Political science

Recent research suggests that prior exposure of several months to elevated irradiance induces enhanced thermal tolerance in scleractinian corals. While this tolerance has been reported at the species level, individual coral colonies may react differently due to individual variability in thermal tolerance. As thermal anomalies are predicted to become common in the upcoming future, intraspecific variation may be key to the survival of coral populations. In order to study light-history based thermal stress responses on individual colonies, we developed a preliminary microcosm experiment where three randomly chosen, aquacultured colonies of the model coral Stylophora pistillata were exposed to two irradiance treatments (200 and 400 μmol photons m−2 s−1) for 31 days, followed by artificially induced heat stress (∼33.4 °C). We found different responses to occur at both the intraspecific and the intracolonial levels, as indicated by either equal, less severe, delayed, and/or even non-necrotic responses of corals previously exposed to the irradiance of 400 compared to 200 μmol photons m−2 s−1. In addition, all individual colonies revealed light-enhanced calcification. Finally, elevated irradiance resulted in a lower chlorophyll a concentration in one colony compared to the control treatment, and the same colony displayed more rapid bleaching compared to the other ones. Taken together, this study highlights the potential importance of intra-individual variability in physiological responses of scleractinian corals and provides recommendations for improving methodological designs for future studies

Adding insult to injury : effects of chronic oxybenzone exposure and elevated temperature on two reef -building corals

Coral bleaching due to global warming currently is the largest threat to coral reefs, which may be exacerbated by altered water quality. Elevated levels of the UV filter oxybenzone in coastal waters as a result of sunscreen use have recently been demonstrated. We studied the effect of chronic oxybenzone exposure and elevated water temperature on coral health. Microcolonies of Stylophora pistillata and Acropora tenuis were cultured in 20 flow-through aquaria, of which 10 were exposed to oxybenzone at a field-relevant concentration of ~0.06 μg L−1 at 26 °C. After two weeks, half of the corals experienced a heat wave culminating at 33 °C. All S. pistillata colonies survived the heat wave, although heat reduced growth and zooxanthellae density, irrespective of oxybenzone. Acropora tenuis survival decreased to 0% at 32 °C, and oxybenzone accelerated mortality. Oxybenzone and heat significantly impacted photosynthetic yield in both species, causing a 5% and 22–33% decrease, respectively. In addition, combined oxybenzone and temperature stress altered the abundance of five bacterial families in the microbiome of S. pistillata. Our results suggest that oxybenzone adds insult to injury by further weakening corals in the face of global warming

Red light represses the photophysiology of the scleractinian coral Stylophora pistillata

Light spectrum plays a key role in the biology of symbiotic corals, with blue light resulting in higher coral growth, zooxanthellae density, chlorophyll a content and photosynthesis rates as compared to red light. However, it is still unclear whether these physiological processes are blue-enhanced or red-repressed. This study investigated the individual and combined effects of blue and red light on the health, zooxanthellae density, photophysiology and colouration of the scleractinian coral Stylophora pistillata over 6 weeks. Coral fragments were exposed to blue, red, and combined 50/50% blue red light, at two irradiance levels (128 and 256 μmol m−2 s−1). Light spectrum affected the health/survival, zooxanthellae density, and NDVI (a proxy for chlorophyll a content) of S. pistillata. Blue light resulted in highest survival rates, whereas red light resulted in low survival at 256 μmol m−2 s−1. Blue light also resulted in higher zooxanthellae densities compared to red light at 256 μmol m−2 s−1, and a higher NDVI compared to red and combined blue red light. Overall, our results suggest that red light negatively affects the health, survival, symbiont density and NDVI of S. pistillata, with a dominance of red over blue light for NDVI

Global Reorganization of Replication Domains During Embryonic Stem Cell Differentiation

DNA replication in mammals is regulated via the coordinate firing of clusters of replicons that duplicate megabase-sized chromosome segments at specific times during S-phase. Cytogenetic studies show that these “replicon clusters” coalesce as subchromosomal units that persist through multiple cell generations, but the molecular boundaries of such units have remained elusive. Moreover, the extent to which changes in replication timing occur during differentiation and their relationship to transcription changes has not been rigorously investigated. We have constructed high-resolution replication-timing profiles in mouse embryonic stem cells (mESCs) before and after differentiation to neural precursor cells. We demonstrate that chromosomes can be segmented into multimegabase domains of coordinate replication, which we call “replication domains,” separated by transition regions whose replication kinetics are consistent with large originless segments. The molecular boundaries of replication domains are remarkably well conserved between distantly related ESC lines and induced pluripotent stem cells. Unexpectedly, ESC differentiation was accompanied by the consolidation of smaller differentially replicating domains into larger coordinately replicated units whose replication time was more aligned to isochore GC content and the density of LINE-1 transposable elements, but not gene density. Replication-timing changes were coordinated with transcription changes for weak promoters more than strong promoters, and were accompanied by rearrangements in subnuclear position. We conclude that replication profiles are cell-type specific, and changes in these profiles reveal chromosome segments that undergo large changes in organization during differentiation. Moreover, smaller replication domains and a higher density of timing transition regions that interrupt isochore replication timing define a novel characteristic of the pluripotent state

