MARINE BENTHIC SUCCESSION
Lab 10
Reminders!
•
Memory Stick
Key Concepts
•
•
•
•
Primary & secondary succession; Climax
Intermediate disturbance hypothesis
Keystone predator hypothesis
r & K selected species
Student Learning Outcomes
After Lab 10 students will be able to:
1. describe the process and different stages of a
succession in biological communities.
2. explain the relationship between the frequency
of disturbance and species diversity during a
succession.
3. recognize the colonization characteristics of
different species and the role each plays
during a succession.
Book Chapters
•
Campbell: mainly Chp. 54.3, but also Chp. 53.4 and
Chp. 54.2
I. SUCCESSION
Succession is a progressive, often predictable
change in species composition (and abundance) in
a community over time. With time, certain species
may become rare or even disappear, while others
increase in abundance. Primary succession
begins when a previously uninhabited area
becomes available for colonization. For example,
primary succession occurs when retreating
glaciers expose soil that has been sterile for
thousands of years. On the island of Hawai’i,
primary succession occurs on fresh lava from
volcanic flows. Secondary succession follows the
disturbance of a previously inhabited area. A
forest fire or hurricane that damages a forest leads
to secondary succession as a new set of plants
initially begin to replace the fallen trees. Although
these examples involve plants, the concept of
succession also applies to animal communities.
For example, temperate rocky intertidal zones are
first colonized by fast growing algae, then
barnacles, then slower growing algae, and then
mussels.
After the onset of succession, a community may
go through a number of seral stages where
different flora and fauna dominate. A sere is the
sequence of communities encountered in a
particular location over time. Eventually, a stage
may be reached where community structure will
remain relatively constant in the absence of a
major disturbance. This “equilibrium” community
state is called the climax community. The species
composition of a climax community is dependent
on the local environmental conditions (e.g.,
temperature, rainfall, and soil type). Other factors
affecting the pattern of succession and
composition of the climax community include the
rate and sequence of colonization of different
species.
Time
Figure 1. Simplified example of a successional sere
involving three plant communities.
The concept of a monotypic climax, in which
there is a single climax community for a given
environment, has given way to the more dynamic
concept of the pattern-climax. The patternclimax concept recognizes that most forests are
comprised of a patchwork of climax communities
and different seral stages (due to patches of
disturbance).
Some communities never reach a “climax” state
and are maintained in a state of subclimax. This
occurs in communities that are regularly
disturbed. This disturbance can come in a variety
of forms, such as herbivory, wind, fire, flood,
drought, ice scour, or wave action.
10-1
Laboratory 10
Marine Benthic Succession
Mechanisms of Succession
Three primary mechanisms have been proposed to
act during succession: facilitation, inhibition, and
tolerance (Connell & Slayter, 1977). In
facilitation, early successional species modify the
environment, making the environment more
suitable for germination and growth of later
successional species. For example, a nitrogenfixing plant may add nitrogen to nutrient-poor
soil, allowing nitrogen-loving plants to colonize.
Facilitation is extremely important during the
early stages of primary succession, but it can also
be important in secondary succession.
The inhibition model states that once colonizing
species become established, they resist invasion
simply by taking up space (inhibiting later
successional species). When these established
individuals die or are damaged by disturbance,
new, later successional species can replace the
earlier species, assuming that seeds or propagules
are present. This process of replacement following
death of the established species eventually leads
to domination by long-lived species, since longlived species can hold on to a space for a very
long time. Inhibition is one factor that maintains a
climax community. Species that dominate climax
communities tend to be very long lived, providing
few opportunities for species replacement.
