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Coral Gametogenesis Collapse under Artificial Light Pollution
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.
... Demonstrated ALAN impacts on habitat-forming species like marine sessile invertebrates are rare, except for tropical corals [47][48][49] and three species of barnacles [28,29]. Here, we quantified ALAN impacts on two cosmopolitan, sessile invertebrates from temperate marine ecosystems, the barnacle Austrominius modestus and the mussel Mytilus edulis, by measuring larval performance (survival, growth and developmental time) under an ALAN gradient. ...
... Instead, organisms experience a higher metabolic rate, which can be associated with faster production of reactive oxygen species (ROS) and thus oxidative stress reducing lifespan, potentially via higher vulnerability to cellular damage. While ALAN has been shown to increase metabolic demands [57,58], cause overproduction of ROS and increase in oxidative damage from corals [47,48] to vertebrates, including humans [59,60], there is plenty of evidence that ALAN does not necessarily affect organisms via this pathway [61,62]. Alternatives can be endocrine disruptions such as depressed levels of T3, an important hormone for metamorphosis [50]. ...
... As filter feeders with a complex life-cycle involving a larval phase, they couple benthic pelagic systems and contribute to energy flows through trophic chains [5] and the accumulation of calcium and carbon [2,31]. While ALAN impacts have been demonstrated at most scales of biological organization [19,66], few studies have been able to quantify ALAN effects on ecosystems and ecological functioning so far [47,49,64,67]. Targeting ecosystem engineering species can form an entry-point to eventually scale-up ALAN impacts to ecosystem level. ...
Sessile marine invertebrates play a vital role as ecosystem engineers and in benthic–pelagic coupling. Most benthic fauna develop through larval stages and the importance of natural light cycles for larval biology and ecology is long-established. Natural light–dark cycles regulate two of the largest ocean-scale processes that are fundamental to larvae's life cycle: the timing of broadcast spawning for successful fertilization and diel vertical migration for foraging and predator avoidance. Given the reliance on light and the ecological role of larvae, surprisingly little is known about the impacts of artificial light at night (ALAN) on the early life history of habitat-forming species. We quantified ALAN impacts on larval performance (survival, growth, development) of two cosmopolitan ecosystem engineers in temperate marine ecosystems, the mussel Mytilus edulis and the barnacle Austrominius modestus . Higher ALAN irradiance reduced survival in both species (57% and 13%, respectively). ALAN effects on development and growth were small overall, and different between species, time-points and parentage. Our results show that ALAN adversely affects larval survival and reiterates the importance of paternal influence on offspring performance. ALAN impacts on the early life stages of ecosystem engineering species have implications not only for population viability but also the ecological communities that these species support.
This article is part of the theme issue ‘Light pollution in complex ecological systems’.
... Currently, ~13 % of the global population lives within a 100 km distance to coral reefs and population growth rates near coral reefs is higher than global averages (Sing Wong et al., 2022). Nowadays, nearly 15 % of the world's reefs are experiencing light pollution (Ayalon et al., 2021), with the most affected reefs being located in the Singapore Strait, the Gulf of Thailand, and the Persian/Arabian Gulf, where night skies tend to be ~30 % brighter than normal. ...
... Light pollution has been identified as one of the most pervasive forms of environmental pollution (Gaston et al., 2013;Ayalon et al., 2021) because it possesses the capability to impact organisms hundreds of kilometres away from human settlements (Davies and Smyth, 2017). ALAN can disrupt daily cycles, masking natural light signals or providing misleading cues, leading to deleterious physiological and behavioural responses (Duarte et al., 2019;Rosenberg et al., 2019a;Ayalon et al., 2021;Marangoni et al., 2022;Quintanilla-Ahumada et al., 2022;Davies et al., 2023). ...
... Light pollution has been identified as one of the most pervasive forms of environmental pollution (Gaston et al., 2013;Ayalon et al., 2021) because it possesses the capability to impact organisms hundreds of kilometres away from human settlements (Davies and Smyth, 2017). ALAN can disrupt daily cycles, masking natural light signals or providing misleading cues, leading to deleterious physiological and behavioural responses (Duarte et al., 2019;Rosenberg et al., 2019a;Ayalon et al., 2021;Marangoni et al., 2022;Quintanilla-Ahumada et al., 2022;Davies et al., 2023). Nowadays, many street lighting networks are transitioning from low-pressure sodium lamps to LEDs, a change that results in an increased emission of light in the environment (3-8 fold), as well as in a different quality of light (Schulte-Römer et al., 2019;Sánchez de Miguel et al., 2022). ...
Increasing levels of Artificial Light At Night (ALAN) alter the natural diel cycles of organisms at global scale. ALAN constitutes a potential threat to the light-dependent functioning of symbiotic scleractinian corals, the habit-founders of warm, shallow water reefs. Here, we show that ALAN disrupts the natural diel tentacle expansion and contraction behaviour, a key mechanism for prey capture and nutrient acquisition in corals. We exposed four symbiotic scleractinian coral species to different ALAN treatments (0.4-2.5 μmol quanta m-2 s-1). Exposure to ALAN levels of 1.2 μmol quanta m-2 s-1 and above altered the normal tentacle expansion response in diurnal species (Stylophora pistillata and Duncanopsammia axifuga). The tentacle expansion pattern of nocturnal species (Montastraea cavernosa and Lobophyllia hemprichii) was less affected, which may indicate a greater capacity to tolerate ALAN exposure. The results of this work suggest that ALAN has the potential to affect nutrient acquisition mechanisms of symbiotic corals which may in turn result in changes in the coral community structure in shallow water reefs in ALAN-exposed areas.
... For tropical reef-building corals, artificial lighting could constitute a major perturbation to nocturnal light regimes, as it disrupts the natural photoperiod cycle of light and darkness (Lynn and Quijón, 2022;Marangoni et al., 2022). Consequently, ALAN affects crucial processes synchronized with the diel light-dark cycle of corals, including metabolism and photophysiology (Ayalon et al., 2019(Ayalon et al., , 2021aRosenberg et al., 2019;Tamir et al., 2020) as well as gametogenesis and spawning synchronicity (Ayalon et al., 2021b). Recently, light pollution has been shown to induce photoinhibition and oxidative stress in symbiotic corals (Levy et al., 2020) and might thus play an important role in modulating the ecophysiology of corals in urban environments. ...
... Stylophora pistillata corals are interesting to consider with respect to ALAN, as this species dominates the shallow waters of the Gulf of Eilat/Aqaba (GoE/A), the Red Sea, from juveniles to adults (Kramer et al., 2019(Kramer et al., , 2020Loya, 1976). It is worth noting that on a global scale, the northern coast of the GoE/A has been identified as a heavily light-polluted area, with Eilat's reef night sky brightness being on average 470 % brighter than the natural night sky (Ayalon et al., 2021b;Tamir et al., 2017), thus making it a fundamental location for studying the effects of ALAN on coral species. ...
... For example, Loya et al. (2004) found that although coral growth is accelerated under chronic eutrophication, it also renders corals more susceptible to lower reproductive output. As previously mentioned, corals exposed to photopollution at night exhibit lower fecundity (Ayalon et al., 2021b), which subsequently reduces the supply of planulae and further hinders successful settlement . Taken together with previous research, we suggest that ALAN may favor faster coral growth at the cost of reduced reproductive investment (Ayalon et al., 2021b;Loya et al., 2004;Tamir et al., 2020). ...
Urbanization and infrastructure development have changed the night-time light regime of many coastal marine habitats. Consequently, Artificial Light at Night (ALAN) is becoming a global ecological concern, particularly in nearshore coral reef ecosystems. However, the effects of ALAN on coral architecture and their optical properties are unexplored. Here, we conducted a long-term ex situ experiment (30 months from settlement) on juvenile Stylophora pistillata corals grown under ALAN conditions using light-emitting diodes (LEDs) and fluorescent lamps, mimicking light-polluted habitats. We found that corals exposed to ALAN exhibited altered skeletal morphology that subsequently resulted in reduced light capture capacity, while also gaining better structural and optical modifications to increased light levels than their ambient-light counterparts. Additionally, light-polluted corals developed a more porous skeleton compared to the control corals. We suggest that ALAN induces light stress in corals, leading to a decrease in the solar energy available for photosynthesis during daytime illumination.
