Abstract:As the human population increases there is an increasing reliance on aquaculture to supply a safe, reliable, and economic supply of food. Although food production is essential for a healthy population, an increasing threat to global human health is antimicrobial resistance. Extensive antibiotic resistant strains are now being detected; the spread of these strains could greatly reduce medical treatment options available and increase deaths from previously curable infections. Antibiotic resistance is widespread due in part to clinical overuse and misuse; however, the natural processes of horizontal gene transfer and mutation events that allow genetic exchange within microbial populations have been ongoing since ancient times. By their nature, aquaculture systems contain high numbers of diverse bacteria, which exist in combination with the current and past use of antibiotics, probiotics, prebiotics, and other treatment regimens-singularly or in combination. These systems have been designated as "genetic hotspots" for gene transfer. As our reliance on aquaculture grows, it is essential that we identify the sources and sinks of antimicrobial resistance, and monitor and analyse the transfer of antimicrobial resistance between the microbial community, the environment, and the farmed product, in order to better understand the implications to human and environmental health.

Iron supply has a key role in stimulating phytoplankton blooms in high-nitrate low-chlorophyll oceanic waters. However, the fate of the carbon fixed by these blooms, and how efficiently it is exported into the ocean's interior, remains largely unknown. Here we report on the decline and fate of an iron-stimulated diatom bloom in the Gulf of Alaska. The bloom terminated on day 18, following the depletion of iron and then silicic acid, after which mixed-layer particulate organic carbon (POC) concentrations declined over six days. Increased particulate silica export via sinking diatoms was recorded in sediment traps at depths between 50 and 125 m from day 21, yet increased POC export was not evident until day 24. Only a small proportion of the mixed-layer POC was intercepted by the traps, with more than half of the mixed-layer POC deficit attributable to bacterial remineralization and mesozooplankton grazing. The depletion of silicic acid and the inefficient transfer of iron-increased POC below the permanent thermocline have major implications both for the biogeochemical interpretation of times of greater iron supply in the geological past, and also for proposed geo-engineering schemes to increase oceanic carbon sequestration.

We made surveys for whale sharks Rhincodon typus on a total of 99 d from April through June each year from 2006 to 2008 along the southern fringe of the South Ari Atoll, Maldives Archipelago. We recorded the length and sex of each shark observed and made photographs to facilitate repeated identification from their spot patterns using pattern-recognition software. We identified 64 whale sharks from digital photographs taken during 220 sightings over 3 yr. Approx. 87% of those sharks were immature males. The average length of recognisable sharks was 5.98 m (range 2.5 to 10.5 m), significantly shorter than that reported for whale sharks in other aggregations in the Indian Ocean. Our findings suggest that these sharks are either a small proportion of a local population or perhaps an even smaller component of a regional population in the western Indian Ocean. We applied a Lincoln-Petersen closed-population mark-recapture model and a Jolly-Seber openpopulation model to estimate population size, but found that neither model provided reliable results because key assumptions of each were not met.

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While the intricate frustules of diatoms have been well described, understanding of function lags behind that of form. Here, we show that in the presence and absence of tangential flows of up to 800 µm s -1 , diatom surface microtopographies control the diffusion and advection of submicrometre particles across their surfaces. With no flow, particles were localised on the solid areas of diatom frustules and had reduced diffusion compared to diffusion over flat glass. The magnitude of the effect was dependent on the ratio of the bead radius to the areolae radius (a/R o ). Under flow, particles were deflected from the direction of flow by up to 170°, with over 60% of particles shifted more than 20°from the direction of flow. These results suggests that diatom frustules act as particle sorting structures, determining which particles reach the cell membrane and its receptors. This effect has important implications for nutrient uptake and fouling of cells by colloids and particulates, particularly when the particles are much smaller than the areolae. Variations in the hydrodynamic effects of different frustule microstructures on the diffusion and advection of Brownian particles may help explain the diverse range of frustule morphologies observed amongst diatoms. KEY WORDS: Diatom frustules · Particle diffusion · Brownian motion · Functional morphologyResale or republication not permitted without written consent of the publisher