Temporal patterns in the intertidal faunal community at the mouth of a tropical estuary

The use of intertidal sandy beaches by fish and macrocrustaceans was studied at different temporal scales at the mouth of a tropical estuary. Samples were taken along the lunar and diel cycles in the late dry and rainy seasons. Fish assemblage (number of species, density and biomass), crustaceans and wrack biomass, showed significant interactions among all studied factors, and the combination of moon phase and diel cycle, resulting in different patterns of environmental variables (depth, water temperature and dissolved oxygen), affected habitat use by the different species. Variances in faunal community were detected between seasons, stimulated by salinity fluctuations from freshwater input during the rainy season. These differences suggest an important cycling of habitats and an increase in connectivity between adjacent habitats (estuary and coastal waters). Moreover, the results showed that this intertidal sandy beach also provides an alternative nursery and protected shallow‐water area for the initial development phase of many marine and estuarine species. In addition, this intertidal habitat plays an important role in the maintenance of the ecological functioning of the estuarine–coastal ecosystem continuum.     

Perception and possible utilization of moonlight intensity for reproductive activities in a lunar-synchronized spawner, the golden rabbitfish

Rabbitfishes are known to spawn synchronously around the species-specific lunar phase. It is considered that they perceive and utilize cues from the moon in order to be synchronized gonadal development and spawning with the lunar cycle. Using the golden rabbitfish, Siganus guttatus, which spawns synchronously around the first quarter moon during the reproductive season, we measured the fluctuation of melatonin levels and examined the response of the fish to moonlight intensity. Daily fluctuation of melatonin concentration in the blood of golden rabbitfish showed low levels during daytime and high levels during night-time, suggesting that melatonin functions in the perception and utilization of photoperiod. Plasma melatonin concentration at the new moon was higher than that at the full moon. When the fish were exposed to moonlight at midnight of the both moon phases, the melatonin concentrations decreased to the control levels. These results show that the fish possibly perceive moonlight intensity and plasma melatonin fluctuates according to 'lightness' at a point of night. At the first spawning period (experiment was started one month before the spawning), the fish reared under natural conditions spawned at the expected spawning dates, whereas the fish reared under the constant darkness and lightness of night did not spawn. At the second spawning period (experiment was started 2 weeks before the spawning), the fish reared under the conditions of natural and constant darkness of night spawned but not that of constant lightness of night. It is possible that night conditions are related to synchronous gonadal development and spawning in the golden rabbitfish.     

Temporal activity patterns of North China leopards and their prey in response to moonlight and habitat factors

The nocturnal activities of predators and prey are influenced by several factors, including physiological adaptations, habitat quality and, we suspect, corresponds to changes in brightness of moonlight according to moon phase. In this study, we used a dataset from 102 camera traps to explore which factors are related to the activity pattern of North China leopards (Panthera pardus japonensis) in Shanxi Tieqiaoshan Provincial Nature Reserve (TPNR), China. We found that nocturnal activities of leopards were irregular during four different lunar phases, and while not strictly lunar philic or lunar phobic, their temporal activity was highest during the brighter moon phases (especially the last quarter) and lower during the new moon phase. On the contrary, roe deer (Capreolus pygargus) exhibited lunar philic activity, while wild boar (Sus scrofa) and tolai hare (Lepus tolai) were evidently lunar phobic, with high and low temporal activity during the full moon, respectively. In terms of temporal overlap, there was positive overlap between leopards and their prey species, including roe deer and tolai hare, while leopard activity did not dip to the same low level of wild boar during the full moon phase. Human activities also more influenced the temporal activity of leopards and wild boar than other species investigated. Generally, our results suggested that besides moonlight risk index (MRI), cloud cover and season have diverse effects on leopard and prey nocturnal activity. Finally, distinct daytime and nighttime habitats were identified, with leopards, wild boar, and tolai hare all using lower elevations at night and higher elevations during the day, while leopards and roe deer were closer to secondary roads during the day than at night.     