Interactive effects of oxygen, carbon dioxide and flow on photosynthesis and respiration in the scleractinian coral Galaxea fascicularis

Rates of dark respiration and net photosynthesis were measured for six replicate clonal fragments of the stony coral Galaxea fascicularis (Linnaeus 1767), which were incubated under 12 different combinations of dissolved oxygen (20%, 100% and 150% saturation), dissolved carbon dioxide (9.5 and 19.1 μmol l-1) and water flow (1-1.6 versus 4-13 cm s-1) in a repeated measures design. Dark respiration was enhanced by increased flow and increased oxygen saturation in an interactive way, which relates to improved oxygen influx into the coral tissue. Oxygen saturation did not influence net photosynthesis: neither hypoxia nor hyperoxia affected net photosynthesis, irrespective of flow and pH, which suggests that hyperoxia does not induce high rates of photorespiration in this coral. Flow and pH had a synergistic effect on net photosynthesis: at high flow, a decrease in pH stimulated net photosynthesis by 14%. These results indicate that for this individual of G. fascicularis, increased uptake of carbon dioxide rather than increased efflux of oxygen explains the beneficial effect of water flow on photosynthesis. Rates of net photosynthesis measured in this study are among the highest ever recorded for scleractinian corals and confirm a strong scope for growth.</p

Meer milieuvriendelijk papier : verkennend onderzoek naar de mogelijkheden voor gebruik van milieuvriendelijk papier op de Universiteit Utrecht

In dit onderzoek is onderzocht hoe het gebruik van milieuvriendelijk papier op de Universiteit Utrecht (UU) gestimuleerd kan worden. Het onderzoek is gedaan in opdracht van het Universitair Milieu Platform Utrecht (UMP). Het UMP is een studentenorganisatie die duurzaamheid en milieuvriendelijkheid aan de UU probeert te bevorderen. Eén van de doelen die het UMP nastreeft is dat medewerkers en studenten minder papier gaan gebruiken en als ze papier gebruiken, dat er dan milieuvriendelijk papier wordt gebruikt. In dit onderzoek is daarom gekeken naar het papiergebruik op de UU en de beweegredenen van papierinkopers om bepaalde papiersoorten in te kopen. De informatie is verkregen aan de hand van interviews bij een aantal papierinkooppunten. Ten eerste is geprobeerd de beweegredenen te achterhalen waarom bij inkooppunten voor bepaalde papiersoorten wordt gekozen. Hierbij is gebruik gemaakt van het Fishbein & Ajzen-model. Dit model verklaart rationeel gedrag door de aspecten die hierbij een rol spelen in verschillende categorieën in te delen. In dit onderzoek is vooral aandacht besteed aan de categorieën attitude, intentie en mogelijkheid, omdat deze het gedrag van mensen het meest direct beïnvloeden. Het blijkt dat vooral de attitude van papierinkopers ten aanzien van milieuvriendelijk papier bepaalt welke papiersoorten ingekocht worden. De soorten milieuvriendelijk papier die momenteel al her en der gebruikt worden op de UU zijn met in het rapport vastgestelde criteria beoordeeld. Hieruit komen een aantal papiersoorten naar voren die aan de criteria voldoen en die in aanmerking komen voor algemeen gebruik als milieuvriendelijk papier: Neusiedler Biotop, Neusiedler Nautilus, Seagull Laser 80 en Xerox Planet Recycled. Van deze vier papiersoorten lijkt Xerox planet recycled de beste keuze: dit papier komt goed uit de selectie op milieuaspecten en voldoet aan andere criteria voor inkoop (zoals een aantrekkelijke prijs). Behalve het aanbevelen van deze papiersoort bij de universiteit, kan het UMP op meerdere fronten proberen het gebruik van milieuvriendelijk papier verder te bevorderen. De belangrijkste aanbeveling aan het UMP is echter om, in overleg met relevante universitaire onderdelen, een voorlichtingscampagne naar de papierinkopers op te zetten. Uit dit onderzoek blijkt namelijk dat de attitude van de papierinkopers ten aanzien van milieuvriendelijk papier een beperkende factor is voor gedragsverandering als ondersteuning voor de invoering van milieuvriendelijk papier. Een manier om deze attitude te veranderen is via voorlichting: de papierinkopers zouden persoonlijk benaderd moeten worden met goed onderbouwde en voor hen relevante informatie over milieuvriendelijk papier

