Temperature tolerance of symbiotic and non-symbiotic coral larvae

Abstract

Coral larvae represent the ideal model with Which to test many aspects of the relationship between symbiotic zooxanthellae and the coral host because this is the only stage in the life history of the organism where it is easy to produce both symbiotic and nonsymbiotic individuals for comparison. We used this larval model to investigate the effect of the presence of the symbiont on the thermal tolerance of coral larvae. We exposed symbiotic and non-symbiotic larvae of Acropora muricata to 3 temperatures under a mildly stressful level of light (125-150 p.E m-l sol) fur a 7-day period_ Many larvae survived well at 2& and 32° C. In contrast, all larvae died within 40 h at 360 C. Interestingly, there was no major difference in survivorship between symbiotic and non-symbiotic larvae at any temperature indicating that the symbionts had little influence on larval susceptibility to heat and light. However, the density of symbionts in the larvae when the experiments were initiated was low and therefore, unlikely to affect the physiology of the host.