David W. Crawford
University of Victoria
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Featured researches published by David W. Crawford.
Journal of Phycology | 2011
Diana E. Varela; Valeria Willers; David W. Crawford
We investigated the effect of Zn availability on growth rate (μ), cell morphology, and elemental stoichiometry and incorporation rate in two marine diatoms. For the coastal diatom Skeletonema costatum (Grev.) Cleve, the half‐saturation constant (KS) for growth was 4.1 pM Zn2+, and growth ceased at ≤ 2.6 pM Zn2+, whereas for the oceanic diatom Thalassiosira oceanica Hasle, KS was 0.5 pM Zn2+, and μ remained at ∼40%μmax even at 0.3 pM Zn2+. Under Zn‐limiting (Zn‐L) conditions, S. costatum decreased cell size significantly, leading to an 80% increase in surface area to volume ratio (SA/V) at Zn2+ of 3.5 pM compared to Zn‐replete (Zn‐R) conditions (at Zn2+ of 13.2 pM), whereas T. oceanica’s morphology did not change appreciably. Cell quotas of C, N, P, Si, and chl a significantly decreased under Zn limitation in S. costatum (at Zn2+ of 3.5 pM), whereas Zn limitation in T. oceanica (at Zn2+ of 0.3 pM) had little effect on quotas. Elemental stoichiometry was ∼85C:10N:9Si:1P and 81C:9N:5Si:1P for S. costatum, and 66C:5N:2Si:1P and 52C:6N:2Si:1P for T. oceanica, under Zn‐R and Zn‐L conditions, respectively. Incorporation rates of all elements were significantly reduced under Zn limitation for both diatoms, but particularly for Si in S. costatum, and for C in T. oceanica, despite its apparent tolerance of low Zn conditions. With [Zn2+] in some parts of the ocean being of the same order (∼0.2 to 2 pM) as our low Zn conditions for T. oceanica, our results support the hypothesis that in situ growth and C acquisition may be limited by Zn in some oceanic species.
Global Biogeochemical Cycles | 2015
David W. Crawford; Shea N. Wyatt; Ian A. Wrohan; Adrián O. Cefarelli; Karina E. Giesbrecht; Brianne Kelly; Diana E. Varela
During the Canada Three Oceans and Joint Ocean Ice Study projects in the summers of 2007 and 2008, we measured particulate organic carbon to nitrogen ratios (POC:PON) throughout the euphotic zone in subarctic and arctic waters. Depth-integrated values averaged 2.65 (±0.19) in the Beaufort Sea and Canada Basin (BS-CB domain), and were much lower than both the Redfield ratio (6.6) and the average ratios (3.9 to 5.6) measured across other arctic-subarctic domains. Average uptake ratios of C and N (ρC:ρN) were also lower (0.87±0.14) in BS-CB than in the other four domains (2.10 to 3.51). Decreasing POC:PON ratios were associated with low concentrations of phytoplankton C, reduced abundance of biogenic silica (bSiO2), a smaller relative contribution of the >5 µm fraction to total chlorophyll a and a larger relative contribution of small flagellates (<8 µm) to phytoplankton C. In the subsurface chlorophyll a maximum (SCM) within the BS-CB domain, phytoplankton C represented only ~13% of POC, and therefore low POC:PON may be influenced by the presence of heterotrophic microbes. These ratios are supported by data obtained during other arctic programs in 2006, 2008 and 2009. Previous work has suggested a link between freshening of surface waters and increasing dominance of picophytoplankton and bacterioplankton in the Canada Basin, and the low POC:PON ratios measured during this study may be a consequence of this shift. Our results have ramifications for the conversion between C- and N-based estimates of primary productivity, and for biogeochemical modeling of marine arctic waters.
Marine Ecology Progress Series | 1989
David W. Crawford
Journal of Geophysical Research | 2013
Diana E. Varela; David W. Crawford; Ian A. Wrohan; Shea N. Wyatt; Eddy C. Carmack
Marine Ecology Progress Series | 2011
Tawnya D. Peterson; David W. Crawford; Paul J. Harrison
Progress in Oceanography | 2007
Michael S. Lipsen; David W. Crawford; James F. R. Gower; Paul J. Harrison
Journal of Geophysical Research | 2013
Shea N. Wyatt; David W. Crawford; Ian A. Wrohan; Diana E. Varela
Deep-sea Research Part I-oceanographic Research Papers | 2011
Tawnya D. Peterson; David W. Crawford; Paul J. Harrison
Progress in Oceanography | 2018
David W. Crawford; Adrián O. Cefarelli; Ian A. Wrohan; Shea N. Wyatt; Diana E. Varela
Journal of Geophysical Research | 2013
Diana E. Varela; David W. Crawford; Ian A. Wrohan; Shea N. Wyatt; Eddy C. Carmack