Coral reef survival under accelerating ocean deoxygenation

Hughes, David; Alderdice, Rachel; Cooney, Christopher; Kühl, Michael; Pernice, Mathieu; Voolstra, Christian R.; Suggett, David J.

doi:10.1038/s41558-020-0737-9

Cited by 160 publications

(162 citation statements)

References 135 publications

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“…This compares to 'normal' levels for coral reefs of 5-8 mg l −1 , and Haas et al 11 found that dissolved oxygen content less than 4 mg l −1 is detrimental to acroporid corals. Moreover, branching coral forms have been reported to be more susceptible to hypoxic episodes than spherical or massive forms 5 . Corals are routinely exposed to fluctuations in oxygen levels at the tissue level due to photosynthesis and respiration processes of endosymbionts 7 , but are negatively impacted when (sub-) lethal thresholds of hypoxia exposure are exceeded 1,5,11 .…”

Section: Resultsmentioning

confidence: 99%

Low oxygen levels caused by Noctiluca scintillans bloom kills corals in Gulf of Mannar, India

Raj

Mathews

Obura

et al. 2020

Sci Rep

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Coral reefs around the world are undergoing severe decline in the past few decades. Mass coral mortalities have predominantly been reported to be caused by coral bleaching or disease outbreaks. Temporary hypoxic conditions caused by algal blooms can trigger mass coral mortalities though are reported rarely. In this study in Gulf of Mannar (GoM), southeast India, we report a significant coral mortality caused by a bloom of the ciguatoxic dinoflagellate Noctiluca scintillans during September–October 2019. Dissolved oxygen levels declined below 2 mg l−1 during the bloom causing temporary hypoxia and mortality (up to 71.23%) in the fast growing coral genera Acropora, Montipora and Pocillopora. Due to global climate change, more frequent and larger algal blooms are likely in the future. Hence, it is likely that shallow water coral reefs will be affected more frequently by episodic hypoxic conditions driven by algal blooms. More studies are, however, required to understand the mechanism of coral mortality due to algal blooms, impacts on community composition and the potential for subsequent recovery.

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Section: Resultsmentioning

confidence: 99%

Low oxygen levels caused by Noctiluca scintillans bloom kills corals in Gulf of Mannar, India

Raj

Mathews

Obura

et al. 2020

Sci Rep

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“…Strehlow), and oxygen levels were above lethal and sublethal thresholds of many fish and invertebrates (12). Nevertheless, in a separate study, a single individual of G. barretti drastically reduced its pumping rate following ex situ oxygen depletion (20% air saturation) (98), and feeding rates in one individual (out of three) of H. panicea were reduced in low-oxygen concentrations (3% air saturation) (17).…”

Section: Potential Adaptations Of the Sponge Host To Seasonal Anoxiamentioning

confidence: 95%

“…Considering the past also yields clues about the future. Some previous mass extinction events were probably driven by acidification, warming and deoxygenation of the oceans following extensive volcanism (12,(110)(111)(112)(113). Since similar stressors are facing modern oceans as a result of anthropogenic CO 2 release, could sponges outcompete corals in future scenarios (e.g 114, 115)?…”

Section: Implications For Early Animal Evolution and Future Oceansmentioning

confidence: 99%

“…While motile species can escape such hypoxic/anoxic areas, many sessile organisms like sponges (Porifera) and corals (Cnidaria) must either cope with these extremes or suffer mass mortalities as observed in Tropical dead zones (11). Nevertheless, the lethal thresholds of, and potential adaptations to, deoxygenation are understudied in these organisms (12), particularly in sponges.…”

Section: Introductionmentioning

confidence: 99%

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The effects of seasonal anoxia on the microbial community structure in demosponges in a marine lake (Lough Hyne, Ireland)

