No abstract

Reef-building corals respond to the temporal integration of both pulse events (i.e., heat waves) and press thermal history (i.e., local environment) via physiological changes, with ecological consequences. We used a "press-pulse-press" experimental framework to expose the brooding coral Porites astreoides to various thermal histories to understand the physiological response of temporal dynamics within and across generations. We collected adult colonies from two reefs (outer Rim reef and inner Patch reef) in Bermuda with naturally contrasting thermal regimes as our initial "press" scenario, followed by a 21-day ex situ "pulse" thermal stress of 30.4°C during larval brooding, and a "press" year-long adult reciprocal transplant between the original sites. Higher endosymbiont density and holobiont protein was found in corals originating from the lower thermal variability site (Rim) compared to the higher thermal variability site (Patch). The thermal pulse event drove significant declines in photosynthesis, endosymbiont density, and chlorophyll a, with bleaching phenotype convergence for adults from both histories. Following the reciprocal transplant, photosynthesis was higher in previously heated corals, indicating recovery from the thermal pulse. The effect of origin (initial press) modulated the response to transplant site for endosymbiont density and chlorophyll a, suggesting contrasting acclimation strategies. Higher respiration and photosynthetic rates were found in corals originating from the Rim site, indicating greater energy available for reproduction, supported by larger larvae released from Rim corals post-transplantation. Notably, parental exposure to the pulse thermal event resulted in increased offspring plasticity when parents were transplanted to foreign sites, highlighting the legacy of the pulse event and the importance of the environment during recovery in contributing to cross-generational or developmental plasticity. Together, these findings provide novel insight into the role of historical disturbance events in driving differential outcomes within and across generations, which is of critical importance in forecasting reef futures.

Coral reefs are threatened both locally and globally by anthropogenic impacts, which to date have contributed to substantial declines in coral cover worldwide. However, some corals are more resilient to these environmental changes and therefore have increased relative abundance on local scales and may represent prominent members shaping future reef communities. Here, we provide the first draft reference genome for one such reef-building coral, the mustard hill coral, Porites astreoides. This reference genome was generated from a sample collected in Bermuda, with DNA sequenced via Pacific Biosciences HiFi long-read technology to provide an initial draft reference genome assembly. Assembly of the PacBio reads with FALCON UnZip resulted in a 678 Mbp assembly with 3,051 contigs with an N50 of 412,256. The genome BUSCO completeness analysis resulted in 90.9% of the metazoan gene set. An ab initio transcriptome was also produced with 64,636 gene models with a transcriptome BUSCO completeness analysis of 77.5% when compared to the metazoan gene set. The function annotation was obtained through a hierarchical approach of SwissProt, TrEMBL, and NCBI nr database of which 86.6% of proteins were annotated. Through our ab initio gene prediction for structural annotation and generation of a functional annotation for the P. astreoides draft genome assembly, we provide valuable resources for improving biological knowledge, which can facilitate comparative genomic analyses for corals, and enhance our capacity to test for the molecular underpinnings of adaptation and acclimatization to support evidence-based restoration and human assisted evolution of corals.

Anthropogenic climate change threatens the persistence of coral reefs by impacting reproduction and accelerating coral loss. Adult corals depend on nutritional exchange with their endosymbiotic algae (Symbiodiniaceae) to fulfill their energetic demands. However, the mechanisms underlying the onset of this exchange during early life stages and how it contributes to developmental energy demands are unclear. We conducted an integrative analysis of the dependence on nutritional exchange across developmental stages inMontipora capitata, a vertically transmitting coral (Symbiodiniaceae are passed from parent to offspring) in Hawaiʻi. We applied physiological (metabolism and symbiont density) and multi-omic (metabolomics, transcriptomics, and microbial amplicon sequencing) approaches over 13 time points (1-255 hours post-fertilization; eggs, embryos, larvae, and settled recruits) to understand ontogenetic shifts in metabolism. Energetic demand (respiration) and symbiont population photosynthetic capacity (photosynthesis and cell density) increased with development, and metabolism shifted from using stored reserves to relying on symbiont-derived resources. Specifically, pathways associated with nutritional exchange, including organic compound transport, glucose and fatty acid metabolism, nitrogen metabolism, and reactive oxygen regulation were enriched in larvae. Recruits expanded utilization of carbohydrate and lipid pathways in response to the energetic demands of settlement and calcification. Our study shows that symbiotic nutritional exchange buffers the energetic demands of development in vertically transmitting corals, suggesting that in environmentally stressful conditions, these stages may be increasingly vulnerable to the loss of symbiont-derived nutrition. Therefore, intervening early to reduce stress during sensitive developmental stages could enhance coral reef recruitment and recovery as climate change intensifies.