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Sea‐level rise is predicted to cause major damage to tropical coastlines. While coral reefs can act as natural barriers for ocean waves, their protection hinges on the ability of scleractinian corals to produce enough calcium carbonate (CaCO3) to keep up with rising sea levels. As a consequence of intensifying disturbances, coral communities are changing rapidly, potentially reducing community‐level CaCO3 production. By combining colony‐level physiology and long‐term monitoring data, we show that reefs recovering from major disturbances can produce 40% more CaCO3 than currently estimated due to the disproportionate contribution of juvenile corals. However, the buffering effect of highly productive juvenile corals is compromised by recruitment failures, which have been more frequently observed after large‐scale, repeated bleaching events. While the size structure of corals can bolster a critical ecological function on reefs, climate change impacts on recruitment may undermine this buffering effect, thus further compromising the persistence of reefs and their provision of important ecosystem services. [ABSTRACT FROM AUTHOR]

Seawater acidification from increasing CO2 is often enhanced in coastal waters due to elevated nutrients and sedimentation. Our understanding of the effects of ocean and coastal acidification on present‐day ecosystems is limited. Here we use data from three independent large‐scale reef monitoring programs to assess coral reef responses associated with changes in mean aragonite saturation state (Ωar) in the Great Barrier Reef World Heritage Area (GBR). Spatial declines in mean Ωar are associated with monotonic declines in crustose coralline algae (up to 3.1‐fold) and coral juvenile densities (1.3‐fold), while non‐calcifying macroalgae greatly increase (up to 3.2‐fold), additionally to their natural changes across and along the GBR. These three key groups of organisms are important proxies for coral reef health. Our data suggest a tipping point at Ωar 3.5–3.6 for these coral reef health indicators. Suspended sediments acted as an additive stressor. The latter suggests that effective water quality management to reduce suspended sediments might locally and temporarily reduce the pressure from ocean acidification on these organisms. [ABSTRACT FROM AUTHOR]

A five-year period (2002-2006) of below-median rainfall followed by a six-year period (2007-2012) of above-median rainfall and seasonal flooding allowed a natural experiment into the effects of runoff on the water quality and subsequent coral community responses in the Whitsunday Islands, Great Barrier Reef (Australia). Satellite-derived water quality estimates of total suspended solids (TSS) and chlorophyll- a (Chl) concentration showed marked seasonal variability that was exaggerated during years with high river discharge. During above-median rainfall years, Chl was aseasonally high for a period of 3 months during the wet season (February-April), while TSS was elevated for four months, extending into the dry season (March-June). Coinciding with these extremes in water quality was a reduction in the abundance and shift in the community composition, of juvenile corals. The incidence of coral disease was at a maximum during the transition from years of below-median to years of above-median river discharge. In contrast to juvenile corals, the cover of larger corals remained stable, although the composition of communities varied along environmental gradients. In combination, these results suggest opportunistic recruitment of corals during periods of relatively low environmental stress with selection for more tolerant species occurring during periods of environmental extremes. [ABSTRACT FROM AUTHOR]

Early establishment of coral-microbial symbioses is fundamental to the fitness of corals, but comparatively little is known about the onset and succession of bacterial communities in their early life history stages. In this study, bacterial associates of the coral Acropora millepora were characterized throughout the first year of life, from larvae and 1-week-old juveniles reared in laboratory conditions in the absence of the dinoflagellate endosymbiont Symbiodinium to field-outplanted juveniles with established Symbiodinium symbioses, and sampled at 2 weeks and at 3, 6 and 12 months. Using an amplicon pyrosequencing approach, the diversity of both nitrogen-fixing bacteria and of bacterial communities overall was assessed through analysis of nifH and 16S rRNA genes, respectively. The consistent presence of sequences affiliated with diazotrophs of the order Rhizobiales (23-58% of retrieved nifH sequences; 2-12% of 16S rRNA sequences), across all samples from larvae to 12-month-old coral juveniles, highlights the likely functional importance of this nitrogen-fixing order to the coral holobiont. Dominance of Roseobacter-affiliated sequences (>55% of retrieved 16S rRNA sequences) in larvae and 1-week-old juveniles, and the consistent presence of sequences related to Oceanospirillales and Altermonadales throughout all early life history stages, signifies their potential importance as coral associates. Increased diversity of bacterial communities once juveniles were transferred to the field, particularly of Cyanobacteria and Deltaproteobacteria, demonstrates horizontal (environmental) uptake of coral-associated bacterial communities. Although overall bacterial communities were dynamic , bacteria with likely important functional roles remain stable throughout early life stages of Acropora millepora. [ABSTRACT FROM AUTHOR]

