Migration patterns of juvenile Lutjanus argentimaculatus in a mangrove estuary in Trang province, Thailand, as revealed by ultrasonic telemetry

Migrational patterns of mangrove jack Lutjanus argentimaculatus were studied in a mangrove estuary in Trang province, Thailand, using ultrasonic telemetry. Ultrasonic coded transmitters were surgically implanted in 18 fish and 16 of them were subsequently monitored by nine fixed receivers installed along Sikao Creek estuary in June and November 2006. Due to technical limitations all of the individuals were released in the middle of the creek. Their movements were monitored for a period of up to 1 month, the data being used to describe short term migration of juvenile Lutjanus argentimaculatus in the creek and to find possible environmental cues for the observed movements. All of the individuals showed a tide related movement pattern, suggesting foraging in the small mangrove channels and/or mangrove forest during high tides. 50% of the fish left the study area for the open coast area within a short time following release, indicating that a part of juvenile L. argentimaculatus may move in between estuarine habitats instead of being site attached. As the fish were reared in fish cages for a certain period of time before the study this behavior could partly be explained by the time spent in captivity. It was found that L. argentimaculatus showed higher movement activity during night high tides possibly explained by an increased availability of the sough after food items.     

Fluctuations in the reproductive condition of Cassidula auris-felis, a Malayan mangrove ellobiid snail (Pulmonata: Gastropoda)

Cassidula auris-felis Brug, occurs abundantly on flat, mangrove mud on the west coast of Malaya at a level within three feet of the highest spring tides. Ovotestesof only very few snails lacked developing male gametes but oocytes were often very uncommon, becoming abundant at irregular intervals. Abundant oocytes were found in large proportions of the population after periods of more than eight days without tidal wetting. Abundant oocytes were not found after periods when the mud was left exposed for periods of seven days or less. Statistically, proportions of "predominantly female" snails are shown to be correlated with the number of days without tidal wetting in a complete period of continuous exposure prior to collection. In addition, rather more snails bore abundant oocytes in the lunar "weeks" following new and full moon than in "weeks" following half moons. Conditions leading to abundant oocytes also appear to promote copulation in adults and commencement of gametogenesis in young snails.     

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.     

The climbing behaviour of Cerithidea anticipata (Mollusca: Gastropoda): The roles of physical and biological factors

Abstract Many molluscs in tidal wetlands climb trees as the tide rises, a behaviour usually assumed to be a means of avoiding subtidal predators. Some species are more active during neap tides, when the access of subtidal predators to the forest is limited, but rest on trees during spring tides. Cerithidea anticipata, which inhabits the mangrove forests around Darwin Harbour (Northern Territory, Australia), displayed almost exactly the opposite pattern. This species climbed higher, and was less active, during neap tides that did not flood the forest than during spring tides. In experiments with tethered snails, individuals prevented from climbing died during neap tides, apparently from physiological stress. Further, individuals resting on trees around clearings, usually selected shaded sites. These results suggest that the major reason C. anticipata climbed was to avoid physiological stress during neap tides, not subtidal predators during spring tides. There was some evidence of predation under the canopy, but the rate was relatively low and the species responsible appeared to be resident in the forest.     

Tidal migration and patterns in feeding of the four-eyed fish Anableps anableps L. in a north Brazilian mangrove

The tidal migration, temporal and spatial patterns in feeding of the surface-swimming four-eyed fish Anableps anableps (Anablepidae) were studied in a macrotidal mangrove area in north Brazil to exemplify the ecology of a tropical intertidal fish. Visual censuses in the main channel showed that abundances were high at low water (LW) and low at high water (HW). Anableps anableps entered the intertidal creeks with the first flood rise. They fed in the inundated mangrove at HW and returned gradually after the ebb current maximum to concentrate again in the subtidal parts of the main channel at LW. This pattern occurred at neap, mid and spring tides throughout the year. The tidal migration was triggered by water level, not by time. In the study area the diet of A. anableps caught with block nets was dominated by intertidal red algae ( Catanella sp.). Other important food items were Insecta and Grapsidae. The combination of high inundation and daylight (spring tide-day) provided the best foraging conditions, probably emphasizing the importance of the above-water eye. Darkness and low inundation was linked to poorest foraging conditions (neap tide-night). The quantity of food consumed by A. anableps was clearly influenced by the factors tide, time of day and creek location, but not by size and sex. The qualitative composition of the diet was not influenced by any of the factors, except for mud, which was only ingested at neap tides. The temporal and spatial variability in food consumption suggests that food web modelling in macrotidal areas may lead to misinterpretations of the overall systems dynamics if the spring and neap tide alternation and the diurnal cycle are not considered.     

