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Andrea Skloss's picture

Trophic LevelsTrophic levels provided by Nathan McTigue.

In past Dunton Team journals I have discussed a myriad of topics dealing with benthos "Benthic Organisms and More..." and "What's Going on in the Mud Part 1 and 2." It does not stop here...there is more!

Water and sediment chemistry, and plankton samples were taken too. Why? To help us better understand arctic food webs and how they respond to natural and anthropogenic (man-induced) changes. Are arctic food webs resilient? What are the major food sources for the rich benthic and pelagic fauna of the Chukchi Sea?
We can begin to answer these questions through chemical analysis of organism's tissues. An animal's diet is reflected in the chemical makeup of it tissues. For example, organisms at higher trophic levels contain more heavy carbon (C13) and nitrogen (N15) than at lower trophic levels. Based on these chemical signatures, they have discovered that predatory snails like Neptunea occupy the highest trophic levels.

Double van Veen grabThe double van Veen grab collects bottom sediments. Qualitative, quantitative, and chemical analysis are gathered from this grab.

Collecting samplesCollecting samples from the surface mud. You are looking at the top of the van Veen.

Christina and JordannAfter the surface mud samples are collected on one side of the van Veen, the rest of that side is used for qualitative isotope study. The untouched side of the grab is used for quantitative analysis. The tubs contain the mud.

Sieve TableStarting from the front going to the back are Jordann, Christina, Molly, Susan, and myself all around the sieve table.

For example, as trophic levels increase (as you go from producer to herbivore to predator) abundance of C13 and N15 increase relative to C12 and N14. Benthic microalgae are at the lowest trophic level. Where do animals at high trophic levels get their carbon? Possible sources include phytoplankton, benthic diatoms (the microphytobenthos), and terrestrial plant matter.

Isotope study samplesThe samples you see are gathered from the qualitative sieving of the sediments and items from the trawl to used to isotope analysis.

Christina and the ovenChristina (Dunton's PhD student) is putting the samples in the oven to be dried. The last step is to freeze items and finish the analysis back in Texas.

So, by looking at the isotopic ratios of both heavy and light carbon and nitrogen, science can determine what the organism consumed. This ratio is like a fingerprint. Why is this important? Not only does this information establish the carbon demand of the community, it creates a baseline for the current state of the food web of the Chukchi Sea ecosystem. How could you determine if there is a change in the ecosystem by natural or anthropogenic means without a baseline? You got it! You cannot; hence the study.