Quantitative distribution of meiobenthos and the structure of the free-living nematode community of the mangrove intertidal zone in Nha Trang bay (Vietnam) in the South China Sea

Meiobenthic studies were performed in an intertidal area in the Be River estuary (Nha Trang Bay, Vietnam). The study area is an area of riverine-type mangroves that have been heavily damaged by human impacts, including timber cutting and waste. Three biotopes are situated in the middle intertidal zone: a fringe of Rhizophora stylosa, a bush area composed of Avicennia aff. alba behind it, and muddy sand with fiddler crabs (Uca spp.), which is free of mangrove plants. Three replicate samples of meiobenthos were collected in each biotope and each sample was subdivided into two layers: 0–1 and 1–4 cm. The abundance of metazoan meiobenthos varied from 735 specimens/10 cm² in the Uca spp. biotope to 244 specimens/10 cm² beneath the Rhizophora trees. Six taxonomic groups of high rank were found among the meiofauna: Nematoda, Copepoda (Harpacticoida), Oligochaeta, Turbellaria, Kinorhyncha, and Foraminifera (Allogromiida). The spatial variability of meiobenthos and its key taxa was estimated and the spatial distribution patterns of free-living nematode species were described. About 90% of the total meiobenthos inhabited the upper 0–1 cm of the sediments. Nematodes constituted 90–95% of all meiobenthic organisms in the samples. A total of 48 species of free-living nematodes were found in the investigated mangrove intertidal area. In terms of species composition and set of dominants, the nematode community is comprised of three local assemblages: one of them inhabits the uppermost centimeter in the Uca and Avicennia biocenoses; the second assemblage occupies the upper sediment layer in the Rhizophora stand; a less abundant but specific assemblage of several nematode species occurs in the subsurface sediments at all three sites.     

Morphological and ecological shifts in a land snail caused by the impact of an introduced predator

Introduced predators have become major threats to native animal species in oceanic islands. A number of studies have shown that alien predators have caused serious extinctions of island endemics. However, little attention has been paid to the evolutionary impacts of alien predators on native species. The present study shows that predation by black rats, Rattus rattus, has resulted in ecological and morphological changes in the land snail Mandarina anijimana from the island of Anijima in the Ogasawara archipelago. The frequency of empty predated shells has increased over the past 17–19 years in southern areas of the island. The shells of these snails were found to be significantly higher, smaller and darker in the survey in 2006 than in the survey in 1987–1989 performed in central and southern parts of Anijima, where predation by Rattus was serious. M. anijimana were formerly restricted to shallow broad-leaved litter, whereas they are currently found in deep palm litter, where predation pressure from Rattus may be lower. This suggests that increased predation pressure by Rattus has changed the habitat use of M. anijimana. The close association between shell morphology and habitat use of Mandarina species suggests that the habitat shift induced by the predation of Rattus has caused these changes in the shell morphology of M. anijimana over a period of 17–19 years.     

Land hermit crabs use odors of dead conspecifics to locate shells

A series of experiments at two tropical locations tested the ability of land hermit crabs Coenobita perlatus (H. Milne Edwards) and Coenobita compressas (H. Milne Edwards) to detect and respond to odors of dead conspecifics. An attraction array compared numbers of crabs attending hidden food odors and dead conspecific odors. Pit experiments tested crab shell-acquisition behaviors at different hidden odors. Bucket experiments confined crabs collected from various categories (feeding crabs, wandering crabs and crabs aggregated at dead conspecific odors) and tested behavioral responses to odors and an empty shell. Land hermit crab behavior at both sites was similar. Crabs were attracted to dead conspecific odors up to 10 times more than to food odors. Crabs attracted to dead conspecifics displayed significantly more shell-acquisition behaviors: touching other crab's shells in an exploratory manner and switching shells if an empty shell was available. In buckets, crabs from each category switched into shells. Results are compared to previous reports of similar shell-seeking behaviors by marine hermit crabs in response to dead conspecific odors. It is suggested that responding to dead conspecific odors for shell source location is an evolutionarily conserved behavior developed before hermit crabs became terrestrial.     