Recruitment,growth, and vertical distribution of the endangered mud snail Cerithidea rhizophorarum A. Adams, 1855: implications for its conservation

Some fundamental natural-history traits of the endangered mud snail Cerithidea rhizophorarum were investigated for three years in an open, bare, sandy tidal flat located on the east of Shikoku Island in southwestern Japan. Our study demonstrated a highly aggregated distribution of younger snails and complicated differences in vertical migration patterns between younger and older snails that might have prevented comprehensive understanding of the precise demography of C. rhizophorarum in previous studies. From late summer, juveniles of the first-year cohorts appeared patchily at 12–16 cm lower tidal heights than snails of the oldest cohorts and reached 5.0–7.5 mm in mean shell length by the first mid-autumn. In the second year, juveniles gradually moved upward and appeared at higher tidal heights. The second-year cohorts reached 15.6–19.1 mm in mean shell length by the end of the second autumn and converged into the oldest cohorts during the third year or later. Our results suggest that C. rhizophorarum matures sexually and starts reproduction from the fourth summer at the earliest. On the other hand, older snails showed a similar seasonal migration pattern every year—downward movement in summer and upward movement in autumn—probably associated with their reproductive activity and/or a seasonal change in the maximum tidal height. For conservation of C. rhizophorarum, it is very important to preserve both the higher area as a main habitat for older snails and the lower tidal flat as the nursery ground.     

Activity patterns, feeding and burrowing behaviour of the crab Ucides cordatus (Ucididae) in a high intertidal mangrove forest in North Brazil

Activity patterns, feeding and burrowing behaviour of the economically important semi-terrestrial mangrove crab Ucides cordatus (Ucididae, L. 1763) was studied in a high intertidal Rhizophora mangle forest stand in Bragança, North Brazil. Video observations in the rainy and dry season were conducted over 24 h cycles at different lunar phases to investigate the behaviour of these litter-feeding crabs outside their burrows. During the rainy season, crabs stayed inside their burrows for 79% and 92% of the time during day and night, respectively. Time spent for feeding, burrowing and other activities outside their burrows was significantly longer during the day with 9.9% (night: 1.7%) and at waning and waxing moon with 9% (full and new moon: 0.9%). At neap tides (no tidal inundation) foraging and feeding activities outside burrows were clearly light-dependent, increasing at dawn and decreasing at dusk. Highest activities during daytime relate to the visual localisation of food. During the dry season, crabs spent less time inside burrows at neap tides than during the rainy season (80% and 91%, respectively). However, time spent for feeding activities was similar during both seasons. During almost all observation periods crabs collected leaf litter, but rarely fed on it outside burrows. At neap tides nearly all available litter was collected, suggesting that the U. cordatus population is litter-limited during these times. At spring tides (regular tidal inundation) the surface activity of U. cordatus was tide-dependent. Crabs closed their burrow entrances 2-3 h before flooding and re-emerged as soon as the tide retreated. During the day, burrow maintenance was the second most frequent behaviour after feeding. Agonistic interactions were regularly observed and were mainly related to burrow defence. The mean foraging radius of the crabs was only 19 cm (max: 1 m) underneath high Rhizophora mangle trees where crab densities were high. The results point to a high competition for burrows and show that U. cordatus is territorial. It is concluded that several exogenous factors, in particular light, leaf litter availability, flooding of burrows and the presence of conspecifics are important in controlling the crabs' activity patterns.     

