Altered Oceanic pH Impairs Mating Propensity in a Pipefish Josefin Sundin*, Gunilla Rosenqvist†,‡ & Anders Berglund* * Department of Ecology and Genetics/Animal Ecology, Uppsala, Sweden † Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway ‡ Department of Biology, Gotland University College, Visby, Sweden Correspondence Josefin Sundin, Department of Ecology and Genetics/Animal Ecology, Norbyv€ agen 18 D, SE-752 36 Uppsala, Sweden. E-mail: josefin.sundin@ebc.uu.se Received: July 11, 2012 Initial acceptance: September 5, 2012 Final acceptance: November 1, 2012 (M. Herberstein) doi: 10.1111/eth.12039 Abstract Anthropogenic disturbance is currently altering the environment of terrestrial as well as aquatic organisms. Those changes affect a variety of animal behaviours, which in turn may cause changes in species interactions, population dynamics and evolutionary processes. In marine ecosystems, nutrient enrichment may elevate pH, while it is reduced by carbon diox- ide-induced ocean acidification. These two processes are not expected to balance one another but rather to affect the environment at different times and scales. We here show experimentally that an increase in water pH has a negative effect on mating propensity in the broad-nosed pipefish Syngnathus typhle, whereas lowered pH did not elicit the same detrimental effect. This study provides, to our knowledge, the first evidence that mating propensity is impaired by an increase in pH, suggesting that anthropogenic nutrient enrichment in aquatic ecosystems may change the processes of sexual selection and population dynamics solely on the basis of altered water pH. Introduction Aquatic ecosystems are affected by anthropogenic disturbance in the form of overfishing, eutrophication and habitat disturbance and destruction (Cloern 2001; Jackson et al. 2001; Thrush & Dayton 2002). In addi- tion, rising atmospheric carbon dioxide, primarily caused by rapidly increasing anthropogenic CO 2 emissions, reduces pH and shifts seawater carbonate chemistry (Doney et al. 2009; H€ onisch et al. 2012). Compared with current day levels, the increase in dis- solved CO 2 corresponds to a reduction of 0.3–0.5 units in oceanic pH by the year 2100 (Caldeira & Wickett 2005). On the other hand, eutrophication may increase pH by reducing the amount of dissolved car- bon dioxide (Perus & Bonsdorff 2004). In addition, algal photosynthesis may cause a rise in pH, resulting in an increase to over nine during daytime (Lapointe & Matzie 1996; Perus & Bonsdorff 2004). An organ- ism’s resilience to such fast environmental change lar- gely depends on its ability to disperse, how mobile it is, its behavioural plasticity, and the fitness conse- quences related to the environmental change (Dall et al. 2005; Donaldson-Matasci et al. 2008). The initial response, most often a behavioural adjustment, is important because the first reaction to rapid human-induced environmental change will determine whether individuals or populations survive the early stages of changing environments (Tuomainen & Candolin 2010). Changes in water pH have been shown to alter the behaviour of crustaceans (Allison et al. 1992; de la Haye et al. 2011), molluscs (Bibby et al. 2007; Turner & Chislock 2010) and fish (Kitamura & Ikuta 2000; Leduc et al. 2004; Heuschele & Candolin 2007; Ishimatsu et al. 2008; Munday et al. 2009; Dixson et al. 2010; Cripps et al. 2011; Ferrari et al. 2011, 2012a,b; Domenici et al. 2012; Nilsson et al. 2012). While many studies typically have focused on the interaction between altered water pH and olfactory cues (Kitamura & Ikuta 2000; Leduc et al. 2004; Bibby et al. 2007; Heuschele & Candolin 2007; Munday et al. 2009; Dixson et al. 2010; Cripps et al. 2011; Ferrari et al. 2011; de la Haye et al. 2011), more resent research have addressed other effects on behaviour, such as the impact on hearing (Simpson et al. 2011), the use of visual cues (Ferrari et al. 2012a), the impact on the cognitive ability (Ferrari et al. 2012b) and the impact on behavioural lateralization Ethology 119 (2013) 86–93 © 2012 Blackwell Verlag GmbH 86 Ethology