What is blue carbon and why is it important?

The Earth’s warming climate is reducing snow and ice. The warming of the polar seas causes the sea surface to freeze less in winter and glaciers to retreat, generating more open, ice-free water. Less sea ice provides a longer growing season for marine plants called microalgae (phytoplankton) and removes more carbon, in the form of carbon dioxide, from the atmosphere. The growth of microalgae provides more food for animals that eat the algae and store this carbon through growth of their bodies. The carbon stored by marine life is called blue carbon. When marine animals die some of the blue carbon is buried in the seabed, and that carbon is removed from the carbon cycle. This trapping of carbon in the seabed or in other places is called sequestration. The amount of polar blue carbon increases with climate warming. This is known as negative feedback on climate change. Any negative feedback on climate change is important to help combat global warming. In this article explains what we have learned from measuring blue carbon

Turning on the heat: ecological response to simulated warming in the sea

Significant warming has been observed in every ocean, yet our ability to predict the consequences of oceanic warming on marine biodiversity remains poor. Experiments have been severely limited because, until now, it has not been possible to manipulate seawater temperature in a consistent manner across a range of marine habitats. We constructed a "hot-plate'' system to directly examine ecological responses to elevated seawater temperature in a subtidal marine system. The substratum available for colonisation and overlying seawater boundary layer were warmed for 36 days, which resulted in greater biomass of marine organisms and a doubling of space coverage by a dominant colonial ascidian. The "hot-plate'' system will facilitate complex manipulations of temperature and multiple stressors in the field to provide valuable information on the response of individuals, populations and communities to environmental change in any aquatic habitat

Functional group diversity is key to Southern Ocean benthic carbon pathways

High latitude benthos are globally important in terms of accumulation and storage of ocean carbon, and the feedback this is likely to have on regional warming. Understanding this ecosystem service is important but difficult because of complex taxonomic diversity, history and geography of benthic biomass. Using South Georgia as a model location (where the history and geography of benthic biology is relatively well studied) we investigated whether the composition of functional groups were critical to benthic accumulation, immobilization and burial pathway to sequestration–and also aid their study through simplification of identification. We reclassified [1], [2]) morphotype and carbon mass data to 13 functional groups, for each sample of 32 sites around the South Georgia continental shelf. We investigated the influence on carbon accumulation, immobilization and sequestration estimate by multiple factors including the compositions of functional groups. Functional groups showed high diversity within and between sites, and within and between habitat types. Carbon storage was not linked to a functional group in particular but accumulation and immobilization increased with the number of functional groups present and the presence of hard substrata. Functional groups were also important to carbon burial rate, which increased with the presence of mixed (hard and soft substrata). Functional groups showed high surrogacy for taxonomic composition and were useful for examining contrasting habitat categorization. Functional groups not only aid marine carbon storage investigation by reducing time and the need for team size and speciality, but also important to benthic carbon pathways per se. There is a distinct geography to seabed carbon storage; seabed boulder-fields are hotspots of carbon accumulation and immobilization, whilst the interface between such boulder-fields and sediments are key places for burial and sequestration

Microplastic pollution in a rapidly changing world: Implications for remote and vulnerable marine ecosystems

Ecosystems in remote regions tend to be highly specific, having historically evolved over long timescales in relatively constant environmental conditions, with little human influence. Such regions are amongst those most physically altering and biologically threatened by global climate change. In addition, they are increasingly receiving anthropogenic pollution. Microplastic pollution has now been found in these most remote places on earth, far from most human activities. Microplastics can induce complex and wide-ranging physical and chemical effects but little to date is known of their long-term biological impacts. In combination with climate-induced stress, microplastics may lead to enhanced multi-stress impacts, potentially affecting the health and resilience of species and ecosystems. While species in historically populated areas have had some opportunity to adapt to mounting human influence over centuries and millennia, the relatively rapid intensification of widespread anthropogenic activities in recent decades has provided species in previously ‘untouched’ regions little such opportunities. The characteristics of remote ecosystems and the species therein suggest that they could be more sensitive to the combined effects of microplastic pollution, global physical change and other stressors than elsewhere. Here we discuss how species and ecosystems within two remote yet contrasting regions, coastal Antarctica and the deep sea, might be especially vulnerable to harm from microplastic pollution in the context of a rapidly changing environment

