Coral Reefs of the Red Sea

Inhaltsverzeichnis

1. Frontmatter

2. 1. The Red Sea: Environmental Gradients Shape a Natural Laboratory in a Nascent Ocean

   Michael L. Berumen, Christian R. Voolstra, Daniele Daffonchio, Susana Agusti, Manuel Aranda, Xabier Irigoien, Burton H. Jones, Xosé Anxelu G. Morán, Carlos M. Duarte

   Abstract

   This chapter introduces the environmental gradients that characterize the broader Red Sea habitat. The Red Sea is formed by an actively spreading rift and notably has only one natural connection to the Indian Ocean – a narrow, shallow opening known as the Strait of Bab al Mandab. The resultant isolation undoubtedly plays a key role in shaping the environmental gradients, species endemism, and distinct evolutionary trajectory observed within the Red Sea. While this young ocean is known to be among the saltiest and warmest seas on Earth, there are important spatial and temporal gradients that likely influence the biological communities residing in its waters.

3. 2. Environmental Setting for Reef Building in the Red Sea

   James Churchill, Kristen Davis, Eyal Wurgaft, Yonathan Shaked

   Abstract

   The Red Sea is a distinct marine system, which, due to its limited lateral extent, is strongly influenced by the surrounding arid and semiarid terrestrial environment. Among large marine bodies, it is unusually saline, owing to a high rate of evaporation relative to precipitation, and warm. The physical environment of the Red Sea has been subject to scientific research for more than a century, with considerable advances in understanding achieved in the past two decades. In this chapter, we review the current state of knowledge of the Red Sea’s physical/chemical system. The bulk of the chapter deals with the marine environment. Attention is given to a variety of topics, including: tides and lower-frequency motions of the sea surface, circulation over a range of space and time scales, the surface wave field, and the distributions of water properties, nutrients, chlorophyll-a (chl-a) and light. We also review the current understanding of atmospheric conditions affecting the Red Sea, focusing on how atmospheric circulation patterns of various scales influence the exchange of momentum, heat, and mass at the surface of the Red Sea. A subsection is devoted to geology and reef morphology, with a focus on reef-building processes in the Red Sea. Finally, because reef building and health are tightly linked with carbonate chemistry, we review the Red Sea carbonate system, highlighting recent advances in the understanding of this system.

4. 3. Ecophysiology of Reef-Building Corals in the Red Sea

   Maren Ziegler, Anna Roik, Till Röthig, Christian Wild, Nils Rädecker, Jessica Bouwmeester, Christian R. Voolstra

   Abstract

   The Red Sea is one of the warmest and most saline seas on the planet. Yet, scleractinian corals have managed to flourish under these distinct conditions supporting one of the largest networks of coral reef ecosystems worldwide. Here, we summarize current knowledge on the ecophysiology of reef-building corals gained from 60 years of research in the Red Sea starting from insights in the 1960s to the most recent studies of the past few years. We provide a brief overview over seasonal dynamics and environmental gradients in the Red Sea that are used to study ecophysiological processes of corals under changing environmental and extreme conditions (i.e., temperature, salinity, nutrient, and light availability). We then focus on how this environmental variability shapes the central processes of coral physiology in the Red Sea covering the topics of photosynthesis, calcification, nutrient cycling, and reproduction. We continue by reporting the first physiological measurements of Red Sea deep-sea corals. Last, we discuss how, through the integration of traditional methods with recent developments in the omics field and model systems, we are now beginning to understand the complexity of processes that contribute to the ecological success of corals under these variable conditions. This synthesis may serve as a basis for future studies that aim to contribute to a better understanding of the impacts of environmental change on coral reefs in the Red Sea and the rest of the world.

5. 4. Microbial Communities of Red Sea Coral Reefs

   Matthew J. Neave, Amy Apprill, Greta Aeby, Sou Miyake, Christian R. Voolstra

   Abstract

   This chapter explores the microorganisms that inhabit different components of the coral reef ecosystem in the Red Sea. Microbes play crucial roles in numerous reef processes, including primary production as well as nutrient and organic matter cycling. Microbes are also ubiquitous symbionts of eukaryotic organisms, providing the host with nutrients, chemical cycling, and defensive functions. The Red Sea is a particularly interesting study system due to its unusual physiochemical properties, such as a strong north-south temperature and salinity gradient. Here we examine the influence of these unusual characteristics on microbes in the water column and sediments, and those associated with corals, sponges, and fish. In the water column, the microbial community indeed appears to correlate with prevailing north-south environmental conditions. For example, heterotrophic picoplankton and the cyanobacteria Synechococcus tend to be more abundant in the warmer, less saline, southern waters. On the other hand, the microbes associated with corals, sponges, and fish seem to be conserved throughout the Red Sea and many other parts of the world. For example, several coral species in the Red Sea harbor Endozoicomonas bacteria, and this is also observed world-wide. Moreover, the dominance of Epulopiscium bacteria in surgeonfish and highly conserved microbial communities in sponges are also commonly reported in other regions. In terms of microbial-based diseases, Red Sea corals display many typical disorders, including white syndromes, skeletal eroding band, black band disease, and growth anomalies, but these are rare within Red Sea waters. Thus, despite strong environmental extremes driving free-living microbial communities in the Red Sea, the microbes in tightly regulated symbiotic environments appear to be conserved, although strain-level and genotype specialization are areas of continuing research.

