It has been anticipated that the placement of anchors or other bottom hardware associated with offshore renewable energy devices could result in localized areas of scour or deposition. As macrofaunal organism distributions are highly influenced by sediment characteristics, there is potential for changes to organismal distributions and or abundances. When anchors are removed, there may be scour holes or settlement pits remaining on the seafloor that will be void of macrofauna (due to the previous existence of the anchor). We sought to assess potential changes to sediment characteristics and macrofaunal communities around anchor deployed from 2013 to 2015 at Oregon State University’s PacWave-North test site (formerly called PMEC-NETS and referred to as such throughout this document) off Newport, Oregon, and to determine the degree to which any effects were detectable in spring 2016, five months after anchor removal.
With the anchors in place, box core samples collected around the anchors had a significantly larger proportion of residual material: small gravel and shell hash (broken pieces of mostly bivalve shells) relative to reference locations. However, the median grain size of the collected sediment samples and the macrofaunal organism communities were not statistically different from reference locations of similar depths. In our single survey five months after anchor removal, the anchor stations still showed relatively higher residual proportions than reference locations, and one of the anchor locations had the second highest proportion of gravel ever recorded. Again, the median grain size of the sediment samples and macrofaunal organism communities were not statistically different from the reference locations.