Dalhousie University

Introduction to subject/research

Climate change does not only affect shallow marine ecosystems, but also the deeper ocean, with so far unknown impacts on its ecosystems. Corals are important habitat-forming species in the deep sea, where they form rich benthic communities that host a variety of invertebrate and fish species. Up to date our knowledge of potential climate change impacts on coral communities is scarce, as baseline knowledge on coral physiology is limited to very few species. In this experiment, we studied for the first time the thermal tolerance of two common coral species in the NW Atlantic, the octocorals Paragorgia arborea, and Primnoa resedaeformis.

FIG. 1 Incubation setup (A) Preparation of respiration chambers in water bath (B) Sensors attached to respiration chamber for continuous measurements.

Set-up

Our experiments took place in a thermoregulated room onboard the NOAA research vessel Henry B. Bigelow. Performing the experiments onboard provided proximity to the sampling site which limited transport and handling of the corals and allowed us to maintain them in water collected from the depth where they occur. Coral fragments were collected by the Remotely Operated Vehicle ROPOS at 700 m, and were maintained in four temperatures (2, 5, 8, 12 ◦C) for 48h. Subsequently we measured coral respiration by performing closed-cell incubations.  Corals were placed in custom-made Polypropylene chambers equipped with a mini 3V water pump which maintained water circulation within them. All chambers were placed in custom-made water baths that stabilized the set-up against the movements of the vessel and were equipped with temperature controllers and heaters/chillers. Oxygen measurements were made by using the PyroScience Firesting-O2 device, connected to four robust oxygen sensors (OXROB10) and a temperature sensor (TSUB21). Each oxygen sensor was calibrated to one of the four temperatures and was used to measure oxygen in the respective treatment.

Obtained data

During our experiments we successfully collected respiration data from 7 colonies of each species at 2, 5, and 8 ◦C, while coral fragments at 12◦C showed high mortality. The collected data increase our understanding of how the two species respond to different temperatures, and allow us to define tipping points for the two species.

FIG. 2 Oxygen consumption rates of the two species under different temperatures

Conclusion from data and application

The setup provided by PyroScience allowed us to define the end point of our incubations easier and perform accurate measurements of oxygen concentration along a range of different temperatures. Our results contribute to the physiological knowledge of extremely understudied species, leading to a better understanding of climate change impacts on deep-sea ecosystems.