Ecological studies on intertidal and infralittoral brazilian tanaidacea (crustacea,peracarida)

Three species of Tanaidacea were found on the ¡ntertidal and shallow infralittoral at Enseada do Flamengo, Ubatuba, southeastern Brazil. Their vertical and horizontal distributions, as well as their density, seasonal variation and constancy are studied in relation to substrate and degree of exposure to wave action.

Leptochelia savignyi and Teleotanais sp. have their vertical distribution from the midlittoral to 5–6 m depth, and Zeuxo coralensis from the midlittoral to 1 m depth. Leptochelia savignyi and Zeuxo coralensis are present on exposed, semi‐exposed and sheltered places, while Teleotanais sp. is absent from the last.

The importance of the substrate as a factor influencing the distribution and the abundance of tanaids was again confirmed: sometimes the effect of the substrate is more significant on the animals than the wave action. The highest density of tanaids was found on the calcareous algae. Leptochelia savignyi is the most abundant species.

There is some seasonal variation in the number of individuals in the littoral zone; higher numbers are found in September (late winter).

The constancy and dominance of the species is calculated for the two zones, and Leptochelia savignyi is constant and dominant in both.     

Feeding Habits of Percnon gibbesi (H. Milne Edwards, 1853) in the Sicily Strait

The subtropical grapsid crab Percnon gibbesi (H. Milne Edwards, 1853) is one of the most recent alien decapods found in the Mediterranean, where it was discovered at Linosa (Pelagie Islands, Sicily Strait) in summer 1999. At present, the invasion of this species has been recorded in several other insular localities. We studied the feeding habits of the crab in an attempt to understand its success in the Mediterranean. The morphological characteristics of the chela, the feeding adaptations of the gastric mill and the analysis of stomach contents indicate that P. gibbesi is a strictly herbivorous species, a characteristic not shared with any other large-sized infralittoral Mediterranean crab.     

Seasonal dynamics of fish assemblage structures in a surf zone on an exposed sandy beach in Japan

Seasonal dynamics in fish assemblage structure, comprising postlarval to early adult stages, in the surf zone on an exposed sandy beach on the Kashimanada coast were studied over a 2-year period. A total of 32 species and two higher group taxa were found. In terms of abundance, Salangichthys ishikawae, Mugil cephalus cephalus, Plecoglossus altivelis altivelis, and Engraulis japonicus were the four most dominant species. The results of cluster analysis and canonical correspondence analysis using 12 dominant species in terms of abundance revealed that water temperature and wind factor (wind speed × wind direction) had significant independent associations on species occurrence patterns for 11 species; that is, occurrence of 11 species was significantly related to water temperature and occurrence of 7 species was related to wind factor. Two species (S. ishikawae and P. altivelis altivelis) showed clear monthly increases in size, consequently suggesting their use of the surf zone as a nursery area. In contrast, M. cephalus cephalus and E. japonicus showed few increases in standard length, indicating their use of the surf zone only in their postlarval and/or juvenile stage. It is suggested that numerous fish species use the surf zone as shelter and/or a nursery area, even in the harsh conditions of an exposed sandy beach with great wave action.     

Population dynamics of alien gammarid species in the River Odra estuary

During the period of 1988–2000, three alien gammarid species, i.e. Gammarus tigrinus Sexton, 1939, Pontogammarus robustoides G. O. Sars, 1894, and Dikerogammarus haemobaphes (Eichwald, 1841) were recorded in the Odra estuary. This study, the first record of G. tigrinus and P. robustoides in Poland, focuses on the distribution, abundance, and biomass as well as on population structure of the three new species found in the coastal zone of the estuary. G. tigrinus and P. robustoides were first sampled in the Szczecin Lagoon (mid-part of the estuary) in 1988. The densities of both species were high from the time they were first recorded and exceeded 10 000 ind. m^–2, while the biomass was 25 and 140 g m^–2, respectively. G.tigrinus occurred at higher densities in northern and eastern parts of the Lagoon, while P. robustoides was particularly abundant in the south-eastern part, most heavily affected by River Odra discharge. In 1999, the third gammarid, D. haemobaphes, was recorded in the southern part of the estuary. Both in 1999 and 2000, the species was found in qualitative samples (dredge collections of Dreissena polymorpha) taken from the western branch of the river. As estimated from quantitative samples, densities and biomass in the eastern branch were rather low and did not exceed 150 ind. m^–2 and 2.7 g m^–2, respectively. The Szczecin Lagoon population of G. tigrinus produces at least two generations within a year: a summer one and an overwintering one. The latter is dominated by older and larger specimens. The species may reproduce in the Lagoon from April until November.     

