Citation:

Henkel, S. AND Walt Nelson. Assessment of spatial patterns in benthic macrofauna of the U.S. west coast continental shelf. Journal of Biogeography. Blackwell Publishing, Malden, MA, 45(12):2701-2717, (2018). https://doi.org/10.1111/jbi.13451

Impact/Purpose:

In order to provide optimal approaches to interpretation of regional scale monitoring data such as the National Aquatic Resource Surveys, research assessed whether currently described marine biogeographic boundaries for the U.S. West coast apply to shelf macrofauna. The environmental drivers that were most associated with species differences among biogeographic regions was also assessed. Benthic infauna on the continental shelf from the Strait of Juan de Fuca in Washington to the California-Mexico border were sampled together with a range of sediment and water column metrics. The biographic boundaries proposed under the Marine Ecoregions of the World schema are more closely aligned with shelf fauna distributions than those developed based on west coast rocky intertidal communities. However, the proposed province boundary at Cape Mendocino is not apparent in the shelf macrofauna, and a transition appears to occur closer to the Oregon-California border. Further, the shelf fauna indicate the Channel Islands should be a separate subregion from the mainland southern California Bight.

Description:

Aim: We assessed whether currently described marine biogeographic boundaries apply to shelf macrofauna and which environmental drivers were most associated with species differences among regions. Location: Pacific coast of North America from the Strait of Juan de Fuca in Washington to the California–Mexico border. Methods: Van Veen grab samples were collected from soft sediment 28–138 m deep and sieved using 1 mm mesh. Spatial patterns of species richness, diversity,and abundance were examined in relation to latitude and environmental parameters (temperature, salinity, dissolved oxygen, sediment % fines, and total organic carbon). Analyses of latitudinal distribution patterns of individual species were combined with multivariate analyses of community composition to determine biogeographic and habitat boundaries for mid‐depth continental shelf macrofauna. Results: Species richness, diversity, and abundance significantly decreased with increasing latitude, primarily between 32 and 40°N. There were positive associations of richness, diversity (H’), and abundance with upwelling index, sediment % fines, and TOC (<2%). Temperature and DO also were significant for richness and H’ but not abundance. Assessment of individual species ranges found major faunal transitions at latitudes 33–34°, 37°, 44°, and 46–47°. Major assemblage differences were found at 34.5° and 42°. Within each latitudinal region, significantly different macrofauna communities were found in sediment with <5% fines. Main conclusions: The biogeographic boundaries proposed under the Marine Ecoregions of the World schema are more closely aligned with shelf fauna distributions than those developed using west coast rocky intertidal communities. However, the proposed province boundary at Cape Mendocino is not apparent in the shelf macro- fauna, and a transition appears to occur closer to the Oregon–California border. Further, the shelf macrofauna indicate the Channel Islands should be a separate subregion from mainland southern California Bight. Multivariate community analyses minimizing the impact of rare species appeared more useful in determining macrofaunal community biogeographic boundaries than analysis of individual species range endpoints, which are strongly influenced by uncommon species.

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