The tolerance model proposes that free resources
become scarce in later successional stages, and
those species that can tolerate the lowest resource
conditions (e.g. low light, low nutrients) will
survive better and eventually out-compete those
species requiring more resources. The tolerance
model predicts that over time, the fast-growing,
high resource-demanding species will reduce
resource levels, leading to their replacement with
species that are more tolerant of low resource
conditions. Tolerance, inhibition, and facilitation
are not mutually exclusive and may act together
during a successional series.
r and K Selected Species
The first species to colonize a newly
area are often termed pioneer species,
species are usually characterized
reproductive output, high growth rate,
disturbed
and these
by high
short life
span, and low competitive ability over the long
term. Species possessing this particular set of
traits are said to be “r selected”. At the other end
of the spectrum, later successional species are
often characterized by lower reproductive output,
higher maternal investment per offspring, high
competitive ability, long life span, and slow
growth rate. Species possessing this set of traits
are said to be “K selected”. The “r” and the “K”
refer to the parameters of the logistic growth
equation (also see Figure 2). Recall the “K” is the
carrying capacity. A “K selected” species
typically does well in a crowded environment
(near carrying capacity). In contrast, “r” is the
intrinsic rate of increase (growth rate when
population density is low). “r-selected” species
are often found colonizing open areas associated
with frequent disturbance. Of course, most species
do not fit perfectly into either of these groups.
These categories represent the extreme ends of a
continuum, and many species exhibit some r and
some K selected characteristics.
Figure 2. Relationship between poplations size and rate of
population increase for r- and K-strategists.
Diversity and Succession
Your first impression might be that diversity
should be lowest at the onset of a successional
series (sere) and highest at the climax. In reality,
maximal diversity usually occurs before the
climax community. In a community that
experiences very frequent disturbance, only a few,
rapid growing species can survive and reproduce.
Likewise, in a climax community experiencing
little or no disturbance, climax species outcompete most other organisms, leading to lower
species diversity. Intermediate disturbance will
tend to maintain a patchwork of low, mid, and late
10-2
Laboratory 10
seral stages (including some species typical of
early succession and others typical of climax
communities),
thus
maintaining
maximal
diversity.
The intermediate disturbance hypothesis
(Connell, 1978) proposes that diversity is highest
at intermediate levels of community disturbance
(Figure 3). It should be noted that the intermediate
disturbance hypothesis is based on the assumption
that competition is an important regulator of
community diversity. Therefore, even if there is
no or minimal disturbance occurring in a
community, highest species diversity will be
present at intermediate stages of a succession (i.e.
before the climax) because there is a mix of
primary and secondary succession species present
competing with each other.
Marine Benthic Succession
the intertidal community, mussels dominated the
community, leading to very low species diversity.
In the natural community, the seastar acted as an
agent of disturbance by eating the mussels and
preventing their competitive dominance. Although
not reported in Paine’s study, if sea stars become
too abundant they will start eating the mussels’
competitors (along with everything else) and
diversity may decrease. These findings again
emphasize the importance of intermediate levels
of disturbance in maximizing diversity.
Rocky shores provide another good example
supporting
the
intermediate
disturbance
hypothesis (Sousa, 1979). Small rocks, which are
frequently overturned by pounding waves, are
colonized by few or no species because they tend
to be crushed as the rocks roll. In contrast, very
large rocks are rarely moved by wave action, and
they are usually covered by one or only a few
encrusting (permanently attached) species.
Medium sized rocks, which are moved by waves
at an intermediate frequency, harbor the most
species.
Experimental Studies of
Succession
Figure 3. The “intermediate disturbance”
hypothesis according to Connell 1978.
Predators can play an important role in reducing
competition among prey, thereby increasing
diversity. The results of Paine’s (1966) study of
an intertidal community in Washington led to the
keystone predator hypothesis, a hypothesis that
predation by certain “keystone” species is
important in maintaining community diversity.
This experiment also supported the intermediate
disturbance hypothesis, since you can consider
predation to be a disturbance. When the top
predator, a seastar Pisaster sp., was removed from
Studying succession of a forest is often very
difficult because of the length of time involved.
