Association between light exposure at night and insomnia in the general elderly population: The HEIJO-KYO cohort

Chronic circadian misalignment between the internal and environmental rhythms, which is typically related to night-shift work and clock-gene variants, is associated with disruption of suprachiasmatic nucleus function and increased risk of insomnia. Under controlled laboratory conditions, light at night (LAN) suppresses melatonin secretion, delays the internal biological rhythm, and reduces sleepiness. Therefore, LAN exposure may cause circadian misalignment and insomnia, though it remains unclear in real-life situations whether LAN exposure is associated with insomnia. To evaluate an association between LAN exposure and sleep quality in home settings, we conducted a cross-sectional community-based study in 857 elderly individuals (mean age, 72.2 years). We evaluated bedroom light intensity using a light meter and subjectively and objectively measured sleep quality using the Pittsburgh Sleep Quality Index and an actigraph, respectively, along with urinary 6-sulfatoxymelatonin excretion. Compared with the lowest quartile group of LAN intensity, the highest quartile group revealed a significantly higher odds ratio (OR) for subjective insomnia in a multivariate model adjusted for age, gender, body mass index, daytime physical activity, urinary 6-sulfatoxymelatonin excretion, bedtime, rising time, and day length (adjusted OR, 1.61, 95% confidence interval, 1.05–2.45, p?=?0.029). In addition, higher OR for subjective insomnia was significantly associated with the increase in quartiles of LAN intensity (p_trend?=?0.043). Consistently, we observed significant association trends between the increase in quartiles of LAN intensity and poorer actigraphic sleep quality, including decreased sleep efficiency, prolonged sleep-onset latency, increased wake-after-sleep onset, shortened total sleep time, and delayed sleep-mid time in multivariate models adjusted for the covariates mentioned above (all p_trend?<?0.001). In conclusion, we demonstrated that LAN exposure in home settings is significantly associated with both subjectively and objectively measured sleep quality in a community-based elderly population.     

Association between light exposure at night and nighttime blood pressure in the elderly independent of nocturnal urinary melatonin excretion

Circadian misalignment between internal and environmental rhythms dysregulates blood pressure (BP) variability because of disruption of the biological clock, resulting in increased nighttime BP. Although exposure to light-at-night is associated with the circadian misalignment, it remains unclear whether exposure to light-at-night in home settings is associated with nighttime BP. In this cross-sectional analysis of 528 elderly individuals (mean age: 72.8 years), we measured bedroom light intensity at 1-min intervals on two consecutive nights along with ambulatory BP, overnight urinary melatonin excretion and actigraphy. With regard to adjusted mean comparisons using analysis of covariance, the light-at-night group (average: ≥5?lux; n?=?109) showed significantly higher nighttime systolic BP (SBP; adjusted mean: 120.8 vs. 116.5?mmHg, p?=?0.01) and diastolic BP (70.1 vs. 67.1?mmHg, p?<?0.01) compared with the Darker group (average: <5?lux; n?=?419) independently of potential confounding factors including overnight urinary melatonin excretion and actigraphic sleep quality. We observed consistent associations between light-at-night and nighttime BP in different cutoff values for light-at-night intensity (i.e. 3 and 10?lux). In conclusion, exposure to light-at-night in home settings is significantly associated with increased nighttime BP in elderly individuals independently of overnight urinary melatonin excretion. A 4.3?mmHg increase in nighttime SBP is associated with a 6.1% increase in total mortality, which corresponds to approximately 10?000 annual excess deaths in Japanese elderly population.     

Light exposure at night is associated with subclinical carotid atherosclerosis in the general elderly population: The HEIJO-KYO cohort

Epidemiological and cellular biological studies indicate the influence of impaired circadian biological rhythmicity on atherosclerosis. Increased exposure to light at night (LAN) is common in modern life, and LAN exposure is the most important environmental cue for circadian misalignment. However, the association between LAN exposure and atherosclerosis has never been explored in humans. In this cross-sectional study, we measured nighttime light intensity in the bedroom along with the intima-media thickness (IMT) of the common carotid artery using ultrasonography in 700 elderly individuals (mean age 71.6 years). Averages of mean and maximal carotid IMT were 0.88?±?0.15?mm and 1.09?±?0.32?mm, respectively. Median intensity of LAN exposure was 0.74?lux (interquartile range, 0.08–3.34). Both mean and maximal carotid IMT significantly increased across quartiles of increasing LAN intensity (p for trend?=?0.002 and <0.001, respectively). After adjustment for confounding factors, including age, gender, body mass index, current smoking status, hypertension, diabetes, dyslipidemia, sleep medication, estimated glomerular filtration rate, nocturia, bedtime, duration in bed (scotoperiod), day length (photoperiod), urinary 6-sulfatoxymelatonin excretion and daytime and nighttime physical activity, multivariate linear regression models revealed significant associations of LAN exposure with carotid IMT measurements [mean: β, 0.032 (fourth versus first quartiles); 95% confidence intervals (CI), 0.002–0.061; p?=?0.037; maximal: β, 0.100 (fourth versus first quartiles); 95% CI, 0.034–0.165; p?=?0.003]. In conclusion, these results suggested that LAN exposure in home settings is significantly associated with subclinical carotid atherosclerosis in the general elderly population.     

