Transcript Chapter 14 Estuaries

Estuaries
 An
estuary is a semi-enclosed
.
body of water that has a free
connection with the sea
 Estuaries
have more food
for organisms, but the
organisms usually have to
deal with large
temperature and salinity
changes, high silt content
and pollution.

Hint How
does this
organism get
its food?
 Estuaries
are regions of
transition and sharp
gradients.
 Estuaries support fauna
recruited mostly from the sea
 For
those
organisms that
can survive the
problems of
the estuary,
there is a great
deal of food.
 These
organisms
tend to be in
large
numbers.

The Chesapeake Bay is a
drowned river valley. This is the
most common type of estuary. It
was formed during the last ice
age some 12,000 – 18,000 years
ago.
106 ft.
 56 ft
 32 ft.
 21 ft.
 14ft.
 9ft.

 21
feet is the correct answer.
The deepest spot in the bay is
174 feet near Annapolis Md.
 Can
you name the 6 states
that make up the
watershed of the
Chesapeake Bay?
 Virginia
 Maryland
 West
Virginia
Delaware
 New York
 Pennsylvania
From South to
North
 James
 York
 Rappahannock
 Potomac
 Susquehanna

 The
Susquehanna River
provides about 50% of the
fresh water coming into the
Bay.
 The river empties an average
of 19 million gallons of water
per minute.

About 50,000
commercial
vessels enter
the Bay each
year.
 All
these
people and
activities
put a strain
on the Bay
ecology.
 The
Bay is home to over
3600 living organisms!

Marsh dwellers
are located in
and around
marshes. They
include small
fish, birds, and
marsh grasses.

Submerged
Aquatic
Vegetation
Communities
are important
for many
reasons. They
include ducks,
crabs, and
eelgrass.
 The
plankton
community
includes the
drifters of
the Bay.
 It
includes
phytoplankt
on, bacteria,
and
zooplankton.

Benthic refers
to the bottom
of the Bay.
Benthic
organisms
include
oysters, clams,
barnacles, and
mud crabs.
 Nekton
refers to the
swimmers
of the Bay.
 Croaker,
Spot, and
menhaden
use shallow
water in the
Bay as a
nursery

Formation of an estuary
 embayments—coastal areas where portions of
the ocean are partially cut off from the rest of
the sea
 rivers and streams carry freshwater runoff from
land into some embayments
 estuary forms where fresh and salt water are
mixed
 all estuaries are partially isolated from the sea
by land, and diluted by fresh water


Coastal plain estuary—forms between glacial
periods when melting glaciers raise the sea level
and flood coastal plains
 found along the Gulf of Mexico and eastern
Atlantic coasts
Drowned river valley estuary—forms when
melting glaciers raise the sea level and flood lowlying rivers
 e.g. Chesapeake Bay, Long Island Sound

Tectonic estuary—forms when an earthquake
causes the land to sink, allowing seawater to
cover it

e.g. San Francisco Bay

Fjord—estuary formed when a deep valley cut
into the coast by retreating glaciers fills with
water

found in Alaska and Scandinavia


Tidal flats—deltas formed in the upper part
of a river mouth by accumulated
sediments, which divide and shorten an
estuary
Bar-built estuary—estuary in which
deposited sediments form a barrier
between the fresh water from rivers and
salt water from the ocean
 e.g. Cape Hatteras region of North
Carolina, Texas/Florida Gulf Coasts, etc.

Salinity varies horizontally


salinity increases from the mouth of the river toward
the sea
Salinity varies vertically


uniform salinity results when currents are strong
enough to thoroughly mix salt and fresh water from top
to bottom
layered salinity may occur, with the layers moving at
different rates

Mixing patterns

tidal overmixing—seawater at the surface moves
upstream more quickly; denser seawater at the surface
sinks as lighter freshwater beneath it rises, creating a
mixing action

Water circulation patterns

positive estuary
 influx of fresh water from the river more than replaces the
amount of water lost to evaporation
 surface water is less dense and flows out to sea
 denser salt water from the ocean flows into the estuary
along the bottom
 most estuaries are positive estuaries

Water circulation patterns (continued)

negative estuary
 occur in hot, arid regions
 lose more water through evaporation than the river is able




to replace
surface water flows toward the river; its salinity is
increased by evaporation
water along the bottom moves out to sea
usually low in productivity
e.g. Laguna Madre estuary in Texas

Salt-wedge estuary
occur in the mouths of rivers that are flowing into
seawater
 freshwater flows rapidly out to sea at the surface
 denser saltwater flows upstream along the river bottom
 rapid flow of the river prevents saltwater from entering
and produces an angled boundary between the
freshwater moving downstream and the seawater
moving upstream called a salt wedge


Well-mixed estuary



river flow is low and tidal currents play a major role in
water circulation
seaward flow of water and uniform salinity at all
depths
lines of constant salinity move back and forth with the
tides

Partially-mixed estuary



strong surface flow of freshwater and a strong influx of
seawater
tidal currents force seawater upward to mix with
surface water
rapid exchange of surface water between the estuary
and ocean



Shallowness of estuaries allows temperatures to
fluctuate dramatically
Warmth comes from solar energy and warm tidal
currents
In some estuaries, winter turnover results when
cooler surface water sinks and warmer deep
water rises

circulates nutrients vertically between water and
bottom sediments

Nutrients in fresh and saltwater complement one
another




freshwater contains nitrogen, phosphorus and silica
surface seawater has less nitrogen and silica but more
phosphorus
Silt and clay dumped by rivers hold, then release
excess nutrients
Filter feeders consume more plankton than they
can absorb, producing pseudofeces which
provide food for bottom feeders



Many are species are generalists, and can feed on
a variety of foods depending on what is available
Species that tolerate temperature and salinity
changes can exploit estuaries and grow large
populations
So, estuaries contain abundant individuals from
relatively few species

