Download The Intertidal Zone Zones Rocky Intertidal Rocky shores

Zones
The Intertidal Zone
• Supralittoral: area just above high water mark, only
submerged during storms; otherwise ocean spray
• Littoral: intertidal zone between low and high water
marks
• Sublittoral: subtidal zone below low water mark,
permanently submerged; extends down to the
continental shelf break (~200 m)
• Below the shelf break, benthic habitats are classified into
bathyal, abyssal, and hadal zones; all are aphotic.
• The abyssal zone is the largest benthic area (75%):
temperature 4°C, high hydrostatic pressure, little food
Rocky Intertidal
• Harsh environment: loss of water at low tide; physical
forces of waves; variation in temperature; UV radiation;
ice formation; variation in salinity (rain exposure)
• Adaptation to life between water and air:
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Hard shells and solid attachment against wave action
High temperature and water-loss tolerance (60-90% of water
in some algae)
Retreat into shells and housings at low tide to minimize water
loss and exposure to grazers
Synchronized spawning
Cluster formation
Rocky shores
• Most organisms live on the surface (epifauna)
• Zonation of rocky shores:
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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
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INTERTIDAL ADAPTATIONS
Rocky shores: Intertidal zonation and organisms
Vertical Zonation
• Highest zones
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black lichen on highest zone
periwinkle zone (gastropods)
barnacle-dominated zone
zone dominated by different spp.
(i.e. mussels in N. America)
• Zone correlates with tidal levels (i.e. upper limit of
seaweed)
• Laminaria - extreme low water in sheltered areas
Causes of Zonation
Zonation
Maintenance of zone:
1) selective larval settlement
2) behavioral patterns
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2.
3.
4.
Physiological tolerance
Larval and adult preference
Competition
Predation
3) physical tolerance of org.
4) wave action and tidal range
8 wave splash can extend zones
5) intraintra- and interspecies competition
6) predation and algal grazing that is
tidal range dependent
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Pioneering Experimental Study by Joseph Connell
Desiccation
Graphical representation of
Connell’s results
Chthamalus
•
Chthamalus stellatus (high intertidal)
Semibalanus balanoides (low intertidal)
• Used experimental manipulations
• Thinned density of potential competitors
• Excluded potential predators with cages
MHW spring
MHW neap
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• Rocky intertidal of Scotland: two barnacle species
Mean tide
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Sh
Pr
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Physical
factors
Interspecific effects
MLW neap
Adult density
MLW spring
Settlement of cyprids
Intertidal Paradigm
Chthamalus
MHW neap
Desiccation
Chthamalus
s
ion
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etit
ala
mp
mib
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nu
ala
mib
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Mean tide
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alu
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MHW neap
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MHW spring
Mean tide
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Pr
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MHW spring
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• Upper limits determined by physical stress
• Lower limits determined by ecological factors, e.g.
competition and predation
Desiccation
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av
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Sh
Pr
ed
oc
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k
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Physical
factors
Interspecific effects
ck
n
Physical
factors
MLW neap
MLW neap
Adult density
MLW spring
Interspecific effects
Adult density
MLW spring
Settlement of cyprids
Settlement of cyprids
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ISSUE: Temperature Stress and Desiccation
• Seaweeds and mussel beds retain moisture and
harbor invertebrates
• In winter Ilyanassa obsoleta moves to subtidal regions
to avoid danger of freezing
• Different fauna live on light and dark surfaces
(volcanic vs. sandstones and limestones)
ISSUE: Water Loss
• Barnacles, mussels, limpets - can seal off loss more
effectively than soft-bodied animals - polychaetes,
anemones, ascidians
• Ulva - can dominate shallow mud flats in winter but
dies off in summer
• Ascophyllum nodosum, Fucus vesiculosus very
tolerant - when >5% water loss photosynthesis is
affected
Effects of displacement
ISSUE: Dissolved Oxygen and Gas Exchange
• Mytilus calif. - under moist conditions
• Guekensia demissus - takes air in at low tide
• Anaerobic metabolism when oxygen reserve is
depleted
• Also respiratory pigments • Hemoglobin, hemocyanin, chlorocruorin - many polychaetes
have these compounds.
• Reduced feeding times
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time spent feeding reduced in upper zone; these animals tend
to be smaller
• Wave action >
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Spisula solidissima
Emerita
Donax denticulatus
Ensis
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Larval Biology and Supply-side Ecology
Larval settlement
behavior in water column
R. K. Grosberg
Ecology 1982
Maybe supply varies with depth?
