Respiration rate measurements for antipatharians (black corals; Stichopathes gracilis and Antipathella wollastoni) from the Canary Islands Archipelago.

Row data for respiration rate measurements used in the manuscript entitled "Higher daily temperature range at depth is linked with higher thermotolerance in Antipatharians from the Canary Islands". 

Ramp experiments were performed with coral fragments from the three populations (Antipathella wollastoni from 25 m and 40 m and Stichopathes gracilis from 80 m). Each ramp was divided in two legs, respectively called 'hot ramp' and 'cold ramp', both starting at the acclimation temperature. Here, we define 'ramp experiment', as the progressive increase/decrease (hot/cold ramp) by gradual steps of temperature. The minimum temperature tested corresponded to the lower seasonal temperature experienced by the organism in its environment. The maximum temperature tested was the highest seasonal temperature experienced by the organism in its environment +3°C. Each time, one fragment of a colony was used for the hot ramp and the second fragment, from the same colony, was used for the cold ramp. This allowed every fragment to be used only in a single ramp (and not reused), as well as to have paired replicates (fragments from the same colony) between hot and cold ramps.

Each ramp proceeded identically for specimens from the three populations. Seven fragments from different colonies were moved from their acclimation tank to one of the eight respirometry chambers held in the experimental tank. They were first left to acclimate for 1 hour in darkness and then the chambers were closed, and oxygen consumption was measured for 40 min in darkness, starting at the acclimation temperature. After this period of stable temperature, the chambers were opened in the experimental tank (allowing water exchange between the water in the chambers and in the experimental tank) and temperature was increased/decreased for 30 min to the next step of temperature. Once reached, the fragments were left 30 more min in their open chambers to acclimate to the new temperature, before starting a new 40 min measurement period (with closed chambers). Oxygen saturation in the chambers was always above 80%. This procedure was repeated for each step of temperature. At the end of the last respiration rate measurement, chambers were opened, temperature was decreased back to the acclimation temperature and new measurements of respiration rate were taken after 2.5 hours and 12 hours, to evaluate whether the fragments were able to recover from the heat stress (recovery capacity). The recovery capacity was only assessed at the end of the hot ramp (not at the end of the cold ramp). During all ramps, one chamber was left free from any fragment (blank/control chamber) to account for background respiration (i.e., part of the respiration attributed to seawater microbes and/or instrument drift).

Respiration rates were calculated by measuring the oxygen consumption (expressed in oxygen saturation) of the fragments through time, for the eight respirometry chambers simultaneously. One measure was recorded every 5 s on each chamber using fibre-optic oxygen sensors connected to two 4-channel Fibre Optic Oxygen Transmitter (OXY-4 SMA G2 and OXY-4 SMA G3, Pre-Sens Precision Sensing GmbH, Germany). The volume and shape of the chambers changed based on the morphology of the species: fragments of A. wollastoni (bushy) were placed in 400 mL cylindrical plastic chambers and fragments of S. gracilis (unbranched, long and thin corallum) in 50 mL Falcon tubes. A new oxygen sensor spot (PreSens SP-PSt3-NAU-D5-YOP-SA) was glued in every chamber and calibrated according to the supplier’s manual. A magnetic stir bar, separated from the fragment by a mesh, allowed to maintain constant homogenization of the dissolved gas in the chambers.