Reproductive periodicity of the sparid,Acanthopagrus pacificus,on a hierarchy of temporal scales

The reproductive periodicity of the sparid, Acanthopagrus pacificus, over four temporal scales is described. Acanthopagrus pacificus had a short spawning season between June and September, and within this, a peak reproductive period from July to early September. During the peak period there were several spawning peaks corresponding to a lunar periodicity, with intense reproductive activity on new and full moons that peaked during the period of the full moon when the tidal range was greatest. At the smallest temporal scale, spawning occurred at night on ebb tides. Because this study draws on data collected in 1991 and 1995, it provides a useful baseline against which to judge future changes in reproductive periodicity.     

Variability in the numbers of post-settlement King George whiting (Sillaginidae: Sillaginodes punctata, Cuvier) in relation to predation, habitat complexity and artificial cage structure

The importance of predation by fish in altering abundances of juvenile King George whiting (Sillaginodes punctata) was examined at multiple locations in Port Phillip Bay, Australia, by manipulating the numbers of piscivorous fish in unvegetated sand and seagrass habitats using cages. Additional information regarding the local abundances of, and habitat use by, the most common piscivorous fish, Western Australian salmon (Arripidae: Arripis truttacea, Cuvier), was gathered using netting surveys and underwater video. Regardless of habitat, abundances of S. punctata were similar in partial cages and uncaged areas. In unvegetated sand, S. punctata were more abundant inside cages than partial cages or uncaged areas. In seagrass, there was no difference in the numbers of S. punctata between caging treatments. Patterns in abundances of S. punctata between cage treatments in each habitat were consistent between sites, but the relative difference in the abundances of S. punctata between habitats was site specific. Abundances of A. truttacea varied significantly between sites, and they consumed a variety of epibenthic fishes including atherinids, clupeids, gobiids, syngnathids and pleuronectids. At one site in Port Phillip Bay (Blairgowrie), A. truttacea occurred more commonly in patches of unvegetated sand than seagrass. Over unvegetated sand, abundances of A. truttacea varied little between partial cages and uncaged areas. The numbers of S. punctata varied between caging treatments and habitats in a manner that was consistent with a model whereby seagrass interferes with foraging by predatory fish and provides juvenile fish with a refuge from predation. The almost total absence of A. truttacea in seagrass habitats and the lack of S. punctata in their diets implies, however, that patterns in S. punctata in seagrass/unvegetated sand mosaics are driven by processes other than direct predation.     

Contrasting patterns of amphipod dispersion in a seagrass meadow between day and night: consistency through a lunar cycle

Changes in light intensity, typically over the course of a day, affect the dispersion of aquatic organisms at short temporal scales. Amphipods, for example, have strong behavioural responses to light conditions. In this study, we used amphipod assemblages inhabiting a Cymodocea nodosa seagrass meadow on the east coast of Gran Canaria Island (eastern Atlantic) to test whether short-term dispersion of seagrass-associated amphipods differed between day and night, testing the consistency throughout an entire lunar cycle. Replicated artificial seagrass units were deployed, and subsequently retrieved, during the day (from 8:00 am to 18:00 pm) and the night (from 18:00 pm to 8:00 am) on three consecutive days within each of the four moon phases of a complete lunar cycle. We collected 13,467 amphipods corresponding to 32 species and 17 families. Significantly larger abundances of amphipods were collected during the night through the entire moon cycle. The total abundance of amphipods was also affected by the moon phases; under full moon, larger abundances of amphipods dispersed into the artificial seagrass units followed by the third quarter, the new moon and the first quarter. The species density of amphipods per unit followed the same pattern. In conclusion, the short-term dispersion of amphipods living in a seagrass meadow was considerably greater during the night than the day, while dispersion of amphipods was more intense under full moon.     

