NOAA Salt excreting leaves of grass slow currents and provide a place of attachment to prevent animals from smothering in the sediments. NOAA NOAA Marine Biology and Oceanography© by Carol Matthews Published by Teaching Point

Estuaries are usually the first dumping site for pollution and industrial discharges. Dredge and fill operations that improve navigation and drainage, damage wildlife and stir up pollution trapped in sediments. Marine Biology and Oceanography© by Carol Matthews Published by Teaching Point

People thought estuaries (swamps) could be “improved” by filling them in for housing developments. Retention ponds and detention lakes do not replace estuaries if there is no outlet to the sea. Marine Biology and Oceanography© by Carol Matthews Published by Teaching Point

They are the seas’ nursery! Estuaries are important because they support a large commercial seafood industry, prevent coastal erosion, trap sediments from entering the sea, provide recreation, wildlife habitat and … They are the seas’ nursery! Marine Biology and Oceanography© by Carol Matthews Published by Teaching Point