Spatial structuring of mid-trophic level forage communities in the Gulf of Alaska (GoA) is poorly understood, even though it has clear implications for the health of fisheries and marine wildlife populations. Here, we test the hypothesis that summertime (May-August) mesozooplankton communities are spatially-persistent across years of varying ocean conditions, including during the marine heatwave of 2014-2016. We use spatial ordinations and hierarchical clustering of Continuous Plankton Recorder (CPR) sampling over 17 years (2000-2016) to (1) characterize typical zooplankton communities in different regions of the GoA, and (2) investigate spatial structuring relative to variation in ocean temperatures and circulation. Five regional communities were identified, each representing distinct variation in the abundance of 18 primary zooplankton taxa: a distinct cluster of coastal taxa on the continental shelf north of Vancouver Island; a second cluster in the western GoA associated with strong currents and cold water east of Unimak Pass; a shelf break cluster rich in euphausiids found at both the eastern and western margins of the GoA; a broad offshore cluster of abundant pelagic zooplankton in the southern GoA gyre associated with stable temperature and current conditions; and a final offshore cluster exhibiting low zooplankton abundance concentrated along the northeastern arm of the subarctic gyre where ocean conditions are dominated by eddy activity. When comparing years of anomalous warm and cold sea surface temperatures, we observed change in the spatial structure in coastal communities, but little change (i.e., spatial persistence) in the northwestern GoA basin. Whereas previous studies have shown within-region variability in zooplankton communities in response to ocean climate, we highlight both consistency and change in regional communities, with interannual variability in shelf communities and persistence in community structure offshore. These results suggest greater variability in coastal food webs than in the central portion of the GoA, which may be important to energy exchange from lower to upper trophic levels in the mesoscale biomes of this ecosystem.
Zooplankton data: taxonomic data for each zooplankton taxa identified from Gulf of Alaska CPR transects (2000-2016) was spatially summarized within each year into 2 by 2 degree spatial bins (Dataset A: "Zooplankton_by_Year.csv"; Bins are numbered 1-41). For analysis, data for each taxa was then averaged across all years (Dataset B: "Zooplankton_Community_AllYears.csv") and for warm vs. cold years (Dataset C: "Zooplankton_Community_WarmColdYears.csv"). Hierchical Clustering of Principal Components and other analyses were conducted on Dataset B to determine the baseline community composition analysis, and on Dataset C to determine community patterns during warm years (2004, 2005, 2015-2017) vs. cold years (2007, 2008, 2010-2012).
Oceanographic data was downloaded as described in the methods: SST data were obtained from the NOAA Optimal Interpolation SST, a combined and corrected interpolation of data from different platforms (satellites, ships, buoys) with a daily resolution of 1/4°  Ocean surface current data are from the Ocean Surface Currents Analysis Real-time (OSCAR, version 1) data set [31,32]. OSCAR currents, representing the geostrophic and ageostrophic flow at 15 m depth, were calculated from satellite sea surface height gradients, ocean vector winds, and SST data every 5-days on a 1/3° global grid. Bathymetric data was obtained from ETOPO1 dataset, with a 1 arc-minute resolution (doi: 10.7289/V5C8276M).
Zooplankton_Community_AllYears.csv: Taxonomic data from CPR transects collected from 2012-2016 summarized into 2 by 2 degree lat/long cells. Columns include 18 taxa, Lat, Long, Bin ID.
Zooplankton_Community_WarmColdYears.csv: Taxonomic data from CPR transects by year summarized into 2 by 2 degree lat/long cells and organized by Temperature Assignment. Columns include 18 taxa, Lat, Long, Bin ID, Temperature.
Zooplankton_by_Year.csv: Taxonomic data for 18 different taxa listed by Year and Bin. This sheet was used to make the previous two spread sheets used for analysis.