Patterns of diatom diversity correlate with dissolved trace metal concentrations and longitudinal position in the northeast Pacific coastal-offshore transition zone

Abstract

Diatoms are important primary producers in the northeast Pacific Ocean, with their productivity closely linked to pulses of trace elements in the western high nitrate, low chlorophyll (HNLC) region of the oceanographic time series transect 'Line P.' Recently, the coastal−HNLC transition zone of the Line P transect was identified as a hotspot of phytoplankton productivity, potentially controlled by a combination of trace element and macronutrient concentrations. Here we describe diatom community composition in the eastern Line P transect, including the coastal− HNLC transition zone, with a method using high-throughput sequencing of diatom 18S gene amplicons. We identified significant correlations between shifting diatom community composition and longitude combined with concentrations of dissolved copper and 2 other dissolved trace metals (dissolved Fe [dFe] and/or dissolved zinc) and/or a physical factor (salinity or density). None of these variables on its own was significantly correlated with shifts in community composition, and 3 of the factors (dFe, salinity, and density) correlated with one another. Longitude could incorporate multiple factors that may influence diatom communities, including distance from shore, proximity of sampling stations, and an integration of previous pulses of macro-and micro-nutrients. We also evaluated in situ Fe limitation of the diatom Thalassiosira oceanica using a quantitative reverse-transcription polymerase chain reaction method, and found biological evidence of Fe stress in samples from the coastal−HNLC transition zone. Combined, our results support a prior hypothesis that dissolved trace metals as well as longitudinal distance may be important to diatom diversity in the coastal−HNLC transition zone of the Line P transect.

Seasonal Variations in the Biodiversity, Ecological Strategy, and Specialization of Diatoms and Copepods in a Coastal System With Phaeocystis Blooms: The Key Role of Trait Trade-Offs

“…Moreover, copepods live much longer than diatom cells (several months/up to 1 year for copepods, but a few days for diatoms) and their traits enable them to survive in unfavorable conditions. Large unexplained variance (>50%), as we quantified in the VP analysis, is common in ecological studies (Brasil et al, 2020 and references therein) and is often the result of (i) unmeasured environmental drivers, such as trace metals (Chappell et al, 2019); and (ii) potential antagonistic responses among species within a community (Brasil et al, 2020). Brasil et al (2020) have also recently provided evidence that the assessment of biodiversity and FD is influenced by the presence/lack of rare species: rarity can contribute to large residuals when varpart models are computed.…”

Taxonomic and nutrient controls on phytoplankton iron quotas in the ocean

“…5b). Coastal species of both centric (e.g., Guinardia sp., Thalassiosira pacifica) and pennate (e.g., Pseudo-nitzschia pungens) diatoms were replaced by oceanic species (e.g., Thalassiosira oceanica and Pseudo-nitzschia granii, respectively) offshore (Chappell et al 2019) (Fig. 5d).…”

“…Given the relative dominance of Pseudo-nitzschia in the diatom community offshore (Fig. 5d) (Chappell et al 2019), the ability to acquire and/or store iron appears to provide members of this genus with a competitive advantage. These data demonstrate the biogeochemical impact of niche partitioning, with diverse phytoplankton groups having distinct iron strategies and using external iron sources differently, even as they occupy the same system.…”

Probing the Bioavailability of Dissolved Iron to Marine Eukaryotic Phytoplankton Using In Situ Single Cell Iron Quotas

“…Ocean phytoplankton were collected from the South Pacific (red), North Pacific (blue), coastal California current (green), and the North Atlantic (brown). Data are from(Buck et al, 2015(Buck et al, , 2018Chappell et al, 2019;Mellett et al, 2018;Twining et al, 2015aTwining et al, , 2015bTwining et al, , 2021. Laboratory phytoplankton data are from(Sunda & Huntsman, 1995).…”