Download Intertidal communities

Marine ecological communities:
coastal and intertidal zones
• What key physical factors structure
intertidal and coastal communities?
• Consist of organisms in a defined area
• Who lives in these communities?
• What determines the nature of a
community?
• How do they make a living?
• What are the main challenges that
organisms face in these communities?
Intertidal and coastal
communities
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Ecological communities
Rocky intertidal
Sandy beaches
Estuaries
Salt marshes
Mangroves
Lagoons
– E.g. Sonoran desert, coral reef, intertidal
– Physical stresses
– Organisms’ interactions
Characteristic stresses
• Physical stresses include
– Submersion/exposure
– Waves
– Temperature extremes
• Biological Stresses
– Space
– Competition
– Predation
• Chemical stresses
– Salinity changes (balance seawater-freshwater
inputs; evaporation/precipitation)
– Human impacts from pollution, nutrients, runoff
changes
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Limiting factors
Zonation
• Physical, biological: examples?
• Physical stresses
vary along vertical
gradient
• Biological stresses
can also be
structured vertically
• Coastal/intertidal
ecosystems are
usually vertically
zoned
stress
Optimum
stress
Low
Optimal range
intolerance
intolerance
Temperature (or any physical variable)
Rocky Intertidal - British Columbia
Exposure to air
Always
exposed (=
most stressful
for a marine
organism!)
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Intertidal height (m)
Abundance
Population size
High
1.5
1
0.5
0
0
2000
4000
Hours exposed in 6 months
Always
submerged
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Barnacles, mussels, and algae
Anemone and mussels
Rocky intertidal zonation
Rocky intertidal zonation
• Organisms live at specific levels in intertidal
• Level is determined by how the organism
handles physical and biological stresses
• Lichens and
cyanobacteria
• Algae
• Mussels and
barnacles
• Sea stars
and
anemones
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How to cope with exposure to air?
• Build a tight shell
• Live in a tide pool
• Be very mobile so you can follow a falling tide
Competition between intertidal barnacles
Wave stress
How to manage this?
Hold on tight!
Hide in a crevice or behind a rock
Competition for space
• Anemone Anthopleura
elegantissima common on W coast
• Massive clonal groupings
separated by clear demarcations
• Anemones “fight” - sometimes to
the death!
• Chthamalus tolerates dry conditions better, but can also grow submerged:
their potential range overlaps with Balanus.
• Balanus can outcompete Chthamalus for space by dislodging them
• Result is zonation with C above, B below.
-Lower limit of C is set by competition with B.
-The upper range of both C and B is set by tolerance for drying.
http://life.bio.sunysb.edu/marinebio/rockyshore.html
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Starfish and mussels
• Starfish are predators on mussels,
barnacles
• Feed at lower edge of mussel beds
• Set lower limit of mussels (mussel
beds expand when starfish
removed)
Tidepools in the rocky intertidal
• Tide pools:
– Oases of water during low tide
– Concentrations of food for predators!
– Physical conditions can change rapidly
(warm/cold, salty/fresh)
Algae and anemones
Tide pool inhabitants
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Nudibranch
Sea hare
Sandy beach - intertidal
• Sandy beaches:
– High-energy waves
– Soft substrate; hard to hold on
– Sand in motion: abrasion
– Pebbles and cobbles rolling around
– Waves deliver constant supply of food particles
Octopus in a clam shell
Life in the sandy intertidal
• Crabs: run away
from waves; burrow
• Clams: burrow
• Worms: burrow
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Estuaries
• Productive but not diverse
• Support critical life stages
of many mobile organisms
– Migratory birds
– Young fish (including sharks)
Adaptations to counter salinity stresses
Estuarine environments have strong salinity gradients
associated with fresh and salt water mixing; few organisms
can tolerate the full range of salinities
• Move to avoid highly variable regions
(typically, avoid freshest parts)
• Close your shell
• Burrow underground
• Internal stabilization of water and ionic
concentrations
– When external salinity low, some orgs can
absorb ions from blood and come into osmotic
equilibrium that way
Salt marsh and mangrove distribution
• Mangroves tropical and subtropical (dark blue)
• Salt marshes temperate to higher latitude (aquamarine)
Salt marshes: vegetated intertidal flats
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Mostly temperate-zone ecosystem
Low-energy environments; estuarine
Plants are terrestrial - rooted in mud
Drained by a meandering network of tidal channels
Highly productive
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Salt marsh zonation
Spartina alterniflora adaptations to salty environment
• special tissues (aerenchyma)
increase oxygen availability
to the roots
• salt and organic substances
to increase the solute
concentration in cells
http://life.bio.sunysb.edu/marinebio/spartina.html
• excretion of excess salt from
leaves and stems
Spartina alterniflora
Spartina patens
• likes high marsh but competitively
displaced to low marsh by S.p.
