Use of an Autonomous Surface Vehicle reveals small-scale diel vertical migrations of zooplankton and susceptibility to light pollution under low solar irradiance

Artificial light and cloud cover interact to disrupt celestial migrations at night

The growth of human activity and infrastructure has led to an unprecedented rise in the use of Artificial Light at Night (ALAN) with demonstrable impacts on ecological communities and ecosystem services. However, there remains very little information on how ALAN interacts with or obscures light from celestial bodies, which provide vital orientating cues in a number of species. Furthermore, no studies to date have examined how climatic conditions such as cloud cover, known to influence the intensity of skyglow, interact with lunar irradiance and ALAN over the course of a lunar cycle to alter migratory abilities of species. Our night-time field study aimed to establish how lunar phase and climatic conditions (cloud cover) modulate the impact of ALAN on the abundance and migratory behaviour of Talitrus saltator, a key sandy beach detritivore which uses multiple light associated cues during nightly migrations. Our results showed that the number and size of individuals caught decreased significantly as ALAN intensity increased. Additionally, when exposed to ALAN more T. saltator were caught travelling parallel to the shoreline, indicating that the presence of ALAN is inhibiting their ability to navigate along their natural migration route, potentially impacting the distribution of the population. We found that lunar phase and cloud cover play a significant role in modifying the impact of ALAN, highlighting the importance of incorporating natural light cycles and climatic conditions when investigating ALAN impacts. Critically we demonstrate that light levels as low as 3 lx can have substantial effects on coastal invertebrate distributions. Our results provide the first evidence that ALAN impacted celestial migration can lead to changes to the distribution of a species.

Artificial light at night alters the feeding activity and two molecular indicators in the plumose sea anemone Metridium senile (L.)

Artificial light at night (ALAN) is becoming a widespread stressor in coastal ecosystems, affecting species that rely on natural day/night cycles. Yet, studies examining ALAN effects remain limited, particularly in the case of sessile species. This study assessed the effects of ALAN upon the feeding activity and two molecular indicators in the widespread plumose sea anemone Metridium senile. Anemones were exposed to either natural day/night or ALAN conditions to monitor feeding activity, and tissue samples were collected to quantify proteins and superoxide dismutase (SOD) enzyme concentrations. In day/night conditions, sea anemones showed a circadian rhythm of activity in which feeding occurs primarily at night. This rhythm was altered by ALAN, which turned it into a reduced and more uniform pattern of feeding. Consistently, proteins and SOD concentrations were significantly lower in anemones exposed to ALAN, suggesting that ALAN can be harmful to sea anemones and potentially other marine sessile species.

Hypometabolism to survive the long polar night and subsequent successful return to light in the diatom Fragilariopsis cylindrus

Diatoms, the main eukaryotic phytoplankton of the polar marine regions, are essential for the maintenance of food chains specific to Arctic and Antarctic ecosystems, and are experiencing major disturbances under current climate change. As such, it is fundamental to understand the physiological mechanisms and associated molecular basis of their endurance during the long polar night. Here, using the polar diatom Fragilariopsis cylindrus, we report an integrative analysis combining transcriptomic, microscopic and biochemical approaches to shed light on the strategies used to survive the polar night. We reveal that in prolonged darkness, diatom cells enter a state of quiescence with reduced metabolic and transcriptional activity, during which no cell division occurs. We propose that minimal energy is provided by respiration and degradation of protein, carbohydrate and lipid stores and that homeostasis is maintained by autophagy in prolonged darkness. We also report internal structural changes that manifest the morphological acclimation of cells to darkness, including the appearance of a large vacuole. Our results further show that immediately following a return to light, diatom cells are able to use photoprotective mechanisms and rapidly resume photosynthesis, demonstrating the remarkable robustness of polar diatoms to prolonged darkness at low temperature.

