Getting lost in the tangle of connections called the Puget Sound food web

I’m increasingly amazed at the interwoven nature of the Puget Sound food web. Whenever I become focused on a specific species — Chinook salmon, for example — one of the first questions I ask is: What is this species eating?

I soon learn that the answer depends on the size of the individual doing the eating. Prey for a baby salmon is much different from prey for an adult.

If you really want to learn about why a species is doing well or poorly, you need to look beyond prey availability for your species of interest and find out what the prey are eating as well. Healthy prey must be abundant for any species to do well, so the prey of the prey must also do well.

When we combine features of this prey base with varying conditions among predators and competitors, we begin to build a model of the food web. Nearly every diagram of a food web model I’ve seen reminds me of tangled spaghetti with each strand connected to tiny meatballs representing groups of species. Sounds crazy, but it’s a food web model.

A computer-based model being developed for Puget Sound can simulate animals eating each other at unimaginable speeds. For each predator-prey interaction, there is a transfer of energy to a higher level in the food web. The model expresses the transfer of energy as units of nitrogen, since nitrogen is essential to all common forms of life. Thus nitrogen becomes the “currency” to calculate transfers in the food web, explains modeler Chris Harvey of NOAA’s Northwest Fisheries Science Center. I briefly mentioned this modeling effort in the final installment of a four-part series about the Salish Sea Marine Survival Project.

As I described in a recent blog post (Water Ways, July 6), the Marine Survival Project is all about figuring out why wild Chinook salmon and steelhead seem to be headed for extinction in the waters of Puget Sound. The project involves more than 200 scientists in the U.S. and Canada, all searching for answers.

As of Monday, all four parts of the series are now published in the Encyclopedia of Puget Sound:

For those who would like to dive deeper into the complexities of the Puget Sound food web, I recommend a video (first on this page) featuring Chris Harvey and his colleague Correigh Greene, another research scientist at NWFSC. To better follow the explanations on the videos, you can download Correigh’s slide show (PDF 2 mb) as well as Chris’ slide show 3.8 mb) from the Washington Department of Ecology’s website regarding the Puget Sound Nutrient Forum, for which there are a variety of other videos.

A little less technical but quite informative is a presentation by Tessa Francis, an ecologist at Puget Sound Institute who described the food web by putting forage fish in the middle, emphasizing the importance of herring to many Puget Sound species (second video). Tessa prepared her talk for a general audience, and it was sponsored by KCTS-9 television and Seattle’s Pacific Science Center.

Related information about the fate of salmon and steelhead can be found on the website of the Salish Sea Marine Survival Project.

One thought on “Getting lost in the tangle of connections called the Puget Sound food web

  1. Yes, this issue is what is driving us at Sound Action. We have been working to protect the near shore from development that specifically harms spawning grounds. WDFW requires Hydraulic Permits (HPAs). They have never turned down one in many years. We review each HPA and challenge ones that are going to have an impact on spawning habitat, i.e. overly long docks, construction during spawning season, etc. Thanks for the great article, I’ll take a look at the videos.

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