Centre for Ice, Cryosphere, Carbon and Climate (iC3). Closing large-scale uncertainty in Polar ice sheet impacts on the global carbon cycle

Poster presentation at the International UK Arctic Conference, Cambridge, UK, 11.09.23 - 13.09.23: https://www.bas.ac.uk/event/uk-arctic-science-conference-2023/

Seasonality of oxygen consumption in five common Antarctic benthic marine invertebrates

The waters of the Southern Ocean exhibit extreme seasonality in primary production, with marine life living below 0 °C for much of the year. The metabolic cold adaptation (MCA) hypothesis suggests that polar species need elevated basal metabolic rates to enable activity in such cold which should result in higher metabolic rates, or at least rates similar to temperate species. This study aimed to test whether any of the five common marine invertebrates around Adelaide Island (Western Antarctic Peninsula) displayed MCA: the suspension-feeding holothurian Heterocucumis steineni, the grazing limpet Nacella concinna, and the omnivorous brittle star, cushion star and sea-urchin Ophionotus victoriae, Odontaster validus and Sterechinus neumayeri, respectively. We also tested a second hypothesis that secondary consumers will exhibit less seasonal variation of metabolic rate than primary consumers. Routine oxygen consumption was measured in both the austral summer and winter using closed circuit respirometry techniques. Metabolic rates for all the species studied were low compared with temperate species, in a fashion consistent with expected temperature effects on biological systems and, therefore, the data do not support MCA. All the species studied showed significant seasonal differences for a standard mass animal except N. concinna. In two species N. concinna and H. steineni, size affected the seasonality of metabolism. There was no difference in seasonality of metabolism between primary and secondary consumers. Thus, for secondary consumers seasonal factors, most likely food availability and quality, vary enough to impact metabolic rates, and produce seasonal metabolic signals at all trophic levels. Other factors such as reproductive status that are linked to seasonal signals may also have contributed to the metabolic variation across trophic levels

Benthic biodiversity, carbon storage and the potential for increasing negative feedbacks on climate change in shallow waters of the Antarctic Peninsula

Seafloor biodiversity provides a key ecosystem service, as an efficient route for carbon to be removed from the atmosphere to become buried (long-term) in marine sediment. Protecting near intact ecosystems, particularly those that are hotspots of biodiversity, with high numbers of unique species (endemics), is increasingly being recognised as the best route to protect existing blue carbon. This study measured globally significant stocks of blue carbon held within both rocky (17.5 tonnes carbon km−2) and soft (4.1 t C km−2) substrata shallow (20 m) seafloor communities along the Antarctic Peninsula. Along the 7998 km of seasonally ice-free shoreline, 59% of known dive sites were classified as rocky and 12% as soft substratum. This gave estimates of 253k t C in animals and plants found at 20 m depth, with a potential sequestration of 4.5k t C year−1. More carbon was stored in assemblages with greater functional groups. Of the Antarctic Peninsula shore, 54% is still permanently ice covered, and so blue carbon ecosystem services are expected to more than double with continued climate warming. As one of the few increasing negative feedbacks against climate change, protecting seafloor communities around the Antarctic is expected to help tackle both the biodiversity and climate crises

Use of emerging technologies to help measure fjordic biodiversity and blue carbon: mini-manned submarines and autonomous underwater vehicle swarms

Meaningful protection of global oceans lags far behind that of land and has taken little consideration of climate mitigation potential to date (such as through assessment of blue carbon stocks and change). With the new emphasis on synergistic approaches to the identification and conservation of both carbon- and species- rich habitats, we need much better knowledge of the geography and status of blue carbon habitats beyond coastal wetlands. In subpolar and polar regions, some blue carbon habitats are still emerging and work as negative (mitigating) feedback on climate change, yet remain unprotected despite strong evidence of threat overlap. Scientific research expeditions are gradually increasing our understanding, but appropriate vessels are a limiting factor due to high costs and carbon footprints. Even when available such vessels cannot access all areas (e.g., remote fjords with sills) and may struggle to measure certain aspects of habitats (e.g., steep or vertical surfaces). New technologies and opportunities have advanced to aid some of these problems, and here, two of them are considered, mini-manned submersibles and autonomous underwater vehicles. These two platforms have both become much more available and affordable (through novel partnerships) while also being much more scientifically capable. This technology has the potential to reduce the carbon footprint of science and particularly aid in assessing biology and environment status and change on steep sides, such as fjord walls

