Download Benthic habitat association of sessile invertebrate and algal species

Benthic habitat association of sessile invertebrate and algal species at
Hopkins Marine Station [[4/4 clear and specific title that gets the main points across]]
Anneliese Kupfrian
[[12/14 Overall Clarity – overall this is quite a nice and easy read - line-by-line edits
provided for the intro only, try to apply these concepts to the rest of the paper and consider
in your future work.
 Carefully choose your connecting words (e.g. whereas, while, however, in contrast,
thus) so that they are appropriate to the sentence, because each of these words
means something slightly different.
 Make sure you understand the difference between “varying,” which means changing,
and “variety,” which means a number of different types of things that probably don’t
change.
Introduction [[13/20 This could be improved by: clear articulation of the specific
hypotheses as well as the questions, explanation of the novelty of this study, identification
of WHERE you conducted this study (i.e. Hopkins, Monterey), and a slightly more direct
explanation of why the kelp forest is an appropriate study system for the study questions.]]
Kelp forest ecosystems can support an extremely diverse community of marine
organisms comprised of a broad range of phyla. Although light and nutrient availability is
crucial for photosynthesizing organisms, it is clear that all benthic species are fighting for
space along the sea floor. So how then can this long-term co-occurrence of so many species
persist, considering such severe competition for the same resources? [[these three
introductory sentences are a nice conversational way to get at why we care to do these
kind of studies!]] Basic community ecology principles tell us that two species competing
for the same resource cannot exist together in time and space. Instead, the species that is
better at attaining the limiting resource will eventually outcompete and eliminate the
inferior species (Gause 1934). This common ecological phenomenon is known as the
competitive exclusion principle; however this is certainly not what we see while kicking
through a lush kelp forest, booming with a wide variety of life forms. So the mystery
remains: how are so many species able to coexist with apparent tolerance? Ecologists have
shown that differences in how species interact with their environment counteract the
inevitable loss of biodiversity that results from competitive exclusion (Chesson 2000).
These variations in environmental utilization techniques are called niche differences. The
niche-partitioning hypothesis states that interspecific competition drives each species into
progressively condensed niches until each of the competing species becomes specialized in
its individual niche, and is no longer at risk of competitive exclusion. Therefore as long as
each species maintains a niche that does not significantly overlap with another species,
then high biodiversity is preserved (Hutchinson 1961). [[Nice use of the scientific literature
and a conversational tone to set up the context and importance of this study]]
The purpose of our investigative study is to specifically determine how various
marine organisms utilize the complex, three-dimensional benthic zone characteristic of a
kelp forest ecosystem. Which niche axes are exploited by what types of organisms to allow
for species coexistence? Do certain species preferentially inhabit particular substrates, or
is vertical relief a better predictor of where a species will occur? [[remember, there’s more
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than just what the species prefer at work here. A species may be excluded from its most
preferred habitat by competition, which this study cannot assess. All this study looks at is
the ASSOCIATION between organisms and habitat characteristics, not why]] Or is it
perhaps a combination of these two variables that produce the ideal environment for a
particular organism? We are interested in finding patterns and varying strengths of
association between certain species and a particular habitat. With this practical
information, we can better implement marine life protection policies aimed at preserving
these highly valuable kelp forest ecosystems. This study will give us insight as to where we
need to focus our conservation efforts in order to best protect endangered species as well
as facilitate the replenishment of depleted fish stocks. [[you laid out the questions, but not
the hypotheses]]
Methods [[6/18 - The methods section should begin by briefly describing the general
approach (observational, UPC method to characterize primary substrate holders, substrate
type, and relief). Then talk about the system and expand on why it’s a good site for this
study (something that should be introduced in the intro). Then you need to identify the
specific hypotheses and explain how your data collection methods will allow you to test
each hypothesis. After you’ve explained WHY you did things the way you did, you want to
provide a detailed description of methods, including data analysis.
To gain a better understanding of general habitat association among species, 22
scuba divers conducted an observational field study at Hopkins Marine Station in Pacific
Grove, California on April 10th, 2012. [[continue this brief description of the approach
before you launch into the site description]] Located along the Monterey Peninsula,
Stanford University’s marine laboratory (36° 37’ 17.02” N, 121° 54’ 07.28” W) is protected
from major south swells, but often subject to waves prevailing from the north and west. As
cold, deep water upwells, it is channeled through the Monterey Submarine Canyon
supplying extremely nutrient-rich waters to coastal ecosystems along the Monterey Bay.
