Description: Cold-water corals (CWC) are thought to be especially vulnerable to ocean acidification. However, in situ studies on the response of CWC to low aragonite saturation (Ωar) are still scarce. The Comau Fjord in southern Patagonia (Chile) is naturally stratified with vertical and horizontal pH gradients and high abundances of the cosmopolitan CWC Desmophyllum dianthus at Ωar ≤ 1. Previous studies reveal high growth rates of D. dianthus in summer but it is not known if skeletal growth and the ability of internal pH up-regulation show seasonal fluctuations due to changes in Ωar and/or food supply. In the present study, we compare D. dianthus skeletal carbonate accretion (buoyant weight technique) and linear extension rates (fluorescent microscopy) with the physico-chemical conditions in the water column (T, Ωar) in austral summer 2016/2017 and winter 2017. Corals were sampled at six stations at 20m water depth along the presumed horizontal pH gradient of Comau Fjord.

Description: 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.

Description: 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.

Description: The Comau Fjord is located at the northern part of the Chilean fjord system (Patagonia). Caused by its great amount of geological structures it contains a vast biodiversity that is dominated by a unique benthic community. At the same time, it is one of the least studied regions in the world. Due to the exploding economy, the pressure on the local marine ecosystems increases, especially by salmon farms and the development of the coastline. That is the reason for pushing further researches to focus the public interest on the necessity to protect this sensitive marine live. In the Comau Fjord three species of the cosmopolitan cold-water coral Scleractinia were found (Tethocyathus endesa, Caryophyllia huinayensis and Desmophyllum dianthus) in a high abundance of shallow water in less than 20m. This achievable depth makes it ideal for in situ experiments. In principal, there is little knowledge about juvenile growth and the recruitment time of the Scleractinia. Based on a two and a half year seasonal photodocumentary the behaviour of their growth was observed. The Calyx-Diameter of the found individuals was determined and their respective growth rates were calculated. The results were compared regarding possible seasonal fluctuations and differences between the substrate inclinations they were growing on. To find out more about their recruitment period the shape of the curve of their growth was extrapolated. There are no outcomes about T. endesa and C. huinayensis because of their slight abundances. The individuals of D. dianthus are showing a linear as well as exponential associated growing. Some of them also contained a partial phase growing. In the summer the growth rates appear to be highest and in spring at their lowest point. A pattern of the different growth rates between the substrate inclinations was not detected. For more precise statements about the growing and recruitment of the Scleractinia corals more data must be raised.

Description: The dataset contains temperature, salinity, oxygen saturation, chlorophyll a and turbidity data from the AWIPEV underwater observatory from the year 2021 in a temporal resolution of 1 hour. The cabled observatory is located in 12m water depth and comprises single or multiple sensors for a specific parameter (see https://www.awi.de/en/science/biosciences/shelf-sea-system-ecology/main-research-focus/cosyna/underwater-node-spitsbergen.html). For a detailed description of the data see associated metadatafile metadata_svulobs_2021_hydrography.pdf

Description: The dataset contains temperature, salinity, oxygen saturation, chlorophyll a and turbidity data from the Helgoland MarGate underwater observatory from the year 2017 in a temporal resolution of 1 hour. The cabled observatory is located in 10m water depth and comprises single or multiple sensors for a specific parameter (see https://www.awi.de/en/science/biosciences/shelf-sea-system-ecology/main-research-focus/cosyna/underwater-node-helgoland.html). For a detailed description of the data see associated metadatafile "metadata_heluwobs_2017_hydrography.pdf"

Description: The dataset contains temperature, salinity, oxygen saturation, chlorophyll a and turbidity data from the Helgoland MarGate underwater observatory from the year 2022 in a temporal resolution of 1 hour. The cabled observatory is located in 10m water depth and comprises single or multiple sensors for a specific parameter (see https://www.awi.de/en/science/biosciences/shelf-sea-system-ecology/main-research-focus/cosyna/underwater-node-helgoland.html). For a detailed description of the data see associated metadatafile metadata_heluwobs_2022_hydrography.pdf.

Description: The dataset contains temperature, salinity, oxygen saturation, chlorophyll a and turbidity data from the Helgoland MarGate underwater observatory from the year 2023 in a temporal resolution of 1 hour. The cabled observatory is located in 10m water depth and comprises single or multiple sensors for a specific parameter (see https://www.awi.de/en/science/biosciences/shelf-sea-system-ecology/main-research-focus/cosyna/underwater-node-helgoland.html). For a detailed description of the data see associated metadatafile metadata_heluwobs_2023_hydrography.pdf.

Description: The dataset contains temperature, salinity, oxygen saturation and turbidity data from the Helgoland MarGate underwater observatory from the year 2013 in a temporal resolution of 1 hour. The cabled observatory is located in 10m water depth and comprises single or multiple sensors for a specific parameter (see https://www.awi.de/en/science/biosciences/shelf-sea-system-ecology/main-research-focus/cosyna/underwater-node-helgoland.html). For a detailed description of the data see associated metadatafile metadata_heluwobs_2013_hydrography.pdf

Description: The dataset contains temperature, salinity, oxygen saturation, chlorophyll a and turbidity data from the Helgoland MarGate underwater observatory from the year 2021 in a temporal resolution of 1 hour. The cabled observatory is located in 10m water depth and comprises single or multiple sensors for a specific parameter (see https://www.awi.de/en/science/biosciences/shelf-sea-system-ecology/main-research-focus/cosyna/underwater-node-helgoland.html). For a detailed description of the data see associated metadatafile metadata_heluwobs_2021_hydrography.pdf