Coral histology reveals consistent declines in tissue integrity during a marine heatwave despite differences in bleaching severity.

Marine heatwaves are starting to occur several times a decade, yet we do not understand the effect this has on corals across biological scales. This study combines tissue-, organism-, and community-level analyses to investigate the effects of a marine heatwave on reef-building corals. Adjacent conspecific pairs of coral colonies of and that showed contrasting phenotypic responses (, bleached .

Extreme Environmental Variability Induces Frontloading of Coral Biomineralisation Genes to Maintain Calcification Under pCO Variability.

Corals residing in habitats that experience high-frequency seawater pCO variability may possess an enhanced capacity to cope with ocean acidification, yet we lack a clear understanding of the molecular toolkit enabling acclimatisation to environmental extremes or how life-long exposure to pCO variability influences biomineralisation. Here, we examined the gene expression responses and micro-skeletal characteristics of Pocillopora damicornis originating from the reef flat and reef slope of Heron Island, southern Great Barrier Reef. The reef flat and reef slope had similar mean seawater pCO, but the reef flat experienced twice the mean daily pCO amplitude (range of 797 v.

Comparative physiology reveals heat stress disrupts acid-base homeostasis independent of symbiotic state in the model cnidarian Exaiptasia diaphana.

Climate change threatens the survival of symbiotic cnidarians by causing photosymbiosis breakdown in a process known as bleaching. Direct effects of temperature on cnidarian host physiology remain difficult to describe because heatwaves depress symbiont performance, leading to host stress and starvation. The symbiotic sea anemone Exaiptasia diaphana provides an opportune system to disentangle direct versus indirect heat effects on the host, as it can survive indefinitely without symbionts.

Divergent bleaching and recovery trajectories in reef-building corals following a decade of successive marine heatwaves.

Increasingly frequent marine heatwaves are devastating coral reefs. Corals that survive these extreme events must rapidly recover if they are to withstand subsequent events, and long-term survival in the face of rising ocean temperatures may hinge on recovery capacity and acclimatory gains in heat tolerance over an individual's lifespan. To better understand coral recovery trajectories in the face of successive marine heatwaves, we monitored the responses of bleaching-susceptible and bleaching-resistant individuals of two dominant coral species in Hawai'i, and , over a decade that included three marine heatwaves.

Acute heat priming promotes short-term climate resilience of early life stages in a model sea anemone.

Across diverse taxa, sublethal exposure to abiotic stressors early in life can lead to benefits such as increased stress tolerance upon repeat exposure. This phenomenon, known as hormetic priming, is largely unexplored in early life stages of marine invertebrates, which are increasingly threatened by anthropogenic climate change. To investigate this phenomenon, larvae of the sea anemone and model marine invertebrate were exposed to control (18 °C) or elevated (24 °C, 30 °C, 35 °C, or 39 °C) temperatures for 1 h at 3 days post-fertilization (DPF), followed by return to control temperatures (18 °C).

Characterization of a sperm motility signalling pathway in a gonochoric coral suggests conservation across cnidarian sexual systems.

Most stony corals liberate their gametes into the water column via broadcast spawning, where fertilization hinges upon the activation of directional sperm motility. Sperm from gonochoric and hermaphroditic corals display distinct morphological and molecular phenotypes, yet it is unknown whether the signalling pathways controlling sperm motility are also distinct between these sexual systems. Here, we addressed this knowledge gap using the gonochoric, broadcast spawning coral .

Parental exposure to ocean acidification impacts gamete production and physiology but not offspring performance in Nematostella vectensis.

Ocean acidification (OA) resulting from anthropogenic CO2 emissions is impairing the reproduction of marine organisms. While parental exposure to OA can protect offspring via carryover effects, this phenomenon is poorly understood in many marine invertebrate taxa. Here, we examined how parental exposure to acidified (pH 7.

Unified methods in collecting, preserving, and archiving coral bleaching and restoration specimens to increase sample utility and interdisciplinary collaboration.

