Endosymbiont Communities in Pachyseris speciosa Highlight Geographical and Methodological Variations

Abstract

Reef-building corals live in symbiosis with the phototrophic dinoflagellate family Symbiodiniaceae, which comprises diverse genera such as Cladocopium and Durusdinium. Pachyseris speciosa, a widely distributed Indo-Pacific coral found in a variety of reef habitats, is known to be associated with these two Symbiodiniaceae genera, but little is known about the biogeographic variability of the endosymbiont communities across the region. In this study, the diversity and dominance patterns of Symbiodiniaceae at the western and eastern areas of the Central Indo-Pacific region were examined. We sampled Pachyseris speciosa colonies at seven and six sites in Singapore and Papua New Guinea, respectively, and genotyped their endosymbionts based on the internal transcribed spacer (ITS) markers using two distinct methods, quantitative polymerase chain reaction (qPCR) and high-throughput sequencing (HTS). Results showed 92% of all colonies in Singapore exhibiting Cladocopium dominance. There was a higher abundance of Durusdinium compared to Cladocopium in certain colonies from one site, Pulau Hantu (mean Durusdinium abundance of 90%, compared to 0–14% among all other sites). In contrast, variation in the endosymbiont communities was generally higher among sites in Papua New Guinea. Cladocopium expectedly dominated most colonies (75%), although colonies from Kimbe Bay (85%) and Kavieng (65%) showed Durusdinium dominance. Between localities, relative genus abundances based on qPCR were not significantly different, but HTS showed that the ratio of Durusdinium over Cladocopium was significantly higher in Papua New Guinea corals. Notably, 6% of colonies from Singapore and 15% from Papua New Guinea showed endosymbiont dominance patterns that were inconsistent between the two methods, underscoring the need for further validation of symbiotic algal quantification based on HTS. The richness of ITS2 type profiles was clearly lower among colonies from the impacted and turbid reefs of Singapore compared to the less urbanized reefs of Papua New Guinea. These coral intraspecific variations of Symbiodiniaceae communities within and among localities suggest that local conditions are important drivers of endosymbiosis and may ultimately influence corals’ resilience against global stressors such as ocean warming.

Coral persistence despite marginal conditions in the Port of Miami

“…For instance, Rubin et al 54 found that P. strigosa in the Port of Miami primarily hosted more heat-tolerant zooxanthellae in the genus Durusdinium vs. those at our natural control site, Emerald Reef, which primarily hosted Breviolum . Similar associations with stress-tolerant symbionts have been observed in urbanized habitats in Singapore 60 , 61 , as well as in environmentally-variable lagoon environments 62 . Prokaryotic communities also tend to reflect the environment in which the coral resides, where corals in marginal habitats can host divergent mucus-associated bacteria 63 .…”

Wallace’s line structures seagrass microbiota and is a potential barrier to the dispersal of marine bacteria

“…This was unexpected since numerous studies suggest anything smaller than 1 mm is unlikely to show biogeographic patterns [71], and that for microscopic organisms dispersal is assumed to be rarely, if ever, limited by geographical barriers [72]. However, work in Southeast Asia examining mangrove [73,74], seagrass [66,75], and coral associated microbiota [76][77][78] shows that microbial biogeographic structure can exist over comparatively small spatial scales (< 6 km in some instances). Further supporting these observations, work by Jenkins et al, [79] similarly showed that a smaller size does not lead to further dispersal and a more cosmopolitan distribution.…”

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

“…For instance, the proportion of Durusdinium in Orbicella faveolata increased differently in response to short-and long-term heat stress exposure, depending on the severity of the disturbance (Cunning et al, 2015). Similarly, several studies have revealed that a largescale spread of heat-stress tolerant symbionts is correlated with corals living in warmer oceans (Pettaya et al, 2015;Jain et al, 2021); this rapid shift in Symbiodiniaceae can potentially enhance the corals' survival in the face of unstable environmental conditions. Nevertheless, this mechanism may not be sufficient to ensure the survival of all corals under the predicted conditions of future climate change, which can vary depending on the severity of stress, geographic locations, coral taxa, etc.…”