Effects of acute ocean acidification on spatially-diverse polar pelagic foodwebs: Insights from on-deck microcosms

Abstract

The polar oceans are experiencing some of the largest levels of ocean acidification (OA) resulting from the uptake of anthropogenic carbon dioxide (CO 2 ). Our understanding of the impacts this is having on polar marine communities is mainly derived from studies of single species in laboratory conditions, while the consequences for food web interactions remain largely unknown. This study carried out experimental manipulations of natural pelagic communities at different high latitude sites in both the northern (Nordic Seas) and southern hemispheres (Scotia and Weddell Seas). The aim of this study was to identify more generic responses and greater experimental reproducibility through implementing a series of short term (4 day), multilevel (3 treatment) carbonate chemistry manipulation experiments on unfiltered natural surface ocean communities, including grazing copepods. The experiments were successfully executed at six different sites, covering a diverse range of environmental conditions and differing plankton community compositions. The study identified the interaction between copepods and dinoflagellate cell abundance to be significantly altered by elevated levels of dissolved CO 2 (pCO 2 ), with dinoflagellates decreasing relative to ambient conditions across all six experiments. A similar pattern was not observed in any other major 2 phytoplankton group. The patterns indicate that copepods show a stronger preference for dinoflagellates when in elevated pCO 2 conditions, demonstrating that changes in food quality and altered grazing selectivity may be a major consequence of ocean acidification. The study also found that transparent exopolymeric particles (TEP) generally increased when pCO 2 levels were elevated, but the response was dependent on the exact set of environmental conditions. Bacteria and nannoplankton showed a neutral response to elevated pCO 2 and there was no significant relationship between changes in bacterial or nannoplankton abundance and that of TEP concentrations. Overall, the study illustrated that, although some similar responses exist, these contrasting high latitude surface ocean communities are likely to show different responses to the onset of elevated pCO 2 .

Geographical CO2 sensitivity of phytoplankton correlates with ocean buffer capacity

“…The first cruise (D366) took place in northwest European shelf seas during summer on the RRS Discovery (2011 June 6-July 12) (Richier et al, 2014). Two subsequent cruises (JR271 and JR274 respectively) were carried out in the Arctic (2012 June 1-July 2) (Poulton et al, 2016) and Southern (2013 January 9-February 12) (Tarling et al, 2016) oceans, both on board the RRS James Clark Ross. Locations, oceanographic settings, and treatments applied within each experiment are presented in Tables 1 and 2. Specific cleaning and handling techniques were followed during setup of each of the experiments.…”

Oceanography and Marine Biology

“…Other Antarctic pelagic species investigated include copepods (Bailey et al 2016), where acidification had little or no effect on development of early life stages, and krill where Kawaguchi et al (2011) found no effect on embryos and larvae of elevating CO 2 to 1000 µatm but found negative impacts at 2000 µatm. In a microcosm-based community-level study, Tarling et al (2016) showed that exposure to pCO 2 levels of 750 and 1000 µatm altered the community balance, and the interaction between copepods and their dinoflagellate prey was particularly affected. It should be noted that all of the pelagic experimental studies, because of restrictions to shipboard experiments, have been short-term, often with large changes to levels of pCO 2 in the system to values beyond those predicted for the year 2100, and as seen for benthic species, increasing the duration of exposure significantly alters the outcomes of experimental trials.…”

Status, Change, and Futures of Zooplankton in the Southern Ocean

“…This plasticity is demonstrated by the high levels of variability in krill's association with and apparent dependence on sea ice (Meyer et al, 2017) and by rapid acclimation of individuals to the effects of reduced pH (Saba et al, 2021). Adults are able to survive long periods without food using a combination of lipid reserves and reductions in body size (Quetin et al, 1994;Tarling et al, 2016b). Krill have successfully colonized a range of habitats from the ocean surface to abyssal depths, and from continental ice shelves to the APF (Atkinson et al, 2008).…”

“…Effects from the gradual increase in OA are hard to determine experimentally, but in an acute response microcosm experiment, Tarling et al (2016b) found that copepods show a stronger preference for dinoflagellates when in elevated pCO 2 conditions, demonstrating that changes in food quality and altered grazing selectivity may be a major consequence of OA (Tarling et al, 2016b).…”