Effect of light intensity on the phase and period response curves in the nocturnal field mouse Mus booduga

The effect of light intensity on the phase response curve (PRC) and the period response curve (τRC) of the nocturnal field mouse Mus booduga was studied. PRCs and τRCs were constructed by exposing animals free-running in constant darkness (DD), to fluorescent light pulses (LPs) of 100 lux and 1000 lux intensities for 15min duration. The waveform of the PRCs and τRCs evoked by high light intensity (1000 lux) stimuli was significantly different compared to those constructed using low light intensity (100 lux). Moreover, a weak but significant correlation was observed between phase shifts and period changes when light stimuli of 1000 lux intensity were used; however, the phase shifts and period changes in the 100 lux PRC and τRC were not correlated. This suggests that the intensity of light stimuli affects both phase and period responses in the locomotor activity rhythm of the nocturnal field mouse M. booduga. These results indicate that complex mechanisms are involved in entrainment of circadian clocks, even in nocturnal rodents, in which PRC, τRC, and dose responses play a significant role.     

Independent associations of exposure to evening light and nocturnal urinary melatonin excretion with diabetes in the elderly

Circadian misalignment between internal and environmental rhythms dysregulates glucose homeostasis because of disruption of the biological clock, and increases risk of diabetes. Although exposure to evening light and decreased melatonin secretion are both associated with the circadian misalignment, it remains unclear whether they are associated with diabetes. In this cross-sectional study on 513 elderly individuals (mean age, 72.7 years), we measured ambulatory light intensity during the 4?h prior to bedtime at 1-min intervals during two consecutive days and overnight urinary 6-sulfatoxymelatonin excretion (UME) along with glucose metabolism. The median average intensity of evening light exposure and UME were 25.4?lux (interquartile range 17.5–37.6) and 6.6?μg (interquartile range 3.9–9.7), respectively. Both log-transformed average intensity of evening light exposure and log-transformed UME were significantly associated with diabetes in a multivariate logistic regression model adjusted for covariates, including gender, body mass index, duration in bed, and night-time light exposure [adjusted odds ratio (OR), 1.72; 95% confidence interval (CI), 1.12–2.64; p?=?0.01; and adjusted OR, 0.66; 95% CI, 0.44–0.97; p?=?0.04; respectively]. An increase in evening light exposure from 17.5 to 37.6?lux (25–75th percentiles) was associated with a 51.2% (95% CI, 8.2–111.4%) increase in prevalent diabetes, and an increase in UME from 3.9 to 9.7?μg (25–75th percentiles) was associated with a 32.0% (95% CI, 1.9–52.8%) decrease in prevalent diabetes. In conclusion, this study in elderly individuals demonstrated that evening light exposure in home settings and UME were significantly and independently associated with diabetes.     

Association between light exposure at night and manic symptoms in bipolar disorder: cross-sectional analysis of the APPLE cohort

ABSTRACT

Previous studies have found that keeping the room dark at night was associated with a decrease in manic symptoms for patients with bipolar disorder (BD). However, the association between light at night of real-life conditions and manic symptoms is unclear. We investigated the association between bedroom light exposure at night and manic symptoms in BD patients. One-hundred and eighty-four outpatients with BD participated in this cross-sectional study. The average light intensity at night during sleep was evaluated using a portable photometer for seven consecutive nights. Manic symptoms were assessed using the Young Mania Rating Scale (YMRS), and scores ≥5 were treated as a “hypomanic state.” The median (interquartile range) YMRS score was 2.0 (0–5.0), and 52 (28.2%) participants were in a hypomanic state. The prevalence of a hypomanic state was significantly higher in the participants with an average light intensity at night exposure of ≥3 lux than in those with <3 lux (36.7% versus 21.9%; P = .02). In multivariable logistic regression analysis adjusted for BD type, depressive symptoms, sleep duration, and daytime physical activity, the odds ratio (OR) for a hypomanic state was significantly higher for the participants with an average light intensity at night exposure of ≥3 lux than for those with <3 lux (OR: 2.15, 95% confidence interval: 1.09–4.22, P = .02). This association remained significant at the cutoff value of YMRS score ≥6 (OR: 2.51, 95% confidence interval: 1.15–5.46; P = .02). The findings of this study indicate bedroom light exposure at night is significantly associated with manic symptoms in BD patients. Although the results of this cross-sectional investigation do not necessarily imply causality, they may serve to inform beneficial nonpharmacological intervention and personalized treatment of BD patients.     

