Most of the world experiences drastic seasonal variation in the amount of food that is available throughout the year. In deep-sea habitats as well as the poles a single or sometimes few pulses of food provide nourishment for the entire year. Now you may wonder what that means to you? Why does it matter what happens in the deep, dark ocean or far away in a frozen waste land? The answer is that these communities decide how much of the carbon that we are putting into the atmosphere stays in the ocean, only to be released again and how much is buried for geologic time periods (meaning largely beyond the age of humans). However, we know very little about how the biology of how these habitats actually function, what makes them decide whether they break down and release the carbon and nitrogen or burry for, as far as humans are concerned, ever? Quite simply, that is the goal of this research.
The poles provide access to communities that have similar seasonality as the deep sea but at a depth that allows manipulative research. Most biology does poorly with a rapid rise of 4,000m (12,000ft), the average depth of the ocean, however in the Antarctic we can take a community that is adapted to a similar long period of starvation from a mere 20m (60 ft) below the sea surface and experiment with it to figure out how it ‘functions.’ To do this we head to the most southerly place on the planet where we can access the ocean through SCUBA, McMurdo Station. This site is not only far south but holds another important community that is an enigma: the densest habitat on earth.
Spiophanes tcherniai is a species of Polychaete that occurs in incredible densities. To be exact in every square meter of sediment there are 150,000 to 180,000 individuals of this species as well as a variety of other species that we call ‘macrofauna.’ The macrofauna are visible to the eye but amazing under a microscope and all are, by definition, greater than 0.3mm in size. Its an diverse community with small shrimp looking animals, worms of every shape and colors, not to mention clams and anemones. They co-occur with an incredible variety of bacteria and what we really want to know with this research is whether the bacteria are competing with the animals or facilitating the persistance of these animals, allowing this incredible density in a veritable dessert of food.
Understanding the roll of bacteria is key. Animals have a relatively simple diet of what they can digest. Easy to digest food (which we call labile) is usually fresh and not the most abundant form of carbon in the oceans. Refractory compounds are the dominant source of potential food but cannot be digested by animals without help. Cows, for example, get help by special bacteria in their rumen giving them greater access to the food in grass. In the Antarctic, the shortage of food is really a shortage of ‘labile’ food. Refractory compounds are present year round in the sediment. Yet both bacteria and animals prefer the labile compounds and that leads to competition for a limiting food resource.
I should mention that the Antarctic is cold. The water is as cold as salt water can be without freezeing, a balmy -1.8C or 28F. Prevailing knowledge would suggest that bacteria have enzymes which are not very good at those cold temperatures and thus the animals are better at digesting the labile compounds. Since the bacteria cannot digest the fresh food, the food stays fresh throughout the year until the next pulse of food. The other idea is that the bacteria and animals compete for this labile compound, both as competitors, yet as the food turn refractory, the animals switch and start eating the bacteria.
This is one that I took many weeks ago at Cape Evan’s wall. The sea urchin in the foreground is using some bryozoan as camo to avoid being seen.
During this research we will test to see which of these actually occur. Do the bacteria and both consume the same labile food source when it is present or are the bacteria inferior competitors? To do this we will collect many many sediment cores (called microcosms) from the the dense Spiophanies beds and keep them in the lab for 6 weeks. We will knock out the bacteria using a series of antibiotics and see how the macrofaunal communities differ with and without bacteria, as well as how much carbon gets burried vs how much is released. With this we hope to gain a better understanding of how the world around us works.
The following have resulted from this work:
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This research is supported by the National Science Foundation, Office of Polar Programs. The content of this website is not representative of NSF. Data generated from this project are archived and available for download: files.cgrb.oregonstate.edu/Thurber_Lab/Antarctica_2012/
