The Algae “Strike Back”: Post Dam Removal Benthic Surveys at the Elwha River Mouth

By Sean Sheldrake, Steve Rubin, and Rob Pedersen

EPA science diver photographs kelp samples on board boat.

EPA diver Rob Pedersen photographs samples.

Some of you may have followed our previous blog posts about EPA’s scientific diving program, including 2011 and 2012 reports from the Elwha River mouth in the Strait of Juan de Fuca.

The field site is downstream from the largest dam removal and restoration project to date, a large scale effort to restore wild salmon habitat and other aspects of the natural ecosystem. (For a great overview of the project, check out the webinar series posted by Olympic National Park.)

In this 2013 installment, we share some interesting findings about our benthic survey on how the dam removal is affecting things at the mouth of the river.

This survey involves counting 72 species of invertebrates and 13 species of algae—all of which are experiencing changes, some dramatic, as a result of the largest dam removal and restoration project to date: an experiment of grand scale for Elwha River mouth seafloor residents!  The survey is led by the U.S. Geologic Survey, and the team includes Washington Sea Grant, the Lower Elwha Klallam Tribe, and EPA divers.

Stationary light sensor placed near the Elwha River mouth.

Stationary light sensor placed near the Elwha River mouth.

Although divers reported seeing fewer algae, the scientists are still crunching the numbers. Early indications suggest a decrease in algae abundance, including the famed, forest-forming “bull kelp” since the removal of the dam. These changes may be due to decreased light levels, a loss of suitable substrate (a growing surface like a rock of some size, or even as small as gravel), or a combination of the two.  The team of divers used light sensors at many stations to help to document whether changes in light penetration were occurring at the dive sites to supplement quantitative data about the changes in the seafloor substrate.

In addition, it seems that tubeworms are on the increase in some areas.

This year, early reports indicate a late growing season for algae, perhaps due to the “silt cloud” hanging over areas near the river mouth. A few surprises may be in the works, too, such as the appearance of the rare kelp species pictured below, a sample the team of scientific divers could not immediately identify underwater—a discovery suggesting that as algae are faced with reduced light levels, a species or two not found during previous surveys might be trying to join the party.

Diver holds kelp sample underwater.

Mystery kelp.

Early suspicions from USGS and other experts narrowed down the mystery alga to either Laminaria ephemera or Laminaria yezoensis, and follow up examination confirmed it to be Laminaria ephemera. The unfolding story was covered in the local Peninsula Daily News.

To answer a few questions you might be wondering about all this:

  • Why does algae matter?
    Answer: Well it’s quite a nursery for young marine life and a grocery store for young and old that live in the sea.  It’s not unusual to see gray whales and their young grazing in the ‘kelp forest.’ Changes for shellfish are also of great importance to local fisheries.  The river is connected to the ocean in so many ways—and the silt keeps coming!
  • What other changes are there?
    Answer: The ongoing study will show changes for nearly 100 species of algae and invertebrates, in addition to fish, for the largest dam removal effort in North America to date.

For more information on the USGS-led study, see:,  For a full set of 2013 photographs, see: Elwha 2013.

Read more about the latest in EPA scientific diving at

About the AuthorsSean Sheldrake is part of the Seattle EPA Dive unit and is also a project manager working on the Portland Harbor cleanup in Oregon.  Sean Sheldrake serves on the EPA diving safety board, responsible for setting EPA diving policy requirements, where Rob Pedersen has served for many years.  In addition, they both work to share contaminated water diving expertise with first responders and others.  Steve Rubin is an aquatic biologist specializing in algal species with the USGS and a lead scientist on the survey.

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