Download Ecology of Estuaries I. Importance of Estuaries

Ecology of Estuaries
I. Importance of Estuaries
I.
Importance of Estuaries
II.
Physical Conditions
A. Productivity
III. Habitats
B. Nursery Areas
IV. Biological Attributes & Interactions
C. Filtration
V.
D. Spawning Sites
Threats to Estuaries
E. Migration Routes
F.
A. Productivity
Resting and Feeding Areas
B. Nursery Areas
•
high levels of nutrients
•
high productivity lots of food high growth
•
shallow and tidal lots of solar radiation for
primary production
•
reduced predation low mortality
•
warmer than surrounding ocean during
summer
C. Filter for nutrients and toxicants
•
outflowing groundwater and rivers pass through
estuaries on way to ocean
•
plants, animals, and sediments take up nutrients
and toxicants
•
keeps these chemicals out of ocean (good), but
concentrates them in estuaries (bad)
example species: California halibut, shrimps
D. Spawning Sites
•
many species migrate to estuaries to spawn
•
presumably so offspring can take advantage of
high productivity
examples: striped bass, herring
Pacific herring spawning
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E. Migration Routes
•
F. Resting & Feeding Areas
many species migrate through estuaries to reach
spawning/feeding grounds
•
long distance migratory species (birds)
•
Pacific Flyway (Alaska to Patagonia)
examples: ducks & geese
examples: salmon spawn in freshwater but adults live in ocean
II. Physical Conditions
A. Physical Configuration
- gradients
A. Physical Configuration
•
partially enclosed bodies of water where rivers meet
oceans (or huge freshwater lakes, but we won’t talk about
•
sometimes are completely enclosed when mouth of
estuary closes (usually seasonally)
•
where topography is steep (narrow coastal plain)
estuaries are usually small (US West Coast)
•
types of Estuaries based on Geology…
that)
B. Mixing of fresh and seawater
C. Tidal Fluctuations
D. Resulting Abiotic Variation
E. Adaptations to Abiotic Conditions
Categories of Estuaries based on Geology:
Coastal Plain: Chesapeake Bay
1. Coastal Plain – flooded river valley
(Chesapeake Bay, Narragansett Bay, RI)
2. Bar-Built – sand bar builds in front of river mouth
(Tijuana River Estuary, Carpinteria Salt Marsh)
3. Delta – sediments deposited at mouth by river
(Mississippi River delta)
4. Tectonic – tectonic movements along fault lines
form estuary
(San Francisco Bay)
5. Fjords – dug out by advancing glaciers, form when
glacier retreats
(Glacier Bay Alaska)
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Bar-built: Carpinteria Salt Marsh, CA
Delta: Mississippi Delta
Tectonic: San Francisco Bay, CA
Fjord: Glacier Bay, Alaska
B. Mixing of Fresh & Seawater
• freshwater mixes with seawater to create brackish water
(0.5-35 ppt salt)
• salinity gradients form from mouth (ocean) to back (river)
— many species have a limited range of salinities they can tolerate
— salinity gradients change over time: depending on weather
(rainfall) and tidal flushing
– seasonality: wet season in Mediterranean climates is low
salinity season
B. Mixing of Fresh & Seawater
Estuaries can also be classified by how thoroughly the fresh
& salt water mixes vertically…
1. Salt-wedge: freshwater rides over dense saltwater
wedge at mouth; the most stratified type of estuary
•
2. Slightly stratified: like salt-wedge but with more mixing;
stratification not as complete
•
– tides: high tide pushes saltwater in
• requires tolerance to variable salinity (euryhaline species)
— limits diversity of organisms in estuaries
— sets patterns of distribution within estuaries
requires high freshwater input (e.g., Mississippi River delta)
less freshwater input or more tidal influence (e.g. San
Francisco Bay)
3. Vertically mixed: no vertical stratification
•
low river flow and strong tidal currents; prevalent in shallow
estuaries (e.g., most So. Cal estuaries)
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C. Tidal Influences
Salt-wedge estuary
freshwater
saltwater
• estuaries are tidal (just like the rocky intertidal)
• organisms face extreme & changing conditions:
completely submerged to completely dry
Slightly stratified estuary
freshwater
brackish
saltwater
low tide
high tide
Vertically mixed estuary
freshwater
saltwater
brackish
estuary
ocean
river
C. Tidal Influences
A tidal sequence at Elkhorn Slough, California
D. Resulting Abiotic Variation
• Salinity
low tide
• Oxygen (low oxygen in flooded soils)
• Submergence
• Temperature
high tide
Pattern of salinity change with elevation differs with
latitude (due to differences in evaporation)
low
latitude
Soil
Salinity
high
latitude
subtidal
Elevation
E. Adaptations to Abiotic Conditions
Salinity
• salt tolerance in vascular plants
Salicornia
Distichlis
- filter out salts at roots (e.g., cordgrass, Spartina spp.)
