Article

Coral Gametogenesis Collapse under Artificial Light Pollution

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Abstract

Artificial light at night (ALAN) can have negative impacts on the health of humans and ecosystems.1, 2, 3, 4 Marine organisms, including coral reefs in particular, rely on the natural light cycles of sunlight and moonlight to regulate various physiological, biological, and behavioral processes.5, 6, 7, 8 Here, we demonstrate that light pollution caused delayed gametogenesis and unsynchronized gamete release in two coral species, Acropora millepora and Acropora digitifera, from the Indo-Pacific Ocean. Given the urbanization along major coasts, light pollution could thus further threaten coral communities’ populations, which are already under severe degradation. A worldwide-modeled light pollution impact assessment is provided, which can help incorporate an important variable in coral reef conservation planning.

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... interferes with lunar guided migration [20], orientation [21], sleep time [22] and reproduction [23] at intensities similar to natural moonlight. ...
... ALAN is known to affect lunar-guided reproductive phenology [23], orientation [20,21] and community structure [19]. Our results demonstrate that ALAN can also alter temporal patterns in foraging tuned to the naturally changing nightly lunar brightness throughout the lunar cycle. ...
... A growing body of evidence indicates that ALAN has notable impacts on lunar-guided biological processes [18][19][20][21]23]. Here we show that ALAN impacts also depend on natural regimes of lunar brightness. ...
Article
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Mounting evidence shows that artificial light at night (ALAN) alters biological processes across levels of organization, from cells to communities. Yet, the combined impacts of ALAN and natural sources of night-time illumination remain little explored. This is in part due the lack of accurate simulations of the complex changes moonlight intensity, timing and spectra throughout a single night and lunar cycles in laboratory experiments. We custom-built a novel system to simulate natural patterns of moonlight to test how different ALAN intensities affect predator–prey relationships over the full lunar cycle. Exposure to high intensity ALAN (10 and 50 lx) reversed the natural lunar-guided foraging pattern by the gastropod mesopredator Nucella lapillus on its prey Semibalanus balanoides . Foraging decreased during brighter moonlight in naturally lit conditions. When exposed to high intensity ALAN, foraging increased with brighter moonlight. Low intensity ALAN (0.1 and 0.5 lx) had no impact on foraging. Our results show that ALAN alters the foraging pattern guided by changes in moonlight brightness. ALAN impacts on ecosystems can depend on lunar light cycles. Accurate simulations of night-time light cycle will warrant more realistic insights into ALAN impacts and also facilitate advances in fundamental night-time ecology and chronobiology.
... We now know that at least 22% of coastal regions are exposed to ALAN (Davies et al., 2014), and the light from cities is sufficient to elicit biological responses in animals on the seafloor in adjacent habitats (Ayalon, Rosenberg, et al., 2021;Davies et al., 2020). 1.9 million km 2 of the world's coastal seas are exposed to ALAN at 1 m depth, 1.6 million km 2 at 10 m depth, and 840,000 km 2 at 20 m depth ( Figure 1a) (Smyth et al., 2021). ...
... The potential for ALAN to impact the wide array of organisms, processes, and habitats in the sea for which light cycles are critical had remained largely unexplored until recently (Davies et al., 2014;Longcore & Rich, 2004). These include: diel vertical migrations (Berge et al., 2020)-the largest migration of biomass on the planet (Hayes, 2003); coral spawning (Ayalon, Rosenberg, et al., 2021), and symbiosis -which are key for the maintenance of coral reefs; consumer-resource interactions (Bolton et al., 2017;Maggi, Bongiorni, et al., 2020;Underwood et al., 2017) that are known to drive top down structuring of marine ecosystems (Paine, 1966); migrations and orientation of marine organismscritical for their survival (Navarro-Barranco & Hughes, 2015;Torres et al., 2020); and the recruitment of sessile invertebrate larvae into marine habitats (Davies et al., 2015;Lynn, Quintanilla-Ahumada, et al., 2021), (Figure 2). All these processes are fundamental to the health of marine ecosystems, and all are known to depend on the cycles, spectra or intensity of sun or moonlight. ...
... ALAN has been detected in fringing reefs localized in strongly urbanized locations. Mean night sky brightness levels at reef locations (see Ayalon, Rosenberg, et al., 2021) show that many coral reef areas worldwide are affected by ALAN. An applicable example is the coast in the Gulf of Eilat/Aqaba in the Red Sea, where most of the studies on the effects of ALAN on reef building corals have been conducted (e.g., Ayalon et al., 2019;Levy et al., 2020;Tamir et al., 2017). ...
Article
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The globally widespread adoption of Artificial Light at Night (ALAN) began in the mid‐20th century. Yet, it is only in the last decade that a renewed research focus has emerged into its impacts on ecological and biological processes in the marine environment that are guided by natural intensities, moon phase, natural light and dark cycles and daily light spectra alterations. The field has diversified rapidly from one restricted to impacts on a handful of vertebrates, to one in which impacts have been quantified across a broad array of marine and coastal habitats and species. Here we review the current understanding of ALAN impacts in diverse marine ecosystems. The review presents the current state of knowledge across key marine and coastal ecosystems (sandy and rocky shores, coral reefs and pelagic) and taxa (birds and sea turtles), introducing how ALAN can mask seabirds and sea turtles navigation, cause changes in animals predation patterns and failure of coral spawning synchronization, as well as inhibition of zooplankton Diel Vertical Migration. Mitigation measures are recommended, however, while strategies for mitigation were easily identified, barriers to implementation are poorly understood. Finally, we point out knowledge gaps that if addressed would aid in the prediction and mitigation of ALAN impacts in the marine realm.
... The ever-increasing amount of nighttime light, known as Artificial Light at Night (ALAN), is an inherent consequence of population growth along ocean coastlines, and a major emerging sensory pollutant concern for coral reef ecosystems (Becker et al., 2013;Tamir et al., 2017;Ayalon et al., 2019Ayalon et al., , 2021. This is in addition to the other insults that these complex populations have been exposed to over the last few decades, either due to human actions (overfishing, chemical pollution), or natural stressors (storms, diseases, sedimentation, heatwaves), Baker et al. (2008), Dubinsky and Stambler (2010), Caroselli et al. (2017), Tamir et al. (2017), Hughes et al. (2018), Ayalon et al. (2019Ayalon et al. ( , 2021. ...
... The ever-increasing amount of nighttime light, known as Artificial Light at Night (ALAN), is an inherent consequence of population growth along ocean coastlines, and a major emerging sensory pollutant concern for coral reef ecosystems (Becker et al., 2013;Tamir et al., 2017;Ayalon et al., 2019Ayalon et al., , 2021. This is in addition to the other insults that these complex populations have been exposed to over the last few decades, either due to human actions (overfishing, chemical pollution), or natural stressors (storms, diseases, sedimentation, heatwaves), Baker et al. (2008), Dubinsky and Stambler (2010), Caroselli et al. (2017), Tamir et al. (2017), Hughes et al. (2018), Ayalon et al. (2019Ayalon et al. ( , 2021. The threedimensional habitats that comprise a coral reef are among the most diverse marine ecosystems on earth, supporting thousands of organisms that live in close association and dependency. ...