Onset of zooplanktivory and optimal water flow rates for prey capture in newly settled polyps of ten Caribbean coral species

Zooplanktivory is an important source of nutrients in corals, providing up to 35% of daily metabolic energy requirements in some species. However, little is known about coral zooplanktivory shortly after larval settlement and metamorphosis. In most species it is unclear if, when and under which conditions newly settled polyps are able to capture and ingest prey. This remains a critical knowledge gap, as zooplanktivory could allow coral settlers to replenish energy reserves shortly after metamorphosis, possibly improving settler condition during one of their most vulnerable life stages. Here, we documented the onset of prey (Artemia salina nauplii) capture in ten Caribbean coral species and assessed optimal water flow rates (WFR) for prey capture in five of these species. All species initiated zooplanktivory within six days following metamorphosis, with the exception of Acropora palmata which was never observed capturing nauplii during our 20-day study. Optimal WFR for prey capture varied among species, with Favia fragum displaying maximum prey capture rates in zero flow and Diploria labyrinthiformis most effectively capturing nauplii under WFR of 5–20 cm s−1. Under each species’ optimum WFR, prey capture abilities varied considerably, with F. fragum capturing up to one nauplius every two minutes compared to one nauplius every nine minutes in Colpophyllia natans. Using these findings, we make species-specific recommendations to optimize coral husbandry and larval-based restoration practices for these ten coral species

Development of an Integrated Mariculture for the Collagen-Rich Sponge Chondrosia reniformis

In this study, novel methods were tested to culture the collagen-rich sponge Chondrosia reniformis Nardo, 1847 (Demospongiae, Chondrosiida, Chondrosiidae) in the proximity of floating fish cages. In a trial series, survival and growth of cultured explants were monitored near a polluted fish farm and a pristine control site. Attachment methods, plate materials, and plate orientation were compared. In a first trial, chicken wire-covered polyvinyl chloride (PVC) was found to be the most suitable substrate for C. reniformis (100% survival). During a second trial, survival on chicken wire-covered PVC, after six months, was 79% and 63% for polluted and pristine environments, respectively. Net growth was obtained only on culture plates that were oriented away from direct sunlight (39% increase in six months), whereas sponges decreased in size when sun-exposed. Chicken wire caused pressure on explants and it resulted in unwanted epibiont growth and was therefore considered to be unsuitable for long-term culture. In a final trial, sponges were glued to PVC plates and cultured for 13 months oriented away from direct sunlight. Both survival and growth were higher at the polluted site (86% survival and 170% growth) than at the pristine site (39% survival and 79% growth). These results represent a first successful step towards production of sponge collagen in integrated aquacultures.</p

Epizoic acoelomorph flatworms impair zooplankton feeding by the scleractinian coral Galaxea fascicularis

Summary Many scleractinian coral species host epizoic acoelomorph flatworms, both in aquaculture and in situ. These symbiotic flatworms may impair coral growth and health through light-shading, mucus removal and disruption of heterotrophic feeding. To quantify the effect of epizoic flatworms on zooplankton feeding, we conducted video analyses of single polyps of Galaxea fascicularis (Linnaeus 1767) grazing on Artemia nauplii in the presence and absence of symbiotic flatworms. 18S DNA analysis revealed that flatworms inhabiting G. fascicularis belonged to the genus Waminoa (Convolutidae), which were hosted at a density of 3.6±0.4 individuals polyp−1. Polyps hosting flatworms exhibited prey capture rates of 2.2±2.5, 3.4±4.5 and 2.7±3.4 nauplii polyp−1 30 min−1 at prey concentrations of 250, 500 and 1,000 nauplii L−1, respectively. Polyps that had their flatworms removed displayed prey capture rates of 2.7±1.6, 4.8±4.1 and 16.9±10.3 nauplii polyp−1 30 min−1. Significant main and interactive effects of flatworm presence and ambient prey concentration were found, reflected by the fact that flatworms significantly impaired host feeding rates at the highest prey density of 1,000 nauplii L−1. In addition, flatworms displayed kleptoparasitism, removing between 0.1±0.3 and 0.6±1.1 nauplii 30 min−1 from the oral disc of their host, or 5.3±3.3 to 50.0±2.1% of prey acquired by the coral. We suggest classifying the coral-associated Waminoa sp. as an epizoic parasite, as its presence may negatively affect growth and health of the host