6. 5. Symbiodiniaceae Diversity in Red Sea Coral Reefs & Coral Bleaching

   Maren Ziegler, Chatchanit Arif, Christian R. Voolstra

   Abstract

   This chapter introduces Symbiodiniaceae, the diverse group of dinoflagellate microalgae, that form an obligate symbiosis with corals and other coral reef organisms. The Symbiodiniaceae cells reside within the coral tissue, their photosynthesis fuels the productivity and diversity of coral reef ecosystem, and the breakdown of this symbiosis leads to coral bleaching and may entail the death of the host. Here, we summarize Symbiodiniaceae taxonomy and phylogeny and the molecular tools that are used to study Symbiodiniaceae diversity in the Red Sea. We provide an overview over all described Symbiodiniaceae species and discuss the functional diversity within this phylogenetically diverse group as well as the implications of this diversity for coral-Symbiodiniaceae pairings and ecological niche partitioning in coral reef ecosystems. We review host-Symbiodiniaceae associations of 57 host genera in the Red Sea and discuss the emerging patterns in light of their wider biogeographic distribution. Last, we summarize how climate change-induced thermal anomalies have repeatedly led to coral bleaching and mortality in the Red Sea and how they threaten these reef ecosystems, otherwise thought to be comparatively resilient. We conclude with a perspective of important topics for Symbiodiniaceae research in the Red Sea that have the potential to contribute to a broader understanding of the basis of thermotolerance in this fragile symbiosis.

7. 6. Sponges of the Red Sea

   Michael K. Wooster, Oliver Voigt, Dirk Erpenbeck, Gert Wörheide, Michael L. Berumen

   Abstract

   Sponges are found in virtually all marine habitats. The Red Sea is no exception, harboring a diverse community of sponge species. However, the state of knowledge of the Red Sea sponge fauna remains in early stages. Various taxonomic efforts have been initiated, starting with early explorers at the beginning of the nineteenth century. Subsequently, published work has focused on modern taxonomic approaches, potential bioactive molecules, microbiological associations of host sponges, and a variety of ecological topics. The majority of studies are restricted to few locations and/or small numbers of species. Overall, this collective knowledge represents a sound foundation but there remains great potential for Red Sea sponges to inform the broader context of sponge work throughout the tropics. This chapter aims to provide an overview of previous work in the region and identify fruitful areas of potential future work.

8. 7. Corals of the Red Sea

   Michael L. Berumen, Roberto Arrigoni, Jessica Bouwmeester, Tullia I. Terraneo, Francesca Benzoni

   Abstract

   The biodiversity of Red Sea corals captured the attention of some of the earliest European natural historians. Many of the first descriptions of tropical reef corals were based on Red Sea material. Modern approaches to resolve the notorious challenges of coral taxonomy have only recently been applied to Red Sea taxa. This chapter reviews current knowledge of the distributions of coral species in the Arabian region, including assessments of endemism. We also review new species described (or resurrected) since the last major assessment (in 2002). Where sufficient data is available, we highlight within-region distribution patterns. The Red Sea has the highest levels of endemism among all regions of the Indian Ocean. Analysis of the similarity of species composition among the Arabian subregions shows that the Red Sea and Socotra Island are the most speciose, but also have distinct community compositions. The regional diversity of Red Sea corals is likely influenced by the unique environmental gradients of the Arabian region. Despite evolving in testing conditions, Red Sea corals have been impacted by global climate change. Recent thermal bleaching events in the Red Sea highlight the pressures and challenges to future recovery.

9. 8. Fishes and Connectivity of Red Sea Coral Reefs

   Michael L. Berumen, May B. Roberts, Tane H. Sinclair-Taylor, Joseph D. DiBattista, Pablo Saenz-Agudelo, Stamatina Isari, Song He, Maha T. Khalil, Royale S. Hardenstine, Matthew D. Tietbohl, Mark A. Priest, Alexander Kattan, Darren J. Coker

   Abstract

   The coral reefs of the Red Sea are host to a diverse fish fauna. Ichthyofauna studies began in the Red Sea during expeditions undertaken by some of the earliest European naturalists. In the more than 200 years that have passed, much has been learned about Red Sea fishes. Nonetheless, many knowledge gaps remain. Although it is a relatively young sea, the geologic history of the Red Sea provides an interesting context for many evolutionary biology studies. The strong environmental gradients within the Red Sea and the broader Arabian region may play a role in structuring some observed biodiversity patterns, perhaps most notably in the context of high numbers of Arabian and Red Sea endemics. As such, Red Sea fishes provide ideal opportunities for connectivity studies, both based on adult movement and larval dispersal patterns. These studies are increasingly important as multiple modern “mega-developments” are planned on Red Sea shores in locations where a lack of scientific information may still hinder conservation efforts and planning for sustainable development. Coupled with increasing pressures from global climate change, each of the Red Sea countries faces unique challenges for the preservation of the rich biological resources for which their reefs are historically known.