Quantification of plasticity of plant traits in response to light intensity: comparing phenotypes at a common weight

Summary Plasticity of plant traits is commonly quantified by comparing different phenotypes at the same age. In this paper, we present a method in which the effect of resource conditions on plant weight is used as a basis for quantifying the plasticity of individual plant traits. Abutilon theophrasti individuals were grown in, and some transferred between, high and low intensity light conditions, resulting in four phenotypes. Plant traits were found to exhibit different degrees of plasticity, decreasing in this order: height; specific leaf area; allocation to branch roots; allocation to leaf area; number of nodes; allocation to tap roots; allocation to stem; allocation to leaf weight. Under these conditions, individuals of the four phenotypes had very similar heights when compared at the same age, but very different heights when compared at the same plant weight. The latter comparison indicates that light intensity influences height independently of its influence on plant weight. Individuals that were transferred from high to low light had greater allocation that had not been transferred, but individuals of all phenotypes had nearly the same leaf weight allocation when compared at the same plant weight. The latter comparison indicates that light intensity influeces leaf weight allocation mostly by influencing plant weight. In the phenotype resulting from the transfer of plants from low to high light, reproduction was stimulated much less than plant weight and axillary leaf growth, and reproductive allocation was delayed relative to the other three phenotypes. We conclude that when plasticity is measured by comparing phenotypes at the same plant weight, the effects of resources on plant size can be excluded from the quantification.     

Expression of circadian rhythmicity in Djungarian hamsters under constant light: Effects of light intensity and the circadian system's state

Summary Djungarian hamsters (Phodopus sungorus), were exposed to constant light with increasing intensities (20, 60, 350 lux), and wheel running activity was recorded. With increasing light intensity the percentage of hamsters showing a split in their daily activity pattern increased and the free running period was lengthened for both the unsplit and the split state. The fact that the free running period of both states depended on the light intensity together with the observation that the highest incidence of acircadian activity occurred under 350 lux, provoked the idea that the emergence of splitting or acircadian rhythmicity is a direct consequence of the light induced lengthening of the free running period. However, analysis of the data failed to support the idea that emergence of a split or acircadian activity is a threshold phenomenon with respect to the free running period.Due to differences in circadian function some Djungarian hamsters do not exhibit photoinduction following short day exposure. In these individuals splitting also occurred but required exposure to a higher light intensity than in photo-responsive hamsters. This observation is in accordance with the idea that the two phenotypes differ in the interaction of the two component oscillators underlying circadian rhythmicity.Abbreviations LD long day photoperiod - LL constant light - SD short day photoperiod - free running period     

Late circadian phase in adults and children is correlated with use of high color temperature light at home at night

Light is the strongest synchronizer of human circadian rhythms, and exposure to residential light at night reportedly causes a delay of circadian rhythms. The present study was conducted to investigate the association between color temperature of light at home and circadian phase of salivary melatonin in adults and children. Twenty healthy children (mean age: 9.7 year) and 17 of their parents (mean age: 41.9 years) participated in the experiment. Circadian phase assessments were made with dim light melatonin onset (DLMO). There were large individual variations in DLMO both in adults and children. The average DLMO in adults and in children were 21:50 ± 1:12 and 20:55 ± 0:44, respectively. The average illuminance and color temperature of light at eye level were 139.6 ± 82.7 lx and 3862.0 ± 965.6 K, respectively. There were significant correlations between color temperature of light and DLMO in adults (r = 0.735, p < 0.01) and children (r = 0.479, p < 0.05), although no significant correlations were found between illuminance level and DLMO. The results suggest that high color temperature light at home might be a cause of the delay of circadian phase in adults and children.     

