What
is the source of primary
production in rocky intertidal ecosystems?
So, what would a food web/energy
diagram look like for a seagrass ecosystem?
Ecology of rocky intertidal ecosystems
Many "classic" studies in marine
biology, and ecology in general, have come from work done within the
rocky intertidal. Why?
- competition: What
is limiting
in the intertidal?
Like corals, macroalgal (seaweed) species vary in competitive
strategies based on ability for fast growth (e.g. kelp)
versus ability to resist disturbance (e.g. crustose red algae).
Like seagrasses, some species produce secondary metabolites that
discourage grazers (e.g. the brown alga Fucus); small invertebrate grazers
can actually take up the compounds, thus conferring protection on the
grazer from predators.
Joseph Connell's
classic study demonstrates the importance of
competition. At mid-depths both
Balanus and
Chthamalus
both can settle as larvae but only
Balanus survives. When
Balanus
was removed experimental,
Chthamalus can survive (i.e.
competition
restricted lower distribution of
Chthamalus).
- physical
factors: Tides expose organisms to varying degrees of
desiccation and temperature
extremes. In a reciporical treatment in the
above experiment, Balanus
could not survive in Chthamalus zone even when Chthamalus
was removed.
Wave
stress can also be an important stress and an organism body shape in
such an environment is a compromise between the
forces
of drag, lift, and acceleration.
Species diversity on intertidal boulders is highest for
intermediate-sized boulders.
Why?
- predation: For
example, a study by Robert Paine demonstrated that experimental
removal of the predator Piaster
results in near total dominance of the intertidal by the mussel Mytilus
californicus excluding of other intertidal
macroinvertebrates.
- grazing: Grazers can affect algal zonation,
species diversity, and distribution. For example, crabs can
influence succession on intertidal
algae on boulders by removing early
colonizing algae (green Ulva) allowing colonization of
late succession alga
(reds)
resistant to crab grazing.
- larval
recruitment: Vertical zonation in some barnacles species
mirrors zonation of planktonic barnacle larvae in the water column,
suggesting that passive recruitment process may influence vertical
distributions (and horizontal
patterns along coasts as well).
Is a
plankton larval stage common for marine organisms?
Recruitment of larvae is highly variable in
time and space due to changes in currents and weather (i.e. a function
of oceanographic principles that we studied earlier this
semester). Therefore, many interactions and patterns found in
benthic community may be strongly influenced by processes 'outside'
that system. This has challenged the more traditional approach in
ecology that tends to consider ecological systems as 'closed' rather
than 'open'.
Bottom line: Each
marine ecosystem we have considered is relatively unique in patterns of
energy flow and feeding interactions. However, each of these
systems are linked to others and function as they do because of
their connection to the whole!
Rocky
intertidal ecosystems tend to be diverse.
What strategy is necessary for the
success of rocky intertidal organisms?
While a hard substrate may be of advantage
in a high energy environment, what is a disadvantage of hard substrate
(relative to soft-sediments) for an intertidal organisms?