... 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. ...
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). ...
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. ...
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.
... ALAN can also disrupt the coral-dinoflagellate symbiosis [28,31], and alter pathways of gene expression, with approximately 25 times more differentially expressed genes that regulate cell cycle, cell proliferation, cell growth and protein synthesis under ALAN [26]. Furthermore, ALAN can affect gametogenesis and the timing of gamete release, impacting coral reproduction ( [32]; see §2c Biological timings). Though research on the physiological impacts of ALAN on corals is only in its infancy, these studies demonstrate the potential for ALAN as a significant threat to coral fitness and survival, and consequently the resilience of coral reef ecosystems. ...
... By masking the natural light cues from the lunar cycle that marine organisms rely on to time spawning events, ALAN can suppress spawning (e.g. in the coral Dipastrea specisosa; [45]), or delay the gametogenesis cycle (e.g. Acropora millepora and Acropora digitofera; [32]), leading to desynchronized gamete release of broadcast spawners such as corals. Desynchronization of spawning events reduces the probability of fertilization [54], and could reduce the supply of new recruits to the population. ...
Despite 22% of the world's coastal regions experiencing some degree of light pollution, and biologically important artificial light at night (ALAN) reaching large portions of the seafloor (greater than 75%) near coastal developments, the impacts of ALAN on temperate and tropical reefs are still relatively unknown. Because many reef species have evolved in response to low-light nocturnal environments, consistent daily, lunar, and seasonal light cycles, and distinct light spectra, these impacts are likely to be profound. Recent studies have found ALAN can decrease reproductive success of fishes, alter predation rates of invertebrates and fishes, and impact the physiology and biochemistry of reef-building corals. In this paper, we integrate knowledge of the role of natural light in temperate and tropical reefs with a synthesis of the current literature on the impacts of ALAN on reef organisms to explore potential changes at the system level in reef communities exposed to ALAN. Specifically, we identify the direct impacts of ALAN on individual organisms and flow on effects for reef communities, and present potential scenarios where ALAN could significantly alter system-level dynamics, possibly even creating novel ecosystems. Lastly, we highlight large knowledge gaps in our understanding of the overall impact of ALAN on reef systems.
This article is part of the theme issue ‘Light pollution in complex ecological systems’.
... Artificial light exposure decreases marine organismal growth rates and survival, and reduces reproductive success, all reducing population health in ALAN-exposed conditions (Fobert, da Silva & Swearer, 2019;Schligler et al., 2021;Ayalon et al., 2021b). ...
... Some organisms have demonstrated a cumulation of negative physiological response to ALAN exposure. Corals are one such group that have exhibited largely negative reactions to ALAN, with changes in cellular and organismal health, with effects on fitness through delayed gametogenesis and desynchronized gamete release (Ayalon et al., 2021a;Ayalon et al., 2021b). Other similar studies have found varied responses of corals to light, but, largely, the results of these studies point to negative impacts such as altered photosynthetic rates, changed symbiotic relationships with zooxanthellae and increased stress particularly in response to shorter wavelength light (Wijgerde, Henkemans & Osinga, 2012;Ayalon et al., 2019;Tamir et al., 2020). ...
Light pollution is a pervasive global stressor to natural systems. However, due to the proximity of human activities along the coasts and open ocean, light is a pervasive yet commonly overlooked pollutant in many marine habitats.
There is a well‐developed body of literature on the visual physiology, behaviour and ecology of many marine taxa, and a re‐evaluation of these data can help inform risks of light pollution to impact marine organisms and ecosystems. This paper identifies key knowledge gaps in the study of marine light pollution ecology and recommends research and management foci for future study.
Most work on this pollutant has focused on terrestrial ecosystems and taxa, where experts have learned how anthropogenic light influences behaviour, reproduction cycles and population dynamics. However, light pollution bleeds far beyond the shores, affecting many sensitive ecosystems with light available at unnatural times with varied makeup, such as varying intensities or spectra.
This review discusses the current understanding of light dynamics underwater, photoreceptive systems of marine taxa and the documented ecological impacts. This lends a critical basis of understanding for the many gaps in marine light pollution biology. For example, little is known about effects of light on broad groups of marine taxa such as cetaceans, ecosystem‐level effects, or interactive impacts of light and other anthropogenic stressors. Light is a key structuring factor of the marine environment and can therefore elicit immense downstream effects on marine organisms individually, at the population‐ or ecosystem‐level.
Light pollution is an urgent concern for marine ecosystems because marine organisms have tight relationships with their natural light environment. As the world moves deeper into the Anthropocene, assessing and mitigating the risks of this pollutant to key environmental and economic marine systems is critical to maintaining a healthy ocean.
... Artificial light that hampers the perception of natural light cycles may in turn disrupt the synchronization of reproductive activities. For instance, artificial light disturbs the moonlight dependent synchronization of gamete release in two coral species, Acropora millepora and A. digitifera (Ayalon et al. 2021b). Artificial light can also alter hormonal levels and thereby influence seasonal reproductive activities (Buchanan and Partecke 2012). ...
... Moreover, artificial light that hampers their detection of suitable oviposition sites when returning to water to reproduce can reduce reproductive success Kriska et al. 2008). Artificial light that obscures lunar cycles can again disrupt the synchronizing of mass spawnings in species that depend on the lights for the timing of the event, such as corals (Ayalon et al. 2021b). ...
Artificial light at night (ALAN) is a growing global problem altering the behavior of organisms and thereby community composition and ecosystem processes. Research has mostly focused on terrestrial ecosystems, but a growing number of studies show that aquatic ecosystems are increasingly affected. Here, we provide a conceptual framework that describes how ALAN can influence aquatic ecosystems through effects on the behavior of ecologically important invertebrates. These organisms provide a range of critical ecological functions, from serving as food for other organisms to nutrient cycling and the translocation of energy and matter within and between ecosystems. In addition, we systematically searched the literature to assess the current state of the field and identify knowledge gaps. The literature search reveals that an increasing number of studies find light pollution to alter the behavior of aquatic invertebrates, such as their movements, habitat choice, and foraging behavior, but that the fitness consequences of these behavioral changes are largely unknown, as are their impacts on populations, communities, and ecosystems. Yet, assessing the consequences of behavioral changes for higher ecological levels is of vital importance given the central role of these invertebrates in ecosystems. Thus, more research needs to be directed to the ecological consequences of behavioral responses of aquatic invertebrates to light pollution. Overall, more effort should be made to assess the ecological consequences of behavioral responses to ALAN, and, importantly, how negative effects of light pollution could be mitigated.
Significance statement
Light pollution is of growing ecological concern and influencing ecosystems through effects on the behavior of organisms. Aquatic ecosystems are increasingly exposed and an ecologically important group of organisms in these systems are invertebrates. Here, we discuss how artificial light at night alters the behavior of aquatic invertebrates and how this in turn influences ecosystem structure and function. Such an understanding of the mechanisms and pathways that underlie the effect of light pollution on aquatic ecosystems is needed if we are to develop efficient strategies to reduce negative effects of human-made lighting systems on ecosystems.
... 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. ...
Significance
Mass coral spawning is a perplexing annual event that occurs over a few nights following a full moon. This paper demonstrates that the period of darkness between sunset and moonrise that occurs after the full moon is a trigger for spawning in coral species Dipsastraea speciosa . As this species shares similar spawning patterns with many other coral taxa, we expect this model for spawning to be applicable to other coral species. Our discovery provides insights into how coral spawning is synchronized via the lunar cycle.
... ALAN can also intervene in the survival of coral symbionts (specifically green algae) in species such as Pocillopora damicornis and Acropora euristoma, that after 120 days of exposure to light, the density of their microbial communities exhibits significant differences (Ayalon et al. 2019;Levy et al. 2020). Studies indicate that lunar irradiance affects both the maturation of gametes and their release, and it is a precursor of speciation in populations distributed along a bathymetric/light gradient. ...