The effects of gastropod shell availability and habitat characteristics on shell utilization by the intertidal hermit crab Pagurus longicarpus Say

The shell utilization patterns of two intertidal populations of the hermit crab, Pagurus longicarpus Say, were studied. The populations differed with respect to the physical characteristics of their habitats and the availability of empty gastropod shells. The first population was in an estuary connected to Narragansett Bay. This population had few, if any. empty shells available in the area. The second population was in a rock-cobble area directly on Block Island Sound. There were large numbers of empty gastropod shells available for this population. The consistently high gastropod mortality on this shore appears to be caused by the animals being washed up on the beach, where they die due to desiccation.Data from samples collected from June to November of both 1974 and 1975 showed that there were distinct differences in the shell utilization patterns of the two populations. A greater proportion of the animals collected from the estuary population inhabited damaged shells and/or shells with symbionts compared to the individuals from the population with large numbers of empty shells available.The results of shell selection experiments indicated that individuals from both populations inhabited less than preferred shells. The population with large numbers of empty shells available was qualitatively shell-limited because of the effect of physical factors on the morphology of the gastropod species of that area. In addition, the shell selection experiments showed that individuals from the two areas had significantly different shell preferences. This result may be explained by the effects of the environment on the growth rates of the hermit crabs and/or as an indication that shell preferences may vary in response to the physical factors of a given habitat.     

Plant-parasitic nematodes and yellowing of leaves associated with black pepper plants in Vietnam

Thirty-five nematode species belonging to 19 genera were extracted from 432 soil and root samples collected in 19 districts in six provinces in the North Central Coast, Central Highlands and Phu Quoc Island. Based on our study, the predominant nematode species associated with black pepper plants in Vietnam is Meloidogyne incognita: almost every soil and root sample examined during our study was infected with this root-knot nematode species. No difference in frequency of occurrence of M. incognita among the three agro-ecological regions surveyed was observed. However, the root population density of M. incognita in black pepper plants was on average about five times higher in the North Central Coast and Central Highlands than in Phu Quoc Island. Large differences in root population density of M. incognita on black pepper plants were observed in different districts within the same agro-ecological region. Black pepper roots infected with M. incognita showed the same type of galls as described in the literature. The percentage of root galling averaged about 40% in all the three agro-ecological regions. The percentage of black pepper plants with yellow leaves was on average about 20–25% in the North Central Coast and Central Highlands, which was somewhat higher compared to Phu Quoc Island (16.9%). Large differences in percentage of black pepper plants with yellow leaves were observed in different districts within the same agro-ecological region. The same type of yellow leaves as described in the literature for black pepper plants infected with Meloidogyne species was observed in our study. In general, a positive relationship between the soil and root population densities of M. incognita on black pepper plants and percentage of plants with yellow leaves was observed. However, in one district (Quang Tri) a relatively low nematode population density was associated with a high percentage of plants with yellow leaves. Five nematode species were recorded for the first time on black pepper plants in Vietnam. Our study reconfirms previous reports that Radopholus similis does not occur in Vietnam.     

Decomposers and root feeders interactively affect plant defence in <Emphasis Type="Italic">Sinapis alba</Emphasis>

