Chapter 12EstuariesWhere Rivers meet the Sea

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Estuaries

• Semi-enclosed areas where fresh water and seawater meet and mix.

• Interaction of land and sea!

• Some of the most productive environments on earth!

• Most affected by humans!– Harbors– Cities

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Value of Estuaries

• Protected fertile habitat – Home for many!

• Vital breeding and feeding grounds

• Cities built near estuaries because of great fishing. (shrimp and crab)

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Cape Hatteras EstuaryIn N. Carolina

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Milford Sound in New Zealand is a fjord – a finger-like inlet surrounded by sheer walls with a shallow entrance and deep basin

resulting in stagnant, oxygen-depleted deep water.

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4 Types of Estuaries

• Drowned River Valleys or Coastal Plain – Sea invaded lowlands– Most common– Chesapeake Bay

• Bar-built– Sand builds up to form sand bars and barriers– Along Texas coast of Gulf of Mexico

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4 Types of Estuaries

• Tectonic– Land sinks or earth moves

• Fjords – Glacier Carved– Retreating glaciers cut deep valleys that are

partially submerged– Common near Alaska

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Isohaline are the same salt content water. How many are there?

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High Tide

Low Tide

The Salt wedge moves in and out with the tide

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Physical Characteristics of Estuaries

• Salinity in a salt wedge

• Substrate– Rivers carry nutrients into estuary by size and

weight. Which travels farther?– Mud = silt and clay high in nutrients– Anoxic = low oxygen in mud b/c bacteria

respiration.– Anaerobic bacteria thrive in mud. Why?

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Physical Characteristics of Estuaries

• Water temp varies. Why? When? So?

• Exposed organisms during low tides.– Sun, Drying out, Predation

• Low water clarity causes what problem?

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Types of species living in an idealized estuary in relation to salinity. The width of the bars = relative numbers of species

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The body fluids of estuarine animals responds in various ways to the salinity of the water. Osmoregulator = blood salinity stays the same. Osmoconformer=blood salinity will change with the water salinity.

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Look at the shallow roots of

this mangrove tree reaching above the

mud to get oxygen.

Why does mud not have much oxygen

in it?

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Cordgrass is an important component of salt water marshes

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Pickle Weed is a common succulent plant in salt marshes around the world.

19The Atlantic menhaden is an important commercial fish spawn

offshore and larvae drift with tides into the estuary to grow.

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The California horn snail is abundant on

mudflats

21Mudflat animals in temperate estuaries

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Fiddler on the Mud

What is this behavior for?

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The daily tides play a crucial role in salt marshes.

They help circulate detritus and nutrients and

expose mudflat organisms to predation by

shorebirds and other animals

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A salt marsh near Atlantic Beach, NC. Many of these types of marshes have been filled in and destroyed.

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A mudskipper from the mudflats of a mangrove forest in New Guinea. Its eyes can see in air.

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An Oyster reef formed by the eastern oyster near Beaufort, NC are exposed at low tide.

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