... Broadcast spawning, the main mode of coral reproduction, depends on very precise timing of gamete release into the water column to be successful (Shlesinger and Loya, 1985). This is achieved by synchronization of the corals with the lunar cycle (Babcock et al., 1986;Kaniewska et al., 2015;Ayalon et al., 2021). Corals possess an array of sensitive photoreceptors, including GPCRs rhodopsins and cryptochromes, which operate in the blue region of the light spectrum (Gorbunov and Falkowski, 2002;Levy et al., 2007), and are synchronized with the moon phase. ...
Article
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Artificial Light at Night, ALAN, is a major emerging issue in biodiversity conservation, which can negatively impact both terrestrial and marine environments. Therefore, it should be taken into serious consideration in strategic planning for urban development. While the lion’s share of research has dealt with terrestrial organisms, only a handful of studies have focused on the marine milieu. To determine if ALAN impacts the coral reef symbiotic algae, that are fundamental for sustainable coral reefs, we conducted a short experiment over a period of one-month by illuminating isolated Symbiodiniaceae cell cultures from the genera Cladocopium (formerly Clade C) and Durusdinium (formerly Clade D) with LED light. Cell cultures were exposed nightly to ALAN levels of 0.15 μmol quanta m –2 s –1 (∼4–5 lux) with three light spectra: blue, yellow and white. Our findings showed that even in very low levels of light at night, the photo-physiology of the algae’s Electron Transport Rate (ETR), Non-Photochemical Quenching, (NPQ), total chlorophyll, and meiotic index presented significantly lower values under ALAN, primarily, but not exclusively, in Cladocopium cell cultures. The findings also showed that diverse Symbiodiniaceae types have different photo-physiology and photosynthesis performances under ALAN. We believe that our results sound an alarm for the probable detrimental effects of an increasing sensory pollutant, ALAN, on the eco-physiology of symbiotic corals. The results of this study point to the potential effects of ALAN on other organisms in marine ecosystem such as fish, zooplankton, and phytoplankton in which their biorhythms is entrained by natural light and dark cycles.
... Under the current model, based on spawning behavior of Acropora millipora, moonlight is thought to positively regulate coral spawning (i.e., corals receive a moonlight signal via a light sensor [cryptochrome]), which then changes the expression of genes that induces spawning (24,25). This model is supported by evidence that corals in genus Acropora do not spawn in the absence of moonlight (24) and that night-light pollution disturbs spawning synchronicity (26,27). However, it remains unknown exactly how corals determine the spawning day by sensing a moonlight signal and whether this model is applicable to the majority of coral species. ...
... dependent) is influenced by the disturbance of moonlight by clouds, whereas the former (dark dependent) is not. Additionally, the gametogenesis and spawning time in Acropora corals can be influenced by artificial light at night (24,26,27). Therefore, as the dark period plays a vital role in triggering spawning in our proposed mechanism, light pollution may also have the potential to influence spawning in D. speciosa. ...
Article
Synchronized mass coral spawning typically occurs several days after a full moon once a year. It is expected that spawning day is determined by corals sensing environmental change regulated by the lunar cycle (i.e., tide or moonlight); however, the exact regulatory mechanism remains unknown. Here, we demonstrate how moonlight influences the spawning process of coral, Dipsastraea speciosa . When corals in the field were shaded 1 and 3 d before the full moon or 1 d after the full moon, spawning always occurred 5 d after shading commenced. These results suggest moonlight suppresses spawning: a hypothesis supported by laboratory experiments in which we monitored the effects of experimental moonlight (night-light) on spawning day. Different night-light treatments in the laboratory showed that the presence of a dark period between day-light and night-light conditions eliminates the suppressive effect of night-light on spawning. In nature, moonrise gets progressively later during the course of the lunar cycle, shifting to after sunset following the day of the full moon. Our results indicate that this period of darkness between sunset and moonrise triggers synchronized mass spawning of D. speciosa in nature.
... Second, exposure to ALAN can alter the feeding, growth, reproduction, and survival of individual wild organisms (67)(68)(69)(70)(71), something that should come as no surprise given that artificial lighting is used to such ends in cultivation settings (e.g., 72,73) and also has unintended impacts on crops (74). For example, in a field experiment wild juvenile orange-fin anemonefish (Amphiprion chrysopterus) exposed to underwater illuminance of 4.3 lux were found to have reduced growth and survival compared to individuals exposed to natural moonlight (75). ...
Article
The nighttime is undergoing unprecedented change across much of the world, with natural light cycles altered by the introduction of artificial light emissions. Here we review the extent and dynamics of artificial light at night (ALAN), the benefits that ALAN provides, the environmental costs ALAN creates, approaches to mitigating these negative effects, and how costs are likely to change in the future. We particularly highlight the consequences of the increasingly widespread use of light-emitting diode (LED) technology for new lighting installations and to retrofit pre-existing ones. Although this has been characterized as a technological lighting revolution, it also constitutes a revolution in the environmental costs and impacts of ALAN, particularly because the LEDs commonly used for outdoor lighting have significant emissions at the blue wavelengths to which many biological responses are particularly sensitive. It is clear that a very different approach to the use of artificial lighting is required. Expected final online publication date for the Annual Review of Environment and Resources, Volume 47 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... Artificial light at night (e.g. via reflected skyglow from coastal cities) is identified as a threat to many ecosystems [21][22][23]79,80], and it is increasing [81]. On coral reefs, light pollution can affect physiology [82][83][84][85][86][87] and demographic rates of many species [88,89]. In the pelagic, light pollution can affect diel vertical migrants [90,91]. ...
Article
The lunar cycle drives variation in nocturnal brightness. For the epipelagic larvae of coral reef organisms, nocturnal illumination may have widespread and underappreciated consequences. At sea, the onset of darkness coincides with an influx of mesopelagic organisms to shallow water (i.e. 'diel vertical migrants') that include predators (e.g. lanternfishes) and prey (zooplankton) of zooplanktivorous coral reef larvae. Moonlight generally suppresses this influx, but lunar periodicity in the timing and intensity of nocturnal brightness may affect vertically migrating predators and prey differently. A major turnover of species occurs at sunset on the reef, with diurnal species seeking shelter and nocturnal species emerging to hunt. The hunting ability of nocturnal reef-based predators is aided by the light of the moon. Consequently, variation in nocturnal illumination is likely to shape the timing of reproduction, larval development, and settlement for many coral reef organisms. This synthesis underscores the potential importance of trophic linkages between coral reefs and adjacent pelagic ecosystems, facilitated by the diel migrations of mesopelagic organisms and the ontogenetic migrations of coral reef larvae. Research is needed to better understand the effects of lunar cycles on life-history strategies, and the potentially disruptive effects of light pollution, turbidity, and climate-driven changes to nocturnal cloud cover. These underappreciated threats may alter patterns of nocturnal illumination that have shaped the evolutionary history of many coral reef organisms, with consequences for larval survival and population replenishment that could rival or exceed other effects arising from climate change.