Coral reefs are declining worldwide primarily because of bleaching and subsequent mortality resulting from thermal stress. Currently, extensive efforts to engage in more holistic research and restoration endeavors have considerably expanded the techniques applied to examine coral samples. Despite such advances, coral bleaching and restoration studies are often conducted within a specific disciplinary focus, where specimens are collected, preserved, and archived in ways that are not always conducive to further downstream analyses by specialists in other disciplines.

Environmental memory gained from exposure to extreme pCO variability promotes coral cellular acid-base homeostasis.

Ocean acidification is a growing threat to coral growth and the accretion of coral reef ecosystems. Corals inhabiting environments that already endure extreme diel pCO fluctuations, however, may represent acidification-resilient populations capable of persisting on future reefs. Here, we examined the impact of pCO variability on the reef-building coral originating from reefs with contrasting environmental histories (variable reef flat versus stable reef slope) following reciprocal exposure to stable (218 ± 9) or variable (911 ± 31) diel pCO amplitude (μtam) in aquaria over eight weeks.

The Costs and Benefits of Environmental Memory for Reef-Building Corals Coping with Recurring Marine Heatwaves.

Marine heatwaves are occurring more frequently as climate change intensifies, resulting in global mass coral bleaching events several times per decade. Despite the time between marine heatwaves decreasing, there is evidence that reef-building corals can develop increased bleaching resistance across repetitive marine heatwaves. This phenomenon of acclimatization via environmental memory may be an important strategy to ensure coral persistence; however, we still understand very little about the apparent acclimatization or, conversely, sensitization (i.

V-type H-ATPase in the symbiosome membrane is a conserved mechanism for host control of photosynthesis in anthozoan photosymbioses.

In reef-building corals (order Scleractinia) and giant clams (phylum Molluca), V-type H-ATPase (VHA) in host cells is part of a carbon concentrating mechanism (CCM) that regulates photosynthetic rates of their symbiotic algae. Here, we show that VHA plays a similar role in the sea anemone , a member of the order Actinaria and sister group to the Scleractinia, which in contrast to their colonial calcifying coral relatives is a solitary, soft-bodied taxa. Western blotting and immunofluorescence revealed that VHA was abundantly present in the host-derived symbiosome membrane surrounding the photosymbionts.

Molecular mechanisms of sperm motility are conserved in an early-branching metazoan.

Efficient and targeted sperm motility is essential for animal reproductive success. Sperm from mammals and echinoderms utilize a highly conserved signaling mechanism in which sperm motility is stimulated by pH-dependent activation of the cAMP-producing enzyme soluble adenylyl cyclase (sAC). However, the presence of this pathway in early-branching metazoans has remained unexplored.

Coral bleaching response is unaltered following acclimatization to reefs with distinct environmental conditions.

Urgent action is needed to prevent the demise of coral reefs as the climate crisis leads to an increasingly warmer and more acidic ocean. Propagating climate change-resistant corals to restore degraded reefs is one promising strategy; however, empirical evidence is needed to determine whether stress resistance is affected by transplantation beyond a coral's native reef. Here, we assessed the performance of bleaching-resistant individuals of two coral species following reciprocal transplantation between reefs with distinct pH, salinity, dissolved oxygen, sedimentation, and flow dynamics to determine whether heat stress response is altered following coral exposure to novel physicochemical conditions in situ.

Marine heatwaves depress metabolic activity and impair cellular acid-base homeostasis in reef-building corals regardless of bleaching susceptibility.

Ocean warming is causing global coral bleaching events to increase in frequency, resulting in widespread coral mortality and disrupting the function of coral reef ecosystems. However, even during mass bleaching events, many corals resist bleaching despite exposure to abnormally high temperatures. While the physiological effects of bleaching have been well documented, the consequences of heat stress for bleaching-resistant individuals are not well understood.

Regulation of coral calcification by the acid-base sensing enzyme soluble adenylyl cyclase.

