Recruit symbiosis establishment and Symbiodiniceae composition influenced by adult corals and reef sediment

Abstract

19For most reef-building corals, the establishment of symbiosis occurs via horizontal 20 transmission, where juvenile coral recruits acquire their algal symbionts (family Symbiodiniaceae) 21 from their surrounding environment post-settlement. This transmission strategy allows corals to 22 interact with a diverse array of symbionts, potentially facilitating adaptation to the newly settled 23 environment. We exposed aposymbiotic Pseudodiploria strigosa recruits from the Flower Garden 24Banks to natal reef sediment (C-S+), symbiotic adult coral fragments (C+S-), sediment and coral 25 fragments (C+S+), or seawater controls (C-S-) and quantified rates of symbiont uptake and 26Symbiodiniaceae community composition within each recruit using metabarcoding of the ITS2 27 locus. The most rapid uptake was observed in C+S+ treatments and this combination also led to 28 the highest symbiont alpha diversity in recruits. While C-S+ treatments exhibited the next highest 29 uptake rate, only one individual recruit successfully established symbiosis in the C+S-treatment, 30suggesting that sediment both serves as a direct symbiont source for coral recruits and promotes 31 (or, potentially, mediates) transmission from adult coral colonies. In turn, presence of adult corals 32 facilitated uptake from the sediment, perhaps via chemical signaling. Taken together, our results 33 reinforce the key role of sediment in algal symbiont uptake by P. strigosa recruits and suggest that 34 sediment plays a necessary, but perhaps not sufficient, role in the life cycle of the algal 35Symbiodinaceae symbionts. 36 37

Ontogenetic shifts in Symbiodiniaceae assemblages within cultured Acropora humilis across hatchery rearing and post-transplantation phases

“…Several variables influence the structure of the Symbiodiniaceae assemblage in coral, including biological traits (e.g., age, life-history strategies) and environmental factors (e.g., temperature, light) (LaJeunesse et al, 2010;Stat et al, 2013). The distinct modes of Symbiodiniaceae cell acquisition (vertical and horizontal) can significantly impact the Symbiodiniaceae community in coral offspring (Ali et al, 2019;Swain et al, 2021). For example, the early developmental stages of horizontal symbiont transmission is often correlated with increased diversity of the Symbiodiniaceae communities within corals (Yuyama et al, 2012b;Yamashita et al, 2014).…”

Help Me, Symbionts, You’re My Only Hope: Approaches to Accelerate Our Understanding of Coral Holobiont Interactions

“…These differences in transmission strategies can also lead to differences in adaptive potential of the holobiont across life stages (reviewed in (Putnam, 2021)), and may specifically constrain coral dispersal between environments if algae are locally adapted (S. W. Davies et al, 2020;Howells et al, 2011a). In addition to different algal symbiont transmission strategies, corals exhibit different algal symbiont and microbial community structure across life history stages (Ali et al, 2019;Epstein et al, 2019), highlighting the complexity of holobiont fitness across ontogeny. These complex life cycles combined with differences in transmission strategies across hosts and partners makes predicting coral performance under changing environments challenging.…”