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MARINFORSK-Marine ressurser og miljø

Fate of cold-water coral reefs - identifying drivers of ecosystem change

Alternative title: Havklima og kaldtvannskorallrev - drivkrefter bak økosystemforandringer

Awarded: NOK 14.7 mill.

Project Number:

244604

Application Type:

Project Period:

2015 - 2019

Partner countries:

The physical, chemical and biological environment in the deep-sea has long been regarded as extremely stable. New data from the FATE field campaigns do not support this. On the contrary, our measurements show that temperature, pH and alkalinity varies naturally and can change quickly in time, making it hard to detect long-term trends as well as biological effects of predicted ocean warming and acidification. Around the Hola reefs bottom water temperature can shift from 6 to 8 degrees within only a few hours when up-welling causes Atlantic bottom water to fill the Hola trough. Alkalinity can change rapidly when new water masses move over the reefs but also due to biological production. When the coral skeleton grows calcium carbonate is taken up from the surrounding water causing reductions in alkalinity in the sea water. Long-term monitoring of the growth of the Hola reefs clearly show that at the time point when the alkalinity changes are most extreme the coral reefs exhibit a very rapid burst in growth, after a 2 year period of growth hiatus. The role of variability in enhancing the resilience of cold-water coral reefs to chromic environmental changes is not known. However, measurements from a range of coral reefs on the Norwegian shelf from 2018 showed that corals exposed to large variabilities in maximum temperature, such as the Hola reefs, are not more resistant to acute temperature stress than other corals, unlike that described for tropical corals. Our long-term experiments indicate that Lophelia pertusa and Acesta excavata have fairly well developed mechanisms to adjust pH internally and can growth in water with pH levels predicted for the end of this century provided they get sufficient food. The situation looked much worse for the sponges. Sponges are simple organisms functioning without specialized organs and with low capacity for acid-base regulation which could help them to sustain growth in water with lower pH. All three groups of animals tested, corals, sponges and deep-sea bivalves appeared highly sensitive to temperature increases. Field experiments corroborate results from lab experiment in that temperature is the strongest diver of the survival, growth and health state of these organisms. Using the vertical gradient in environmental condition around wall reefs we found that temperature is the strongest driver for the distribution of all large habitat forming corals and sponges in Norwegian waters. In waters where temperature is elevated by 2-3 degrees coral and sponge communities are dominated by very small and delicate species. Jointly, our lab and field studies indicate that the future reefs will be dominated by small and delicate species while the large structure forming corals and sponges will gradually become less and less abundant.

Results from the FATE project, with regards to the sensitivity and coral and sponge ecosystems to ocean acidification and ocean warming, have recently been communicated to the Norwegian Environment Agency and to OSPAR, though the Norwegian Environment Agency (in the requested report Seamounts in the OSPAR maritime area: from species to ecosystems, chapter Threats). Results from the project will be incorporated in the next report from Overvåkningsgruppa, Status for miljøet i Norskehavet: rapport fra Overvåkingsgruppen 2019, where members from the FATE team are active. Overvåkningsgruppa is a working group formed as a part of the following up work of the integrated management plans for the Barents and Norwegian Seas, i.e. Integrated Management of the Marine Environment of the Barents Sea and the Sea Areas off the Lofoten Islands and Integrated Management of the Marine Environment of the Norwegian Sea (http://www.miljodirektoratet.no/no/Havforum/Forside/English/).

This research proposal aims to enhance existing knowledge regarding the effects of ocean acidification and warming on the functioning of cold-water coral ecosystems. This will be achieved through a combined field and laboratory investigation. The two year field study will for the first time characterise seasonal variability in water masses associated with two distinct CWC ecosystems using benthic lander systems with ADCPs, sediment traps, an array of sensor technology, and seasonal water sampling. These measures will be correlated to the natural variability in the biology, physiology and geobiology of CWC fauna also sampled seasonally. The laboratory study will assess the 12 months effects of ocean acidification and warming in a flow through system supplied with unfiltered deep water from a near-by CWC ecosystem. Three different food regimes will be used; low (encompassing filtered water), ambient and high (enriched with copepods and phytoplankton) to elucidate if enhanced food availability will alleviate the energetic stress of internal pH up-regulation in the coral when exposed to acidified conditions. This project will take current climate research on CWC ecosystems one step further by investigating not only the response of reef building coral Lophelia pertusa, but also other key organisms associated with CWC ecosystems (i.e. sponges and bivalves). In addition, functional shifts in the bioeroding community in the coral reef framework will also be studied, to provide further information on the structural resilience of coral reef framework. This approach will provide a more holistic ecosystem study and the resulting data will be combined with energetic and ecosystem models to enhance our understanding of how the functioning of CWC ecosystems and associated ecosystem services will change under predicted acidification scenarios.

Funding scheme:

MARINFORSK-Marine ressurser og miljø