... Anthropogenic disturbance of natural daily, lunar, or annual life cycles (e.g., due to artificial light pollution at night) may lead to shifts in coral holobiont evolutionary trajectories (Rosenberg et al. 2019;Ayalon et al. 2019;Levy et al. 2020). This may occur by impacting important processes of reproduction and recruitment (Richmond et al. 2018;Ayalon et al. 2021). ...
Article
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Recent human activity has profoundly transformed Earth biomes on a scale and at rates that are unprecedented. Given the central role of symbioses in ecosystem processes, functions, and services throughout the Earth biosphere, the impacts of human-driven change on symbioses are critical to understand. Symbioses are not merely collections of organisms, but co-evolved partners that arise from the synergistic combination and action of different genetic programs. They function with varying degrees of permanence and selection as emergent units with substantial potential for combinatorial and evolutionary innovation in both structure and function. Following an articulation of operational definitions of symbiosis and related concepts and characteristics of the Anthropocene, we outline a basic typology of anthropogenic change (AC) and a conceptual framework for how AC might mechanistically impact symbioses with select case examples to highlight our perspective. We discuss surprising connections between symbiosis and the Anthropocene, suggesting ways in which new symbioses could arise due to AC, how symbioses could be agents of ecosystem change, and how symbioses, broadly defined, of humans and “farmed” organisms may have launched the Anthropocene. We conclude with reflections on the robustness of symbioses to AC and our perspective on the importance of symbioses as ecosystem keystones and the need to tackle anthropogenic challenges as wise and humble stewards embedded within the system.
... However, some masking still occurred, with the observed circalunar brightness patterns being weaker than would be expected under natural sky conditions, and lunar brightness seemingly determining only the minimum observed sky brightness and not the maximum. The ecological effects caused by artificial light masking the lunar cycle are chronically understudied, although some research has explored the impact on coral gametogenesis (Ayalon et al. 2021;Puschnig et al. 2020). This knowledge gap is in spite of the high likelihood that a multitude of biological responses are impacted by the masking of the lunar cycle, given its importance as a cue for the physiology and behaviour of many taxa Kronfeld-Schor et al. 2013). ...
Article
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Light pollution is an issue of global significance for urban ecosystems, especially where areas of natural and ecological importance are located in and around cities. We investigated levels of night sky brightness around Auckland, Aotearoa-New Zealand, to determine the extent of sky glow, its potential to mask the lunar cycle, its relation to land use and the risks it poses to nearby areas of natural and ecological importance. Annual measurements of night sky brightness were carried out over 3 years at 115 randomly chosen sites within 15 km of Auckland’s city centre. In addition, continuous nightly measurements of sky brightness were taken at 6 urban residential sites for 18 months. We found that levels of sky glow in urban Auckland mask the lunar cycle to some extent and modelling suggests that nearby marine and terrestrial areas of ecological importance are at risk. In 2015 and 2016, > 95% of the total expanse of these areas was predicted to be experiencing night skies brighter than natural levels. Increased night sky brightness was associated with proximity to the city centre, commercial and industrial land use, and densities of buildings and streetlights. Reducing sky glow in and around the city should be a management priority, directed at commercial and industrial land-use zones while restricting urban sprawl near areas of natural and ecological importance.
... Marine ALAN affects cell processes, physiology, behaviours, recruitment, communities and entire ecosystems (Ayalon et al., 2020;Davies et al., 2015;Fobert et al., 2019;Navarro-Barranco & Hughes, 2015;O'Connor et al., 2019). The interdisciplinary nature of ALAN research, limitations in technology and complexities of researching most marine ecosystems present numerous challenges that researchers should be aware of when entering the field. ...
Article
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The increasing illumination of our world by artificial light at night (ALAN) has created a new field of global change research with impacts now being demonstrated across taxa, biological ranks and spatial scales. Following advances in terrestrial ecology, marine ALAN has become a rapidly growing research area attracting scientists from across all biomes. Limitations in technology, complexities of researching many coastal and marine ecosystems, and the interdisciplinary nature of ALAN research present numerous challenges. Drawing on expertise from optical oceanographers, modellers, community ecologists, experimental and molecular biologists, we share practical advice and solutions that have proven useful for marine ALAN research. Discussing lessons learnt early on can help in the effective and efficient development of a field. The guide follows a sensory ecology approach to marine light pollution and consolidates physics, ecology and biology. First, we introduce marine lightscapes highlighting how these differ from terrestrial ones and provide an overview of biological adaptations to them. Second, we discuss study design and technology to best quantify ALAN exposure of and impacts on marine and coastal organisms including molecular tools and approaches to scale‐up marine ALAN research. We conclude that the growing field of marine ALAN research presents opportunities not only for improving our understanding of this globally widespread stressor, but also for advancing fundamental marine photobiology, chronobiology, and night‐time ecology. Interdisciplinary research will be essential to gain insights into natural marine lightscapes shaping the ecology and evolution coastal and marine ecosystems.
... It is likely that artificial light pollution plays a role in shifting in situ spawning times (Ayalon et al., 2020;, and the observations in this study support that light pollution after sunset results in later gamete release times in D. cylindrus. Spectral LED output during the twilight phases was not precisely measured for this study, but the addition of a twilight phase may have prevented corals from perceiving sunset at the correct time. ...
Article
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Members of the family Meandrinidae are highly susceptible to stony coral tissue loss disease, resulting in population reductions up to 88% in both Dendrogyra cylindrus and Meandrina meandrites along the Florida Reef Tract. Reductions in abundance on this scale leave these species susceptible to limitations in sexual reproduction and natural recovery without intervention. In response to the ongoing outbreak of the disease across the Caribbean, a variety of genetic rescue projects have been implemented to bring disease susceptible species into ex situ culture and preserve living genetic diversity. In this study, corals being held in a long-term ex situ genetic bank were maintained using artificial lighting and temperature cues programmed to mimic natural cycles in Key Largo, FL, United States. Synchronized broadcast spawning events in both species were documented in aquaria over two annual spawning cycles in 2019 and 2020. Timing of gamete release relative to the perceived date and sunset was highly synchronized with wild observations. Up to 21 unique D. cylindrus genotypes collected from reef locations spanning over 230 km contributed gametes to the larval pool. The majority of these parental colonies are no longer alive in the wild. Repeatable and predictable ex situ spawning events such as these will become an essential tool for managed breeding and assisted fertilization in species suffering from severe population declines. These annual events have the potential to produce thousands of genetically diverse offspring for restoration efforts and offer future hope for the long-term survival of these threatened species.