Aboveground herbivory is well known to change plant growth and defence. In contrast, effects of soil organisms, acting alone or in concert, on allocation patterns are less well understood. We investigated separate and combined effects of the endogeic earthworm species Aporrectodea caliginosa and the root feeding nematode species Pratylenchus penetrans and Meloidogyne incognita on plant responses including growth and defence metabolite concentrations in leaves of white mustard, Sinapis alba. Soil biota had a strong impact on plant traits, with the intensity varying due to species combinations. Nematode infestation reduced shoot biomass and nitrogen concentration but only in the absence of earthworms. Earthworms likely counteracted the negative effects of nematodes. Infestation with the migratory lesion-nematode P. penetrans combined with earthworms led to increased root length. Earthworm biomass increased in the presence of this species, indicating that these nematodes increased the food resources of earthworms—presumably dead and decaying roots. Nitrogen-based defence compounds, i.e. glucosinolates, did not correlate with nitrogen levels. In the presence of earthworms, concentrations of aromatic glucosinolates in leaves were significantly increased. In contrast, infection with P. penetrans strongly decreased concentrations of glucosinolates (up to 81%). Infestation with the sedentary nematode M. incognita induced aromatic glucosinolates by more than 50% but only when earthworms were also present. Myrosinase activities, glucosinolate-hydrolysing enzymes, were unaffected by nematodes but reduced in the presence of earthworms. Our results document that root-feeding nematodes elicit systemic plant responses in defence metabolites, with the responses varying drastically with nematode species of different functional groups. Furthermore, systemic plant responses are also altered by decomposer animals, such as earthworms, challenging the assumption that induction of plant responses including defence traits is restricted to herbivores. Soil animals even interact and modulate the individual effects on plant growth and plant defence, thereby likely also influencing shoot herbivore attack.     

Persistence of antibodies in blood and body fluids in decaying fox carcasses, as exemplified by antibodies against Microsporum canis

To assist in evaluating serological test results from dead animals, 10 silver foxes (Vulpes vulpes) and 10 blue foxes (Alopex lagopus), 6 of each species previously vaccinated against and all challenged with Microsporum canis, were blood sampled and euthanased. Fox carcasses were stored at +10°C, and autopsy was performed on Days 0, 2, 4, 7, and 11 post mortem during which samples from blood and/or body fluid from the thoracic cavity were collected. Antibodies against M. canis were measured in an enzyme-linked immunosorbent assay (ELISA) as absorbance values (optical density; OD). To assess the degradation of antibodies, the ratio between post mortem and ante mortem absorbance was calculated. The mean absorbance from samples collected during autopsy was generally lower than from samples from live animals. In blood samples, this difference increased significantly with time (P = 0.04), while in body fluid samples the difference decreased (not significant; P = 0.18). We suggest that a positive serological result from testing blood or body fluid of a dead animal may be regarded as valuable, although specific prevalences obtained by screening populations based on this type of material may represent an under-estimation of the true antibody prevalence. Negative serological test results based on material from carcasses may be less conclusive, taken into account the general degradation processes in decaying carcasses, also involving immunoglobulin proteins.     

Lacustrine profundal meiobenthos as an environmental indicator

Organic loading and eutrophy is indicated at profundal depths by large numbers of resting copepodid stages of cyclopoid copepods, by the occurrence of the naidid oligochaete species, Amphichaeta leydigii and Specaria josinae, and the harpacticoid species Canthocamptus staphylinus, and by a low meiobenthos/macrobenthos biomass ratio. An oligotrophic environment is indicated by the occurrence of the aeolosomatid oligochaetes Aeolosoma quaternarium, A. hemprichi and Rheomorpha neiswestnovae, the naidid oligochaete Chaetogaster langi and the harpacticoid species Attheyella crassa and a high meiobenthos/macrobenthos biomass ratio.     

Evidence for Scavenging Behavior in the Western Diamondback Rattlesnake (Crotalus atrox)

The use of dead and decaying animals for food appears often as an adaptive strategy in birds and mammals but is apparently rare within the reptiles. Scanty evidence exists for the utilization of such a scavenging strategy by rattlesnakes but convincing data gathered under properly controlled circumstances in this regard have not been forthcoming. Western diamondback rattlesnakes (Crotalus atrox) were cage and arena tested for putrescent mouse preference and putrescent mouse location ability. Adults and neonates readily accepted mice that had been aged up to 48 h while black rat snakes (Elaphe obsoleta) failed to accept putrescent mice and would accept fresh-killed rodents only if the latter were moving. Adult rattlesnakes could locate putrescent mice buried in gravel but failed to find fresh-killed animals. The results were used to document strong evidence for a scavenging feeding strategy for this species and perhaps for the viperids as a whole.     