Marine biodiversity of Antarctic hard rock communities: species biomass and energy use

This thesis presents the first seasonal study in the Antarctic of shallow water hard rock communities, including surveys to quantify biodiversity and biomass (Ash Free Dry Mass, AFDM). In addition temporal changes in biodiversity since 1998 were evaluated in the same location. To do this all benthic organisms greater than 3mm in size were collected at 6m, 12m and 20m depth from three transects near Rothera Point, Adelaide Island (67° 34’ S, 68° 07’ W) in the summer and winter of 2015. Organisms were identified and their wet, dry and ash free dry masses obtained. Benthic community structure did not vary seasonally, low metabolic costs due to slowed growth rates, reproduction, development with the ability to cease feeding for the winter months may explain the lack of change between season. Community structure did, however, vary with depth, which agrees with previous studies of shallow water Antarctic hard substratum communities. Comparisons between the 2015 and 1998 survey showed reductions of both biodiversity and organic biomass at all three depths over the intervening 17 years. The greatest change was at 12m where faunal density, diversity, richness and biomass all declined significantly between 1998 and 2015. Ice scour is thought to be the main driver of this change as previous studies have shown an increase in ice scour frequency around 10m depth.The effects of seasonality on metabolism were also investigated using the five most common marine invertebrates and significant energy transformers Odontaster validus, Sterechinus neumayeri, Nacella concinna, Heterocucumis steineni and Ophionotus victoriae. Measurements of metabolic rates using closed circuit respirometry were carried out across a size range (juveniles to fully reproductive adults), to represent the population of five locally abundant species during the austral summer and winter. Oxygen consumption of Sterechinus neumayeri and Odontaster validus was significantly higher (by 39% & 44% respectively) in summer than winter. However, metabolic rates showed no consistent seasonal trends in Nacella concinna, and in Ophionotus victoriae and Heterocucumis IV steineni were higher in summer than winter, but only in large individuals which could be due to feeding and reproducing during the summer months. Seasonal metabolic changes were in line with previous studies on Antarctic marine invertebrates.Having established the metabolic rates of these species, identifying how much organic carbon there is in each and what they eat (diet), it is possible to estimate the energy required within the ecosystem to meet their metabolic demands long term. Molecular methods were employed to advance our understanding of diet. Gut contents from the same five species were analysed using DNA extraction and molecular techniques. This project forms a baseline to understand future changes in Antarctic benthic biodiversity and to analyse energy flows in these communities

Juveniles are more resistant to warming than adults in 4 species of Antarctic marine invertebrates

Juvenile stages are often thought to be less resistant to thermal challenges than adults, yet few studies make direct comparisons using the same methods between different life history stages. We tested the resilience of juvenile stages compared to adults in 4 species of Antarctic marine invertebrate over 3 different rates of experimental warming. The species used represent 3 phyla and 4 classes, and were the soft-shelled clam Laternula elliptica, the sea cucumber Cucumaria georgiana, the sea urchin Sterechinus neumayeri, and the seastar Odontaster validus. All four species are widely distributed, locally abundant to very abundant and are amongst the most important in the ecosystem for their roles. At the slowest rate of warming used (1°C 3 days−1) juveniles survived to higher temperatures than adults in all species studied. At the intermediate rate (1°C day−1) juveniles performed better in 3 of the 4 species, with no difference in the 4th, and at the fastest rate of warming (1°C h−1) L. elliptica adults survived to higher temperatures than juveniles, but in C. georgiana juveniles survived to higher temperatures than adults and there were no differences in the other species. Oxygen limitation may explain the better performance of juveniles at the slower rates of warming, whereas the loss of difference between juveniles and adults at the fastest rate of warming suggests another mechanism sets the temperature limit here