• can’t live in low marsh due to anoxic
soils; displaces S.a. from high marsh
Marsh animals - fiddler crabs
• Fiddler crabs (Uca pugnax) - burrow to escape
most extremes; aerate sediments and help
drainage with burrows
Marsh animals - Ribbed mussels
• Ribbed mussels (Geukensia demissa)
cluster at the base of S. alterniflora; attach to
each other and the substrate with threads
that help stabilize the plants and sediment
• Filter feeders; their excretions fertilize the
plants.
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Marsh animals - predators
Salt marsh and mangrove distribution
• These herons prey on small
fish and invertebrates
• Predators also include
raccoons and other
terrestrial mammals
• Mangroves tropical and subtropical (dark blue)
• Salt marshes temperate to higher latitude (aquamarine)
Mangroves
Mangrove food web
• Detritus of mangrove trees supports diverse aquatic ecosystem
• 60% is consumed by detritovores; just 1-2% becomes soil; rest
is flushed away
• Diverse invertebrate fauna (especially crabs!)
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Mangroves are dominant intertidal plants of tropics/subtropics
Woody, tree-like plants with exposed roots
Grow in soft sediment, low-energy environments
Zonation - different species dominate different zones
http://www.specola.unifi.it
/mangroves/fauna/Inv/inv
ertnew.htm
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Other mangrove fauna
www.mykenya.co.uk/ info_htm/funzi.htm
Mangroves and fish
http://cars.er.usgs.gov/pics/manatee/manatee/
• Reefs adjacent to mangroves had more and larger fish
• Mangroves provide refuge from predation for sub-adults
• Local extinction of prominent fish species has occurred when
mangroves removed
http://www.tracc.org.my/Borneo
coast/MANGROVES/MANG_FA
UNA.html
http://www.stockpix.com/stock/animal
s/endangeredspecies/indexb.htm
www.duke.edu/~cwcook/
pix/panama/birds4.html
Mangroves under threat
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Deforestation
Development
Shrimp aquaculture
Sea level rise
Mangroves and shoreline protection
“IPS News Agency 2005-02-14
PENANG, Malaysia, Feb 14 (IPS) - When the Indian
Ocean tsunami struck the coastlines of South and
South-east Asia, areas with dense mangroves
suffered fewer human casualties compared to areas
without them.”
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Lagoons
Laguna San Ignacio
• Grey whale breeding ground
• Desirable salt plant location!
(Mitsubishi)
• Semi-isolated bodies of shallow water without significant
freshwater input (i.e. not an estuary)
• Exchange with ocean depends mainly on tides
• Salinity brackish to hypersaline
– Extreme evaporation can lead to reverse flow: deep water flows
out, fresh in on top
• Can be populated with mangroves, sea grass, marsh
plants, coral reef organisms, or be barren…
Coastal ecosystems and
“ecosystem services”
Human impacts on coastal ecosystems
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Pollution
Nutrient overloads
Freshwater diversions
Development
Aquaculture
Sedimentation increases
Invasive species
Sea level rise
Over half of all coastal wetlands have been
lost.
• Ecosystem services = services (not goods, resources)
provided by an ecosystem
• Can be evaluated in monetary terms
• Coastal ecosystems are disproportionately valuable
(Costanza et al. 1997)
– 6% of world area, 43% of ecosystem value
• Services include:
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Nutrient cycling
Water storage and purification
Recreation
Coastal protection
Fish nurseries
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