Where we are coming from
(geographically and scientifically)
The Benthic Lab is an affiliate of Moss Landing Marine Laboratories, a graduate research institution of the California State University system. We are located in Monterey Bay, California, fog capital of the West Coast. The Benthic Lab is headed by two Adjunct Professors, Dr. John Oliver and Dr. Stacy Kim. Our general interests are in Disturbance Ecology, or how communities respond to sudden changes in their environment. We have worked in the Antarctic for decades, and the disturbances we focus on there are those caused by humans. This project, ASPIRE, is based at McMurdo Station, the largest base on the Antarctic continent, where we are taking advantage of the human presence as a large scale experiment. Human impacts are isolated in the relatively pristine Antarctic ecosystem, and in working here we seek better understanding of basic tenants of disturbance ecology that can be applied where human activity is more common and complex.
The Sordid Details
Up to 1200 people live at McMurdo Station during the summer months, and its impact on the continent is relatively large. With people come their waste products, and we are examining how the seafloor community around McMurdo Station is recovering from sewage. The station is built on the edge of the annual sea ice, and when it was established in 1957, sewage was released in the intertidal. This continued until 1988, and by 1991 the outfall was extended to 24 m water depth, but sewage treatment just started in January 2003. The organic pile at the outfall pipe is one of our experimental sites.
These are examples of the animals that we are looking at. Though not as visually appealing as big sponges, fishes, and mammals, the small worms, crustaceans and clams that live buried in the sediments are very important bioindicators. These are the animals that live in closest contact with contamination, feed directly on contaminated material, and first introduce contaminants into the food web (and hence to those "charismatic megafauna"). We have learned which particular species are indicative of different levels of contamination.
I first worked at McMurdo in 1988, as a graduate student. Over subsequent years, there has been a group of collaborators who have collected data opportunistically, so that we have a ten year history of how the marine communities have changed. This "multidimensional scaling plot of community similarity" is a way of mapping how much change has occured. The numbers indicate the years, and green color, communties far away from the outfall. These reference sites have stayed very similar over 10 years. The brown communities, near the outfall, have changed over that time, especially between 1991 and 1992, which was when the sewage outfall was extended. This history shows us that the community has degraded with the approach of the outfall. The data we will collect this year will show us whether, and how, the community is recovering.
(the wheels of science grind on)
One question we need to settle is whether any changes that we see are local and due to the sewage treatment plant, or whether they are more widespread and due to more global factors. We have several study sites at different distances from the outfall, where we can observe whether similar ecological changes are occuring. The plot of organic carbon (a scientific term that includes poop) shows that organic concentrations fall to background 1-10 km away from the station. Thus, we know that the contamination from the outfall is fairly localized.
One of the surprises we found in last years data was that chemical contamination at the nearby old dumpsite in Winter Quarters Bay seems to be improving. One reason for this improvement could be burial by sediments, and this picture shows one of the natural processes that move sediment. This is Bratina Island, which is actually not an island, but a place where the ice shelf has ploughed up sediment from the seafloor, and the "terra firma" is not so firm because it is overlying ice. If the ice melts, the sediments are deposited, burying anything below. There may be a beneficial effect of the outfall as the mass of organic material released buries more toxic contaminants, such as heavy metals. The plot shows copper in the sediments, and the concentrations in the top layer are lower than in the buried layer. Though the burial has immediate deleterious effects on the community as it smothers organisms, it is also isolating other contaminants from biological interactions. This prevents animals from ingesting metals and moving them into the food web.
We have collected other evidence of potentially rapid recovery in Antarctic marine communities. In the early 1970ís, researchers in McMurdo Sound tagged sponges and over 10 years recorded growth and predation. Weíve been able to relocate Dr. Paul Daytonís (http://sio.ucsd.edu/rab/act_detail.cfm?state=%26)NK.T%2C%3F%5C%0A) old study sites and and find settling plates and other experimental structures that were placed on the seafloor. By looking at the size of animals growing on these structures, and knowing exactly when they were deployed, we can estimate growth rates over a 30 year time span.
In the 30 years since Dr. Dayton first set experiments on the seafloor, a surprising amount of growth has occurred in species we had thought of as incredibly slow growing. The sponges you see here, which are over 80 cm high, are less than 25 years old. Sponges of this age should be much smaller; other growth measurements suggest a maximum of 25 cm, or three times smaller! How do we reconcile this?
It is possible that the sponges grow very rapidly when they are young, and slower as they age. Thus, recovery of habitat-forming sponges following disturbance may begin within a few decades rather than a few centuries. This example highlights the importance of long term continuity in scientific studies; without Dr. Dayton's initial work and his continuing interest in this project, these measurements would have been impossible.
Experiments in Organics, Burial and Seastars
In 2002 we set up experiments to test the hypotheses suggested by the observed patterns. Though the outfall is anthropogenic, the processes it represents mimic natural occurrences. Burial happens from movement of ice shelves and ice bergs, which plow into the bottom and move sediment around. Concentrated organic input occurs wherever large animals congregate, along tidal cracks that Weddell seals use to breathe or around rookeries of Adelie penguins, as well as at human sewage outfalls. And there is an interesting bacteria versus seastar story: when there are small deposits of organic material (also known as seal poop) the red stars pictured here, Odontaster validus, move in very quickly and rapidly consume all the organic material. But at the outfall, the seastars donít eat the poo. The most noticeable difference between the outfall pile and the seal piles is the same reason that the outfall is nicknamed Mt. Charmin, it is covered by a white bacterial shag carpet. Possibly the bacteria are in some way preventing the seastars from getting to the food, and hogging it all for themselves. If this is so, and we can give the stars access to Mt. Charmin, then we may be able to help community recovery around the outfall happen more rapidly.
We can only do some of this work at the outfall itself; to make small specific tests of the three things we are focusing on (burial, organics, and bacteria) we need to also work in areas that have not previously experienced contamination. We have 4 experimental sites, two on Ross Island, and two across the sound on the continent. There are large, oceanographic scale differences between the island-side and the continent-side of the sound, in circulation patterns, ice formation and break out, and food and larval availability. By testing our hypotheses in a variety of locales, we can tell whether our conclusions only apply to a localized ecosystem, or whether we are justified in extrapolating further. This becomes even more important if we want to expand our concepts to a continent scale.
Today and tomorrow
(and the next dayÖ)
This is a work in progress; this year we finish collecting our experiment. The data from this study will allow us to apply what we learn about community ecology at the outfall to larger areas and to natural processes in and around the Antarctic.
The Antarctic is a place we are learning about by studying small pieces. Nearly all of the nearshore is still inaccessible. However, we are reaching a point where we can begin comparing what we have learned in different locations, and looking for patterns that are continent-wide. In these efforts, we are communicating with Australian, New Zealand, and Italian colleagues who conduct research around the continent.