Description: The West Antarctic Peninsula is one of the fastest warming regions on Earth. Faster 20 glacier retreat and related calving events lead to more frequent iceberg scouring, 21 fresh water input and higher sediment loads, which in turn affect shallow water 22 benthic marine assemblages in coastal regions. In addition, ice retreat creates new 23 benthic substrates for colonization. We investigated three size classes of benthic 24 biota (microbenthos, meiofauna and macrofauna) at three sites in Potter Cove (King 25 George Island, West Antarctic Peninsula) situated at similar water depths but 26 experiencing different disturbance regimes related to glacier retreat. Our results 27 revealed the presence of a patchy distribution of highly divergent benthic assemblages within a relatively small area (about 1 km2). In areas with frequent ice 29 scouring and higher sediment accumulation rates, an assemblage mainly dominated 30 by macrobenthic scavengers (such as the polychaete Barrukia cristata), vagile 31 organisms, and younger individuals of sessile species (such as the bivalve Yoldia 32 eightsi) was found. Macrofauna were low in abundance and very patchily distributed 33 in recently ice-free areas close to the glacier, whereas the pioneer nematode genus 34 Microlaimus reached a higher relative abundance in these newly exposed sites. The 35 most diverse and abundant macrofaunal assemblage was found in areas most 36 remote from recent glacier influence. By contrast the meiofauna showed relatively 37 low densities in these areas. The three benthic size classes appeared to respond in 38 different ways to disturbances likely related to ice retreat, suggesting that the 39 capacity to adapt and colonize habitats is dependent on both body size and specific 40 life traits. We predict that, under continued deglaciation, more diverse, but less 41 patchy, benthic assemblages will become established in areas out of reach of glacier-42 related disturbance.

Description: To understand the adaptation of euphausiid (krill) species to oxygen minimum zones (OMZ), respiratory response and stress experiments combining hypoxia/reoxygenation exposure with warming were conducted. Experimental krill species were obtained from the Antarctic (South Georgia area), the Humboldt Current system (HCS, Chilean coast), and the Northern California Current system (NCCS, Oregon). Euphausia mucronata from the HCS shows oxyconforming pO2-dependent respiration below 80% air saturation (18 kPa). Normoxic subsurface oxygenation in winter posed a “high oxygen stress” for this species. The NCCS krill, Euphausia pacifica, and the Antarctic krill, Euphausia superba maintain respiration rates constant down to low critical pO2 values of 6 kPa (30% air saturation) and 11 kPa (55% air saturation), respectively. Antarctic krill had low antioxidant enzyme activities, but high concentrations of the molecular antioxidant glutathione (GSH) and was not lethally affected by 6 h exposure to moderate hypoxia. Temperate krill species had higher SOD (superoxide dismutase) values in winter than in summer, which relate to higher winter metabolic rate (E. pacifica). In all species, antioxidant enzyme activities remained constant during hypoxic exposure at the typical temperature for their habitat. Warming by 7°C above their typical temperature in summer increased SOD activities and GSH levels in E. mucronata (HCS), but no oxidative damage occurred. In winter, when the NCCS is well mixed and the OMZ is deeper, +4°C of warming combined with hypoxia represents a lethal condition for E. pacifica. In summer, when the OMZ expands upwards (100 m subsurface), antioxidant defences counteracted hypoxia and reoxygenation effects in E. pacifica, but only at mildly elevated temperature (+2°C). In this season, experimental warming by +4°C reduced antioxidant activities and the combination of warming with hypoxia again caused mortality of exposed specimens. We conclude that a climate change scenario combining warming and hypoxia represents a serious threat to E. pacifica and, as a consequence, NCCS food webs.

Description: Future oceans are predicted to contain less oxygen than at present. This is because oxygen is less soluble in warmer water and predicted stratification will reduce mixing. Hypoxia in marine environments is thus likely to become more widespread in marine environments and understanding species-responses is important to predicting future impacts on biodiversity. This study used a tractable model, the Antarctic clam, Laternula elliptica, which can live for 36 years, and has a well characterised ecology and physiology to understand responses to hypoxia and how the effect varied with age. Younger animals had a higher condition index, higher adenylate energy charge and transcriptional profiling indicated that they were physically active in their response to hypoxia, whilst older animals were more sedentary, with higher levels of oxidative damage and apoptosis in the gills. These effects could be attributed, in part, to age-related tissue scaling; older animals had proportionally less contractile muscle mass and smaller gills and foot compared with younger animals, with consequential effects on the whole-animal physiological response. The data here emphasize the importance of including age effects, as large mature individuals appear less able to resist hypoxic conditions and this is the size range that is the major contributor to future generations. Thus the increased prevalence of hypoxia in future oceans may have marked effects on benthic organisms abilities to persist and this is especially so for long-lived species when predicting responses to environmental perturbation.