Twenty-six Years After the Exxon Valdez Oil Spill: Volunteers Continue Monitor Long-term Variability of Intertidal Biology in Western Prince William Sound

Abstract

Marine populations - including fisheries, plankton, seabirds, kelp beds and biota of exposed rocky shorelines - undergo dramatic long term and inter-annual variability due in part to climate variability. Less is known about long-term variability of inter-tidal marine populations on protected rocky shorelines impacted by oil spills. Following over a decade (1989 to 2000) of detailed monitoring of rocky intertidal marine life at previously oiled and unoiled sites in Prince William Sound, the senior author continued photo-monitoring at up to nine sites, with substantial and grateful assistance of other scientists and local citizens. These observations, between 2001 and 2016, added 15 years to the previous 11 years of detailed intertidal monitoring conducted by NOAA HazMat. Further, a landslide in 2000 produced a 300 m long bare rock intertidal surface, not unlike oiled rocky sites areas that were subjected to high-pressure hot-water washing in 1989. This provided an additional unique opportunity to document colonization of fresh substrate on a bare-rock shoreline for more than 12 years. Recovery of conspicuous rocky inter-tidal biota on nearly barren surfaces occurred rapidly and returned to within the range of natural variability in 3 to 4 years. The additional decades of monitoring helped confirm the nature of natural variability and further that there have been 4 - o 10-year fluctuations in the abundance (percent cover) of dominant seaweeds and mussels in Western Prince William Sound. Four periods of heavy rockweed cover were separated by many years of little or no cover both at previously-oiled and unoiled sites indicating this variability had little to do with the spill and subsequent clean up. This variability challenged a common definition of recovery (return to conditions prior to the spill), and added further support to the results of our first decade of detailed monitoring that recovery may be defined as “a return to within the natural range of variability”. This poster acknowledges the assistance of volunteers who went out of their way to visit and photograph the sites, describes the approach and methods used during the most recent 15 years provides graphics highlighting the long-term and inter-annual variability and, hopefully, stimulates others to use annual photography to document and visualize linter-annual biological variability and long-term changes in shoreline biology.