DOI: 10.5061/dryad.3r2280gv8
title: Copper and light shape coastal picophytoplankton communities via their combined effects on growth limitation and toxicity

description: Copper (Cu) and light are two resources that can limit phytoplankton
 growth at very low (deficiency) or very high (toxicity) levels. In this
 study, Cu and light interactive effects on picophytoplankton growth and
 community composition southern California were assessed during four bottle
 incubation experiments using a 7x7 matrix of overlapping Cu and light
 gradients. Consistent with prior knowledge, sensitivity to Cu in the two
 September experiments was greatest in Prochlorococcus, followed by
 Synechococcus, and then picoeukaryotes. Prochlorococcus abundance declined
 gradually with Cu additions &gt;6 nM, whereas Synechococcus showed a
 sharp toxicity threshold at &gt;10 nM added Cu. Synergistic effects
 between Cu and light exacerbated toxicity in both taxa, suggesting that
 shared stress response pathways become saturated and less effective when
 Cu and light are both high. An unexpected increase in ambient seawater Cu
 concentration prior to the two October experiments brought Prochlorococcus
 and Synechococcus close to their toxicity thresholds, potentiating their
 apparent sensitivity to light and leading to steeper population declines
 in the experiments. Addition of 10 mM nitrate at the start of one of the
 experiments did not rescue the populations from toxicity, suggesting that
 relief of N limitation did not allow for greater acclimation via de novo
 stress response enzyme synthesis. Across all experiments, picoeukaryotes
 were more resilient to high light and Cu, allowing them to persist or
 increase under conditions that limited Prochlorococcus and Synechococcus.
 This robustness combined with relief from competition for other resources
 (possibly phosphate) upon decline of the other two taxa, ultimately led
 picoeukaryotes to dominate the communities despite having very low
 baseline relative abundances. Selection for different Synechococcus clades
 and picoeukaryote species likely permitted each of these populations to
 thrive over a broader range of Cu and light combinations than would be
 possible for less biodiverse populations.
description: Trace metal concentrations (including Al, Cd, Co, Cu, Fe, Mn, Ni,
 Pb, V, and Zn) were determined on 0.22 micrometer filtered samples by
 inductively coupled plasma mass spectrometer (ICP-MS). The method’s LOQs
 were the following: dAl = 0.30 nM, dCd= 0.03 nM, dCo= 0.12 nM, dCu= 0.82
 nM, dFe= 3.35 nM, dMn= 0.08 nM, dNi=0.23 nM, dPb= 0.03 nM, dV= 0.34 nM,
 dZn=1.39 nM. Picophytoplankton were enumerated by flow
 cytometry at the Center for Aquatic Cytometry, Bigelow Laboratory for
 Ocean Sciences on a Bio-Rad ZE5 with 405 nm, 488 nm, and 640 nm lasers
 activated following standard methods (Poulton and Martin. 2010. Imaging
 flow cytometry for quantitative phytoplankton analysis — FlowCAM. In:
 Intergovernmental Oceanographic Commission of ©UNESCO. Karlson, Cusack,
 and Bresnan (editors). Microscopic and molecular methods for quantitative
 phytoplankton analysis. UNESCO. (IOC Manuals and Guides, no. 55.), 110
 pages.) Chlorophyll a was determined from cells
 filtered from 100mL of sample water and extracted in 5mL 90% acetone in
 the dark for 24h at -20<sup>o</sup>C. Extracted chlorophyll
 was measured fluorometrically using the Turner Trilogy non-acidified
 chlorophyll filter module (excitation 436/10nm, emission
 685/10nm).
