Abstract
Acroporids are threatened by varying stressors, including rising ocean temperatures due to anthropogenic climate change. Increased temperature for prolonged period causes a coral to become stressed and can lead to coral bleaching which is the coral’s response and causes the expelling of the coral's zooxanthellae. However, it is also important to note the effects of cold temperatures or cold stress which could also become both more frequent and severe under climate change which can be detrimental to corals. For a coral to be successful, they need ample energy through means of photosynthesis and use that energy to calcify and grow. If the balance is not stable, the coral needs to be able to mitigate the issue, but if it is, it is at high risk of bleaching. The objective of this study was to understand the effects of cold stress on Acropora cervicornis.
To determine the effects of low temperatures on A. cervicornis, there were three tanks which were set at varying temperature treatments. These were set up to be 14˚ C, 16˚ C, 18˚ C. There were varying genotypes included in this experiment to understand which coral genotypes of A. cervicornis were or showed greater tolerance to cold stress. Additionally, buoyant weight data was collected to show the growth and mass of the coral throughout the experiment therefore determining if there was an effect of thermal stress on coral’s ability to grow and calcify. Moreover, respiration and net photosynthesis (NP) were also be observed using intermittent flow respirometers. Once treatment temperature was reached corals were observed daily for signs of loss of fitness and eventually death. The metric used for cold stress tolerance was LT50, the median lethal time (time until death), measured in days. Percent mortality curves were created for each experiment and the best-fit log-logistic curve to the data. It was concluded that there was a hyperbolic relationship between LT50 and temperature where from it, the lower lethal temp was determined as 18.9C and its degree cooling days was 26+/- 10 days.