Apparent semi-lunar spawning rhythmicity in a brackish cardinalfish

The purpose of the present study was to examine the lunar-related spawning rhythmicity of the amboina cardinalfish Apogon amboinensis, which is a euryhaline species inhabiting mangrove creeks in the Indo-Pacific area. During the reproductive season, the gonado-somatic index increased towards and peaked within a week of the first and last quarter moon. Histological observations of the ovaries also showed development of yolk-laden oocytes towards the first and last quarter moon; postovulatory follicles, an indicator of spawning, appeared around these lunar phases. Fish with immature oocytes in the ovary were also collected in the same lunar phases, suggesting that at least two fish populations with different oocyte development stages exist at any given time. The levels of two steroid hormones secreted from the ovarian pieces into a culture medium with human chorionic gonadotropin were measured using enzyme-linked immunosorbent assay (ELISA). The level of oestradiol-17β increased around the new and full moon periods. On the other hand, 17α,20β-dihydroxy-4-pregnen-3-one levels increased around the first and last quarter moon, suggesting that the fish are actively undergoing vitellogenesis and final oocyte maturation around the respective lunar phase. These results suggest that with the 1 month ovarian development process, A . amboinensis exhibits a semi-lunar spawning pattern with peaks around the first and last quarter moon. When A . amboinensis were reared under laboratory conditions without the tidal stimuli, mouth-brooding was initiated in 13 of 20 males within a week of the first and last quarter moon. The possibility of a lunar-related endogenous rhythm in A . amboinensis is discussed.     

Linkages between seagrass,mangrove and saltmarsh as fish habitat in the Botany Bay estuary,New South Wales

Shallow-water vegetated estuarine habitats, notably seagrass, mangrove and saltmarsh, are known to be important habitats for many species of small or juvenile fish in temperate Australia. However, the movement of fish between these habitats is poorly understood, and yet critical to the management of the estuarine fisheries resource. We installed a series of buoyant pop nets in adjacent stands of seagrass, mangrove and saltmarsh in order to determine how relative abundance of fishes varied through lunar cycles. Nets were released in all habitats at the peak of the monthly spring tide for 12 months, and in the seagrass habitat at the peak of the neap tide also. The assemblage of fish in each habitat differed during the spring tides. The seagrass assemblage differed between spring and neap tide, with the neap tide assemblage showing greater abundances of fish, particularly those species which visited the adjacent habitats when inundated during spring tides. The result supports the hypothesis that fish move from the seagrass to the adjacent mangrove and saltmarsh during spring tides, taking advantage of high abundances of zooplankton, and use seagrass as a refuge during lower tides. The restoration and preservation of mangrove and saltmarsh utility as fish habitat may in some situations be linked to the proximity of available seagrass.     

Temporal scales of variation in settlement and recruitment of the mussel Perna perna (Linnaeus, 1758)

Population dynamics of many intertidal organisms are strongly affected by the abundance and distribution of larvae arriving on the shore. In particular, not only absolute numbers of settlers but also the degree of synchronisation of settlement can have a strong influence on whether density-dependent or density-independent processes shape adult shape populations. Temporal variation in rates of settlement and recruitment of the mussel Perna perna on the south coast of South Africa was investigated using a nested spatial design at different temporal scales. Variability in settlement at spring tides was examined at two temporal scales: lunar (to investigate the effect of state of the moon on settlement) and tidal (to investigate the influence of state of the tide on mussel settlement). Recruitment over neap tides was examined at one temporal scale, fortnight (to investigate the effect of date on mussel recruitment).Strong temporal variation was evident for both settlement and recruitment, but not at all time scales. Distinct peaks of settler/recruit abundance were observed during the lunar and neap tide studies. Recruitment intensity differed over the course of the year, and pulsing of recruitment was generally synchronised among locations. However, the strength of pulsing differed dramatically among locations, giving a significant interaction between fortnight and location. The finest temporal scale, investigated in the tidal study, did not reveal a significant effect of the state of the tide on settlement. The state of the moon (new or full) was not significant as a main factor (p = 0.052), although generally more settlers arrived on the shore during new moon. Phase of the moon appeared to have an effect on settler abundances, but only when and where densities were high.     

