Tropical scleractinian corals are particularly vulnerable to global warming as elevated sea surface temperatures (SSTs) disrupt the delicate balance between the coral host and their algal endosymbionts, leading to symbiont expulsion, mass bleaching and mortality. While satellite sensing of SST has proved a reliable predictor of coral bleaching at the regional scale, there are large deviations in bleaching severity and mortality on the local scale that are poorly understood. Here, we show that internal waves play a major role in explaining local coral bleaching and mortality patterns in the Andaman Sea. Despite a severe region-wide SST anomaly in May 2010, frequent upslope intrusions of cold sub-pycnocline waters due to breaking large-amplitude internal waves (LAIW) mitigated coral bleaching and mortality in shallow waters. In LAIW-sheltered waters, by contrast, bleaching-susceptible species suffered severe bleaching and total mortality. These findings suggest that LAIW benefit coral reefs during thermal stress and provide local refugia for bleaching-susceptible corals. LAIW are ubiquitous in tropical stratified waters and their swash zones may thus be important conservation areas for the maintenance of coral diversity in a warming climate. Taking LAIW into account can significantly improve coral bleaching predictions and provide a valuable tool for coral reef conservation and management.

Tsunami waves leave sedimentary signatures both onshore and offshore, although the latter are hardly known. The objective of the present study is to provide new evidence for the 2004 Indian Ocean tsunami deposits left on the inner continental shelf of the Andaman Sea (Thailand) and to identify diagnostic sedimentological and geochemical properties of these deposits. Based on extensive seafloor mapping, three sediment cores were selected for study and were analysed for their sedimentary structures, grain size composition, chemical elemental composition, physical properties and 210 Pb activity. Sediment cores retrieved from shallow water (9-15 m) within 7.5 km off the shore revealed distinct event layers, which were interpreted as being tsunami deposits. These 20-25 cm thick deposits were already covered with post-tsunami marine sediments. They were composed of several units, marine sand layers alternating with poorly sorted mud with terrigenous and anthropogenic components, representing different hydrodynamic conditions (probably during run-up and backwash phase). These sedimentological observations were supported by geochemical and physical data and were confirmed using 210 Pb dating. A sediment core taken from a depth of 57 m at a distance of 25 km offshore did not reveal clear event deposits. Comparisons with available data from offshore tsunami deposits showed that there is no single set of signatures that could be applied to identify this kind of deposits.

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The trophic response of the scleractinian coral Pocillopora meandrina (Dana, 1846) to large amplitude internal waves (LAIW) was investigated in the Andaman Sea. Corals living on the western sides of the Similan Islands (Thailand) exposed to LAIW showed significantly higher biomass and protein content than sheltered corals on the eastern sides. LAIW-exposed corals were also more heterotrophic, displaying lower δ 13 C ratios in their tissues and higher rates of survival in artificial darkness compared to sheltered counterparts. Heterotrophic nutrition in concert with photosynthesis leads to higher energy reserves in corals from LAIW-exposed reefs, making them more resilient to disturbance. As these differences in trophic status are due to LAIW-enhanced fluxes of organic matter, LAIW may play an important role in supporting coral metabolism and survival in these monsoon beaten reefs.KEY WORDS: Large amplitude internal waves · Corals · Heterotrophic plasticity · Current regime · Pocillopora meandrina · Andaman Sea Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 412: [113][114][115][116][117][118][119][120][121][122][123][124][125][126][127][128] 2010 solved organic materials (Muscatine et al. 1989, Grottoli 2002.Along with photosynthesis, heterotrophy enhances skeletal (Houlbrèque et al. 2003) and tissue growth by building up energy stores including lipids (Anthony 2006, Treignier et al. 2008 and proteins , Houlbrèque et al. 2003. Heterotrophy has been shown to support coral photosynthesis (Grottoli 2002, Borell et al. 2008) and resilience to stresses such as turbidity (Anthony 2006), warming (Borell et al. 2008) and bleaching , Palardy et al. 2008. Although active feeding does not generally constitute the dominant carbon source for zooxanthellate corals, it may reduce temporary energy deficits (Anthony 2000) so that corals with a high capability to heterotrophically assimilate carbon may be more effective in surviving multiple bleaching events and become dominant in future reefs .The relative proportion of heterotrophy in coral metabolism may vary markedly between species , and has been documented in several studies. For example, Wellington (1982) observed that the branching coral Pocillopora damicornis grew independent of zooplankton supply, and was more markedly affected by shading than the massive coral Pavona clavus. Sebens & Johnson (1991) documented higher zooplankton capture rates by Madracis decactis with increasing current strength, but not by Meandrina meandrites. showed that the δ 13 C ratios of Montipora capitata host tissue decreased when bleached because of increased heterotrophic feeding, while Porites compressa did not alter its nutrition. Moreover, Palardy et al. (2008) observed that the feeding response to one disturbance may vary significantly between different coral species.The importance of heterotrophic feeding in coral metabolism may further vary between environments (Palardy et al. 2005). Decreasing light and photosynthesis (Mus...

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