Description: Warming over Antarctica is leading to changes in the zooplankton communities inhabiting the Southern Ocean. It has been observed that zooplankton not only regulates phytoplankton through grazing, but also through the recycling of nutrients that are essential for phytoplankton growth. In this way, the effects of warming on zooplankton populations will change the amount or proportion at which recycled nutrients are restored. To estimate how the recycled nutrients released by zooplankton populations, dominated by krill ( Euphausia superba ), amphipods or copepods, affect the phytoplankton uptake and communities, we performed four incubation experiments: two close to the Antarctic Peninsula and two at the Southern Atlantic Ocean. Our results showed a stimulating effect of the addition of metabolites on ammonia removal rates and on the net growth of phytoplankton communities, with different responses amongst the different phytoplankton groups. According to our results, phytoplankton net growth and community composition may be altered if this relevant source of nutrients is lost due to projected changes in the abundance or distribution of these zooplankton populations.

Description: Sedimentary organic matter (OM) represents the energy supply for the shelf benthos at the Antarctic Ocean, and has yet to be properly characterized in terms of sources and composition for the Potter Cove region, King George/25 de Mayo Island. This energy input occurs mainly during the brief summer and provides the majority of available energy for the year, in a region with high endemism and limited source variety of sedimentary OM. Thus, the aim of this study is to identify the OM origin and degradation degree based on the spatial distribution and type of organic biomarkers. Twelve surficial sediment samples were collected and analyzed for the presence of n -alkanols and sterols. The different spatial patterns between the analyzed compounds indicated distinct OM sources and degradation degrees. First, relatively fresh phytoplankton organic matter and an enhanced bacterial activity were associated with the occurrence of seaweeds detritus and represent the source of n -alkanols. Second, relatively fresh material mainly associated with seaweeds debris were identified as the source of macroalgae sterols. Our results shed some light into the base of the Potter Cove trophic benthic chain and increase our understanding on the region’s biogeochemical processes relating to OM recycling. It also provides a baseline for assessing future changes in the structure of the benthic food web in this environment, which is subject to noticeable glaciers retreat.

Description: Invasive species present a risk to Antarctic ecosystems by altering community structure and function. Reports of non-native invertebrates are increasing at Antarctic sites subject to tourism industry and national operator activity. Furthermore, dispersal of existing non-native species to other Antarctic sites may greatly expand their distributions and increase the spatial scale of potential impacts. Consequently, non-native species occurring near logistical hubs present an enhanced risk. The non-native Collembolon, Hypogastrura viatica , was introduced to Léonie Island, Ryder Bay, near the logistical hub of Rothera Research Station, Rothera Point, Adelaide Island, at some point before 1993, but no attempt had been made to assess the extent of its distribution in the local area. In this study, we surveyed the regularly frequented islands of Ryder Bay and Rothera Point to attempt to assess the continued presence and distribution of this species. Hypogastrura viatica was not identified amongst the 36,796 Collembola specimens extracted from 138 samples taken from the islands and Rothera Point. With no evidence of the continued presence of this non-native Collembolon in the local area, either H. viatica has become extinct or has such a restricted spatial distribution that our monitoring programme failed to detect it. In light of these results, existing local biosecurity measures will be maintained as a precautionary measure to reduce the risk of further anthropogenic dispersal of this potentially invasive Collembolon as well as of any other species imported unintentionally in future.

Description: Following the retreat of a glacier, microbial colonization paves the way for future plant successions as nutrients are gradually introduced into the ecosystem. Characterizing the dynamics of this initial microbial colonization process is a key to understanding how these rapidly receding glacier areas are colonized. This study examines primary successions of bacteria, fungi and algae in two glacier forefields chronosequences on opposite slopes of Cordillera Darwin (Tierra del Fuego, Chile). Both slopes (southern and northern) show contrasting climate factors along with rapid rates of plant succession. Through a high-throughput sequencing approach, we identified Cyanobacteria as the dominant bacteria in younger soils close to the glacier terminus, whereas abundances of Alphaproteobacteria and Acidobacteria increased with soil surface age. Lichen-forming fungi and parasitic fungi were the most abundant fungal groups in younger succession stages, while saprophytic and mycorrhizal orders dominated later stages. The order Prasiolales predominated algal communities close to the glacier terminus, while Microthamniales and Chlamydomonadales orders dominated subsequent succession stages. Our observations reflect a changing community structure over time of the three microbial groups examined, and the replacement of taxa during the succession. Changes in composition are especially marked between the youngest succession states and subsequent ones in both forefields. Simultaneous analysis of bacterial, fungal and algal communities revealed the different trajectories of the three groups, with bacterial and fungal communities showing more marked succession patterns. Our results point to more relevant roles for bacteria at the initial stages of succession, while fungi could play a dominant role over bacteria as succession progresses. The ubiquity of algal taxa along the chronosequences was also observed. The two glacier forefields showed different microbial temporal dynamics, indicating that local factors affect the rate of microbial community assembly and, consequently, drive the primary succession process.