The degradation of the night sky’s quality due to artificial light sources negatively affects marine environments, because many organisms use natural light as cues for reproductive and dispersal behaviors, find favorable habitats, and for the biochemistry of their symbiotic microorganisms. Despite the tremendous effect on marine life, measuring the effects of artificial light pollution is difficult because our understanding of natural light brightness coming from celestial bodies like the Moon is minimal. Here, we fill this gap by quantifying the sky’s brightness and Artificial Light Pollution at Night (ALAN). This study assessed light pollution along the reefs around San Andrés Island, which Hurricane Iota significantly impacted. We modified and installed Sky Quality Meters (LU-DL) at both leeward and fringing reefs, down to 11 m depth. The results indicate the highest ALAN values in the area of Johnny Cay (18 msas) compared to Acuario (20 msas) and West View (21 msas). Additionally, National Oceanic and Atmospheric Administration NOAA and Unihedron databases show an increase in artificial light on land, where constant artificial light and coastal vegetation loss due to Hurricane Iota (between 15 and 19th November 2020), are the main factors that may be generating this increase in artificial light.
... Two coral species obtained from the Indo-Pacific Ocean i.e. Acropora millepora and Acropora digitifera, showed delayed gametogenesis and unsynchronised gamete release on exposure to artificial light (Ayalon et al., 2021). ...
Humans have relied on oceans since time immemorial and have exploited them for natural resources and recreational activities. With the advancement of technologies, rapid population growth and land-use change, the dependability on marine ecosystems has increased tremendously. Anthropogenic activities are causing increased global temperatures, altered weather conditions, melting glaciers, rising sea levels, acidification etc. The biological processes of marine ecosystems are getting affected indirectly or directly from the molecular level to rock pools to ocean basins, thus impacting overall ecosystem services. Out of various disturbances being caused by humans, global warming has been one of the most threatening factors with other anthropogenic inputs such as nutrient enrichment, sewage and microplastics, thereby causing significant changes in the symbiotic relationship between algae and corals. The coral associations with algae, macroalgae and other groups play a very important role in the functioning of ocean ecosystems and are very sensitive to anthropogenic inputs. The symbiotic association of algae with corals results in enriched biodiversity as well as it maintains the biogeochemistry of oceans and open coastal areas. The review outlines the importance of algal associations towards the maintenance of coral reefs, along with discussing the ecological services offered by them. One of the sections also discusses the impact of anthropogenic activities on the association between corals and algae. Also, the potential adaptive response of corals to the changing climatic conditions, and conservation strategies for the conservation of coral ecosystems to ensure a sustainable environment have also been discussed.
Graphical Abstract
... Secondly, we posit that artificial light present in Hurghada (northwest Red Sea), as a result of intensive urban development, could have disrupted the natural spawning timing of corals, as compared to Shushah Island (northeast Red Sea) where such pollution is currently absent. Hurghada is a well-developed city known for experiencing significant light pollution along its coastline (Davies et al., 2023), and light pollution has been observed to disrupt gametogenesis in several Acropora species in the Indo-Pacific Ocean (Ayalon et al., 2021). Although all our survey sites were located approximately 5-15 km from the shoreline, it is possible that proximity of the Hurghada sites closer to a welldeveloped city with light pollution might impact the offshore reefs. ...
Sexual reproduction is a crucial process for reef building coral populations to maximize genetic diversity and recover from large scale disturbances. Mass spawning events by Acropora species represent critical opportunities for populations to persist, and a process that is increasingly exploited to actively restore degraded reefs. However, the timing and predictive capacity of coral spawning throughout the broad thermal and environmental regime of the Red Sea – a region also undergoing significant development and active reef restoration – remains patchy. We, therefore, conducted three parallel reef surveys in the central Red Sea (Al-Fahal Reef, Thuwal - Saudi Arabia) and the eastern (Shushah Island - Saudi Arabia) and western (Hurghada – Egypt) coast of the northern Red Sea. Surveys assessed the gravidity of gonads, spawning timing, alignment with the lunar cycle of 21 Acropora spp. (total n= 572 colonies) around the full moons of April and May 2023. Consistent with past observations, synchronous spawning was observed for Acropora spp. in both the central and northern Red Sea during April and May, respectively. Interestingly, corals spawned on the full moon in both Shushah and Thuwal sites. In contrast, corals in Hurghada were independent of the lunar cycle and spawned 7-9 nights before the full moon in May. By integrating our 2023 observations with the historical spawning events in Hurghada and Thuwal (2002-2022), we found that the deviation of spawning timing from the full moon day was correlated with absolute Sea Surface Temperature (SST) (earlier spawning before the full moon day, lower SST) and warming rate (earlier spawning, more rapid warming) in 6-weeks prior to spawning. As such, temperature pattern is likely one of the primary factors governing gamete release, among other factors, that likely influence spawning day within the lunar month. These correlations between SST metrics and spawning timing suggest a potential framework to predict future Acropora spp. spawning dates. Our observations demonstrate the importance of parallel efforts across borders to collect critical data needed to inform management strategies aimed at conserving and restoring coral reefs in this ecologically diverse region.
... Such disturbances lead to unsynchronized gamete development, altered spawning timings, and decreased coral settlement. These shifts come with physiological repercussions, like oxidative stress and impaired photosynthesis (Ayalon et al., 2019(Ayalon et al., , 2021Levy et al., 2003Levy et al., , 2011Lin et al., 2021;Tamir et al., 2020). Mardones et al. (2023a), have highlighted how ALAN interferes with daily tentacle movements in scleractinian corals, which most probably influences their feeding mechanisms. ...
... The majority of this research has focused on corals, which are highly photosensitive and have well-developed circadian behaviors (Rosenberg et al., 2019), and are thus intensely vulnerable to the effects of ALAN (Fobert et al., 2023). In coral species collected from oceanic environments, ALAN exposure reduced reproductive fitness by delaying gametogenesis and inhibiting synchronization of gamete release (Ayalon et al., 2021). Furthermore, it has also been demonstrated that spawning occurs closer to a full moon in corals exposed to ALAN, suggesting that speeding up the spawning time can lead to decreased fertilization and survival of gametes (Davies et al., 2023). ...
The effects of anthropogenic sources of light on the circadian biology of marine animals are largely unexplored at the molecular and cellular level. Given that light is a major driver of circadian rhythms at the behavioral, physiological, cellular, and even molecular levels, it is important to consider the effects that anthropogenic light, especially at night, has on aquatic species. With the expanding data generated from circadian clock research, it is surprising that these techniques have not been applied more frequently to better understand how artificial light affects animal circadian rhythms. Circadian research has been limited to behavioral and physiological observations in wild marine animals rather than a cellular and molecular understanding due to the logistical constraints. While there are some benefits to using artificial light at night (ALAN), there have also been many studies reporting physiological and behavioral consequences in response to exposure to ALAN. Here, the benefits and consequences of using ALAN in the marine environment are reviewed. Furthermore, perspectives on research limitations and future research directions are discussed. Taken together, this is an important area in which more information is required to translate our understanding of circadian biology into better practices to promote the health and welfare of marine animals.
... While ALAN offers substantial convenience for human activities, it concurrently appears to present a potential threat to coastal ecosystems [2,[5][6][7][8][9]. For example, in shallow water coral reef ecosystems, recent studies reported the gametogenesis cycle of Acropora millepora was delayed or masked by exposure to ALAN [10]. In sandy beach ecosystems, sea turtle orientation was negatively affected by ALAN, impairing the ability of hatchlings to respond to natural orientation cues [11,12]. ...
Simple Summary
The sea urchin (Heliocidaris crassispina) is an ecologically important invertebrate in structuring marine benthic communities. Most dwell within intertidal regions, rendering them highly susceptible to elevated artificial light at night. However, their potential acclimation to artificial light exposure remains largely unexplored. This study investigates the changes of prolonged artificial light pollution on the fitness-related traits of sea urchins. Following a six-week exposure to artificial light at night, survival remained unaffected, while behavioral responses exhibited slower reactions. Concurrently, growth inhibition was observed in sea urchins, which might be attributed to reduced mouthparts weight and decreased food consumption. This study also revealed that sea urchin gonads are more susceptible to artificial light than guts. Pax6 gene expression may serve as a sensitive indicator to assess the impact on the photosensitive system of sea urchins. These results increase our understanding of the effects of artificial light at night on sea urchins and provide valuable information about coastal animals’ safety.