With a considerable supply of nutrients delivered to this protected marine reserve,
Hopkins is an ideal site to observe high species diversity devoid of direct anthropogenic
influences that could easily disrupt the natural ecosystem dynamics of the area [[there’s
plenty of human influence at Hopkins, you think all you monkeys kicking around down
there isn’t an influence?]]. A permanent 270-meter long cable runs right offshore, through
a lush kelp forest characterized by large rocky outcroppings paired with smaller sand
patches and scattered boulders. This ideal substratum yields a dense multi-layer kelp
canopy of mainly Macrocystis pyrifera, Cystoseira osmundacea, and Dictyoneurum
californicum in addition to many red and coralline algae species. The many cracks and
crevices, as well as open rock face and sand patches, provide an ideal habitat for a wide
variety of benthic invertebrate species. [[AND it also provides us with enough variety of
substrate type and relief to conduct a robust analysis of species-habitat relationships]]
[[Before you get into all the details, introduce each hypothesis and explain how yor
sampling methods will enable you to test it]] After a short surface swim from shore, 11
pairs of divers reached a buoy, which designated the 100-meter mark along the main cable.
From here, we dropped down and located our assigned meter marks where each buddy
pair used a uniform point contact sampling method to record substrate, relief, possible
super-layer, and species association along two 30-meter transects (one offshore at 90 and
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the other inshore at 270). The entire transect was divided into 6 sections of 5 meters
each, and each section was further divided with 10 sampling points, uniformly spaced 0.5
meters apart. The precise spot to be sampled corresponded to the point located directly
under each half-meter mark. Each diver was assigned to either the first or last half of each
set of 10 sampling points, evenly staggering the sampling between the buddy pair –
reducing sampling bias across the transect by balancing individual data collection habits.
At every sampling point (30 per diver, per transect) each diver was responsible for
recording four pieces of information: substrate, relief, possible super-layer, and specific
substrate-holding species (or lack there of). Designated substrate types included bedrock
(rock substrate > 1 m), boulder (rocks with diameter between 10 cm – 1 m), cobble
(diameter < 10 cm), or sand. Vertical relief was measured within a visual box of 1 meter
wide by a half meter long, centered on the sampling point with four designated recording
options: flat (0-10 cm), slight (10 cm – 1 m), moderate (1 – 2 m), and high (>2 m).
Occasionally it was possible to encounter a super-layer of either drift algae or juvenile
Laminariales. In the case of drift algae, it was noted then removed to record the underlying
species or substrate. Finally, the primary substrate holder was recorded as either a sessile
species (invertebrate or algae) or an inanimate classification including bare rock, bare
sand, shell debris, sediment or mud, or a dead kelp holdfast. Designated sessile species
included the most commonly encountered red, brown, and coralline algae, tubeworms,
snails, cnidarians, tunicates, and others (scallop, cucumber, barnacle, bryozoan, sponge,
and mussel).
By using UPC sampling methods to record substrate and measure relief we are able
to better determine local habitat structure. Also by making note of present species and
their frequencies along a transect, we can further analyze the relative densities of these
organisms and their associated habitats. The data collected by each of the 22 divers was
compiled and analyzed as a whole.
[[you need to describe the data analysis methods in here too, as well as how you
interpret them to test your hypotheses]]
Results
[[12/16 - would be improved by inclusion of: 1) more clear organization of the results
relative to each hypothesis including whether associations were positive or negative and
whether or not the results supported your hypotheses, and 2) better figure formatting (try
using a 1x2 table for your figures with the actual figure/table in one cell and the caption in
the other an combine all the figures into a single section, either within the results section or
at the end of the paper to avoid formatting problems and interrupted flow)]]
Substrate and Relief: Percent Cover and Relative Associations
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The most commonly encountered substrate at our study site is sand, covering 40%
of the seafloor, while bedrock is also fairly common at 34% coverage. Boulders make up
about 20% of the substratum, and coble covers a mere 6% (Figure 1A). Overall, relief is
primarily less than a meter: almost entirely either flat or with a slight vertical lift at 40%
and 41% coverage respectively; both being over twice as common as moderate relief at
14% and high relief at 5% coverage (Figure 1B).
Figure 1
A
B
A) Percent coverage of various substrate
types. (SA=sand, CO=cobble, BO=boulder,
BR=bedrock)
B) Percent coverage of various relief zones.
(F=flat, S=slight, M=moderate, H=high)
Figure 2
Sand is very commonly found
in flat relief regions, with a 66% cover
of areas with zero vertical lift, but
bedrock, boulders, and cobble are
relatively rare in these flat regions. As
for slight, moderate, and high relief
zones, primary substrate is
predominately bedrock for all zones,
followed by boulder and sand in
relatively similar frequencies, trailed
by cobble in rare occurrence (Figure
2). [[good general discussion of
results]]
Percent
cover
(relative
association)
of each
substrate
type (sand,
cobble,
boulder, and
bedrock)
within each
relief zone
(flat, slight,
moderate,
high).
