Yellowstone oil spill and macroinvertebrate ecology

The Yellowstone Floods and with it the oil moves to riparian areas

The Exxon-Mobil oil spill on the Yellowstone River made national and international news this weekend; indeed, my first awareness of it came from the BBC news website.

As a macroinvertebrate ecologist, I cannot help but reflect how the aquatic insects might be affected.  It might seem silly to worry about “bugs” when images of beautiful white pelicans in oil-soiled plumage comprise the most interesting internet images. Still, it only takes a little imagination to reckon that pelicans eat fish, and fish eat bugs… so… the long-term ecosystem effects will be reflected in aquatic insect communities before they are manifest elsewhere.

There are many ways in which oils cause mortality in aquatic insects. First, were not just concerned with the heavy fraction of crude, but also the lighter petrochemical fractions which are toxic to insects. Obviously, we’re worried about accumulations of heavy fractions decomposing and reducing oxygen concentrations; the Yellowstone River’s fish and invertebrates require much greater dissolved oxygen concentrations than bottom dwellers of the Gulf of Mexico. Furthermore, exposure to lighter fractions can foul aquatic insect gills and directly suffocate them as well.

Additionally, there are issues with consumption of contaminated particles. Insects eat a variety of food-sources, but many of them are rather specific. Many of the Yellowstone River’s invertebrates scrape algae from the surfaces of stones (e.g., Glossomoma sp.). Some filter small particles from water using parts of their bodies (Brachycentrus) or structures they build along the river’s bottom (Hydropsyche sp.).   Among these filterers there those that filter very fine particles (e.g., Simulium), fine (e.g., Brachycentrus) medium (e.g., Hydropsyche), and larger (Arctopsysche) particle sizes. Similarly there are some aquatic insects that gather small particles from pools and eddies (e.g., Baetis sp. Paraleptophlebia sp.). Both the filterers and gatherers focus on relatively fine (<1mm) organic detritus. However, some focus on coarser detritus (Pteronarcys sp.) These groups could possibly exhibit differential responses.  Of Course there are predatory insects as well, and my surveys around Billings in 2005 suggest that there are many large burrowing dragonfly (Gomphidae; Ophiogomphus) larvae (incorrectly called nymphs, naiads).

Predatory insects are particularly compelling because they will eat what is alive and capture able. They will consume many prey as they live, often for 2 or more years, and build up organic compounds in their tissues.  Thus they have the capacity to bio-concentrate lipophilic compounds (many petro che

micals are lipophilic) and move them up the food chain. Thus, it is important to document the how petrochemicals persist in the food chain to ensure that the spill does not result in fishes that are unfit for human consumption. This would be detrimental to our lifestyle and livelihood in Montana.   In the Yellowstone River, if this were to occur, large predatory insects are the most likely avenue of bio-concentration. Fortunately, there are so many insects (usually) in the Yellowstone River, it is easy to assess this; we can assure this does not become a problem…

From a Bug’s perspective, the timing of the oil spill is terrible: This is the time of year that many species leave the water to fly about, mate, disperse, and lay eggs in the water. I have seen regular old treated sewage foam interfere with insects leaving the water (called emergence) by adhering to their wings. The entire emergence process is driven by the surface tension of water…  Fortunately many tributaries and upstream areas are not exposed to the oil sheen, and the recolonization potential of aquatic insects is tremendous

(wings are very useful for such an endeavor). It is likely, if clean up is well executed, that many aquatic insect species will have normal populations in about 1-3 years.

This may sound strange to readers, but it is discovering exactly how these ecosystems rebound from tremendous

Burrowing dragonflies

stressors that I find is the most fascinating facet of my job.

Well the bugs themselves are pretty amazing in their own right… but ecosystem

recovery is pretty darn interesting.

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