Non-Destructive Measurements of Reef Coral Respiration, Photosynthesis and Calcification Using A Newly Developed Diver-Deployed In Situ Respirometer: CISME

CISME (Coral reef In Situ Metabolism; pronounced “KISS ME”, to reflect the gentle interactions between coral and instrument) is a new tool we have developed to non-destructively measure coral and algal bioenergetics in situ. Such a tool will facilitate research and monitoring of corals and similar benthic organisms affected by ocean acidification, global warming, and other anthropogenic disturbances. CISME is deployed over the organism of interest, and held in place by locking retractors. A foam layer at the bottom of the sensor package seals CISME against the coral, and isolates a volume of ca. 88 ml of seawater for the incubation. Changes over time in dissolved oxygen (O₂, measured with a Presens optode, and pH (measured with a Honeywell ISFET) in the incubation seawater are used to calculate rates of respiration (R) and photosynthesis (P). A sample port is used to withdraw water samples for discrete analyses such as total alkalinity used to calculate calcification rates, and can also be used to introduce experimental reagents (e.g. metabolic inhibitors, CO₂ enriched seawater).The instrument can be deployed over coral species with fairly smooth surface structure, as well as benthic reef organisms such as algal turf, coralline algae and macroalgae. Field tests show that CISME can produce quick, consistent and non-destructive (to the coral) measurements of R (5 minutes), P (5-10 minutes), P vs I (irradiance) response curves (30-40 minutes), and calcification rates (15-20 minutes) on corals and reef algae in their natural environment. By calculating changes in CO₂ (from the pH and total alkalinity data using 'co2sys') we also calculated R and P rates based on delta CO₂ in order to calculate RQ and PQ ratios, which are indicative of the substrates used for R and produced by P, respectively. Our ability to calculate P/R ratios, RQ and PQs with just a few minutes of in situ measurement shows that CISME has the potential to greatly improve our ability to study coral physiology in situ and non-destructively. This is the first time that we know of that such measurements have been made for any coral underwater. A year-long field experiment following seasonal changes in these measures is in progress. Redesign of a new model rated to 70 m, and operated through a wireless tablet, should be ready by mid-2016.