14 August 2013 Being At The Top Is Where It's At...Trophic Levels

In past Dunton Team journals I have discussed a myriad of topics dealing with benthos "BenthicBenthic organisms live on or in the bottom sediments of a sea or lake. 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.

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. BenthicBenthic organisms live on or in the bottom sediments of a sea or lake. 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.

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.