Many successional experiments, therefore, are
based on smaller scale systems. Studying the
succession of plankton communities is relatively
easy because the experiments can be conducted in
a controlled environment and results can be
obtained quickly. Trees may live for 1000 years,
but phytoplankton and zooplankton have much
shorter life spans. Phytoplankton experiments can
be easily replicated and don’t take up much space.
Experimental studies of aquatic successions have
been conducted in containers ranging in size from
a beaker (microcosm) to an above ground
swimming pool (mesocosm) (Duffy & Hay,
2000).
Studies on succession in marine benthic
communities have also been popular. A benthic
community is an aquatic community that is
associated with the bottom, whether it is sand,
mud, or rock. Coral reefs are famous benthic
10-3
Laboratory 10
communities and were used by Connell and
Slatyer (1977) in developing their ideas about the
mechanisms of succession. Marine benthic
communities make good study subjects because
the organisms are fairly small and succession
occurs rapidly compared to terrestrial forests.
Benthic communities have also received a lot of
attention because they grow on ship hulls, costing
millions of dollars in extra fuel and carrying
invasive species from one location to another as
ships move to new regions.
Benthic succession is often studied by putting a
bare substrate (settling plates) into the water and
photographing or collecting them periodically.
Successional patterns are studied by analyzing the
composition of replicated settling plates over
time. If there is minimal disturbance, you can
typically expect to see a climax community on the
settling plates within a year or two.
II. METHODS
Today we will be studying primary succession of
a Hawaiian marine benthic community. To initiate
a successional series, PVC settlement plates were
deployed at Coconut Island in Kaneohe Bay. The
8cm x 8cm (64cm2/side) plates were sanded to
provide a favorable settling surface and hung
beneath a floating dock about a foot below the
water’s surface. Ten plates were deployed
monthly for the last year, and all plates were
collected last weekend.
During this laboratory, you will work in small
groups to analyze the community that has
developed on the settling plates. Your TA will
assign you a specific time period in the
successional sere. Towards the end of the period,
data from the entire class will be compiled to
provide a picture of how the community on the
settling plates changed over time.
Marine Benthic Succession
A. Taxa Identification and
Percent Cover
1.
Your first task is to describe the
communities on all of the settlement plates
(page 10-7, Datasheet 1). Settlements are
placed in big Petri dishes under a dissecting
scope. Keep the plates submerged in
seawater at all times. Identify all of the
taxa on the settlement plates. Identification
books and close-up photos of invertebrates
and algae will be available. Your TA will
let you know when you can switch to the
next dissecting scope with a settlement
plate of a different age.
2.
Once everybody described all the
settlement plates, your TA will assign you a
specific time period’s settlement plate to
examine. You will also be given a 6 by 6
quadrat grid.
3.
You will randomly sample ten quadrats on
each side of the plate. Handle your
settlement plate very carefully because
other students will be sharing your plate.
4.
On page 10-8 is a worksheet to help you
keep track of your data (Datasheet 2).
There is also a file with the same worksheet
on laulima. This file also has a random
number generator for choosing your
quadrat coordinates.
5.
For each quadrat, identify the taxa present
and estimate the percent cover of each
taxon. Enter these data in the excel
worksheet. If your random number
generator gives you repeat quadrat
coordinates, select a different one.
Note: zooming in too close will only cause
more confusion…zoom back out to estimate
community structure and cover! Use your
best judgment with the taxon IDs. Once you
have identified the taxa in your quadrat,
you should spend no more than about 10-20
seconds to estimate the cover of each taxon.
10-4
Laboratory 10
6.
7.
Marine Benthic Succession
Competition for space may be a major
factor influencing succession in benthic
communities. Within each quadrat where
you had estimated % cover, record whether
you see any evidence of taxa overgrowing
each other (enter 1 for “Yes” or 0 for “No”
on your excel worksheet).
Using the life history attributes provided
(Table I), take note of the taxa that can be
classified roughly as r selected or K
selected based on their known life histories.
