GLOBEC 2000: Coastal Gulf of Alaska Copepod Egg Production and Viability - Do Interactions Between Climate and Microplankton Assemblages Produce Variability in Prey for Forage Fish and Salmon?
J. Napp and C. Baier (NOAA-Alaska Fisheries Science Center), S. Strom (Western Washington University)

Climate variability affects the productivity and food web dynamics of ecosystems. The Northeast Pacific Ocean (NEP) ecosystem is particularly sensitive to climate-driven change. The mechanisms, however, by which biological production are affected are unknown. Process studies, as part of GLOBEC's NEP program for the coastal Gulf of Alaska (CGOA), will: 1) document spatial and temporal variability in key biological rate processes and compare these to variability in physical processes affected by climate, and 2) test competing hypotheses of what controls productivity in the CGOA.

The CGOA is a highly productive ecosystem that provides a nursery area for many commercially exploited fish (e.g. salmon, walleye pollock, halibut). Copepods are important prey for both early juveniles of these fish species, and for the forage fish (herring, capelin, and sandlance) that later replace zooplankton in the diets of juvenile fish. Recruitment by copepods, the dominant biomass component of CGOA zooplankton, depends on the quantity and viability of egg produced by females. Together, they are a "vital rate" (i.e. birth rate). Recent laboratory and field studies have demonstrated that food quality is an important determinant of egg production and viability. To our knowledge no one has simultaneously measured egg production and viability in the CGOA.

The investigators propose to quantify copepod egg production and viability of three numerically abundant copepod genera (Calanus, Metridia, and Pseudocalanus), and compare these to physical, chemical and biological attributes of the water column directly affected by weather and climate. These results will be linked to concurrent studies of the microplankton community (Strom and Dagg), and copepod grazing (this proposal). Shipboard incubations to determine egg production and viability will be accomplished on GLOBEC process cruises in March/April, May, and July/August, of 2001 and 2003, in four different hydrographic regimes. In addition, methods that do not require shipboard incubations will be developed to estimate egg production. Data emerging from the experiments will: 1) provide the first in situ reproduction data for important copepod species in the CGOA, 2) allow a test of the hypothesis that (in nature) egg production or viability is reduced from physiological maximum levels, 3) determine if diet is the causative factor, 4) allow prediction of how mesoscale transport of organisms from one regime to another affects vital rates, and 5) provide key data to GLOBEC ecosystem modelers to parameterize mechanistic models to investigate how copepod recruitment in the CGOA will respond to changes in climate.

Specific measurements:

• Abundance and distribution of female copepods.
• Egg production rates of Calanus spp., Pseudocalanus spp. and Metridia pacifica feeding on different natural microplankton assemblages.
• Egg viability for Calanus spp., Pseudocalanusspp. and Metridia pacifica as a function of the microplankton community.
• Feeding rates and prey selectivity of female Calanus spp., Pseudocalanus spp. and Metridia pacifica grazing on natural microplankton assemblages.

This page was last updated on October 18, 2000.

Maintained by:
Hal Batchelder [hbatchelder@coas.oregonstate.edu
College of Oceanic & Atmospheric Sciences
Oregon State University
Corvallis, OR 97331-5503
phone: 541-737-4500; FAX 541-737-2064