Impact of climate change on Antarctic krill

Antarctic krill Euphausia superba (hereafter ‘krill’) occur in regions undergoing rapid environmental change, particularly loss of winter sea ice. During recent years, harvesting of krill has increased, possibly enhancing stress on krill and Antarctic ecosystems. Here we review the overall impact of climate change on krill and Antarctic ecosystems, discuss implications for an ecosystem-based fisheries management approach and identify critical knowledge gaps. Sea ice decline, ocean warming and other environmental stressors act in concert to modify the abundance, distribution and life cycle of krill. Although some of these changes can have positive effects on krill, their cumulative impact is most likely negative. Recruitment, driven largely by the winter survival of larval krill, is probably the population parameter most susceptible to climate change. Predicting changes to krill populations is urgent, because they will seriously impact Antarctic ecosystems. Such predictions, however, are complicated by an intense inter-annual variability in recruitment success and krill abundance. To improve the responsiveness of the ecosystem-based management approach adopted by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), critical knowledge gaps need to be filled. In addition to a better understanding of the factors influencing recruitment, management will require a better understanding of the resilience and the genetic plasticity of krill life stages, and a quantitative understanding of under-ice and benthic habitat use. Current precautionary management measures of CCAMLR should be maintained until a better understanding of these processes has been achieved.

Effect of increased pCO2 on bacterial assemblage shifts in response to glucose addition in Fram Strait seawater mesocosms

Ocean acidification may stimulate primary production through increased availability of inorganic carbon in the photic zone, which may in turn change the biogenic flux of dissolved organic carbon (DOC) and the growth potential of heterotrophic bacteria. In order to investigate the effects of ocean acidification on marine bacterial assemblages, a two-by-three factorial mescosom experiment was conducted using surface seawater from the East Greenland Current in Fram Strait. Pyrosequencing of the V1-V2 region of bacterial 16S ribosomal RNA genes was used to investigate differences in the endpoint (Day 9) composition of bacterial assemblages in mineral nutrient-replete mesocosms amended with glucose (0 μM, 5.3 μM and 15.9 μM) under ambient (250 μatm) or acidified (400 μatm) partial pressures of CO₂ (pCO₂). All mesocosms showed low richness and evenness by Chao1-estimator and Shannon-Wiener diversity index, respectively, with general dominance by Gammaproteobacteria and Flavobacteria. Non-metric multidimensional scaling analysis and two-way analysis of variance of the Jaccard dissimilarity matrix (97% similarity cut-off) demonstrated that the significant community shift between 0 μM to 15.9 μM glucose addition at 250 μatm pCO₂ was eliminated at 400 μatm pCO₂. These results suggest that the response potential of marine bacteria to DOC input may be altered under acidified conditions.

Measuring gross and net calcification of a reef coral under ocean acidification conditions: methodological considerations

Ongoing ocean acidification (OA) is rapidly altering carbonate chemistry in the oceans. The projected changes will likely have deleterious consequences for coral reefs by negatively affecting their growth. Nonetheless, diverse responses of reef-building corals calcification to OA hinder our ability to decipher reef susceptibility to elevated pCO₂. Some of the inconsistencies between studies originate in measuring net calcification (NC), which does not always consider the proportions of the “real” (gross) calcification (GC) and gross dissolution in the observed response. Here we show that microcolonies of Stylophora pistillata (entirely covered by tissue), incubated under normal (8.2) and reduced (7.6) pH conditions for 16 months, survived and added new skeletal CaCO₃, despite low (1.25) Ω_arg conditions. Moreover, corals maintained their NC and GC rates under reduced (7.6) pH conditions and displayed positive NC rates at the low-end (7.3) pH treatment while bare coral skeleton underwent marked dissolution. Our findings suggest that S. pistillata may fall into the “low sensitivity” group with respect to OA and that their overlying tissue may be a key determinant in setting their tolerance to reduced pH by limiting dissolution and allowing them to calcify. This study is the first to measure GC and NC rates for a tropical scleractinian corals under OA conditions. We provide a detailed, realistic assessment of the problematic nature of previously accepted methods for measuring calcification (total alkalinity and ⁴⁵Ca).

Federal plan on ocean acidification is important first step to save sea life

SAN FRANCISCO— The National Oceanic and Atmospheric Administration today announced the first steps of a national strategy to protect sea life from ocean acidification. The draft plan is intended to guide federal research and monitoring on ocean acidification, and ultimately lead to the development of adaptation and mitigation strategies.

“This plan is a good first step toward addressing the tragedy unfolding in our oceans,” said Emily Jeffers, a staff attorney with the Center for Biological Diversity’s oceans program, which recently called on President Barack Obama to develop a national action plan for ocean acidification. “But if we’re going to save sea life from ocean acidification, we need to move quickly on big, bold steps that dramatically reduce carbon pollution.”

Every day, the world’s oceans absorb 22 million tons of carbon dioxide pollution from cars, factories and power plants. The oceans have become about 30 percent more acidic since the Industrial Revolution as a result of a chemical change in seawater that happens when ocean waters absorb CO2 pollution. This rate of change in ocean chemistry has no precedent in geologic time; the last time seawater was so acidic, about 55 million years ago, there were massive species extinctions.

Ocean acidification makes it hard for animals like corals and oysters to grow and survive. It also erodes the shells of tiny plankton that form the basis of the marine food web, which will likely result in large-scale problems up the food chain for sea stars, salmon, sea otters, whales and ultimately people, many of whom rely on seafood to survive.

“We need to take immediate action to address ocean acidification or the impacts will be catastrophic,” said Jeffers. “We need a bold national action plan to ensure a future for our sea life.”

In 2009 the Center for Biological Diversity sued the EPA for failing to address the impacts of ocean acidification in the state of Washington. As a result of a settlement, EPA acknowledged that ocean acidification is a water pollution problem that can and should be addressed by the Clean Water Act. In April of this year, the Center launched a campaign calling on President Obama and the EPA to develop a national plan to protect the oceans from acidification.

Read more about our Endangered Oceans campaign, read our FAQ about ocean acidification and see profiles of affected wildlife and U.S. regions.

Contact: Emily Jeffers, (415) 632-5309 or ejeffers@biologicaldiversity.org

Center for Biological Diversity, 11 July 2012. Press release.