毛木耳不同生长期菌棒微生物群落研究

为探究毛木耳(Auricularia cornea)代料栽培子实体不同生育阶段菌棒内细菌和真菌群落，基于Illumina Miseq测序平台，对毛木耳4个出耳期(ful、pri、ope和mat)菌棒的微生物群落进行分析。获得细菌16S rRNA有效序列503 724条，真菌ITS有效序列712 728条。细菌物种注释分属25门54纲85目134科199属；真菌物种注释隶属5门9纲15目12科19属。菌棒中有非常丰富的细菌群落，主要分属于变形菌门(Proteobacteria)、厚壁菌门(Firmicutes)、放线菌门(Actinobacteria)和拟杆菌门(Bacteroidetes)。相对丰度最高的前2个属：ful期是Lysinibacillus(25.71%)和Acinetobacter(14.38%);pri期是Pseudomonas(35.85%)和Solibacillus(14.85%);ope期是Lysinibacillus(36.42%)和Pseudomonas(21.73%);mat期是Acinetobacter(27.94%)和Ochrobactrum(14.92...     

Impact scenario for the invasive red king crab <Emphasis Type="Italic">Paralithodes camtschaticus</Emphasis> (Tilesius, 1815) (Reptantia,Lithodidae) on Norwegian,native, epibenthic prey

Large invasive predators like the king crab, Paralithodes camtschaticus, deserve particular attention due to their potential for catastrophic ecological impact on recipient communities. Conspicuous, epibenthic prey species, such as the slow growing commercial scallop Chlamys islandica, are particularly exposed to the risk of local extinction. A research program integrating experiments and field monitoring is attempting to predict and track the impact of invasive king crab on scallop beds and associated fauna along the north Norwegian coast. The claw gape of the crab shows no limitations in handling the flat-bodied scallop. However, the potential impact of the crab on scallop may depend on the availability of other calcified prey associated with scallop beds, such as the sea star, sea urchin, and blue mussel, all species recorded in the diet of P. camtschaticus. To address this issue, a laboratory experiment on foraging behaviour of P. camtschaticus was conducted. The experimental results show that all size classes of red king crab prefer scallops, but small juveniles and medium sized crabs demonstrate active selection for starfish (Asterias rubens) that equals or surpasses the electivity of the large crab. The selection of sea urchin (Strongylocentrotus droebachiensis) and blue mussel (Mytilus edulis) is slightly positive or neutral for the three crab size classes. These results suggest that scallop beds with a rich associated fauna are less vulnerable to red king crabs predation and possibly more resilient than beds with few associated species. Also, crab size distribution is likely relevant for invasion impact, with increasing abundance of small and medium sized crabs being detrimental for alternative calcified prey associated with scallop beds. Successive stages of crab invasion will see an acceleration of scallop mortality rates associated with (i) decreasing availability of alternative prey, due to protracted predation pressure intensified by recruitment of juvenile crabs, and (ii) increased number of large crabs. Estimates of crab density and intake rates suggest that the accelerated loss rates will eventually endanger scallop beds persistence.     

Modifications des écosystèmes des vasières cotières du sud-Bretagne

Summary The northern part of the Bay of Biscaye consists of muddy areas which were the subject of many surveys conducted from the early sixties revealing important modifications. Communities living in these muddy areas are very rich in quality as well as quantity and with high interactions between the different species. With their trophic ethology, their biogenic actions, these species modify largely the sediment quality, its compactness for example is related to the tubicolous species presence. The disappearance of certain dominant species is due to some climatic anomalies causing an important disturbance of the ecosystem. In the infralittoral muddy areas, Zostera beds had been replaced momently by the abundant populations of Melinna. In the coastal muddy sites the recent disappearance of the Maldane cause a momentary imbalance, and for many long years, an equilibrium based on a new dominant species may appear. The intervention of an allogenic factor may in this case, opposite autogenic succession of the community or call the equilibrium which seems established in question again.

     

Polychaete zonation and its relation to algal distribution down a vertical cliff in the western Mediterranean (Italy): a structural analysis

The zonation of polychaetes down a vertical cliff (0–5 m in depth) at Cape Romito, Leghorn, Italy, was investigated. The structural organization of the community changed with depth. A community typical of photophilic environments was found in the superficial zone (0–2 m), while in the deeper zone (3–5 m), a more diversified community characterized by species typical of sciaphilic environments was present. At the surface (0 m) the community was very poor in species and individuals and thus probably corresponds to the midlittoral fringe. In fact, some species typical of the midlittoral zone were found. This distribution pattern was constant for samples taken in February and August 1985. The distribution of polychaetes was closely related to that found for macroalgae. It is hypothesized that algae condition the substratum and that this is the main factor responsible for the zonation of polychaetes.     

