III. Rocky Shores --
E. Tropical Intertidal Shores --
not as well
studied
1. more herbivorous fishes
and crabs; more predaceous fish
2. intense consumer pressure,
desiccation, extreme heat
3. high intertidal -
barnacles; mid to low - mostly encrusting algae (26-90%) with
few sessile animals; only in low intertidal is there high
diversity
4. no keystone species that
prevent overgrowth by superior competitors
5. persistent herbivory
on invertebrates and fleshy algae maintains crustose algae
6. recruitment may be
important
F. Patchiness -- small scale patterns within
bigger
picture
1. temporally and spatially
variable
2. slope
3. rock texture (rock type,
cracks)
4. wave action (storms…)
5. desiccation differences
(aspect of rock)
6. clones -- create local
patchiness -- actively fight each other
7. sweeping clear of
patches
8. territoriality
9. succession in disturbed
patches
10. random events
G. Succession
1. quick colonists of
disturbed
areas -- opportunistic or fugitive
species
a. small filamentous green and red algae
b. small animals (e.g., hydroids
)
2. seasonal succession
3. Evidence for inhibition
and facilitation model
a. Inhibition model example
b. Facilitation model example
H. Age Structure
1. major
long-lived
species are invertebrate animals
2. sometimes areas are
dominated
by a single year class -- time when settlement or survivorship was good
3. may be few young in
certain
areas
I. Tide Pools
1. many organisms are
similar
to those of the surrounding rocky intertidal
2. higher tidal pools
- fewer species and lower biomass than lower
tidal
pools
3. refuges from
desiccation
4. large temperature
variations
5. salinity changes
6. oxygen concentration
changes as heat up
7. larger pools experience
smaller physical changes
8. grazing effects example
J. Cobble beaches
1. prone to disturbance
2. extreme temperature changes (rock heats quickly)
3. few organisms
4. if salt marsh plants colonize, can stabilize and promote species diversity
SOFT BOTTOM COMMUNITIES
IV. Sandy Shores
A. Types
1. sand flats --
less exposure, little or no slope, large numbers of macro-organisms are
on the surface
2. sand beaches --
exposed, more wave action, pronounced slope; most organisms are buried
a. dissipative beach -- wave energy is spread over a wide, flat
surf zone; fine sediments
b. reflective beach -- wave action hits the beach face
directly;
sediment is coarse; steep slope
B. Environmental Conditions
1. no solid place for
attachment
2. wave action --
waves move and sort sand grains
3. slope
4. particle size is
important -- determined by the previous two factors –
5. swash -- water
running up a beach after a wave breaks -- carries particles
6. backwash --
water
flowing back down the beach -- removes particles
7. deeper sediments --
temperature
and salinity are buffered; no UV radiation
8. oxygen can become
limiting
C. Adaptations of Organisms
1. ability to burrow within
the sediment and remain there
thixotrophy
2. reproduction - often
timed with lunar cycle
3. predation avoidance
4. respiration - preventing
clogging by sand
D. Types of Organisms
1. no large flowering plants
or algae occur on open beaches
2. low primary production
- only within the upper few cm of sediments
a. phytoplankton and detritus are the main sources of energy
b. suspension (filter feeding common) and deposit feeding (less common)
c.
also carrion feeding
d. few carnivores on the open beach (polychaetes and moon snails); on
sand
flats are crabs, snails and horseshoe crab, Limulus)
3. no large sessile animals
4. polychaete worms, bivalve
mollusks (prefer protected beaches) and crustaceans (more abundant on
exposed
beaches)
5. number of species
increases
in less exposed areas, but the highest biomass is in more exposed
places
E. Community Organization on Exposed Sand Beaches
1. wave action makes it
difficult to study
2. food -- dead algae and
animals (POM), DOM, plankton and benthic algae
3. three-zone division
a. highest parts similar to the supralittoral fringe
b. midlittoral area is more variable -- isopods, sand crabs
c. infralittoral fringe or surf zone -- greatest number of
species
4. are many tidal migrations
(few sessile organisms)
5. may be seasonal changes
6. fauna sparse -- no
apparent
competition for space
7. fish and birds may be
important predators
F. Community Organization on Protected Sand Flats
1. more studied
2. physical factors --
a. grain size can set limits
(1) more deposit feeders in fine sediments that hold more organic
matter
(2) more suspension feeders in coarse sand
b. seasonal temperature changes -- some organisms migrate from
intertidal
to deeper water in the winter
3. biological factors
a. predation particularly important
b.