Effect of the Razdol’naya River on structure of the free-living nematode community of the Amursky Bay,Sea of Japan

The effect of the Razdol’naya River on the littoral and sublittoral nematode community was studied in the innermost part of the Amursky Bay. Thanks to the seasonal abundance of juveniles of macrobenthic animals, pseudomacrobenthic species prevailed in the meiobenthos littoral community. Juvenile amphipods dominated (39.5%), the percentage of nematodes was 18.4% (45 species). The nematodes dominated in the meiobenthos community (65.7%, 71 species) at the sublittoral zone. The similarity of the species structure of littoral and sublittoral nematodes reached 36.5%. Low population density (2.6±1.7 thousand ind/m²) and poor species diversity of nematodes (7 species), the dominating form being Oncholaimium paraolium, were recorded at the littoral zone, which was subjected to direct riverine influence (1‰salinity). The correlation analysis revealed no relationship between salinity and population density of nematodes at the littoral zone. At the sublittoral zone (at stations of salinity less than 2.85‰) the parameters of population density (73.9±32.3 thousand ind/m²) and species diversity (12 species) of nematodes were the lowest, Parodontophora timmica dominated. A poor expressed dependence between the density of nematode populations and salinity was revealed. The correlation between the average size of ground particles and population density of nematodes was recorded. The greatest similarity of the species structure of littoral and sublittoral nematodes (26.67%) was recorded on gravel-sand bottoms.     

Influence of bacterivorous nematodes on the decomposition of cordgrass

The influence of bacterivorous nematodes (Diplolaimelloides meyli, Diplolaimelloides oschei, Diplolaimella dievengatensis, Panagrolaimus paetzoldi) on the decomposition of a macrophyte (Spartina anglica) in an aquatic environment was investigated by using laboratory microcosm experiments. Several earlier studies have shown enhancement of the decomposition process in the presence of nematodes, but nematode species-specific effects were never tested. In this study four bacterivorous nematode species were applied separately to microcosms to investigate such species-specific influences.No stimulation of the decomposition process nor of the microbial community was observed in the presence of the nematodes, both were highest in the absence of nematodes. However, clear differences were found between nematode treatments. P. paetzoldi reached much higher numbers than the other species, causing a decrease in microbial activity, probably due to (over)grazing. Remarkably this low microbial activity did not result in a slow-down of the decomposition process compared to the other nematode treatments, raising the question whether P. paetzoldi might be able to directly assimilate detrital compounds. Other nematode species reached much lower densities, but nevertheless an influence on the decomposition process was observed. However, this experiment does not support the view that bacterivorous nematodes enhance decomposition rate.The experimental results show that in nematode communities the use of functional groups is inadequate for biodiversity studies. The four nematode species used in this study belong to the same functional group, but are clearly not functionally redundant since they all have a different influence on the cordgrass decomposition. This suggests that the relationship between nematode species diversity and ecosystem functioning may be idiosyncratic.     

The Meiobenthos in the Area of Japanese Scallop Cultivation in Minonosok Bay (Peter the Great Bay,Sea of Japan)

In Minonosok Bay, in a region of long-term industrial mariculture of mollusks, a steady biohydrochemical complex with increased organic matter content has been formed, in which the meiobenthos community was represented by a rather complete set of taxonomic groups of low population density. There were 16 groups (order, class) of the meiobenthos revealed, and the greatest population density was recorded in the central part of the bay under installations with suspended mollusks, (333000 ind./m²). Nematodes dominated in the eumeiobenthos; however, crustaceans prevailed in the bottom water layer and sediments at stations with increased oxygen content. Bivalves and gastropods dominated in the pseudomeiobenthos. Correlation analysis has revealed the dependence of the population density of the total meiobenthos and eumeiobenthos on the type of ground. There were 42 nematode species revealed; Axonolaimus seticaudatus, Enoplolaimus medius, Daptonema sp., Paracomesoma sp., and Oncholaimium paraolium dominated. Three nematode taxocens were discriminated by dominating species in the population density and results of cluster analysis of the data. Detritivorous nematodes prevailed in all types of ground. A correlation was found between the index of species diversity of nematodes and the content of organic carbon in the ground.     

