Juvenile morphology of the large Antarctic canopy-forming brown alga, Desmarestia menziesii J. Agardh

Open Access via Springer Compact Agreement. We are grateful to the UK Natural Environment Research Council for funding to FCK (grants NE/D521522/1 and NE/J023094/1), in particular through the Collaborative Antarctic Science Scheme (Grant CASS-134, 2017) to FCK and LSP. Funding for cruise-based observations in 2019 was from US National Science Foundation award OPP-1744550 to CDA. We thank Kate Stanton, Teresa Murphy and Ben Robinson (British Antarctic Survey) for support with diving operations around Rothera in January–February 2018, and also Richard L. Moe (UC Berkeley) for locating specimens corresponding to the morphology described here in the UC collection. Special thanks are due to Charlie Bibby (Financial Times) for taking professional photographs of the unknown Desmarestia sp. in the aquarium of the Bonner Lab at Rothera (Fig. 2a). We would also like to thank Richard L. Moe (UC Berkeley) and Christian Wiencke (AWI Bremerhaven) for their very helpful reviews of this paper. Also, the MASTS pooling initiative (Marine Alliance for Science and Technology for Scotland, funded by the Scottish Funding Council and contributing institutions; grant reference HR09011) is gratefully acknowledged for supporting FCK. This research contributes to the SCAR Ant-ERA research programme.Peer reviewedPublisher PD

What Happens After – Succession of an Epibenthic Hard-Bottom Community after Coral Mass Mortality in Chilean Patagonia

Climate-related extremes and anthropogenic impacts cause disturbances in benthic marine ecosystems. The fjords of Chilean Patagonia host a highly diverse benthic community, including three species of cold-water corals. The dominant scleractinian Desmophyllum dianthus Esper, 1794 shapes its habitat by forming calcareous skeletons and is assumed to be an important ecosystem engineer. After a significant disturbance in 2012 in Comau Fjord (42°20´S, 72°30´W), >99.9 % of the highly abundant scleractinian D. dianthus died along 8.4 km of coastline. This study was conducted to analyze the effect of the mortality event and subsequent recovery of the benthic community. To further investigate the role of D. dianthus in the community, a coral removal experiment was conducted. Underwater pictures of the community affected by the coral die-off (starting 2014) and the experimentally disturbed community (starting 2015) were taken annually to document the species succession, and abiotic parameters were measured. Image analysis was conducted to identify the occurring benthic species and measure abundance and percentage cover. Species richness S, Shannon-Wiener diversity H’ and Pielou’s evenness J’ were calculated and statistical community analysis was applied. After the mortality event, total abundance and percentage cover increased continuously from 2014 to 2016. The scleractinian Caryophyllia huinayensis Cairns, Häussermann and Försterra, 2005 became significantly more abundant. Octocorals and hydrozoans significantly increased in percentage cover, colonizing dead coral skeletons. No taxon exhibited continuous decline in abundance or cover. Individuals of D. dianthus resettled in the benthic community, exhibiting normal growth rates and a steady rise in abundance, and this coral is expected to return to a dominant role in the community. Biodiversity indices were stable over the monitored time span and agreed with results of previous studies conducted in Comau Fjord. At coral removal sites, percentage cover increased due to expansion of encrusting bryozoans and immigration of actinians. Cover reached values comparable to control sites within one year. The changes in the benthic community in both monitoring stations may be attributed to the availability of free substrate and the relief of biotic pressure. The community showed high resilience and stability after the disappearance of the dominant species D. dianthus and no changes in biodiversity were shown. Due to the slow growth of cold-water communities, full recovery of the pre-mortality community structure is estimated to be a long process. This highlights the need for protection of this diverse ecosystem

In situ growth rates of the cold-water coral Desmophyllum dianthus are highest in aragonite undersaturated waters

