Ecological role of <Emphasis Type="Italic">Phyllophora antarctica</Emphasis> drift accumulations in coastal soft-sediment communities of McMurdo Sound,Antarctica

At Cape Evans on Ross Island, Antarctica, the rhodophyte Phyllophora antarctica is the dominant primary producer in terms of biomass from 10 to >30 m depth. The vast majority of Phyllophora occurs as accumulations of unattached plants. Whilst decomposition and incorporation of macroalgal drift material into the food web is rapid in temperate ecosystems, we predicted these processes to be slow in Antarctica. We address the functional role of macroalgal detritus in fuelling the biodiversity of benthic communities at Cape Evans during the summers of 2001 and 2002. Specifically we (a) describe the distribution and biomass of attached and drift algae, (b) assess the photosynthetic capacity and degradation of drift accumulations using in situ fluorometry, (c) assess the effect of patches of drift Phyllophora on underlying macrofaunal communities, and, (d) use stable isotopes to investigate the possible uptake of Phyllophora by macrofauna. We found drift Phyllophora accumulations throughout the depth range investigated (3–31 m), with peak biomasses of 140±30 g dwt m^–2 in the 15–25 m depth strata. At this depth stratum Phyllophora was a conspicuous habitat element with the % cover on the seafloor averaging 30%. While initially the drift algal accumulations appeared in good health we measured significant declines in photosynthetic capacity between years suggesting ongoing, albeit slow, degradation of the drift algal accumulations. Our results demonstrate that Phyllophora drift accumulations have a structuring role on soft-sediment communities, which increases in strength with the gradual degradation of the algae. The longevity of Phyllophora is enhanced by secondary metabolites, which serve as protection against grazers, and their extreme shade adaptation. However, our carbon and nitrogen stable isotope data of polychaetes and amphipods associated with Phyllophora suggest that macroalgal detritus enters the food web, and although this process is slow, Phyllophora accumulations might serve to dampen the seasonality in food supply providing higher trophic levels with a more constant food source.     

Pair-level approximations to the spatio-temporal dynamics of epidemics on asymmetric contact networks

The process of infection during an epidemic can be envisaged as being transmitted via a network of routes represented by a contact network. Most differential equation models of epidemics are mean-field models. These contain none of the underlying spatial structure of the contact network. By extending the mean-field models to pair-level, some of the spatial structure can be contained in the model. Some networks of transmission such as river or transportation networks are clearly asymmetric, whereas others such as airborne infection can be regarded as symmetric. Pair-level models have been developed to describe symmetric contact networks. Here we report on work to develop a pair-level model that is also applicable to asymmetric contact networks. The procedure for closing the model at the level of pairs is discussed in detail. The model is compared against stochastic simulations of epidemics on asymmetric contact networks and against the predictions of the symmetric model on the same networks. DEFRA funded project FC1153     

Skeletal muscle mitochondrial FAT/CD36 content and palmitate oxidation are not decreased in obese women

A reduction in fatty acid oxidation has been associated with lipid accumulation and insulin resistance in the skeletal muscle of obese individuals. We examined whether this decrease in fatty acid oxidation was attributable to a reduction in muscle mitochondrial content and/or a dysfunction in fatty acid oxidation within mitochondria obtained from skeletal muscle of age-matched, lean [body mass index (BMI) = 23.3 +/- 0.7 kg/m2] and obese women (BMI = 37.6 +/- 2.2 kg/m2). The mitochondrial marker enzymes citrate synthase (-34%), beta-hydroxyacyl-CoA dehydrogenase (-17%), and cytochrome c oxidase (-32%) were reduced (P < 0.05) in obese participants, indicating that mitochondrial content was diminished. Obesity did not alter the ability of isolated mitochondria to oxidize palmitate; however, fatty acid oxidation was reduced at the whole muscle level by 28% (P < 0.05) in the obese. Mitochondrial fatty acid translocase (FAT/CD36) did not differ in lean and obese individuals, but mitochondrial FAT/CD36 was correlated with mitochondrial fatty acid oxidation (r = 0.67, P < 0.05). We conclude that the reduction in fatty acid oxidation in obese individuals is attributable to a decrease in mitochondrial content, not to an intrinsic defect in the mitochondria obtained from skeletal muscle of obese individuals. In addition, it appears that mitochondrial FAT/CD36 may be involved in regulating fatty acid oxidation in human skeletal muscle.     

Effects of inhaled corticosteroids on sputum cell counts in stable chronic obstructive pulmonary disease: a systematic review and a meta-analysis

Background

Whether inhaled corticosteroids suppress airway inflammation in chronic obstructive pulmonary disease (COPD) remains controversial. We sought to determine the effects of inhaled corticosteroids on sputum indices of inflammation in stable COPD.