Using spatially‐explicit capture–recapture models to explain variation in seasonal density patterns of sympatric ursids

Understanding how environmental factors interact to determine the abundance and distribution of animals is a primary goal of ecology, and fundamental to the conservation of wildlife populations. Studies of these relationships, however, often assume static environmental conditions, and rarely consider effects of competition with ecologically similar species. In many parts of their shared ranges, grizzly bears Ursus arctos and American black bears U. americanus have nearly complete dietary overlap and share similar life history traits. We therefore tested the hypothesis that density patterns of both bear species would reflect seasonal variation in available resources, with areas of higher primary productivity supporting higher densities of both species. We also hypothesized that interspecific competition would influence seasonal density patterns. Specifically, we predicted that grizzly bear density would be locally reduced due to the ability of black bears to more efficiently exploit patchy food resources such as seasonally abundant fruits. To test our hypotheses, we used detections of 309 grizzly and 597 black bears from two independent genetic sampling methods in spatially‐explicit capture–recapture (SECR) models. Our results suggest grizzly bear density was lower in areas of high black bear density during spring and summer, although intraspecific densities were also important, particularly during the breeding season. Black bears had lower densities in areas of high grizzly bear density in spring; however, density of black bears in early and late summer was best explained by primary productivity. Our results are consistent with the hypothesis that smaller‐bodied, more abundant black bears may influence the density patterns of behaviorally‐dominant grizzly bears through exploitative competition. We also suggest that seasonal variation in resource availability be considered in efforts to relate environmental conditions to animal density.     

Within-trophic group interactions of bacterivorous nematode species and their effects on the bacterial community and nitrogen mineralization

Knowledge of the interactions between organisms within trophic groups is important for an understanding of the role of biodiversity in ecosystem functioning. We hypothesised that interactions between bacterivorous nematodes of different life history strategies would affect nematode population development, bacterial community composition and activity, resulting in increased N mineralization. A microcosm experiment was conducted using three nematode species (Bursilla monhystera, Acrobeloides nanus and Plectus parvus). All the nematode species interacted with each other, but the nature and effects of these interactions depended on the specific species combination. The interaction between B. monhystera and A. nanus was asymmetrically competitive (0,–), whereas that between B. monhystera and P. parvus, and also A. nanus and P. parvus was contramensal (+, –). The interaction that affected microcosm properties the most was the interaction between B. monhystera and P. parvus. This interaction affected the bacterial community composition, increased the bacterial biomass and increased soil N mineralization. B. monhystera and P. parvus have the most different life history strategies, whereas A. nanus has a life history strategy intermediate to those of B. monhystera and P. parvus. We suggest that the difference in life history strategies between species of the same trophic group is of importance for their communal effect on soil ecosystem processes. Our results support the idiosyncrasy hypothesis on the role of biodiversity in ecosystem functioning.     

An analysis of competitive interactions between 3 hermit crab species

Summary Competition for empty gastropod shells in a group of three sympatric hermit crabs (Pagurus hirsutiusculus, Pagurus granosimanus, and Pagurus beringanus) was studied in the San Juan Archipelago, Washington State. Estimates of the competitive effects of each species on the others' shell supplies were derived using field data on shell utilization and the results of laboratory experiments to determine rates of acquisition and exchange of shells and preferences for different shell species. Each species experienced approximately an order of magnitude more intraspecific competition than interspecific competition for empty shells. This resulted from differences in preference for shell shapes, shell size use, and habitat use between P. hirsutiusculus and P. granosimanus, and largely from differences in habitat use between P. beringanus and the other two species. Experiments involving the release and recensusing of marked empty shells were used to estimate competitive effects more directly for the interaction between P. hirsutiusculus and P. granosimanus. Results were consistent with the estimates derived from data on resource partitioning. Possible causes of the low levels of interspecific competition are discussed, and results are compared with studies of other organisms that estimated both inter- and intra-specific competition.     