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Sessile invertebrates often engage in synchronized spawning events to increase likelihood of fertilization. Although coral reefs are well studied, the reproductive behavior of most species and the relative influence of various environmental cues that drive reproduction are not well understood. We conducted a comparative examination of the reproduction of the well-studied Hawaiian coral Montipora capitata and the relatively unknown reproduction of its congener, Montipora flabellata. Both are simultaneous hermaphroditic broadcast spawners that release egg-sperm bundles with external fertilization. Montipora capitata had a distinct reproductive pattern that resulted in coordinated gamete maturation and the synchronized release of thousands of egg-sperm bundles across two spawning pulses tightly coupled to consecutive new moon phases in June and July. Montipora flabellata exhibited a four month reproductive season with spawning that was four-fold less synchronous than M. capitata; its spawning was aperiodic with little linkage to moon phase, a broadly distributed release of only dozens or hundreds of bundles over multiple nights, and a spawning period that ranged from late June through September. The reproductive strategy of M. flabellata might prove detrimental under climate change if increased frequency and severity of bleaching events leave it sparsely populated and local stressors continue to degrade its habitat.
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Coral reefs are in global decline due to climate change and anthropogenic influences (Hughes et al., 2013). Near coastal cities or other densely populated areas, coral reefs face a range of additional challenges. While considerable progress has been made in understanding coral responses to acute individual stressors (Dominoni et al., 2020), the impacts of chronic exposure to varying combinations of sensory pollutants are largely unknown. To investigate the impacts of urban proximity on corals, we conducted a year‐long in‐natura study ‐ incorporating sampling at diel, monthly, and seasonal time points – in which we compared corals from an Urban area to corals from a proximal Non‐Urban area. Here we reveal that despite appearing relatively healthy, natural biorhythms and environmental sensory systems were extensively disturbed in corals from the Urban environment. Transcriptomic data indicated poor symbiont performance, disturbance to gametogenic cycles, and loss or shifted seasonality of vital biological processes. Altered seasonality patterns were also observed in the microbiomes of the Urban coral population, signifying the impact of urbanization on the holobiont, rather than the coral host alone. These results should raise alarm regarding the largely unknown long‐term impacts of sensory pollution on the resilience and survival of coral reefs close to coastal communities
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Corals are known to synchronously undergo gonadal development during a period of 1 year and release gametes simultaneously during the spawning season. Synchronization of reproduction may be caused by changes in the external environment; particularly, the effects of light on reproduction have been extensively reported. In this study, we specifically focused on the type of wavelength, with the intention to elucidate whether there are wavelengths that promote reproduction in two Acropora. We exposed coral colonies to four types of light-emitting diode conditions with wavelengths suitable for keeping coral: “Coral,” “Reef,” “Fresh,” and “Sunset,” and monitored gamete maturation every 3 months, as well as the number of released gametes during the spawning season. In A. intermedia, “Sunset” conditions promoted gamete maturation; however, there was no spawning observed. In contrast, in A. muricata, the same conditions promoted a series of processes ranging from gamete maturation to gamete release. In “Fresh” and “Coral” conditions, gamete maturation was also promoted. “Sunset” condition is characterized by longer wavelengths within the red light visible spectrum, which is relatively predominant in the shallow waters where the two target species live. Therefore, this indicates that these longer wavelengths represent a light stimulus that promotes reproduction. By contrast, gamete maturation was promoted by even shorter wavelengths in A. muricata; therefore, further experiments considering different light sensitivities among species and growth promotion through the photosynthesis of zooxanthellae are recommended. It is also suggested that, in addition to wavelength type, spawning may be affected by water temperature increase after winter season.
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Artificial light at night (ALAN) is closely associated with modern societies and is rapidly increasing worldwide. A dynamically growing body of literature shows that ALAN poses a serious threat to all levels of biodiversity - from genes to ecosystems. Many “unknowns” remain to be addressed however, before we fully understand the impact of ALAN on biodiversity and can design effective mitigation measures. Here, we distilled the findings of a workshop on the effects of ALAN on biodiversity at the first World Biodiversity Forum in Davos attended by several major research groups in the field from across the globe. We argue that 11 pressing research questions have to be answered to find ways to reduce the impact of ALAN on biodiversity. The questions address fundamental knowledge gaps, ranging from basic challenges on how to standardize light measurements, through the multi-level impacts on biodiversity, to opportunities and challenges for more sustainable use.
Chapter
In this chapter, we discuss the evidence for climate change through global warming and the evidence that this global heating has an anthropogenic origin. We discuss the inter-linked issue of the increasing human population and then turn to the ongoing efforts to mitigate or arrest climate change. Finally, we discuss why massive efforts to decrease greenhouse gas emissions are needed so urgently. This area has also become a major political issue.
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Artificial light at night (ALAN) and its associated biological impacts have regularly been characterised as predominantly urban issues. Although far from trivial, this would imply that these impacts only affect ecosystems that are already heavily modified by humans and are relatively limited in their spatial extent, at least as compared with some key anthropogenic pressures on the environment that attract much more scientific and public attention, such as climate change or plastic pollution. However, there are a number of reasons to believe that ALAN and its impacts are more pervasive, and therefore need to be viewed from a broader geographic perspective rather than an essentially urban one. Here we address, in turn, 11 key issues when considering the degree of spatial pervasiveness of the biological impacts of ALAN. First, the global extent of ALAN is likely itself commonly underestimated, as a consequence of limitations of available remote sensing data sources and how these are processed. Second and third, more isolated (rural) and mobile (e.g., vehicle headlight) sources of ALAN may have both very widespread and important biological influences. Fourth and fifth, the occurrence and impacts of ALAN in marine systems and other remote settings, need much greater consideration. Sixth, seventh and eighth, there is growing evidence for important biological impacts of ALAN at low light levels, from skyglow, and over long distances (because of the altitudes from which it may be viewed by some organisms), all of which would increase the areas over which impacts are occurring. Ninth and tenth, ALAN may exert indirect biological effects that may further expand these areas, because it has a landscape ecology (modifying movement and dispersal and so hence with effects beyond the direct extent of ALAN), and because ALAN interacts with other anthropogenic pressures on the environment. Finally, ALAN is not stable, but increasing rapidly in global extent, and shifting towards wavelengths of light that often have greater biological impacts.
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The growth in human population along coastal areas is exposing marine environments to increasing anthropogenic light sources. Despite the potential effects of this modern phenomenon, very few studies have examined its implications for corals. Here, we present a long-term study of coral early life stages under light pollution conditions at night. Coral larvae were collected from Stylophora pistillata colonies, and then settled and grown under experimental conditions of two different common city lighting methods (fluorescent or LED). Effects of the artificial lighting on the coral settlement success, survivorship, growth rate, photosynthetic efficiency, and calcification rate were examined over a period of one year. The control exhibited ~30% higher settlement success compared to the two light treatments, while under the light treatments corals showed higher survivorship, growth, and calcification rates. In addition, an indication of damage to the photosynthetic system was found in the light-polluted corals, which was reflected in their photosynthesis efficiency parameters: i.e., lower maximum light utilization coefficient (α), lower maximum potential photosynthetic rate (Pmax), and lower photosynthetic maximal quantum yield (Fv/Fm). Our findings provide evidence of the potential adverse effects of artificial lighting methods on the natural environment of coral reefs. We conclude that the use of the LED lighting method has high interference potential for the early life stages of corals.