Distribution,abundance, and feeding of a disjunct population of lady crab in the southern Gulf of St. Lawrence,Canada

The lady crab (Ovalipes ocellatus) is one of the most common native species of swimming crab (Portunidae) of the Atlantic Coast of North America but most populations occur south of Cape Cod, Massachusetts. There is a disjunct population in Northumberland Strait (southern Gulf of St Lawrence), which was the focus of this study. Adult lady crabs were collected by trawling in water >4 m deep from May to October 1999 to 2005 to determine abundance, distribution, and diet. Lady crab occurred only in a small area (about 2,500 km²) in the central part of Northumberland Strait where bottom water temperature was >18°C during summer, and the substrate was mainly sand or sandy gravel. Male lady crab attained a maximum carapace width (CW) of 112 mm compared to 92 mm CW for females. The summer and autumn diet consisted mainly of infauna. The principal prey (each >5% of diet by weight) were: small bivalve molluscs (primarily Atlantic razor clam Siliqua costata and Macoma sp.; 43%), small rock crab (Cancer irroratus; 13%), polychaetes (11%), fish remains (9%), and small lady crab (9%). All stomachs collected during May (water temperature ≤10°C) were empty. There was little evidence of any difference in feeding intensity between 0700 h and 1900 h.     

Composition and abundance of shorebird and macroinvertebrate communities differ according to densities of burrowing fiddler crabs in tropical intertidal flats

The burrowing activity of fiddler crabs inhabiting intertidal flats creates visually distinct patches within these habitats. However, differences in the composition and abundance of shorebirds and their macroinvertebrate prey between areas inhabited or not by crabs are yet to be studied. Here, we compare the macroinvertebrate and shorebird assemblages in low and high crab density areas in the intertidal flats of the Bijagos archipelago, Guinea-Bissau. High crab density areas are associated with lower richness and densities of macroinvertebrates. Shorebird assemblages were also less rich at high crab density areas and the differences in species composition occurred according to prey type preferences. Fiddler crab density was the most important variable explaining macroinvertebrate abundance, after accounting for the effects of fine fraction of sediment and distance to coast. Nonetheless, a controlled experimental setup would be required to attribute differences found to the engineering activity of fiddler crabs rather than other unaccounted habitat features. Our findings suggest that crab patches should be taken into account when assessing the distribution and abundance of macroinvertebrates and shorebirds in intertidal areas. Since low and high crab density areas differ markedly in terms of shorebird carrying capacity, monitoring variations in their extent will be important to interpret past and present population trends.

     

Diel and tidal changes in the distribution and feeding habits of Japanese temperate bass Lateolabrax japonicus juveniles in the surf zone of Ariake Bay

Japanese temperate bass Lateolabrax japonicus juveniles recruit to the surf zone and grow by feeding on commonly occurring coastal copepods. However, little is known about diel and tidal patterns in their migration and feeding habits. We sampled wild juveniles during the neap and spring tides, over periods of 24 h, with small seine nets in the sand flat of the eastern part of Ariake Bay, Kyushu, western Japan. In both the neap and spring tides, abundance of juveniles significantly increased during the daytime, being highest around the time of high tide. The relative gut fullness indices of juveniles drastically increased in the morning (0700–0900) and during the flood tide in the daytime, while major prey copepod (Paracalanus spp.) density in the ambient water was relatively constant. We summarized that L. japonicus juveniles would migrate to the surf zone after sunrise to feed on copepods, and then emigrate from the surf zone after sunset. The migratory behavior of L. japonicus juveniles would be influenced by light (daytime) and feeding activity influenced by both light (morning) and tidal condition (flood tide). The intertidal region of the tidal flat was recognized to be one of the important habitats for L. japonicus during their early life history.     

