SPATIAL AND TEMPORAL PATTERNS IN PLANT STANDING STOCK AND PRIMARY PRODUCTION IN A TEMPERATE SEAGRASS SYSTEM

The spatial patterns of standing stock and net above-ground primary production (NPP) of benthic autotrophic components (Zostera marina and Zostera japonica, epiphytic algae and benthic sediment associated algae) of the eelgrass meadow in Padilla Bay, Washington, were studied seasonally for one year. Eelgrass extended from approximately 1.0m above MLLW down to subtidal depths. However, density decreased at depths below 0.3 m MLLW. Zostera japonica formed a band at upper elevations, and mixed with Z. marina at about 0.3 m to 0.6 m MLLW. Epiphytic algae were abundant in the meadow, and reached greatest standing stock at between 0.3 and −0.4m MLLW. Sediment associated algae were abundant at all elevations as indicated by chlorophyll a concentrations. The standing stock of all components varied seasonally. Sediment algae reached peak abundance in early spring, followed by rapid growth of epiphytic macroalgae in early summer. Eelgrass biomass was greatest in early to late summer depending upon depth. Annual NPP for the system was 351 g C m−2. Epiphytic algae, Z. japonica and Z. marina were responsible for 50, 2 and 48% of this production, respectively. Total annual production from the 3 000 ha system was approximately 28 000 mt dry plant matter. © 1990, Walter de Gruyter. All rights reserved.