The Impact of Nutrients on Picophytoplankton Populations Along the Atlantic Coast Melinda Norris and Dr. Jessica Nolan Conclusions  The phytoplankton populations became more nutrient limited as the summer progressed  The picophytoplankton, <3μm, population became healthier in a constant low nutrient environment, as shown by the variable fluorescence throughout the summer. This likely indicates a succession of species which are optimized to these conditions.  The percentage of chlorophyll in the picophytoplankton size class decreased as the summer progressed * As picophytoplankton became “healthier” they became a better source of food providing a cycling of elements and flow of energy (Raven 1998) * It is proposed that the grazers that consume the picophytoplankton are able to grow at a rate similar to picophytoplankton Introduction Phytoplankton support life in marine environments and help maintain water quality by recycling nutrients (Hoff and Snell 1987). The dominant contributors to the primary phytoplankton production biomass in the open oceans are picophytoplankton (Moon-van der Staay et al. 2001). Picophytoplankton are the smallest known size class of phytoplankton with a diameter of 2-3µm or less. Picophytoplankton becomes so minute by “scaling down” the cell components within to contain only the essential components, e.g. genome and plasma membranes (Raven 1998). Being so minute is advantageous for the picophytoplankton for several reasons:  Obtain and use resources more effectively for growth and/ or reproduction  Need lower concentrations of nutrients to survive  Smaller resource cost in energy production (Raven 1998) The species composition and abundance of observed dominant phytoplankton changes season to season, which is called seasonal succession. This seasonal succession is dependant on temperature and nutrient levels (Nybakken 2001). Picophytoplankton have not been studied from an ecological perspective, especially along the coast, so it is not known whether the picophytoplankton become the dominant species when the nutrient levels lessen. Hypotheses H o 1:There will be no difference in the percentage of chlorophyll in the picophytoplankton size class through the duration of the summer H o 2:There will be no difference in how picophytoplankton and the larger phytoplankton population respond to nutrient addition H o 3: There will be no change in the photochemical efficiency (Fv/Fm) of the phytoplankton population over the summer as nutrient levels decline Acknowledgements I would like to thank NASA, and NOAA for the allowing me to go out with them on the boat to collect the data. I would also like to thank the Marine Science Consortium for putting me up in housing while in Wallops, VA and for the use of their labs. And I’d like specially thank Dr. Nolan for all the help she gave me throughout the project. Literature Cited Hoff, F.H., and Snell, T.W Plankton Culture Manual. 5 th ed. Florida Aqua Farms, Inc., Dade City, FL. Moon-van der Staay, S.Y., Wachter, R.D., and Vaulot, D Oceanic 18S rDNA sequences from picoplankton reveal unsuspected eukaryotic diversity. Nature 409: Nybakken, J.W Marine Biology: An Ecological Approach. 5th ed. Benjamin Cummings, San Francisco, CA. Raven, J.A The twelfth Tansley lecture, Small is beautiful: The Picophytoplankton. Functional Ecology 12: Methods Filtration.3μm filter, vacuum pump Water Sample Collected Atlantic Ocean, Wallops Island, VA Temperature Recorded Phytoplankton Separation No Filtration Picophytoplankton Total Phytoplankton 45mL added to 50mL conical Treatment added 3 repetitions each <.3μm Control NO 3 Urea PO 4 Total Control Total w/ nutrients (NO 3, Urea, and PO 4 ) Incubation At recorded Ocean temperature, 24 hour light/dark cycle Fluorescence Measured Every 48 hours, Variable Fluorescence Fluorescence Heat Light 3.1. Light Fluorescence Photosynthesis Heat 2. Close reaction centers Light or DCMU (dichloromethylurea) Variable Fluorescence Results July AB Figure 3. The growth response of different phytoplankton size classes to nutrient enrichment over time as determined by (A) Fluorescence and (B) Variable Fluorescence in July (A). Phytoplankton concentrations were approximately at the limit of detection on the fluorometer. The percentage of chlorophyll expressed by the picophytoplankton size class was calculated as 6.4%. (B). The picophytoplankton, 3μm size class, population had a larger initial photochemical efficiency than the total phytoplankton population. April AB Figure 1. The growth response of different phytoplankton size classes to nutrient enrichment over time as determined by (A) Fluorescence and (B) Variable Fluorescence in April 2005 (A). Total with nutrients became significantly different than the Total Control 50 hours after nutrient addition. In the <3μm population the <3μm NO 3 became significantly different from the <3μm Control 338 hours after nutrient addition. The percentage of chlorophyll in picophytoplankton size class was calculated as 17.2%. (B). The total phytoplankton population had a higher initial photochemical efficiency compared to the <3μm population. The error bars represent one standard deviation of the mean. * * June A B Figure 2. The growth response of different phytoplankton size classes to nutrient enrichment over time as determined by (A) Fluorescence and (B) Variable Fluorescence in June (A). Total with nutrients became significantly different than the Total Control 48 hours after nutrient addition. In the <3μm population <3μm Urea became significantly different than the <3μm Control 48 hours after nutrient enrichment. The percentage of chlorophyll expressed by the picophytoplankton size class was determined to be 9.5%. (B). The photochemical efficiency was approximately the same for both the total and picophytoplankton population. * * Department of Biological Sciences, York College of Pennsylvania