Lecture 18:  Estuaries and Coastal Marine Communities

Focus Question:  Why are estuaries so productive? or  Where are the Nurseries of the Sea?
 
 

Feel free to email the instructor (dpalmer@kent.edu) with any
comments about the format and ease of use of these online notes.

1.  Coastal Marine Communities

Marine life lives in a variety of substrates and habitats, with specific adaptations to the environments

There are special areas of especially high productivity that provide special coastal environments: 

Estuaries,  Mangrove Forests, and Kelp Forests

2.  Rocky Intertidal Communities

•Intertidal = band below high and low tides
•- high energy environment
•- rapid changes in temperature, moisture, salinity
•- many different habitats
•- abundant food
 

3.  Sand and Cobble Beach Communities

•Sand and cobble beaches are hostile environments
•Difficulties:
•- loose and abrasive material
•- temperature changes
•- wave shock
•- exposure
•Conditions favor larger animals

4.  Coastal Sand and Mud

•In sandy and muddy environments, living subsurface provides protection and access to food.
•Larger organism that live below the surface are called infauna
•Smaller ones may be interstitial.
 

5.  Communities below wave base

•On cobble bottoms, one successful approach is to live below wave base in calmer water.
•Scallops and Sponges thrive on cobble bottoms off the Maine Coast.
•Note thick plankton which serves as food for filter feeders.
 

6.  Lots of places to live, but where do you raise the kids?  Where are the Nurseries of the Sea

Today we’ll look at three coastal communities that fill the bill         They all have the essentials

Abundant Nutrients

High Productivity

Shelter from Predators

Variety of Environments

 

They are     Estuaries and Salt Marshes

                    Mangrove Swamps and Forests

                        Kelp Forests

7.  Estuaries:  What is an estuary?
•Geology:  A body of water partially surrounded by land where fresh water mixes with the sea.
•Estuaries fill rapidly with sediment and are short-lived, geologically speaking-lifespan is on the order of hundreds to thousands of years
•Biology:  Estuaries are biologically productive and important ecosystems, yet also extremely sensitive to pollution and land-use changes.
-  Easily Polluted by
 sewage
 fertlizer runoff
 heavy metals
 solid waste
 organic compounds
 oil spills

8.  Estuarine Circulation:  How Rivers Meet the Sea…
  •Unique circulation patterns occur where fresh and salty water meet in estuaries
•Influences on estuarine circulation include:
•- shape of estuary
•-  volume and variation of river flow
•-  tides


9.  Different kinds of estuaries:   See Figure 15-5

  •  Salt Wedge estuary-the ocean water is more dense than the river water, and moves up the estuary during high tide in the form of a dense wedge of salty water, with the river water moving up and over it-very little mixing.  Example:  Mississippi River Estuary
  • Well Mixed Estuary-the river flow coming into the estuary is not as strong as in the Salt Wedge estuary, and you have good mixing with the salt water moving up the estuary.  Example:  Columbia River Estuary
  • Partially Mixed Estuary-the river flow coming into the estuary is very strong-Example is Chesapeake Bay.
  • Fjord Estuary-narrow but very deep, with river water flow is strong, but with little tidal mixing.  Example is Norwegian Fjords
  • Reverse Estuaries-where river water has ceased to flow, and tidal ocean water starts to evaporate, creating an increase in salinity from the sea upstream in the estuary.


10.  Biological Success in Estuaries demands tolerance of big fluctuations in salinity and temperature,
and tolerance for occasional or even daily exposure to the air.

11.  Salt Marsh Communities
 Where salt tolerant grasses grow in estuaries-the most productive parts of estuaries.
 Each tidal cycle flushes through the wetlands, bringing in more nutrients
 The source of nutrients comes from the tidal cycle, as well as from rivers carrying dissolved nutrients down to the sea.

12.  Nurseries of the Sea
 When you see a salt marsh estuary, you are looking at a place where many birds, mammals, and invertebrates
lay their eggs, hatch their young, and raise them until they are ready to move out into the ocean or away from the salt marsh.
 Estuaries provide protection from predators
 Estuaries provide lots of food.