基于MAXENT模型评估北部湾潮间带中国鲎和圆尾鲎稚鲎的潜在地理分布及种群保育对策

鲎具有极高的经济价值和科研意义。近年来由于过度捕捞和栖息地受损等原因,亚洲鲎种群数量正急剧下降。鲎漫长的生命周期使得鲎资源的保护和增殖迫在眉睫。生态位模型已经广泛应用于物种的潜在地理分布预测。基于实地调研数据和公开发表的北部湾中国海域中国鲎和圆尾鲎地理分布数据,运用MAXENT模型得到中国鲎和圆尾鲎在广西北部湾(中国部分)的栖息地适宜度指数(Habitat suitability index, HSI),确定了这两种稚鲎在北部湾中国海域潜在适生区。模型分析结果表明,潮间带坡度和地形指数是影响中国鲎分布的主要环境因子,而潮间带底质的有机物含量和植被指数是影响圆尾鲎分布的主要环境因子,根据研究结果建议在两种稚鲎适生区建立保护区,进行人工放流稚鲎,加强对海草和红树林的生态建设,进而促进鲎资源种群恢复和发展。     

Native species vulnerability to introduced predators: testing an inducible defense and a refuge from predation

To manage the impacts of biological invasions, it is important to determine the mechanisms responsible for the effects invasive species have on native populations. When predation by an invader is the mechanism causing declines in a native population, protecting the native species will involve elucidating the factors that affect native vulnerability. To examine those factors, this study measured how a native species responded to an introduced predator, and whether the native response could result in a refuge from predation. Predation by the green crab, Carcinus maenas, has contributed to the decline in numbers of native soft-shell clams, Mya arenaria, and efforts to eradicate crabs have proven futile. We tested how crab foraging affected clam burrowing, and how depth in the sediment affected clam survival. Clams responded to crab foraging by burrowing deeper in the sediment. Clams at shallow depths were more vulnerable to predation by crabs. Results suggest soft-shell clam burrowing is an inducible defense in response to green crab predation because burrowing deeper results in a potential refuge from predation by crabs. For restoring the native clam populations, tents could exclude crabs and protect clams, but when tents must be removed, exposing the clams to cues from foraging crabs should induce the clams to burrow deeper and decrease vulnerability. In general, by exposing potential native prey to cues from introduced predators, we can test how the natives respond, identify whether the response results in a potential refuge, and evaluate the risks to native species survival in invaded communities.     

Reproductive Stage of the Life Cycle in the Rhizocephalan Barnacle Polyascus polygenea (Crustacea: Cirripedia)

The specific features of the reproductive stage of the life cycle have been studied in the rhizocephalan barnacle Polyascus polygenea, a parasite of the coastal crab Hemigrapsus sanguineus. It is shown that a single crab can bear 1 to 8 externae of P. polygenea. The fecundity of the parasite depends on the size of the externae and their number on the host and may reach as much as 50000 eggs for one externa. In Peter the Great Bay, Sea of Japan, this species repeatedly reproduces during the entire spring–autumn period; externae with developing embryos in the mantle cavity occur from May to September, and planktonic larvae occur from June to October. One externa produces during the season of reproduction no less than three generations of larvae. Thus, the reproductive strategy in P. polygenea comprises a three-stage cascade of reproduction: asexual reproduction via budding of the interna; the development of several generations of one or several externae; and several reproduction cycles of each externa. This allows the parasite to produce a very great number of larvae and ensures the parasitization of a significant proportion of the host crab population. The structure of the ovaries and oogenesis in rhizocephalans and free-living cirripede barnacles have many common features, which provides evidence for integration of these two groups within one monophyletic taxon.     

Burrowing behavior and ecology of the crab-eating Indian snake eel Pisoodonophis boro

Synopsis The snake eel Pisoodonophis boro burrows, causing leaks in the embankments and damaging the paddy fields and salt pans near estuaries. Field observations and laboratory experiments were made to study this behavior. P. boro was burrowing to eat the fiddler crab Uca annulipes in the mud flats. The eel showed a patchy distribution within the Uca zone. Salinity and the physical nature of the deposits controlled the distribution of the eel. Eel population density was low when the estuary was completely filled with neritic waters during the summer and fresh water during the monsoon period. The region of greatest abundance contained a good mixture of sand, silt and clay. Eels were not found where medium and fine sand formed the bulk of the substratum. The laboratory experiments showed that P. boro preferred loam soil although it could invariably burrow into hard substratum like sand for protection. The eel adapted itself to the experimental substrates ranging from sand to fine clay. However, their natural distribution was determined by Uca distribution. As U. annulipes is not found either in salt pans or in paddy fields P. boro rarely occurs in these habitats.     

