Three-decades of Rocky Intertidal Photo Series Documenting interannual variability in western Prince William Sound

During summer 2021 we re-visited and re-photographed intertidal community scenes at seven rocky intertidal sites in Western Prince William Sound, adding another year of photos to a 32-year monitoring effort. The sites include both previously-oiled and un-oiled locations that were the subject of repeated annual photos beginning in 1990, one year after the March 24, 1989 Exxon Valdez Oil Spill. Photos from summer 2021 were compared with those available from the previous 31 years, visually revealing multi-year cycles of variation in the cover of dominant intertidal community organisms, mainly rockweed (Fucus distichus) and mussels (Mytilus trossulus). The repeated photos, together with basic time series graphs of percent cover estimated from many photos, provide a visual sense of major year-to-year variations in the cover of rockweed, mussels and to some extent, barnacles. In summer 2021 the cover of rockweed at five of the seven sites was low compared to recent previous years. The entire photo-timeseries shows that during the last three decades there have been four or five episodes of growth and senescence of rockweed and mussels. This variability shows how difficult it is to define “recovery” and supports the idea that recovery is a return to the natural range of variability, not necessarily the condition that prevailed immediately before the disturbance.