- excrete salt through leaves (e.g., Spartina & Distichlis)
- succulence: water in tissues dilutes salts (e.g., pickleweed, Salicornia spp.)
terrestrial
• euryhalinity in animals
- oysters close shells when salinity drops & switch to anaerobic metabolism
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E. Adaptations to Abiotic Conditions
III. Estuarine Habitats
Sumbergence/Oxygen availability
• adaptations in plants
• salt marshes
• mangrove forests
- extra roots near soil surface
- well-developed tissues that transport O2 from aboveground parts of
plants to roots
- greater reliance on anaerobic metabolism
• mud flats
• tidal creeks
• subtidal channels
• subtidal basins (bays, sounds)
cross section of
Spartina foliosa leaf
showing hollow
tubes used to
transport O2
• rocky intertidal shores
• reefs
• barrier beaches
Salt Marsh
Tidal Creek
Subtidal Channel
Mudflat
Subtidal Basin (Bay)
Mangrove Forest
Reef
IV. Biological Interactions
A. Competition
B. Predation
Rocky Intertidal
Barrier Beach
C. Parasitism
D. Facilitation
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A. Competition
•
common and intense
•
structures estuarine communities
•
occurs along gradients & competitive ability changes
along gradients
•
dominant competitors usually live in least stressful zone;
weakest competitors live in most stressful zone
•
A. Competition
Examples:
• salt marsh plants are usually found in dense
monospecific stands that…
- suppress germination of seeds & survival of seedlings
- cause density-dependent survival and growth
•
competition among mussels Geukensia demissa causes
slow growth, but they are less susceptible to mortality
from predators and suffocation by mud (Bertness and
Grosholz 1985)
most work has been done on plants…
•
A. Competition
competition among juvenile fish limits growth (Kneib 1993)
B. Predation
Examples:
•
competitive hierarchies in salt marsh plants
•
Herbivory of vascular plants relatively unimportant
- only about 10% or less eaten by herbivores
— NE coast of US
- plant tissues eaten mainly as detritus by inverts & fishes
Iva > Juncus > Spartina patens > Spartina alterniflora
- mirrors pattern of distribution from high to low elevations
- all species can be transplanted higher, but all die if
transplanted lower
•
Predation
- common and intense
- affects abundance and sets patterns of distribution
— California estuaries
- causes competition by forcing prey to crowd into refuge habitats
with less food
- more complex in CA marshes because salinity pattern is
more complex
- predation intensity varies seasonally: highest in summer, lowest in
winter (when preds are less active)
- nutrient addition can reverse competitive hierarchies and
change zonation (Levin et al. 1998)
B. Predation
C. Parasitism
Example: Southern California
Examples: E. Coast
•
shrimp and small fish eat small invertebrates and limit
them to high, inaccessible elevations
(Pennings & Callaway 1996)
•
dodder (Cuscuta salina) preferentially
parasitizes pickleweed (Salicornia
virginica)
•
helps promote coexistence of competing
plant species because...
