Though we expect that the outfall itself will take many years to recover completely, we also expect that recovery around the edges of the outfall site will begin immediately.
| A plot of community similarity showing how natural communities (in green) did not change much over 10 years, while the community at the outfall (in brown) degraded significantly. |
Question
3: Which
has a stronger impact on the community, burial or added organic material?
The old outfall both buried and organically enriched the seafloor community. We set up an experiment last year to separate the impacts of these two variables, and will be collecting it this year.
| Burial at the outfall mimics the natural process of burial that occurs when ice plows up and moves sediment. The sediment you see here, at Bratina Island, lies over a layer of ice, and would fall to the seafloor if the ice melted. |
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Question
4: Does
it matter how big an area is disturbed?
There are natural deposits of organic material near McMurdo Station, wherever mammals and bird congregate. Another of our experiments started last year test the differences in community response to small, 'natural' disturbances and the larger 'anthropogenic' disturbance of the outfall.
|
Weddell seals congregate at tidal cracks and leave organic enrichments (a scientific term for poop) on the seafloor below. |
In addition to the main
research questions, we have several additional questions:
Question 5: What
decadal changes have occurred in marine communities near McMurdo Station?
Hard substrates in
near-shore Antarctic environments are dominated by sponges.
These organisms can cover over half of the available space and grow to
sizes of up to 2 meters tall and 1 meter wide.
Studies on the growth and survival of these sponges have been conducted
since the 1960's and suggest that some of the largest species grow very slowly
- almost imperceptibly - and are therefore probably extremely long-lived.
On the other hand, some species which are at times very rare are capable
of reproducing and growing rapidly and dominating the available space.
During our field research we will have the opportunity to revisit
study sites where data on abundance and the size of individual sponges has been
recorded since 1967. This will
allow us to add to a 35 year long record and generate insights into the
population cycles and longevity of species in this unique community.
Additional questions we will be pursuing include the following:
If as previous studies suggest space is not limiting for settlement of
new sponges, why are fast growing sponges in the genus Mycale
often seen overgrowing other sponges? Are
they using other sponges as settlement sites/ substrate? More
importantly, are they able to escape from predation by the sponge-eating
sea-stars Perknaster and Acodontaster
by settling on or near chemically defended sponge species that these predators
avoid?
Question 6:
What role does bacterioplankton play in the Benthic Food Web: a stable isotope
approach.
In many of the coastal
oceans around the world the water column is productive throughout the year with
variations with season but food is always present. The Antarctic,
especially at McMurdo Station, has a very short time period every year where
food is abundant in the water column. This is in the spring when the ice
breaks up and lets light get to the depths. The rest of the year the water
column is devoid of food in the larger size classes. Instead the water
column harbors bacterioplankton and ciliates . These animals are
between 0.2 and 2 and 2 to 10 microns (*10-6 meters) in size, respectively.
The animals that feed either have the option of waiting for the seasonal
abundant food and starving for 10 months of the year or feeding on this
"fine" fraction of the seston. This is really only key for suspension
feeding animals, of which the Antarctic ecosystem is full from sponges to
anemones to tunicates (aka sea squirts.) So the question is
are the animals capable of feeding on the bacteria size particles that are
ubiquitous throughout the year.
| Since the outfall at McMurdo sound
spits out bacteria that came from humans it will have the isotopic
signature of humans rather than that of the surrounding ecosystem.
The particulate matter drops out of the water column near the outfall and
the bacteria then spread downstream. The animals that eat this
bacteria then retain the isotopic signature of what they are eating, in
this case human waste along with the natural bacterioplankton. By taking
the tissue from these suspension feeders and measuring their isotopic
composition (Carbon and Nitrogen) one can tell if they were in fact
consuming bacteria sized parcticles. Isotopes are measured with a
Mass Spectrometer back in the lab. |
The sewage outfall at McMurdo Sound. |
Question 7:
Does the sponge spicule map change the infaunal community structure.
The infaunal (animals that
live in sediment) community in the Antarctic has been hypothesized to
"save" food in the sediment by mixing food below the surface when it
is available. They then eat it throughout the year. Year after year
sponges have been laying down spicules, small glass or calcium carbonate
toothpick-like structures, and these form layers and possible inhibit this burying
of food. Two treatments, one with fake spicules and one without these
spicules are going to be put out in the environment for one year. At the
end of the year one can see whether the spicules caused different communities to
form or not.
 |
Here
is a previous experiment similar what is planned. Photo Courtesy of Norbert
Wu, www.norbertwu.com |
Question 8: How are
the movements of Trematomus bernachii influenced by density?
This project
is based on the observation that scientists fishing for the emerald rockcod,
Trematomus bernachii, through holes in the ice appear to fish out areas
after a short period of time. It appears as if the fishermen catch all of the
fish in a given area, and they are unable to catch any more in that area for
a period of time , which indicates that it takes time for fish to recolonize
the areas and that these fish do not move around much (they have small activity
spaces or home ranges). This project has two parts, a removal portion and a
site fidelity portion. The goal of the removal part of the project is to assess
how the populations of T. bernachii within the study sites react to artificially
lowered densities, which would mimic the impact of fishing. After tagging and
determining a baseline density of fish within the study sites, we will then
be able to remove a certain proportion of the fish and survey the sites to see
how long it takes for the densities to reach pre-removal levels (how long it
takes for fish to recolonize the sites). Tagging the fish serves the dual purpose
of allowing us to see if the fish that we are counting are the same fish, and
to see both the number fish that are moving back into the study sites and when
they arrive.
The site fidelity part of the project is designed to see how much or little a fish
moves around its environment and how these movements might change according to the density of the fish. To do this you tag some fish with tags that allow you to
recognize individual fish (i.e. you use color coded tags). We will then lay a grid on the bottom around the study area, which will give us a frame of reference. Then we
will survey the site and observe the movements of the fish. By analyzing this data we will be able to see the general activity space or home range of the individual fish
and how their movements change when the fish are at different densities.
Picture courtesy of Dr.
John MacDonald
