The coral core microbiome identifies rare bacterial taxa as ubiquitous endosymbionts

© 2015 International Society for Microbial Ecology All rights reserved. Despite being one of the simplest metazoans, corals harbor some of the most highly diverse and abundant microbial communities. Differentiating core, symbiotic bacteria from this diverse hostassociated consortium is essential for characterizing the functional contributions of bacteria but has not been possible yet. Here we characterize the coral core microbiome and demonstrate clear phylogenetic and functional divisions between the micro-scale, niche habitats within the coral host. In doing so, we discover seven distinct bacterial phylotypes that are universal to the core microbiome of coral species, separated by thousands of kilometres of oceans. The two most abundant phylotypes are co-localized specifically with the corals' endosymbiotic algae and symbiont-containing host cells. These bacterial symbioses likely facilitate the success of the dinoflagellate endosymbiosis with corals in diverse environmental regimes

An Indo-Pacifc coral spawning database

The discovery of multi-species synchronous spawning of scleractinian corals on the Great Barrier Reef in the 1980s stimulated an extraordinary effort to document spawning times in other parts of the globe. Unfortunately, most of these data remain unpublished which limits our understanding of regional and global reproductive patterns. The Coral Spawning Database (CSD) collates much of these disparate data into a single place. The CSD includes 6178 observations (3085 of which were unpublished) of the time or day of spawning for over 300 scleractinian species in 61 genera from 101 sites in the Indo-Pacific. The goal of the CSD is to provide open access to coral spawning data to accelerate our understanding of coral reproductive biology and to provide a baseline against which to evaluate any future changes in reproductive phenology

Coral larval ecology and biogeography in a warming ocean

The distribution and diversity of species is changing in response to global climate change, particularly increased temperature. However, the specific response, both within and among species, is often dependent on geographical location. For instance, the greatest negative effects of global warming are predicted to occur in the tropics because lowlatitude species tend to have a narrower range of thermal tolerance when compared with higher latitude species. Corals are expected to be at a particularly high risk from increased temperatures because thermal anomalies as little as 1°C above average annual summer maximums can cause mass bleaching in adult coral assemblages. Raised temperatures are also deleterious to coral larvae (the dispersive life stage), which are crucial for recruitment and replenishment of coral populations. However, studies into the effects of temperature on these early life stages have so far been limited to single locations and upper thermal limits. In addition, the effects of reduced temperature are also rarely examined. Therefore, the aims of my PhD were to 1) determine thermal tolerance breadths for the development and survival of coral larvae 2) assess the extent to which this tolerance varies across space and among species 3) test whether differences between adult coral assemblages across a dispersal barrier can be predicted by species traits, in particular larval traits including the rate of development and mode of larval nutrition. To address these aims, I combined small-scale larval experiments at three sites along the east coast of Australia, and large-scale biogeographical analyses. My major findings were that 1) raised temperatures increased the proportion of abnormal embryos, increased the rate of larval development and decreased larval lifespan, 2) lowered temperatures reduced the rate of development but did not affect larval lifespan 3) in relation to local ambients, upper thermal thresholds were greater in coral larvae from higher latitudes 4) the rate of larval development was the best predictor for the differences in assemblage structure between the Great Barrier Reef and Lord Howe Island, with coral cover at Lord Howe Island overwhelmingly dominated by species which brood larvae that are ready to settle on release. Although local temperature ranges projected by the end of the century exceed the thermal tolerance breadths at most locations, rising temperatures pose a greater threat to low-latitude coral populations because of their narrower range of thermal tolerance. Furthermore, the effects of ocean warming are likely to vary among species. In particular, species with larvae that develop quickly may be pre-adapted to survive changing climates because they are better colonisers and therefore have a greater potential to expand their range size to track suitable climate

The effects of temperature on embryonic development and larval survival in two scleractinian corals