Ecosystem functioning across the diel cycle in the Anthropocene

Given the marked differences in environmental conditions and active biota between daytime and nighttime, it is almost inevitable that ecosystem functioning will also differ. However, understanding of these differences has been hampered due to the challenges of conducting research at night. At the same time, many anthropogenic pressures are most forcefully exerted or have greatest effect during either daytime (e.g., high temperatures, disturbance) or nighttime (e.g., artificial lighting, nights warming faster than days). Here, we explore current understanding of diel (daily) variation in five key ecosystem functions and when during the diel cycle they primarily occur [predation (unclear), herbivory (nighttime), pollination (daytime), seed dispersal (unclear), carbon assimilation (daytime)] and how diel asymmetry in anthropogenic pressures impacts these functions.

The impacts of artificial light at night on the ecology of temperate and tropical reefs

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'.

Plasticity and seasonality of the vertical migration behaviour of Antarctic krill using acoustic data from fishing vessels

Understanding the vertical migration behaviour of Antarctic krill is important for understanding spatial distribution, ecophysiology, trophic interactions and carbon fluxes of this Southern Ocean key species. In this study, we analysed an eight-month continuous dataset recorded with an ES80 echosounder on board a commercial krill fishing vessel in the southwest Atlantic sector of the Southern Ocean. Our analysis supports the existing hypothesis that krill swarms migrate into deeper waters during winter but also reveals a high degree of variability in vertical migration behaviour within seasons, even at small spatial scales. During summer, we found that behaviour associated with prolonged surface presence primarily occurred at low surface chlorophyll a concentrations whereas multiple ascent-descent cycles per day occurred when surface chlorophyll a concentrations were elevated. The high plasticity, with some krill swarms behaving differently in the same location at the same time, suggests that krill behaviour is not a purely environmentally driven process. Differences in life stage, physiology and type of predator are likely other important drivers. Finally, our study demonstrates new ways of using data from krill fishing vessels, and with the routine collection of additional information in potential future projects, they have great potential to significantly advance our understanding of krill ecology.

Spectral and RGB analysis of the light climate and its ecological impacts using an all-sky camera system in the Arctic

The ArcLight observatory provides an hourly continuous time series of all-sky images providing light climate data (intensity, spectral composition, and photoperiod) from the Arctic (Svalbard at 79°N). Until recently, no complete annual time series of light climate relevant for biological processes has been provided from the high Arctic because of insufficient sensitivity of commercial light sensors during the Polar Night. The ArcLight set up is unique, as it provides both all-sky images and the corresponding integrated spectral irradiance in the visible part of the solar electromagnetic spectrum (E P A R ). Here we present a further development providing hourly diel-annual dynamics from 2020 of the irradiance partitioned into the red, green, and blue parts of the solar spectrum and illustrate their relation to weather conditions, and sun and moon trajectories. We show that there is variation between the RGB proportions of irradiance throughout the year, with the blue part of the spectrum showing the greatest variation, which is dependent on weather conditions (i.e., cloud cover). We further provide an example of the biological impact of these spectral variations in the light climate using in vivo Chl a-specific absorption coefficients of diatoms (mean of six low light acclimated northern-Arctic bloom-forming species) to model total algal light absorption (AQ t o t a l ) and the corresponding fraction of quanta used by Photosystem II (AQPSII) (O 2 production) in RGB bands and the potential impacts on the photoreceptor response, suggesting periods where repair and maintenance functions dominate activity in the absence of appreciable levels of red or green light. The method used here can be applied to light climate data and spectral response data worldwide to give localized ecological models of AQ.

The effects of light pollution on migratory animal behavior

Light pollution is a global threat to biodiversity, especially migratory organisms, some of which traverse hemispheric scales. Research on light pollution has grown significantly over the past decades, but our review of migratory organisms demonstrates gaps in our understanding, particularly beyond migratory birds. Research across spatial scales reveals the multifaceted effects of artificial light on migratory species, ranging from local and regional to macroscale impacts. These threats extend beyond species that are active at night - broadening the scope of this threat. Emerging tools for measuring light pollution and its impacts, as well as ecological forecasting techniques, present new pathways for conservation, including transdisciplinary approaches.