Species & Relief Associations
We expect to see a uniform distribution of species across all forms of substrate and
relief. Strong habitat associations signify high positive deviations from this expected
species distribution, specifically any result greater than 2 standard measures of deviation.
A standard deviation value between 1 and 2 indicates moderate habitat association.
Diopatra ornata are very commonly found in areas of flat relief (Figure 3A) and lacy red
algae shows moderate association with this zone. Areas of slight to moderate relief
(vertical lift between 10 cm – 2 m) are primarily dominated by algae species. Both
branching red algae and Dictyoneurum califonricum show strong associations for slight
relief zones of 10 cm – 1 m (Figure 3B & C), while crustose coralline algae, encrusting red
algae, and Desmarestia show moderate association. Moderate associations for slight relief
are also seen in sponges, Serpulorbis squamigerus, solitary and colonial tunicates, as well as
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Macrocystis holdfasts. Leafy red algae, as well as crustose and articulated coralline algae
show strong associations for moderate relief zones of 1 – 2 m (Figure 3D & E), while turf
and encrusting red algae are moderately associated. Sessile invertebrates often colonize
areas of high relief (greater than 2 m), most notably cup corals and Phragmatopoma
californica with the strongest association values (Figure 3F & G). Colonial tunicates and
anemones also show moderate association for areas of high relief.
[[I like the way you organized and captioned your figures, but you should probably put
them all together in one place (either in the results or at the end to avoid formatting
problems and messing up the flow of the text]]
A
D
C
B
E
F
G
Species & Substrate Associations
Species that are most strongly associated with a sandy substrate include Diopatra
ornata and lacy red algae (Figure 4A & B), while solitary tubeworms show a moderate
association. Shell debris has a strong association for both sand and cobble (rocks with
diameter < 10 cm) substrate, and sponges have a moderate association with cobble.
Boulders (rocks with diameter between 10 cm and 1 m) are predominantly covered in
various algae species. Crustose and articulated coralline algae (Figure 4C & D), as well as
branching, bushy, and leafy red algae species all have strong association values
corresponding to boulder substrate (Figure 4E – G), while hydroids and turf algae show
moderate association. A wide variety of species show strong association for a bedrock
substrate (rock greater than a meter in diameter). These species include bryozoan,
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branching and encrusting red algae, crustose coralline algae, barnacles, colonial tunicates,
A
B
C
D
E
J
F
G
H
I
K
L
M
N
Corynactis californica, cup corals, and Macrocystis holdfasts (Figure 4H – N). Species
showing moderate association for bedrock include Petaloconchus montereyensis, sponges,
and Phragmatopoma califonica.
Significant Negative Associations
Analysis of our results also produced negative species-habitat associations. As
Figure 5: Strong Species-Habitat
Disassociations
A
B
A) Strong negative correlation of Diopatra
ornata association with bedrock substrate
B) Strong negative correlation of crustose
coralline algae association with sandy substrate
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mentioned before, we expected [[confusing because this was not your hypothesis, but the
null]] to see a uniform distribution of species across all forms of substrate and relief.
Deviations from this expected distribution with values of less than -2 standard measures
implies that we saw that particular species less frequently than originally expected,
indicating strong habitat disassociation. This was especially prevalent with Diopatra
ornata, having a noteworthy deviation of -4 in regards to association with bedrock
substrate (Figure 5A). In a similar fashion, crustose coralline algae was strongly
disassociated with sandy substrate, with a considerable deviation of -7 (Figure 1B).
Discussion
[[16/22 - Overall you did a nice job summarizing and interpreting the key results, including
suggesting mechanisms for why the species-habitat relationships you observed exist and
how they might be maintained. You also did a nice job of tying this study back to some
relevant scientific literature, but did not directly compare your results tothose from
previous similar studies, which would be preferable. To improve this discussion: 1) more
directly address whether or not your results results supported your hypotheses, including
problems with your study design that may have influenced your results, and 2) frame your
overall conclusions in terms of their implications for our ecological understanding and for
informing management.]]
It is clear from our observations that certain species show strong associations with
specific habitats, influenced by the vertical relief and substrate type. The precise reason for
habitat preference may fluctuate between species due to the available resources of that
environment. For example, at our study site, areas of flat relief almost always consisted of
sand substrate and Diopatra ornata was frequently found in this habitat. This common
association should come as no surprise as D. ornata live their lives buried in the sand. The
parchment tubes of these worms are often covered with shell and algae debris that
naturally accumulate in these areas of flat relief (Gotshall). Therefore it should also come
as no surprise that D. ornata has a strong negative habitat association with boulder
substrate. Solid bedrock is not an ideal habitat for D. ornata as it offers no soft sediment in
which to take refuge, leaving the worm exposed to hungry predators.