13.  Economic value of wetlands:

  • critical for life cycles of many marine organisms
  • Filter sediments and pollutants• Buffer water levels
  • Slow erosion and stabilize shorelines
14.  -Major Threats to estuaries
  • habitat destruction due to development
  • nutrient pollution (e.g., nitrates, phosphates, fertilizers, sewage)
  • non-nutrient pollution (e.g.,oil, heavy metals, solid waste)

15.  Mangrove Forests and Mangrove Swamps

Mangrove forests and swamps are like coastal wetlands because they

are critical for life cycles of many marine organisms

filter sediments and pollutants

Buffer water levels, and

Slow erosion and stabilize shorelines

 

Mangrove Forests also offer a unique set of environments that shelter and nurture life and are highly productive for the Ocean
 
Mangrove Forests are located along warm water coastlines, and are thus their locations are controlled by Ocean Circulation

Mangrove forest may be separated from the Ocean by sand bars and beaches

Or, they may exist right against the Ocean in mud flats or coastal plains

Complex and Extensive Root Systems of the Mangrove Trees Stabilize Coastlines and Provide Habitats for Many Marine Organisms

 
The Root Systems also Provide Hiding Places and Shelter for Many Land Species

What are the human impacts on Mangrove Forests?

The productive coastal land is being used in Mariculture – Especially in Southeast Asia.   Mariculture is the farming of sea life. - we will talk about this much more later.

This involves stripping the forest, contouring the land into large basins, and flooding the basins with sea water.  The product in Sumatra and Thailand is shrimp.  (Yes, those nice Tiger shrimp in our markets)

There are large impacts in the loss of the Mangrove Forests:  There is destabilization of coastline, loss of habitat, and pollution from the processes of farming the sea.  Sludge (read sewage) drained from Shrimp Ponds has a large environmental impact on Remaining Mangrove Forests and the Surrounding Coast.

 

16.  Kelp Forests are among the most biologically productive environments in the ocean.  They are real forests with many of the same properties we see in land forests.

They have
    Multiple levels - canopy, midlevels, understory, base
Numerous niches - for many different organisms at the different levels, and
Complete ecosystems

17.  The basic components of the kelp plant are the   Leaf-like Blades or Fronds,  Stems or Stipes, the gas-filled floats called pnematocysts, the reproductive organs known as sporophylls, and the holdfast.

The blades or fronds form the major photosynthetic part of the Kelp.  They are anchored to the bottom by the stipes.  The stipes are very flexible and strong, but cannot hold the fronds up in the water column.  Therefore the plant has the buoyant pneumatocysts which hold the fronds up near or at the surface.  Kelp plants may be 10's of feet high and the record lengths of the plants are over 100 feet.  Kelp plants may grow rapidly - by as much as 20 inches per day.

The holdfasts look like roots, but do not serve all the functions of the roots in land plants.  They serve the function of holding the Kelp plant in place, but do not provide the nutrients that are provided by the roots of land plants.

Habitats:

Holdfast and bottom communities are very rich.  The rock substrate and the holdfasts provide shelter and the abundant organic matter from the forest above provides food for a wide variety of animals.  Plants at deeper levels need to harvest bluer light.

The mid-level, understory of the Kelp Forest provides a number of habitats as well.  There are specific understory plants that thrive in the reduced light.  But competition for light important in the growth and success of plants. 

The canopy of the forest is often at the surface.  It may be thick enough to slow coastal currents.  The reduced flow rates are beneficial to the growth of some juvenile species who use the canopy for "cover".  The canopy is full of life and is a site of grazing and hunting by many larger fish and marine mammals.

Ecological balance:  A main predator of Kelp are Sea Urchins.  Where they are very abundant, they may threaten life of the kelp forest.  Urchins are kept in check by predation by carnivores like starfish and sea otters.  Control of the grazers allows the forest to develop the dense stands that are critical to the many species inhabiting the Kelp Forests

Next lecture:  Marine Plankton

Focus Question:  What is the role of plankton in the Ocean?