The short-term effects of planktivorous fish foraging in the presence of artificial light at night on lake zooplankton

Numerous studies have revealed that artificial light at night alters the natural patterns of light in space and time and may have various ecological impacts at different ecological levels. However, only a few studies have assessed its effect on interactions between organisms in aquatic environments, including predator-prey interactions in lakes. To fill this gap, we performed a preliminary enclosure experiment in which we compared the foraging effect of juvenile perch (Perca fluviatilis) on a natural lake zooplankton community in the absence and presence of light of high-pressure sodium (HPS) lamps mimicking artificial light emitted by a boat. The results revealed that even short-lasting exposure to HPS lamps may result in increasing fish predation, which in turn decreased the mean body size in zooplankton populations (e.g. Bosmina thersites) and affected the relative proportion between different taxa in zooplankton communities.

Impacts of artificial light at night in marine ecosystems-A review

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 seabird and sea turtle 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.

Artificial light at night reverses monthly foraging pattern under simulated moonlight

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.

Animal behavior is central in shaping the realized diel light niche

Animal behavior in space and time is structured by the perceived day/night cycle. However, this is modified by the animals’ own movement within its habitat, creating a realized diel light niche (RDLN). To understand the RDLN, we investigated the light as experienced by zooplankton undergoing synchronized diel vertical migration (DVM) in an Arctic fjord around the spring equinox. We reveal a highly dampened light cycle with diel changes being about two orders of magnitude smaller compared to the surface or a static depth. The RDLN is further characterized by unique wavelength-specific irradiance cycles. We discuss the relevance of RDLNs for animal adaptations and interactions, as well as implications for circadian clock entrainment in the wild and laboratory.

Minimizing Ecological Impacts of Marine Energy Lighting

Marine energy is poised to become an important renewable energy contributor for the U.S., but widespread deployment of the technology hinges on its benefits outweighing the potential ecological impacts. One stressor marine energy installations introduce is light, which is known to cause varying responses among wildlife and has not yet been addressed as an environmental concern. This review discusses requirements and regulations for similar structures and how lighting design choices can be made to meet these requirements while minimizing environmental consequences. More practical guidance on implementing lighting for marine energy is needed, as well as updated guidelines to reflect technological and research advances. Known responses of wildlife to light are introduced in addition to how the responses of individuals may lead to ecosystem-level changes. The impact of light associated with marine energy installations can be reduced by following basic guidance provided herein, such as removing excess lighting, using lights with high directionality, and employing controls to reduce light levels. Continued research on animal responses to light, such as findings on minimum light levels for animal responses, alongside the development of highly-sensitivity spectral characterization capabilities can further inform lighting guidelines for deploying future open ocean marine energy devices.

How moonlight shapes environments, life histories, and ecological interactions on coral reefs

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.

Photophysiological cycles in Arctic krill are entrained by weak midday twilight during the Polar Night

Light plays a fundamental role in the ecology of organisms in nearly all habitats on Earth and is central for processes such as vision and the entrainment of the circadian clock. The poles represent extreme light regimes with an annual light cycle including periods of Midnight Sun and Polar Night. The Arctic Ocean extends to the North Pole, and marine light extremes reach their maximum extent in this habitat. During the Polar Night, traditional definitions of day and night and seasonal photoperiod become irrelevant since there are only "twilight" periods defined by the sun's elevation below the horizon at midday; we term this "midday twilight." Here, we characterize light across a latitudinal gradient (76.5° N to 81° N) during Polar Night in January. Our light measurements demonstrate that the classical solar diel light cycle dominant at lower latitudes is modulated during Arctic Polar Night by lunar and auroral components. We therefore question whether this particular ambient light environment is relevant to behavioral and visual processes. We reveal from acoustic field observations that the zooplankton community is undergoing diel vertical migration (DVM) behavior. Furthermore, using electroretinogram (ERG) recording under constant darkness, we show that the main migratory species, Arctic krill (Thysanoessa inermis) show endogenous increases in visual sensitivity during the subjective night. This change in sensitivity is comparable to that under exogenous dim light acclimations, although differences in speed of vision suggest separate mechanisms. We conclude that the extremely weak midday twilight experienced by krill at high latitudes during the darkest parts of the year has physiological and ecological relevance.

