Project description:Mesophotic coral reefs have been proposed as refugia for corals, providing shelter and larval propagules for shallow-water reefs that are disproportionately challenged by global climate change and local anthropogenic stressors. Yet, knowledge of the capacity of coral larvae to adjust to different depth environments is still limited. In this study, planulae of the reef-building coral Stylophora pistillata from 5-8 and 40-44 m depth in the Gulf of Aqaba were tested in a long-term in situ translocation experiment for their ability to settle and acclimate to reciprocal depth conditions. We assessed survival rates, photochemical, physiological and morphological characteristics, as well as gene expression variations in juveniles grown at different depths, comparing them to non-translocated adults, juveniles and planulae. We found high mortality rates among mesophotic-origin planulae, irrespective of translocation depth. Gene expression patterns suggested that deep planulae lacked settlement competency and experienced increased developmental stress upon release. Symbiont photochemical acclimation to depth occurred rapidly within 8 days, with symbiont populations showing changes in photochemical traits but no symbiont species shuffling between deep and shallow juveniles. In contrast, coral host physiological and morphological acclimation were less evident. We observed minimal overlap in gene expression patterns between different life stages and depths, indicating that gene expression significantly depends on life stage. The study also identified a set of DEGs associated with initial stress responses following translocation, lingering stress response, and environmental effects of depth. In conclusion, though our data reveal rapid symbiont acclimation, host acclimation to match deep coral phenotypes was incomplete within 60 days for planulae translocated to different depths. These results have implications for understanding the ecological significance of mesophotic reefs as potential larval sources in the face of environmental stressors.

Project description:Marine phytoplankton are a diverse group of photoautotrophic organisms and key mediators in the global carbon cycle. Phytoplankton physiology and biomass accumulation are closely tied to mixed layer depth, but the intracellular metabolic pathways activated in response to changing mixed layer depths remain unexplored. Here, metatranscriptomics was used to characterize the phytoplankton community response to a mixed layer shallowing from 233 meters to 5 meters over the course of two days during the late spring in the Northwest Atlantic. Most phytoplankton genera downregulated core photosynthesis, carbon storage, and carbon fixation genes as the system transitioned from a deep to a shallow mixed layer and shifted towards catabolism of stored carbon ic pathways supportive of rapid cell growth. In contrast, phytoplankton genera exhibited divergent transcriptional strategies for photosystem light harvesting complex genes during this transition. Active infection, taken as the ratio of virus to host transcripts, increased in the Bacillariophyta (diatom) phylum and decreased in the Chlorophyta (green algae) phylum upon mixed layer shallowing. A conceptual model is proposed to provide ecophysiological context for our findings, in which light limitation during deep mixing induces populations into a transcriptional state which maximizes interrupts the oscillating levels of transcripts related to photosynthesis, carbon storage, and carbon fixation found in shallow mixed layers with relatively higher growth rates. We propose that upon sensing high light levels during mixed layer shallowing, phytoplankton resume diel oscillation of core sets of genes enabling photoprotection, biosynthesis and cell replication. Our findings highlight the shared and unique transcriptional response strategies within phytoplankton communities acclimating to the dynamic light environment associated with transient deep mixing and shallowing events during the annual North Atlantic bloom.

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Marine metagenome

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