Pelagic Sargassum community change over a 40-year period: temporal and spatial variability.

Pelagic forms of the brown algae (Phaeophyceae) Sargassum spp. and their conspicuous rafts are defining characteristics of the Sargasso Sea in the western North Atlantic. Given rising temperatures and acidity in the surface ocean, we hypothesized that macrofauna associated with Sargassum in the Sargasso Sea have changed with respect to species composition, diversity, evenness, and sessile epibiota coverage since studies were conducted 40 years ago. Sargassum communities were sampled along a transect through the Sargasso Sea in 2011 and 2012 and compared to samples collected in the Sargasso Sea, Gulf Stream, and south of the subtropical convergence zone from 1966 to 1975. Mobile macrofauna communities exhibited changes in community structure and declines in diversity and evenness within a 6-month time period (August 2011-February 2012). Equivalent declines in diversity and evenness were recorded in the same region (Sargasso Sea, 25°-29°N) in 1972-1973. Recent community structures were unlike any documented historically, whether compared to sites of the same latitude range within the Sargasso Sea, or the broader historical dataset of sites ranging across the Sargasso Sea, Gulf Stream, and south of the subtropical convergence zone. Recent samples also recorded low coverage by sessile epibionts, both calcifying forms and hydroids. The diversity and species composition of macrofauna communities associated with Sargassum might be inherently unstable. While several biological and oceanographic factors might have contributed to these observations, including a decline in pH, increase in summer temperatures, and changes in the abundance and distribution of Sargassum seaweed in the area, it is not currently possible to attribute direct causal links.

Capillary electrochromatography on silica columns: factors influencing performance.

Much capillary electrochromatography (CEC) work is carried out on bonded silica packings which offer many advantages: the number of such packings which are available; the fact that the chemistry of bonding and the separation process are fairly well understood; and the possibility of the transfer to CEC of existing HPLC methods. Packing methods for the preparation of CEC columns have been investigated. The problems inherent in the use of burned-in frits remains an obstacle, but can be at least partially overcome by minimising the length and by silanisation. The influence of a variety of mobile phase variables on aspects of CEC is in agreement with theory for: ionic strength, organic content (including isoeluotropy), and pH. Temperature can be used as a variable to change column selectivity in CEC. The influence of pH on electroosmotic flow (EOF) by changing the degree of ionisation of residual silanol groups is similar for a wide range of neutral bonded groups, but is much less marked for bonded sulphonic acid groups. The EOF may be reversed for bonded groups containing nitrogen.

Oxygenated mixed venous PCO2 in healthy subjects.

Despite the large number of blood gas measurements made over the years, precise information is lacking on intrasubject and intersubject variability of carbon dioxide tension. Accordingly, the oxygenated mixed venous CO2 tension was measured in 202 healthy volunteers and the influence of potentially disturbing factors such as intake of coffee and food, exercise and menstruation on the stability of this tension was studied in selected subjects. In the 102 men the mean value was 5.1 mm Hg (SD, 2.9 mm Hg), significantly higher (P less than 0.001) than that of the 100 women, 46.03 mm Hg (SD, 2.48 mm Hg). Among the women the value was significantly lower (P less than 0.01) in those taking oral contraceptives (mean, 44.9 mm Hg; SD, 2.3 mm Hg) than in those not taking these agents (mean, 46.5 mm Hg; SD, 2.4 mm Hg). Intrasubject variability of values was greatest in women taking oral contraceptives, mean day-to-day variation over two mentrual cycles being +/- 3.26 mm Hg. After moderate exercise the tension usually returned to +/- 1 mm Hg of resting values within 5 minutes. Intake of food and coffee had negligible effects on the tension.