Multiple anthropogenic stressors in Indonesia : Impacts on metabolism, spatial distribution and community composition of coral reef organisms

of the additional manuscript . 175 Appendices . 177 General Introduction General Introduction Coral reefs in Indonesia Coral reefs are among the most biologically diverse and productive systems in the world (Moberg and Folke 1999, Crossland et al. 1991). They occur mainly in tropical oceans within 30° of the equator (Veron 2000). Most corals live in symbiosis with unicellular dinoflagellates, the zooxanthellae, which can provide > 90 % of the energy for the coral from carbon fixed during photosynthesis (Falkowski et al. 1984). Coral reefs are primarily formed by calcification processes of scleractinian corals, which provide a habitat for benthic organisms and fish (Moberg and Folke 1999, Veron 2000). About 1/3 of all fish species worldwide occur in coral reefs (Crabbe et al. 2009). In addition, coral reefs can provide physical protection from storms, thereby protecting associated ecosystems such as seagrass beds and mangrove forests, which further provide habitats as well as hatching and fishery grounds (Hoegh-Guldberg et al. 2007). Indonesia is the world’s largest archipelago nation and one of the fastest growing countries in the world with immense urbanization, industrialization and coastal development over the last decades (Pelling and Blackburn 2014). Coral reefs in Indonesia belong to the most diverse reefs worldwide (Hoeksema and Putra 2000). They are part of the Coral Triangle, a global hotspot of biodiversity (Veron et al. 2009, Burke et al. 2012). With more than 17,000 islands and a coastline of 81,000 km (Syarif 2009), 95 % of the current population of 252 million people lives near the coast (Martinez et al. 2007). Coral reefs support fisheries and tourist sectors and millions of people in Indonesia depend directly on marine resources from coral reefs for their daily lives (Moberg and Folke 1999, Burke et al. 2012). Anthropogenic stress Coral reefs are increasingly under threat due to the simultaneous impact of multiple environmental stressors (Halpern et al. 2007, Hoegh-Guldberg et al. 2007, Burke et al. 2012, Ban et al. 2014 a). Growing urbanization and industrialization in coastal areas, especially in many developing countries, has led to an increase in diversity and intensity of stressors and thereby caused an enormous speed in worldwide coral reef degradation. Over 60 % of reefs worldwide are considered at immediate risk from direct human activities (Burke et al. 2012) and at least 19 % have already been permanently lost (Wilkinson 2008). Some of the most pressing stressors on coral reefs are local anthropogenic stressors such as eutrophication, General Introduction increased sedimentation, pollution with toxic chemicals and overfishing (Fabricius 2005, van Dam et al. 2011, Burke et al. 2012), as well as global stressors such as ocean warming (Pandolfi et al. 2011) (see Fig. 1). Organisms are able to tolerate stress to a certain extent, however the exposure to multiple stressors poses an increasing threat to reefs (Wilson et al. 2010), potentially causing a higher sensitivity to further stressors (Beyer et al. 2014). Research into cumulative and interactive impacts of multiple stressors is still not very frequent (Crain et al. 2008) and even less so on coral reef organisms (Ban et al. 2014 b). Effects of multiple stressors have mostly been assumed to be additive (Halpern et al. 2007). However, current literature indicates that multiple stressors tend to interact with each other. Stressors can act directly with another, or the response of an organism to one factor can be altered by the occurrence of another (Crain et al. 2008). This interaction can be a synergism (i.e. amplification), e.g. increased UV radiation greatly increases the negative effects of a toxin (reviewed by Pelletier et al. 2006), or an antagonism (i.e. reduction), e.g. when nutrient enrichment dampens the negative effect of a second stressor, such as toxic chemicals or UV (Breitburg et al. 1998). These combined effects can occur on both species levels, as well as on community or population levels (see Fig. 1).