Abstract
The wave and wind climates along the west coast of North America provide some of the best prospects for offshore renewable energy development, yet initial assessments of the seafloor have been patchy. The Bureau of Ocean Energy Management (BOEM) requires knowledge of the seafloor environment and of seafloor-associated (benthic) organisms that may be affected by renewable energy activities. This program of research on benthic habitats and organisms of the Outer Continental Shelf off Washington, Oregon and northern California was designed to provide baseline knowledge of seafloor geology and marine invertebrate distributions at a regional scale by undertaking new mapping, synthesizing existing mapping data, conducting biological assessments and developing new predictive models. By focusing on the physical properties of the seafloor and species-habitat associations throughout the region, this study has delivered tools and information directly useful for assessing renewable energy development in the Pacific Northwest and for determining the nature and extent of future seafloor explorations.
The Active Tectonics and Seafloor Mapping Lab at Oregon State University (OSU) mapped the seafloor at five sites during the summers of 2010 (four sites) and 2011 (one site) located 4.8 to 19 km (three to 12 miles) offshore. Bathymetry was mapped using high-resolution multibeam sonar, accurate to within a few centimeters resolution, and seabed hardness and texture were interpreted from multibeam backscatter data. Seabed grab samples were acquired from soft-bottom areas and analyzed using a laser diffraction particle size analyzer to identify relationships between grain size, the bathymetry and backscatter data. With this wealth of new seabed imagery and sampling data, the project team mapped 848 km2 of seafloor. This significantly narrows the information gap for seafloor imagery in the region. Opportunities to partner with Oregon and California’s extensive state waters mapping efforts, the National Science Foundation-funded Ocean Observing Initiative, National Oceanic and Atmospheric Administration’s (NOAA) Ocean Explorer Program and the US Geological Survey accounts for a combined total of seven percent of the continental shelf now mapped in the study area. At 13 of these mapped sites, habitat maps were developed at a local-scale. Regionally, the Surficial Geologic Habitat (SGH Version 4) map of the continental shelf of Oregon and Washington has been extended to include northern California and updated with both the local-scale habitat maps over shelf areas and new mapping of canyons and channels in deep-water slope areas. An underlying map series representing data density and quality was updated and extended to accompany the SGH Version 4 map. A predictive rock outcrop model for the continental shelf extends was created from seismic reflection profiles, interpreted isocore and slope stability contours. This is a large update from previous rock outcrop maps and together with the SGH Version 4 map can aid in marine spatial planning.
Additionally we sampled benthic invertebrates, and the habitats in which they were found, to identify species-habitat associations and classify benthic habitats based on biological species groupings or assemblage distributions, rather than geological features alone. Rocky reefs and soft-bottom sediments such as sand and mud were classified and sampled separately. We visited three sites with rocky reef habitat using a remotely operated vehicle: Grays Bank, Washington, and Siltcoos and Bandon-Arago, Oregon during the summers of 2011 and 2012. Substrate type (on and off the reefs) was quantified and observed invertebrates living on or attached to the sediments (mega-invertebrates) were identified from the resulting footage. We found four main substrate associations of these mega-invertebrate assemblages: (1) pure sand/mud dominated by sea whips and burrowing brittle stars; (2) mixed mud-rock (which may be further divided based on size of mixed-in rocks) characterized by various species in low density; (3) consolidated rocks characterized by high diversity and density of sessile and motile mega-invertebrates; and (4) rubble rocks showing less diversity and density than the consolidated rocks. Mega-invertebrate assemblages found in both consolidated and rubble rock habitats were not distinct among sites; however, there were considerably more organisms observed on the rocks at Bandon-Arago than Grays Bank and Siltcoos. All four main habitat types were associated with mega-invertebrates that provided structure and complexity to the seafloor environment. Some taxa groups such as gorgonians and sponges, which are long-lived and slow growing, were found not just on rocky reefs but also were characteristic of the areas with smaller rocks around the reef. The four habitat classifications described above based on associated observed invertebrates are different than geological classifications and should be considered in future surveys as distinct seafloor habitats. Analysis of surveys done with distinct methodology from 1992-1995 supported many of these habitat classifications but also indicated that depth is a critical component to distinguishing among mega-invertebrates assemblages.
Prior to this study, invertebrate assemblages living on or in seafloor sediments (macrofauna) had not been comprehensively sampled since 2003. To sample macrofauna living in soft-bottoms, we visited the six originally proposed sites during summer 2010 and collected 118 macrofaunal and sediment samples across the region using a 0.1 m2 box-corer. These samples were used for community characterization, analyzing organics in the sediment and ground-truthing the backscatter mapping results. We sampled two additional sites during the summer of 2012 to fill in latitudinal and habitat gaps. Sediment samples were sieved using 1 mm mesh and all macrofaunal organisms were identified and counted after a sub-sample of sediment was removed for particle size analysis. As expected, significant differences in species assemblages were observed when comparing sandy and silty habitats. Areas comprised of very high percentages of sand (> 87%) contained multiple significantly different assemblages, differentiated based on particle size. Additionally, depth-related changes were observed within sediment types, occurring at approximately 10 m depth intervals. Similar to the habitat associations of mega-invertebrates, these biological-based sediment classifications of habitat differ somewhat from the geologic classifications mapped. While the lithological classification of “sand habitat” is defined as having > 90 % sand, these analyses indicate that from the organisms’ perspective, this seemingly homogenous seafloor is actually multiple distinct habitats. Knowing how macrofaunal communities respond to changes in grain size and depth can inform future site surveys and led us to develop tools for mapping macrofauna based primarily on these physical factors.
Bayesian Networks were developed to statistically infer suitable habitat for seven species of soft-sediment associated benthic macrofauna along on the continental shelf of the Pacific Northwest. The final products are static Habitat Suitability Probability maps communicating areas along the shelf that are likely good habitat for species of interest. We also developed maps communicating error or uncertainty associated with the each Habitat Suitability Probability map. Models were learned from benthic macrofauna sampling data collected from the eight sites along the Pacific Northwest continental shelf. Netica software was implemented for the design and analysis of statistical models. A benthic macrofauna model structure was developed for reusability and update capacity. Modeling metrics were applied to ascertain the effectiveness of each model in its accuracy and robustness, aiding in the final model selection. This effort represents the first attempt to map any benthic invertebrate in the Pacific Northwest using a Bayesian Network model. Low uncertainty values, strong error measurements in the initial cross validation and field validation efforts all support this novel approach for mapping benthic species across large regions of the seafloor and have several applications that can inform future spatial and science-based planning.
This study provides BOEM with information on seafloor habitats and invertebrate communities to be used in consideration of Outer Continental Shelf renewable energy development. Because benthic resources are an important factor contributing to the production of benthic fish species and some commercial fisheries, this project provides important baseline data that can be used by other Federal agencies and states in their efforts to understand and manage marine resources. Data gathered from this project may be used in documents and analyses that are necessary for the National Environmental Policy Act. The regional scale of these data can aid in marine spatial planning efforts and provide a context for siting seafloor construction activities and future surveys. Overall, the information derived from this study has greatly contributed to the greater body of knowledge regarding seafloor habitats and biological communities in the Pacific Northwest.
See Benthic Habitat Characterization Offshore the Pacific Northwest Volume 2: Evaluation of Continental Shelf Benthic Communities for the second volume of this report.