Abstract
Limited data are available regarding the effects of elevated coastal artificial light at night (ALAN) on intertidal echinoderms. In this study, we investigated the behavioral, morphological, and physiological responses of the sea urchin (Heliocidaris crassispina) after continuous exposure to ALAN at light intensities of 0.1, 300, and 600 Lux for 6 weeks. Our findings revealed that ALAN at 300 Lux substantially reduced food consumption, Lantern weight, and gonadosomatic index (GSI). On the other hand, ALAN at 600 Lux notably prolonged the righting and covering response times and elevated the 5-HIAA/5-HT ratio, while concurrently decreasing food consumption, body weight, Lantern weight, GSI, and Pax6 gene expression. These results indicated that continuous exposure to ALAN could cause an adverse effect on fitness-related traits, including behavioral responses, growth, reproductive performance, and photoreception of sea urchins. The present study provides new insights on the impact of light pollution on echinoderms.
... Masking the moonlight cycle could alter its perception by oysters and thus disrupt their behavioral lunar rhythm (Payton and Tran, 2019). ALAN masking effects on the natural lunar cycle have been investigated in the corals Acropora millepora and Acropora digitifera for which ALAN induces a delay in corals' gametogenesis, having for consequence the desynchronization of their spawning (Ayalon et al., 2021). ALAN is also susceptible to alter oysters' reproduction success since their spawning synchronization mainly depends on daily, lunar, and annual cycles, as many parameters that ALAN can disrupt by altering their perception by oysters (Bernard et al., 2016;Payton et al., 2017b). ...
Artificial Light at Night (ALAN) is a fast-spreading threat to organisms, especially in coastal environments, where night lighting is increasing due to constant anthropization. Considering that ALAN affects a large diversity of coastal organisms, finding efficient solutions to limit these effects is of great importance but poorly investigated. The potential benefit of one strategy, in particular, should be studied since its use is growing: part-night lighting (PNL), which consists in switching off the lights for a few hours during nighttime. The aim of this study is to investigate the positive potential of the PNL strategy on the daily rhythm of the oyster Crassostrea gigas, a key species of coastal areas of ecological and commercial interest. Oysters were exposed to a control condition and three different ALAN modalities. A realistic PNL condition is applied, recreating a strategy of city policy in a coastal city boarding an urbanized bay (Lanton, Arcachon Bay, France). The PNL modality consists in switching off ALAN direct sources (5 lx) for 4 h (23−3 h) during which oysters are in darkness. Then, a PNL + skyglow (PNL + S) modality reproduces the previous one mimicking a skyglow (0.1 lx), an indirect ALAN source, during the direct lighting switch off, to get as close as possible to realistic conditions. Finally, the third ALAN condition mimics full-night direct lighting (FNL). Results revealed that PNL reduces some adverse effects of FNL on the behavioral daily rhythm. But, counterintuitively, PNL + S appears more harmful than FNL for some parameters of the behavioral daily rhythm. PNL + S modality is also the only one that affect oysters' clock and melatonin synthesis gene expression, suggesting physiological consequences. Thus, in realistic conditions, the PNL mitigation strategy might not be beneficial in the presence of skyglow, seeing worse for a coastal organism such as the oysters.
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... The daily processes we observe in A. digitifera are necessary for adaptation and homeostasis. When circadian processes are perturbed, for example when corals are subjected to artificial light or anthropogenic stressors, individuals cannot anticipate and respond efficiently to the daily challenges associated with the day-night cycle (Shlesinger and Loya, 2019;Ayalon et al., 2021;Rosenberg et al., 2022). In this paper, we highlight the synchronicity between the daily environment-imposed challenges and their harmonization with the biological processes of the corals. ...
The study aimed to gain a deeper understanding of the daily fluctuations in gene expression at a transcript level in the coral Acropora digitifera and create a comprehensive map of the biological processes that occur under natural environmental conditions. The coral is a key organism in marine ecosystems, and understanding its physiology and the adaptation mechanisms it uses to cope with daily environmental changes is vital for its survival and the preservation of coral reefs. The study’s results showed that certain genes in the coral exhibit specific patterns of expression at different times of the day. These genes play critical roles in regulating a wide range of physiological and behavioral processes, such as metabolism, development, and DNA damage repair. During the day, the coral expends energy on growth and development, and these genes are actively involved in these processes. On the other hand, at night, the coral’s focus shifts toward repair and recovery. The genes that are active during this period are involved in processes like DNA repair, hypoxia response, and transcription. This is a crucial time for the coral, as it’s exposed to a range of environmental stressors that can damage its DNA and impact its overall health. In conclusion, this study provides valuable insights into the cyclic regulatory processes that help the coral adapt to daily external variations and sustain its physiology. It highlights the importance of understanding the daily rhythms of gene expression in marine organisms and the role they play in maintaining the health of coral reefs. This research can be used to develop strategies to preserve coral reefs and mitigate the effects of environmental changes on coral physiology.
... ALAN from coastal developments disrupts these cycles presenting a potential threat to coral reproduction 15 . ALAN has demonstrated impacts on coral gamete development and spawning in experimental settings 14,16 . Whether ALAN disrupts coral spawning in the real world is currently unquantified. ...
Coral broadcast spawning events - in which gametes are released on certain nights predictably in relation to lunar cycles - are critical to the maintenance and recovery of coral reefs following mass mortality. Artificial light at night (ALAN) from coastal and offshore developments threatens coral reef health by masking natural light:dark cycles that synchronize broadcast spawning. Using a recently published atlas of underwater light pollution, we analyze a global dataset of 2135 spawning observations from the 21st century. For the majority of genera, corals exposed to light pollution are spawning between one and three days closer to the full moon compared to those on unlit reefs. ALAN possibly advances the trigger for spawning by creating a perceived period of minimum illuminance between sunset and moonrise on nights following the full moon. Advancing the timing of mass spawning could decrease the probability of gamete fertilization and survival, with clear implications for ecological processes involved in the resilience of reef systems.
... in which exposition to ALAN delayed or masked their gametogenesis leading to a spawning desynchronization (Ayalon et al., 2021). Another example of ALAN effect on lunar rhythm is the disruption of the monthly nocturnal foraging pattern of the gastropod Nucella lapillus, based on the lunar cycle, by ALAN produced by LED lighting at an intensity of 10 lx (Tidau et al., 2022). ...
Artificial Light At Night (ALAN) masks the natural light cycles and thus can disturb the synchronization of organisms' biological rhythms with their environment. Although coastlines are highly exposed to this growing threat, studies concerning the impacts of ALAN on coastal organisms remain scarce. In this study, we investigated the ALAN exposure effects at environmentally realistic intensities (0.1, 1, 10, 25 lx) on the oyster Crassostrea gigas, a sessile bivalve subject to light pollution on shores. We focused on the effects on oyster's daily rhythm at behavioral and molecular levels. Our results showed that ALAN disrupts the oyster's daily rhythm by increasing valve activity and annihilating day / night differences of expression of circadian clock and clock-associated genes. ALAN effects occur starting from 0.1 lx, in the range of artificial skyglow illuminances. We concluded that realistic ALAN exposure affects oysters' biological rhythm, which could lead to severe physiological and ecological consequences.
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... For instance, corals synchronise their spawning using, among other external cues, moonlight. When exposed to light conditions similar to those created by ALAN, this synchrony has been shown to be disrupted (Ayalon et al., 2020;Kaniewska et al., 2015). However, to date, these studies are among the very few papers documenting the impacts of ALAN on monthly rhythms related to lunar cycles . ...