Coral calcification is intricately linked to the chemical composition of the fluid in the extracellular calcifying medium (ECM), which is situated between the calcifying cells and the skeleton. Here we demonstrate that the acid-base sensing enzyme soluble adenylyl cyclase (sAC) is expressed in calcifying cells of the coral Stylophora pistillata. Furthermore, pharmacological inhibition of sAC in coral microcolonies resulted in acidification of the ECM as estimated by the pH-sensitive ratiometric indicator SNARF, and decreased calcification rates, as estimated by calcein labeling of crystal growth.

A vesicular Na+/Ca2+ exchanger in coral calcifying cells.

The calcium carbonate skeletons of corals provide the underlying structure of coral reefs; however, the cellular mechanisms responsible for coral calcification remain poorly understood. In osteoblasts from vertebrate animals, a Na+/Ca2+ exchanger (NCX) present in the plasma membrane transports Ca2+ to the site of bone formation. The aims of this study were to establish whether NCX exists in corals and its localization within coral cells, which are essential first steps to investigate its potential involvement in calcification.

Identification of a molecular pH sensor in coral.

Maintaining stable intracellular pH (pHi) is essential for homeostasis, and requires the ability to both sense pH changes that may result from internal and external sources, and to regulate downstream compensatory pH pathways. Here we identified the cAMP-producing enzyme soluble adenylyl cyclase (sAC) as the first molecular pH sensor in corals. sAC protein was detected throughout coral tissues, including those involved in symbiosis and calcification.

The Vulnerability and Resilience of Reef-Building Corals.

Reef-building corals provide the foundation for the structural and biological diversity of coral-reef ecosystems. These massive biological structures, which can be seen from space, are the culmination of complex interactions between the tiny polyps of the coral animal in concert with its unicellular symbiotic algae and a wide diversity of closely associated microorganisms (bacteria, archaea, fungi, and viruses). While reef-building corals have persisted in various forms for over 200 million years, human-induced conditions threaten their function and persistence.

Energetic differences between bacterioplankton trophic groups and coral reef resistance.

Coral reefs are among the most productive and diverse marine ecosystems on the Earth. They are also particularly sensitive to changing energetic requirements by different trophic levels. Microbialization specifically refers to the increase in the energetic metabolic demands of microbes relative to macrobes and is significantly correlated with increasing human influence on coral reefs.

Lytic to temperate switching of viral communities.

Microbial viruses can control host abundances via density-dependent lytic predator-prey dynamics. Less clear is how temperate viruses, which coexist and replicate with their host, influence microbial communities. Here we show that virus-like particles are relatively less abundant at high host densities.

Stable and sporadic symbiotic communities of coral and algal holobionts.

Coral and algal holobionts are assemblages of macroorganisms and microorganisms, including viruses, Bacteria, Archaea, protists and fungi. Despite a decade of research, it remains unclear whether these associations are spatial-temporally stable or species-specific. We hypothesized that conflicting interpretations of the data arise from high noise associated with sporadic microbial symbionts overwhelming signatures of stable holobiont members.

Differential localization of ion transporters suggests distinct cellular mechanisms for calcification and photosynthesis between two coral species.

Ion transport is fundamental for multiple physiological processes, including but not limited to pH regulation, calcification, and photosynthesis. Here, we investigated ion-transporting processes in tissues from the corals Acropora yongei and Stylophora pistillata, representatives of the complex and robust clades that diverged over 250 million years ago. Antibodies against complex IV revealed that mitochondria, an essential source of ATP for energetically costly ion transporters, were abundant throughout the tissues of A.

Coral host cells acidify symbiotic algal microenvironment to promote photosynthesis.

Symbiotic dinoflagellate algae residing inside coral tissues supply the host with the majority of their energy requirements through the translocation of photosynthetically fixed carbon. The algae, in turn, rely on the host for the supply of inorganic carbon. Carbon must be concentrated as CO2 in order for photosynthesis to proceed, and here we show that the coral host plays an active role in this process.