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

What is the greatest concern to the intertidal organisms?

• Water loss or desiccation

• Take advantage of crevices, clustering, shade, tidepools, other organisms, etc.

Fig. 11.2

• 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. 11.3Fig. 11.4

Fig. 11.5

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. 11.7

Fig. 11.8

• Distribution, diversity, & abundance partially defined by exposure

• Why the differences?

Fig. 11.11

• Sheltered– Less wave force

– Higher profile

• Heavier wave action– Lower profile to reduce drag

Fig. 11.12

• Flexibility to deal with wave action

Fig. 11.13

• 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

Fig. 11.14

• 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

• 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. 11.16

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. 11.17

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. 11.19

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

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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. 11.23 & 11.24

What about sandy intertidal areas? Beaches?

• Still get zonation patterns…– However, here many organisms are adapted for

sand/sediments rather than rocks and tidepools

Fig. 11.33 & 11.34