Pulse amplitude modulation (PAM) chlorophyll a fluorometry for monitoring the health of corals along the coast of Qatar

Abstract

The Arabian Gulf is shallow, sub-tropical and semi-enclosed, all factors that promote large variations in the properties of its water. The extreme natural variations, in association with global changes such as the increasing pH of the oceans and climate change, make the ecosystem balance of the Gulf very fragile. A one-year-long study was designed to evaluate the effectiveness of PAM (pulse amplitude modulation) chlorophyll a fluorometry in monitoring the health of sensitive ecosystems, such as coral reefs, around Qatar. The immediate objectives were: (i) to evaluate the efficacy of the PAM chlorophyll fluorometry technique as a means of assessing sub-lethal stress in corals; (ii) to calibrate and validate this technique for future ecosystem monitoring applications in this local environment; and (iii) to collect environmental data to attempt to correlate detected changes in stress status to changes in the magnitude of environmental factors that are known to affect these organisms. The study consisted of four field surveys conducted at approximately quarterly time intervals, at two monitoring stations. PAM fluorometry measurements were complemented by detailed visual assessments of the health status of the ecosystems following a traditional belt transect method, continuous recording of seawater temperature, underwater light intensity measurement and water quality monitoring. Results of both types of observations indicated different degrees of sub-lethal stress on most of the coral species at Fuwayrit and Halul. While the visual signs of stress were difficult to quantify, the PAM fluorescence data provided a clearer indication of the stress being experienced by the organisms at the time of the surveys. For one particular species of coral at the Fuwayrit site, PAM measurements of photosynthetic efficiency proved to be a good predictor of imminent mortality. Based on data from the Halul site, it can be inferred that the PAM fluorometry method did not give false indications of stress for healthy corals. This study has demonstrated that PAM fluorometry can improve our ability to monitor the health of corals in the Qatar and Gulf environment by providing objective data on the photosynthetic performances and the state of stress of these organisms.