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Larval behavior in water column
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Larval behavior at settlement
Swimming behavior in the coral Agaricia humilis
Zonation with Depth on St. Croix
Site 1
Site 2
Depth (meters)
Raimondi and Morse.
2000. Ecology
Reef
Crest
1.5
3.0
6.0
9.0
Favia fragum
0
1
2
Abundance (#
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5
corals/m2)
D. B. Carlon. 2002. J. Exp. Mar. Biol. Ecol.
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Zonation and Larval Behavior
Zonation with Depth
Do larvae select substrata from different depths?
Do larvae select substrata from different depths?
Design
• Larval settlement on coral rubble in lab
• Rubble collected from 3 depths x 2 sites
• Larvae from shallow-water parents
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Site 1
Site 2
% Settlement
70
60
50
a
Favia fragum
a
40
30
20
b
10
0
Back reef 1.5 m
Fore reef 3 m
Fore reef 10 m
Origin of Substrata
Larval Biology and Supply-side Ecology
ISSUE: Territoriality
Supply can vary with depth
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Larval behavior in water column (barnacles and corals)
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Larval behavior at settlement (corals)
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Upper and lower limits can be set by supply
• many limpets remain at one spot at time of low tide and
graze on algae at high in this vicinity
• Scars develop on substrate
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Pacific Owl Limpet - Lottia gigantea - defends space
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ISSUE: Competition
ISSUE: Competition
• Acorn barnacle Chthamatus stellatus and Balanus
balanoides (better competition in lower zone)
Barnacle vs. barnacle (Connell, 1961)
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Transplanted rocks with newly settled C. stell. to all levels in the
intertidal
Some rocks were caged to avoid predation by Thais lapillus
C. stell. - survivorship was greater in upper but not so in lower
(fig. 16-1)
Algae vs. algae
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• Mussel vs. Algae Caging Exp. (Lubchenco, 1980)
• In headlands wave exposed coasts removal of Asterias
forbesi and vulgaris and T. lapillus results in Mytilus
domination.
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ISSUE: Competition
Mussel vs. mussel (Hager, 1968, 1970, 1972)
• M. edulis vs. M. calif.
• M. edulis - more mobile, active, in bays
• M calif. - thick shell, on wave-exposed coast
Chondrus crispus - lower - resistant to grazing Gastropods dessication restricts upper
F. vesiculosus restricted by gastropods in lower
Lubchenco and Menge, 1978
ISSUE: Competition
• Mussel - Barnacle
• Paine, 1966 - Mukkan Bay (outer Wash. coast)
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removed individuals of Pisaster ochraceus capable of
devastating both mussel and barnacle
following removal - 60-80% of space occupied by barnacle next
year in fall
by summer, Mytilus competition dominant and Mitella spp.
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Predation and Species Interactions
• Predators reduce prey density
• Prey species compete
• Conclude: predation may promote coexistence of
competing prey species
Predation intensity varies depending on the
distribution of refuges
A rocky shore in the
U.K. At the time of low
tide on hot dry days, the
gastropod Nucella
lapillus retreats into the
crack where it is moist
and cool. Note the
areas cleared of
mussels adjacent to the
cracks.
Field Experiments of Robert Paine
• Rocky shores of outer coast of Washington State
• Principle predator - starfish Pisaster ochraceus
• Pisaster preys on a wide variety of sessile prey species,
including barnacles, mussels, brachiopods, gastropods
Dense population of the barnacle
Semibalanus balanoides
Pacific coast starfish Pisaster ochraceus, flipped over
Left: eating a mussel, Right: eating barnacles
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Paine Experiment: Results
• Removal of Pisaster ochraceus
• Successful settlement of recruits of mussel Mytilus
californianus
Keystone Paradigm
• Predators increase species diversity by reducing the
effects of competitive dominants
• Other species greatly reduced in abundance, Mytilus
californianus became dominant
• Conclusion: Pisaster ochraceus is a keystone species, a
species whose presence has strong effects on
community organization mediated by factors such as
competition and predation
Complications with the keystone paradigm
Larval supply of competitive dominants fluctuates
Because…..
1. Current structure changes and prevents larvae from
returning to shore
2. Predation in subtidal habitats reduces the abundance of
larvae returning to shore
3. Changes in productivity decrease survivorship of
feeding larvae (few examples).