Increased temperatures are deleterious to early life stages in many organisms; however, the biological effects of decreased temperatures are rarely explored. For example, the tolerance of marine invertebrate larvae to temperatures lower than ambient might affect the capacity of species to disperse from tropical to subtropical locations. In addition, reduced rates of development are likely to affect the proportion of larvae retained on natal reefs. Here, we explore the relationship between temperature, embryonic development and larval survival over an 8°C temperature range (-4 to +4°C around the ambient temperature at the time of spawning of 24°C) in 2 reef-building corals, Goniastrea favulus and Acropora spathulata from One Tree Island in the southern Great Barrier Reef. Rates of development were generally slower at lower temperatures: embryos of both species took longer to complete gastrulation and to become motile at temperatures below ambient. In contrast, temperatures below ambient did not affect larval survivorship in either species. A. spathulata larvae were more sensitive to increased temperatures than G. favulus, which also had higher survivorship than A. spathulata at all temperatures except 20°C. These results suggest that fluctuations in temperature at the time of spawning will influence patterns of coral larval dispersal. Furthermore, cold water is unlikely to prevent the dispersal of tropical corals to subtropical locations

Latitudinal variation in thermal tolerance breadth of early life stages of corals

Organisms living in habitats characterized by a marked seasonal temperature variation often have a greater thermal tolerance than those living in more stable habitats. To determine the extent to which this hypothesis applies to reef corals, we compared thermal tolerance of the early life stages of five scleractinian species from three locations spanning 17° of latitude along the east coast of Australia. Embryos were exposed to an 8 °C temperature range around the local ambient temperature at the time of spawning. Upper thermal thresholds, defined as the temperature treatment at which the proportion of abnormal embryos or median life span was significantly different to ambient controls, varied predictably among locations. At Lizard Island, the northern-most site with the least annual variation in temperature, the proportion of abnormal embryos increased and life span decreased 2 °C above ambient in the two species tested. At two southern sites, One Tree Island and Lord Howe Island, where annual temperature variation was greater, upper temperature thresholds were generally 4 °C or greater above ambient for both variables in the four species tested. The absolute upper thermal threshold temperature also varied among locations: 30 °C at Lizard Island; 28 °C at One Tree Island; 26 °C at Lord Howe Island. These results support previous work on adult corals demonstrating predictable differences in upper thermal thresholds with latitude. With projected ocean warming, these temperature thresholds will be exceeded in northern locations in the near future, adding to a growing body of evidence indicating that climate change is likely to be more detrimental to low latitude than high latitude corals

Coral reproduction on the world's southernmost reef at Lord Howe Island, Australia

Despite a recent expansion in the geographic extent of coral reproductive research, there remain many regions in the Indo-Pacific where knowledge is limited. For example, Lord Howe Island is the southernmost reef system in the world (31°S); however, very little is known of the reproductive biology of the coral fauna. Here, aspects of the reproductive biology and the timing of reproduction for 40 of the approximately 65 species that occur on Lord Howe Island are documented. In December 2010, field assessments of the stage of gamete maturity in Acropora spp. colonies suggested that 5 species spawned in December 2010 and 11 in January 2011. In January 2012, similar sampling suggested that 12 Acropora species spawned in January and 1 in February. In addition, 11 species from 10 genera broadcast spawned gametes from 17:30 to 24:00 h in January 2012, 10 to 12 d after full moon. Goniastrea favulus was inferred to spawn prior to 17:00 h, 6 to 12 d after full moon and Porites heronensis released brooded larvae. The reproductive biology of 3 other brooding species was examined using dissections and histology monthly for 1 yr from April 2011. Of these, Seriatopora hystrix contained planulae between November 2011 and March 2012, Stylophora pistillata contained planulae between November 2011 and February 2012. No eggs or planulae were observed in Pocillopora damicornis. In conclusion, the spawning patterns on Lord Howe Island are consistent with other locations in the Indo-Pacific: multi-species synchronous spawning episodes occur after full moons, when water temperatures are relatively high

An Indo-Pacific coral spawning database

The authors would like to thank the ARC Centre of Excellence for Coral Reef Studies for funding the Coral Spawning Workshop in Singapore in 2017 where the database was initially developed.The discovery of multi-species synchronous spawning of scleractinian corals on the Great Barrier Reef in the 1980s stimulated an extraordinary effort to document spawning times in other parts of the globe. Unfortunately, most of these data remain unpublished which limits our understanding of regional and global reproductive patterns. The Coral Spawning Database (CSD) collates much of these disparate data into a single place. The CSD includes 6178 observations (3085 of which were unpublished) of the time or day of spawning for over 300 scleractinian species in 61 genera from 101 sites in the Indo-Pacific. The goal of the CSD is to provide open access to coral spawning data to accelerate our understanding of coral reproductive biology and to provide a baseline against which to evaluate any future changes in reproductive phenology.Publisher PDFPeer reviewe