Temperature and Water Quality-Related Patterns in Sediment-Associated Symbiodinium Communities Impact Symbiont Uptake and Fitness of Juveniles in the Genus Acropora

Abstract

The majority of corals acquire their photo-endosymbiont Symbiodinium from environmental sources anew each generation. Despite the critical role that environmental availability of Symbiodinium plays in the potential for corals to acclimate and adapt to changing environments, little is known about the diversity of free-living Symbiodinium communities and how variation in these communities influences uptake and in hospite communities in juvenile corals. Here we characterize Symbiodinium community diversity in sediment samples collected from eight reefs representing latitudinal and cross-shelf variation in water quality and temperature regimes. Sediment-associated Symbiodinium communities were then compared to in hospite communities acquired by A. tenuis and A. millepora juveniles following 11-145 days of experimental exposure to sediments from each of the reefs. Communities associated with juveniles and sediments differed substantially, with sediments harboring four times more unique OTUs than juveniles (1,125 OTUs vs. 271). Moreover, only 10.6% of these OTUs were shared between juveniles and sediments, indicating selective uptake by acroporid juveniles. The diversity and abundance of Symbiodinium types differed among sediment samples from different temperature and water quality environments. Symbiodinium communities acquired by juveniles also differed among the sediment treatments, despite juveniles having similar parentage. Moreover, Symbiodinium communities displayed different rates of infection, mortality, and photochemical efficiencies, important traits for coral fitness. This study demonstrates that the biogeography of free-living Symbiodinium types found within sediment reservoirs follows patterns along latitudinal and water quality environmental gradients on the Great Barrier Reef. We also demonstrate a bipartite strategy for Symbiodinium uptake by juvenile corals of two horizontally-transmitting acroporid species, whereby uptake is selective within the constraints of environmental availability.

The use of larvae or recruits in coral restoration initiatives: Symbiodinium acquisition does not differ between coral life stages in the wild

“…However, it is unclear whether corals naturally obtain Symbiodinium : (1) as larvae only, (2) as settled juveniles only (<1 month old), (3) or through continuous exposure and infection during the larval and juvenile phases. Strong biogeographical and environmental gradients in free‐living and in hospite Symbiodinium are consistent with local thermal adaptation of the coral holobiont (Howells et al ; Quigley et al ) and supports the hypothesis that it may be more beneficial to acquire Symbiodinium post‐settlement to avoid uptake of non‐locally adapted strains. Larvae also differ transcriptomically compared to juveniles (Reyes‐Bermudez et al ) and may also undergo winnowing of Symbiodinium communities during ontogeny (Abrego et al ).…”

Symbiodiniaceae probiotics for use in bleaching recovery

“…This process involves either uptake of novel exogenous Symbiodiniaceae from the environmental pool ("switching"), or a change in relative abundances of Symbiodiniaceae already present within the coral ("shuffling") (Baker 2003) which appears to be a more common process (Jones et al 2008;Cunning & Baker 2013;Bay et al 2016), whereas the evidence for switching during heat stress is limited (Boulotte et al 2016), and may not be maintained long term (Coffroth et al 2010). The ability to shuffle or switch may be limited by host genetic constraints and/or the environmental scarcity of certain symbiont taxa (Poland & Coffroth 2017;Quigley et al 2017aQuigley et al , 2017b.…”

Structural rearrangements drive extensive genome divergence between symbiotic and free-living Symbiodinium

“…The genetic diversity in Symbiodiniaceae is in line with their broad range of symbiotic associations with other organisms, covering a broad spectrum depending on host specificity, transmission mode and permanence in the host 11,12 . Furthermore, some taxa are considered free-living because they have been found only in environmental samples, and in experiments fail to infect potential hosts 13–15 .…”