Chapter 14 - Shallow Communities

Notes for Chapter 14: Life in Shallow Water

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Case History: M.A.D. (Mutual Assured Destruction)
at Marcus Island

Summary from The Scientist (1988):

The biota of Malgas Island off the west coast of South Africa is dominated by seaweeds and by
rock lobsters that consume settling mussels, preventing them from becoming established, they
also prey on whelks. Marcus Island, four km away, has extensive mussel beds and whelks at
high densities, but rock lobsters and seaweeds are virtually absent. Rock lobsters transferred to
Marcus Island are overwhelmed and consumed by the whelks—a reversal of the normal
predator-prey relation between the two species.

A. Barkai, C. McQuaid, “Predator-prey role reversal in a marime benthic ecosystem,”
Science, 242 (4875), 62-4,7 October 1988.

RQ 14.1: Why are whelks unable to become established when
        rock lobsters are dominant, nor rock lobsters when whelks
        dominate? Explain why this could be an example of what
        community ecologists refer to as "alternative persistent
        steady states."

I. Deep versus Shallow Waters

RQ 14.2 (Fig. 14.1): Give two reasons why shallow water
        depths are more likely to be productive than deeper
        water depths. Why doesn't wind tend to directly cause
        upwelling of nutrients?

II. Life on Intertidal and Shallow Rocky Bottoms

a) Rocky Intertidal Communities

RQ 14.3: What are a few of the reasons why the rocky intertidal
        has been so important for ecological studies, even though
        it represents a relatively tiny portion of the Earth's marine
        habitat?

        1) Ecological process 1: Disturbance increases species
            diversity.
        terms: keystone species, stability-time hypothesis,
            intermediate disturbance hypothesis (described but
            not referred to by this name in text), zonation patterns

Featured organisms:
Pisaster ochraceus (ochre seastar)

Featured marine ecologist (published classic studies):
Robert Paine

Visit Source of Image

RQ 14.4: Why is Pisaster ochraceus referred to as a keystone
predator?

RQ 14.5: Why does disturbance increase species diversity?
What is the stability-time hypothesis?

Other members of the genus, Pisaster, have similar ecolotical importance in the kelp forest
(P. giganteus) and on sandy bottoms (P. brevispinus).

2) Ecological process 2: Many species live in
suboptimal habitats.

         Featured organisms:
      Chthamalus spp. (say "thamalus" or little brown acorn barnacle)
      Balanus spp. (larger white acorn barnacle)
       Nucella lapillus (predatory whelk, a carnivorous snail)

        Featured marine ecologist (published classic studies):
      Joseph Connell
          Connell performed his studies in Scotland, but similar species of
        Balanus, Chthamalus, and Nucella live on the California coast.
          Compare these species to similar "high zone" species in Australia.

RQ 14.6 (Fig. 14.3): Note that the barnacle, Chthamalus, settles from
        the plankton from high to low on the shore but only survives to
        adulthood in the high intertidal. Connell formulated three (and more)
        alternative hypotheses to explain this failure to survive in the
        lower intertidal: predation, drowning, and competition. Explain
        how Connell's "experimental manipulation" experiments were
        able to test between these alternative hypotheses.

3) Ecological process 3: Systems can have more
than one persistent steady state.

RQ 14.7 (Fig. 14.4): Relate the example of New England tidepools,
        studied by Jane Lubchenco, to the above "M.A.D." example.
        How are these studies similar? Explain how "crab" and "snail"
        pools each resist change through time. How was this experimentally
        demonstrated?

b) Rocky Subtidal Communities

1) Kelp forests are among the most productive communities
on Earth.

RQ 14.8: In what ways are kelp forest communities considered to
be among the most productive marine communities?

2) Unconstrained feeding by urchins appears to eliminate
kelp on shallow rocky bottoms (see Ch. 9 notes).

RQ 14.9: Keep the following study guides in mind as you
    read the remainder of Chapter 14. Compare the following
    habitats with respect to:
    1) physical characteristics; 2) typical communities;
    3) amount of productivity; 4) source of productivity;
    5) relative degree of disturbance; 6) long-term fluctuations

        Rocky intertidal
        Kelp Forests
        Cobble beaches
        Sandy beaches
        Muddy beaches
        Salt marshes
        Mangrove forests
        Sea grass communities
        Estuaries
        Coral reefs

III. Life on Sediment Bottoms

a) Cobbles, Sand, and Mud

RQ 14.10: Contrast sediment habitats: cobbles, sand, and mud.

b) The Interstitial Fauna
terms: interstitial fauna, meiofauna

RQ 14.11: What are some typical characteristics of interstitial fauna?
        Why does the interstitial fauna produce more biomass each year
        than the macrofauna, even though the macrofauna typically
        outweighs the interstitial fauna?

c) Predation on Sediment Bottoms

RQ 14.12: What did Robert Virnstein conclude from his experiments
with predator-exclusion cages on sandy bottoms that was different
from Robert Paine’s study of the rocky intertidal?

d) Sandy Shores

RQ 14.13 (Figs. 14.11-12): Briefly describe the "zonation" of organisms
from exposed shore to inland dunes for the Padre Island, Texas,
shoreline.

IV. Vascular Plant Communities

a) Salt Marshes
terms: energy subsidy

RQ 14.14: Why are West Coast salt marshes poorly developed?
Why are they so productive, even if they are not diverse in
numbers of species?

b) Mangrove Forests
terms: mangals

RQ 14.15: Where are mangrove forests found? How are trees
able to survive submerged in salt water?

c) Sea Grasses

1) Sea grasses have active roots, symbiotic partners,
and high productivity.

2) Sea grasses feed herbivores, detritus feeders, and
bacteria; and they moderate disturbance by predators.

3) Was the great eelgrass epidemic of 1931 a preview
of an effect of global warming?

V. Estuaries

a) Biological Makeup, Productivity, and Unique Features of
Estuaries

RQ 14.16: In what ways are estuaries important?

b) Important Nurseries and Vulnerable Invasion Ports
terms: exotic species

VI. Coral Reefs

    a) The Reef Builders and Their Giant Living Monument
        terms: algal ridges, patch reefs, hermatypic corals,
            bioerosion

b) Plants and Food Webs
terms: cryptic

RQ 14.17: Why are coral reefs important? What characterizes most
of the plants in coral reef habitats?

c) Herbivores, Competitors, Predators - Major Agents of
Disturbance

RQ 14.18: What are major forms of disturbance to coral reefs?

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