Autonomous Surface and Underwater Vehicles as Effective Ecosystem Monitoring and Research Platforms in the Arctic-The Glider Project

Effective ocean management requires integrated and sustainable ocean observing systems enabling us to map and understand ecosystem properties and the effects of human activities. Autonomous subsurface and surface vehicles, here collectively referred to as “gliders”, are part of such ocean observing systems providing high spatiotemporal resolution. In this paper, we present some of the results achieved through the project “Unmanned ocean vehicles, a flexible and cost-efficient offshore monitoring and data management approach—GLIDER”. In this project, three autonomous surface and underwater vehicles were deployed along the Lofoten–Vesterålen (LoVe) shelf-slope-oceanic system, in Arctic Norway. The aim of this effort was to test whether gliders equipped with novel sensors could effectively perform ecosystem surveys by recording physical, biogeochemical, and biological data simultaneously. From March to September 2018, a period of high biological activity in the area, the gliders were able to record a set of environmental parameters, including temperature, salinity, and oxygen, map the spatiotemporal distribution of zooplankton, and record cetacean vocalizations and anthropogenic noise. A subset of these parameters was effectively employed in near-real-time data assimilative ocean circulation models, improving their local predictive skills. The results presented here demonstrate that autonomous gliders can be effective long-term, remote, noninvasive ecosystem monitoring and research platforms capable of operating in high-latitude marine ecosystems. Accordingly, these platforms can record high-quality baseline environmental data in areas where extractive activities are planned and provide much-needed information for operational and management purposes.

Cloud shadows drive vertical migrations of deep-dwelling marine life

Many zooplankton and fishes vertically migrate on a diel cycle to avoid predation, moving from their daytime residence in darker, deep waters to prey-rich surface waters to feed at dusk and returning to depth before dawn. Vertical migrations also occur in response to other processes that modify local light intensity, such as storms, eclipses, and full moons. We observed rapid, high-frequency migrations, spanning up to 60 m, of a diel vertically migrating acoustic scattering layer with a daytime depth of 300 m in the subpolar Northeastern Pacific Ocean. The depth of the layer was significantly correlated, with an ∼5-min lag, to cloud-driven variability in surface photosynthetically available radiation. A model of isolume-following swimming behavior reproduces the observed layer depth and suggests that the high-frequency migration is a phototactic response to absolute light level. Overall, the cumulative distance traveled per day in response to clouds was at least 36% of the round-trip diel migration distance. This previously undescribed phenomenon has implications for the metabolic requirements of migrating animals while at depth and highlights the powerful evolutionary adaptation for visual predator avoidance.

All-sky camera system providing high temporal resolution annual time series of irradiance in the Arctic

The ArcLight observatory provides hourly continuous time series of light regime data (intensity, spectral composition, and photoperiod) from the Arctic, Svalbard at 79° N. Until now, no complete annual time series of biologically relevant light has been provided from the high Arctic due to insufficient sensitivity of commercial light sensors during the Polar Night. We describe a camera system providing all-sky images and the corresponding integrated spectral irradiance (E_PAR) in energy or quanta units, throughout a complete annual cycle. We present hourly-diel-annual dynamics from 2017 to 2020 of irradiance and its relation to weather conditions, sun and moon trajectories.

Pelagic organisms avoid white, blue, and red artificial light from scientific instruments

In situ observations of pelagic fish and zooplankton with optical instruments usually rely on external light sources. However, artificial light may attract or repulse marine organisms, which results in biased measurements. It is often assumed that most pelagic organisms do not perceive the red part of the visible spectrum and that red light can be used for underwater optical measurements of biological processes. Using hull-mounted echosounders above an acoustic probe or a baited video camera, each equipped with light sources of different colours (white, blue and red), we demonstrate that pelagic organisms in Arctic and temperate regions strongly avoid artificial light, including visible red light (575–700 nm), from instruments lowered in the water column. The density of organisms decreased by up to 99% when exposed to artificial light and the distance of avoidance varied from 23 to 94 m from the light source, depending on colours, irradiance levels and, possibly, species communities. We conclude that observations from optical and acoustic instruments, including baited cameras, using light sources with broad spectral composition in the 400–700 nm wavelengths do not capture the real state of the ecosystem and that they cannot be used alone for reliable abundance estimates or behavioural studies.

