Hydrography, Zooplankton, and Ichthyoplankton
Much of the oceanographic data shown in this report came from sampling along the Newport Hydrographic Line (arrow in figure below). We sample the coastal waters off Newport at biweekly intervals during the upwelling season in spring, summer, and fall. Sampling cruises are conducted monthly during stormy winter months. This program began in 1996, but we also have data from these same stations from sampling conducted in 1973 (Peterson and Miller 1975), 1983 (Miller et al. 1985), and summer 1990–1992 (Fessenden 1995). Most data presented here were collected during these cruises, which initiated in May 1996.
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| Figure 25. |
Transects and stations sampled during cruises by the NOAA Fisheries Service. |
From May 1996 through September 2001, all cruises were made during daylight hours because our research vessel, the rv sacajawea was only 37 ft in length, rendering it unsafe to work at night. With the acquisition of a new (and larger, 55 ft) research vessel in September 2000, we were able to sample at night. Thus in fall 2000, we began collecting data for an adult euphausiid time series.
This work includes measurements of copepod and euphausiid egg production and molting rates. We are also developing a long time–series of copepod and euphausiid production, which should prove useful in evaluating if in fact there are measurable differences in zooplankton production in association with changes in sign of the Pacific Decadal Oscillation.
At each station, a CTD profile (conductivity, temperature, and depth) is taken (Seabird‡ SBE 19+ CTD), and transparency of surface waters is measured (Secchi disc). A bucket of seawater is collected from the surface for analysis of chlorophyll–a and nutrients. A vertical plankton net fitted with a flowmeter is towed from near the sea floor to the surface (or from 100 m to the surface in deeper waters). The plankton net is 0.05 m in diameter with a mesh size of 202 micrometers (µ). A double oblique tow is made for ichthyoplankton (1–m diameter net with 333–µm mesh) over the upper 20 m. Since 2005, CTD casts have included fluorometry (WetLabs fluorometer) and oxygen (Seabird oxygen sensor).
From 1998 to 2003, we sampled each transect line five times per year as part of the U.S. Global Ocean Ecosystem Dynamics (GLOBEC) program. Since the GLOBEC project ended, we have continued to sample these same transect lines as frequently as possible. Thus far, we have been able to sample each transect in May (2004 2006), along with several visits to the Newport Line, out to 85 miles from shore, in summer 2004. As a result, the Newport biweekly data are nested within larger scale quarterly surveys, an approach that is useful in helping us interpret locally derived data from the inner portions of the Newport Line.
Nutrients are analyzed using a Technicon Autoanalyzer. Chlorophyll–s is extracted from glass–fiber filters in 90% acetone then analyzed using a Turner Designs Fluorometer. Zooplankton samples are processed in the laboratory by subsampling with a Stempel pipette. Species and developmental stage of copepods are enumerated with the aid of a dissecting microscope. Counts are converted to number of individuals per m³ of water using appropriate conversion factors. Biomass is estimated by multiplying the number of individuals per m³ by the dry weight of the taxa (using values from either literature or our own measurements). Carbon content is calculated assuming carbon is 40% of dry weight.
‡ Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA.
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