Our research focuses on several hypothesis or questions:

Question 1:  How will the benthic, or seafloor, community near McMurdo Station change when sewage treatment begins? 

Now that sewage treatment has begun, we expect to see a rapid change in the community surrounding the outfall. This year, we hope to see some of the 'weedy' species typical of contaminated areas replaced by the species found in uncontaminated areas.

Ophryotrocha notialis, the polychaete worm on the right, is one of the species indicative of organic contamination. On the left is the amphipod Heterophoxus videns that is found in uncontaminated areas.

 

 

Question 2:  How long will it take for the community to recover? 

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.

 

 

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