Effect of Various Local Anthropogenic Impacts on the Diversity of Coral Mucus-Associated Bacterial Communities

The global continued decline in coral reefs is intensifying the need to understand the response of corals to local environmental stressors. Coral-associated bacterial communities have been suggested to have a swift response to environmental pollutants. This study aims to determine the variation in the bacterial communities associated with the mucus of two coral species, Pocillopora damicornis (Linnaeus, 1758) and Stylophora pistillata (Esper, 1792), and the coral-surrounding seawater from three areas exposed to contamination at the Jordanian coast of the Gulf of Aqaba (Red Sea), and also explores the antibacterial activity of these bacteria. Corals were collected from three contaminated zones along the coast, and the bacteria were quantified and identified by conventional morphological and biochemical tests, as well as 16S rRNA gene sequencing. The average number of bacteria significantly varied among the coral mucus from the sampling zones and between the coral mucus and the surrounding seawater. The P. damicornis mucus-associated bacterial community was dominated by members of the classes Gammaproteobacteria, Cytophagia, and Actinomycetia, while the mucus of S. pistillata represented higher bacterial diversity, with the dominance of the bacterial classes Gammaproteobacteria, Actinomycetia, Alphaproteobacteria, and Bacilli. The effects of local anthropogenic impacts on coral mucus bacterial communities were represented in the increased abundance of bacterial species related to coral diseases. Furthermore, the results demonstrated the existence of bacterial isolates with antibacterial activity that possibly acted as a first line of defense to protect and maintain the coral host against pathogens. Indeed, the dynamics of coral-associated microbial communities highlight the importance of holistic studies that focus on microbial interactions across the coral reef ecosystem

Effects of Water Column Mixing and Stratification on Planktonic Primary Production and Dinitrogen Fixation on a Northern Red Sea Coral Reef

The northern Red Sea experiences strong annual differences in environmental conditions due to its relative high-latitude location for coral reefs. This allows the study of regulatory effects by key environmental parameters (i.e., temperature, inorganic nutrient, and organic matter concentrations) on reef primary production and dinitrogen (N2) fixation, but related knowledge is scarce. Therefore, this study measured environmental parameters, primary production and N2 fixation of phytoplankton groups in the water overlying a coral reef in the Gulf of Aqaba. To this end, we used a comparative approach between mixed and stratified water column scenarios in a full year of seasonal observations. Findings revealed that inorganic nutrient concentrations were significantly higher in the mixed compared to the stratified period. While gross photosynthesis and N2 fixation rates remained similar, net photosynthesis decreased from mixed to stratified period. Net heterotrophic activity of the planktonic community increased significantly during the stratified compared to the mixed period. While inorganic nitrogen (N) availability was correlated with net photosynthesis over the year, N2 fixation only correlated with N availability during the mixed period. This emphasizes the complexity of planktonic trophodynamics in northern Red Sea coral reefs. Comparing mixed and stratified planktonic N2 fixation rates with those of benthic organisms and substrates revealed a close seasonal activity similarity between free-living pelagic and benthic diazotrophs. During the mixed period, N2 fixation potentially contributed up to 3% of planktonic primary production N demand. This contribution increased by ca. one order of magnitude to 21% during the stratified period. Planktonic N2 fixation is likely a significant N source for phytoplankton to maintain high photosynthesis under oligotrophic conditions in coral reefs, especially during stratified conditions

Caribbean scleractinian corals exhibit highly variable tolerances to acute hypoxia

IntroductionClimate change, and the increase in sea surface temperature, is exacerbating ocean deoxygenation because of the inherent property of seawater to sequester less dissolved gas, such as oxygen, at warmer temperatures. While most coral reef studies focus on the effects of thermal stress and ocean acidification, few studies acknowledge the threat of hypoxia. Hypoxia is traditionally defined as 6.3 kPa (2 mg L-1 O2), however, a universal hypoxia threshold is not useful given the vast range of responses among marine organisms. The range of metabolic responses and tolerances to hypoxia are unknown for Caribbean coral species and their algal symbionts.ObjectiveHere, we quantified the spectrum of acute hypoxia tolerances and the range of metabolic responses of six ecologically and structurally important Caribbean coral species (Acropora cervicornis, Siderastrea radians, Siderastrea siderea, Porites astreoides, Porites porites, and Orbicella faveolata) and their algal symbionts (Symbiodinium, Breviolum, and Durusdinium spp.).MethodsA total of 24 coral fragments (4 individuals per species) were exposed to 10 distinct oxygen concentrations ranging from normoxia (20.38 kPa) to severe hypoxia (3.3 kPa). We used intermittent flow respirometry to measure coral host respiration in the dark and algal symbiont photosynthesis in the light at each oxygen level. We determined a line of best fit for the metabolic rate vs. PO2 data and calculated the critical oxygen partial pressure (PO2 crit), a method that has not been tested on symbiotic species.ResultsCoral species and their algal symbionts measured here displayed a wide range of hypoxia tolerances. For the coral hosts, PO2 crit values differed roughly two-fold ranging from 5.74 kPa to 16.93 kPa, and for the algal symbionts, PO2 crit values differed roughly three-fold ranging from 3.9 kPa to 11.3 kPa.DiscussionThese results should be regarded as a first step to characterizing the metabolic response and acute tolerance of multiple coral hosts and algal symbionts to a wide range of oxygen concentrations. Given that some PO2 crit values were above the generally accepted hypoxia threshold, these results have implications for the community composition of reefs under a rapidly changing climate and can guide purposeful reef restoration