Effects of 17-α-estradiol on a free-living marine nematode community: a microcosm experiment

A microcosm experiment was used to examine the effects of 17-α-estradiol on a nematode community. Four 17-α-estradiol concentrations (0.15, 0.31, 0.62 and 1.24 ppm) were tested, and effects were examined after 30 days. Significant differences were noted between nematode assemblages from the control and those from 17-α-estradiol treatments. Total nematode abundance, Shannon–Wiener index and evenness were affected by 17-α-estradiol contamination, but species richness was unaffected. Chromadorina metulata and Ascolaimus elongatus were eliminated at all doses tested and seemed to be intolerant to estradiol. Kraspedonema octogoniata decreased at all doses and could be categorised as sensitive to estradiol contamination. Spirinia gerlachi increased at all doses tested and seemed to be an opportunistic species at the doses tested.     

The Structure of a Free-living Nematode Community in Wrangel Bay of the Sea of Japan

The qualitative composition and distribution of the meiobenthos in Wrangel Bay (Nakhodka Bay of the Sea of Japan) depend on the bottom sediment grain composition and on the concentration of heavy metals in the ground. It was established that the meiobenthos in the bay was represented by 13 groups of animals (class, order) and was relatively evenly distributed. The nematodes dominated (50–80%), and their settlement density was slightly higher in silty ground than in silty–sandy ground. Forty-eight species of nematodes were found; Dorylaimopsis peculiaris, Viscosia stenostoma, Axonolaimus seticaudatus, Metasphaerolaimus japonicus, and Pseudosteineria inaequispiclata dominated in the silty–sandy sediments; Sabatieria pulchra, S. palmaris, Metalaimus pumilus, Sphaerolaimus limosus, and Oncholaimium ramosum dominated in the silty ground. A slightly expressed correlation of the settlement density with the ground type and lead concentration in the bottom sediments emerged for two species (S. pulchra and S. palmaris).     

The rhabditid nematode Phasmarhabditis hermaphrodita as a potential biological control agent for slugs

A nematode, Phasmarhabditis hermaphrodita, known to be associated with slugs but not previously thought to be parasitic, was shown to be a parasite capable of killing the pest slug Deroceras reticulatum. The parasite infects slugs in the area beneath the mantle surrounding the shell, causing a disease with characteristic symptoms, particularly swelling of the mantle. Infection leads to death of the slug, usually between seven and 21 days afterwards. The nematode then spreads and multiplies in the cadaver. In an experiment where individual D. reticulatum were exposed to different numbers of P. hermaphrodita, a significant positive relationship was found between nematode dose and slug mortality. In two experiments on host range, the nematode was found to infect and kill all pest slug species tested: Deroceras caruanae, Arion distinctus, Arion silvaticus, Arion intermedius, Arion ater, Tandonia sowerbyi and T. budapestensis, in addition to D. reticulatum.     

Metazoan meiobenthos and nematode assemblages in the Nyegga Region of methane seepage (Norwegian Sea)

Based on visual observations in the Nyegga (Norwegian Sea) methane seep area we defined arbitrary boundaries and defined the following types of microbiotopes: the siboglinid field, bacterial mat, and background sediment. The metazoan meiobenthos consisted of 14 major taxa; the Nematoda dominated at seven of the eight stations. The taxonomic diversity of metazoan meiobenthos in the siboglinid fields was higher than that in the background bottom area. The average population density in siboglinid microbiotope exceeded the abundance of organisms in the background sediments by 1.3 times. The nematode population and total meiobenthos varied in bacterial maths. The modal size fraction of meiobenthos and nematodes regardless of microbiotopes fell on samples that were obtained on sieves with 63–125 μm mesh sizes. In total, 88 nematod species belonging to 26 families and 63 genera were recorded. The species diversity decreased in the direction from the background biotope to siboglinid fields and further to bacterial mats.