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Life on earth has evolved under constant environmental changes; in response to these changes, most organisms have developed an endogenous clock that allows them to anticipate daily and seasonal changes and adapt their biology accordingly. Light cycles synchronize biological rhythms and are controlled by an endogenous clock that is entrained by environmental cues. Light is known to play a key role in the biology of symbiotic corals as they exhibit many biological processes entrained by daily light patterns. In this study, we aimed at determining the effect of constant dim light on coral's perception of diel and monthly cycles. Our results show that under constant dim light corals display a loss of rhythmic processes and constant stimuli by light, which initiates signal transduction that results in an abnormal cell cycle, cell proliferation, and protein synthesis. The results emphasize how constant dim light can mask the biological clock of Acropora digitifera.
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Coral reefs represent the most diverse marine ecosystem on the planet, yet they are undergoing an unprecedented decline due to a combination of increasing global and local stressors. Despite the wealth of research investigating these stressors, Artificial Light Pollution at Night (ALAN) or “ecological light pollution” represents an emerging threat that has received little attention in the context of coral reefs, despite the potential of disrupting the chronobiology, physiology, behavior, and other biological processes of coral reef organisms. Scleractinian corals, the framework builders of coral reefs, depend on lunar illumination cues to synchronize their biological rhythms such as behavior, reproduction and physiology. While, light pollution (POL) may mask and lead de‐synchronization of these biological rhythms process. To reveal if ALAN impacts coral physiology, we have studied two coral species, Acropora eurystoma and Pocillopora damicornis, from the Gulf of Eilat/Aqaba, Red Sea, which is undergoing urban development that has led to severe POL at night. Our two experimental design data revealed that corals exposed to ALAN face an oxidative stress condition, show lower photosynthesis performances measured by electron transport rate (ETR), as well as changes in chlorophyll and algae density parameters. Testing different lights such as Blue LED and White LED spectrum showed more extreme impact in comparison to Yellow LEDs on coral physiology. The finding of this work sheds light on the emerging threat of POL and the impacts on the biology and ecology of Scleractinian corals, and will help to formulate specific management implementations to mitigate its potentially harmful impacts. The illustration shows how Artificial Light Pollution at Night (ALAN) can impact coral reefs by causing different physiological responses leading to photosynthetic performances and increasing oxidative stress.
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Light emitted or reflected up to the sky can interact with clouds or fog changing Night Sky Brightness (NSB). So the evaluation of NSB in any place can be affected by this meteorological features and needs to be analyzed. To evaluate this effect, data of NSB obtained with the Catalan Light Pollution Network (XCLCat) has been analyzed accurately and shows how the effect is completely different in urban and protected areas. The study, including for the first time independent cloud coverage data from ceilometer in combination with Sky Quality Meters (SQM), shows how in a city NSB increases dramatically and in a protected area the sky appears darker than in cloudless situation.
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Light pollution is considered a threat for biodiversity given the extent to which it can affect a vast number of behavioral and physiological processes in several species. This comes as no surprise as light is a fundamental, environmental cue through which organisms time their daily and seasonal activities, and alterations in the light environment have been found to affect profoundly the synchronization of the circadian clock, the endogenous mechanism that tracks and predicts variation in the external light/dark cycles. In this context, birds have been one of the most studied animal taxa, but our understanding of the effects of light pollution on the biological rhythms of avian species is mostly limited to behavioral responses. In order to understand which proximate mechanisms may be affected by artificial lights, we need an integrated perspective that focuses on light as a physiological signal, and especially on how photic information is perceived, decoded, and transmitted through the whole body. The aim of this review is to summarize the effects of light pollution on physiological and biochemical mechanisms that underlie changes in birds’ behavior, highlighting the current gaps in our knowledge and proposing future research avenues.
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Marine benthic communities face multiple anthropogenic pressures that compromise the future of some of the most biodiverse and functionally important ecosystems in the world. Yet one of the pressures these ecosystems face, night-time lighting, remains unstudied. Light is an important cue in guiding the settlement of invertebrate larvae, and altering natural regimes of nocturnal illumination could modify patterns of recruitment among sessile epifauna. We present the first evidence of night-time lighting changing the composition of temperate epifaunal marine invertebrate communities. Illuminating settlement surfaces with white light-emitting diode lighting at night, to levels experienced by these communities locally, both inhibited and encouraged the colonization of 39% of the taxa analysed, including three sessile and two mobile species. Our results indicate that ecological light pollution from coastal development, shipping and offshore infrastructure could be changing the composition of marine epifaunal communities. © 2015 The Author(s) Published by the Royal Society. All rights reserved.
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Coastal zones are exposed to a range of coastal hazards including sea-level rise with its related effects. At the same time, they are more densely populated than the hinterland and exhibit higher rates of population growth and urbanisation. As this trend is expected to continue into the future, we investigate how coastal populations will be affected by such impacts at global and regional scales by the years 2030 and 2060. Starting from baseline population estimates for the year 2000, we assess future population change in the low-elevation coastal zone and trends in exposure to 100-year coastal floods based on four different sea-level and socio-economic scenarios. Our method accounts for differential growth of coastal areas against the land-locked hinterland and for trends of urbanisation and expansive urban growth, as currently observed, but does not explicitly consider possible displacement or out-migration due to factors such as sea-level rise. We combine spatially explicit estimates of the baseline population with demographic data in order to derive scenario-driven projections of coastal population development. Our scenarios show that the number of people living in the low-elevation coastal zone, as well as the number of people exposed to flooding from 1-in-100 year storm surge events, is highest in Asia. China, India, Bangladesh, Indonesia and Viet Nam are estimated to have the highest total coastal population exposure in the baseline year and this ranking is expected to remain largely unchanged in the future. However, Africa is expected to experience the highest rates of population growth and urbanisation in the coastal zone, particularly in Egypt and sub-Saharan countries in Western and Eastern Africa. The results highlight countries and regions with a high degree of exposure to coastal flooding and help identifying regions where policies and adaptive planning for building resilient coastal communities are not only desirable but essential. Furthermore, we identify needs for further research and scope for improvement in this kind of scenario-based exposure analysis.
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Dramatically improved nighttime lights capabilities are presented by the launch of the National Polar-orbiting Partnership (NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) Day Night Band (DNB) sensor. Building on 18 years of experience compositing nighttime data from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS), NOAA’s NGDC Earth Observation Group has started adapting their algorithms to process these new data. The concept of compositing nighttime data comprises combining only high quality data components over a period of time to improve sensitivity and coverage. For this work, flag image are compiled to describe image quality. The flag categories include: daytime, twilight, stray light, lunar illuminance, noisy edge of scan data, clouds, and no data. High quality data is defined as not having any of these attributes present. Two methods of reprojection are necessary due to data collection characteristics. Custom algorithms have been created to terrain-correct and reproject all data to a common 15 arc second grid. Results of compositing over two time periods in 2012 are presented to demonstrate data quality and initial capabilities. These data can be downloaded at http://www.ngdc.noaa.gov/eog/viirs/download_viirs_ntl.html.
