Technical Report No. 21

BENTHIC ASSEMBLAGES OF THE PADILLA BAY NATIONAL ESTUARINE RESEARCH RESERVE, MOUNT VERNON, WASHINGTON

Gary Ray

August 1997

Bibliographic Citation
Ray, Gary 1997. Benthic assemblages of the Padilla Bay National Estuarine Research Reserve, Mount Vernon, Washington. Washington State Department of Ecology (Publication No. 00-06-044), Padilla Bay National Estuarine Research Reserve Technical Report No. 21, Mount Vernon, Washington. 91 pp.

Abstract
Despite the importance of benthic invertebrates as forage for a wide range of fish, shellfish and migratory shorebirds, relatively little is known about their distribution or community strucure among habitats in Padilla Bay. In this study sediment texture and infaunal community structure of the most common intertidal and subtidal habitats of Padilla Bay are characterized and compared. Five intertidal habitats including unvegetated flats, Ulva covered sediment, Zostera japonica beds, and low- and high-density Z. marina beds were examined as well as four subtidal habitats including Z. marina beds, unvegetated sands less than 5m deep, unvegetated sands between 5 and 20m deep and sites with depths greater than 20m. Diversity, total numerical abundance, biomass, and species composition varied among habitats corresponding to changes in elevation, vegetation type and sediment type. Diversity increased with decreasing elevation to a maximum in shallow unvegetated subtidal sand habitat, numerical abundances were highest in low- and high-density intertidal Zostera marina beds, and biomass, although variable, was generally highest in vegetated intertidal habitats. Diversity, numerical abundance and biomass were highest in the upper sediment layers although secondary peaks of biomass at greater depths due to the presence of large deep-burrowing bivalves. Two types of species assemblages dominated Padilla Bay habitats, a single widely distributed and a number of habitat specific assemblages. The wide-ranging assemblage was comprised of Barantolla americana, Mediomastus sp, Exogene molesta, Tubificoides foliatus, Transenella tantilla. Mysella tumida, Corophium acheruscium, and Amphioda occidentalis. Common eelgrass taxa included Lacuna variegata, Haminoea vesicula, Idotea resecata, Caprella laeviscula while the Owenia fusiformis, Prionospio cirrifera, P. steenstrupi, Admete gracilior, Acila castraensis, and Eudorella sp. were found only in subtidal or near subtidal habitats.