Effects of elevated CO2 on phytoplankton community biomass and species composition during a spring Phaeocystis spp. bloom in the western English Channel

Abstract

A 21-year time series of phytoplankton community structure was analysed in relation to Phaeocystis spp. to elucidate its contribution to the annual carbon budget at station L4 in the western English Channel (WEC).Between 1993-2014 Phaeocystis spp. contributed $4.6% of the annual phytoplankton carbon and during the March À May spring bloom, the mean Phaeocystis spp. biomass constituted 17% with a maximal contribution of 47% in 2001. Upper maximal weekly values above the time series mean ranged from 63 to 82% of the total phytoplankton carbon ($42-137 mg carbon (C) m À3 ) with significant interannual variability in Phaeocystis spp. Maximal biomass usually occurred by the end of April, although in some cases as early as mid-April (2007) and as late as late May (2013).The effects of elevated pCO 2 on the Phaeocystis spp. spring bloom were investigated during a fifteenday semi-continuous microcosm experiment. The phytoplankton community biomass was estimated at $160 mg C m À3 and was dominated by nanophytoplankton (40%, excluding Phaeocystis spp.), Phaeocystis spp. (30%) and cryptophytes (12%). The smaller fraction of the community biomass comprised picophytoplankton (9%), coccolithophores (3%), Synechococcus (3%), dinoflagellates (1.5%), ciliates (1%) and diatoms (0.5%). Over the experimental period, total biomass increased significantly by 90% to $305 mg C m À3 in the high CO 2 treatment while the ambient pCO 2 control showed no net gains. Phaeocystis spp. exhibited the greatest response to the high CO 2 treatment, increasing by 330%, from $50 mg C m À3 to over 200 mg C m À3 and contributing $70% of the total biomass.Taken together, the results of our microcosm experiment and analysis of the time series suggest that a future high CO 2 scenario may favour dominance of Phaeocystis spp. during the spring bloom. This has significant implications for the formation of hypoxic zones and the alteration of food web structure including inhibitory feeding effects and lowered fecundity in many copepod species.Crown

Effects of elevated CO<sub>2</sub> and temperature on phytoplankton community biomass, species composition and photosynthesis during an experimentally induced autumn bloom in the western English Channel

“…A variable response in Phaeocystis spp. to elevated pCO 2 has also been reported with increased growth (Chen et al, 2014;Keys et al, 2017), no effect (Thoisen et al, 2015) and decreased growth (Hoogstraten et al, 2012) observed. Phaeocystis spp.…”

Northern High-Latitude Organic Soils As a Vital Source of River-Borne Dissolved Iron to the Ocean

“…Figure visualizes the steep increase of the oceanic sink for anthropogenic CO 2 (the anthropogenic CO 2 flux from the atmosphere to the ocean) for the period 1960–2018 . This remarkable increase (by a factor of approximately 3.5) suggests that marine phytoplankton may benefit from rising CO 2 levels, despite the widespread scarcity of iron and/or other nutrients in marine surface waters. , Recent studies have shown that phytoplankton may be more adaptable to the increasing atmospheric partial pressure of CO 2 (pCO 2 ) than previously thought, with the limitation that different species react differently. − In Subarctic and Arctic waters, prymnesiophytes (including coccolithophores) are negatively impacted, whereas small picoeukaryotes benefit from increasing pCO 2 . There is also evidence that diatoms, which play a key role in the biological carbon pump, show a statistically significant increase in growth rate in response to rising atmospheric CO 2 whereby larger diatom species tend to have a more pronounced growth rate enhancement in response to elevated CO 2 partial pressure than smaller ones. − Moreover, it has also been shown that increasing CO 2 levels improve cyanobacterial growth and increase cyanobacterial biomass …”