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Most studies in chronobiology focus on solar cycles (daily and annual). Moonlight and the lunar cycle received considerably less attention by chronobiologists. An exception are rhythms in intertidal species. Terrestrial ecologists long ago acknowledged the effects of moonlight on predation success, and consequently on predation risk, foraging behaviour and habitat use, while marine biologists have focused more on the behaviour and mainly on reproduction synchronization with relation to the Moon phase. Lately, several studies in different animal taxa addressed the role of moonlight in determining activity and studied the underlying mechanisms. In this paper, we review the ecological and behavioural evidence showing the effect of moonlight on activity, discuss the adaptive value of these changes, and describe possible mechanisms underlying this effect. We will also refer to other sources of night-time light ('light pollution') and highlight open questions that demand further studies.
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In this article, we present a satellite-based approach to gather information about the threat to coral reefs worldwide. Three chosen reef stressors – development, gas flaring and heavily lit fishing boat activity – are analysed using nighttime lights data derived from the Defense Meteorological Satellite Program (DMSP) produced at the National Oceanic & Atmospheric Administration, National Geophysical Data Center (NOAA/NGDC). Nighttime lights represent a direct threat to coral reef ecosystems and are an excellent proxy measure for associated human-caused stressors. A lights proximity index (LPI) is calculated, measuring the distance of coral reef sites to each of the stressors and incorporating the stressor's intensity. Colourized maps visualize the results on a global scale. Area rankings clarify the effects of artificial night lighting on coral reefs on a regional scale. The results should be very useful for reef managers and for state administrations to implement coral reef conservation projects and for the scientific world to conduct further research.
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Although the invention and widespread use of artificial light is clearly one of the most important human technological advances, the transformation of nightscapes is increasingly recognized as having adverse effects. Night lighting may have serious physiological consequences for humans, ecological and evolutionary implications for animal and plant populations, and may reshape entire ecosystems. However, knowledge on the adverse effects of light pollution is vague. In response to climate change and energy shortages, many countries, regions, and communities are developing new lighting programs and concepts with a strong focus on energy efficiency and greenhouse gas emissions. Given the dramatic increase in artificial light at night (0 -20% per year, depending on geographic region), we see an urgent need for light pollution policies that go beyond energy efficiency to include human well-being, the structure and functioning of ecosystems, and inter-related socioeconomic consequences. Such a policy shift will require a sound transdisciplinary understanding of the significance of the night, and its loss, for humans and the natural systems upon which we depend. Knowledge is also urgently needed on suitable lighting technologies and concepts which are ecologically, socially, and economically sustainable. Unless managing darkness becomes an integral part of future conservation and lighting policies, modern society may run into a global self-experiment with unpredictable outcomes.
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Animal species have evolved different diel activity rhythms that are of adaptive value. Theory suggests that diel temporal partitioning may facilitate co-existence between competitors and between predators and prey. However, relatively few studies demonstrate a temporal shift that is predation-or competition-induced. Recorded shifts are usually within the preferred activity phase of animal species (day or night), although there are some inversions to the opposite phase cycle. Temporal partitioning is not perceived as a common mechanism of coexistence. This rarity has been variously ascribed to theoretical considerations and to the rigidity of time-keeping mechanisms, as well as to other physiological and anatomical traits that may constrain activity patterns. Our decade-long study of spiny mice of rocky deserts demonstrates that, while different factors select for activity patterns, endogenous rhythmicity may be an evolutionary constraint.
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Ecologists have long studied the critical role of natural light in regulating species interactions, but, with limited exceptions, have not investigated the consequences of artificial night lighting. In the past century,the extent and intensity of artificial night lighting has increased such that it has substantial effects on the biology and ecology of species in the wild. We distinguish “astronomical light pollution”, which obscures the view of the night sky, from “ecological light pollution”, which alters natural light regimes in terrestrial and aquatic ecosystems. Some of the catastrophic consequences of light for certain taxonomic groups are well known, such as the deaths of migratory birds around tall lighted structures, and those of hatchling sea turtles disoriented by lights on their natal beaches. The more subtle influences of artificial night lighting on the behavior and community ecology of species are less well recognized, and constitute a new focus for research in ecology and a pressing conservation challenge.
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The diurnal cycle of light and dark is one of the strongest environmental factors for life on Earth. Many species in both terrestrial and aquatic ecosystems use the level of ambient light to regulate their metabolism, growth, and behavior. The sky glow caused by artificial lighting from urban areas disrupts this natural cycle, and has been shown to impact the behavior of organisms, even many kilometers away from the light sources. It could be hypothesized that factors that increase the luminance of the sky amplify the degree of this "ecological light pollution". We show that cloud coverage dramatically amplifies the sky luminance, by a factor of 10.1 for one location inside of Berlin and by a factor of 2.8 at 32 km from the city center. We also show that inside of the city overcast nights are brighter than clear rural moonlit nights, by a factor of 4.1. These results have important implications for choronobiological and chronoecological studies in urban areas, where this amplification effect has previously not been considered.
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There are dramatic and physiologically relevant changes in both skylight color and intensity during evening twilight as the pathlength of direct sunlight through the atmosphere increases, ozone increasingly absorbs long wavelengths and skylight becomes increasingly blue shifted. The moon is above the horizon at sunset during the waxing phase of the lunar cycle, on the horizon at sunset on the night of the full moon and below the horizon during the waning phase. Moonlight is red shifted compared with daylight, so the presence, phase and position of the moon in the sky could modulate the blue shifts during twilight. Therefore, the influence of the moon on twilight color is likely to differ somewhat each night of the lunar cycle, and to vary especially rapidly around the full moon, as the moon transitions from above to below the horizon during twilight. Many important light-mediated biological processes occur during twilight, and this lunar effect may play a role. One particularly intriguing biological event tightly correlated with these twilight processes is the occurrence of mass spawning events on coral reefs. Therefore, we measured downwelling underwater hyperspectral irradiance on a coral reef during twilight for several nights before and after the full moon. We demonstrate that shifts in twilight color and intensity on nights both within and between evenings, immediately before and after the full moon, are correlated with the observed times of synchronized mass spawning, and that these optical phenomena are a biologically plausible cue for the synchronization of these mass spawning events.
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Circadian regulation of plant-animal endosymbioses is complicated by a diversity of internal and external cues. Here, we show that stress-related genes in corals are coupled to the circadian clock, anticipating major changes in the intracellular milieu. In this regard, numerous chaperones are "hard-wired" to the clock, effectively preparing the coral for the consequences of oxidative protein damage imposed by symbiont photosynthesis (when O(2) > 250% saturation), including synexpression of antioxidant genes being light-gated. Conversely, central metabolism appears to be regulated by the hypoxia-inducible factor system in coral. These results reveal the complexity of endosymbiosis as well as the plasticity regulation downstream of the circadian clock.
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Hundreds of species of reef-building corals spawn synchronously over a few nights each year, and moonlight regulates this spawning event. However, the molecular elements underpinning the detection of moonlight remain unknown. Here we report the presence of an ancient family of blue-light–sensing photoreceptors, cryptochromes, in the reef-building coral Acropora millepora. In addition to being cryptochrome genes from one of the earliest-diverging eumetazoan phyla, cry1 and cry2 were expressed preferentially in light. Consistent with potential roles in the synchronization of fundamentally important behaviors such as mass spawning, cry2 expression increased on full moon nights versus new moon nights. Our results demonstrate phylogenetically broad roles of these ancient circadian clock–related molecules in the animal kingdom.