description: # Copper and light shape coastal picophytoplankton communities via their
 combined effects on growth limitation and toxicity Dataset DOI:
 [10.5061/dryad.3r2280gv8](10.5061/dryad.3r2280gv8) ## Description of the
 data and file structure * The experiments in this study were designed to
 probe the responses picophytoplankton to overlapping Cu and light levels
 in the dynamic California Current ecosystem where trace metals are likely
 to play a role in shaping community structure and abundance. We targeted
 the late summer picophytoplankton community because of its relatively
 simple structure, comprising three groups that have well-characterized
 adaptations for trace metal use and tolerance. Our goal was to determine
 the extent to which the combined effects of Cu and light influence
 competition and acclimation potential among the three groups. We
 hypothesized that differences in Cu nutritional requirements and toxicity
 thresholds would be the main factor to influence community composition,
 and that the effects of Cu would be enhanced synergistically by light. We
 further hypothesized that acclimation to high Cu and light, such as via de
 novo synthesis of enzymes for oxidative stress, would be stimulated
 following relief of N limitation. - This dataset contains biological and
 chemical data from bottle manipulation experiments in the Southern
 California Bight off of Newport Beach (33.5649oN, -117.9567oE) in 2020. *
 Four incubation experiments were conducted Experiment A used surface
 seawater collected on September 1, 2020, B used water from 30m collected
 on September 1, 2020, C used surface seawater collected on October 22,
 2020, and D used surface seawater collected on October 22, 2020with 10
 micomolar added Na NO3. - For each experiment, forty-nine bottles were
 prepared in a 7x7 matrix of copper sulphate with equimolar sodium EDTA (0,
 0.6, 1, 6, 10, and 60nM Cu’ above background) and light (14, 16, 26, 37,
 62, and 84% of the ambient natural sunlight levels). Bottles were
 incubated for two days. - Four baseline samples were also collected for
 each experiment. These had IDs A50, A51, A52, A53, B150, B151, B152, B153,
 C50, C51, C52, C53, D150, D151, D152, and D153. * Multiple linear
 regression was used to analyze the datasets, and showed that the combined
 effects of copper and light influenced the community composition of
 picophytoplankton. Prochlorococcus was the most sensitive to copper,
 followed by Synechococcus, then picoeukaryotes. Synergistic effects with
 light were observed in two of the four experiments. ### Files and
 variables - Sample_ID.xlsx The column headers in the file are: * ID *
 Added copper concentration (nM) * Light treatment (% of ambient) -
 Chlorophyll.xlsx The column headers in the file are: * ID * Chlorophyll a
 concentration (micrograms L-1) - Flow_Cytometry.xlsx The column headers in
 the file are: * Sample ID * Picoeukaryote Concentration (cell mL-1) *
 Synechococcus Concentration (cell mL-1) * Prochlorococcus Concentration
 (cell mL-1) * Flag - Trace_Metals.xlsx The column headers in the file are:
 * Sample IDs * Cd (nM) * Pb (nM) * Fe (nM) * Ni (nM) * Cu (nM) * Zn (nM) *
 Mn (nM) * Co (nM) * Al (nM) * Ti (nM) * V (nM) - The file “Sample
 IDs.xlxs” shows the treatment identification codes for the experiment.
 These IDs are used in the remaining files. - Samples below the limit of
 quantitation are annotated with the flag “LOQ” for all of the files. - For
 some of the flow cytometry samples, Prochlorococcus counts were low due to
 reduced autofluorescence from stress caused by the experimental treatments
 (as expected in a toxicity experiment). Typically, &gt;200 cell or
 particle count is required for statistical accuracy, but given that
 toxicity was expected, these low values are included in the dataset.
 Samples falling into this category are noted with an asterisk (*) in the
 “Flag” column. Outliers &gt;2x standard deviation are flagged with two
 asterisk (**) in the “Flag” column and were omitted from further analysis.
 ## Code/software No specialized software is needed to view the dataset.
 All files are in .xlsx format. ## Access information Data was derived from
 the following sources: * This study used CMEMS Level 4, 0.125 degree SLA
 and geostrophic velocity gridded global ocean dataset, version 008_047
 ([https://doi.org/10.48670/moi-00148](https://doi.org/10.48670/moi-00148)). The OceanParcels v. 3.0.4 Python package was used to conduct Lagrangian particle simulations44 (Delandmeter and Ven Sebille, 2019).