Flexi-chambers and 3D photogrammetry effectively measure coral fragment physiology in situ

Abstract

Non-invasive techniques for measuring the physiological performance of corals in situ are important for understanding responses to changing environmental conditions. Two such methods are the ‘flexi-chamber’ and three-dimensional (3D) photogrammetry. While these have been verified for coral colonies, they have not been tested on coral fragments which are commonly used in field experiments. This study aimed to determine if these methods can effectively measure respiration, photosynthesis, and growth of fragments of massive and sub-massive coral species in the intertidal and subtidal habitats in Park Rynie, South Africa (30.3167° S, 30.7333° E). Differences in respiration and photosynthesis rates between species and habitat were successfully measured using the flexi-chambers. The coral fragments did not show any visual signs of stress (excess mucus production or loss of pigmentation) during the 3-h incubations or an hour after the incubations. 3D models were successfully constructed for all fragments. This study showed that flexi-chambers and 3D photogrammetry can be effectively used to measure the respiration, photosynthesis, and growth of individual coral fragments (3 cm > 4 cm) of different morphology and habitats. The combination of the two methods permits measures of fundamental physiological processes to be attained at relatively low cost and low complexity. This will facilitate studies of a wide range of coral species in situ generating more knowledge on responses to environmental variability.