Electric lights have proliferated rapidly over the last century and have changed the night-time environment globally. Over the past decades, scientific studies have shown the effects of artificial light at night (ALAN) on biodiversity. Light pollution has been shown to disrupt a wide range of ecological processes and taxa. In this PhD, we aimed to fill some of the knowledge gaps that could prevent the effects of light pollution on biodiversity from being effectively addressed by mitigation measures. We used bats as model species because they are considered good indicators of the effect of anthropogenic pressures on biodiversity and because, being nocturnal, they are directly exposed to ALAN.We advocated considering the temporal distribution of species in conservation measures, a prerequisite being to have access to knowledge on their temporal ecology. We used data from a national bat monitoring program (Vigie-Chiro) based on acoustic monitoring to characterise bat diel activity patterns (9807 nights monitored, 20 species). We found that bat species could be separated into three functional groups characterised by a crepuscular activity, an activity that occurs when it is completely dark or an intermediate activity. We showed variations of diel activity patterns depending on the season. Accounting for these complex diel activity patterns would help to design efficient mitigation measures. For instance, it would allow the design of part-night lighting schemes covering the range of activity of the target species. Early emerging bats are mostly “light tolerant” species known to feed on insects attracted to lights. However, at the landscape scale, these species tend to be less abundant because of ALAN. This could be explained by disruptions in the diel activity patterns of bats due to ALAN, with potential consequences for population dynamics. Using the Vigie-Chiro dataset, we tested whether ALAN was responsible for such disruptions on a “light tolerant” species (Eptesicus serotinus). ALAN, and to a lesser extent moonlight, reduced its abundance. ALAN delayed activity, this delay was amplified during overcast nights, probably because cloud cover amplified skyglow. Further analyses suggested that two other “light tolerant” species might delay their activity because of ALAN. Thus, even “light tolerant” species should be protected from light pollution. Where it is not possible to switch off lights, other mitigation measures include changing the intensity, directionality and spectrum of light. Many countries are retrofitting lighting equipment with light emitting diodes (LEDs). Despite potential impacts on biodiversity, few studies have focused on this shift. By reanalysing the data from a previously published study, we found that changes in light spectrum and intensity during such a shift have additive and interactive effects on bats. Bat activity decreased with increasing LED intensity. Using the Vigie-Chiro dataset, we showed that the adoption of LEDs would decrease landscape connectivity for bats, with this impact possibly being mitigated by better orienting the light flux. We recommended using LEDs with warmer colours and reduced light intensity. Multiscale spatiotemporal approaches are needed to assess ALAN effect on biodiversity. Although some knowledge gaps remain, there is overwhelming evidence of the impact of light pollution on ecosystems. Mitigation measures are being developed, so there is a need to assess their effectiveness and possible improvements. Considering the reduction of ALAN at the landscape scale is a necessary next step, hence the emergence of the concept of dark ecological networks. A transdisciplinary project on lighting practices and their evolution in municipalities was initiated during this PhD. Indeed, as ALAN has not only ecological but also health and socio-cultural implications, a transdisciplinary perspective is needed to shift the paradigm from conventional lighting to new forms of lighting.
... Special aquaria can be used to induce corals to spawn ex-situ (Craggs et al., 2017), but their capacity to hold many and large corals is limited, so maintaining corals in a field nursery allows for upscaling and ensuring access to environmental cues required for gametogenesis. Field nurseries are more likely to be shielded from light pollution as well, which can disrupt the sexual cycle (Ayalon et al., 2020). Corals in a mid-water floating nursery may also be more protected from impacts like predation, sedimentation, and destructive human activities. ...
Given the rapid, global decline in the health and abundance of coral reefs, increased investments in restoration-based interventions -including asexual and sexual propagation- are being made by coral reef scientists at research institutions, but also at zoos and aquariums. Mote Marine Laboratory & Aquarium is an independent, non-profit marine science organization dedicated to the conservation and restoration of Florida’s Coral Reef, and does so, using science-based strategies. In order to promote the long-term persistence, resilience, and adaptive potential of restored coral populations on Florida’s Coral Reef, Mote scientists are performing critical research and restoration activities related to assisted sexual reproduction (ASR). The objective of this study was to optimize ASR of Acropora cervicornis by (1) evaluating broodstock compatibility for genets actively used within Mote’s restoration gene pool, (2) optimizing larval settlement by testing spectral cues, (3) and optimizing the grow-out of sexual recruits by testing the impact of light on growth, survival, and algal symbiont uptake in the presence of adult corals or not. Overall, we found that corals and genets spawned with high synchrony, both within and across years, and in terms of predicted spawning times related to nights after the full moon and minutes after sunset. Across two years, overall fertilization success was high (~95%), but we did find one pair of genets that was not compatible. During settlement, larvae preferred pink and purple-colored substrates, which was consistent with our expectation that they would select substrates similar in color to crustose coralline algae (CCA). Interestingly though, they only did so when a matching chemical cue from CCA was also present, indicating that larvae integrate multiple cues simultaneously to determine the most appropriate place to settle. Growth and symbiont uptake were faster in recruits reared in the presence of adult corals and additional lighting, but survivorship was not different through the first ten weeks post-settlement between treatments. A subset of corals was outplanted using two different techniques based on single or clustered corals. We report the initial 1-month survival results. We also provide a detailed protocol and general recommendations for ASR based on years of coral sexual propagation experience.
... ALAN impacts range from altering organismal physiology to changes wrought in ecological communities . Underwater ALAN affects multiple aspects of the life histories of marine organisms, including reducing reproductive success in fish (Fobert et al., 2019;Fobert et al., 2021) and turtles (Witherington and Bjorndal, 1991); disrupting migration in zooplankton (Ludvigsen et al., 2018;Berge et al., 2020) and sandhoppers (Torres et al., 2020); altering recruitment in marine epifaunal communities (Davies et al., 2015); shifting interspecific interactions in estuarine fish (Becker et al., 2013), symbiotic reef building corals (Levy et al., 2020), and intertidal invertebrates (Underwood et al., 2017); delaying coral gametogenesis (Ayalon et al., 2021); and changing phytoplankton abundance (Diamantopoulou et al., 2021). For a recent review of the impacts of ALAN in marine ecosystems, see Marangoni et al. (2022). ...
Half of globally significant megacities are situated near the coast, exposing urban marine ecosystems to multiple stressors such as waste-water discharge containing a host of organic and inorganic pollutants, air and noise pollution. In addition to these well recognized sources, artificial light at night (ALAN) pollution is inseparable from cities but poorly quantified in marine ecosystems to date. We have developed a time- and wavelength-resolving hydrological optical model that includes solar (daylight and twilight components), lunar and ALAN source terms and propagates these spectrally through a tidally varying water column using Beer’s Law. Our model shows that for 8 globally distributed cities surface ALAN dosages are up to a factor of 6 greater than moonlight, as ALAN intensities vary little throughout the night, over monthly or seasonal cycles. Moonlight only exceeds ALAN irradiances over the ±3-day period around full moon, and particularly during the brightest moons (mid-latitude winter, at zenith). Unlike the relatively stable surface ALAN, underwater ALAN varies spectrally and in magnitude throughout the night due to tidal cycles. The extent of ALAN in-water attenuation is location-specific, driven by the season, tidal range and cycle, and water clarity. This work highlights that marine ALAN ecosystem pollution is a particularly acute global change issue near some of the largest cities in the world.
... There is increasing evidence that ALAN can alter physiology (Forsburg et al., 2021;Luarte et al., 2016;Raap et al., 2016a;Zubidat et al., 2018), metabolism (Finch et al., 2020;Nelson, 2019;Raap et al., 2018a;Welbers et al., 2017), foraging Farnworth et al., 2018) reproduction and mating behaviour (Ayalon et al., 2021;Botha et al., 2017;Touzot et al., 2019), often in a species specific manner (Amadi et al., 2021;Baskir et al., 2021;Brisbane and van den Burg, 2020;Polak et al., 2011), making understanding ALAN's impacts challenging. However, changes in physiology and behaviour could alter interspecific dynamics, having significant ecological consequences disrupting entire ecological communities (Bennie et al., 2018;Sanders et al., 2018Sanders et al., , 2015. ...