Effects of light dynamics on coral spawning synchrony

Synchrony of spawning in many hermatypic corals, typically a few nights after the full moon, is putatively dependent on solar and lunar light cycles in conjunction with other possible cues such as tides and temperature. We analyze here the contributions of separate components of light dynamics, because the effects of twilight and lunar skylight on coral spawning synchrony have previously been conflated and the alternative hypothesis that these components have differential contributions as proximate cues has not been tested. Moonlight-dependent changes in spectra during twilight, rates of decreasing twilight intensities, and changes in lunar photoperiod were experimentally decoupled using programmed light-emitting diodes and compared for their separate effects on spawning synchrony in Acropora humilis. Effects on synchrony under the control of synthetic lunar cues were greatest in response to changes in lunar photoperiod; changes in light intensities and spectra had lesser influence. No significant differences among treatment responses were found at the circa-diel time scale. We conclude that spawning synchrony on a particular lunar night and specific time of night is a threshold response to differential periods of darkness after twilight that is primarily influenced by lunar photoperiod and secondarily by discrete optical components of early nocturnal illumination.     

Moonlighting? - Consequences of lunar cues on anuran reproductive activity

While the influence of environmental variables, particularly temperature and rainfall, on the breeding behavior of amphibians is widely recognized, relatively few studies have addressed how the moon affects amphibian behavior. Yet, the lunar cycle provides several rhythmic temporal cues that animals could use to time important group events such as spawning, and the substantial changes in light levels associated with the different moon phases may also affect the behavior of nocturnal frogs. Using seven years of field observation data, we tested for lunar effects on the reproductive activity of male and female Eastern Gray Treefrogs (Hyla versicolor). We found that chorusing and breeding activity was statistically more likely to occur around the first quarter of the moon and during intermediately bright nights, but that reproductive activity also occurred during various other times during the lunar cycle. We discuss these findings in relation to the two main hypotheses of lunar effects on animals: predator avoidance and temporal synchronization of breeding.     

Quantifying movement of the tropical Australian cubozoan <Emphasis Type="Italic">Chironex fleckeri</Emphasis> using acoustic telemetry

Cubomedusae are considered to have superior swimming abilities compared to other pelagic cnidarians, yet many of the theories describing such behaviours are based on anecdotal evidence, sting records or opportunistic sightings, rather than quantitative data. Acoustic telemetry was used to document the movements of adult Chironex fleckeri medusae within both coastal and estuarine habitats. The rate at which tagged medusae moved was influenced by an interaction between time period (day or night) and habitat (coastal or estuarine), with rates of travel being relatively similar during the day and night within the coastal habitat, but significantly greater at night than during the day within the estuarine habitat. Medusae in coastal habitats travelled at similar rates throughout all tidal states while estuarine medusae travelled at significantly faster rates towards the middle of the tide than at the low and high ebbs. Such movements occurred with, and independent of, tidally generated currents, but at increased current speeds, medusae tended to travel with the current. Data are also presented that show that large medusae may move from coastal to estuarine habitats. Guest editors: K. A. Pitt & J. E. Purcell Jellyfish Blooms: Causes, Consequences, and Recent Advances     

Spawning Site Selection and Contingent Behavior in Common Snook,Centropomus undecimalis

Reproductive behavior affects spatial population structure and our ability to manage for sustainability in marine and diadromous fishes. In this study, we used fishery independent capture-based sampling to evaluate where Common Snook occurred in Tampa Bay and if it changed with spawning season, and passive acoustic telemetry to assess fine scale behavior at an inlet spawning site (2007–2009). Snook concentrated in three areas during the spawning season only one of which fell within the expected spawning habitat. Although in lower numbers, they remained in these areas throughout the winter months. Acoustically-tagged snook (n = 31) showed two seasonal patterns at the spawning site: Most fish occurred during the spawning season but several fish displayed more extended residency, supporting the capture-based findings that Common Snook exhibit facultative catadromy. Spawning site selection for iteroparous, multiple-batch spawning fishes occurs at the lifetime, annual, or intra-annual temporal scales. In this study we show colonization of a new spawning site, indicating that lifetime spawning site fidelity of Common Snook is not fixed at this fine spatial scale. However, individuals did exhibit annual and intra-seasonal spawning site fidelity to this new site over the three years studied. The number of fish at the spawning site increased in June and July (peak spawning months) and on new and full lunar phases indicating within population variability in spawning and movement patterns. Intra-seasonal patterns of detection also differed significantly with sex. Common Snook exhibited divergent migration tactics and habitat use at the annual and estuarine scales, with contingents using different overwintering habitat. Migration tactics also varied at the spawning site at the intra-seasonal scale and with sex. These results have important implications for understanding how reproductive behavior affects spatio-temporal patterns of fish abundance and their resilience to disturbance events and fishing pressure.     