Description: Antarctic krill ( Euphausia superba ) play a central role in the food web of the Southern Ocean, forming a link between primary production and large predators. Krill produce large, faecal pellets (FP) which can form a large component of mesopelagic particulate organic carbon (POC) fluxes. However, the patchy distribution of krill swarms, highly variable pellet composition, and variable sinking and attenuation rates means that these episodic, but potentially large, carbon fluxes are difficult to sample or model. We measured particle flux and type using Marine Snow Catchers (MSC) in the marginal ice zone near the South Orkneys, Antarctica. Krill FP were the dominant component of the POC flux in the upper 200 m (typically 60–85%). FP sinking velocities measured onboard were highly variable (15–507 m d −1 ) but overall high, with mean equivalent velocities of 172, 267, and 161 m d −1 at our three stations. The high numbers of krill FP sinking through the mesopelagic suggest that krill FP can be transferred efficiently and/or that rates of krill FP production are high. We compared our direct MSC-derived estimates of krill FP POC flux (33–154 mg C m −2 d −1 ) and attenuation to estimates of krill FP production based on previous measurements of krill density and literature FP egestion rates, and estimated net krill FP attenuation rates in the upper mesopelagic. Calculated attenuation rates are sensitive to krill densities in the overlying water column but suggest that krill FP could be transferred efficiently through the upper mesopelagic, and, in agreement with our MSC attenuation estimates, could make large contributions to bathypelagic POC fluxes. Our study contrasts with some others which suggest rapid FP attenuation, highlighting the need for further work to constrain attenuation rates and assess how important the contribution of Antarctic krill FP could be to the Southern Ocean biological carbon pump.

Description: Based on prior knowledge of the in-air hearing thresholds of seals at the time, Terhune (Polar Biol 27:810–812, 2004) suggested that Weddell seals ( Leptonychotes weddellii ) likely could not hear underwater calls, while they were on the ice. However, recent data on phocid hearing thresholds in the air reveal that seals have much lower detection thresholds than previously thought. A re-analysis of the situation using the lower hearing threshold data finds that many of the Weddell seal underwater calls, especially those with high-frequency components, will be audible to seals resting on the ice. Territorial males vocally defending territories under the ice during the breeding season may also be communicating with females on the ice directly above them. This communication may facilitate later mating success of those males.

Description: Nutrient availability is one of the most important factors controlling Arctic plant productivity. It is also sensitive to climate change, with increased nitrogen (N) mineralization arising from warmer soils and deeper snow. However, warming also tends to reduce snow cover duration, leading to antagonistic effects of climate change on mineralization. Furthermore, since snow melt is also a trigger for seasonal nutrient pulses, changes to snow melt timing may alter seasonal availability to plants. To investigate the impacts of environmental conditions on ecosystem nutrient availability and seasonal dynamics, we undertook regular, high-frequency measurements of soil extractable and plant N and phosphorus (P) concentrations along with winter and summer N and P mineralization rates along a sub-Arctic catchment representing a gradient in temperature, snow melt timing and vegetation composition. Our data show that a delay in snow melt timing of 11 days did not alter the seasonal dynamics of soil or leaf N and P concentrations. Net N mineralization, however, was highest at the warmest site and at the site with the most productive vegetation, while P was strongly immobilized at all sites, both in winter and summer. N:P ratios suggest that plants were generally P limited at all sites, probably due to strong P immobilization. Our data suggest that where warming and resulting vegetation change increase net N mineralization rates, in combination with strong P immobilization this may impose greater P limitation, possibly limiting the extent to which Arctic ecosystems can increase productivity under warming.

Description: Benthic hydroids are an important component of the Antarctic benthic ecosystem. They have been studied since the first Antarctic expeditions, and in recent years, there has been an important increase in biodiversity studies. In order to analyse the relationship among different areas and validate/dismiss previous biogeographical hypotheses, we have compiled all valid records of the known benthic hydroid species from the Antarctic and Sub-Antarctic regions, and used two previous scheme divisions of the Southern Ocean. In both cases, a hierarchical cluster was performed with the SIMPROF test. Our results suggest the division of the Southern Ocean into three main regions: the first corresponds to the classical Patagonian region; the second consists of the Kerguelen Archipelago, Crozet Island, Prince Edward Islands and Bouvet; the third, here referred to as the Antarctic region, is formed by South Georgia, the Scotia Arc archipelagos and High Antarctica. The results obtained also support the classical division of High Antarctica into two subregions, corresponding to West and East Antarctica. Nevertheless, the limits between both regions are still unclear, mainly because of the scarcity of data from some areas and the complete absence of information from others.