Efectos del cambio en la temperatura del agua en la fotosíntesis y la calcificación del Coral Escleractiniario Galaxea fascicularis medidos con microsensores de O2, Ca2+ y pH

Single polyps of Galaxea fascicularis were fixed to glass vials with underwater epoxy resin. After regeneration into microcolonies they were used for microsensor measurements of photosynthesis and calcification under different incubating temperatures. Gross photosynthesis was found highest at temperatures of 23 and 26°C (ca. 0.022 mole O2 m-3 s–1), close to the ambient temperature (i.e. 26°C). At 35°C, gross photosynthesis was irreversibly inhibited as the microcolonies bleached. The net photosynthesis rapidly decreased with temperature and became negative at temperatures higher than 29°C. Profiles of O2 and Ca2+ showed a strong effect of temperature on them. The concentrations of Ca2+ measured on the polyp surface also showed temperature dependence of Ca2+ uptake. In the dark and below 29°C, the surface Ca2+ concentration was temperature independent. During illumination, the surface Ca2+ concentration showed a dip at 26°C (ca. 8.7 mM), indicating maximum uptake rates at ambient temperature. However, at 32°C and higher, Ca2+ was slightly higher at the tissue surface than in the seawater, in both light and dark, resulting from calcium dissolution. The surface pH in light increased gradually from 8.3 to 8.6 with increasing temperature to 23°C, and thereafter remained constant to 29°C. At 32°C, the pH became slightly acidic compared with the water phase, probably due to a decrease in the uptake of CO2 by photosynthesis. The largest difference in pH between light and dark incubations was at temperatures between 23 and 29°C (7.5-7.7 in dark versus 8.6-8.7 in light), which indicate high rates of photosynthesis and respiration in this temperature range. It is concluded that photosynthetic activity in the coral is maintained up to rather high temperatures (32°C), but corals at super-optimum temperatures (above 26°C) consume more O2 than they produce, decalcify and produce CO2Se fijaron pólipos de Galaxea fascicularis sobre viales de cristal con resina epoxy. Una vez generaron pequeñas colonias se utilizaron como sensores para medir los cambios en la fotosíntesis y calsificación a diferentes temperaturas. Los valores de fotosíntesis total (bruta) fueron más elevados a temperaturas entre 23 y 26°C (ca. 0,022 mole O2 m-3 s-1), similares a los del ambiente (26°C). A valores de 35°C, la fotosíntesis total se inhibió irreversiblemente y las pequeñas colonias se blanquearon. La fotosíntesis neta disminuyó rápidamente con la temperatura hasta llegar a valores negativos en temperaturas mayores de 29°C. Los perfiles de O2 y Ca2+ mostraron un elevado efecto de la temperatura. Las concentraciones de Ca2+ medidas en la superficie de los pólipos también mostraron una influencia en la incorporación de Ca2+. En condiciones de oscuridad y temperatura por debajo de 29°C, la concentración de Ca2+ era dependiente de la temperatura. En periodos iluminados, el Ca2+ concentración mostró un pico 26°C (ca. 8,7 mM) hecho que indicaba una tasa de incorporación a temperatura ambiente. hecho que indica que las máximas incorporaciones se efectuaron a temperatura ambiente. Sin embargo, a 32°C o más, los valores de Ca2+ fueren ligeramente altos en la superficie del tejido que en agua de mar, en ambas situaciones de iluminación y oscuridad, resultado de la disolución de la disolución de Calcio. El pH en periodos iluminados se incrementó ligeramente de 8.3 a 8.6, incrementándose la temperatura se y permaneció constante hasta 23°C aunque permenecía constante hasta los 29°C. A 23°C el pH se transformó en un pH ligeramente ácido, probablemente debido a la disminución de en la tasa de retención de CO2 mediante la fotosíntesis. Las mayores diferencias en pH en peiodos iluminados y oscuros fue de 23-29°C (7.5-7.7 en oscuridad versus 8.6-8.7) lo que infica un alta tasa de fotosíntesis y respiración a estos datos en este margen de temperaturas. La conclusión del trabajo es que, la actividad fotosintética en el coral es claramente elevada y se mantiene alta a temperaturas hasta alcanzar los 32°C, pero los corales, en el periodo óptimo de temperaturas de verano (por encima de 26°C) consume mas O2 que el que produce, se descalcifica y produce CO