Effect of exposure to evening light on sleep initiation in the elderly: A longitudinal analysis for repeated measurements in home settings

Epidemiologic data have demonstrated associations of sleep-onset insomnia with a variety of diseases, including depression, dementia, diabetes and cardiovascular diseases. Sleep initiation is controlled by the suprachiasmatic nucleus of the hypothalamus and endogenous melatonin, both of which are influenced by environmental light. Exposure to evening light is hypothesized to cause circadian phase delay and melatonin suppression before bedtime, resulting in circadian misalignment and sleep-onset insomnia; however, whether exposure to evening light disturbs sleep initiation in home settings remains unclear. In this longitudinal analysis of 192 elderly individuals (mean age: 69.9 years), we measured evening light exposure and sleep-onset latency for 4 days using a wrist actigraph incorporating a light meter and an accelerometer. Mixed-effect linear regression analysis for repeated measurements was used to evaluate the effect of evening light exposure on subsequent sleep-onset latency. The median intensity of evening light exposure and the median sleep-onset latency were 27.3?lux (interquartile range, 17.9–43.4) and 17?min (interquartile range, 7–33), respectively. Univariate models showed significant associations between sleep-onset latency and age, gender, daytime physical activity, in-bed time, day length and average intensity of evening and nighttime light exposures. In a multivariate model, log-transformed average intensity of evening light exposure was significantly associated with log-transformed sleep-onset latency independent of the former potential confounding factors (regression coefficient, 0.133; 95% CI, 0.020–0.247; p?=?0.021). Day length and nighttime light exposure were also significantly associated with log-transformed sleep-onset latency (p?=?0.001 and p?<?0.001, respectively). In conclusion, exposure to evening light in home setting prolongs subsequent sleep-onset latency in the elderly.     

Diel cycle in Hoplosternum littorale (Teleostei): evidence for synchronization of locomotor, air breathing and feeding activity by circadian alternation of light and dark

Diel cycles of voluntary food intake, locomotor activity and air breathing were studied in Hoplosternum littorale (Hancock, 1828), a siluriform fish of the Callichtyidae family living in marshes in northern South America. The study was carried out with six groups of 30 fish each reared in 200-1 tanks equipped with demand-feeders and maintained under artificial light-dark conditions (13.5 L/10.5 D). Feed demand started at dusk and increased throughout the night with a peak between 02.00 and 05.00 hours, during which 3-h period the fish ate 40% of their total daily ration. There was a marked peak in air breathing and locomotion at dusk, followed by an increased feed intake. When the light-dark cycle was advanced by 9 h the observed phenomena were the same, so it is assumed that the light-dark alternation is the synchronizer. In starved fish, locomotor activity and air breathing were increased in the light phase.     

Circadian genes and lithium response in bipolar disorders: associations with PPARGC1A (PGC‐1α) and RORA

Preliminary studies suggest that lithium (Li) response might be associated with some circadian gene polymorphisms, we therefore performed a pharmacogenetic study on the core clock genes in two independent samples suffering from bipolar disorder (BD) and thoroughly characterized for their Li response. Two independent Caucasian samples (165 and 58 bipolar patients) treated with Li were selected from samples recruited in a French multicenter study and assessed for their Li response using the Alda scale. The two samples were genotyped using the Human660 (H660) and OmniExpress (OE) BeadChips and gene‐based association analyses of 22 core clock genes were conducted. In the first sample (H660 chip), the RAR‐related orphan receptor‐a gene (RORA) and the Peroxisome Proliferator‐Activated Receptor Gamma, Coactivator 1 Alpha gene (PPARGC1A or PGC‐1α) were significantly associated with the Li response (empirical P‐value = 0.0015 and 0.04, respectively), and remained significant only for RORA after Bonferroni correction. In the second sample (OE chip), PPARGC1A was significantly associated with the Li response (empirical P‐value = 0.04), and did not remain significant after Bonferroni correction. PPARGC1A is a master regulator of mitochondrial function and a key component of the endogenous clock that stimulates the expression of Bmal1 and Rev‐erb‐alpha through coactivation of RORA. Although the observed associations deserve further replication and investigation, our results suggest genetic associations between Li response and these two close biological partners: PPARGC1A and RORA involved in circadian rhythms and bioenergetics processes in Li response.     

