Southern Ocean Acidification: potential effect on the

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Research of OA on corals has expanded widely over the last years (Roberts et al. 2006; Ries et al. 2009; Thresher et al. 2011; Movilla et al. 2012; 2014a; 2014b;.

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Southern Ocean Acidification: potential effect on the Antarctic coral Malacobelemnon daytoni Sevetto Natalia Supervisor: Sahade Ricardo

Summary: Ocean acidification is recognized threat to marine ecosystems. High latitude regions are predicted to be particularly affected, this is of concern for organisms utilizing calcium carbonate to generate shells or skeleton, among them, the Antarctic coral Malacobelemnon daytoni. Overview: The ocean is `sinks’ for the excess atmospheric CO2 produced by burning of fossil fuels, deforestation, etc. Approximately one-third of the anthropogenic CO2 produced in the past 200 years has been taken up by the oceans (Sabine et al. 2004). This excess CO2 dissolves in the ocean surface causing increased hydrogen ions and decreased concentrations of carbonate ions (CO3-2). The result is a decrease in ocean pH and the saturation state of calcium carbonate (CaCO3), called Ocean Acidification (OA). Through this process, the pH has decreased 0. 1 pH relative to pre-industrial level sand it is expected that this decrease will reach 0.3–0.4 units by the end of the century (Orr 2011). Taxonomic groups considered most susceptible to acidification are organisms that use CaCO3 to build their shells or skeletons this is due to the reduction in the availability of CO3-2 ions needed for precipitation of CaCO3 (Fabry et al. 2008). Nevertheless, the ecological consequences for marine life are difficult to predict. Research of OA on corals has expanded widely over the last years (Roberts et al. 2006; Ries et al. 2009; Thresher et al. 2011; Movilla et al. 2012; 2014a; 2014b; Jantzen et al. 2013; Fillinger et al. 2014). However, although it is considered a global effect is likely that its severity will vary locally (Turley et al. 2010). For instance, the Southern Ocean (and deep-water ecosystems) are where most rapid rates of change is expected due to the low water temperatures and therefore higher solubility of CaCO3, besides being the levels of CO3-2 lower than in temperate regions, may be the first to be exposed to under-saturated conditions (McNeil et al. 2008). However, studies of the potential effects on octocorals at high latitudes are very limited. In Potter Cove in the last years there has been a marked change in the structure of benthic communities, which is characterized by the increase in the distribution and

abundance of the sea pen Malacobelemnon daytoni (Octocoralia, Pennatulacea, Kophobelemnidae) (Fig. 1) (Sahade et al. 1998; Sahade et al. 2015). This is striking because is the first recorded case where this species is dominant and its dominance include highly ice impact zones, this could be explained by a high population turn-over and high growths rates. In this context it will be extremely interesting to study M. daytoni in order to increase the basic knowledge of the species and predict the effect in the population that could be caused by the change in the pH values expected in the coming decades (according to data from IPCC-IS92a). In this work we propose to study the effect of acidification on the ecosystem of Potter Cove (Antarctica) using the sea-pen M. daytoni as a model. The specific objectives include i) analyze the effect of different pH values on the metabolism of M. daytoni, via measurement of enzymatic activities (catalase, superoxide dismutase, etc); ii) get transcriptome-sequencing in M. daytoni and analyze the effects of different pH values, via measurement of gene expression (heat shock proteins-HSP70, alphacarbonic anhydrase, mannose-binding C-type lecithi, etc.), and iii) compare these results with those observed in other cold water corals (CWCs). By examining this range of interlinked variables we will be able to build a more comprehensive picture of the likely effect of OA on the populations of this Antarctic sea pen. Experimental design The experimental part was performed in the station Carlini (South Shetland Islands, Antarctica) (62 º 14'S, 58 ° 40'W) where the Argentine-German Dallmann laboratory is located. Samples of M. daytoni were randomly distributed in six aquaria subjected to two pH treatment (3 replicates per treatment with 4 or 5 colonies each replicate) (Fig. 2). Control was kept at pH of 8. 04, used as control conditions directly from the Cove (approximately 380 ppm CO2), while treatment 1 consisted of a pH of 7. 8 simulating the Antarctic seawater in future levels (Orr et al. 2005). In order to achieve the desired pH levels, seawater was bubbled with CO2 (approximately 800 ppm CO2in acidification treatment). Seawater pH was continuously monitored by glass electrodes connected to a pH controller (multi channel controler; Consort R305). The glass electrodes were calibrated daily with a Tris buffer. In addition, small volumes of water were taken periodically to analyze total alkalinity (TA). Water in each aquarium was mixed with a pump and a plastic wrap was used to reduce evaporation and surface-air gas exchange. The pH manipulative experimental set-up was installed inside a temperature-controlled room, ensuring constant values during the whole experiment.

Fig. 1: (A) External morphology of Malacobelemnon daytoni. (B y C) Tips of colonies showing mature autozooid (arrow). (D y E) Lower rachis and peduncle, showing autozooids (arrow) in D and siphonozooids (arrow) in E (Image from Servetto et al. 2013).

M. daytoni colonies were sampled in T0 directly from Potter Cove, Ti: after 3 days, T54 after 54 days. During each sampling events colonies were cut in 3 peaces and kept on eppendorfs: one for organic material determination, another for enzimatic studies, both of these were stored at -80 ºC, and the last one in RNAlater for gene expression analyses with the collaboration of Dr. Raul Bettencourt of the Universidade dos Açores

(DOP). Axial rods were dried at room temperature. Samples for transcriptome were also obtained.

Fig. 2: Experimental setup used to control and modify the seawater pH in each aquarium. 4) and 5) large ~100 L tanks for seawater conditioning at pH ~7.8 and ~8.04, respectively; 2) glass electrodes for pH and PT100 probes for temperature measurements; 1) pH controller and data logger; 3) CO2 bottle; 6) and 7) low pH experimental and control aquarium, respectively (three replicates per treatment) (Figure adapted from Movilla el al. 2012).

Outcomes In this study, the response of M. daytoni to OA will be analyzed. This will be performed in terms of gene expression, signals in calcifying structures and in the metabolism of sea pen colonies. The study of M. daytoni is important to improve current understanding of the Potter Cove benthic communities dynamics. Since it is one of the dominant species in this area and it is likely to be affected by the OA process predicted (Cumming et al. 2011).

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