Metagenomic Analysis of Microbial Community Associated with Coral Mucus from the Gulf of Aqaba

© 2019 The Author(s) Coral-associated microbial communities contribute to a wide variety of useful roles regarding the their host, and therefore, the arrangement of the general microbiome network can emphatically impact coral wellbeing and survival. Various pollution sources can interfere and disrupt the microbial relationship with corals. Here, we adopted the bacterial tag-encoded FLX amplicon pyrosequencing (bTEFAP®) technique to investigate the shift of microbial communities associated with the mucus of the coral Stylophora pistillata collected from five sites (Marine Science Station, Industrial Complex, Oil Terminal, Public Beach, and Phosphate Port) along the Gulf of Aqaba (Red Sea). Our results revealed a high diversity in bacterial populations associated with coral mucus. Proteobacteria were observed to be the dominating phylum among all sampling sites. The identified bacterial taxa belong to the pathogenic bacteria from the genus Vibrio was presented in varying abundances at all sampling sites. Diversity and similarity analysis of microbial communists based on rarefaction curve and UniFrac cluster respectively demonstrated that there are variances in microbial groups associated with coral mucus along sites. The pollution sources among different locations along the Gulf of Aqaba seem to affect the coral-associated holobiont leading to changes in bacterial populations due to increasing human activities

Indications of mutual functional benefits within a polychaete-sponge association in the northern Red Sea

Many polychaetes are commensals or parasitic symbionts of metazoan hosts that provide them with shelter and food. The genus Polydorella currently contains six species of polydorid polychaetes, of these five are described as inconspicuous epibionts (sized <2 mm) of Indo-Pacific sponges. Potential functional benefits generated by polydorid-sponge associations are still unresolved. Polydorid polychaetes may feed on detrital material accumulating on the sponge surface, but related evidence is lacking, as is knowledge on more basic properties, such as their feeding modes. Here, we report on a polydorid-sponge association observed in the Red Sea and provide new insights into potential functional benefit

Seasonality in dinitrogen fixation and primary productivity by coral reef framework substrates from the northern Red Sea

N-2 fixation by coral reef benthic substrates may support primary productivity on oligo trophic coral reefs. However, little is known regarding the influence of environmental para meters on coral reef benthic N-2 fixation. This study quantified N-2 fixation and photosynthesis in 3 common reef framework substrates: turf algae, coral rock, and the abundant encrusting sponge Mycale fistulifera over 4 seasons in the northern Gulf of Aqaba. N-2 fixation activity was detected during day and night for all substrates, but on an annual average was significantly higher for turf algae (4.4 +/- 3.9 nmol C2H4 cm(-2) h(-1)) and coral rock (3.5 +/- 2.8 nmol C2H4 cm(-2) h(-1)) compared to M. fistulifera (0.2 +/- 0.2 nmol C2H4 cm(-2) h(-1)). There was strong seasonality in N-2 fixation, with rates one order of magnitude higher in summer when temperature and irradiance were highest but inorganic nutrient concentrations lowest. During summer and fall, when nutrients were low, we found a significant positive linear relationship between gross photosynthesis (P-gross) and N-2 fixation in turf algae and coral rock. Further, we estimate N-2 fixation can supply up to 20 and 27% of the N demand for net photosynthesis (P-net) in coral rock and turf algae, respectively. By contrast there was no significant relationship between N-2 fixation and Pgross in M. fistulifera, which displayed negative Pnet and heterotrophic metabolism (P-gross: respiratio

Data from: Differential recycling of coral and algal dissolved organic matter via the sponge loop