Disturbance and Community Structure
• Disturbances are physical events that influence the distribution
and abundance of organisms
• Disturbances may reduce abundance of competing species
• Therefore, disturbance may allow coexistence of competitively
inferior species, or may allow colonization of species adapted to
disturbance
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Postelsia palmaeformis : the seapalm
Spatial Scale of Disturbance is Crucial in Subsequent
Colonization events
• A very small scale disturbance in a mussel bed might just
result in the mussels moving and sealing off the opened
patch
• Larger patches might be colonized by other species and the
patch might last many months or even indefinitely
• Therefore, spatial scale of disturbance might affect the
spatial pattern of dominance of species, creating a mosaic of
long-lived patches
• Invades rocks that have been severely disturbed by storms
• Spores are released and travel just a few cm from the plant
• Permits local spread of a colonizing individual
Sediment-covered shores
California mussels California mussels
California mussels
• Most organisms burrow into the sediment (infauna)
• Sediment-covered shores include:
Small
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Newly
Opened
Patch
California mussels California mussels
Bay
Mussels
And
Seaweeds
Large
California mussels
California mussels
California mussels
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Beaches
Salt marshes
Mud flats
California mussels
Disturbance and spatial scale: events following the
opening of a small and large patch in a Pacific coast
mussel bed
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Soft-Sediment Redox Potential Discontinuity (RDP)
Sediment-covered shores: Intertidal zonation and organisms
Sediment surface
0
5
10
mg/l
Light brown
15 oxidized layer
O2 RPD
Reduced
black layer
H2S
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Microbial communities and the RPD
Photosynthetic bacteria and algae (cyanobacteria and diatoms)
Aerobic bacteria (use oxygen to break down organic substrates)
RPD
RPD
Fermenting bacteria (break down organic cpds. --> alcohols,fatty acids)
100 200
Gray layer
300 400
mg/l
Macrobenthos: Deposit Feeders
Feed upon sediment, within the sediment or at sediment
surface
1. Head-down deposit feeders feed within the sediment
at depth, usually on fine particles, defecate at surface
2. Surface browsers often feed on surface
microorganisms such as diatoms
Sulfate reducing bacteria (reduce SO4 to H2S)
Methanogenic bacteria (break down organic cpds. --> methane)
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Deposit Feeders
Deposit feeders: potential food sources
• Microbial communities
• Particulate Organic Material (POM)
Surface tentacle
feeding polychaete
Tentacle feeding
bivalve
Deep feeding
polychaete
Surface feeding
amphipod
Surface siphonate
feeding bivalve
Deep feeding polychaete
Microbial Stripping Hypothesis
• Macrobenthos cannot digest and assimilate POM as
readily as the microbial communities living on the
surfaces of POM.
POM broken down in three ways
• Fragmentation- physical disturbance or grazers breaks
material down
• Leaching- loss of DOM from POM
• Microbial decay- Surface bound microbes colonize, enrich
in nitrogen (Fungi) and take up POM (Heterotrophic
bacteria)
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Habitat and food sources
• Sand flats- microbial communities
• Salt marshes and seaweed communities- POM
• Seaweed POM is easier to digest and assimilate
Burrowing by deposit feeders affect sediment
structure
Energetic arguments against strict microbe diets
• Salt marshes- Not enough microbes to support all the
macrobenthos
• POM utilized directly?
• External sources of food?
Active Suspension Feeders
• Fecal pellets increase grain
size
• Head down feeders may
selectively feed on small
grained sediments and
transport them to the surface
Bivalve, x-section
Polychaete Serpula
Barnacle
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Hard Bottom Suspension Feeders
Hard Bottom Suspension Feeders
Hard Bottom Suspension Feeders
Hard Bottom Suspension Feeders
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Passive Suspension Feeding:
Net Hypothesis
Hard Bottom Suspension Feeders
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How can passive suspension feeding work?
Requires small mesh size
Flow must be low
Reynolds numbers are therefore low
Net or paddle?
How can passive suspension feeding work?
• Sieving- limits capture to particles > distance between
feeding structures (mesh size)
• Direct interception
• Inertial impaction- requires higher Reynolds numbers
• Motile particle deposition
• Gravitation deposition- requires higher Reynolds
numbers
Motile
particle
deposition
Direct
interception
Sieving
Inertial
impaction
= fiber
Gravitational
deposition
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