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

Abstract

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

Cladocopiumcommunity divergence in twoAcroporacoral hosts across multiple spatial scales

“…Initial symbiont infection is probably determined by local availability of symbionts, either free‐living or, those that have been recently evacuated from local coral hosts (Thornhill et al., 2017). Diverse infections are made possible by the flexibility of arriving coral recruits (Abrego et al., 2009; Ali et al., 2019; Cumbo et al., 2013; Little et al., 2004). After infection, a winnowing process ‐ competition between symbiont strains modulated both by the host and by the environment ‐ leads to the eventual dominance of a single asexual lineage of symbionts in a single host colony and distinct symbiont communities across coral hosts in a specific habitat (Rowan et al., 1997; Thornhill et al., 2017).…”

“…Vertically transmitting corals guarantee the maintenance of symbiosis in their offspring, however if larvae encounter novel environments, their symbiont composition may be suboptimal resulting in reduced fitness (Byler et al., 2013; Douglas, 1998; Wilkinson & Sherratt, 2001). During horizontal transmission, aposymbiotic larvae have flexibility in symbiont acquisition and upon arrival to new environments, they can uptake novel symbionts not present in parental populations (Abrego et al., 2009; Ali et al., 2019; Gómez‐Cabrera et al., 2008; Little et al., 2004), but availability of symbionts upon arrival is not guaranteed.…”

Impact of Ocean Warming and Acidification on Symbiosis Establishment and Gene Expression Profiles in Recruits of Reef Coral Acropora intermedia

“…In addition, the symbiotic status of recruits was defined as follows: (1) aposymbiotic or low abundance of symbionts when the polyp tissue was translucent and lacked pigmentation, with the white skeleton clearly visible under the tissue, and (2) symbiotic when symbiont cells were clearly present and when the oral disk and tentacles of juvenile polyps were brown and pigmented (Abrego et al, 2012). It is important to note that although this visual assessment of symbiont uptake success could not preclude the possibility of symbiont infection, it did represent a good proxy for the establishment of symbiosis, where symbiont cells had not only entered the coral cells but also reproduced successfully in hospite; hereafter referred to as symbiosis establishment (Abrego et al, 2012;Nitschke et al, 2016;Ali et al, 2019). The symbiosis establishment rates were calculated as the proportion of pigmented juveniles relative to the total number of living recruits on the last day, and the budding state of each recruit was determined by recording the occurrence of new buds on the periphery of primary polyps.…”

Temperature transcends partner specificity in the symbiosis establishment of a cnidarian

“…However, this is not a universal feature of coral-Symbiodiniaceae symbioses [20,21] given that some hosts and symbionts can be less flexible in their association than others. The onset and maintenance of a persistent symbiosis depends on the functional compatibility between the two (or more) partners [22][23][24] and environmental settings [25][26][27][28].…”