Effects of Tidal and Diel Cycles on Dugong Habitat Use

ABSTRACT Quantifying the factors influencing behaviors of aquatic mammalian grazers may enhance the generic understanding of grazer ecology. We investigated diel and tidal patterns in movements of the dugong (Dugong dugon) by Global Positioning System—tracking 12 animals in 5 inshore—intertidal and 3 offshore—subtidal habitats along the coast of Queensland, Australia. We examined effects of tide height and time of day on the dugong's distance from 1) the nearest coast, 2) water >3 m deep, 3) actual water depth (bathymetry + tide ht) experienced, and 4) distribution of the directions of movements. Both tidal and diel cycles influenced dugong movement. Tracked dugongs tended to be closer to shore at high tide than at low tide and closer to shore at night than during the day. Onshore movement was more prevalent on incoming tides and in the afternoon and evening. Offshore movement was more prevalent on outgoing tides and from midnight through the morning until midday. Tidal and diel variation in water depths used by the inshore—intertidal dugongs was small, but probably underestimated, hidden by a sampling bias in the telemetry equipment. Onshore movement at high tide allowed dugongs to exploit intertidal seagrass beds. Dugongs are closer to shore in afternoons and evenings than in mornings. This behavior may be related to the avoidance of predators or watercraft. Our findings can be used to predict spatial patterns of dugongs within areas of conservation management significance and to assess, avoid, and mitigate adverse effects of anthropogenic disturbance.     

Patterns of temporal occurrence of brachyuran crab larvae at Saco mangrove creek, Inhaca Island (South Mozambique): implications for flux and recruitment

Temporal patterns of larval occurrence of brachyuran taxa weredescribed from Saco mangrove creek, Mozambique, based on planktonsamples. Brachyuran larvae were collected hourly in four 24h cycles during neap and spring tidal periods at a fixed station,in November 1997 and February 1998. Results indicate a semilunarcycle of larval release activity for most species. Newly-hatchedstages of sesarmids showed a peak occurrence in post-crepuscularebbing tides, Macrophthalmus spp. and Uca spp. showed highestdensities during ebbing tides at night. Dotilla fenestrata andPinnotheridae, in spite of showing a semilunar pattern, didnot display significant differences between day and night. Mostmangrove taxa showed thus a clear larval exportation behaviourduring ebb tides, with little return during the following floods,with varying degrees of dependence on the diel period. Megalopaewere restricted to the night period, and highest values wereobtained during spring tidal periods. However, maximum valuesof megalopae were obtained both during flood and ebb periods,contrary to most previous studies. This is interpreted as abi-directional transport of non-competent megalopae into andfrom the mangrove area.     

Feeding clusters and olfaction in the mangrove snail Terebralia palustris (Linnaeus) (Potamididae: Gastropoda)

Large numbers of the snail Terebralia palustris (Linnaeus) (Potamididae; Gastropoda) are frequently observed feeding in a cluster on a single fallen mangrove leaf, yet none are present on leaves nearby. Consequently, we investigated the food-finding ability of T. palustris in a Kenyan mangrove forest using field experiments. We estimated the attractive effect of different cues and analysed the paths (video-recorded) of snails when approaching a food-related odour. This intertidal snail can potentially use both air-borne and water-borne odours to locate food. T. palustris is attracted to conspecifics feeding on leaves, while intact leaves as well as non-feeding snails are not attractive. Moreover, the guiding stimulus appears to be compounds released when the leaves are damaged.T. palustris also seems able to discriminate between different food items; it is more strongly attracted to green mangrove leaves than senescent or fallen ones or mangrove propagules, probably because green leaves release a greater amount of attractive cues.Feeding snails thus recruit more snails to feed on the same leaf. The ecological implications of this behaviour are discussed: a large number of snails on the same leaf counteracts the ability of crabs to remove the leaf being eaten by the snails.     