Partitioning of leaf nitrogen with respect to within canopy light exposure and nitrogen availability in peach (Prunus persica)

Summary Relationships between leaf nitrogen content and within canopy light exposure were studied in mature nectarine peach trees (Prunus persica cv. Fantasia) that had received 0, 112, 196, 280 or 364 kg of fertilizer nitrogen per hectare per year for the previous 3 years. The relationships between light saturated leaf CO₂ assimilation rates and leaf nitrogen concentration were also determined on trees in the highest and lowest nitrogen fertilization treatments. The slope of the linear relationship between leaf N content per unit leaf area and light exposure was similar for all nitrogen treatments but the y-intercept of the relationship increased with increasing N status. The slope of the relationship between leaf N content per unit leaf area and light saturated CO₂ assimilation rates was greater for the high N trees than the low N trees, but maximum measured leaf CO₂ assimilation rates were similar for both the high and low N treatments. A diagrammatic model of the partitioning of leaf photosynthetic capacity with respect to leaf light exposure for high and low nitrogen trees suggests that the major influence of increased N availability is an increase in the photosynthetic capacity of partially shaded leaves but not of the maximum capacity of highly exposed leaves.     

Circadian rhythms of melatonin in European starlings exposed to different lighting conditions: relationship with locomotor and feeding rhythms

In passerine birds, the periodic secretion of melatonin by the pineal organ represents an important component of the pacemaker that controls overt circadian functions. The daily phase of low melatonin secretion generally coincides with the phase of intense activity, but the precise relationship between the melatonin and the behavioral rhythms has not been studied. Therefore, we investigated in European starlings (Sturnus vulgaris) (1) the temporal relationship between the circadian plasma melatonin rhythm and the rhythms in locomotor activity and feeding; (2) the persistence of the melatonin rhythm in constant conditions; and (3) the effects of light intensity on synchronized and free-running melatonin and behavioral rhythms. There was a marked rhythm in plasma melatonin with high levels at night and/or the inactive phase of the behavioral cycles in almost all birds. Like the behavioral rhythms, the melatonin rhythm persisted for at least 50 days in constant dim light. In the synchronized state, higher daytime light intensity resulted in more tightly synchronized rhythms and a delayed melatonin peak. While all three rhythms usually assumed a rather constant phase relationship to each other, in one bird the two behavioral rhythms dissociated from each other. In this case, the melatonin rhythm retained the appropriate phase relationship with the feeding rhythm. Accepted: 10 December 1999     

Circadian Rhythm of Gastric Acid Secretion in Active Duodenal Ulcer: Chronobiological Statistical Characteristics and Comparison of Acid Secretory and Plasma Gastrin Patterns with Healthy Subjects and Post-Vagotomy and Pyloroplasty Patients

Twenty-one male patients with active duodenal ulcer underwent hourly 24-hr gastric acid collections under controlled, calorically deprived conditions. The 24-hr hourly acid secretory output for the group displayed a statistically significant (p < 0.001) rhythm, with peak rates occurring during the evening hours and low rates during the early morning hours, by population-mean cosinor statistical analysis. Population-mean cosinor analysis also verified the occurrence of a significant (p=0.034) circadian rhythm in unstimulated acid secretion in a group (N=14) of healthy male subjects similarly studied and reported previously. In contrast, population-mean cosinor analysis confirmed the absence of any detectable circadian rhythm in unstimulated acid secretion in a group (N=17) of post-vagotomy and pyloroplasty patients studied 2-11 years after surgery. Population-mean cosinor analysis of 4-hr plasma gastrin determinations, obtained in all groups during the 24-hr gastric acid collection, revealed an absence of any detectable circadian rhythm in plasma gastrin. This latter finding is compatible with the interpretation that the circadian rhythm of unstimulated gastric acid secretion, observed in the clinically healthy and active ulcer groups, is unrelated to changes in plasma gastrin levels. The employment of quantitative chronobiological inferential statistical techniques is important to the analysis of any time-dependent measurement in gastrointestinal function, of which gastric acidity is one example.     

Changes in the circadian flight activity of the mosquito Anopheles stephensi associated with insemination, blood-feeding, oviposition and nocturnal light intensity

Abstract. The circadian activity patterns of Anopheles stephensi Liston were examined before and after mating and throughout the gonotrophic cycle. In LD 12:12h, males and virgin females are active at dusk. After insemination, females are active at dusk and also for short bursts during much of the night. After blood-feeding, inseminated females are inactive for two nights. On becoming gravid, these females become highly active at dusk and, to a lesser extent, are also active later in the night. In contrast, blood-feeding and egg maturation have minimal effects on the activity pattern of virgin females, who continue to fly only during dusk periods, i.e. virgins continue with the activity pattern which would most likely lead to mating encounters. After oviposition, parous females resume the activity pattern characteristic of inseminated nulliparous females. In a light regime which simulates moonlit nights and normal days, inseminated females are more active overall and flight-burst durations are much longer than in LD 12:12h.     