Anthropogenic disturbances are known to cause significant physiological and behavioural changes in animals and, thus, are the critical focus of numerous studies. Light pollution is an increasingly recognised source of disturbance that has the potential to impact animal physiology and behaviour. Here, we investigate the effect of constant light on a personality trait and metabolic rate in the European hermit crab Pagurus bernhardus. We used Bayesian mixed models to estimate average behavioural change (i.e. sample mean level behavioural plasticity) and between- and within-individual variation in boldness in response to laboratory light. Hermit crabs experiencing constant light were consistently less bold and had a higher metabolic rate than those kept under a standard laboratory light regime (12:12 h light/dark). However, there was no effect of light on individual consistency in behaviour. As boldness is associated with coping with risk, hermit crabs exposed to light pollution at night may experience increased perceived predation risk, adjusting their behaviour to compensate for the increased conspicuousness. However, reduced boldness could lead to lower rates of foraging and this, in combination with elevated metabolic rate, has the potential for a reduction in energy balance.
... Light intensity and photoperiod will affect the photosynthesis of zooxanthellae and ultimately the growth and survival of corals. However, inappropriate light intensity and photoperiod can also disrupt the physiology of coral symbiosis by affecting the cell cycle, metabolism, and other physiological mechanisms (Rosenberg et al. 2017;Levy et al. 2020). Therefore, appropriate light intensity and photoperiod in coral cultivation are of vital importance. ...
Coral reefs are one of the most diverse, productive ecosystems in the world, and light plays crucial role in its survival. Notably, the effects of light conditions on soft coral and its adaptive mechanism were unclear . Thus, the present study aimed to investigate and evaluate the effects of different light intensities (30, 80 and 130μmol m ⁻² s ⁻¹ ) and photoperiods (18D:6L, 12D:12L and 6D:18L) on cultivation of soft coral Sarcophyton trocheliophorum . During two 50-day of the experiments, we monitored the zooxanthellae density, Chl a content, enzyme activities (SOD, CAT and GST) and microbial diversity of S . trocheliophorum . Our study's outcomes found that, at the end of the experiment, the 80μmol m ⁻² s ⁻¹ light intensity group and 12D:12L photoperiod group both possessed the highest zooxanthellae density (2.54×10 ⁸ ± 0.14×10 ⁸ cells g ⁻¹ DW and 2.40×10 ⁸ ± 0.07×10 ⁸ cells g ⁻¹ DW, respectively), Chl a content (295.01 ± 14.13µg g ⁻¹ DW and 287.78 ± 16.13µg g ⁻¹ DW, respectively) and microbial diversity and relatively stable enzyme activities level. Besides, we speculated that the reason for the decline of zooxanthellae density Chl a content and microbial diversity under other light conditions might be that it induced light stress and caused oxidative damage. The main bacterial composition of S . trocheliophorum in different light conditions was similar at the phylum level, showing the stability of microbial community structure. Proteobacteria, Actinobacteria and Firmicutes were dominant under all light conditions, so we hypothesized that these bacteria phylum play a crucial role in coral growth and survival. In conclusion, compared with the other treatments, 80μmol m ⁻² s ⁻¹ light intensity and 12D:12L photoperiod were more beneficial to the growth performance of S . trocheliophorum and could be recommended for its cultivation condition. Our study could provide helpful information for sustainable management plans for the cultivation and conservation of soft corals, which was especially important to the protection and restoration of degraded coral reefs.
... 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). ...
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.
... ALAN affects all living organisms at the molecular, physiological, behavioral and ecological level. For example, it was shown to disrupt foraging and feeding behavior, alter biological rhythms, cause mistimed reproductive behavior, and increase stress hormone levels (e.g., [9][10][11][12][13][14][15][16][17][18][19][20], and it is clear that actions must be taken to mitigate its effects. However, to design effective mitigation measures, we must better understand the adverse effects of light pollution, which is currently based mostly on observational eld studies or laboratory studies, mostly focusing on changes in species behavior and physiology 5,8,20,21 . ...
Use of artificial at night (ALAN) exposes the world to continuously increasing levels and distribution of light pollution. Our understanding of the adverse effects of ALAN is based on observational or laboratory studies, and its effects are probably underestimated. Demonstration of direct experimental fitness consequences of ALAN is missing. We studied the effects of chronic light pollution at different wavelengths on fitness and stress hormone levels under semi-natural conditions in two closely related species: the nocturnal common spiny mouse ( Acomys cahirinus ) and the diurnal golden spiny mouse ( Acomys russatus ). Our results clearly demonstrate the adverse effects of ALAN exposure on fitness of both nocturnal and diurnal species, manifested by changes in cortisol levels and reproductive timing, reduced reproductive output and reduced survival, which differed between species and wavelengths. In A. russatus exposure to blue ALAN had the strongest effect on fitness, followed by white and yellow ALAN exposure. In A. cahirinus results are more complex and suggest it suffered from combined effect of ALAN and competition. Our research shows that light pollution presents a real threat to both nocturnal and diurnal species, affecting the species fitness directly and through its interspecific interactions. Worryingly, these effects are probably not specific to spiny mice. The clear adverse effects we documented, as well as the differences between wave lengths, contribute to our ability present science-based recommendations to decision makers regarding the use of artificial light at night. Such information and guidelines are highly important nowadays when lighting systems are being replaced to promote energy efficiency.
... 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]. ...
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). ...
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). ...
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. ...
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. Technological limitations, 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.
Heat-tolerant Porites spp exhibit divergent sexual modes and morphs. Porites cylindrica are gonochoric, but their sex ratios vary geographically, additionally, sympatric color morphs in brown and yellow have been documented. However, we lack comprehensive insights into gametogenesis, spawning synchrony, gamete compatibility, and environmental influence; therefore, we aimed to investigate these aspects in P. cylindrica. We demonstrated that P. cylindrica exhibits two color morphs within the same population, characterized by gonochoric females and hermaphrodites with male function dominance in terms of sexual modes. The gametogenesis of both morphotypes correlates with temperature rather than light. Oogenesis is initiated 2 months post-spawning (in September), progressing into mature eggs with rising water temperatures from March. Conversely, spermatogenesis commenced in March, coinciding with increased water temperature. Despite both color morphotypes belonging to the same species, their sex ratios diverge. Notably, the spawning periods of the two morphotypes overlap, demonstrating high gamete compatibility. Although spawning is split, the colonies of both morphs synchronize their spawning times, leading to selfing in the eggs of male function-dominated hermaphroditic colonies. Analyzing the morphotypes and sexes of all colonies at the research sites (50 × 100-m patched reefs) revealed that fewer yellow morphs were presented relative to brown morphs. Moreover, the sex ratios differed between the two morphs, with the brown morphs exhibiting more gonochoric females than the yellow morphs. These findings highlight intricate reproductive strategies in P. cylindrica and suggest that the observed sex ratio differences between morphs may be related to their adaptation and survival in varying environmental conditions.
The moon has significant impact on the timing of organisms. Can the study of molecular timing mechanisms of marine animals and algae help to understand some of the “weird” correlations between human physiological/behavioral rhythms and the lunar cycle? [Image: see text]
As marine species adapt to climate change, their heat tolerance will likely be under strong selection. Yet trade-offs between heat tolerance and other life history traits could compromise natural adaptation or assisted evolution. This is particularly important for ecosystem engineers, such as reef-building corals, which support biodiversity yet are vulnerable to heatwave-induced mass bleaching and mortality. Here, we exposed 70 colonies of the reef-building coral Acropora digitifera to a long-term marine heatwave emulation experiment. We tested for trade-offs between heat tolerance and three traits measured from the colonies in situ – colony growth, fecundity, and symbiont community composition. Despite observing remarkable within-population variability in heat tolerance, all colonies were dominated by Cladocopium C40 symbionts. We found no evidence for trade-offs between heat tolerance and fecundity or growth. Contrary to expectations, positive associations emerged with growth, such that faster-growing colonies tended to bleach and die at higher levels of heat stress. Collectively, our results suggest that these corals exist on an energetic continuum where some high-performing individuals excel across multiple traits. Within populations, trade-offs between heat tolerance and growth or fecundity may not be major barriers to natural adaptation or the success of assisted evolution interventions.
