Habitat and bathymetry influence the landscape-scale distribution and abundance of drift macrophytes and associated invertebrates

We used a remotely operated vehicle to investigate landscape-scale patterns of subtidal drift material and invertebrates within a 60-km(2) marine basin in Washington State. Specifically, we quantified the distribution and abundance of drift macrophytes (seaweed and seagrass) and four macroinvertebrate species across depth and habitat type to depths of 170 m. Drift macrophytes were present on 97% of all video segments deeper than 30 m, with large drift piles particularly associated with low-angle habitats at depths exceeding 70 m. Two commercially harvested species (Strongylocentrotus franciscanus and Pandalus platyceros) that feed directly on drift material appear to be distributed in space (depth and substrate type) so as to maximize access to drift macrophyte food resources, according to their respective feeding modes. Basin shape and depth drive the landscape-scale distribution of drift material and indirectly the consumers that feed on it. The export of large amounts of detritus derived from nearshore macrophyte production into deep-water habitats likely fuels extensive secondary production in these aphotic zones.