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Remote sensing of night light emissions in the visible band offers a unique opportunity to directly observe human activity from space. This has allowed a host of applications including mapping urban areas, estimating population and GDP, monitoring disasters and conflicts. More recently, remotely sensed night lights data have found use in understanding the environmental impacts of light emissions (light pollution), including their impacts on human health. In this review, we outline the historical development of night-time optical sensors up to the current state of the art sensors, highlight various applications of night light data, discuss the special challenges associated with remote sensing of night lights with a focus on the limitations of current sensors, and provide an outlook for the future of remote sensing of night lights. While the paper mainly focuses on space borne remote sensing, ground based sensing of night-time brightness for studies on astronomical and ecological light pollution, as well as for calibration and validation of space borne data, are also discussed. Although the development of night light sensors lags behind daytime sensors, we demonstrate that the field is in a stage of rapid development. The worldwide transition to LED lights poses a particular challenge for remote sensing of night lights, and strongly highlights the need for a new generation of space borne night lights instruments. This work shows that future sensors are needed to monitor temporal changes during the night (for example from a geostationary platform or constellation of satellites), and to better understand the angular patterns of light emission (roughly analogous to the BRDF in daylight sensing). Perhaps most importantly, we make the case that higher spatial resolution and multispectral sensors covering the range from blue to NIR are needed to more effectively identify lighting technologies, map urban functions, and monitor energy use.
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Increased concentrations of atmospheric greenhouse gases have led to a global mean surface temperature 1.0°C higher than during the pre-industrial period. We expand on the recent IPCC Special Report on global warming of 1.5°C and review the additional risks associated with higher levels of warming, each having major implications for multiple geographies, climates, and ecosystems. Limiting warming to 1.5°C rather than 2.0°C would be required to maintain substantial proportions of ecosystems and would have clear benefits for human health and economies. These conclusions are relevant for people everywhere, particularly in low- and middle-income countries, where the escalation of climate-related risks may prevent the achievement of the United Nations Sustainable Development Goal.
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Coral populations continue to decline in many regions because of natural and anthropogenic disturbances; and the persistence of coral populations mainly relies on natural recruitment through coral reproduction. However, studies on the reproduction of many important reef-building coral species in one of the most biodiverse region, the Coral Triangle, are very limited. Here, we investigated the reproductive biology of the coral Acropora millepora in Bolinao-Anda Reef Complex, northwestern Philippines from February 2014 to March 2015, through in situ assessment of gamete maturity, histological examination of gamete development and ex situ spawning observations. Results showed that A. millepora exhibited an annual gametogenic cycle. Formation of oocytes took place within 8 months, whereas spermatocytes developed in 3 months before the gamete release. Abundance and size of eggs in A. millepora were greatest during the months nearest to the spawning period, which coincides with the rapid increase in sea surface temperature. Ex situ broadcast spawning occurred around the months of February–March, which suggests an extended spawning pattern. Results provide additional information on coral reproduction in the region and reveal the potential of A. millepora in providing coral propagules for the replenishment and recovery of degraded coral populations.
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Tropical reef systems are transitioning to a new era in which the interval between recurrent bouts of coral bleaching is too short for a full recovery of mature assemblages. We analyzed bleaching records at 100 globally distributed reef locations from 1980 to 2016. The median return time between pairs of severe bleaching events has diminished steadily since 1980 and is now only 6 years. As global warming has progressed, tropical sea surface temperatures are warmer now during current La Niña conditions than they were during El Niño events three decades ago. Consequently, as we transition to the Anthropocene, coral bleaching is occurring more frequently in all El Niño–Southern Oscillation phases, increasing the likelihood of annual bleaching in the coming decades.
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The use of artificial lighting to illuminate the night has provided substantial benefits to humankind. It has also disrupted natural daily, seasonal, and lunar light cycles as experienced by a diversity of organisms, and hence it has also altered cues for the timings of many biological activities. Here we review the evidence for impacts of artificial nighttime lighting on these timings. Although the examples are scattered, concerning a wide variety of species and environments, the breadth of such impacts is compelling. Indeed, it seems reasonable to conclude that the vast majority of impacts of artificial nighttime lighting stem from effects on biological timings. This adds support to arguments that artificial nighttime lighting has a quite pervasive and marked impact on ecological systems, that the rapid expansion in the global extent of both direct illuminance and skyglow is thus of significant concern, and that a widespread implementation of mitigation measures is required.
Article
Mesophotic coral ecosystems (MCEs, between 30 and 150 m depth) are hypothesized to contribute to the recovery of degraded shallow reefs through sexually produced larvae (referred to as Deep Reef Refuge Hypothesis). In Okinawa, Japan, the brooder coral Seria-topora hystrix was reported to be locally extinct in a shallow reef while it was found abundant at a MCE nearby. In this context, S. hystrix represents a key model to test the Deep Reef Refuge Hypothesis and to understand the potential contribution of mesophotic corals to shallow coral reef recovery. However, the reproductive biology of mesophotic S. hystrix and its potential to recolonize shallow reefs is currently unknown. This study reports for the first time, different temporal scales of reproductive periodicity and larval settlement of S. hystrix from an upper mesophotic reef (40 m depth) in Okinawa. We examined reproductive sea-sonality, lunar, and circadian periodicity (based on polyp dissection, histology, and ex situ planula release observations) and larval settlement rates in the laboratory. Mesophotic S. hystrix reproduced mainly in July and early August, with a small number of planulae being released at the end of May, June and August. Compared to shallow colonies in the same region, mesophotic S. hystrix has a 4-month shorter reproductive season, similar circadian periodicity, and smaller planula size. In addition, most of the planulae settled rapidly, limiting larval dispersal potential. The shorter reproductive season and smaller planula size may result from limited energy available for reproduction at deeper depths, while the similar circa-dian periodicity suggests that this reproductive aspect is not affected by environmental conditions differing with depth. Overall, contribution of mesophotic S. hystrix to shallow reef rapid recovery appears limited, although they may recruit to shallow reefs through a multi-step process over a few generations or through random extreme mixing such as typhoons.
Article
Natural light cycles are important for synchronizing behavioral and physiological rhythms over varying time-periods in both plants and animals. An endogenous clock, regulated by positive and negative elements, interacting in feedback loops, control these rhythms. Many corals exhibit diel cycles of polyp expansion and contraction entrained by solar light patterns and monthly cycles of spawning or planulation that correspond to nocturnal lunar light cycles. However, despite considerable interest in studies of coral reproduction, there is currently not enough molecular information about the cellular pathways involved with synchronizing spawning/planulation in broadcast spawners and brooders. To determine whether the endogenous clock is implicated in the regulation of reproductive behavior in corals, we characterized the transcriptome of Acropora digitifera colonies at twelve time points over a two-month period of full and new moons, starting with the day of spawning in June 2014. We identified 608 transcripts with differential expression only on the spawning night during the coral setting phase and gamete release. Our data revealed an upregulation of light-sensing molecules and rhodopsin-like receptors that initiate signaling cascades, including the glutamate, SMAD signaling, and WNT signaling pathways, neuroactive ligand-receptor interactions and calcium signaling. These are all involved in cell cycling, cell movement, tissue polarity, focal adhesion, and cytoskeleton reorganization, and together lead to gamete release. These findings can improve the understanding of many time-based cycles and extend our knowledge of the interplay between exogenous signals and the endogenous clock in cnidarians. This article is protected by copyright. All rights reserved.