Spatial heterogeneity in recruitment of larval trematodes to snail intermediate hosts

Spatial variation in parasitism is commonly observed in intermediate host populations. However, the factors that determine the causes of this variation remain unclear. Increasing evidence has suggested that spatial heterogeneity in parasitism among intermediate hosts may result from variation in recruitment processes initiated by definitive hosts. I studied the perching and habitat use patterns of wading birds, the definitive hosts in this system, and its consequences for the recruitment of parasites in snail intermediate hosts. Populations of the mangrove snail, Cerithidea scalariformis, collected from mangrove swamps on the east coast of central Florida are parasitized by a diverse community of trematode parasites. These parasites are transmitted from wading birds, which frequently perch on dead mangrove trees. I tested the hypothesis that mangrove perches act as transmission foci for trematode infections of C. scalariformis and that the spatial variation of parasitism frequently observed in this system is likely to emanate from the distribution of wading birds. On this fine spatial scale, definitive host behaviors, responding to a habitat variable, influenced the distribution, abundance and species composition of parasite recruitment to snails. This causal chain of events is supported by regressions between perch density, bird abundance, bird dropping density and ultimately parasite prevalence in snails. Variation between prevalence of parasites in free-ranging snails versus caged snails shows that while avian definitive hosts initiate spatial patterns of parasitism in snails through their perching behaviors, these patterns may be modified by the movement of snail hosts. Snail movement could disperse their associated parasite populations within the marsh, which may potentially homogenize or further increase parasite patchiness initiated by definitive hosts.     

Feeding on gastropods by lake-dwelling Polycelis in the absence and presence of Dugesia polychroa (Turbellaria, Tricladida)

SUMMARY. Using a serological technique, the extent of feeding upon snails by Polycelis tenuis was compared in habitats lacking and containing Dugesia polychroa which is the major triclad predator of snails. It was found that P. tenuis ate significantly more snails when D. polychroa was absent. It was concluded that in the field interspecific competition for snails between these two triclad species was a more powerful process than any social feeding by P. tenuis on snails captured by D. polychroa .
Feeding on snails as a group by P. tenuis and P. nigra in the habitat where the two triclads co-existed was of a similar magnitude and this was also true of their feeding on the common snail species and genera. Approximately 10% of the triclads gave a positive reaction to snail antisera.
Feeding on snails by P. nigra in the three habitats lacking D. polychroa was similar in extent and did not differ from that of P. tenuis . It was concluded that P. nigra would be similarly affected by the presence and absence of D. polychroa as shown for P. tenuis .
No definitive seasonal pattern was detected in the incidence of feeding upon snails by either Polycelis species but this may have been obscured by seasonal changes in the detection period of snail antigens due to temperature effects. There was some evidence that such feeding increased during the period when small snails were present in the population.     

Vertical migration and spawning inNodilittorina exigua (Gastropoda: Littorinidae)

The relation between the vertical migration in summer and spawning of a littoral-fringe periwinkle,Nodilittorina exigua, was studied by field observations and laboratory experiments. The snails moved down soon after the first appearance of their planktonic eggs in the sea and stayed at low shore-levels until early August. It was shown that the migration increased the chance of immersion of the snails, and therefore of releasing eggs by the females. Females immersed every day in the laboratory released more eggs than those which experienced some days of exposure to air, during the same period. The results obtained suggest the reproductive advantage of immersion at low levels. Nevertheless, the snails moved upward before the end of the spawning season. Typhoon swells increasing in frequency through the summer seemed to be responsible for the upward migration.     

Predation induced changes in behavior and growth rate in three populations of the intertidal snail, Littorina sitkana (Philippi)