Along those same lines, it is obvious that crustose coralline algae has a strong
disassociation with sandy substrate. Crustose coralline algae requires a hard surface on
which to adhere, and therefore prefers a solid boulder or bedrock substrate instead of
loose sand. In fact, our results indicate that boulders in a slight to moderate relief zone are
almost entirely dominated by a variety of algal species. This distribution may be a resulting
effect of infrequent disturbance. Consistent with the results of Wayne P. Sousa’s rolling
boulder experiment (Sousa 1979), designed to test Connell’s intermediate disturbance
hypothesis (reference), we found low overall phyla diversity on boulders, but a variety of
red algae species were relatively abundant. Sousa’s experiment demonstrated that during
large storms, boulders are rolled over by heavy wave action and the attached species
become damaged or dislodged. Smaller boulders are overturned more easily while larger
boulders tend to stay in place. Frequently rolled boulders are colonized by fast recruiting
r-selected species such as sea lettuce and barnacles, while larger, undisturbed boulders are
dominated by persistent K-selected species that outcompete the early recruits over time
with no disturbance (Sousa 1979). Our findings imply infrequent disturbance of our study
site as the results actually show a negative correlation of opportunistic settling barnacles
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on boulder substrate. This suggests that our study site is relatively well protected from
heavy wave action, allowing these red algae species enough time to monopolize boulders
found in slight to moderate relief. A quick peek at a coastal map of the Monterey Peninsula
supports this presumption, showing Hopkins Marine Station tucked safely away in the
southern pocket of the Monterey Bay, protected from most all wave action except that from
the northwest [[east?]].
Many algae species may prefer habitats of slight to moderate relief in response to
light availability. In this moderately level environment, a photosynthetic organism will
have reasonable access to sunlight throughout most of the day; however this same
organism might not survive in areas of high relief. For example, an alga growing on the
south side of a large rock pinnacle will be shaded through a good portion of the day. Being
deprived of much needed light, this species may easily be outcompeted and die off,
providing available habitat space for other organisms. Most sessile invertebrates on the
other hand, do not require light to sustain life and will gladly inhabit the open space. In
fact, high relief zones appear to be the ideal environment for these filter-feeding organisms.
Large changes in relief can easily disrupt natural water movement, channeling the water
elsewhere (Zawada, et al., 2010). If a large rock pinnacle blocks the flow of a current, that
water may be forced straight up the face of the rock. This is especially advantageous for
the invertebrate species attached to that rock face, as they rely on filter feeding to survive.
With more water movement across their habitat, these species will enjoy high survival
rates in response to increased access to suspended food particles. This would explain why
cup corals, Phragmatopoma califonica, colonial tunicates, and anemones are so strongly
associated with areas of high relief.
In the benthic community of a kelp forest ecosystem, intense competition for limited
resources can literally drive a species right off a rock face. Yet despite the shortage of open
settlement space, vast amounts of species have managed to find a means to coexist
together. By continually dividing the available resources and further allocating the
subsequent shares across a broad range of phyla, a particular environment can in fact
support an enormous number of species. This has certainly proven to be the case at
Hopkins Marine Station. It would be interesting however, to continue this observational
study over the course of a few years to assess the temporal differences in species-habitat
associations with respect to seasonality, or even larger climactic events such as El Nino.
References [[6/6 – at LEAST 6 references were required for this assignment, but more
would be better]]
Chesson, P. Mechanisms of maintenance of species diversity. Annual Review of Ecology
and Systematics. 31, 343–366 (2000).
Gause, G. F. The struggle for existence. New York, NY: Hafner Publishing Company, 1934.
Gotshall, Daniel. Guide to marine invertebrates: Alaska to Baja California. 2nd ed. Monterey,
CA: Sea Challengers, 2005. Print.
Hutchinson, G. E. The paradox of the plankton. The American Naturalist. 95, 137–145
(1961).
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Sousa, Wayne P. “Disturbance in marine intertidal boulder fields: the nonequilibrium
maintenance of species diversity.” Ecology 60 (1979): Ecological Society of America.
Zawada, David G., Gregory A. Piniak, and Clifford J. Hearn. "Topographic complexity and
roughness of a tropical benthic seascape." Geophysical Research Letters 37 (2010):
GEOPHYSICAL RESEARCH LETTERS.
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