Lunar phase-dependent expression of cryptochrome and a photoperiodic mechanism for lunar phase-recognition in a reef fish, goldlined spinefoot

Lunar cycle-associated physiology has been found in a wide variety of organisms. Recent study has revealed that mRNA levels of Cryptochrome (Cry), one of the circadian clock genes, were significantly higher on a full moon night than on a new moon night in coral, implying the involvement of a photoreception system in the lunar-synchronized spawning. To better establish the generalities surrounding such a mechanism and explore the underlying molecular mechanism, we focused on the relationship between lunar phase, Cry gene expression, and the spawning behavior in a lunar-synchronized spawner, the goldlined spinefoot (Siganus guttatus), and we identified two kinds of Cry genes in this animal. Their mRNA levels showed lunar cycle-dependent expression in the medial part of the brain (mesencephalon and diencephalon) peaking at the first quarter moon. Since this lunar phase coincided with the reproductive phase of the goldlined spinefoot, Cry gene expression was considered a state variable in the lunar phase recognition system. Based on the expression profiles of SgCrys together with the moonlight's pattern of timing and duration during its nightly lunar cycle, we have further speculated on a model of lunar phase recognition for reproductive control in the goldlined spinefoot, which integrates both moonlight and circadian signals in a manner similar to photoperiodic response.     

马鞍列岛多种生境中鱼类群聚的昼夜变化

为了解岛礁水域鱼类群聚的昼夜变化特征,以便更全面地设计采样方法和掌握采样的时间尺度,于2009年9月对马鞍列岛7种生境进行了共计24网次的刺网昼夜采样,结合排序和聚类方法,从种类组成、相对生物量和丰度、种类丰富度、多样性和相似性等方面对研究海域鱼类群聚特征的昼夜变化作了探讨.在采获的55种鱼类中,昼夜出现的分别为41和46种,数量差别不大,但其昼夜组成却随栖息水层的变化而不同,底层鱼类更趋向于夜间在硬相生境集群活动;近底层鱼类的昼夜集群随生境变化而变化,在同一生境中既有偏向白天也有趋向夜间的;中上层鱼类更多地出现在白天的人工生境(AH).AH白天的丰度渔获率显著大于晚上,而天然生境(NH)昼夜差别不大;生物量渔获率无论NH还是AH皆无显著昼夜差异.具体到种类,仅有小黄鱼Larimichthys polyactis和赤鼻棱鳗Thryssa kammalensis等少数种类的数量在AH有显著的昼夜差别,其他多数种类虽然昼夜的出现率大多有别,但渔获率昼夜差异皆不明显.多样性差异更多的表现在不同生境之间,而同一生境的昼夜差异往往不甚显著.各个生境中鱼类的昼夜种类交替现象非常明显,形成了以褐菖(鲐)Sebastiscus marmoratus和鳗鲇Plotosus anguillaris为代表的夜间优势类群为主的硬相生境群聚格局、以丝背细鳞鲀Stephanolepis cirrhifer和细刺鱼Microcanthus strigatus为代表的白天优势类群为主的硬相生境群聚格局以及缺乏底层优势类群、以石首鱼科鱼类为代表的近底层鱼类为绝对优势类群的软相生境群聚格局.因此,采用被动性渔具在近岸典型生境进行鱼类等相关生物调查时,应使采样时间覆盖昼夜两个时段,且至少保证24h.     

Biological availability and humic properties of dissolved organic carbon in Lake Balaton (Hungary)

The nursery role of the Mondego estuary for marine fish species was studied between June 2003 and May 2004. The spatial and temporal distribution and abundance patterns of 0-group Dicentrarchus labrax (Linnaeus, 1758), Platichthys flesus (Linnaeus, 1758) and Solea solea (Linnaeus, 1758) were analyzed based on monthly sampling surveys in five stations along the estuarine gradient. Fishing took place during the night at low water of spring tides, using a 2 m beam trawl. The spatial patterns of estuarine colonization were different according to species. D. labrax showed a wider distribution, but the main nursery ground was the same as for S. solea. Highest densities of S. solea juveniles were found in oligohaline areas, with muddy bottoms and high benthic invertebrates availability, while P. flesus occurred mainly in the sandy uppermost areas. D. labrax was found in both these areas. Fish abundance in the estuary mainly reflected seasonal changes.     