Maintaining osmotic balance

osmoconformers—animals with tissues and cells that
tolerate dilution
 e.g. tunicates, jellyfishes, sea anemones

Maintaining osmotic balance

osmoregulators—animals that maintain an optimal salt
concentration in their tissues, regardless of the salt
content of the environment
 concentrate or excrete salts, or shield themselves from
their environment

Remaining stationary in a changing environment


natural selection favors benthic organisms because of
the difficulty in staying still to feed in constantlymoving water
non-benthic animals (e.g. crustaceans, fishes) maintain
position by actively swimming or by moving back and
forth with the movement of the tides

Estuaries as nurseries



high level of nutrients + few predators makes a great
habitat for juveniles
juveniles live in the estuary until they grow large
enough to be successful in the open sea
e.g. striped bass, shad, bluefish, blue crabs, white
shrimp


Many hardy organisms are euryhaline
—species that can tolerate a broad range of
salinity
Oyster reefs



reefs form from numerous oysters growing on the
shells of dead oysters
provide a habitat for many organisms, which may
depend on oysters for food, protection, and a surface
for attachment
oyster drill snails prey on oysters

Mud flats




contain rich deposits of organic material + small
inorganic sediment grains
bacteria and other microbes thrive in the mud,
producing sulfur-containing gases
mud provides mechanical support for organisms
cohesiveness permits construction of a permanent
burrow

Mud flats (continued)

mud flat food webs
 main energy base = organic matter consisting of decaying
remains and material deposited during high tides
 bacterial decomposition channels organic matter to other
organisms, and recycles nitrogen and phosphate back to
the sea floor
 deposit feeders prey on bacteria
 larger organisms eat secondary consumers of bacteria, and
so forth

Mud flats (continued)

animals of the mud flats
 most are burrowers living just below surface
 closely-packed silt prevents good water circulation, so
many animals have a “snorkel”
 soft-shelled clams use a siphon to filter feed and obtain
oxygenated water, then metabolize anaerobically during
low tide
 lugworms are common mud flat residents
 innkeeper worms house many other organisms in their
burrows, as do ghost shrimp

Seagrass meadows

seagrass productivity
 depends on the ability of seagrasses to extract nutrients
from the sediments
 depends on activity of symbiotic, nitrogen-fixing bacteria
 also depends on productivity of algae that grow on and
among seagrasses
 nutrients from drawn from sediments are released into the
water by seagrasses, for use by algae

Seagrass meadows (continued)

seagrass food webs
 seagrasses are tough, and seldom consumed directly by
herbivores
 seagrasses are a food source to many animals as detritus,
when their dead leaves are eaten by bacteria, crabs, sea
stars, worms, etc.
 organisms from other communities feed in seagrass
meadows during high tide, exporting nutrients to other
communities

Seagrass meadows (continued)

seagrass meadows as habitat
 epiphytes and epifauna attach to seagrasses
 filter feeders live in the sand among blades
 rhizoids and root complexes provide more permanent
attachment sites, and protect inhabitants from predators
 larvae and juveniles of many species live here, protected
from predators by changing salinity, plentiful hiding
places, and shallow water

Salt marsh communities

distribution of salt marsh plants
 low marsh—region covered by tidal water much of the
day and typically flushed twice each day by the tides
 high marsh—region covered briefly by saltwater each day
and only flushed by the spring tides
 cordgrass dominates the low marsh
 short, fine grasses dominate the high marsh

Salt marsh communities (continued)

salt marsh productivity
 tides bring in replenishing supplies of nutrients
 most primary production supports detrital food chains
 bacteria eat decaying plant material
 deposit feeders eat bacteria
 some salt marshes export large amounts of detritus to
nearby communities; in others, resident organisms
consume most of the detritus

Salt marsh communities (continued)

animals of the salt marsh
 permanent residents include periwinkles, tidal marsh
snails, ribbed mussels, purple marsh crabs, fiddler crabs,
amphipods, grass shrimp
 burrowing animals play an important role in bringing
nutrient-rich mud from deeper down to the surface, while
oxygenating deeper sediments
 tidal visitors that come to the salt marsh to feed include
predatory birds, herbivorous animals from land, fishes
and blue crabs

Salt marsh communities (continued)

succession in salt marshes
 salt marshes can be the first stage in a succession process
that produces more land
 roots of marsh plants trap sediments until the area
becomes built up with sand/silt that combine with organic
material to make mud
 mud islands appear and merge, and high tide covers less
and less of them
 tall cordgrass is replaced by short cordgrass, which is
replaced by rushes and then land plants

Mangrove communities

distribution of mangrove plants
 red mangroves are usually pioneering species, and grow
close to the water where the amount of tidal flooding is
greatest
 black mangroves occupy areas that experience only
shallow flooding during high tide
 white mangroves and buttonwoods (not true mangroves)
live closest to land, but can tolerate flooding during high
tide and saline soil

Mangrove communities (continued)

mangrove root systems
 shallow, widely spread root systems anchor the plants and
provide oxygen for parts buried in the mud
 red mangroves have prop roots, and black mangroves
have many pneumatophores
 prop roots and pneumatophores slow water movement,
causing suspended materials to sink to the bottom
 eventually, this sediment build-up can transform the
estuary into a terrestrial habitat

Mangrove communities (continued)

mangal productivity
 primary producers (mangroves, algae and diatoms)
support a productive detrital food web;
burrowing/climbing crabs eat the leaves

Mangrove communities (continued)

mangroves as habitat
 many animals live on prop roots and pneumatophores,
such as bivalves and snails
 roots provide habitat for many organisms found in salt
marshes and mud flats
 sheltered waters provide a nursery as well