Response of root and sediment phosphatase activity to increased nutrients and salinity

Wetlands of northern Belize, distributed along a salinity gradient, are strongly phosphorus limited and dominated largely by three species of emergent macrophytes: Eleocharis cellulosa, Cladium jamaicense, and Typha domingensis. We assessed changes in root and sediment phosphatase activities of each species to simultaneous changes of nutrients (N, P) and salinity in a mesocosm experiment. Phosphorus and nitrogen treatment effects on both root and sediment phosphatase were highly significant for all the species, while salinity significantly affected root phosphatase activity in Cladium only. All species showed a significant negative correlation between root phosphatase activity and increasing tissue P content until a threshold of 0.2% P, 0.15% P and 0.12% P in Eleocharis, Cladium and Typha, respectively. There was also a significant negative correlation between soil available P and root and sediment phosphatases in all species. Activity of root phosphatases of Eleocharis and Typha were positively correlated with root tissue N. Both root and sediment phosphatases of all three species were positively correlated with soil available N. The strongest (positive) correlation was found between phoshatase activites and N/P ratios. The results confirmed that these systems are P-limited and that extracellular phosphatases respond to P enrichment by decreasing their activities. Expression of root phosphatase activity by dry root weight, sediment volume, or whole plant biomass gave very different relative results across nutrient treatments and species, suggesting that root phosphatase activities need to be interpreted in a wider context that considers root density.     

Differential seed and seedling predation by crabs: impacts on tropical coastal forest composition

Recently, the importance of seed predation by crabs on mangrove species distributions and densities has been established by several studies. In a tropical coastal terrestrial forest in Costa Rica, we investigated the relative importance of predation by land crabs, Gecarcinus quadratus, and hermit crabs, Coenobita compressus, on measured forest composition through a series of seed removal and seedling establishment experiments. We also used natural light-gaps and adjacent non-gap sites to test how canopy cover affects crab predation (seed removal) and seedling establishment. We found fewer tree species (S=18) and lower densities (seedlings, saplings, and adults) in the coastal zone within 100 m of coastline, than in the inland zone (S=59). Land crab densities were higher in the coastal zone (3.03±1.44 crabs m^–2) than in the inland zone (0.76±0.78 crabs m^–2), and hermit crabs were not present in the inland zone. Seed removal and seedling mortality also were higher in the coastal zone than in the inland zone, and in the open controls than in the crab exclosures. Mortality of seeds and seedlings was two to six times higher in the controls than exclosures for four of the five experiments. Crabs preferred seeds and younger seedlings over older seedlings but showed no species preferences in the seed (Anacardium excelsum, Enterolobium cyclocarpum, and Terminalia oblonga) and seedling (Pachira quinata and E. cyclocarpum) stages. We conclude that the observed differences in tree densities were caused by differential crab predation pressure along the coastal gradient, while the differences in species composition were due to predator escape (satiation) by seed quantity. Canopy cover did not affect seed removal rates, but did affect seedling survival with higher mortality in the non-gap versus gap environments. In summary, crab predation of seeds and seedlings, and secondarily canopy cover, are important factors affecting tree establishment in terrestrial coastal forests.     

Temporal variation in abundance of the egg predator Carcinonemertes epialti (Nemertea) and its effect on egg mortality of its host,the shore crab,Hemigrapsus oregonensis

An outbreak of the nemertean, Carcinonemertes epialti, was observed on Hemigrapsus oregonensis during October, 1982 at Campbell Cove, Bodega Harbor, California. Mean worm intensity (296 worms/crab) was the highest recorded for this nemertean egg predator on H. oregonensis. During the outbreak, male crabs were found to harbor more worms than both non-ovigerous and ovigerous females. Crab egg mortality was substantial; 83% of the ovigerous females experienced 75–100% brood mortality. The seasonal peak in worm abundance coincided with the seasonal low in crab reproduction at this locality. A method for estimating the impact of C. epialti on H. oregonensis natality was developed using crab size and fecundity, and worm prevalence and intensity. For a non-outbreak sampling period, a mean of 5.6% egg mortality was experienced by infested crabs for the period selected. Thus, brood mortality during the outbreak was much greater than that experienced at non-outbreak periods. Heavy fishing pressure on some commercially important crab species has been suggested as a possible factor inducing worm outbreaks and facilitating their continued persistence. These observations suggest that fisheries are not necessarily responsible for the outbreaks of nemerteans on commercially important crab species. However, fishing pressure may still be a sufficient condition to promote nemertean outbreaks.     

Intraspecific relationships of the hermit crab Diogenes pugilator: predation and competition

The population of the hermit crab Diogenes pugilator is numerically quite substantial in the examined area, therefore it is analysed if the population was subject to any pressure by predators and by other species of hermit crabs living in that zone. It was found there is a potential pressure by predators which might influence it. Only Liocarcinus depurator is able to keep the population trend of D. pugilator under control. With regard to the relationships with the other species of hermit crab, D. pugilator dominates only over Pagurus anachoretus, while in the other cases, there was just competition for food.