The purpose of this study was to assess the impact to the benthic infauna by alternative to carbaryl for the control of burrowing shrimp, an important pest of shellfish in Willapa Bay and Grays Harbor. Our studies complemented those of others who 1) measured the efficacy of the alternative compounds against burrowing shrimp, and 2) examined ways to modify sediment structure to suppress shrimp colonization and development. Results will also complement other recent and ongoing studies of the benthic infauna in Willapa Bay and Puget Sound to present a comprehensive picture of community structure and dynamics in relation to not only human intervention but also natural, especially seasonal, events.
We collected four to six cores (15 cm deep x 10.2 cm in diameter) per treatment plot. Each core was immediately sieved through 0.5 mm mesh using salt water, stored in a 10% buffered formalin solution for 2 weeks, then stained with rose bengal and re-sieved through 250 um mesh to remove excess detritus and stored in 70% ethanol. Benthic invertebrates were further sorted from detritus by hand than identified and enumerated by species. Species attributes (type and abundance) of key benthic invertebrates, as well as community descriptors (Absolute Abundance, Species Richness, and Simpson Diversity) were compared among treatments using analysis of variance. Samples were taken shortly after treatment (4 weeks) and again at 3 and 9 months after treatment.
We have compared six compounds, most applied at multiple rates, from two different growing regions in 2005 and 2006, respectively. Processing and analysis of samples from similar treatments in 2007 are ongoing. All samples were from small plot trials. Plans for 2008 include examination of the benthic infauna in plots treated at the commercial scale, whether funded within the Initiative or not.
Treatment affects on abundance, richness, and diversity were usually not signficant, although some compounds show greater selectivity against certain groups. Mollusks, for example, are impacted the most by carbaryl. Diversity and abundance was much greater near Bay Center on the eastern side of the bay, where sediments are siltier and have a more particulate organics compared to the Nahcotta treatment side, where sediments are sandier.