Short- and long-term conditioning of a temperate marine diatom community to acidification and warming

Abstract

Ocean acidification and greenhouse warming will interactively influence competitive success of key phytoplankton groups such as diatoms, but how long-term responses to global change will affect community structure is unknown. We incubated a mixed natural diatom community from coastal New Zealand waters in a short-term (two-week) incubation experiment using a factorial matrix of warming and/or elevated p CO 2 and measured effects on community structure. We then isolated the dominant diatoms in clonal cultures and conditioned them for 1 year under the same temperature and p CO 2 conditions from which they were isolated, in order to allow for extended selection or acclimation by these abiotic environmental change factors in the absence of interspecific interactions. These conditioned isolates were then recombined into ‘artificial’ communities modelled after the original natural assemblage and allowed to compete under conditions identical to those in the short-term natural community experiment. In general, the resulting structure of both the unconditioned natural community and conditioned ‘artificial’ community experiments was similar, despite differences such as the loss of two species in the latter. p CO 2 and temperature had both individual and interactive effects on community structure, but temperature was more influential, as warming significantly reduced species richness. In this case, our short-term manipulative experiment with a mixed natural assemblage spanning weeks served as a reasonable proxy to predict the effects of global change forcing on diatom community structure after the component species were conditioned in isolation over an extended timescale. Future studies will be required to assess whether or not this is also the case for other types of algal communities from other marine regimes.

Emiliania huxleyi increases calcification but not expression of calcification-related genes in long-term exposure to elevated temperature and p CO 2

“…Approximately after 500 generations, cells adapted to elevated pCO 2 exhibited as much as 50% higher calcification rate when compared with those adapted to ambient pCO 2 when grown under elevated pCO 2 . Thus, our results along with those from other longterm culture studies [17] underscore the necessity of longterm studies in order to accurately understand likely responses of coccolithophores to OA.…”

“…Regardless of outcome, these earlier studies tested the response of E. huxleyi to elevated pCO 2 in short-term experiments (less than 20 generations). This is potentially problematic, because organisms with short generation times and large population size, such as E. huxleyi, have high potential for acclimation and adaptation to natural environmental change [16,17], and adaptation to future ocean conditions might change calcification responses compared with short-term acclimation. A few studies have tested the evolutionary responses of E. huxleyi to elevated pCO 2 in long-term experiments (several hundreds of generations).…”

“…The response of coccolithophores to elevated pCO 2 must be considered in the context of other oceanic variables such as temperature [17,19,20], light availability and nutrient concentrations, all of which are expected to change in the future and hence could have interactive effects on E. huxleyi. While there have been tests of E. huxleyi responses to multiple variables [14,[21][22][23], only one study has tested the effect of multiple environmental factors in long-term experiments [24] and found a synergistic effect of pCO 2 and nitrogen source on carbon partitioning in E. huxleyi.…”

Long-term acclimation to elevated p CO 2 alters carbon metabolism and reduces growth in the Antarctic diatom Nitzschia lecointei

“…Species [51] and strain-specific [26,29] responses to elevated pCO 2 are surprisingly not occurring and this is probably related to the alga's carbon metabolism and CCM efficiency. In our study, carbon metabolism was altered both during the long-term exposure, and also during the switched treatment assay.…”

Ocean acidification and climate change: advances in ecology and evolution

“…Furthermore, even if organisms will be able to adapt to ocean acidification and warming, species-specific competitiveness might be modified. In the final paper of this issue, Tatters et al [66] study the competitiveness of natural diatom communities incubated under future environmental conditions for two weeks, after which the dominant species were isolated and then incubated again for over a year before recombining the now conditioned species to reconstruct the original community. Inter-specific competition was found to be similar in both the unconditioned natural and the conditioned artificial community, suggesting that for diatom communities, short-term manipulative experiments may be used to predict the effects of long-term environmental forcing on community structure.…”