MSI: Zooplankton ID, Standing Stock & Density
Zooplankton standing stock (ml · m-3) can be quickly measured by displacement (DV) or settled (SV) volumes of whole samples; conversely, zooplankton density (number · m-3) requires samples to be split for counting and species identification under the microscope. While more difficult and time consuming, zooplankton composition and density estimates allow us to monitor how key prey taxa respond to climate change in the migration corridors used by juvenile salmon feeding on them en route to the Gulf of Alaska.
Some zooplankters vertically migrate to deep water by day to avoid predators, while others remain in surface waters. Euphausiids (krill) are an important prey for juvenile salmon that exhibit this daily migration. Zooplankton DV for samples collected in 2004 confirmed that standing stock in Icy Strait is greatest at night and lowest by day in the 20-m near-surface (shallow) water column compared to the 200-m integrated (deep) water column.
Calanoid copepods are ubiquitous prey of juvenile salmon and dominate zooplankton samples. “Small calanoids” (<2.5 mm length) produce several generations annually, while “large calanoids” (>2.5 mm) produce only one, timed to the spring phytoplankton bloom. Small calanoids are more abundant than large calanoids. As this figure shows, fluctuations in the annual temperature that regulates both their growth and food supply may not affect large and small calanoid production in the same way, probably because of their different life histories.
Contact:
Molly Sturdevant or Emily Fergusson
Auke Bay Laboratories
Alaska Fisheries Science Center, NOAA Fisheries
Ted Stevens Marine Research Institute
17109 Pt Lena Loop Rd
Juneau, AK 99801
Molly.Sturdevant@noaa.gov
Emily.Fergusson@noaa.gov
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