Synergistic Effects of Thermal Stress and Estuarine Discharge on Transcriptomic Variation of Montastraea cavernosa Corals in Southeast Florida

Coral reefs at the northern extent of Florida’s coral reef tract are exposed to many localized anthropogenic influences including controlled freshwater discharges, runoff, upwelling, and seasonal environmental variability. To better understand coral responses to sublethal stressors in nearshore environments, we conducted complementary experiments to assess the impacts of estuarine runoff and temperature stress on local populations of the scleractinian coral species, Montastraea cavernosa, using Tag-Seq global gene expression profiling. In an in situ time series experiment, fate-tracked colonies were sampled during periods of relatively low and high estuarine discharge over 4 years to investigate temporal trends in transcriptional patterns and to identify if coral stress indicators were regulated through time. There was significant transcriptomic variation through time, but patterns did not appear to be attributed to distance from nearby estuarine tidal flux. In an ex situ factorial experiment, clonal replicates of coral genotypes were exposed to temperature (25°C and 30°C) and water (offshore and estuarine discharge, representing typical oceanic conditions and episodic discharge conditions, respectively) treatments to quantify the potential individual and synergistic effects of sublethal stress on coral and algal gene expression. Comparative analyses suggested that corals and their algal symbionts were more responsive to thermal stress than to estuarine discharge, although there was evidence of a synergistic relationship between the two stressors. Strong genotype effects also demonstrated that transcriptomic responses to thermal stress were largely based on coral genotype, indicating the potential for stress resilience among certain members of coral populations from southeast Florida.

Telomere dysfunction is associated to dark-induced coral bleaching in the reef coral Stylophora pistillata

Telomere DNA length is a complex trait controlled both by multiple loci and environmental factors. Even though the use of telomere DNA length measurement, as a method of assessing stress accumulation and predicting how this will influence survival, is currently being studied in numerous human cohort studies, the importance of telomere length for stress response in ecological studies remains at its infancy. Here, we investigated the telomere changes occurring in the symbiotic coral Stylophora pistillata that has experienced a continuous darkness over six months. This stress condition led to the loss of its symbionts, as what is also observed when bleaching occurs in the field at a large-scale due to climate changes and anthropogenic activities, threatening the worldwide reef ecosystem. We found that the continuous darkness condition was associated with telomere DNA length shortening and a downregulation of the expression of the telomere-associated protein Pot2. These results pave the way for future studies on the role of telomere in coral stress response and the importance of telomere dysregulation in endangered coral species.

Caspases from scleractinian coral show unique regulatory features

Coral reefs are experiencing precipitous declines around the globe with coral diseases and temperature-induced bleaching being primary drivers of these declines. Regulation of apoptotic cell death is an important component in the coral stress response. Although cnidaria are known to contain complex apoptotic signaling pathways, similar to those in vertebrates, the mechanisms leading to cell death are largely unexplored. We identified and characterized two caspases each from Orbicella faveolata, a disease-sensitive reef-building coral, and Porites astreoides, a disease-resistant reef-building coral. The caspases are predicted homologs of the human executioner caspases-3 and -7, but OfCasp3a (Orbicella faveolata caspase-3a) and PaCasp7a (Porites astreoides caspase-7a), which we show to be DXXDases, contain an N-terminal caspase activation/recruitment domain (CARD) similar to human initiator/inflammatory caspases. OfCasp3b (Orbicella faveolata caspase-3b) and PaCasp3 (Porites astreoides caspase-3), which we show to be VXXDases, have short pro-domains, like human executioner caspases. Our biochemical analyses suggest a mechanism in coral which differs from that of humans, where the CARD-containing DXXDase is activated on death platforms but the protease does not directly activate the VXXDase. The first X-ray crystal structure of a coral caspase, of PaCasp7a determined at 1.57 Å resolution, reveals a conserved fold and an N-terminal peptide bound near the active site that may serve as a regulatory exosite. The binding pocket has been observed in initiator caspases of other species. These results suggest mechanisms for the evolution of substrate selection while maintaining common activation mechanisms of CARD-mediated dimerization.

Divergent thermal challenges elicit convergent stress signatures in aposymbiotic Astrangia poculata

Anthropogenic climate change threatens corals globally and both high and low temperatures are known to induce coral bleaching. However, coral stress responses across wide thermal breadths are rarely explored. In addition, it is difficult to disentangle the role of symbiosis on the stress response of obligately symbiotic coral hosts. Here, we leverage aposymbiotic colonies of the facultatively symbiotic coral, Astrangia poculata, which lives naturally with and without its algal symbiont, to examine how broad thermal challenges influence coral hosts. A. poculata were collected from their northern range limit and thermally challenged in two independent 16-day common garden experiments (heat and cold challenge) and behavioral responses to food stimuli and genome-wide gene expression profiling (TagSeq) were performed. Both thermal challenges elicited significant reductions in polyp extension. However, five times as many genes were differentially expressed under cold challenge compared to heat challenge. Despite more genes responding to cold challenge, there was significant overlap in which genes were differentially expressed across thermal challenges. These convergently responding genes (CRGs) were associated with downregulation of motor functions and nematocysts while others were consistent with stress responses previously identified in tropical corals. The fact that these responses were observed in aposymbiotic colonies highlights that many genes previously implicated in stress responses in symbiotic species may simply represent the coral’s stress response in or out of symbiosis.

