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Between the Tides
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La Jolla Grunion Run
Where?
• Shoreline between high
and low tide marks
Organismal adaptations?
• Community has to be
adapted to exposure to
air
• Communities differ
greatly depending on
structure
– Rocky or sandy
bottoms
Fig. 11.2
What is the greatest concern to the intertidal organisms?
• Water loss or desiccation
• Take advantage of crevices, clustering, shade,
tidepools, other organisms, etc.
Fig. 11.3
Fig. 11.4
• Move to moisture & clamp their
ventral surface to the substrate
to conserve water (chitons)
• Closed mussel shells
• Contracted anemone
• Resilient tissues that can
withstand 75-90% water loss
…tidal exposure limits activities
…can be harsh conditions
Fig. 11.5
Fig. 11.7
Wave exposure and wave
shock
• Adaptations to cope?
– Seaweeds?
– Mussels?
– Intertidal fishes?
• Wave energy varies
–
–
–
–
Sheltered coastlines
Angled wave approach
Varied impact to organisms
Gradient of impact (shock)
and exposure
Fig. 11.8
Fig. 11.11
• Distribution, diversity,
& abundance partially
defined by exposure
• Why the differences?
Fig. 11.12
• Sheltered
– Less wave force
– Higher profile
• Heavier wave action
– Lower profile to reduce drag
Fig. 11.13
• Flexibility to deal with wave action
Fig. 11.14
• Safety in numbers
– (a) Wave force can detach higher profile individuals
– Clustering can protect from wave shock (as well as preventing
excessive desiccation).
– (b) Wave force is indirect – reduced or dissipated some
– (c) Too dense can be a problem sometimes
• Shaping the intertidal zones so
far…
– Effects of wave exposure
• Temp, salinity, desiccation
– Effects of wave shock
• What else effects organismal
distribution?
• Food / nutrients
• Trophic interactions
–
–
–
–
–
Many suspension feeders
Grazers
Scavengers
Predators
Detritus is central
• typically most important food
source
Fig. 11.15
Fig. 11.16
• Space is typically most
limiting resource
• Most organisms are
attached to substrate
– Mussel species
– Barnacle species
– Anemones, seaweed
• Much competition for any
freed-up space
Fig. 11.17
What is happening here?
• Juvenile sea palm settled
on mussels
– Increased profile and drag
increases vulnerability of
wave shock
• Mussel clumps detach
• Makes space for juvenile
sea palms on substrate
Fig. 11.19
Trophic interactions &
environmental adaptations
define zones
• Vertical zonation
– Patterns or banding of
distribution
– Upper limit set by physical
factors
• Space often defines upper end
of range – zones
• Exposure
– Lower limit set by biotic
factors
• Predation
• Competition
Fig. 11.18
Fig. 11.20
Fig. 11.21
Diversity and abundance
• At Scripps intertidal, organismal diversity was high.
• Species abundance varies with diversity
– Mussels in mod. abundance; Barnacles – mod.; Sea stars – mod.
• Keystone predators
– A predatory species that significantly affects the community beyond their
abundance
– Can maintain diversity
Fig. 11.22
Fig. 11.23
Page 252
Fig. 11.23 & 11.24
Predation on dominant competitors = disturbance
• ↓ predation = ↓ disturbance = competitive
exclusion
• ↑ disturbance = ↓ establishment = ↓ diversity
• Moderate disturbance = provides a balance
between abiotic and biotic factors; a chance
for diverse species
Fig. 11.33 & 11.34
What about sandy intertidal areas? Beaches?
• Still get zonation patterns…
– However, here many organisms are adapted for
sand/sediments rather than rocks and tidepools