Effects of artificial light at night (ALAN) on gene expression of Aquatica ficta firefly larvae

Artificial light at night (ALAN) is a major driver of firefly population declines, but its physiological effects are not well understood. To investigate the impact of ALAN on firefly development, we exposed larval Aquatica ficta fireflies to ALAN for two weeks. High larval mortality was observed in the periods of 1-68 days and 106-134 days post-treatment, which may represent the short- and long-term impacts of ALAN. We then profiled the transcriptome of larval Aquatica ficta fireflies following two weeks of ALAN exposure. A total of 1262 (1.67% out of 75777 unigenes) were differentially expressed in the treatment group: 1157 were down-regulated, and 105 were up-regulated. Up-regulated unigenes were related to regulation of hormone levels, ecdysteroid metabolic process, and response to stimulus; down-regulated unigenes were related to negative regulation of insulin receptor signaling, germ cell development, oogenesis, spermatid development, and regulation of neuron differentiation. Transcriptome results suggest that the endocrine, reproductive, and neural development of firefly larvae could be impaired by even relatively brief period of ALAN exposure. This report contributes a much-needed molecular perspective to the growing body of research documenting the fitness impacts of ALAN on bioluminescent fireflies.

Artificial Light at Night (ALAN) negatively affects the settlement success of two prominent intertidal barnacles in the southeast Pacific

Many coastal processes are regulated by day/night cycles and are expected to be altered by Artificial Light at Night (ALAN). The goal of this study was to assess the influence of ALAN on the settlement rates of intertidal barnacles. A newly designed settlement plate equipped with a small central LED light source was used to quantify settlement rates in presence/absence of ALAN conditions. "ALAN plates" as well as regular settlement plates were deployed in the mid rocky intertidal zone. Both ALAN and control plates collected early and late settlers of the barnacles Notochthamalus scabrosus and Jehlius cirratus. Early settlers (pre-metamorphosis cyprids) were not affected by ALAN. By contrast, the density of late settlers (post-metamorphosis spats) was significantly lower in ALAN than in control plates for both species, suggesting detrimental ALAN impacts on the settlement process. The new ALAN plates represent an attractive and alternative methodology to study ALAN effects.

Pervasiveness of biological impacts of artificial light at night

Artificial light at night (ALAN) and its associated biological impacts have regularly been characterized 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 toward wavelengths of light that often have greater biological impacts.

Predation landscapes influence migratory prey ecology and evolution

Migratory prey experience spatially variable predation across their life cycle. They face unique challenges in navigating this predation landscape, which affects their perception of risk, antipredator responses, and resulting mortality. Variable and unfamiliar predator cues during migration can limit accurate perception of risk and migrants often rely on social information and learning to compensate. The energetic demands of migration constrain antipredator responses, often through context-dependent patterns. While migration can increase mortality, migrants employ diverse strategies to balance risks and rewards, including life history and antipredator responses. Humans interact frequently with migratory prey across space and alter both mortality risk and antipredator responses, which can scale up to affect migratory populations and should be considered in conservation and management.