Schuster

Strehlow

Eckford-Soper

et al. 2020

Preprint

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Climate change is expanding marine oxygen minimum zones (OMZs), while anthropogenic nutrient input depletes oxygen concentrations locally. The effects of deoxygenation on animals are generally detrimental; however, some sponges (Porifera) exhibit hypoxic and anoxic tolerance through currently unknown mechanisms. Sponges harbor highly specific microbiomes, which can include microbes with anaerobic capabilities. Sponge-microbe symbioses must also have persisted through multiple anoxic/hypoxic periods throughout Earth history. Since sponges lack key components of the hypoxia-inducible factor (HIF) pathway responsible for hypoxic responses in other animals, it was hypothesized that sponge tolerance to deoxygenation may be facilitated by its microbiome. To test this hypothesis, we determined the microbial composition of sponge species tolerating seasonal anoxia and hypoxia in situ in a semi-enclosed marine lake, using 16S rRNA amplicon sequencing. We discovered a high degree of cryptic diversity among sponge species tolerating seasonal deoxygenation, including at least nine encrusting species of the orders Axinellida and Poecilosclerida. Despite significant changes in microbial community structure in the water, sponge microbiomes were species specific and remarkably stable under varied oxygen conditions, though some symbiont sharing occurred under anoxia. At least three symbiont combinations, all including large populations of Thaumarchaeota, corresponded with deoxygenation tolerance, and some combinations were shared between distantly related hosts. We propose hypothetical host-symbiont interactions following deoxygenation that could confer deoxygenation tolerance.ImportanceThe oceans have an uncertain future due to anthropogenic stressors and an uncertain past that is becoming clearer with advances in biogeochemistry. Both past and future oceans were, or will be, deoxygenated compared to present conditions. Studying how sponges and their associated microbes tolerate deoxygenation provides insights into future marine ecosystems. Moreover, sponges form the earliest branch of the animal evolutionary tree and they likely resemble some of the first animals. We determined the effects of variable environmental oxygen concentrations on the microbial communities of several demosponge species during seasonal anoxia in the field. Our results indicate that anoxic tolerance in some sponges may depend on their symbionts, but anoxic tolerance was not universal in sponges. Therefore, some sponge species could likely outcompete benthic organisms like corals in future, reduced-oxygen ecosystems. Our results support the molecular evidence that sponges and other animals have a Neoproterozoic origin, and that animal evolution was not limited by low-oxygen conditions.

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“…Shallow-water tropical habitats, especially coral reefs which host a significant portion of global marine biodiversity, and estuaries which are important nursery grounds for many commercial species, may be at particular risk from these stressors (Duarte et al, 2013). Recent reviews have argued that modern reefs cannot be fully understood without explicitly considering the impacts of oxygen dynamics (Nelson and Altieri, 2019), and yet hypoxia, more than any other stressor, remains significantly under-studied in tropical locations (Altieri et al, 2017;Hughes et al, 2020). In fact, hypoxia-associated mass mortality events and dead zones associated with warm temperatures have recently been reported for the first time at several tropical sites (Laboy-Nieves et al, 2001;Díaz-Asencio et al, 2015;Altieri et al, 2017;van Tussenbroek et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Multi-stressor Extremes Found on a Tropical Coral Reef Impair Performance

2020

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Global change has resulted in oceans that are warmer, more acidic, and lower in oxygen. Individually any one of these stressors can have numerous negative impacts on marine organisms, and in combination they are likely to be particularly detrimental. Understanding the interactions between these factors is important as they often covary, with warming promoting hypoxia, and hypoxia co-occurring with acidification. Few studies have examined how all three factors interact to affect organismal performance, and information is particularly sparse for tropical organisms. Here we documented a strong relationship between high temperatures, low dissolved oxygen (DO), and low pH in and around a tropical bay. We used these field values to inform two multi-stressor experiments. Each experimental factor had two levels, one representing current average conditions and the other representing current extreme conditions experienced in the area. We used sea urchin righting response as a measure of organismal performance for an important reef herbivore. In the first experiment 2-h exposures to a fully factorial combination of temperature, DO, and pH showed that righting success was significantly depressed under low oxygen. To more fully understand the impacts of pH, we acclimated sea urchins to control and low pH for 7 days and subsequently exposed them to the same experimental conditions. Sea urchins acclimated to control pH had significantly reduced righting success compared to animals acclimated to low pH, and righting success was significantly depressed under hypoxia and high temperature, compared to normoxia and ambient temperature. These results show that short, 2 h exposures to the temperature and DO extremes that are already experienced periodically by these animals have measurable detrimental effects on their performance. The positive impact of reduced pH is evident only over longer, 7 days durations, which are not currently experienced in this area.

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Coral reef survival under accelerating ocean deoxygenation

Cited by 160 publications

References 135 publications

Low oxygen levels caused by Noctiluca scintillans bloom kills corals in Gulf of Mannar, India

Low oxygen levels caused by Noctiluca scintillans bloom kills corals in Gulf of Mannar, India

The effects of seasonal anoxia on the microbial community structure in demosponges in a marine lake (Lough Hyne, Ireland)

Multi-stressor Extremes Found on a Tropical Coral Reef Impair Performance

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