Download intertidal zones

Lecture Benthic Ecology
Benthos
• Unlike the drifting plankton and swimming
nekton, benthic organisms – commonly
referred to as benthos – live on or near the
ocean bottom
• A benthic habitat may be shallow or deep
• Most benthic organisms are sessile (immobile)
and anchored to the benthic environment;
others crawl or swim over the ocean bottom
Benthos
• Of the 250,000 known species that inhabit the
marine environment, >98% are benthos!
• The majority of benthic organisms live on the
continental shelf; sunlit areas of relatively high
primary productivity
• Benthos include animals,
protists (algae) and even
plants!
Why are benthic organisms important?
• Benthos link the primary producers
(phytoplankton) with higher levels in the food
web.
• Filter feeders such as clams and oysters
consume plankton and organic particles.
• Many benthic creatures, particularly clams and
worms, serve as food for larger, economically
important species such as blue crabs, striped
bass, spot, croaker and white perch.
Environmental snapshot
• Scientists study benthic organisms because they
provide a good snapshot of environmental conditions in
the Bay and its streams and rivers. Most benthic
creatures cannot move very far, if at all, so they can’t
avoid pollution or unhealthy water conditions.
• Benthic communities are exposed to many stressors,
including low oxygen levels, excess sediment and
chemical contaminants.
• In summer, high temperatures and nutrient pollution
often lead to low-oxygen areas at the bottom of the
Bay and its rivers.
Environmental snapshot
• Excess sediment suspended in the water can block
sunlight from reaching bay grasses growing at the
bottom. When sediment finally settles, it can bury
oyster bars and other benthic species.
• Many chemical contaminants bind to bottom
sediments, remaining there for years. Benthic species
become contaminated when they feed and live in
these toxic sediments.
Intertidal Zones
Intertidal Zones
• Rocky shorelines team with organisms that
live on the ocean floor (epifauna)
• Typical rocky shores are divided into distinct
zones, characterized by the height of the
water (which is itself determined by the tides)
• So called intertidal zones are among the most
densely-populated areas on Earth; hundreds
of species crowd this junction of land and sea
Intertidal Zones
• Epifauna - live attached to hard surfaces such
as rocks, shells and pilings. They also live
directly on the surface of the Bay’s bottom.
Epifauna include oysters, sponges, sea squirts,
sea stars and barnacles. Ex)An oyster reef
• Infauna - burrow into bottom sediments.
Worms, clams and other infauna form their
own communities that are connected to the
water by tubes and tunnels
Life in the intertidal zone is harsh!
• Adverse conditions require special adaptations
of organisms to live both underwater (some of
the time) and exposed to air (the rest of the
time)!
• Strong wave activity, desiccation (drying out),
limited space, rapid changes in temperature,
salinity, pH, and oxygen content, and
predation are just some of the challenges
found here
Biotic factors affecting organisms living
in the intertidal zone:
•
•
•
•
•
Competition for space and food
Predation
Reproduction
Substrate settlement preference
Osmoregulation
Abiotic factors affecting organisms living in the
intertidal zone:
• Salinity
• Temperature
• Air and light exposure
• Tidal flow
• Waves and current action
• Substrate
• Wind direction and strength
• Dissolved O2
• Storms
• Natural Disasters
Spray zone –
region above
the spring high
tide line;
covered by
water only
during storms
Intertidal zone
– region
between the
high and low
tidal extremes
Rocky shores: Intertidal zonation and organisms
Mostly
shelled
organisms
Mostly
softbodied
organisms
and algae
Intertidal Zone
http://www.humboldt.edu/~intertid/zones.html
• High tide zone:
relatively dry
• Middle tide zone:
alternatively wet
and dry
• Low tide zone:
usually wet, but
exposed during
low tides
Life in the intertidal: High tide zone
• Most animals living in the high tide zone have
protective coverings to prevent desiccation
• Seaweeds living in the high tide zone have
thick cell walls to reduce water loss during low
tides
• Many organisms in the high tide zone are
sessile, and remain attached to bottom,
competing with others for limited space
www.armofthesea.info/flora_faunaff_speciespp/moll.htm
Life in the Intertidal: Middle tide zone
• Seawater constantly bathes the middle tide
zone, so a greater variety of seaweeds and
soft-bodied organisms live here
• Greater biomass in middle tide zone, and so
greater competition for space!