Association between coffee,tobacco, and alcohol daily consumption and sleep/wake cycle: an actigraphy study in euthymic patients with bipolar disorders

ABSTRACT

Individuals with bipolar disorder (BD) have higher than average rates of coffee, tobacco and alcohol use. These substances may have deleterious effects on sleep quality and quantity, which may destabilize sleep/wake cycles and negatively impact the clinical course and prognosis of BD. The use of these substances may also be perceived as a self-medication attempt, for example, to induce sleep or to increase vigilance during the day. The objective of the current study was to investigate associations between the self-reported daily use of coffee, tobacco, and alcohol, and objective measures of sleep and activity patterns in adult individuals with BD. A sample of 147 euthymic individuals with BD were assessed for daily coffee, tobacco and alcohol consumption and 21 days of actigraphy monitoring. Actigraphic measures of sleep quantity and daytime activity were compared between groups classified as coffee+/coffee-, tobacco+/tobacco- and alcohol+/alcohol-, defined according to their current daily use. Then, we examined potential correlations between sleep/wake cycle parameters and the amount of daily consumption of each substance. Multivariable analyses identified associations between the use of coffee, tobacco, and alcohol and several sleep and activity parameters, such as between coffee, alcohol, and the relative amplitude of activity (respectively, p = .003 and p = .005), between alcohol and M10 onset (onset time of the 10 most active hours during the 24-h cycle) (p = .003), and between coffee and sleep duration (p = .047). This study supports the hypothesis that there is a relationship, whose direction would be bidirectional, between the daily use of these substances and the sleep/wake cycle in euthymic individuals with BD. These preliminary results require replications in other retrospective and prospective samples. They may have a clinical impact on psycho-education strategies to be proposed to individuals with BD.     

Unmarked individuals in mark–recapture studies: Comparisons of marked and unmarked southern elephant seals at Marion Island

The presence of unmarked individuals is common in mark–recapture study populations; however, their origin and significance in terms of population dynamics remain poorly understood. At Marion Island, southern Indian Ocean, where virtually all southern elephant seal Mirounga leonina pups born annually (1983–2008) were marked in a long‐term mark–resight study, large numbers of unmarked seals occur. Unmarked seals originate either from marker (tag) loss or from immigration. We aimed to identify patterns in the occurrence of marked and unmarked individuals that will allude to the possible origin and significance of the untagged component of the population, predicting that tag loss will add untagged seals to mainly adult age categories whereas migrating untagged individuals will be mostly juveniles. We fitted a generalized linear model using the factors month, year and age‐class to explain the relative abundance of untagged seals (tag ratio) from 1997 to 2009. Site usage of untagged seals relative to tagged seals was assessed using a binomial test. Untagged seals, predominantly juveniles, were present in the highest proportions relative to tagged seals during the winter haulout (tagged seals/total seals less than 0.3) and the lowest proportion (approximately 0.5) during the female breeding haulout, increasing in relative abundance from 1997 to 2009. Untagged seals were distributed evenly across suitable haulout sites while tagged seals displayed high local site fidelity and occurred in greater numbers at or near large breeding beaches. Untagged seals are considered to be mostly migrant seals that disperse from other islands within the southern Indian Ocean and haul out at Marion Island during non‐breeding haulouts in particular. Some of these seals immigrate to the breeding population, which can be a key component of the local population dynamics. We emphasize the need for mark–recapture studies to evaluate the role of the unmarked component of a population, thereby inducing a more confident estimation of demographic parameters from the marked sample.     

Blooming of cyanobacteria in turbulent water with steep light gradients: The effect of intermittent light and dark periods on the oxygen evolution capacity of Synechocystis sp. PCC 6803

Abstract: The influence of intermittent high-light dosage on Synechocystis sp. PCC 6803 with respect to oxygen evolution capacity, fluorescence yield and carotenoid pigment pattern was investigated, using high-light- and low-light-adapted cultures. The results showed that this cyanobacterium was able to survive high light stress for a full day if this stress was applied on and off with intermittently presented recovery periods in darkness. Enhanced respiratory activity in the high-light adapted cells was detected and this may be an important factor in preventing photodamage under high light stress. Cyanobacterial photosynthetic and respiratory electron transfer pathways are both present within the same membrane, and share common electron carriers. The role of respiratory activity in preventing overexcitation of photosystem 2 is discussed with regard to cyanobacterial ecology.