Article
Despite centuries of use, artificial light at night has only recently been recognized as a cause for environmental concern. Its global extent and ongoing encroachment into naturally lit ecosystems has sparked scientific interest into the many ways in which it may negatively affect human health, societal attitudes, scientific endeavors, and biological processes. Yet, perhaps because sources of artificial light are largely land based, the potential for artificial light pollution to interfere with the biology of the ocean has not been explored in any detail. There is little information on how light pollution affects those species, behaviors, and interactions that are informed by the intensity, spectra, and periodicity of natural nighttime light in marine ecosystems. Here, we provide an overview of the extent of marine light pollution, discuss how it changes the physical environment, and explore its potential role in shaping marine ecosystems.
Article
In many species of symbiotic corals, spawning occurs synchronously several nights after the full moon. This process is correlated with the level of lunar irradiance, but the mechanism by which these cnidarian/zooxanthellate symbioses can detect such low levels of light remains unknown. Here we report the first biophysical evidence that the host animal exhibits extraordinarily sensitive photoreception in the blue region of the spectrum. Using a high-resolution laser-induced signal to detect tentacle scattering, we measured the effect of low irradiance on the contraction of polyps in the corals that normally have their tentacles extended in darkness. Similar to most deep-sea invertebrates, the action spectra of coral photoreception reveal a maximum sensitivity in the blue, at 480 nm, with a spectral band width (at full-width half-maximum) of ca. 110 nm. The spectra closely overlap the maximal transparency of oligotrophic tropical waters, thus optimizing the perception of low light at depth. The detected threshold of photoreception sensitivity is ~1.2 x 1015 quanta m-2 s-1 in the blue region. This makes corals capable of sensing the blue portion of lunar irradiance, as evidenced from the recorded slight contractions of polyp tentacles under variations in moonlight intensity.
Article
The ecological impacts of nighttime light pollution have been a longstanding source of concern, accentuated by realized and projected growth in electrical lighting. As human communities and lighting technologies develop, artificial light increasingly modifies natural light regimes by encroaching on dark refuges in space, in time, and across wavelengths. A wide variety of ecological implications of artificial light have been identified. However, the primary research to date is largely focused on the disruptive influence of nighttime light on higher vertebrates, and while comprehensive reviews have been compiled along taxonomic lines and within specific research domains, the subject is in need of synthesis within a common mechanistic framework. Here we propose such a framework that focuses on the cross-factoring of the ways in which artificial lighting alters natural light regimes (spatially, temporally, and spectrally), and the ways in which light influences biological systems, particularly the distinction between light as a resource and light as an information source. We review the evidence for each of the combinations of this cross-factoring. As artificial lighting alters natural patterns of light in space, time and across wavelengths, natural patterns of resource use and information flows may be disrupted, with downstream effects to the structure and function of ecosystems. This review highlights: (i) the potential influence of nighttime lighting at all levels of biological organisation (from cell to ecosystem); (ii) the significant impact that even low levels of nighttime light pollution can have; and (iii) the existence of major research gaps, particularly in terms of the impacts of light at population and ecosystem levels, identification of intensity thresholds, and the spatial extent of impacts in the vicinity of artificial lights.
Article
Several brooding scleractinian coral species are known to release planulae at certain phases of the moon. This study of a brooding coral, Favia fragum, suspected of having a lunar cycle of planulation, had the objective of determining whether there was also a lunar periodicity in gametogenesis and embryogenesis. Histological examination of specimens collected at 2 to 4 day intervals over several lunar cycles revealed a lunar periodicity in the maturation of oocytes and a lunar cycle in spermatogenesis which ended with ovulation and presumably spawning of sperm about day 18 after the new moon. Embryos developed slowly, taking about 4 days to reach the planula stage. After brooding for about 3 weeks the mature planulae were expelled between days 6 and 15 after the new moon, with a peak on day 11. Under natural conditions, planulae were never retained past the end of the planulation period, which was followed closely by a new ovulation event. Therefore, the lunar periodicity in planulation is driven by a lunar cycle of gamete maturation and ovulation. The timing of this ovulation is about 4 to 5 days after the full moon, which is the same time many broadcasting corals are known to spawn.
Article
The long-distance dispersal of larvae provides important linkages between populations of reef-building corals and is a critical part of coral biology. Some coral planulae have symbiotic dinoflagellates (Symbiodinium spp.) that probably provide energy in addition to the lipids provisioned within the egg. However, our understanding of the influence of symbionts on the energy metabolism and survivorship of planulae remains limited. This study examines the relative roles of symbiotic dinoflagellate photosynthesis and stored lipid content in the survivorship of the developing stages of the corals Pocillopora damicornis and Montipora digitata. We found that survivorship decreased under dark conditions (i.e. no photosynthetic activity) for P. damicornis and M. digitata at 31 and 22days after release/spawning, respectively. The lipid content of P. damicornis and M. digitata planulae showed a significant decrease, at a higher rate, under dark conditions, when compared with light conditions. When converted to energy equivalents, the available energy provided by the depletion of lipids could account for 41.9 and 84.7% of larval metabolism for P. damicornis (by day 31) and 38.4 and 90.1% for M. digitata (by day 21) under light and dark conditions, respectively. This finding indicates that not all energy requirements of the larvae are met by lipids: energy is also sourced from the photosynthetic activities of the symbiotic dinoflagellates within these larvae, especially under light conditions. In addition, the amounts of three main lipid classes (wax esters, triglycerides, and phospholipids) decreased throughout the experiment in the planulae of both species, with the wax ester content decreasing more rapidly under dark conditions than under light conditions. The observations that the planulae of both species derive considerable amounts of energy from wax esters, and that symbiotic dinoflagellates enable larvae to use their stores at lower rates, suggested that symbiotic dinoflagellates have the potential to extend larval life under light conditions.
Signaling cascades and the importance of moonlight in coral broadcast mass spawning.
  • Kaniewska P.
  • Alon S.
  • Karako-Lampert S.
  • Hoegh-Guldberg O.
  • Levy O.
Kaniewska, P., Alon, S., Karako-Lampert, S., Hoegh-Guldberg, O., and Levy, O. (2015). Signaling cascades and the importance of moonlight in coral broadcast mass spawning. eLife 4, e09991.
Sexual reproduction of scleractinian corals
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Harrison, P.L. (2011). Sexual reproduction of scleractinian corals. In Coral Reefs: An Ecosystem in Transition, Z. Dubinsky, and N. Stambler, eds. (Springer), pp. 59-85.
Signaling cascades and the importance of moonlight in coral broadcast mass spawning
  • Kaniewska