Dataset Information

Symbiont community stability through severe coral bleaching in a thermally extreme lagoon.

ABSTRACT: Coral reefs are threatened by climate change as coral-algal symbioses are currently living close to their upper thermal limits. The resilience of the algal partner plays a key role in determining the thermal tolerance of the coral holobiont and therefore, understanding the acclimatory limits of present day coral-algal symbioses is fundamental to forecasting corals' responses to climate change. This study characterised the symbiont community in a highly variable and thermally extreme (Max?=?37.5?°C, Min?=?16.8?°C) lagoon located in the southern Persian/Arabian Gulf using next generation sequencing of ITS2 amplicons. Despite experiencing extreme temperatures, severe bleaching and many factors that would be expected to promote the presence of, or transition to clade D dominance, the symbiont communities of the lagoon remain dominated by the C3 variant, Symbiodinium thermophilum. The stability of this symbiosis across multiple genera with different means of symbiont transmission highlights the importance of Symbiodinium thermophilum for corals living at the acclimatory limits of modern day corals. Corals in this extreme environment did not undergo adaptive bleaching, suggesting they are living at the edge of their acclimatory potential and that this valuable source of thermally tolerant genotypes may be lost in the near future under climate change.

SUBMITTER: Smith EG

PROVIDER: S-EPMC5445074 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

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Symbiont community stability through severe coral bleaching in a thermally extreme lagoon.

Smith E G EG Vaughan G O GO Ketchum R N RN McParland D D Burt J A JA

Scientific reports 20170525 1

Coral reefs are threatened by climate change as coral-algal symbioses are currently living close to their upper thermal limits. The resilience of the algal partner plays a key role in determining the thermal tolerance of the coral holobiont and therefore, understanding the acclimatory limits of present day coral-algal symbioses is fundamental to forecasting corals' responses to climate change. This study characterised the symbiont community in a highly variable and thermally extreme (Max = 37.5 ...[more]

PMID: 28546553

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Project description:Widespread coral bleaching has generally been linked to high water temperatures at larger geographic scales. However, the bleaching response can be highly variable among individual of the same species, between different species, and across localities; what causes this variability remains unresolved. Here, we tracked bleached and non-bleached colonies of Acropora muricata to see if they recovered or died following a stress event inside the semi-enclosed lagoon of Bouraké (New Caledonia), where corals are long-term acclimatized to extreme conditions of temperature, pH and dissolved oxygen, and at a nearby control reef where conditions are more benign. We describe Symbiodiniaceae community changes based on next-generation sequencing of the ITS2 marker, metabolic responses, and energetic reserve measures (12 physiological traits evaluated) during the La Niña warm and rainy summer in 2021. Widespread coral bleaching (score 1 and 2 on the coral colour health chart) was observed only in Bouraké, likely due to the combination of the high temperatures (up to 32°C) and heavy rain. All colonies (i.e., Bouraké and reference site) associated predominantly with Symbiodinaceae from the genera Cladocopium. Unbleached colonies in Bouraké had a specific ITS2-type profile (proxies for Symbiodiniaceae genotypes), while the bleached colonies in Bouraké had the same ITS2-type profile of the reef control colonies during the stress event. After four months, the few bleached colonies that survived in Bouraké (B2) acquired the same ITS2 type profiles of the unbleached colonies in Bouraké. In terms of physiological performances, all bleached corals showed metabolic depression (e.g., Pgross and Rdark). In contrast, unbleached colonies in Bouraké maintained higher metabolic rates and energetic reserves compared to control corals. Our study suggests that Acropora muricata enhanced their resistance to bleaching thanks to specific Symbiodiniaceae associations, while energetic reserves may increase their resilience after stress.

Project description:BackgroundCoral bleaching can be defined as the loss of symbiotic zooxanthellae and/or their photosynthetic pigments from their cnidarian host. This major disturbance of reef ecosystems is principally induced by increases in water temperature. Since the beginning of the 1980s and the onset of global climate change, this phenomenon has been occurring at increasing rates and scales, and with increasing severity. Several studies have been undertaken in the last few years to better understand the cellular and molecular mechanisms of coral bleaching but the jigsaw puzzle is far from being complete, especially concerning the early events leading to symbiosis breakdown. The aim of the present study was to find molecular actors involved early in the mechanism leading to symbiosis collapse.ResultsIn our experimental procedure, one set of Pocillopora damicornis nubbins was subjected to a gradual increase of water temperature from 28 degrees C to 32 degrees C over 15 days. A second control set kept at constant temperature (28 degrees C). The differentially expressed mRNA between the stressed states (sampled just before the onset of bleaching) and the non stressed states (control) were isolated by Suppression Subtractive Hybridization. Transcription rates of the most interesting genes (considering their putative function) were quantified by Q-RT-PCR, which revealed a significant decrease in transcription of two candidates six days before bleaching. RACE-PCR experiments showed that one of them (PdC-Lectin) contained a C-Type-Lectin domain specific for mannose. Immunolocalisation demonstrated that this host gene mediates molecular interactions between the host and the symbionts suggesting a putative role in zooxanthellae acquisition and/or sequestration. The second gene corresponds to a gene putatively involved in calcification processes (Pdcyst-rich). Its down-regulation could reflect a trade-off mechanism leading to the arrest of the mineralization process under stress.ConclusionUnder thermal stress zooxanthellae photosynthesis leads to intense oxidative stress in the two partners. This endogenous stress can lead to the perception of the symbiont as a toxic partner for the host. Consequently, we propose that the bleaching process is due in part to a decrease in zooxanthellae acquisition and/or sequestration. In addition to a new hypothesis in coral bleaching mechanisms, this study provides promising biomarkers for monitoring coral health.

Dataset Information

Symbiont community stability through severe coral bleaching in a thermally extreme lagoon.

Publications

Symbiont community stability through severe coral bleaching in a thermally extreme lagoon.

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