Two hundred years of zooplankton vertical migration research

Vertical migration is a geographically and taxonomically widespread behaviour among zooplankton that spans across diel and seasonal timescales. The shorter-term diel vertical migration (DVM) has a periodicity of up to 1 day and was first described by the French naturalist Georges Cuvier in 1817. In 1888, the German marine biologist Carl Chun described the longer-term seasonal vertical migration (SVM), which has a periodicity of ca. 1 year. The proximate control and adaptive significance of DVM have been extensively studied and are well understood. DVM is generally a behaviour controlled by ambient irradiance, which allows herbivorous zooplankton to feed in food-rich shallower waters during the night when light-dependent (visual) predation risk is minimal and take refuge in deeper, darker waters during daytime. However, DVMs of herbivorous zooplankton are followed by their predators, producing complex predator-prey patterns that may be traced across multiple trophic levels. In contrast to DVM, SVM research is relatively young and its causes and consequences are less well understood. During periods of seasonal environmental deterioration, SVM allows zooplankton to evacuate shallower waters seasonally and take refuge in deeper waters often in a state of dormancy. Both DVM and SVM play a significant role in the vertical transport of organic carbon to deeper waters (biological carbon sequestration), and hence in the buffering of global climate change. Although many animal migrations are expected to change under future climate scenarios, little is known about the potential implications of global climate change on zooplankton vertical migrations and its impact on the biological carbon sequestration process. Further, the combined influence of DVM and SVM in determining zooplankton fitness and maintenance of their horizontal (geographic) distributions is not well understood. The contrasting spatial (deep versus shallow) and temporal (diel versus seasonal) scales over which these two migrations occur lead to challenges in studying them at higher spatial, temporal and biological resolution and coverage. Extending the largely population-based vertical migration knowledge base to individual-based studies will be an important way forward. While tracking individual zooplankton in their natural habitats remains a major challenge, conducting trophic-scale, high-resolution, year-round studies that utilise emerging field sampling and observation techniques, molecular genetic tools and computational hardware and software will be the best solution to improve our understanding of zooplankton vertical migrations.

Artificial light at night alters the settlement of acorn barnacles on a man-made habitat in Atlantic Canada

Human growth has caused an unprecedented increase in artificial light at night (ALAN). In coastal habitats, many species rely on day/night cycles to regulate various aspects of their life history and these cycles can be altered by this stressor. This study assessed the influence of ALAN on the early (cyprid) and late (spat) settlement stages of the acorn barnacle Semibalanus balanoides, a species widely distributed in natural and man-made coastal habitats of the North Atlantic. A newly designed settlement plate, originally for studies in rocky intertidal habitats in the southeast Pacific, was adapted to measure settlement rates on man-made habitats -wharf seawalls- located in Atlantic Canada. Plates equipped with a small LED diode powered by an internal battery (ALAN plates) were used to quantify settlement rates in comparison to plates lacking a light source (controls). These plates were deployed for 6 d in the mid-intertidal levels, where adult barnacles were readily visible. ALAN and control plates collected large number of settlers and showed to be suitable for this type of man-made habitats. The number of early settlers (cyprids) did not differ between plates but the number of late settlers (spat) was significantly lower in ALAN plates than in controls. These results suggest that light pollution has little influence on the early stages of the acorn barnacle settlement but is clearly detrimental to its late stages. As barnacles dominate in many natural and man-made hard substrates, it is likely that ALAN also has indirect effects on community structure.

A marine zooplankton community vertically structured by light across diel to interannual timescales

The predation risk of many aquatic taxa is dominated by visually searching predators, commonly a function of ambient light. Several studies propose that changes in visual predation will become a major climate-change impact on polar marine ecosystems. The High Arctic experiences extreme seasonality in the light environment, from 24 h light to 24 h darkness, and therefore provides a natural laboratory for studying light and predation risk over diel to seasonal timescales. Here, we show that zooplankton (observed using acoustics) in an Arctic fjord position themselves vertically in relation to light. A single isolume (depth-varying line of constant light intensity, the value of which is set at the lower limit of photobehaviour reponses of Calanus spp. and krill) forms a ceiling on zooplankton distribution. The vertical distribution is structured by light across timescales, from the deepening of zooplankton populations at midday as the sun rises in spring, to the depth to which zooplankton ascend to feed during diel vertical migration. These results suggest that zooplankton might already follow a foraging strategy that will keep visual predation risk roughly constant under changing light conditions, such as those caused by the reduction of sea ice, but likely with energetic costs such as lost feeding opportunities as a result of altered habitat use.