Coral reefs are one of the most diverse, productive ecosystems in the world, and light plays crucial role in its survival. Notably, the effects of light conditions on soft coral and its adaptive mechanism were unclear. Thus, the present study aimed to investigate and evaluate the effects of different light intensities (30, 80 and 130 μmol m-2 s-1) and photoperiods (18D:6L, 12D:12L and 6D:18L) on cultivation of soft coral Sarcophyton trocheliophorum. During two 50-day of the experiments, we monitored the zooxanthellae density, Chl a content, enzyme activities (SOD, CAT and GST) and microbial diversity of S. trocheliophorum. Our study's outcomes found that, at the end of the experiment, the 80 μmol m-2 s-1 light intensity group and 12D:12L photoperiod group both possessed the highest zooxanthellae density (2.54 × 108 ± 0.14 × 108 cells g-1 DW and 2.40 × 108 ± 0.07 × 108 cells g-1 DW, respectively), Chl a content (295.01 ± 14.13 μg g-1 DW and 287.78 ± 16.13 μg g-1 DW, respectively) and microbial diversity and relatively stable enzyme activities level. Besides, we speculated that the reason for the decline of zooxanthellae density, Chl a content and microbial diversity under other light conditions might be that it induced light stress and caused oxidative damage. The main bacterial composition of S. trocheliophorum in different light conditions was similar at the phylum level, showing the stability of microbial community structure. Proteobacteria, Actinobacteria and Firmicutes were dominant under all light conditions, so we hypothesized that these bacteria phylum play a crucial role in coral growth and survival. In conclusion, compared with the other treatments, 80 μmol m-2 s-1 light intensity and 12D:12L photoperiod were more beneficial to the growth performance of S. trocheliophorum and could be recommended for its cultivation condition. Our study could provide helpful information for sustainable management plans for the cultivation and conservation of soft corals, which was especially important to the protection and restoration of degraded coral reefs.
Many marine organisms synchronously spawn at specific times to ensure the success of external fertilization in the ocean. Corals are famous examples of synchronized spawning at specific lunar phases, and two distinct spawning patterns have been observed in two dominant taxa: merulinid corals spawn at regular lunar phases, several days after the full moon, whereas Acropora corals spawn at more irregular lunar phases around the full moon. Although it has been suggested that the two coral taxa have different responses to moonlight and seawater temperature, their spawning times have never been analyzed by integrating the two environmental factors, resulting in an incomplete understanding of the regulatory mechanisms of spawning. In this study, we developed a new predictive model of coral spawning days by integrating moonlight and temperature effects based on the external coincidence model for the lunar cycle. We performed model fitting using a 10-year monitoring record of coral spawning time in Taiwan. Our model successfully demonstrated the synergistic effects of moonlight and temperature on coral spawning time (days) and provided two testable hypotheses to explain the different spawning patterns regarding the preparation (maturation) process for spawning and the sensitivity to moonlight at different circadian phases: (1) Acropora corals may have an earlier onset and longer period of preparation for spawning than merulinid corals; and (2) merulinid corals may use moonlight signals near sunset, while Acropora corals may have a similar onset at approximately midnight. This is the first study to indicate the difference in circadian phase-dependent moonlight sensitivities between coral taxa, providing a basis for underlying coral spawning mechanisms for rhythmic studies.
As marine species adapt to climate change, their heat tolerance will likely be under strong selection. Yet trade-offs between heat tolerance and other life history traits could compromise natural adaptation or restorative assisted evolution. This is particularly important for ecosystem engineers, such as reef-building corals, which support biodiversity yet are vulnerable to heatwave-induced mass bleaching and mortality. Here, we exposed 70 colonies of the reef-building coral Acropora digitifera to a long-term marine heatwave emulation experiment. We tested for trade-offs between heat tolerance and three traits – colony growth (3D photogrammetry models), fecundity (oocyte counts), and symbiont community composition (ITS2 sequencing). Despite observing remarkable within-population variability in heat tolerance, all coral colonies were dominated by Cladocopium C40 symbionts. We found no evidence for trade-offs between heat tolerance and fecundity or growth. Contrary to expectations, positive associations emerged with growth, such that faster-growing colonies tended to bleach and die at higher levels of heat stress. Collectively, our results suggest that these corals exist on an energetic continuum where some individuals have co-benefits across multiple traits. Within populations, trade-offs between heat tolerance and either growth or fecundity may not be major barriers to natural adaptation or the success of restorative assisted evolution interventions.
Use of artificial at night (ALAN) exposes the world to continuously increasing levels and distribution of light pollution. Our understanding of the adverse effects of ALAN is based mostly on observational or laboratory studies, and its effects are probably underestimated. Demonstration of direct experimental fitness consequences of ALAN on mammals is missing. We studied the effects of chronic light pollution at different wavelengths on fitness and glucocorticoid hormone levels under semi-natural conditions in two closely related species: the nocturnal common spiny mouse ( Acomys cahirinus ) and the diurnal golden spiny mouse ( Acomys russatus ). Our results clearly demonstrate the adverse effects of ALAN exposure on the fitness of both nocturnal and diurnal species, manifested by changes in cortisol levels and reproductive timing, reduced reproductive output and reduced survival, which differed between species and wavelengths. In A. russatus exposure to blue ALAN had the strongest effect on fitness, followed by white and yellow ALAN exposure. In A. cahirinus the results are more complex and suggest it suffered from the combined effects of ALAN and competition. Our research shows that light pollution presents a real threat to both nocturnal and diurnal species, affecting the species fitness directly and through interspecific interactions. Worryingly, these effects are probably not limited to spiny mice. The clear adverse effects we documented, as well as the differences between wave lengths, contribute to our ability to present science-based recommendations to decision makers regarding the use of artificial light at night. Such information and guidelines are highly important nowadays when lighting systems are being replaced to promote energy efficiency.
Moonlight is the strongest naturally and predictably occurring nocturnal light source. Thus, many species have adapted to use moonlight as a reliable timing cue, either by directly reacting to moonlight or by entraining inner oscillators, like the monthly circalunar clock.Natural moonlight is characterized by intensity, spectrum, and complex timing, which regularly changes every night and across additional timescales. In order to understand the molecular and cellular machineries underlying moon-controlled physiology and behavior, lab experiments with organisms exhibiting well-documented lunar cycles are important. Tools such as TALEN- or Cas9/Crispr-engineered mutants or transgenesis are crucial to move from correlative studies to causal relationships. However, lab experiments face the problem that commonly used artificial light sources differ greatly from sun- and moonlight.To start to overcome this limitation, we have developed naturalistic sun- and moonlight sources, which closely mimic the natural light environment.We highlight the use of these naturalistic sun- and moonlight sources using the marine bristle worm Platynereis dumerilii, which controls its timing of reproduction with a circalunar clock. Importantly, while designed for Platynereis research, these methods can also be relatively easily adapted and used to study the effects of moonlight and/or monthly oscillator systems of other species. Finally, we provide an overview on statistical analyses of circalunar data sets.Key wordsMoonSunLightSpectraMarineUnderwaterCircalunarLunarCircalunidianMonthly clocksInner calendarLight engineeringTimingReproductionCircular statistics
Platynereis dumerilii
As natural coral populations decline, thousands of outplanted corals are poised to dominate reefs in the hardest-hit areas, such as the Florida Keys. Genetic management plans are urgently needed to prevent unintended erosion of genetic diversity in managed populations. Drivers of genetic diversity loss include limited nursery genets available for outplanting or that these genets were reared from crosses among a limited number of parent genets. Existing data indicate that captive rearing of coral larvae can impose substantial genetic bottlenecks that result in closely related cohorts. Thus, questions arise about how to safeguard genetic diversity and optimize the adaptation potential of restored populations. What is the optimal ratio of asexually propagated colonies to sexually produced coral recruits at each site? What breeding scheme should be used if a limited number of donor genets are available? Should breeding be selective to achieve a shift in phenotypes such as thermotolerance at the risk of losing genetic diversity? Population viability analyses (PVA) can answer some of these questions, but current models need to be modified to resolve the most pressing issues. This chapter discusses omics methods to determine genetic diversity of corals and their symbionts and outlines strategies to achieve genetic diversity goals.KeywordsGenetic diversityCoral restorationCoral breedingInbreedingEvolutionary potentialPopulation viability model
The regular movements of waves and tides are obvious representations of the oceans’ rhythmicity. But the rhythms of marine life span across ecological niches and timescales, including short (in the range of hours) and long (in the range of days and months) periods. These rhythms regulate the physiology and behavior of individuals, as well as their interactions with each other and with the environment. This review highlights examples of rhythmicity in marine animals and algae that represent important groups of marine life across different habitats. The examples cover ecologically highly relevant species and a growing number of laboratory model systems that are used to disentangle key mechanistic principles. The review introduces fundamental concepts of chronobiology, such as the distinction between rhythmic and endogenous oscillator–driven processes. It also addresses the relevance of studying diverse rhythms and oscillators, as well as their interconnection, for making better predictions of how species will respond to environmental perturbations, including climate change. As the review aims to address scientists from the diverse fields of marine biology, ecology, and molecular chronobiology, all of which have their own scientific terms, we provide definitions of key terms throughout the article.