The majority of reef-building corals acquire their obligate algal symbionts ( Symbiodinium) from the environment. However, factors shaping the initial establishment of coral–algal symbioses, including parental effects, local environmental conditions and local availability of symbionts, are not well understood. This study monitored the uptake and maintenance of Symbiodinium in juveniles of two common corals, Acropora tenuis and Acropora millepora, that were reciprocally explanted between sites where adult colonies host different types of Symbiodinium. We found that coral juveniles were rapidly dominated by type D Symbiodinium, even though this type is not found in adult colonies (including the parental colonies) in four out of the five study populations. Furthermore, type D Symbiodinium was found in less than one-third of a wide range of coral species ( n > 50) sampled at the two main study sites, suggesting that its dominance in the acroporid juveniles is not because it is the most abundant local endosymbiotic type. Moreover, dominance by type D was observed irrespective of the light intensity to which juveniles were exposed in a field study. In summary, despite its relatively low abundance in coral assemblages at the study sites and irrespective of the surrounding light environment, type D Symbiodinium is the main symbiont type initially acquired by juveniles of A. millepora and A. tenuis. We conclude that during early ontogeny in these corals, there are few barriers to the uptake of Symbiodinium types which differ from those found in parental colonies, resulting in dominance by a highly infectious and potentially opportunistic symbiont. [ABSTRACT FROM AUTHOR]

Various coral propagation techniques, including utilization of spawn slicks, have been developed to help restore degraded coral communities. Although, it has been demonstrated that embryos from spawn can be used for sexual propagation of corals, few have quantified fertilization, survival, settlement, post-settlement mortality, and long term survival of transplanted corals, grown from spawn slick. Spawn slicks were collected at night off Anda, northwestern Philippines, following a mass spawning of Acropora spp. The collected spawn, which contained ~4,100,000 developing embryos, was highly viable (96% actively dividing) at 12 h post-mixing. Based on assays, 2-day old larvae exhibited high survival in culture (87.9%), and subsequent settlement competency (92%). All 3330 settlement substrates (coral plug-ins), seeded with approximately 2,100,000 3-day old coral larvae, had at least one settled coral after one month. Forty-five pieces of these plug-ins, which were randomly tagged, had settled coral spats ranging from 3 to 88 spats per plug-in (26.7 ± 3.4 spats per plug-in, mean ± SE). Two and four months after the initial settlement on plug-ins, 76.3 ± 1.2% and 42.5 ± 1.2% of the spats survived, respectively. Two hundred seventy (270) coral plug-ins were then transplanted at six sites. Transplanted corals exhibited varying survival in different sites, from 11 to 62%, five months post-transplantation. Thirty-one months post-transplantation, only two of the six sites had surviving transplanted corals, i.e., four colonies of Acropora millepora , three A. divaricata , and one A. cf. austera. However, setbacks in the survival of transplants highlight the need to further examine drivers affecting long term performance of coral transplants, which is vital in establishing different generations of parent colonies that can be used for sustainable mariculture of corals. • This study presents the first culture and rearing of coral embryos from wild caught spawn slicks in the Philippines. • Coral embryos and larvae from wild caught spawn can exhibit high survival and settlement, and diverse species. • This paper reports the first grown coral colonies (~3 years old) produced from culture and rearing of spawn slicks. • Parent colonies grown from spawn slicks can be used for sustainable mariculture of corals. • Low transplant survival highlights the need to examine drivers affecting long term performance of coral transplants. [ABSTRACT FROM AUTHOR]