Methods

We searched MEDLINE, EMBASE, CINAHL, and the Cochrane Databases for randomized, controlled clinical trials that used induced sputum to evaluate the effect of inhaled corticosteroids in stable COPD. For each chosen study, we calculated the mean differences in the concentrations of sputum cells before and after treatment in both intervention and control groups. These values were then converted into standardized mean differences to accommodate the differences in patient selection, clinical treatment, and biochemical procedures that were employed across original studies. If significant heterogeneity was present (p < 0.10), then a random effects model was used to pool the original data. In the absence of significant heterogeneity, a fixed effects model was used.

Results

We identified six original studies that met the inclusion criteria (N = 162 participants). In studies with higher cumulative dose (≥ 60 mg) or longer duration of therapy (≥ 6 weeks), inhaled corticosteroids were uniformly effective in reducing the total cell, neutrophil, and lymphocyte counts. In contrast, studies with lower cumulative dose (< 60 mg) or shorter duration of therapy (< 6 weeks) did not demonstrate a favorable effect of inhaled corticosteroids on these sputum indices.

Conclusions

Our study suggests that prolonged therapy with inhaled corticosteroids is effective in reducing airway inflammation in stable COPD.     

Changes in Ecosystem Function Across Sedimentary Gradients in Estuaries

The input of terrestrial silt and clay (hereafter mud) into coastal environments can alter sediment grain size distribution affecting the structure and functioning of benthic communities. The relationship between sediment mud content and macrofaunal community structure has been well documented, but not the effects on ecosystem function. In 143 plots from the mid-intertidal sites in 9 estuaries, we measured sediment properties, macrofaunal community composition and fluxes of O₂ and NH₄ ⁺ across the sediment–water interface to derive process-based measures of ecosystem function across the sand–mud gradient. We observed reductions in measures of macrofaunal diversity and decreases in the maximum density of key bioturbating bivalves (Austrovenus stutchburyi and Macomona liliana) with increased mud content. Concurrently, the maximum rates of sediment oxygen consumption (SOC), NH₄ ⁺ efflux (NH₄ ⁺) and biomass standardized gross primary production (GPP_Chl-a ) also decreased with increasing mud content. Environmental predictors explained 34–39% (P = 0.005–0.01) of the total variation in ecosystem function in distance-based linear models. After partitioning out the effect of mud, A. stutchburyi abundance was positively correlated and explained 25 and 23% (P = 0.0001) of the variation of SOC and NH₄ ⁺, respectively. Also, mud content (negatively correlated) and temperature (positively correlated) explained 26% of variability in GPP_Chl-a (P = 0.0001). Our results highlight the importance of increased mud content and the associated reduction in the abundance of strongly interacting key species on the loss of ecosystem function in intertidal sand flats.     

Macroalgal photosynthesis near the southern global limit for growth; Cape Evans,Ross Sea,Antarctica

Photosynthetic characteristics of the red macroalgae Phyllophora antarctica and Phymatolithon foecundum collected from under sea ice at Cape Evans, McMurdo Sound (Ross Sea) were determined using in situ fluorometric and lab-based oxygen exchange techniques. Only 0.16% of incident irradiance penetrated the 2.5 m thick ice cover and photosynthetic parameters for both taxa were characteristic of highly shade-adapted plants. Saturation onset parameter (E _k) did not exceed 13 mol photons m^-2 s^-1 in either taxon. For Phyllophora antarctica the light saturated photosynthetic rate at –1^°C was 10 mol O₂ g^-1 FW h^-1 and respiration averaged 3.3 mol O₂ g^-1 FW h^-1 between sampled depths of 10 and 25 m. A light meter deployed at 15 m depth for a year recorded a marked increase in underwater irradiance on the last day of January 2002 coinciding with ice-breakout, and a maximum value for irradiance of 120 mol photons m^-2 s^-1 on 9 February 2002. The 2-month ice-free period was the only time when irradiance consistently exceeded compensation (photosynthesis=respiration) and enabled Phyllophora antarctica to accumulate sufficient carbon to result in a measurable increase in thallus area equivalent to a biomass increment of 1.87 mg (DW) per frond. Near the southern global limit for marine macroalgae, conditions that dictate the availability of underwater irradiance are extremely variable from year to year. Low respiration rates enhance longevity of the Phyllophora antarctica thallus, enabling it to not only survive the winter darkness, but also to retain photosynthetic capacity and thus take advantage of windows of higher irradiance.