Exposure to Artificial Light at Night and the Consequences for Flora, Fauna, and Ecosystems

The present review draws together wide-ranging studies performed over the last decades that catalogue the effects of artificial-light-at-night (ALAN) upon living species and their environment. We provide an overview of the tremendous variety of light-detection strategies which have evolved in living organisms - unicellular, plants and animals, covering chloroplasts (plants), and the plethora of ocular and extra-ocular organs (animals). We describe the visual pigments which permit photo-detection, paying attention to their spectral characteristics, which extend from the ultraviolet into infrared. We discuss how organisms use light information in a way crucial for their development, growth and survival: phototropism, phototaxis, photoperiodism, and synchronization of circadian clocks. These aspects are treated in depth, as their perturbation underlies much of the disruptive effects of ALAN. The review goes into detail on circadian networks in living organisms, since these fundamental features are of critical importance in regulating the interface between environment and body. Especially, hormonal synthesis and secretion are often under circadian and circannual control, hence perturbation of the clock will lead to hormonal imbalance. The review addresses how the ubiquitous introduction of light-emitting diode technology may exacerbate, or in some cases reduce, the generalized ever-increasing light pollution. Numerous examples are given of how widespread exposure to ALAN is perturbing many aspects of plant and animal behaviour and survival: foraging, orientation, migration, seasonal reproduction, colonization and more. We examine the potential problems at the level of individual species and populations and extend the debate to the consequences for ecosystems. We stress, through a few examples, the synergistic harmful effects resulting from the impacts of ALAN combined with other anthropogenic pressures, which often impact the neuroendocrine loops in vertebrates. The article concludes by debating how these anthropogenic changes could be mitigated by more reasonable use of available technology - for example by restricting illumination to more essential areas and hours, directing lighting to avoid wasteful radiation and selecting spectral emissions, to reduce impact on circadian clocks. We end by discussing how society should take into account the potentially major consequences that ALAN has on the natural world and the repercussions for ongoing human health and welfare.

Biologically important artificial light at night on the seafloor

Accelerating coastal development is increasing the exposure of marine ecosystems to nighttime light pollution, but is anthropogenic light reaching the seafloor in sufficient quantities to have ecological impacts? Using a combination of mapping, and radiative transfer modelling utilising in situ measurements of optical seawater properties, we quantified artificial light exposure at the sea surface, beneath the sea surface, and at the sea floor of an urbanised temperate estuary bordered by an LED lit city. Up to 76% of the three-dimensional seafloor area was exposed to biologically important light pollution. Exposure to green wavelengths was highest, while exposure to red wavelengths was nominal. We conclude that light pollution from coastal cities is likely having deleterious impacts on seafloor ecosystems which provide vital ecosystem services. A comprehensive understanding of these impacts is urgently needed.

Artificial light during the polar night disrupts Arctic fish and zooplankton behaviour down to 200 m depth

For organisms that remain active in one of the last undisturbed and pristine dark environments on the planet-the Arctic Polar Night-the moon, stars and aurora borealis may provide important cues to guide distribution and behaviours, including predator-prey interactions. With a changing climate and increased human activities in the Arctic, such natural light sources will in many places be masked by the much stronger illumination from artificial light. Here we show that normal working-light from a ship may disrupt fish and zooplankton behaviour down to at least 200 m depth across an area of >0.125 km2 around the ship. Both the quantitative and qualitative nature of the disturbance differed between the examined regions. We conclude that biological surveys in the dark from illuminated ships may introduce biases on biological sampling, bioacoustic surveys, and possibly stock assessments of commercial and non-commercial species.

A review on the environmental impacts of shipping on aquatic and nearshore ecosystems

There are several environmental and ecological effects of shipping. However, these are rarely assessed in total in the scientific literature. Thus, the aim of this study was to summarize the different impacts of water-based transport on aquatic and nearshore ecosystems and to identify knowledge gaps and areas for future research. The review identified several environmental and ecological consequences within the main impact categories of water discharges, physical impacts, and air emissions. However, although quantitative data on these consequences are generally scarce the shipping contribution to acidification by SO_x- and NO_x-emissions has been quantified to some extent. There are several knowledge gaps regarding the ecological consequences of, for example, the increasing amount of chemicals transported on water, the spread of non-indigenous species coupled with climate change, and physical impacts such as shipping noise and artificial light. The whole plethora of environmental consequences, as well as potential synergistic effects, should be seriously considered in transport planning.

