Marine Ecology, May 7, 2007
Lecture 7: Biological interactions in the intertidal
I.
II.
III.
IV.
V.
Overview: Effects of biological interactions on zonation/distribution in intertidal
A.
Joe Connell’s hypothesis for upper vs. lower limits of species distribution
Competition for space
A.
Example: Vertical distribution of the barnacles Chthamalus and Balanus.
B.
Example: Algal distribution
C.
Example: Lottia gigantea (owl limpet) territoriality
D.
Example mussel bed succession in the mid-intertidal, “exposed” coast: one possible
sequence of events
Predator-prey interactions.
A.
Example: Pisaster ochraceus. Major studies by R. Paine (1966, 1972, 1985) on P.
ochraceus in Washington.
B.
Example: “Natural” experiment on New England coast (Menge, 1976, Lubchenco and
Menge, 1978) with a diff. star and mussel species.
1.
Pisaster and similar predatory stars are keystone species: Paine coined the term
"keystone predator" based on Pisaster. Term implies that the species
composition of the entire intertidal community is shaped by Pisaster predation.
a)
Contrast keystone species concept with diffuse predation
b)
Important to realize that other conditions may affect the degree to which
a keystone predator influences the community (i.e. role of larval
transport/recruitment, disturbance, and temperature, which we will
discuss shortly...)
c)
What causes the upper limits of Pisaster ochraceus?
C.
Example: Nucella spp.
D.
Predation also influences distribution within a zone
1.
Example: Predation of black oystercatchers on limpets
a)
Frank, 1982; Hahn 1977
Role of grazers
A.
Limitation of algae by grazers
1.
Overview
2.
Case study: Katharina tunicata (a chiton),Diether and Duggins (1988):
B.
Maintenance of diversity by grazers
1.
Comparisons of tide pools with and without grazing snails.
C.
Grazing deterrents
D.
Limitations of grazers by algae (Underwood and Jernakov, 1981)
E.
Physical conditions vs. grazing in affecting distribution of algae
a)
Read p. 262: explanation given is that “on sheltered shores, limpets and
other grazers are rare. This permits the algae to grow and flourish.”

Doesn’t explain why they are rare. Do they have it backwards?
Symbiotic relationships and species distribution
A.
One species creating a suitable habitat for others
1.
Example: Mussel beds
2.
Example: algae
B.
Mutualistic relationships
1.
Green anemones (Anthopleura spp.): Green color due to symbiotic zooxanthellae
and zoochlorellae. Similar to relationship of coral and its symbionts.
Mutualistic.
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Study questions
1. State, in your own words, Joe Connell’s general hypothesis for how upper vs. lower limits of species
are set in the intertidal.
2. Be sure you have a good working knowledge of each example presented in class. In other words, you
should know, at the level of lecture or text (whichever is greater)
 Key concepts being introduced/explained by the example!
 The name of the experimental organism,
 The distribution pattern observed.
 The type of experiments or observations made
 The factor being tested (Predation? Desiccation? Importance of a symbiotic relationship? Etc...)
 The interpretation of the key results
 Limitations of the experiments/observations in explaining the distribution patterns seen or
applying them to broader geographical areas.
3. What physical and/or biological factors appeared responsible for the lower limit of Chthamalus in
the intertidal? What physical and/or biological factors appeared responsible for the upper limit of
growth in Balanus? Describe the observational/experimental evidence upon which your answers are
based.
4. What is a keystone predator? Why is Pisaster considered a keystone predator, while Nucella is not?
5. By what mechanism could a grazing snail actually cause increased algal diversity in a tide pool?
Compare this to the mechanism by which Pisaster ochraceus maintains diversity in the midintertidal. What are the effects of crabs on these small tidepool ecosystems? What are the effects of
gulls?
6. Describe Bob Paine’s initial experimental procedures and key results for Pisaster ochraceus removal
experiments on the Washington coast.
7. When Bob Paine returned to his experimental sites 14-17 years after the Pisaster-exclusion cages
were removed he found that the thick beds of mussels persisted in the low intertidal, even though
Pisaster could now freely enter the area. In contrast, for a similar experiment in Chile, the initial
conditions (clear boundary at bottom of the mid-intertidal) were re-established. Why the difference
in the two studies? Would you expect the thick beds to persist indefinitely?
8. Be able to list the "general" types of both physical factors (i.e. “wave action” et al.,) and biological
interactions (i.e. “competition for space” et. al.) which influence distribution of intertidal organisms.
Then, give real examples of each (as provided in lecture) and explain them clearly.
9. One observation from the rocky intertidal of central California is that the limpet Collisella digitalis is
found on vertical surfaces, while the limpet Collisella scabra is found on horizontal surfaces.
 What are the two hypotheses provided for this observation? Are they mutually exclusive hypotheses?
 What experimental evidence has been provided?
 What additional evidence would be useful in determining which of these factors is key in
determining the distribution?
10. Provide examples of how symbiotic relationships can impact distribution of intertidal organisms.
11. How might the distribution of algae limit the distribution of limpets and other snails?
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