Slow arm regeneration in the Antarctic brittle star Ophiur crassa (Echinodermata, Ophiuroidea)

Regeneration of arms in brittle stars is thought to proceed slowly in low temperature environments. Here a survey of natural arm damage and arm regeneration rates is documented in the Antarctic brittle star Ophiura crassa. This relatively small ophiuroid, a detritivore found amongst red macroalgae, displays high levels of natural arm damage and repair. This is largely thought to be due to ice damage in the shallow waters it inhabits. The time scale of arm regeneration was measured in an aquarium-based 10 mo experiment. There was a delayed regeneration phase of 7 mo before arm growth was detectable in this species. This is 2 mo longer than the longest time previously described, which was in another Antarctic ophiuroid, Ophionotus victoriae. The subsequent regeneration of arms in O. crassa occurred at a rate of approximately 0.16 mm mo−1. To date, this is the slowest regeneration rate known of any ophiuroid. The confirmation that such a long delay before arm regeneration occurs in a second Antarctic species provides strong evidence that this phenomenon is yet another characteristic feature of Southern Ocean species, along with deferred maturity, slowed growth and development rates. It is unclear whether delayed initial regeneration phases are adaptations to, or limitations of, low temperature environments

Quantifying zoobenthic blue carbon storage across habitats within the Arctic’s Barents Sea

Introduction: The Arctic sea ice extent in September (when it is at its lowest) has declined 13% Q10 per decade, and the Arctic Ocean is becoming a more Atlantic-influenced system. Rapid climate-forced changes are taking place in many high-latitude marine ecosystems. The Barents Sea is one such highlatitude shelf ecosystem, between approximately 70° and 80°N in the Norwegian Arctic. The purpose of the current study was to estimate zoobenthic blue carbon across multiple habitats within the Barents Sea (trough, basin, shelf, and shallows), potentially providing values to aid ecosystem-based management of these areas under future climate change scenarios. Method: We tested this by capture and analysis of 947 high-resolution (each 405.7 × 340.6 mm, 12 MB, 5 megapixels) seabed images at 17 sites with latitudinal cline, linked to a collection of corresponding oceanographic data. Biotas within these images were identified to one of the 14 functional groups and the density was calculated. Mean stored carbon per individual was assigned by ash mass (AM) and ash-free dry mass (AFDM) of individuals caught within Agassiz trawl deployments at the same sites. Results: Trough sites, except for one site (B16), have a low quantity of zoobenthic blue carbon compared with the shallow, shelf, and basin habitats. Discussion: The results of a previous study focused entirely on trough habitats and are therefore difficult to scale up as the basis for a meaningful estimate of across-habitat zoobenthic blue carbon in the Barents Sea. Compared with the trough and the basin, the shelf and shallow habitats of the Barents Sea are also subjected to more trawling events through demersal fisheries and showed higher zoobenthic blue carbon stock values

GLM statistics for effects of life history stage (adult vs juvenile), rate of warming and interaction terms on the upper temperature limits in <i>L. elliptica</i>, <i>S. neumayeri</i> and <i>O. validus</i>.

<p>GLM statistics for effects of life history stage (adult vs juvenile), rate of warming and interaction terms on the upper temperature limits in <i>L. elliptica</i>, <i>S. neumayeri</i> and <i>O. validus</i>.</p

Upper temperature limits vs shell length for <i>O. validus</i>, at different warming rates.

<p>°C h⁻¹• = juveniles, ▪ = adults; at 1°C day⁻¹ ○ = juveniles, □ = adults; and at 1°C 3 days⁻¹▴ = juveniles, • =  adults.</p