TITLE:
The Impacts of Nonnative Japanese Eelgrass (Zostera japonica) on Commercial Shellfish Production in Willapa Bay, WA
AUTHORS:
Kim Patten
KEYWORDS:
Shellfish Aquaculture, Invasive Eelgrass, Manila Clams, Pacific Oyster
JOURNAL NAME:
Agricultural Sciences,
Vol.5 No.7,
June
24,
2014
ABSTRACT: Eelgrass species
worldwide are valued for the ecosystem service they provide to estuarine and
marine habitats. One species, Zostera
japonica, however, has some negative impacts outside its native range and
is considered invasive. In Willapa Bay WA, USA, the nonnative eelgrass has expanded
to the level where the shellfish industry is concerned about its potential
impacts on its livelihood. Studies were conducted using paired plots, Z. japonica controlled with the
herbicide imazamox vs. untreated controls, to assess the effects of Z. japonica on Manila clams (Ruditapes
philippinarum) and Pacific oysters (Crassostrea gigas). Recruitment of new
Manila clams was not affected by Z.
japonica. The growth of young clams, total commercial clam harvests, clam
quality and clam harvest efficiency, however, were greater on plots where Z. japonica was chemically controlled
than where it was not treated. The response of oysters to Z. japonica control varied by site; there was no effect at one
site, while the other sites had a 15% increase in shucked meat with Z. japonica control. The potential
economic impact of a Z. japonica infestation of a shellfish bed was ~$47,000 ha-1 for Manila clams and
$4000 ha-1 for oysters for each crop harvest cycle.