Sustainability of coral reefs are affected by ecological light pollution in the Gulf of Aqaba/Eilat

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.

Artificial light pollution influences behavioral and physiological traits in a keystone predator species, Concholepas concholepas

Artificial Light At Night (ALAN) is an increasing global problem that, despite being widely recognized in terrestrial systems, has been studied much less in marine habitats. In this study we investigated the effect of ALAN on behavioral and physiological traits of Concholepas concholepas, an important keystone species of the south-eastern Pacific coast. We used juveniles collected in intertidal habitats that had not previously been exposed to ALAN. In the laboratory we exposed them to two treatments: darkness and white LED (Lighting Emitting Diodes) to test for the impacts of ALAN on prey-searching behavior, self-righting time and metabolism. In the field, the distribution of juveniles was observed during daylight-hours to determine whether C. concholepas preferred shaded or illuminated microhabitats. Moreover, we compared the abundance of juveniles collected during day- and night-time hours. The laboratory experiments demonstrated that juveniles of C. concholepas seek out and choose their prey more efficiently in darkened areas. White LED illuminated conditions increased righting times and metabolism. Field surveys indicated that, during daylight hours, juveniles were more abundant in shaded micro-habitats than in illuminated ones. However, during darkness hours, individuals were not seen to aggregate in any particular microhabitats. We conclude that the exposure to ALAN might disrupt important behavioral and physiological traits of small juveniles in this species which, as a mechanism to avoid visual predators, are mainly active at night. It follows that ALAN in coastal areas might modify the entire community structure of intertidal habitats by altering the behavior of this keystone species.

Beyond All-Sky: Assessing Ecological Light Pollution Using Multi-Spectral Full-Sphere Fisheye Lens Imaging

Artificial light at night is a novel anthropogenic stressor. The resulting ecological light pollution affects a wide breadth of biological systems on many spatio-temporal scales, from individual organisms to communities and ecosystems. However, a widely-applicable measurement method for nocturnal light providing spatially resolved full-spectrum radiance over the full solid angle is still missing. Here, we explain the first step to fill this gap, by using a commercial digital camera with a fisheye lens to acquire vertical plane multi-spectral (RGB) images covering the full solid angle. We explain the technical and practical procedure and software to process luminance and correlated color temperature maps and derive illuminance. We discuss advantages and limitations and present data from different night-time lighting situations. The method provides a comprehensive way to characterize nocturnal light in the context of ecological light pollution. It is affordable, fast, mobile, robust, and widely-applicable by non-experts for field work.

Artificial light at night alters behavior in laboratory and wild animals

Life has evolved to internalize and depend upon the daily and seasonal light cycles to synchronize physiology and behavior with environmental conditions. The nightscape has been vastly changed in response to the use of artificial lighting. Wildlife is now often exposed to direct lighting via streetlights or indirect lighting via sky glow at night. Because many activities rely on daily and seasonal light cues, the effects of artificial light at night could be extensive, but remain largely unknown. Laboratory studies suggest exposure to light at night can alter typical timing of daily locomotor activity and shift the timing of foraging/food intake to the daytime in nocturnal rodents. Additionally, nocturnal rodents decrease anxiety-like behaviors (i.e., spend more time in the open and increase rearing up) in response to even dim light at night. These are all likely maladaptive responses in the wild. Photoperiodic animals rely on seasonal changes in day length as a cue to evoke physiological and behavioral modifications to anticipate favorable and unfavorable conditions for survival and reproduction. Light at night can mask detection of short days, inappropriately signal long days, and thus desynchronize seasonal reproductive activities. We review laboratory and the sparse field studies that address the effects of exposure to artificial light at night to propose that exposure to light at night disrupts circadian and seasonal behavior in wildlife, which potentially decreases individual fitness and modifies ecosystems.