We investigated the sublethal effects of a predatory crab, Cancer productus (Randall), on the behavior and growth of its snail prey, Littorina sitkana, by setting up controlled rearing and prey-size selection experiments. L. sitkana were collected from three sites on San Juan Island, WA, USA. These sites varied in snail size, abundance, and vertical distribution, and in the abundance of the crab predator C. productus. Snails from all three populations were raised for 34 days under the following treatments: no-crab control, a non-feeding C. productus encased in mesh box, and an encased C. productus feeding on L. sitkana. The non-feeding crab treatment did not affect snail foraging behavior or growth rate in comparison with the no-crab control. In contrast, the presence of a feeding crab elicited escape behavior in the snails, halted grazing, and consequently reduced growth rates. A population difference in escape behavior was observed: upward migration in snails from rocky shores and hiding in crevices in snails from a mud flat. It thus appears that chemicals leaching from crushed conspecific snails, rather than the presence of the crab predator, act as the “alarm substance” to which L. sitkana react. The magnitude of the growth depression in the presence of feeding crabs was 85%, with no difference among the three populations. Once the feeding crab stimulus was removed, snails in all populations resumed normal growth, suggesting that this response to feeding predators is reversible with changing environmental conditions. Laboratory experiments were set up to determine if all size classes of L. sitkana are equally susceptible to C. productus predation. C. productus consistently selected the largest of three size classes of L. sitkana. These results suggest that slow growth rate and small size in L. sitkana may actually be an adaptation for coexisting with high C. productus abundance, rather than simply a cost of escape behavior.     

Behavior of Four Species of Fiddler Crabs,Genus Uca,in Southeast Sulawesi,Indonesia

We studied the behaviors of four species of sympatric fiddler crabs on Kaledupa Island, Indonesia. Species differences in activity level, grooming, burrowing and feeding were related to their habitat and food. Uca chlorophthalmus, living in muddy mangrove areas, were inactive and spent most of the time feeding in place. Females fed 50% faster than males and spent more time feeding. U. vocans was the dominant species at the beach in silty sand and was very active. Its feeding rate was about twice that of the former species, females fed more rapidly than males, and many crabs of both sexes fed in droves at the water’s edge during ebb tides. During ebb tides, they spent most of their time feeding, while at flood tide they engaged in a greater variety of activities, including burrow maintenance. They frequently walked while feeding and interacted aggressively. U. tetragonon lived in a pebbly band along one edge of the beach, by a quay. Their feeding rate was comparable in both sexes and slower than that of U. vocans; they fed largely on filamentous algae growing on the quay, which provides better food, and fed faster during flood tide than ebb tide. They spent more time in waving and other sex-related activities, and were seldom aggressive, except during the week of the full moon. Burrowing activities included placing excavated mud balls some distance away from their burrows and re-arranging them. U. dussumieri inhabited the other end of the beach in muddier substrate. They did not have sex differences in feeding rates and their rate of scooping food into their mouths was slow, but feeding claws made multiple pinches of the substrate, thus accumulating more material in each clawful of food.     

Tidal movements of the macrofauna on an exposed sandy beach in South Africa

All epifaunal and shallow-burrowing, intertidal macrofauna on an exposed sandy beach appear to undergo tidal migrations which vary in extent but are all upshore on the incoming tide and downshore on the outgoing tide during day and night. In the crustaceans this is probably endogenous rhythmic behaviour and they show increased activity at night. In the molluscs this movement is not synchronised by an intrinsic mechanism but results from behavioural responses to changing physical conditions. The large wedge clam, Donax serra, shows no tidal migrations but does show a semilunar rhythm of movement from just above mean tide level (MTL) during springs to the low tide level during neap tides.     

红树林恢复初期莱氏锥滨螺分布动态

树栖腹足类动物是红树林底栖动物的重要组成部分,其组成和分布受到红树植被的影响。因此,在红树林生态修复中,腹足类动物的恢复依赖于植被的发育。滨螺科(Littorinidae)锥滨螺属(Mainwaringia)动物是亚洲红树林的广布种,但针对其在红树林中的分布及种群特征的研究较少,对红树林植被恢复过程中锥滨螺属动物的恢复动态更是鲜有研究。调查了厦门下潭尾湿地秋茄(Kandelia obovata)红树林恢复初期,新记录种莱氏锥滨螺(Mainwaringia leithii)种群恢复的时间动态,并分析其与植被参数的关系。研究发现,红树林恢复初期,秋茄植被生长迅速,株高、冠幅、基径和覆盖度分别由0.5年生幼林的41.3 cm、25.0 cm、1.04 cm和25%增长为8年生样地的179.2 cm、76.7 cm、5.96 cm和95%。在秋茄胚轴种植6个月左右开始记录到莱氏锥滨螺的个体,其密度和生物量在1.5 a后达到最大(分别为136个/m²和1.86 g/m²),而后逐渐降低,种植3 a后秋茄林内莱氏锥滨螺仅零星分布。除8年生的样地,莱氏锥滨...     

