Coral bleaching and recovery in the Thai Andaman Sea

Severe coral bleaching in response to increasing sea temperatures threatens coral reefs in many regions of the world, including the Andaman Sea, Thailand. Coral bleaching involves the breakdown of the coral-algae symbiosis, resulting in the loss of the intracellular microalgal dinoflagellates of the diverse genus Symbiodinium, also called a zooxanthellaea . Elevated temperatures and high solar irradiation are considered to be the primary factors causing widespread coral bleaching. In the Andaman Sea, bleaching events have occurred in the years 1991, 1995, 1998, 2003, 2010, and 2016 following abnormally high sea-surface temperatures (SST). The 2010 SST anomaly was the hottest on record with unprecedented bleaching and mortality of corals. However, corals showed different responses to thermal stress and important spatial differences, both between and within reefs. This thesis explores the causes and consequences of coral bleaching events in the Andaman Sea of Thailand on the coral community, organismal and sub-organismal (symbiont) scale. Physico-chemical factors as well as species-specific responses of corals to thermal stress contribute to complex patterns of bleaching and mortality, revealing large differences in acclimatization and adaptation in space and time. Understanding the species-specific bleaching responses in their particular environment provides a promising tool for management, as the identification of bleaching-tolerant corals and the factors enhancing coral tolerance may help improve the design of appropriate rehabilitation techniques. This study highlights potential refuge areas for corals which are necessary to protect and facilitate quick post-bleaching recovery. The protection of reef areas harbouring coral communities tolerant to thermal stress, along with the rehabilitation of degraded coral reef ecosystems with bleaching tolerant species, is a promising approach to improve the success of reef conservation management in a warming ocean

Age-related shifts in bacterial diversity in a reef coral

This study investigated the relationship between microbial communities in differently sized colonies of the massive coral Coelastrea aspera at Phuket, Thailand where colony size could be used as a proxy for age. Results indicated significant differences between the bacterial diversity (ANOSIM, R = 0.76, p = 0.001) of differently sized colonies from the same intertidal reef habitat. Juvenile and small colonies (28 cm mean diam). Bacterial diversity increased in a step-wise pattern from juvenilessmallmedium colonies, which was then followed by a slight decrease in the two largest size classes. These changes appear to resemble a successional process which occurs over time, similar to that observed in the ageing human gut. Furthermore, the dominant bacterial ribotypes present in the tissues of medium and large sized colonies of C. aspera, (such as Halomicronema, an Oscillospira and an unidentified cyanobacterium) were also the dominant ribotypes found within the endolithic algal band of the coral skeleton; a result providing some support for the hypothesis that the endolithic algae of corals may directly influence the bacterial community present in coral tissues.Barbara Brown recieved funding from the Leverhulme Trust [www.leverhulme.ac.uk]; Grant number: EM-2013-058. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Towards enhancing coral heat tolerance: a “microbiome transplantation” treatment using inoculations of homogenized coral tissues

Background: Microbiome manipulation could enhance heat tolerance and help corals survive the pressures of ocean warming. We conducted coral microbiome transplantation (CMT) experiments using the reef-building corals, Pocillopora and Porites, and investigated whether this technique can benefit coral heat resistance while modifying the bacterial microbiome. Initially, heat-tolerant donors were identified in the wild. We then used fresh homogenates made from coral donor tissues to inoculate conspecific, heat-susceptible recipients and documented their bleaching responses and microbiomes by 16S rRNA gene metabarcoding. Results: Recipients of both coral species bleached at lower rates compared to the control group when exposed to short-term heat stress (34 °C). One hundred twelve (Pocillopora sp.) and sixteen (Porites sp.) donor-specific bacterial species were identified in the microbiomes of recipients indicating transmission of bacteria. The amplicon sequence variants of the majority of these transmitted bacteria belonged to known, putatively symbiotic bacterial taxa of corals and were linked to the observed beneficial effect on the coral stress response. Microbiome dynamics in our experiments support the notion that microbiome community evenness and dominance of one or few bacterial species, rather than host-species identity, were drivers for microbiome stability in a holobiont context. Conclusions: Our results suggest that coral recipients likely favor the uptake of putative bacterial symbionts, recommending to include these taxonomic groups in future coral probiotics screening efforts. Our study suggests a scenario where these donor-specific bacterial symbionts might have been more efficient in supporting the recipients to resist heat stress compared to the native symbionts present in the control group. These findings urgently call for further experimental investigation of the mechanisms of action underlying the beneficial effect of CMT and for field-based long-term studies testing the persistence of the effect. [MediaObject not available: see fulltext.]

