1. > Inner Transitional Outer PWS 1.Large zooplankton were collected with 1-m2 square MOCNESS with 500  m mesh. Samples collected in 20 m depth increments from 100 m to the surface at night. 2.Small zooplankton were collected with a 25 cm diameter CalVET net with 150  m mesh. Vertical tows from 100 m to surface during the day. 3.Water column profiles were collected with a Seabird model 911 plus CTD and fluorometer. 4.Samples were collected during years and months listed below: Collection Sites: 1)13 Stations along Seward Line (labeled GAK) 2)5 Stations in Prince William Sound (PWS box) 3)4 Stations at Hinchinbrook Entrance (HE) Animals widely distributed across the shelf tend to occur in the upper mixed layer day and night Animals restricted to the outer or inner shelf tend to occur between the thermocline and permanent halocline Animals which avoid the upper mixed layer, even at night, occur primarily in the fjord Diurnal vertical migrators, residing in the upper mixed layer at night and below the permanent halocline during the day tend to be more abundant on the inner shelf (except E. pacifica) Neocalanus, an oceanic species, was more abundant in 1998 and 2002 than in 2000 and 2001 (error bar are 95% confidence intervals) Correlation between major water column properties and abundance of Neocalanus plumchrus-flemingeri during May, 1998 – 2002; outer nine stations Upper Mixed Temperature0.025283 Lower Mixed Temperature0.421468 Mean Water Column Temperature0.343750 Potential Energy (Stability)-0.223003 Upper Mixed Salinity-0.757058 Lower Mixed Salinity-0.768888 Mean Salinity-0.783464 Total Redundancy: 63%; Canonical R: 0.79; p = 0.0000027 Neocalanus are negatively correlated to salinity, contrary to expectations for an oceanic species (station outside the ACC) Salinity and Copepod abundance; Seward Line; May Line is 32.4 Neocalanus populations were low when oceanic water occurs on the shelf, confining brackish water to the ACC Salinity and Copepod abundance; Seward Line; May Line is 32.4 Neocalanus populations were high when low-salinity water is mixed across the shelf to the shelf break or beyond (color key in right panel) From a poster at ASLO, 2000, by Childers, Whitledge, Stockewll, Weingartner, Danielson, Coyle: Major nutrient distributions in relation to the physical structure of the Gulf of Alaska shelf. Nitrate is on average positively correlated to salinity Iron concentrations (nmol/kg) from Ocean Station P to the Gulf of Alaska shelf break (Martin et al., 1989) Iron concentrations in the euphotic zone are very low from ocean station P in the central Gulf of Alaska gyre northward to the self break off Seward Alaska Wu, Jingfeng: measured iron on the Seward Line in the upper mixed layer during May, 2004 Iron concentration in the euphotic zone increased across the shelf from minimal values near the shelf break to maximum values in the Alaska Coastal Current Summary of observations 1)Copepod abundance is strongly and negatively correlated to salinity. 2)Copepod abundance shows little or negative correlation to water column stability. 3)Copepod abundance shows little or no correlation to upper mixed temperatures. 4)When copepod abundance is low, intrusion of oceanic water onto the shelf constrains the mixing zone to a narrow band near the outer edge of the coastal current. 5)When copepod abundance is high, the mixing zone is spread across the shelf from the coastal current to the shelf break front. 6)Macronutrient concentrations are positively correlated to salinity. 7)Iron concentrations are near threshold detection levels in the mixed layer at the shelf break but about an order of magnitude higher in the Alaska Coastal Current (ACC). Cross Shelf Distribution of Major Zooplankton Species Relative to Depth Distribution (bar graph insets) Animals which occur in the upper mixed layer day and night are moved back and forth across the shelf in the wind-mixed layer (Oithona, Neocalanus plumchrus / flemingeri) Animals residing between the thermocline and permanent halocline tend to be separated on the shelf (Neocalanus cristatus, Eucalanus bungii, Calanus marshallae, Pseudocalanus). Diurnal vertical migrators, residing below the halocline during the day and above the thermocline at night are apparently avected shoreward in the bottom layer and tend to concentrate on the inner shelf (Metridia spp., Euphausiids) Mesopelagic animals that occur below the thermocline, even at night are apparently advected shorward in the bottom layer and tend to concentrate in the fjord system of Prince William Sound (Cyphocaris challengeri, Pasaphaea pacifica, Pareuchaeta elongata, pelagic ostracods) Summary of Distribution Methods Introduction: Zooplankton abundance and distribution on the northern Gulf of Alaska shelf are tightly linked to physical processes influencing production and advection of water on and off the shelf. A primary goal of the LTOP project was to document the cross shelf distribution and abundance of major zooplankton taxa relative to water mass movements and to elucidate processes leading to interannual differences is abundance. This poster illustrates cross shelf distribution of major zooplankton species relative to their depth distribution and water mass movements. Contrary to expectation, the abundance of Neocalanus flemingeri, an oceanic species, is negatively correlated to salinity. The abundance-salinity correlation and interannual differences in Neocalanus abundance are related to physical processes, potentially influencing production. Acknowledgments: This research was conducted on the R. V. Alpha Helix. Technical support was provided by the captain, crew and ships technicians (Steve Hartz, Brian Rowe, Dave Aldridge and Dan Mahalck). Aid in sample processing and data entry was provided by Chris Stark, Janet Ballek and Elizabeth Stockmar. The research was multidisciplinary, involving the cooperation of a number of researchers and institutions. They include: Tom Royer, Old Dominion University; Amy Childers, Tom Weingartner, Seth Daniels, Steve Okkonen, Dean Stockwell and Terry Whitledge, University of Alaska Fairbanks. We thank all of the above for their participation in this research effort. The Long Term Observation Program was funded by US GLOBEC award number NA67RJ0147AMD7 Distribution and abundance of zooplankton on the northern Gulf of Alaska shelf relative to water masses Kenneth O. Coyle; School of Fisheries and Ocean Science, University of Alaska, Fairbanks Alaska Interannual Differences in Abundance of Neocalanus flemingeri Hypothesis : The most likely explanation for the observations is that horizontal mixing between high-nutrient, low-iron oceanic water and high-iron, low-nutrient ACC water promotes elevated primary production in the mixing zone, leading to elevated production of zooplankton grazers. Neocalanus, an oceanic species, was more abundant in 1998 and 2002 than in 2000 and 2001 (error bar are 95% confidence intervals)