Lunar influence on prey availability,diet shifts and niche overlap between Engraulidae larvae in tropical mangrove creeks

The influence of the lunar cycle on prey availability, diet shifts and overlap between larval Anchovia clupeoides and Cetengraulis edentulus was evaluated in mangrove creeks of the Goiana Estuary. Copepod eggs were highly abundant in the first and last quarter, at the full moon and zoea of Ucides cordatus (Ocypodidae) in the new moon. The Engraulidae larvae fed on microcrustaceans, algae and early planktonic stages of benthic organisms. The relative importance of prey varied according to prey availability in all moon phases. Larval diets were more even in the full and new moons, when the relative importance of calanoid copepods and zoeae of U. cordatus as food items increased (index of relative importance, >80% I_RI). Mangrove creeks were very important feeding grounds for engraulid larvae during spring tides. Larval diets were more diverse in the first and last‐quarter moon and included protozoeae of Caridean shrimp, larvae of Anomalocardia brasiliana (Veneridae), Isopoda, Gastropoda, ephippium of Daphnia sp. and nauplii of Cirripedia, Harpacticoidia and cyclopoid Copepoda. The last five items were not found in the creeks, suggesting feeding in the main channel. During neap tides, mangrove creeks were probably also used as refugia. These larvae are opportunistic and feed on highly available prey and both species feed on the same items, leading to high dietary overlap in all moon phases. The lunar cycle, which is related to the spring‐neap tidal cycle, was the major driver of quantitative and qualitative changes in feeding of engraulid larvae on a short time scale.     

Diel variations in Acartia tonsa feeding, respiration and egg production in a Mediterranean coastal lagoon

Short-term changes in abundance, feeding, respiration and spawningby the copepod Acartia tonsa were studied during four 24 h periodsat two stations in a Mediterranean lagoon in May and June of1989 and 1990. Nightly increases of abundance in the upper layer,attributed to nocturnal upward migration, were observed in threeout of the four time series. Nevertheless, occasional dailyincreases were observed too, so that no clear diel patternsin abundance could be defined. Contrarily, diel patterns seemedto appear: (i) for feeding (higher at the beginning of the night),based on gut fluorescence and clearance and ingestion rate measurements;(ii) for respiration (lower at night and based on 8 h incubationperiods); and (iii) for spawning (higher at the end of the night,based on experimental data). The origin of these patterns, aswell as their relationships to environmental data and theirpossible association, are discussed with regard to the availableliterature.     

Feeding dynamics of Terebralia palustris (Gastropoda: Potamididae) from a subtropical mangrove ecosystem

Mangrove gastropods are largely recognised for their roles as benthic deposit feeders that consume macrophyte-derived detritus. However, microalgae may also make a significant contribution towards the diet of these snails. Here we provide the first report on the rates at which microphytobenthos (MPB) is consumed by Terebralia palustris, an Indo-Pacific mangrove gastropod. Although juvenile T. palustris are generally detritivorous, there is increasing evidence that their occurrence on the seaward edge of the mangrove habitat allows them to incorporate a more nutritious food source to their diets in the form of microalgae. Using an experimental approach that incorporated fluorometric techniques, we found that the feeding activity of T. palustris on MPB was not clearly related to diel and tidal cycles at the subtropical location of Kosi Bay, South Africa during two sampling occasions in February and July 2015. However, a faster ingestion rate and higher consumption/digestion efficiency were recorded during experiments carried out in July. On this sampling occasion a higher percentage consumption of the available MPB was recorded, which corresponded to a lower per-capita availability in this resource. As T. palustris is able to consume MPB at variable rates, the impact of this species on benthic primary productivity within Indo-Pacific mangroves should not be overlooked when considering its integral ecological role within these threatened habitats.