Light intensity and suppression of nocturnal plasma melatonin in Arctic charr (Salvelinus alpinus)

Is part-night lighting a suitable mitigation strategy to limit Artificial Light at Night effects on the biological rhythm at the behavioral and molecular scales of the oyster Crassostrea gigas?

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.

Artificial light at night at environmental intensities disrupts daily rhythm of the oyster Crassostrea gigas

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.

Harbours as unique environmental sites of multiple anthropogenic stressors on fish hormonal systems

Fish development and acclimation to environmental conditions are strongly mediated by the hormonal endocrine system. In environments contaminated by anthropogenic stressors, hormonal pathway alterations can be detrimental for growth, survival, fitness, and at a larger scale for population maintenance. In the context of increasingly contaminated marine environments worldwide, numerous laboratory studies have confirmed the effect of one or a combination of pollutants on fish hormonal systems. However, this has not been confirmed in situ. In this review, we explore the body of knowledge related to the influence of anthropogenic stressors disrupting fish endocrine systems, recent advances (focusing on thyroid hormones and stress hormones such as cortisol), and potential research perspectives. Through this review, we highlight how harbours can be used as "in situ laboratories" given the variety of anthropogenic stressors (such as plastic, chemical, sound, light pollution, and invasive species) that can be simultaneously investigated in harbours over long periods of time.

Modulation of physiological oxidative stress and antioxidant status by abiotic factors especially salinity in aquatic organisms

Exposure to a variety of environmental factors such as temperature, pH, oxygen and salinity may influence the oxidative status in aquatic organisms. The present review article focuses on the modulation of oxidative stress with reference to the generation of reactive oxygen species (ROS) in aquatic animals from different phyla. The focus of the review article is to explore the plausible mechanisms of physiological changes occurring in aquatic animals due to altered salinity in terms of oxidative stress. Apart from the seasonal variations in salinity, global warming and anthropogenic activities have also been found to influence oxidative health status of aquatic organisms. These effects are discussed with an objective to develop precautionary measures to protect the diversity of aquatic species with sustainable conservation. Comparative analyses among different aquatic species suggest that salinity alone or in combination with other abiotic factors are intricately associated with modulation in oxidative stress in a species-specific manner in aquatic animals. Osmoregulation under salinity stress in relation to energy demand and supply are also discussed. The literature survey of >50 years (1960-2020) indicates that oxidative stress status and comparative analysis of redox modulation have evolved from the analysis of various biotic and/or abiotic factors to the study of cellular signalling pathways in these aquatic organisms.

Light Pollution, Circadian Photoreception, and Melatonin in Vertebrates

Artificial light at night (ALAN) is increasing exponentially worldwide, accelerated by the transition to new efficient lighting technologies. However, ALAN and resulting light pollution can cause unintended physiological consequences. In vertebrates, production of melatonin—the “hormone of darkness” and a key player in circadian regulation—can be suppressed by ALAN. In this paper, we provide an overview of research on melatonin and ALAN in vertebrates. We discuss how ALAN disrupts natural photic environments, its effect on melatonin and circadian rhythms, and different photoreceptor systems across vertebrate taxa. We then present the results of a systematic review in which we identified studies on melatonin under typical light-polluted conditions in fishes, amphibians, reptiles, birds, and mammals, including humans. Melatonin is suppressed by extremely low light intensities in many vertebrates, ranging from 0.01–0.03 lx for fishes and rodents to 6 lx for sensitive humans. Even lower, wavelength-dependent intensities are implied by some studies and require rigorous testing in ecological contexts. In many studies, melatonin suppression occurs at the minimum light levels tested, and, in better-studied groups, melatonin suppression is reported to occur at lower light levels. We identify major research gaps and conclude that, for most groups, crucial information is lacking. No studies were identified for amphibians and reptiles and long-term impacts of low-level ALAN exposure are unknown. Given the high sensitivity of vertebrate melatonin production to ALAN and the paucity of available information, it is crucial to research impacts of ALAN further in order to inform effective mitigation strategies for human health and the wellbeing and fitness of vertebrates in natural ecosystems.

Changes in Body Growth and Growth-Related Genes under Different Photoperiods in Olive Flounder, Paralichthys olivaceus

This study examined the effects of different photoperiod conditions on olive flounder (Paralichthys olivaceus), a commercially important species in Korea. Daily variations in the expression of mRNA for the growth-related genes ary­lalkylamine N-acetyltransferase2 (AANAT2), preprosomatostatin1 (PSS1), and growth hormone (GH) were examined under a 12 h light:12 h dark photoperiod. All the genes were expressed at higher level during the dark period. Melatonin injections increased the expression of GH, but did not significantly affect the expression of PSS. Under short-day conditions (10 h:14 h), the fish gained more weight than under long-day conditions (14 h:10 h). A long nighttime induced melatonin secretion and increased the expression of GH mRNA, promoting weight gain in this species. Therefore, we thought that the long day condition in raising olive flounder may be effective in inducing body growth.