Technical Report No. 2

DISTRIBUTION OF HABITATS AND SUMMER STANDING CROP OF SEAGRASSES AND MACROALGAE IN PADILLA BAY, WASHINGTON

Douglas A. Bulthuis

May 1991

Bibliographic Citation
 Bulthuis, Douglas A. 1991. Distribution of habitats and summer standing crop of seagrasses and macroalgae in Padilla Bay, Washington, 1989. Washington State Department of Ecology, Padilla Bay National Estuarine Research Reserve Technical Report No. 2, Mount Vemon, Washington. 35 pp.

Abstract
The channels, seagrass and macroalgae beds and intertidal flats in Padilla Bay, Washington were mapped during summer, 1989, based on color aerial photography. At 14 selected sites within apparently homogeneous areas, the density and biomass of seagrasses and macroalgae and the particle size distribution of sediments were determined. Seagrasses, principally Zostera marina L., were the most important habitat, covering about 3200 hectares, 53% of Padilla Bay. Zostera japnica Aschers. & Graebn. was distributed higher in the intertidal than Z. marina and covered about 320 hectares, 6% of the bay. The seagrass, Ruppia maritima, reported from Padilla Bay for the first time, is widely distributed at a very sparse density over about 140 hectares, 3% of the bay. Large accumulations of Ulva and Enteromorpha covered about 160 hectares (3% of the bay) in the southern part of Padilla Bay. Mean density of Zostera marina ranged from 61 to 441 shoots m-2 and for Z. japonica from 394 to 1095 shoots m-2. Mean standing crop (above ground dry weight) of seagrasses ranged from 12 to 103 g dry weight m-2 at 9 seagrass covered sites. Macroalgal biomass at these same seagrass covered sites ranged from less than 1 to 190 g dry weight m-2. Within one Ulva and Enteromorpha covered site, macroalgae standing crop averaged 526 g dry weight m-2. The sediments in most of Padilla Bay are sandy; silt and clay are the dominant particle size only in the southeastern corner. The seagrass beds in Padilla Bay are one of the largest contiguous beds of seagrass in Washington State and along the Pacific Coast of North America.