Copper and light shape coastal picophytoplankton communities via their combined effects on growth limitation and toxicity

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 >6 nM, whereas Synechococcus showed a sharp toxicity threshold at >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 Prochlorococc..., 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 extr..., # 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...,