A test in a high altitude lake of a multi-parametric rapid methodology for assessing life in liquid environments on planetary bodies: A potential new freshwater polychaete Tubeworm community

On our planet, aqueous environments such as deep sea or high-altitude aphotic lakes, subject to present or past volcanic activity and active deglaciation, may provide analogs to the aqueous environments found on such planetary bodies as Europa, Titan or Enceladus. We report here on the methodologies and technologies tested in Laguna Negra, a high altitude lake in the Central Andes, Chile, for exploring and assessing the presence of life within planetary lakes or interior oceans. We adopted a multi-parametric Rapid Ecological Assessment (REA) approach centered around collecting video imagery (by an Underwater Imaging System) and sampling benthic sediments (for sedimentological, biological and geochemical analysis) to depths of 272 m, to complement physico-chemical sampling of the water column and collection of shallow sediments for microbiological analysis (reported in separate publications). This enabled us to classify and assess the apparent status of benthic habitats, based on substrata and environmental characteristics, together with floral and faunal community characteristics and bioturbation artifacts. Video imagery showed that the lower water column was characterized by a variably intense sestonic flux of particles and debris, among which were planktonic organisms such as ostracods, copepods, and possibly cladocerans. Sediment analysis revealed at all depths abundant diatom frustules, mainly of an acidophile pennade diatom Pinnularia acidicola, amid vegetal debris likely originating from littoral macrophytes. Video imagery showed that the lakebed was partly covered by microbial mats and depositional matter and harbored an unexpectedly rich assortment of macrofauna, including sponges, tubificid worms, flatworms, bivalves and crustaceans. Various forms of bioturbation were also encountered, some with the animals in the tracks. Most notably, at the deepest site, a previously undescribed faunal feature was evident, apparently formed by a mat-like community of several layers of what appeared to be polychaete tubeworms, possibly of the family Siboglinidae. It is hypothesized that the hydrothermal activity observed in the region may supply the compounds able to support the deep-water microrganisms from which such tubeworms typically gain sustenance. Such processes could be present on other deep and aphotic liquid-water-bearing planetary bodies

Changing relative abundance and behaviour of silky and grey reef sharks baited over 12 years on a Red Sea reef

There is a lack of studies on how provisioning may influence shark numbers and behaviour. The effects of long-term provisioning were investigated at a Red Sea reef, where both grey reef shark (Carcharhinus amblyrhynchos) and silky shark (Carcharhinus falciformis) occurred. Initially, grey reef sharks outnumbered silky sharks, but over 6 years, silky shark numbers increased almost 20-fold, whereas grey-reef sightings decreased &gt;90%. Following this, silky-shark sightings also declined considerably (&gt;80%). It is suggested that these declines could relate to local overfishing. Many silky sharks were identified individually through distinctive markings or conventional tagging. Some individual silky sharks were recorded regularly over 2 years or more, but most appeared to be transient visitors. Sighting records indicated that provisioning extended the residency of transient individuals. If visiting silky sharks were drawn from a larger regional population, this would explain both their initial accumulation and why, to begin with, sightings were sustained despite local fishing pressure. Conversely, the site fidelity typical of grey reef sharks would have made them more susceptible to local depletion. Silky sharks were recorded as behaving more boldly when present in greater numbers, but the decline in grey reef sharks appears to be unrelated to the initial increase in the numbers of silky shark. </jats:p

Whale Sharks, <em>Rhincodon typus</em>, Aggregate around Offshore Platforms in Qatari Waters of the Arabian Gulf to Feed on Fish Spawn

<div><p>Whale sharks, <i>Rhincodon typus,</i> are known to aggregate to feed in a small number of locations in tropical and subtropical waters. Here we document a newly discovered major aggregation site for whale sharks within the Al Shaheen oil field, 90 km off the coast of Qatar in the Arabian Gulf. Whale sharks were observed between April and September, with peak numbers observed between May and August. Density estimates of up to 100 sharks within an area of 1 km² were recorded. Sharks ranged between four and eight metres’ estimated total length (mean 6.92±1.53 m). Most animals observed were actively feeding on surface zooplankton, consisting primarily of mackerel tuna, <i>Euthynnus affinis,</i> eggs.</p> </div

An image taken by Maersk Oil platform worker Soren Stig on 15^th August 2007, showing an aggregation of whale sharks feeding at the surface in the Al Shaheen Oil Field.

<p>An image taken by Maersk Oil platform worker Soren Stig on 15^th August 2007, showing an aggregation of whale sharks feeding at the surface in the Al Shaheen Oil Field.</p

Bio-volume, in-water surface temperature, salinity and numbers of organisms in plankton samples taken at fixed sampling stations and at sites where feeding whale sharks were encountered.

<p>Bio-volume, in-water surface temperature, salinity and numbers of organisms in plankton samples taken at fixed sampling stations and at sites where feeding whale sharks were encountered.</p

Results of taxonomic inspection of plankton samples showing for each sample the taxa of plankton which accounted for the largest, second largest and third largest portion of the plankton in terms of numbers of individuals, and for each taxa and for fish eggs, the percentage of the zooplankton by numbers for which they accounted.

<p>Results of taxonomic inspection of plankton samples showing for each sample the taxa of plankton which accounted for the largest, second largest and third largest portion of the plankton in terms of numbers of individuals, and for each taxa and for fish eggs, the percentage of the zooplankton by numbers for which they accounted.</p

Map showing the respective locations of Qatar, the United Arab Emirates and the Al Shaheen oil and gas field within the Arabian Gulf, and (inset) of the Arabian Gulf itself in relation the Arabian Peninsula.

<p>Map showing the respective locations of Qatar, the United Arab Emirates and the Al Shaheen oil and gas field within the Arabian Gulf, and (inset) of the Arabian Gulf itself in relation the Arabian Peninsula.</p

Estimated number of whale sharks seen during platform and boat observations and moon phase for May through September 2011.

<p>Estimated number of whale sharks seen during platform and boat observations and moon phase for May through September 2011.</p