Remember, not all species can be neatly
classified as r or K selected.
Table I. Life History Attributes
Organisms
Chlorophyta
Rhodophyta
Hydroides
Bivalvia
Growth
Rate
↑
↓
↑
↓
Age to
Maturity
Body Size
↓
↑
↓
↑
B. Sharing Data
8.
Once you have completed all the steps,
enter your data into your section’s google
doc. Your TA will upload the compiled
data as an excel file on Laulima.
9.
You will use the complete data set from
your section to complete your assignments.
From your section’s data, the following
will be calculated and posted on the web:
• Average total community cover per plate
• Relative % cover for each taxon
encountered
• Frequency (average number of quadrats
per plate) of observed evidence of
overgrowth (will be somewhere between
0 and 25).
• Species (taxon) richness per plate
• Simpson’s index of diversity for each
plate (see lab 9).
C. Clean up
When you are done, return your settlement plate
to the tank or where your TA instructs you.
Return the seawater from your Petri dish to the
tank and rinse the Petri dish and your quadrat
grid as well as any other equipment you used
(e.g. forceps) in fresh water. Make sure there is
no saltwater on the scope, wipe off if needed.
III. ASSIGNMENTS
Do not leave lab early. Complete as many
graphs as possible in class, and save the written
questions for later. Be sure to label your axes
and include a brief description of each graph in
a caption.
Graphs can be shared among classmates, but
each person must individually answer the
questions below.
1. Plot a graph of total % cover (all taxa
combined) vs. duration of submersion. (1 pt.)
a. How does total % cover relate to the
duration of time that the settling plates
were in the water? (1 pt.)
Is this what you expected? Explain.
(2 pts.)
b. Does total % cover seem to reach
equilibrium? (1 pt.)
If yes, is this (if not, would it be) good
evidence that a climax community has
been reached? (5 sentences max) (3 pts.)
2. Plot two graphs:
• Species richness vs. duration of
submersion. (1pt.)
• Species diversity vs. duration of
submersion. (1 pt.)
Describe the patterns in the graphs in a
cohesive
paragraph
including
the
following questions and explain your
reasoning:
- How does species richness and diversity
relate to the duration of time the settlement
plates were in the water?
…continued on next page
10-5
Laboratory 10
- Are the relationships similar? Is this what
you expected?
(4 pts.)
3. Discuss the following in a cohesive paragraph:
- Which taxon seems to be dominant in A)
the first third of the time series, B) the
second third of the time series, and C) the
last third of the time series?
- Is it the same taxon?
- Is this what you expected?
(4 pts.)
4.
Plot the mean number of quadrats showing
evidence of overgrowth versus duration of
settlement plate submersion. (1 pt.)
Describe the pattern and include if
competition appears to be frequent in this
community? (5 sentences max) (3 pts.)
5. Choose one r- selected and one K- selected
taxon and describe (in a cohesive
paragraph) how their cover changes with
increasing duration of submersion.
Discuss if these compare to patterns
theoretically predicted for r and K selected
species and if the patterns for the r and K
species seem to relate to the patterns
observed in the overgrowth graph
(question #4). (4 pts.)
6. Write a draft for the Discussion section of
your final paper. Your discussion should start
with some introductory sentences relating
back to your introduction and setting a
framework for your hypotheses you tested in
the results section. This is the section where
you
interpret
your
results
in
a
biological/ecological context. Make sense of
the data and the outcome of your tests from
the results section in the context of community
ecology on Wa’ahila ridge. Refer to other
referenced studies if possible to put your study
in a bigger context. Once you explain your
results in a biological context you should
address any methodological issues, which
could have affected your data, or things that
you would improve in future studies. End with
some concluding sentences that put your main
Marine Benthic Succession
results into a bigger context and leaves the
reader a simple take home message. (6 pts.)