•
crabs and larger fish limit larger invertebrates to high
elevations
•
juvenile fishes stay in vegetated marsh & tidal creeks to
avoid larger predatory fishes
•
blue crabs limit mussels to high elevations (limits feeding
by mussels)
– dodder can reduce pickleweed cover by
90%
•
blue crabs limited to marsh edge (not higher) by bird
predation (Micheli 1997)
– allows re-invasion of pickleweed
– pickleweed is the dominant competitor
monocultures by subordinate competitors
Limonium, Frankenia, and Arthrocnemum
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D. Facilitation
•
extremely important in estuaries
•
occurs when one species alters conditions and makes
them tolerable for other species
D. Facilitation
Examples: NE coast of US
•
Spartina alterniflora (cordgrass) is the pioneer species
(starts succession)
— Spartina is necessary for establishment of all other plant
species (Bruno 2000; Bruno and Kennedy 2000)
may do so by…
– stabilizing substrate
- stabilizes substrate
– ameliorating abiotic stresses
- shades areas, reducing evaporation and thus salinity
– providing refuges from predators
- provides shelter from predators
- oxygenates soil, improving plant growth (Bertness 1991)
D. Facilitation
D. Facilitation
Examples: NE coast of US
Examples: NE coast of US
•
•
Spartina alterniflora enhances settlement of mussel
Geukensia (by providing solid substrate)
mussel enhances Spartina growth by providing nutrients
and and also reduces erosion (Bertness 1984)
D. Facilitation
Examples: W coast of US, San Francisco Bay
•
Spartina alterniflora is an introduced and invasive species
•
has hybridized with native cordgrass Spartina foliosa
•
hybrid and invasive cordgrass is colonizing and eliminating
mudflat habitat
•
facilitation of colonization by other species in new habitat is
changing physical and community structure
•
Spartina alterniflora and fiddler crabs Uca spp. have a
mutualism
–
crabs increase Spartina growth by their burrowing which
improves drainage and oxygenation of soil
–
Spartina benefits crabs by stabilizing soil for burrows, providing
food, and shelter from predators
D. Facilitation
Examples: W coast of US, Southern California (Callaway 1994)
•
Arthrocnemum subterminale improves survival and
growth of winter annuals
•
increases soil moisture and lowers salinity by shading
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A. Infilling (“land reclamation”)
IV. Threats to Estuaries
•
estuaries filled in to make room for houses and
commercial facilities
•
38% of wetlands lost in US; 60-90% lost in
California
A. Infilling
B. Dredging
C. Eutrophication & Pollution
D. Loss of River Flow
E. Unnatural Freshwater Input
F. Invasive Species
B. Dredging
C. Eutrophication & Pollution
•
deepening to aid boat navigation
•
from industrial discharge, yard &
street runoff, agricultural runoff
•
turns shallow productive habitats into deeper, less
productive habitats
•
biomagnification of toxicants (e.g.,
DDT and mercury)
–
e.g., Los Angeles Harbor, Mission Bay, and many major ports
•
Los Angeles Harbor
nutrient pollution: nitrates &
phosphates cause algal blooms,
deplete O2 at night, cause anoxia
and kill organisms
- comes from sewage treatment
plants & septic tanks, storm water
runoff, overfertilized lawns, golf
courses and agricultural fields
D. Cutting off River Flow
•
upstream dams are common
•
reduced freshwater flow and scouring can change
dynamics of estuary
- e.g., leads to closing of bar-built estuaries which usually
causes fish and invertebrates to die
E. Unnatural input of freshwater: runoff
•
in arid regions (e.g., So. Cal) freshwater input to
estuaries during summer is unnatural
•
freshwater input during summer now common due to
over-watering of lawns, yards, golf courses,
agricultural fields
•
in bar-built estuaries that close during the summer,
this causes the estuaries to go hyposaline rather
than hypersaline, as they did historically
•
effects aren’t well studied yet
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F. Invasive Species
Summary
•
probably present in all estuaries
•
230+ species in San Francisco Bay; 160+ in
Chesapeake Bay
•
includes...
–
–
–
predators (e.g., striped bass)
competitors (e.g., yellowfin goby)
habitat modifiers (e.g., burrowing isopod Sphaeroma
quoyanum; Chinese mitten crab; Spartina alterniflora &
hybrid)
•
may irreversibly change estuaries
Sphaeroma
• estuaries are important, highly productive habitats at the
sea-land interface
• estuarine populations and communities are structured
both by strong abiotic influences (e.g., salinity gradients)
and biotic interactions (e.g., competition, predation,
facilitation)
• a variety of human actions have caused a large fraction
of estuaries to be destroyed (e.g., infilling) or damaged
(e.g., pollution)
Chinese mitten crab
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