Marine colonization and biodiversity at Ascension Island and remote islands

Little is known about colonization of remote island coasts by marine invertebrates, other than corals. The structure of hard substrata assemblages was investigated across Ascension Island's littoral zone in comparison with other sites. Arrays of acrylic panels were deployed at two sites for 2 years at Ascension Island to measure subtidal recruitment. Colonization of panels at Ascension I. was low, though space occupation, abundance and richness varied considerably. After ~1 and 2 years Ascension panels were 30% covered, with >76 recruits per 100 cm2 and with bryozoans well represented after 1 year. Across-littoral surveys of established macrofauna at five remote islands (Ascension I., Easter I., Azores, South Georgia and Signy I., Antarctica) revealed similar trends of a rich sublittoral and lower littoral reducing drastically up-shore; molluscs dominating abundance and species numbers, whilst polychaetes, crustaceans and echinoderms were well represented. Established sessile animals occurred patchily at a mean density of 8.26 m−2 but recruits had mortality levels >99%. Polar or remote temperate/tropical sites are typically less colonized than at non-remote, low latitudes but the lowest levels reported are at remote polar sites. Reduced colonization at Ascension island reflects remoteness

Disturbance, dispersal and marine assemblage structure: A case study from the nearshore Southern Ocean

Disturbance is a key factor in most natural environments and, globally, disturbance regimes are changing, driven by increased anthropogenic influences, including climate change. There is, however, still a lack of understanding about how disturbance interacts with species dispersal capacity to shape marine assemblage structure. We examined the impact of ice scour disturbance history (2009–2016) on the nearshore seafloor in a highly disturbed region of the Western Antarctic Peninsula by contrasting the response of two groups with different dispersal capacities: one consisting of high-dispersal species (mobile with pelagic larvae) and one of low-dispersal species (sessile with benthic larvae). Piecewise Structural Equation Models were constructed to test multi-factorial predictions of the underlying mechanisms, based on hypothesised responses to disturbance for the two groups. At least two or three disturbance factors, acting at different spatial scales, drove assemblage composition. A comparison between both high- and low-dispersal models demonstrated that these mechanisms are dispersal dependent. Disturbance should not be treated as a single metric, but should incorporate remote and direct disturbance events with consideration of taxa-dispersal and disturbance legacy. These modelling approaches can provide insights into how disturbance shapes assemblages in other disturbance regimes, such as fire-prone forests and trawl fisheries

Against the flow: evidence of multiple recent invasions of warmer continental shelf waters by a Southern Ocean brittle star

The Southern Ocean is anomalously rich in benthos. This biodiversity is native, mostly endemic and perceived to be uniquely threatened from climate- and anthropogenically- mediated invasions. Major international scientific effort throughout the last decade has revealed more connectivity than expected between fauna north and south of the worlds strongest marine barrier – the Polar Front (the strongest jet of the Antarctic Circumpolar Current). To date though, no research has demonstrated any radiations of marine taxa out from the Southern Ocean, except at abyssal depths (where conditions differ much less). Our phylogeographic investigation of one of the most ubiquitous and abundant clades at high southern latitudes, the ophiuroids (brittlestars), shows that one of them, Ophiura lymani, has gone against the flow. Remarkably our genetic data suggest that O. lymani has successfully invaded the South American shelf from Antarctica at least three times, in recent (Pleistocene) radiation. Many previous studies have demonstrated links within clades across the PF this is the first in which northwards directional movement of a shelf-restricted species is the only convincing explanation. Rapid, recent, regional warming is likely to facilitate multiple range shift invasions into the Southern Ocean, whereas movement of cold adapted fauna (considered highly stenothermal) out of the Antarctic to warmer shelves has, until now, seemed highly unlikely

