Impact of Light and Temperature on the Uptake of Algal Symbionts by Coral Juveniles

Abstract

The effects of temperature and light on the breakdown of the coral-Symbiodinium symbiosis are well documented but current understanding of their roles during initial uptake and establishment of symbiosis is limited. In this study, we investigate how temperature and light affect the uptake of the algal symbionts, ITS1 types C1 and D, by juveniles of the broadcast-spawning corals Acropora tenuis and A. millepora. Elevated temperatures had a strong negative effect on Symbiodinium uptake in both coral species, with corals at 31°C showing as little as 8% uptake compared to 87% at 28°C. Juveniles in high light treatments (390 µmol photons m−2 s−1) had lower cell counts across all temperatures, emphasizing the importance of the light environment during the initial uptake phase. The proportions of the two Symbiodinium types taken up, as quantified by a real time PCR assay using clade C- and D-specific primers, were also influenced by temperature, although variation in uptake dynamics between the two coral species indicates a host effect. At 28°C, A. tenuis juveniles were dominated by C1 Symbiodinium, and while the number of D Symbiodinium cells increased at 31°C, they never exceeded the number of C1 cells. In contrast, juveniles of A. millepora had approximately equal numbers of C1 and D cells at 28°C, but were dominated by D at 30°C and 31°C. This study highlights the significant role that environmental factors play in the establishment of coral-Symbiodinium symbiosis and provides insights into how potentially competing Symbiodinium types take up residence in coral juveniles.

Considerations for maximizing the adaptive potential of restored coral populations in the western Atlantic

“…Environmental conditions affect larval symbiont acquisition, with increasing temperatures appearing to select for thermotolerant symbionts, at least in Acropora from the Great Barrier Reef (Abrego et al. ). One strategy to facilitate the acquisition of appropriate symbionts is thus to outplant settlers prior to symbiont colonization.…”

Population genetics of reef coral endosymbionts (Symbiodinium, Dinophyceae)

“…Similarly, winnowing of the symbiosis by the host or environmental conditions could also select for particular symbiont genotypes over others (Nyholm & McFall‐Ngai ; Abrego et al . , ).…”

Maternal effects and Symbiodinium community composition drive differential patterns in juvenile survival in the coral Acropora tenuis

“…The timely and specific acquisition of different clades/types of Symbiodinium , a key dinoflagellate genus found in corals, has also been linked to juvenile survival, with clades A and D found in greater proportions in surviving juveniles of Acropora yongei [16]. Acropora millepora juveniles also survived better in low-light treatments when symbiont communities were composed of roughly equal proportions of C1 and D Symbiodinium , whereas corals with C1-dominated communities survived better in high-light treatments [17]. Although it is clear that environmental factors play a role in coral juvenile survival, further work is needed to elucidate and quantify the contributions of parental genotypes versus non-genetic maternal effects and the acquisition of symbionts on coral juvenile fates.…”