Rocky Intertidal Zone Community

Intertidal Zone

Area of the shore between the highest high tide and lowest low tide

Mixed Semi-diurnal Tidal Regime

Two tides per day

Tidal heights not equal

neapspring

spring

Full Half NewHalfZero datum (MLLW)

A

B

C

Position on Shore

Physical Factors Affecting DistributionsPhysical Tolerances

• Temperature (average and extreme)

• Moisture/Desiccation

• Light

• Gasses (respiration)

• Wave shock

• Sand scouring

Biological FactorsBiological Interactions

• Predation

• Grazing

• Competition

• Symbioses

Summary

• Upper distributions of intertidal organisms tend to be determined by physical factors – tolerances

• Lower distributions of intertidal organisms tend to be determined by biological interactions

Intertidal Zonation

Factors Affecting Height of the Intertidal Zone

• Slope of the shore

• Wave exposure

• Local geomorphology

• Tidal flux

Behavioral Adaptations

Morphological Adaptations

• Color

• Shells

Physiological Adaptations

• Quiescence• Acclimation

• Anaerobic Respiration/O2 Debt

• Aerial Respiration

Latitudinal Submergence

Biological Factors

• Competition

• Predation

• Symbioses

J. Connell

Competition between Balanus balanoides and

Chthamalus stellatus

Chthamalus stellatus

Balanus balanoides

DISTRIBUTIONS

Chthamalus

Balanus

Transplant

Transplant

TRANSPLANT ADULTS

Transplant adults

Both Chthalamus and Balanus survive

Chthamalus

Balanus

Clearance

Clearance

BEFORE

CLEARANCE EXPERIMENTS

Chthamalus

Balanus

Clearance

Clearance

RESULTS

CLEARANCE EXPERIMENTS

Clear both Balanus and Chthalamus

Both Chthalamus and Balanus recolonize

Chthamalus

Balanus

Clearance

Clearance

CONTINUOUS REMOVAL AND CONTROLS

Chthamalus removed

Chthamalus removed

CLEARANCE EXPERIMENTS

Continuous removal of Chthalamus from both heights

Ex. Balanus recolonizes and Chthalamus does not

C. Both species recolonizeChthamalus has no effect on

Balanus in lower zone

Chthamalus

Balanus

Clearance

Clearance

CONTINUOUS REMOVAL AND CONTROLS

Balanus removed

Balanus removed

CLEARANCE EXPERIMENTS

Continuous removal of Balanus from both heights

Ex. Chthalamus colonizes in Balanus zone

C. Both species recolonize zones

Balanus cannot survive in upper zone

Chthamalus can survive in lower zone in the absence of Balanus

Chthamalus stellatus

Balanus balanoides

Chthamalus

Balanus

Clearance

Clearance

Conclusions

• Balanus exclusion determines lower distribution bound for Chthamalus

• Competitive interaction responsible• Exclusion mechanism is crushing• Upper distribution of Balanus determined

by physical tolerance

R. Paine

Predation by Pisaster ochraceus on Mytilus

californianus

Mytilus californianus

Algae

Pisaster ochraceus

Remove Pisaster No removal

BEFORE

Remove Pisaster No removal

Remove Pisaster No removal

AFTER

Conclusions

• Pisaster determines the lower distribution bound of Mytilus by predation

• The upper limit of Mytilus distribution determined by physical tolerances