Antarctic macrobenthic communities: a compilation of circumpolar information

Comprehensive information on Antarctic macrobenthic community structure has been publicly available since the 1960s. It stems from trawl, dredge, grab, and corer samples as well as from direct and camera observations (Table 1–2). The quality of this information varies considerably; it consists of pure descriptions, figures for presence (absence) and abundance of some key taxa or proxies for such parameters, e.g. sea-floor cover. Some data sets even cover a defined and complete proportion of the macrobenthos with further analyses on diversity and zoogeography. As a consequence the acquisition of data from approximately 90 different campaigns assembled here was not standardised. Nevertheless, it was possible to classify this broad variety of known macrobenthic assemblages to the best of expert knowledge (Gutt 2007; Fig. 1). This overview does not replace statistically sound community and diversity analyses. However, it shows from where which kind of information is available and it acts as an example of the feasibility and power of such data collections. The data set provides unique georeferenced biological basic information for the planning of future coordinated research activities, e.g. under the umbrella of the biology program “Antarctic Thresholds - Ecosystem Resilience and Adaptation” (AnT-ERA) of the Scientific Committee on Antarctic Research (SCAR) and especially for actual conservation issues, e.g. the planning of Marine Protected Areas (MPAs) by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR)

Factors affecting biodiversity on hermit crab shells

This study explores the abundance, diversity and assemblage structure of epifauna on the shells used by two hermit crab species (Pagurus bernhardus and P. pubescens) in the Arctic (Svalbard and Northern Norway) and investigates the biotic and physical drivers of such patterns. Contrary to our expectations, we found that location (which reflects the variability in environmental conditions and the local species pool of potential colonizers) is a key determinant not only in the cold, ice-scoured, glacier-dominated Arctic shallows of Svalbard but also in boreal Norwegian fjords, where other factors were hypothesized to be more important. Depending on region, shell area and identity were of lesser magnitude, with larger and more irregular shells containing more diverse assemblages. Crab host species also played a role (P. pubescens-inhabited shells supported larger number of individuals and higher diversity than those of P. bernhardus) but this effect might be species or region specific. In this study, no effect of crab gender could be detected. The study indicated that epifaunal assemblages of hermit crab shells are influenced by complex set of factors that interact together to different degree at various locations

Icebergs, sea ice, blue carbon and Antarctic climate feedbacks

Sea ice, including icebergs, has a complex relationship with the carbon held within animals (blue carbon) in the polar regions. Sea-ice losses around West Antarctica's continental shelf generate longer phytoplankton blooms but also make it a hotspot for coastal iceberg disturbance. This matters because in polar regions ice scour limits blue carbon storage ecosystem services, which work as a powerful negative feedback on climate change (less sea ice increases phytoplankton blooms, benthic growth, seabed carbon and sequestration). This resets benthic biota succession (maintaining regional biodiversity) and also fertilizes the ocean with nutrients, generating phytoplankton blooms, which cascade carbon capture into seabed storage and burial by benthos. Small icebergs scour coastal shallows, whereas giant icebergs ground deeper, offshore. Significant benthic communities establish where ice shelves have disintegrated (giant icebergs calving), and rapidly grow to accumulate blue carbon storage. When 5000 km2 giant icebergs calve, we estimate that they generate approximately 106 tonnes of immobilized zoobenthic carbon per year (t C yr−1). However, their collisions with the seabed crush and recycle vast benthic communities, costing an estimated 4 × 104 t C yr−1. We calculate that giant iceberg formation (ice shelf disintegration) has a net potential of approximately 106 t C yr−1 sequestration benefits as well as more widely known negative impacts