Corals and macroalgae release large quantities of dissolved organic matter (DOM), one of the largest sources of organic matter produced on coral reefs. By rapidly taking up DOM and transforming it into particulate detritus, coral reef sponges are proposed to play a key role in transferring the energy and nutrients in DOM to higher trophic levels via the recently discovered sponge loop. DOM released by corals and algae differs in quality and composition, but the influence of these different DOM sources on recycling by the sponge loop has not been investigated. Here, we used stable isotope pulse‐chase experiments to compare the processing of naturally sourced coral‐ and algal‐derived DOM by three Red Sea coral reef sponge species: Chondrilla sacciformis, Hemimycale arabica and Mycale fistulifera. Incubation experiments were conducted to trace 13C‐ and 15N‐enriched coral‐ and algal‐derived DOM into the sponge tissue and detritus. Incorporation of 13C into specific phospholipid‐derived fatty acids (PLFAs) was used to differentiate DOM assimilation within the sponge holobiont (i.e. the sponge host vs. its associated bacteria). All sponges assimilated both coral‐ and algal‐derived DOM, but incorporation rates were significantly higher for algal‐derived DOM. The two DOM sources were also processed differently by the sponge holobiont. Algal‐derived DOM was incorporated into bacteria‐specific PLFAs at a higher rate while coral‐derived DOM was more readily incorporated into sponge‐specific PLFAs. A substantial fraction of the dissolved organic carbon (C) and nitrogen (N) assimilated by the sponges was subsequently converted into and released as particulate detritus (15–24% C and 27–49% N). However, algal‐derived DOM was released as detritus at a higher rate. The higher uptake and transformation rates of algal‐ compared with coral‐derived DOM suggest that reef community phase shifts from coral to algal dominance may stimulate DOM cycling through the sponge loop with potential consequences for coral reef biogeochemical cycles and food webs

Effects of water column mixing and stratification on planktonic primary production and dinitrogen fixation on a northern Red Sea coral reef

The northern Red Sea experiences strong annual differences in environmental conditions due to its relative high-latitude location for coral reefs. This allows the study of regulatory effects by key environmental parameters (i.e., temperature, inorganic nutrient, and organic matter concentrations) on reef primary production and dinitrogen (N-2) fixation, but related knowledge is scarce. Therefore, this study measured environmental parameters, primary production and N-2 fixation of phytoplankton groups in the water overlying a coral reef in the Gulf of Aqaba. To this end, we used a comparative approach between mixed and stratified water column scenarios in a full year of seasonal observations. Findings revealed that inorganic nutrient concentrations were significantly higher in the mixed compared to the stratified period. While gross photosynthesis and N-2 fixation rates remained similar, net photosynthesis decreased from mixed to stratified period. Net heterotrophic activity of the planktonic community increased significantly during the stratified compared to the mixed period. While inorganic nitrogen (N) availability was correlated with net photosynthesis over the year, N-2 fixation only correlated with N availability during the mixed period. This emphasizes the complexity of planktonic trophodynamics in northern Red Sea coral reefs. Comparing mixed and stratified planktonic N-2 fixation rates with those of benthic organisms and substrates revealed a close seasonal activity similarity between free-living pelagic and benthic diazotrophs. During the mixed period, N-2 fixation potentially contributed up to 3% of planktonic primary production N demand. This contribution increased by ca. one order of magnitude to 21% during the stratified period. Planktonic N-2 fixation is likely a significant N source for phytoplankton to maintain high photosynthesis under oligotrophic conditions in coral reefs, especially during stratified conditions

Effect of Various Local Anthropogenic Impacts on the Diversity of Coral Mucus-Associated Bacterial Communities

The global continued decline in coral reefs is intensifying the need to understand the response of corals to local environmental stressors. Coral-associated bacterial communities have been suggested to have a swift response to environmental pollutants. This study aims to determine the variation in the bacterial communities associated with the mucus of two coral species, Pocillopora&nbsp;damicornis (Linnaeus, 1758) and Stylophora pistillata (Esper, 1792), and the coral-surrounding seawater from three areas exposed to contamination at the Jordanian coast of the Gulf of Aqaba (Red Sea), and also explores the antibacterial activity of these bacteria. Corals were collected from three contaminated zones along the coast, and the bacteria were quantified and identified by conventional morphological and biochemical tests, as well as 16S rRNA gene sequencing. The average number of bacteria significantly varied among the coral mucus from the sampling zones and between the coral mucus and the surrounding seawater. The P. damicornis mucus-associated bacterial community was dominated by members of the classes Gammaproteobacteria, Cytophagia, and Actinomycetia, while the mucus of S. pistillata represented higher bacterial diversity, with the dominance of the bacterial classes Gammaproteobacteria, Actinomycetia, Alphaproteobacteria, and Bacilli. The effects of local anthropogenic impacts on coral mucus bacterial communities were represented in the increased abundance of bacterial species related to coral diseases. Furthermore, the results demonstrated the existence of bacterial isolates with antibacterial activity that possibly acted as a first line of defense to protect and maintain the coral host against pathogens. Indeed, the dynamics of coral-associated microbial communities highlight the importance of holistic studies that focus on microbial interactions across the coral reef ecosystem