• Mussels and barnacles are common here –
hard-bodied, filter-feeding organisms which
require seawater to feed and to
support planktonic larval stages
Crying cockles and mussels, alive, alive-O!
• The middle tide zone is also home to
carnivorous snails and sea stars
• You, too, can be a sea sleuth….
• Sea stars pry open clams and mussels with
hundreds of tube feet; Predatory snails bore
holes with scraping tongues and suck out prey
• Hermit crabs, sea urchins, and sea anemones
are also found here
Life in the Intertidal: Low tide zone
• The low tide zone is almost always submerged,
so an abundance of algae (seaweed) is
typically present
• Seaweeds are multi-cellular algae (protists)
• Seaweeds attach themselves with a structure
known as a holdfast and use gas bladders to
reach upward to sunlit surface water;
photosynthetic; important source of habitat
Life in the Intertidal: Low tide zone
• Numerous crabs and shellfish live in the low
tide zone
• Benthic fish swim through the low tide zone,
along with larval nektonic forms which seek
shelter and habitat in this protected area
Rocky shores
• Most organisms live on the surface (epifauna)
• Zonation of rocky shores:
–
–
–
–
Spray zone (rarely covered by water)
High tide zone
Middle tide zone
Low tide zone (rarely exposed)
• Upper zones have mostly shelled organisms
• Lower zones have many soft-bodied organisms and
algae
Rocky shores:
Intertidal zonation and organisms
Figure 15-2a
Spray Zone
• Supratidal zone
• Organisms
– Avoid drying out - eg. thick,
impermeable shells to reduce water
loss and radiation effects.
– Behavioural - eg. seeking small
crevices for shelter to reduce the
drying effects of the wind.
– Physiological - eg. an ability to lower
metabolic rates during exposed
periods to minimise oxygen
consumption.
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Intertidal Zone Organisms
• Middle tide zone
– Soft-bodied animals
• Low tide zone
– Abundant algae
– Many animals hidden by
sea weed and sea grass
– Crabs abundant in all
intertidal zones
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Rocky Bottom Shallow Offshore Ocean Floor
Communities
• Lobsters
– Large, spiny antennae
– Live in water deeper
than 20 meters
(65 feet)
– Scavengers
– Also feed on live animals
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Rocky Bottom Shallow Offshore Ocean Floor
Communities
• Oysters
– Sessile bivalve mollusks
– Thick shell
– Start life as plankton
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Sea anemone
• A vicious
predator
cleverly
disguised as a
harmless
flower but
armed with
stinging cells
Figure 15-4
Sediment-covered shores
: Intertidal zonation and organisms
Figure 15-8
Sediment-covered shores:
Modes of feeding
Figure 15-9
Sandy Beach Organisms and Adaptations
• Crustaceans
– Segmented body, hard
exoskeleton, paired
jointed limbs
– Example: crabs, lobsters
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Sand and Cobble Beach Communities
• In fact, very few organisms survive in waveswept sandy beaches
• Some larger crabs can outrun the crashing
waves and locate food within sand grains
• Coquina shells and mole crabs are common
along Long Island sandy beaches
www.stripersonline.com/surftalkshowthread.php?t=417951
Sand and Cobble Beach Communities
• Not all intertidal areas are rocky or muddy;
some are sandy or consist of gravel or cobbles
• As benign and peaceful as sandy beaches look,
they are among the most hostile
environments for small organisms
• Sand grains are abrasive and many organisms
must have protective coatings and/or be able
to burrow below the surface for protection
Mud Flats
• Eelgrass and turtle grass
common
• Bivalves and other
mollusks
• Fiddler crabs
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