deposit feeding
c. competition
(1) Competitive displacement horizontally: e.g., competition
between
two mud snails determines their intertidal distribution
(2) Competitive displacement vertically in the sand:
(3) competition between bivalves usually results not in movement, but
decreased
growth and fecundity (competition for food)
V. Muddy Shores
A. Physical factors
1. wave action not important
-- muddy flats only form without strong waves
2. topography is flat and
more stable -- organisms build permanent homes
3. water does not drain
from the sediment
4. the anaerobic
sediments
are the most important characteristic
a. just a few cm below the surface the sediments go anoxic
b. redox (measure of anaerobic conditions) potential
discontinuity
- rapid transition from oxic to anoxic zone
(1) upper sediments are aerobic; sediments usually brown or yellow
(2) at RPD the sediments are gray - reduced energy-containing compounds
diffuse upward;
bacteria use limited oxygen to oxidize these compounds and gain energy
(3) lower sediments are anaerobic; decomposition by anaerobic bacteria;
sediments are black
(a) bacterial chemosynthesis in these deep muds -- produce
organic
matter
from CO2 using energy in reduced compounds
(b) so are two layers of production in the muddy intertidal sediments
--
primary production at the surface
and chemosynthetic production in the mud
5. horizontal zonation is
not pronounced
B. Adaptations of organisms
1. burrowing animals are
capable of withstanding low oxygen
2. little selection for
withstanding
being swept away (no waves)
3. how do they burrow?
C. Types of organisms --
1. often have many plants
– diatoms, macroalgae, seagrasses (Zostera)
2. lots of bacteria
decomposing
organic matter in mud
· chemosynthetic sulfur bacteria abundant in anaerobic
sediment
layers
3. nematode worms eat
bacteria
4. many deposit feeders:
polychaetes, and clams: eat organic matter and bacteria
5. some suspension feeders,
but filter feeders are often excluded
6. few herbivores, but some
polychaetes, mollusks and crustaceans graze diatoms
7. carnivores --
VI. Intertidal Fishes
A. Rocky intertidal -- turbulent environment
1. most are small
2. generally compressed
and elongate body shapes - Blenniidae, Pholidae or depressed shape,
Cottidae,
Gobiescosidiae
3. inhabit holes, tubes,
crevices or depressions
4. most lack swim bladders
and are associated with the substrate
5. visual predators
6. most lay eggs on stones,
rocks or vegetation (males may guard them); larvae spend weeks or
months
in the plankton
7. generally live 2-10 years
and mature in first or second year
B. Mud flats and sandy beaches --
1. skates, rays -- prey
by excavating the sediment in search of infauna
2. various flatfishes --
prey on infaunal invertebrates
VII. Birds -- selective foraging; different bill types and leg lengths
A. Can be important in structuring community
1. migrating birds
2. foraging birds on East
Coast are estimated to consume 50-70% of the invertebrate populations
3. more effects of bird
predation on mud flats than on sand flats
B. Bird Islands -- breeding locations
VIII. Human Uses / Impacts
A. Recreation
B. Development
C. Pollution – runoff from shore – eutrophication
and toxins; oil spills
D. Thermal pollution
E. Erosion
F. Introduced species (e.g., European shore crab
Carcinus maenas; periwinkle Littorina littorea)
G. Harvesting of organisms
1. overharvesting of rocky
intertidal organisms (sessile, easily accessible)
2. clams and crabs from
soft-sediment areas
3. Limulus
(horseshoe
crab) -- amebocyte lysate assay for bacterial endotoxins that cause
disease
(e.g., botulism, dysentery, spinal meningitis)