Will krill fare well under Southern Ocean acidification?

So Kawaguchi Haruko Kurihara Robert King Lillian Hale Thomas Berli James P. Robinson Akio Ishida Masahide Wakita Patti Virtue Stephen Nicol Atsushi Ishimatsu Articles on similar topics can be found in the following collections Receive free email alerts when new articles cite this article - sign up in the box at the top right-hand corner of the article or click here References Subject collections Email alerting service To subscribe to Biol. Lett. go to: http://rsbl.royalsocietypublishing.org/subscriptions Biol. Lett. (2011) 7, 288291 doi:10.1098/rsbl.2010.0777 Published online 13 October 2010 Global change biology Will krill fare well under Southern Ocean acidification? So Kawaguchi1,2,*, Haruko Kurihara3, Robert King1, Lillian Hale4, Thomas Berli4, James P. Robinson4, Akio Ishida5, Masahide Wakita5,6, Patti Virtue4, Stephen Nicol1,2 and Atsushi Ishimatsu7 1Australian Antarctic Division, Kingston, Tasmania 7050, Australia 2Antarctic Climate and Ecosystems Cooperative Research Centre, Sandy Bay, Hobart, Tasmania 7001, Australia 3University of the Ryukyus, Okinawa 903-0213, Japan 4University of Tasmania, Sandy Bay, Tasmania 7005, Australia 5Research Institute for Global Change, JAMSTEC, Yokosuka 237-0061, Japan 6Mutsu Institute for Oceanography, JAMSTEC, Mutsu 035-0022, Japan 7Nagasaki University, Nagasaki 851-2213, Japan *Author for correspondence (). Antarctic krill embryos and larvae were experimentally exposed to 380 (control), 1000 and 2000 matm pCO2 in order to assess the possible impact of ocean acidification on early development of krill. No significant effects were detected on embryonic development or larval behaviour at 1000 matm pCO2; however, at 2000 matm pCO2 development was disrupted before gastrulation in 90 per cent of embryos, and no larvae hatched successfully. Our model projections demonstrated that Southern Ocean sea water pCO2 could rise up to 1400 matm in krills depth range under the IPCC IS92a scenario by the year 2100 (atmospheric pCO2 788 matm). These results point out the urgent need for understanding the pCO2-response relationship for krill developmental and later stages, in order to predict the possible fate of this key species in the Southern Ocean. 1. INTRODUCTION The ecosystems of the Southern Ocean are expected to be most severely affected by ocean acidification (OA) because of the higher solubilities of CO2 and CaCO3 in cold waters and because of regional upwelling of hypercapnic deep sea water [1,2]. Moreover, a future rise in surface water pCO2 may be augmented at great depths [3], where sea water pCO2 is already much higher than at the surface ([4]; figure 1). Hence, vertically migrating animals in the Southern Ocean will probably experience the most drastic changes in carbonate chemistry in future oceans. However, OA research has mainly dealt with tropical and temperate shallow-water calcifying organisms [1], and little attention has been paid to polar species [5]. Electronic supplementary material is available at http://dx.doi.org/ 10.1098/rsbl.2010.0777 or via http://rsbl.royalsocietypublishing.org. Antarctic krill (Euphausia superba, hereafter krill) is the key species of the Southern Ocean ecosystem, and is found in a range of water depths. Krill spawn eggs at the surface which sink to 700 1000 m before larvae hatch to swim back to the surface [6]. The post-larval vertical distribution ranges from the surface to at least 3500 m ([7]; figure 1). Thus, krill are already exposed to high CO2 conditions at depth, which will probably become far more hypercapnic than surface waters (electronic supplementary material, S1). The purpose of this study is to examine how elevated CO2 conditions affect krill. We focused on early developmental stages, since larvae and juveniles are generally more vulnerable to environmental perturbations, and their survival will largely determine population abundance, distribution and community structure [8]. 2. MATERIAL AND METHODS The stock population of krill was collected from the Indian Ocean sector of the Southern Ocean between January and March in the 20052006 field season [9]. The krill were maintained in the Australian Antarctic Divisions marine research aquarium, where they matured and spawned naturally [10]. (a) Experimental set-up Experimental sea water was supplied from a 70 l header tank and equilibrated with air (control) or CO2-enriched air before being delivered to experimental jars (250 ml clear polycarbonate) containing krill eggs (see electronic supplementary material, S2). The CO2-enriched air was prepared with a mass flow controller (Horiba STEC SEC-E-40) and by an air valve, to regulate flow rates of pure CO2 and atmospheric air, respectively. The pCO2 levels of the CO2-enriched air and sea water were monitored by a CO2 monitor (Telaire 7001) and indirectly from pH measurement (Radiometer PHM 210 pH metre), respectively. Experimental temperature was set at 0.58C. Effluent from each jar was drained into a 70 l sump, and recirculated through a degassing unit before returning back to the header tank via a filtration and cooling system. For details, see Kawaguchi et al. [10]. Total alkalinity was measured through a two-stage, potentiometric, open-cell titration. The carbonate chemistry of the experimental sea water is summarized in the electronic supplementary material, S3. (b) Hatching experiment Fertilized eggs were obtained in January 2008 and 2009. In the 2008 experiments, three batches of eggs originating from three different females were used. Each batch was randomly distributed into experimental jars, with approximately 2030 eggs per jar. The embryos were incubated at one of the three target CO2 levels: control (380 matm), medium (1000 matm) or high (2000 matm). In the 2009 experiments, four batches of eggs were incubated as in 2008. Hatch rates were determined for each jar after 710 days of spawning. The number of jars in each treatment is summarized in table 1. Embryonic stages were classified at the end of each 2009 experiment after George [11]. (c) Observation of larval swimming activity Three of the four batches in the hatching experiments in 2009 (S2, W2 and Y2) were used for this observation. R2 was not used because of the limited capacity of the set-up. CO2 exposure started within 1 day of spawning and continued throughout the experimental period. Larval behaviour was observed on an average of 3 days after hatching, when they were in the nauplius stage. Since almost no eggs hatched in 2000 matm (table 1), observations were made only for the 380 and 1000 matm groups. (d) Statistical tests Statistical tests were performed using SPLUS v. 8 software. 3. RESULTS The hatch rates of control eggs used in our experiment were highly variable (16.7 74.7%, table 1) but the range is in fact comparable to the rates in field experiments (0 89% [12,13]). There were significant Krill under ocean acidification S. Kawaguchi et al. 289 aNumber of replicates. ) m ( th 2000 p e (...truncated)