1. Estuaries Shipley Marine Biology
Chapter 12
Estuaries
Shipley Marine Biology

2. Types of Estuaries Drowned river valleys Most common type of estuary
They were formed by the “drowning” of low land around the mouths of rivers when sea level rose after the last ice age
Ex: Chesapeake Bay

4. Types of Estuaries Bar built estuary-
Built by the accumulation of sediments into sand bars or barrier islands
Ex: North Carolina (seen in lower part of the photo to the right near Cape Hatteras)

5. Types of Estuaries
Tectonic estuaries –
Formed as a result of land sinking due to movements of the Earth’s crust
Ex: San Francisco Bay

6. Types of Estuaries Fjords –
Deep channels cut in the coastal zone as a result of retreating glaciers
Ex: Alaska, Norway

7. Development of Estuaries
Estuaries are the best developed in areas where the coastal plain is flat and the continental shelf is wide.
The opposite is true in areas with steep, narrow continental shelves and coastal plains

8. Physical Characteristics of Estuaries
Salinity-
Can vary from 5 – 30 ppt
Salinity varies according to distance from saltwater (tides) or freshwater (river) input
Can also vary as a result of storms
Depth also contributes to salinity
The diagram to the right illustrates that the salinity is not uniform (saltwater is heavier and sinks below freshwater) – this is known as a salt wedge

9. Dealing with Salinity Changes
Organisms in the estuaries are normally euryhaline (can tolerate a wide variety of salinities)
Some are osmoregulators that have mechanisms for keeping their internal concentration stable
Others are osmoconformers with internal concentrations that vary with their surroundings

12. Dealing with Salinity Changes
Flowering plants in the estuarine community must either expel excess solutes (such as Spartina and margrove trees using salt glands) or concentrating solutes in specific tissues (such as in Salicornia, a.k.a. “pickleweed” or glasswort

13. Substrate Mostly composed of sand or mud
Mud is difficult to move through
Mud or sand can also shift unlike hard substrate which is a challenge for organisms as well
Particle sizes are so small that most areas are actually anoxic (devoid of oxygen)

14. Water Temperature
Like in the intertidal community (and some areas of estuaries are intertidal), temperature can vary greatly.
Temperatures can vary especially at times when water levels are low.

15. Water Clarity Water clarity is very poor in estuaries
This is due to suspended sediments and particles from rivers in the water
This reduced clarity makes it more difficult for photoautotrophs in the water
Most primary production is the result of flowering plants in the salt marsh as opposed to algae or plankton

16. Communities within an Estuary
Open water in bays and tidal creeks
Predominant organisms include plankton, floating algae, fish and many larval forms (crabs, shrimp, molluscs, fish, etc)
At the right, this diagram shows the EXTREME IMPORTANCE of estuaries as a “nursery” area for larval species
Many marine species spend at least a portion of their life in an estuary, mainly as larvae.

17. Communities within an Estuary
Saltmarsh
The vegetated area of an estuary
Spartina species predominate near the water in most estuaries (Juncus or needlerush can be found near the water in low salinity estuaries < 10 ppt)

18. Representative Inhabitants in a Mudflat of an Estuary

19. Communities within an Estuary
Mangroves or mangals
Found in tropical and subtropical coastal areas
Replace saltmarshes in these areas normally

20. Worldwide Distribution of Saltmarshes and Mangrove Forests

21. Generalized Food Webs in Estuarine Ecosystems

22. Aerial View of a Mangrove

23. Communities within an Estuary
Some mangrove tree species possess pneumatophores, or vertical root extensions, that assist the plant with the exchange of gases (pictured at right)

24. Communities within an Estuary
Seagrass beds can be found in some estuaries) if the water clarity permits
Water clarity must be better than the average estuary to support this growth

25. Communities within an Estuary
“Oyster reefs” are found in many estuaries
These congregations of oysters are the platform on which dozens of other species grow and thrive
The oysters provide the only hard substrate in many estuaries