Large-amplitude internal waves benefit corals during thermal stress

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

Long-term impacts of rising sea temperature and sea level on shallow water coral communities over a ~40 year period

Effects of combined rising sea temperature and increasing sea level on coral reefs, both factors associated with global warming, have rarely been addressed. In this ~40 y study of shallow reefs in the eastern Indian Ocean, we show that a rising relative sea level, currently estimated at ~11 mm y−1, has not only promoted coral cover but also has potential to limit damaging effects of thermally-induced bleaching. In 2010 the region experienced the most severe bleaching on record with corals subject to sea temperatures of >31 °C for 7 weeks. While the reef flats studied have a common aspect and are dominated by a similar suite of coral species, there was considerable spatial variation in their bleaching response which corresponded with reef-flat depth. Greatest loss of coral cover and community structure disruption occurred on the shallowest reef flats. Damage was less severe on the deepest reef flat where corals were subject to less aerial exposure, rapid flushing and longer submergence in turbid waters. Recovery of the most damaged sites took only ~8 y. While future trajectories of these resilient reefs will depend on sea-level anomalies, and frequency of extreme bleaching the positive role of rising sea level should not be under-estimated

Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia

© 2018 The Author(s) Given predicted increases in urbanization in tropical and subtropical regions, understanding the processes shaping urban coral reefs may be essential for anticipating future conservation challenges. We used a case study approach to identify unifying patterns of urban coral reefs and clarify the effects of urbanization on hard coral assemblages. Data were compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong, and Naha (Okinawa). Our review highlights several key characteristics of urban coral reefs, including “reef compression” (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore-offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonization of urban infrastructure by hard corals. We present hypotheses for urban reef community dynamics and discuss potential of ecological engineering for corals in urban areas

Korallenbleichen und -erholung in der thailändischen Andamanensee

Severe coral bleaching in response to increasing sea temperatures threatens coral reefs in many regions of the world, including the Andaman Sea, Thailand. Coral bleaching involves the breakdown of the coral-algae symbiosis, resulting in the loss of the intracellular microalgal dinoflagellates of the diverse genus Symbiodinium, also called a zooxanthellaea . Elevated temperatures and high solar irradiation are considered to be the primary factors causing widespread coral bleaching. In the Andaman Sea, bleaching events have occurred in the years 1991, 1995, 1998, 2003, 2010, and 2016 following abnormally high sea-surface temperatures (SST). The 2010 SST anomaly was the hottest on record with unprecedented bleaching and mortality of corals. However, corals showed different responses to thermal stress and important spatial differences, both between and within reefs. This thesis explores the causes and consequences of coral bleaching events in the Andaman Sea of Thailand on the coral community, organismal and sub-organismal (symbiont) scale. Physico-chemical factors as well as species-specific responses of corals to thermal stress contribute to complex patterns of bleaching and mortality, revealing large differences in acclimatization and adaptation in space and time. Understanding the species-specific bleaching responses in their particular environment provides a promising tool for management, as the identification of bleaching-tolerant corals and the factors enhancing coral tolerance may help improve the design of appropriate rehabilitation techniques. This study highlights potential refuge areas for corals which are necessary to protect and facilitate quick post-bleaching recovery. The protection of reef areas harbouring coral communities tolerant to thermal stress, along with the rehabilitation of degraded coral reef ecosystems with bleaching tolerant species, is a promising approach to improve the success of reef conservation management in a warming ocean

Dominance of the coral Pocillopora acuta around Phuket Island in the Andaman Sea, Thailand

Abstract Pocillopora damicornis (Linnaeus, 1758), a species complex, consists of several genetic lineages, some of which likely represent reproductively isolated species, including the species Pocillopora acuta Lamarck, 1816. Pocillopora acuta can exhibit similar morphological characteristics as P. damicornis, thus making it difficult to identify species‐level taxonomic units. To determine whether the P. damicornis‐like colonies on the reefs in the Andaman Sea (previously often identified as P. damicornis) consist of different species, we sampled individual colonies at five sites along a 50 km coastal stretch at Phuket Island and four island sites towards Krabi Province, Thailand. We sequenced 210 coral samples for the mitochondrial open reading frame and identified six distinct haplotypes, all belonging to P. acuta according to the literature. Recently, P. acuta was observed to efficiently recolonize heat‐damaged reefs in Thailand as well as globally, making it a potentially important coral species in future reefs. Specifically in the light of global change, this study underscores the importance of high‐resolution molecular species recognition, since taxonomic units are important factors for population genetic studies, and the latter are crucial for management and conservation efforts