Meta-analysis of the General Coral Stress Response: Acropora corals show opposing responses depending on stress intensity

As climate change progresses, reef-building corals must contend more often with suboptimal conditions, motivating a need to understand coral stress response. Here we test the hypothesis that there is a stereotyped transcriptional response that corals enact under any stressful conditions, functionally characterized by downregulation of growth and activation of cell death, response to reactive oxygen species, immunity, and protein homeostasis. We analyze RNA-seq and Tag-Seq data from 14 previously published studies and supplement them with four new experiments involving different stressors, totaling over 600 gene expression profiles from the genus Acropora. Contrary to expectations, we found not one, but two distinct types of response. The type A response was observed under all kinds of high-intensity stress, showed strong correlations between independent projects, and was functionally consistent with the hypothesized stereotyped response. Higher similarity of type A responses irrespective of stress type supports its role as the General Coral Stress Response providing a blanket solution to severely stressful conditions. The distinct type B response was observed under lower intensity stress and was weaker and more variable among studies than type A. Unexpectedly, the type B response was broadly opposite the type A response: biological processes up-regulated under type A response tended to be down-regulated under type B response, and vice versa. Gene network analysis indicated that type B response does not involve specific co-regulated gene groups and is simply the opposite of type A response. We speculate that these paradoxically opposing responses may result from an inherent negative association between stress response and cell proliferation.

BUDIDAYA KARANG HIAS POLIP BESAR PADA KEDALAMAN YANG BERBEDA DI ALAM DAN SISTEM RESIRKULASI

Karang polip besar cukup tinggi permintaan sebagai karang hias dari Indonesia sehingga perlu dilakukan penelitian budidayanya. Penelitian ini telah dilakukan pada tahun 2016 untuk melihat tingkat keberhasilan budidayanya dengan adaptasi pada dua sistem yang berbeda yaitu di alam pada kedalaman yang berbeda 5 m, 10 m, dan 15 m dengan tiga jenis karang uji (Plerogyra sp. Physogyra sp., dan Nemenzophyllia sp.) dan sistem resirkulasi. Penelitian ini bertujuan untuk melihat tingkat keberhasilan hidup karang. Pengamatan meliputi tingkat kematian, perubahan warna karang sebagai indikasi stres karang dan kelimpahan zooxanthellae. Berdasarkan hasil penelitian diperoleh karang Physogyra sp. mengalami fluktuasi perubahan warna meskipun kembali membaik, sementara dua jenis lain Plerogyra sp. dan Nemenzophyllia sp. mengalami perubahan warna ke arah kondisi baik pada farm dengan sistem resirkulasi. Pengamatan perubahan warna di alam mengalami stres ditandai dengan perubahan warna ke arah putih baik di kedalaman 5 m, 10 m, dan 15 m. Pengamatan tingkat kematian setelah 33 hari diperoleh tingkat kematian 100% pada kedalaman 5 m, 10 m untuk semua jenis, namun pada kedalaman 15 m karang Nemenzophyllia sp. mengalami kematian 100% dan karang yang dapat bertahan Physogyra sp. dan Plerogyra sp. dengan tingkat kematian berturut-turut adalah 71,4% dan 50,0%. Kematian dan pemutihan yang tinggi berhubungan erat dengan kondisi suhu dan intensitas cahaya pada bulan Juli-Agustus 2017 dan parameter lain TDS dan DO. Budidaya karang berhasil pada sistem resirkulasi dengan tingkat kematian 0%.Large polyp coral are quite high in demand as an ornamental coral from Indonesia so it needs to do research propagation. This research has been conducted in 2016 to see the success rate of propagation with adaptation on two different systems that is in nature at three different depths 5 m, 10 , and 15 m with three species of corals (Plerogyra sp., Physogyra sp., and Nemenzophyllia sp.) and recirculation system. This study aims to see the success rate of coral life. Observations included mortality rates, coral color changes as an indication of coral stress and zooxanthellae abundance. Based on the research results obtained Physogyra sp. coral experience fluctuation of color change although again improved, while two other species Plerogyra sp. and Nemenzophyllia sp. experience color change towards good condition at farm with recirculation system. Observations of color changes in nature experience stress characterized by changes in color towards the white well at depths of 5 m, 10 m, and 15 m. Observation of mortality rate after 33 days was obtained 100% mortality rate at depth 5 m, 10 m for all species, but at 15 m depth Nemenzophyllia sp. suffered 100% mortality and coral that survived Phygogyra sp. and Plerogyra sp. with successive mortality rate was 71.4% and 50.0%. High mortality and bleaching are closely related to conditions of temperature and light intensity in July-August 2017 and other parameters of TDS and DO. Coral propagation was successful in the recirculation system with 0% mortality rate until the research end.

Before platelets: the production of platelet-activating factor during growth and stress in a basal marine organism

Corals and humans represent two extremely disparate metazoan lineages and are therefore useful for comparative evolutionary studies. Two lipid-based molecules that are central to human immunity, platelet-activating factor (PAF) and Lyso-PAF were recently identified in scleractinian corals. To identify processes in corals that involve these molecules, PAF and Lyso-PAF biosynthesis was quantified in conditions known to stimulate PAF production in mammals (tissue growth and exposure to elevated levels of ultraviolet light) and in conditions unique to corals (competing with neighbouring colonies over benthic space). Similar to observations in mammals, PAF production was higher in regions of active tissue growth and increased when corals were exposed to elevated levels of ultraviolet light. PAF production also increased when corals were attacked by the stinging cells of a neighbouring colony, though only the attacked coral exhibited an increase in PAF. This reaction was observed in adjacent areas of the colony, indicating that this response is coordinated across multiple polyps including those not directly subject to the stress. PAF and Lyso-PAF are involved in coral stress responses that are both shared with mammals and unique to the ecology of cnidarians.