Effect of simulated macroalgae on the fish assemblage associated with a temperate reef system

Increased habitat complexity is supposed to promote increased diversity, abundance and biomass. This study tested the effect of the macroalgal cover on temperate reef fishes by mimicking macroalgae on artificial reefs in NW Sicily (Mediterranean Sea). Macroalgal cover affected reef fishes in different ways and independently of intrinsic temporal trends. The fish assemblages of manipulated and control artificial reef units differed in the relative abundances of the associated species, but little in species composition. In line with studies in seagrass habitats, fishes were most abundant in reefs covered by artificial macroalgae. Three species (Boops boops, Serranus scriba and Symphodus ocellatus) exhibited consistently greater abundance on vegetated reef units than on control reef units. The total number of species and the abundance of three particular species (S. scriba, S. ocellatus and Thalassoma pavo) displayed temporal trends which were independent on short and large temporal scales. Only fish total biomass and one species (Spicara flexuosa) displayed strong effects of interaction among the experimental factors. Mechanisms to explain these findings are discussed from observational evidence on habitat use and interactions among multiple species. This study highlights that manipulative experiments involving repeated sampling of fish in artificial habitats appear to be a valid approach to study fish-habitat relationships in fluctuating environments. It is also concluded that macroalgae mimics may serve as a tool for restoring lost marine vegetated habitats when current human-induced conditions prevent the recovery of pristine macroalgal stands.     

Community Structure of Coastal Fishes in Relation to Heavily Impacted Human Modified Habitats

Diversity and community structure of coastal fishes were compared between reforested mangrove and reclaimed sandy habitats at Pasir Ris, in the eastern part of Singapore. Both habitats supported a total of 91 species, but a single species, Ambassis kopsii dominated in abundance. Mean fish density was significantly higher at the reclaimed sandy shore than the reforested mangrove, but the reforested mangrove habitat yielded higher diversity. Apart from A. kopsii, abundant species in the mangroves included Ambassis interrupta, Thryssa hamiltonii, Acentrogobius sp., Scatophagus argus and Arius sagor. Anodontostoma chacunda, Acentrogobius sp., Leiognathus decorus, Sillago sihama and Stolephorus sp. were abundant in the reclaimed sandy habitat. Both habitats exhibited a higher mean density and average species richness during high tide. Several species from the family Gobiidae dominated the catch during low tide while pelagic fishes were most abundant during high tide. Diel variation showed significantly higher density during the day than at night, a result that contrasts to similar studies elsewhere. However, species richness showed no significant variation between day and night catches. Interaction between combined factors of time of the day and tidal height on fish density and average species richness was significantly different. The results indicated both habitat types to be important fish nurseries.     

Ungulate: vehicle collision rates are associated with the phase of the moon

The phase of the moon can affect activity patterns of nocturnal animals, and may also affect visibility for motorists. However, surprisingly little is known about whether the risk of a wildlife-vehicle collision (WVC) is associated with lunar phase. We investigated the relationship between frequency of WVC at night and lunar phase for four large ungulate species that account for a high proportion of serious WVC along roads in agricultural and forested landscapes of two continents: wild boar Sus scrofa, roe deer Capreolus capreolus, and red deer Cervus elaphus in Castile and Leon, Spain, and white-tailed deer Odocoileus virginianus in New York State, USA. Three of the four species most frequently collided with vehicles at night during the full moon phase of the lunar cycle; this pattern was evident throughout the year but was stronger during some months. For roe deer, the species for which WVC was most closely associated with the lunar cycle, the frequency of WVC was 71.3% greater during the full than new moon period. Our results indicate that rates of ungulate WVC at night cycle on a period of a lunar month, which has implications for traffic safety planning and for motor vehicle collision emergency response preparation.