NOTE: Even though this is a draft it will be graded
as part of your homework assignment. The better
your draft, the more feedback your TA is able to
give you and the better your final paper will be
(worth 20% of your final Lab grade)
7. Make a graphical representation of your
overall Ridge project, so that anybody looking
at it can get the whole story in a few minutes.
This should help you putting all the pieces
together and tell a story around your two
hypotheses. You can do this on paper (and
include a picture in your homework) or in
digital format. There are no strict guidelines,
other than it has to fit on one letter sized sheet,
needs to be “legible”, include all parts of your
ridge project, and not be continuous text. Your
TA will show you some examples. (3 pts.)
IV. REFERENCES
Connell, J.H. 1978. Diversity in tropical rain
forests and coral reefs. Science 199: 13021310.
Connell, J.H. & R.O. Slatyer. 1977. Mechanisms
of succession in natural communities and
their role in community stability and
organization. American Naturalist 111:
1119-1144.
Duffy, J.E. & M.E. Hay. 2000. Strong impacts of
grazing amphipods on the organization of
a benthic community.
Ecological
Monographs 70: 237-63.
Paine, R.T. 1966. Food web complexity and
species diversity. American Naturalist
100: 65-75.
Sousa, W.P. 1979. Disturbance in marine
intertidal
boulder
fields:
The
nonequillibrium maintenance of species
diversity. Ecology 60: 1225-1239.
10-6
Laboratory 10
Marine Benthic Succession
StudentName:
Date:
Section/TAName:
No.months 2dominantspecies
submerged
1
otherspecies
Observations
9
10
11
12
13
2
3
4
5
6
7
8
10-7
Laboratory 10
Marine Benthic Succession
Name:_____________________________________
Month#____________________________
First Side
Taxon
Cyanophyta (blue-greens)
Rhodophyta (Peyssonnellia)
Rhodophyta (crustose coralline)
Rhodophyta (Hypoglossum)
Rhodophyta (unknown)
Chlorophyta (Ulva)
Chlorophyta (Cladophora)
Chlorophyta (unknown)
Sponge
Anemone/polyp
Polychaeta (Hydroides)
Polychaeta (Spirorbis)
Bryozoan (encrusting)
Bryozoan (branching)
Bivalvia (Dendostrea)
Cirripedia/barnacles
Tunicate
Quadrat # ♦
Coordinates (x,y) ♦
Phylum
Cyanophyta
Rhodophyta
Rhodophyta
Rhodophyta
Rhodophyta
Chlorophyta
Chlorophyta
Chlorophyta
Porifera
Cnidaria
Annelida
Annelida
Bryozoa
Bryozoa
Mollusca
Arthropoda
Chordata
1
2
3
4
5
6
7
8
9
10
enter percent cover for each of your taxa
average
Does quadrat show overgrowth? (1=yes, 0=no)
0 =Total
Second Side
Taxon
Cyanophyta (blue-greens)
Rhodophyta (Peyssonnellia)
Rhodophyta (crustose coralline)
Rhodophyta (Hypoglossum)
Rhodophyta (unknown)
Chlorophyta (Ulva)
Chlorophyta (Cladophora)
Chlorophyta (unknown)
Sponge
Anemone/polyp
Polychaeta (Hydroides)
Polychaeta (Spirorbis)
Bryozoan (encrusting)
Bryozoan (branching)
Bivalvia (Dendostrea)
Cirripedia/barnacles
Tunicate
Quadrat # ♦
Coordinates (x,y) ♦
Phylum
Cyanophyta
Rhodophyta
Rhodophyta
Rhodophyta
Rhodophyta
Chlorophyta
Chlorophyta
Chlorophyta
Porifera
Cnidaria
Annelida
Annelida
Bryozoa
Bryozoa
Mollusca
Arthropoda
Chordata
1
2
3
4
5
6
7
enter percent cover for each of your taxa
8
9
10
average
Does quadrat show overgrowth? (1=yes, 0=no)
0 =Total
10-8