Friday, August 16, 2013

Tracking community change in the nearshore zone

A red sea urchin (Stronglyocentrotus franciscanus) with a transect survey tape draped over it, at a site off of the Elwha River mouth)

Coastal resilience is not just about the physical interactions (erosion, flooding, tsunami) between the ocean and coastal communities. The concept also includes ecosystems, and the ability of coastal ecosystems (which support coastal communities) to respond to changes. In that vein, I've continued with a project I helped to initiate while a graduate student at UCSC designed to assess how the Elwha dam removal will change or affect the marine biological community that lives in the coastal zone adjacent to the Elwha River delta. Originally a USGS project, our team is now a nice example of multi-agency collaboration, with contributions from USGS, the Lower Elwha Klallam Tribe, WA Sea Grant, EPA and the US Coast Guard. We've just wrapped up our second of three sessions this summer, working to collect data on the fish, invertebrate and algae community at >20 sites at the Elwha and two reference areas (Green Point and Low Point). We also deploy and recover sensors logging temperature and light data, and measure information on the substrate.

There are a few interesting observations from the summer. We've been astonished by the recruitment of juvenile Dungeness Crab (Metacarcinus magister) at many of our sites. Check this video from a site near the base of Ediz Hook:

Our data set really isn't effective at detecting changes in these sorts of mobile and patchy species over time, but we can say that we've never seen anything like this before at our sites. Does it somehow have something to do with the removal? With ocean conditions? Pretty intriguing...

Next, we've hypothesized that the seafloor along parts of the shallow nearshore of the Elwha coastal zone would see substrate transitions as sediment from the Elwha River mouth enters the coastal environment. Furthermore, we expect that new habitats and biological communities would develop in these areas. At most sites, though, (outside of those sites that are more or less right in the river mouth) we haven't yet detected a dramatic shift in the substrate (from gravel to sand, for example)...but there is now at least one notable exception. At a site in shallow water (~25 feet) about 500 yards to the east of the river mouth we've tracked the arrival of sand from the river, which now entirely covers the seafloor. This video, for example, was shot in September of 2009:

That seem piece of sea-floor now looks like this:

We've been able to constrain the timing of the arrival of this sand to the last two months. Now, in the years ahead, our goal will be to assess if this material sticks around, and if and how a different biological community takes shape in these areas.

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