Ice Formation in Model Biological Membranes in the Presence of Cryoprotectors

Ice formation in model biological membranes is studied by SAXS and WAXS in the presence of cryoprotectors: dimethyl sulfoxide and glycerol. Three types of phospholipid membranes: DPPC, DMPC, DSPC are chosen for the investigation as well-studied model biological membranes. A special cryostat is used for sample cooling from 14.1C to -55.4C. The ice formation is only detected by WAXS in binary phospholipid/water and ternary phospholipid/cryoprotector/water systems in the condition of excess solvent. Ice formation in a binary phospholipid/water system creates an abrupt decrease of the membrane repeat distance by delta-d, so-called ice-induced dehydration of intermembrane space. The value of delta-d decreases as the cryoprotector concentration increases. The formation of ice does not influence the membrane structure (delta-d = 0) for cryoprotector mole fractions higher than 0.05.Comment: PDF: 9 pages, 3 figures; sourse in MS Wor

CO2 enrichment and reduced seawater pH had no effect on the embryonic development of Acropora palmata (Anthozoa, Scleractinia).

The effects of decreased pH, caused by carbon dioxide (CO2) dissolution in seawater (known as ocean acidification (OA)), on the development of newly fertilized eggs of the Caribbean reef-building coral, Acropora palmata, was tested in three experiments conducted during the summers of 2008 and 2009 (two repeats). Three levels of CO2 enrichment were used: present day conditions (400 matm, pH 8.1) and two CO2-enriched conditions (700 matm, pH 7.9, and 1000 matm, pH 7.7). No effects on the progression or timing of development, or embryo and larval size, were detected in any of the three experimental runs. The results show that the embryos and larvae of A. palmata are able to develop normally under seawater pH of at least 0.4 pH units lower than the present levels. Acropora palmata larvae do not usually begin to calcify after settlement, so this study only examined the non-calcifying part of the life cycle of this species. Most of the concern about the effects of OA on marine organisms centers on its effect on calcification. Negative effects of OA on the embryonic development of this species were not found and they may not manifest until the newly settled polyps begin to calcify. © 2013 Taylor & Francis

The origin of variations in the isotopic record of scleractinian corals: I. Oxygen

Previous investigations of the δ 18O of the skeletons of Florida specimens of the reef coral Montastraea annularis have failed to produce the full temperature range suggested by calibration studies of other corals. Explanations for this phenomenon include different relationships between temperature and the δ 18O of skeletons of Floridian corals, changing δ 18O of the water, physiological variables (“vital effects”), and an insufficient number of samples taken per year with consequent superposition of calcium carbonate precipitated at different times within an individual sample. In this study, we investigate all of these hypotheses, by measuring the δ 18O of corals grown in the field which were periodically stained with alizarin-red S and where the δ 18O of the water was measured and the temperature continuously recorded. We compare the effect of sampling the coral skeletons at different resolutions and the effect of sampling within different skeletal elements. Our study shows that discrete, high-resolution sampling of coral exotheca (fifty samples a year) is necessary to reproduce temperatures for this species in Florida waters. Coral skeletons sampled using lower resolution methods showed an artificial attenuation of the annual range in skeletal δ 18O, with similar δ 18O minima during the skeleton represented by the summer months, but larger differences in the winter δ 18O maxima. Replicate isotope transects from fast and slow growing areas and different regions of the corallite were also compared. The δ 18O of rapidly growing (8 mm/y) portions of the colony was 0.1 to 0.2‰ heavier than the slowest growing (1.1 mm/y) portions of the colony. This difference as well as the difference between the skeleton sampled at high and low resolutions appears to result in part from the attenuation of the δ 18O signal as a result of the reduced sampling rate in slower growing sections of the coral and is not solely a result of variable kinetic effects

The origin of variations in the isotopic record of scleractinian corals: II. Carbon

This study examines the relationship between theδ13C of the skeleton of a zooxanthellate coral (Montastraea annularis) growing on the Florida Reef Tract and environmental variables (insolation and temperature), physiological variables (growth rate, respiration, calcification, and photosynthesis). Colonies of this species were grown in the field for a212year study period, during which the rates of photosynthesis, respiration, and calcification were measured on fifteen separate occasions, spaced approximately equally throughout the study period. The corals were stained with alizarin-red S within seven days after each set of physiological measurements. At the end of the period the corals were sacrificed and their skeletal extension, density, and skeletalδ13C determined. Despite substantial high-frequency variations, a strong seasonal cycle was evident in the skeletalδ13C records of all the corals throughout the experimental period. The skeletalδ13C andδ18O values varied approximately in phase, and showed a weak, but statistically significant positive relationship with each other. Theδ13C of the coral skeletons, when corrected for changes in theδ13C of dissolved inorganic carbon (DIC), exhibited an inverse correlation with P/R, a finding opposite to what was expected based on current models of isotopic fractionation in coral skeletons. Although such findings tend to support the model of Erez (1978) that increases in photosynthesis act to isotopically deplete theδ13C of the coral skeleton, we note that the inverse association betweenδ13C and P/R arises because of a slight positive association betweenδ13C and respiration. We therefore believe that the association may be a result of seasonal variation in some parameters of the system which was not constrained in our study. Alternatives include (1) variations in theδ13C of the DIC which are translated into theδ13C of the food chain, (2) changes from heterotrophy to autotrophy, and (3) changes in the partitioning ofδ13C between the zooxanthellae and the coral tissue. Based on previous studies which we have carried out we believe that changes in the skeletalδ13C are not related to sexual reproduction or growth rate. Contrary to previous work we were unable to measure any significant differences in the skeletalδ13C between the fast growing tops of the coral and the slower growing sides

Sexual vs. asexual reproduction in an ecosystem engineer: the massive coral Montastraea annularis

Long-lived sedentary organisms with a massive morphology are often assumed to utilize a storage effect whereby the persistence of a small group of adults can maintain the population when sexual recruitment fails. However, employing storage effects could prove catastrophic if, under changing climatic conditions, the time period between favourable conditions becomes so prolonged that the population cannot be sustained solely be sexual recruitment. When a species has multiple reproductive options, a rapidly changing environment may favour alternative asexual means of propagation. Here, we revisit the importance of asexual dispersal in a massive coral subject to severe climate-induced disturbance. Montastraea annularis is a major framework-builder of Caribbean coral reefs but its survival is threatened by the increasing cover of macroalgae that prevents settlement of coral larvae. To estimate levels of asexual recruitment within populations of M. annularis , samples from three sites in Honduras were genotyped using four, polymorphic microsatellite loci. A total of 114 unique genets were identified with 8% consisting of two or more colonies and an exceptionally large genet at the third site comprising 14 colonies. At least 70% of multicolony genets observed were formed by physical breakage, consistent with storm damage. Our results reveal that long-lived massive corals can propagate using asexual methods even though sexual strategies predominate