Cold-Water Coral Reefs in the Langenuen Fjord, Southwestern Norway—A Window into Future Environmental Change

Abstract

Ocean warming and acidification pose serious threats to cold-water corals (CWCs) and the surrounding habitat. Yet, little is known about the role of natural short-term and seasonal environmental variability, which could be pivotal to determine the resilience of CWCs in a changing environment. Here, we provide continuous observational data of the hydrodynamic regime (recorded using two benthic landers) and point measurements of the carbonate and nutrient systems from five Lophelia pertusa reefs in the Langenuen Fjord, southwestern Norway, from 2016 to 2017. In this fjord setting, we found that over a tidal (<24 h) cycle during winter storms, the variability of measured parameters at CWC depths was comparable to the intra-annual variability, demonstrating that single point measurements are not sufficient for documenting (and monitoring) the biogeochemical conditions at CWC sites. Due to seasonal and diurnal forcing, parts of the reefs experienced temperatures up to 4 °C warmer (i.e., >12 °C) than the mean conditions and high CT concentrations of 20 µmol kg−1 over the suggested threshold for healthy CWC reefs (i.e., >2170 µmol kg−1). Combined with hindcast measurements, our findings indicate that these shallow fjord reefs may act as an early hotspot for ocean warming and acidification. We predict that corals in Langenuen will face seasonally high temperatures (>18 °C) and hypoxic and corrosive conditions within this century. Therefore, these fjord coral communities could forewarn us of the coming consequences of climate change on CWC diversity and function.

Environmental stability and phenotypic plasticity benefit the cold-water coral Desmophyllum dianthus in an acidified fjord

“…So far, no studies addressed the ability of CWCs to cope with short-term environmental fluctuations. Data are accumulating on the range of environmental conditions in the natural habitats of CWCs that exhibit high-frequency fluctuations 6 , 7 , 9 , 27 , 29 , underscoring the dynamics that CWCs can be exposed to in their natural habitat, as well as the temporal and spatial range relevant to them. However, we often miss corresponding data on the physiological performance of corals.…”

“…Some previous studies investigated the physiology of CWCs in situ 21 – 23 , but only few studies considered the seasonal differences in biotic and abiotic parameters or the small-scale environmental heterogeneities in the habitat of CWCs 24 , 25 . The few available in situ measurements show that temperature, salinity, oxygen and pH vary seasonally and even daily in response to tides, internal waves and advection 9 , 26 – 29 , suggesting that the environment of CWCs is far less uniform than previously assumed. However, the lack of in situ data limits our ability to assess the extent and ability of CWCs to cope with fluctuating environmental conditions.…”

Living on the edge: environmental variability of a shallow late Holocene cold-water coral mound

“…The main reef-forming CWC, Desmophyllum pertusum (formerly described as Lophelia pertusa , Addamo et al 2016 ), is tolerant to a broad range of bottom water temperatures (BWT, 5–15 °C, Büscher et al 2017 ; Dorey et al 2020 ) suggesting that, to a certain degree, CWCs have the ability to cope with thermal stress. In order to obtain environmental and oceanographic thresholds controlling the occurrence of CWCs, ecological tolerance ranges have been studied by observation of modern reef systems (Dullo et al 2008 ; Flögel et al 2014 ; Juva et al 2020 , 2021 ) or by the correlation of CWC occurrences to global datasets (Freiwald 2002 ; Davies et al 2008 ; Davies and Guinotte 2011 ). Additionally, cultivation experiments have been carried out in order to define parameters that inhibit or increase calcification or growth of CWCs (e.g., Form and Riebesell 2012 ; Büscher et al 2017 ; Gammon et al 2018 ; Maier et al 2009 ).…”

Lophelia reefs off North and West Africa–Comparing environment and health

“…In Areas B and C, the DIC mean values reached 2260 µmol/kg, nearly 100 µmolkg −1 ) higher than is considered to be the threshold for healthy reefs (Flögel et al 2014;DIC of <2170 µmol/kg). High DIC values (2200 µmol/kg) were found on wall reefs in Norwegian fjords and are considered to be sentinels for future climate change (Juva et al, 2021). This suggests that the reef in Ghana may have some adaptive capacity, which has also been indicated for Lophelia reefs in the Mediterranean (Maier et al 2013).…”