According to Eyes Over Puget Sound, a monitoring project of the Washington State Department of Ecology, the basic structure of Puget Sound’s food web might be changing. Under normal conditions, diatoms, a type of photosynthesizing plankton, are the producers that form the base of the food web. New evidence suggests that over time, changing ocean chemistry might push them out in favor of a microbial-based food web.
The infographic above describes some of the consequences of such a change. Normally, in a diatom-based food chain, copepods and other zooplankton are the main predators of diatoms. Copepods are extremely important because they provide food for fish and provide large amounts of the energy to deep water ecosystems where limited light makes photosynthesis difficult.
Recently, instead of the copepods, huge noctiluca blooms have been spotted all over the sound, particularly in the small inlets of the south sound. It seems that the noctiluca, able to thrive in the warmer, more nitrogen rich waters seen today, is taking over the copepods’ role as main diatom predator. The problem is that noctiluca is not as good at spreading out the nutrients as copepods are. Their waste disintegrates quickly in the upper surface waters preventing the cycle of nutrients with the deeper ecosystems. This would explain the declining number of organisms found in the sediment and possibly why so few diatoms have shown up in the fossil record since the 1950s.
When these nutrients are trapped on the surface they promote the growth of microbes instead of diatoms. Copepods are pushed aside because they do not feed on the microbes, while noctiluca can flourish. Unfortunately, this also means less food for fish and sea birds, and more for Jellyfish. Will the Sound adapt to these changes? No one really knows for sure, but we can help it by trying to reduce the other stresses such as habitat loss, pollution and overfishing.
Read more about their findings and see all of Eyes Over Puget Sound’s monthly reports at: http://www.ecy.wa.gov/programs/eap/mar_wat/surface.html
By Anna S.