Cold-water corals (CWC) were long thought to be particularly sensitive to ocean acidification (OA). However, previous laboratory studies indicate no negative effect of low aragonite saturation (Ωar) on growth rates of CWC while the few in situ studies show the same result. The CWC Desmophyllum dianthus is ubiquitous in Comau Fjord (southern Chile), a small but deep (> 400 m) semi-enclosed stratified basin with pronounced horizontal and vertical pH gradients. High densities of D. dianthus can be found below the aragonite saturation horizon (Ωar < 1) but it is not known so far if seasonal changes in Ωar lead to seasonal differences in growth rates. Corals were sampled along the pH gradients of Comau Fjord (Ωar = 0.65-1.45) and cross-transplanted between stations. Skeletal carbonate accretion (buoyant weighing technique) and calcification rates (alkalinity anomaly technique) were measured in austral summer 2016/2017 and winter 2017 and compared to physico-chemical conditions in the water column (T, Ωar). Higher growth rates were found in summer than in winter. Surprisingly, growth of D. dianthus was highest in undersaturated waters in both seasons (Ωar = 0.65 and 0.83) and cross-transplanted specimens were able to acclimatise to Ωar < 1. We conclude that Ωar is a poor predictor of D. dianthus growth and more factors (like plankton food supply) need to be taken into account when investigating the impact of OA on CWC in the future

Seasonal growth and skeletal composition of the cold-water coral Desmophyllum dianthus along an in situ aragonite saturation gradient

Cold-water corals (CWC) have long been considered particularly sensitive to ocean acidification (OA). However, a number of laboratory studies indicate that exposure to acidic waters does not affect CWC growth but in situ OA studies on CWC are scarce. In the naturally acidified Comau Fjord (Chile), high densities of the cosmopolitan CWC Desmophyllum dianthus are found at or below aragonite saturation (Ωar ≤ 1), but it is not known if the corals’ ability to up-regulate the pH in the calcifying fluid (pHcf) and calcify shows seasonal fluctuations due to changes in Ωar and/or food supply. In the present study, corals were sampled along both horizontal and vertical pH gradients in Comau Fjord (equivalent to 0.81 < Ωar < 1.45 and 0.65 < Ωar < 1.45, respectively). We compared D. dianthus’ calcification rates (alkalinity anomaly technique), skeletal carbonate accretion (buoyant weight technique, BWT), linear extension rates (fluorescent microscopy) and pHcf (skeletal δ11B; LA-ICP-MS) with the physico-chemical conditions in the water column (T, Ωar) in austral summer 2016/2017 and winter 2017. Growth rates (BWT) were higher in summer than in winter, with highest values, irritably, at Ωar < 1. Cross-transplant experiments showed that D. dianthus is able to acclimatise to Ωar < 1. A strong biological pHcf up-regulation of 1.13 pH units was found at low pHT with δ11B of 25.6 ‰ compared to ΔpH of 0.77 (δ11B = 23.4 ‰) at higher pHT. The present study shows that Ωar alone is a poor predictor of D. dianthus’ pH up-regulation and growth. They suggest a complex combination of biological and physical factors that need to be considered to constrain the future of CWC in an era of OA

Sustained year-round oceanographic measurements from Rothera Research Station, Antarctica, 1997–2017

Oceanographic changes adjacent to Antarctica have global climatic and ecological impacts. However, this is the most challenging place in the world to obtain marine data due to its remoteness and inhospitable nature, especially in winter. Here, we present more than 2000 Conductivity-Temperature-Depth (CTD) profiles and associated water sample data collected with (almost uniquely) full year-round coverage from the British Antarctic Survey Rothera Research Station at the west Antarctic Peninsula. Sampling is conducted from a small boat or a sled, depending on the sea ice conditions. When conditions allow, sampling is twice weekly in summer and weekly in winter, with profiling to nominally 500 m and with discrete water samples taken at 15 m water depth. Daily observations are made of the sea ice conditions in the area. This paper presents the first 20 years of data collection, 1997-2017. This time series represents a unique and valuable resource for investigations of the high-latitude ocean’s role in climate change, ocean/ice interactions, and marine biogeochemistry and carbon drawdown