Marine Ecology, May 9, 2007
Lecture 8: Biological Interactions 2 (Focus on larval ecology and disturbance)
I.
Larval Types and Strategies
A.
What are larvae?
1.
Larvae are a distinct stage, behaviorally and morphologically, from the adult form
of an organism.
a.
They must undergo a profound change before becoming an adult.
2.
Examples of adults and their larval stages
B.
Larval strategies
1.
Description of key larval strategies
a.
Planktotrophic larvae

“plankton” = drifting; “trophic” = relating to food

Adults produce large numbers of eggs with little to no yolk.

Once hatched, they obtain their nutrition by feeding within
the water column.

May spend a relatively long period of time within the plankton.
b.
Lecithotrophic larvae

“lecitho” = yolk; “trophic” = relating to food

Adults produce relatively low numbers of yolky eggs.

Once hatched, the larvae use the yolk as an energy source
(non-feeding)

Spend relatively less time within the plankton.
c.
Non-pelagic or direct development

The larval stage occurs within the egg case. Neither eggs nor larvae
are released into the plankton. The young hatch out as juveniles that
basically resemble the adults.
C.
Benefits and costs of differing strategies
1.
Planktotrophic larvae
a.
Benefits

Large numbers of produced for a given amount of energy

Offspring can disperse widely; effectively colonize new areas
b.
Costs

Unpredictable food resources

At the mercy of currents (Why a problem?)

Longer time in the plankton  greater predation risk

In sum: A very high proportion of planktotrophic larvae die
2.
Lecithotrophic larvae
a.
Benefits

Have their own energy supply for growth.

Less time to be “at the mercy of currents.”

Less time as plankton  lower risk of predation
b.
Costs

Fewer eggs can be produced

Less time in the plankton means less dispersal
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
Still encounter some of the same risks as planktotrophic larvae.
Non-pelagic or direct development
a.
Benefits

Much lower mortality rate (Why?)higher proportion survive

Begin their juvenile stage in a suitable habitat (Why more likely to
do so than planktotrophic or lecithotrophic larvae?)
b.
Costs

Relatively few offspring can be produced

Little/no opportunity for dispersal. (Why a cost?)
Larval Ecology and Community Establishment
A.
Cues for settlement and their importance
1.
Light
a.
Vertical position in the water column (Why important?)
b.
Sun vs. shade (Why important?)
2.
Pressure (Why important?)
3.
Currents (Why important?)
4.
Salinity (Why important?)
5.
Substrate type (Why important?)
6.
Chemical cues
a.
Pheromones from adults of the same species
b.
Pheromones from prey species
c.
Pheromones from predators
Disturbance and succession
A.
Review: succession
1.
Firs colonizers usually r-selected: lots of larvae or spores, fast-growing, but
relatively poor competitors
2.
Intermediate species next
3.
K-selected can come to dominate a particular region in a “climax community” if
there is no disturbance
a.
Example: Mussels as climax community
B.
Wave action as the major agent of disturbance
1.
Waves cause drift logs to bash into the intertidal zone
2.
Violent storms can also tear off organisms (climax community of mussels at risk)
3.
Bare patches are created where mobile larvae can settle. But who settles?
a.
Available larvae/spores in water column highly variable in space/time

Why? (HINT: Think about specific abiotic and biotic factors that
might impact them.)

Example (Gaines and Roughgarden, 1985)

Predation of juv. rockfish on barnacle larvae, can reduce
stock to 1/50 of released larvae

Juv rockfish decline when kelp forest declines (warm years,
El Nino for ex).

Bad year for kelp means a bad year for rockfish, and thus a
good year for barnacle recruitment.

Ex: Connolly and Roughgarden (1998). Water movement:

Offshore movement of surface water, due to upwelling, can
prevent larvae from settling onto the shore
3.
II.
III.
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
IV.
Larvae can only settle at times/locations with
diminished wind from north (Why? How is this related
to offshore water movement and upwelling?)

Stronger upwelling in CA; less intense larval settlement

Think about El Niño/La Niña (upwelling is reduced during El
Niño...)
4.
End result: Even within a single intertidal zone, a living “mosaic” comprised of
patches of organisms at different stages occurs
Generalizations
A.
Colonization occurs over a relatively wide range compared to adult distribution.
B.
Then, other factors (predation, competition) determine final distributions.
C.
Intensity of recruitment of different species will determine the relative importance of
recruitment vs. other factors in shaping the intertidal community.
Study questions (NOTE: Also be able to answer questions dispersed throughout the outline!)
1.
What are larvae?
2.
Describe the three key larval strategies, and then describe the major benefits and costs of each.
3.
What basic trends have been observed in terms of latitude vs. particular strategies? Explain why
these general trends exist from the perspective of the organisms’ survival. Are exceptions to these
trends common? Provide at least one example.
4.
What basic trends are thought to exist in terms of body size vs. particular strategies? Explain why
this trend might exist from the perspective of the organisms’ survival.
5.
If brooding (non-pelagic strategy) assures a higher percentage of survival of young, why don’t all
marine animals, large and small, pursue this strategy?
6.
List several cues that are used by larvae to find suitable habitats for settlement, and describe why
each cue is important to the larva. Also, be familiar with all cues described in class.
7.
Give an example of succession in an intertidal community, being sure to use the concepts of rselected and K-selected species.
8.
What is thought to be the major cause of disturbance in rocky intertidal communities? Describe a
specific case of how such a disturbance could lead to a bare patch.
9.
What is meant by a “mosaic” distribution of organisms?
10.
Once a bare patch exists, what factors determine which particular organisms will colonize it?
11.
Availability of particular larvae and spores are highly variable in both space and time. Explain
why, using general concepts as well as specific examples to support your answer.
12.
How might upwelling affect the availability of larvae ready to settle in the intertidal?
13.
Describe the roles that larval settlement (i.e. colonization) vs. other factors play in determining
why you see what you see where you see it in the intertidal.
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