Climate induced shifts in the phytoplankton community biomass and community structure along the West Antarctica Peninsula Oscar Schofield1, Alex Kahl1, Grace Saba1, Zoe Finkel2, Andrew Irwin2 Mark Moline3, Maria Vernet4, Barbara Prezelin5, and Hugh Ducklow6 1: Rutgers University, 2: Mount Allison University, 3: University of Delaware, 4: Scripps, 5: UCSB, and 6: MBL Introduction Time Series of Ship Spatial Grid (Phytoplankton Communities) The West Antarctic Peninsula (WAP) is experiencing the fastest rates of regional climate change on Earth. The impact of these changes on the ecosystem is an open question. It has been documented the WAP has a productive ecosystem, however there is evidence that over the past 30 years, the magnitude of WAP phytoplankton blooms have decreased by 12%. Declines in WAP phytoplankton appear to have been accompanied by shifts in the phytoplankton community structure based on satellite data that suggest algal community structure appears to have shifted from large (50-100 microns) to small cells (5-10 microns). Declines in phytoplankton biomass and community structure have been hypothesized to underlie shifts in the zooplankton and apex predators in the WAP food webs. For this poster, using LTER time series we assess phytoplankton communities dynamics that may underlie the suggested shifts in the satellite imagery. Variability in ship sea surface temperature (SST), sea surface salinity (SSS), diatoms (Fuco/chl a), cryptophytes (Allo/chl a) is shown on the left over several years. The variability in the parameters show strong inshore and offshore gradients as well as strong north to south gradients. Generally the inshore waters of the LTER grid is cooler in the summer months by over 1 degree compared to offshore waters. Similarly there is a strong inshore offshore gradient in sea surface salinity with lower salinity found nearshore, presumably reflecting the melting ice. Generally the diatoms and cryptophytes are segregated in space and time. The spatial variability in the two phytoplankton taxa show a great deal of interannual variability. Both taxa are found in the north and south as well as in the nearshore and offshore waters. There is no apparent correlation between the phytoplankton community structure and the sea surface temperature and salinity. Sampling Strategy of Palmer LTER The Palmer LTER sampling consists of two major research strategies. The first component of the PAL LTER is the biweekly sampling conducted at Palmer Station on Anvers Island (indicated by the red circle) for the spring and summer seasons (October through mid-March). The sampling at Palmer consists of time series measurements at several fixed stations. This sampling in time is complemented with a ship sampling grid conducted each January along the WAP, spanning from the waters near Palmer Station to the waters South of Marguerite Bay. For this study we emphasize the sampling of the phytoplankton communities with a focus on the HPLC sampling of phytoplankton pigments that are used as chemotaxonomic markers for the major phytoplankton taxa. Phytoplankton Communities in Hydrologic Space salinity Ship Station Data Time Series at Palmer Station (Phytoplankton Communities) Palmer Station Data 3 3 2 Time-series measurements from Palmer Station show high inter-annual variability in chlorophyll a (bottom right panel). Using ChemTax we calculated the % of the total chlorophyll a associated with the major phytoplankton taxa. Diatoms were the dominant taxa present (panel A). The next most abundant phytoplankton were the cryptophytes. Mixed flagellate communities and prasinophytes rarely dominated the communities. Type-4 haptophytes (Phaoecystis) was the third most abundant taxa at Palmer, consistently accounting for 20% of the communities but showing no interannual variability. 2 Chlorophyll a 1 1 Temperature Temperature -1 -1 -2 32 33 30 34 31 32 33 34 Salinity Salinity To assess the relative distribution of cryptophytes and diatoms for the Palmer and ship data sets we have plotted the data in temperature and salinity space. The blue circles represent diatom pigments and the green circles indicate the cryptophyte pigments. The size of the circles indicates the pigment concentrations. For Palmer Station, the cryptophytes and diatoms segregate in temperature and salinity space. Cryptophytes are generally found in colder and lower salinity water. At Palmer this is largely associated with ice water melt. This association with the cryptophytes with these water masses is robust over the 20 year data set, however the driver of this association remains an open question. In contrast, the ship data does not show the same segregation in temperature salinity space. For the ship surveys, the crypotophytes are distributed across the full temperature and salinity ranges. What might underlie this variable distribution? Time-series measurements within the years for the two dominant phytoplankton taxa generally show strong segregation in time. The cryptophytes (indicated by the marker pigment alloxanthin, green), were found to bloom after the seasonal retreat in sea ice (indicated by the black arrow), The diatoms (indicated by the marker pigment fucoxanthin, blue). The diatoms show major blooms throughout the year that are timed prior to and after the seasonal sea ice retreat. Different cryptophyte species Diatoms and Cryptophytes Relationships The net result was of the seasonal phytoplankton bloom dynamics was the complete separation of the cryptophytes and diatoms. When cryptophytes bloom, the diatoms are not present and vice versa. This shift in phytoplankton communities represents a major shift in the phytoplankton size spectra. Cryptophytes in these waters are typically 5-10x smaller in size then the dominant blooming diatoms. During the 2012 field season we incorporated a video sorting technology (FlowCam) to classify the different phytoplankton species. Above we show the data collected using the new technology. Consistent with the historical pigment data, the diatoms and cryptophytes were segregated in space and time (data not shown). The new technologies provide species information and showed that several different species of cryptophytes were present and differentially distributed across the WAP. Based on this view, our current hypothesis is the differential segregation of cryptophytes between the between the Palmer station and Ship in temperature and salinity space, reflects the relative distribution of these different species cryptophytes. This suggests better incorporation of species identification is a key need to be incorporated into the regional sampling. Conclusions l Diatoms and cryptophytes are the major phytoplankton taxa present within the Palmer LTER sampling grid l Diatoms and cryptophytes are segregated in space and time l The segregation of diatoms and cryptophytes in temperature and salinity space is variable between Palmer station and regional ship surveys. These differences likely reflect species levels responses which suggests important needs to augment the existing Palmer LTER sampling. Acknowledgments: This time series represents a large community effort and we gratefully acknowledge our partners over the lifetime of the program. We also acknowledge the generous funding support of the NASA Biodiversity program and of the Gordon and Betty Moore Foundation.