Expected final online publication date for the Annual Review of Marine Science, Volume 15 is January 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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.
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
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.
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.
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.
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.
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.
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.
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.
Invisible threat
Our changing climate is a threat to corals, causing disfiguring bleaching and mortality to reefs that once teemed with life. Shlesinger and Loya alert us to an equally dangerous yet nearly invisible hazard to coral: loss of breeding synchrony (see the Perspective by Fogarty and Marhaver). They found that environmental changes have resulted in shifts in the timing of gamete release in several species of broadcast-spawning corals in the Red Sea. Similar changes are likely occurring globally. Such a loss of spawning synchrony could result in reproductive failure, a much less obvious but no less insidious threat to coral reefs.
Science , this issue p. 1002 ; see also p. 987
A breakdown in the coral spawning synchrony may threaten coral reef recovery
As human populations grow and lighting technologies improve, artificial light gradually alters natural cycles of light and dark that have been consistent over long periods of geological and evolutionary time. While considerable ecological implications of artificial light have been identified in both terrestrial and aquatic habitats, knowledge about the physiological and molecular effects of light pollution is vague. To determine if ecological light pollution (ELP) impacts coral biological processes, we characterized the transcriptome of the coral Acropora eurystoma under two different light regimes: control conditions and treatment with light at night. Here we show that corals exposed to ELP have approximately 25 times more differentially expressed genes that regulate cell cycle, cell proliferation, cell growth, protein synthesis and display changes in photo physiology. The finding of this work confirms that ELP acts as a chronic disturbance that may impact the future of coral reefs.
Fisheries surveys over broad spatial areas are crucial in defining and delineating appropriate fisheries management areas. Yet accurate mapping and tracking of fishing activities remain largely restricted to developed countries with sufficient resources to use automated identification systems and vessel monitoring systems. For many countries, the spatial extent and boundaries of fishing grounds are not completely known. We used satellite images at night to detect fishing grounds in the Philippines for fishing gears that use powerful lights to attract coastal pelagic fishes. We used nightly boat detection data, extracted by U.S. NOAA from the Visible Infrared Imaging Radiometer Suite (VIIRS), for the Philippines from 2012 to 2016, covering 1713 nights, to examine spatio-temporal patterns of fishing activities in the country. Using density-based clustering, we identified 134 core fishing areas (CFAs) ranging in size from 6 to 23,215 km 2 within the Philippines' contiguous maritime zone. The CFAs had different seasonal patterns and range of intensities in total light output, possibly reflecting differences in multi-gear and multi-species signatures of fishing activities in each fishing ground. Using maximum entropy modeling, we identified bathymetry and chlorophyll as the main environmental predictors of spatial occurrence of these CFAs when analyzed together, highlighting the multi-gear nature of the CFAs. Applications of the model to specific CFAs identified different environmental drivers of fishing distribution, coinciding with known oceanographic associations for a CFA's dominant target species. This case study highlights nighttime satellite images as a useful source of spatial fishing effort information for fisheries, especially in Southeast Asia.
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.
A central aim of the “lighting revolution” (the transition to solid-state lighting technology) is decreased energy consumption. This could be undermined by a rebound effect of increased use in response to lowered cost of light. We use the first-ever calibrated satellite radiometer designed for night lights to show that from 2012 to 2016, Earth’s artificially lit outdoor area grew by 2.2% per year, with a total radiance growth of 1.8% per year. Continuously lit areas brightened at a rate of 2.2% per year. Large differences in national growth rates were observed, with lighting remaining stable or decreasing in only a few countries. These data are not consistent with global scale energy reductions but rather indicate increased light pollution, with corresponding negative consequences for flora, fauna, and human well-being.
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.
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 Seriatopora 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 seasonality, 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 circadian 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 multistep process over a few generations or through random extreme mixing such as typhoons.
Artificial skyglow is constantly growing on a global scale, with potential ecological consequences ranging up to affecting biodiversity. To understand these consequences, worldwide mapping of skyglow for all weather conditions is urgently required. In particular, the amplification of skyglow by clouds needs to be studied, as clouds can extend the reach of skyglow into remote areas not affected by light pollution on clear nights. Here we use commercial digital single lens reflex cameras with fisheye lenses for all-sky photometry. We track the reach of skyglow from a peri-urban into a remote area on a clear and a partly cloudy night by performing transects from the Spanish town of Balaguer towards Montsec Astronomical Park. From one single all-sky image, we extract zenith luminance, horizontal and scalar illuminance. While zenith luminance reaches near-natural levels at 5km distance from the town on the clear night, similar levels are only reached at 27km on the partly cloudy night. Our results show the dramatic increase of the reach of skyglow even for moderate cloud coverage at this site. The powerful and easy-to-use method promises to be widely applicable for studies of ecological light pollution on a global scale also by non-specialists in photometry.
The urbanization of the shores of the Gulf of Aqaba has exposed the marine environment there, including unique fringing coral reefs, to strong anthropogenic light sources. Here we present the first in situ measurements of artificial nighttime light under water in such an ecosystem, with irradiance measured in 12 wavelength bands, at 19 measurement stations spread over 44 square km, and at 30 depths down to 30-m depth. At 1-m depth, we find downwelling irradiance values that vary from 4.6 × 10−4 μW cm−2 nm−1 500 m from the city to 1 × 10−6 μW cm−2 nm−1 in the center of the gulf (9.5 km from the city) in the yellow channel (589-nm wavelength) and from 1.3 × 10−4 μW cm−2 nm−1 to 4.3 × 10−5 μW cm−2 nm−1 in the blue channel (443-nm wavelength). Down to 10-m depth, we find downwelling irradiance values that vary from 1 × 10−6 μW cm−2 nm−1 to 4.6 × 10−4 μW cm−2 nm−1 in the yellow channel and from 2.6 × 10−5 μW cm−2 nm−1 to 1.3 × 10−4 μW cm−2 nm−1 in the blue channel, and we even detected a signal at 30-m depth. This irradiance could influence such biological processes as the tuning of circadian clocks, the synchronization of coral spawning, recruitment and competition, vertical migration of demersal plankton, feeding patterns, and prey/predator visual interactions.
Artificial lights raise night sky luminance, creating the most visible effect of light pollution-artificial skyglow. Despite the increasing interest among scientists in fields such as ecology, astronomy, health care, and land-use planning, light pollution lacks a current quantification of its magnitude on a global scale. To overcome this, we present the world atlas of artificial sky luminance, computed with our light pollution propagation software using new high-resolution satellite data and new precision sky brightness measurements. This atlas shows that more than 80% of the world and more than 99% of the U.S. and European populations live under light-polluted skies. The Milky Way is hidden from more than one-third of humanity, including 60% of Europeans and nearly 80% of North Americans. Moreover, 23% of the world's land surfaces between 75°N and 60°S, 88% of Europe, and almost half of the United States experience light-polluted nights.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
