Three new species of free-living marine nematodes from sublittoral sediments in Liverpool Bay

Three new species of free-living marine nematodes are described from sublittoral sediments in Liverpool Bay, UK. Pselionema longiseta n.sp. (Ceramonematoidea) is closest to P. longissimum Gerlach, 1952, from which it is distinguished by the longer cephalic setae and the larger amphids; Laimella filicaudata n.sp. (Chromadoroidea) is closest to L. longicauda Cobb, 1920, from which it is mainly distinguished by the much greater curvature of the spicules and the longer caudal apophyses of the gubernaculum; Pseudonchus decempapillatus n.sp. (Choanolaimoidea) is closest to P. deconincki Warwick, 1969 and is distinguished by the presence of 10, rather than 13, pre-anal supplements in the male, by the longer cephalic setae, and by the presence of numerous caudal setae.     

The primary productivity of marine macrophytes from a rocky intertidal community

This study represents the first report of primary production rates for Southern California intertidal producers. The production rates of 18 marine macrophytes near Wilson Cove, San Clemente Island, are close to those for other marine algal communities. No apparent relationship was revealed between the productivity of an alga and the division to which it belongs; however, productivity was associated with growth form. Encrusting prostrate forms were the lowest producers in terms of g C/m²/h and g C/g dry weight/h; sheet-like and finely-branched forms showed a greater productivity than coarsely-branched forms. Gelidium pusillum and Ulva californica had considerably greater production rates than the other algae measured.     

Studies on the sublittoral free-living nematodes of Liverpool Bay. II. Influence of sediment composition on the distribution of marine nematodes

Previous work has shown that the composition and diversity of nematode populations in Liverpool Bay (UK) are correlated with sediment granulometry, and possible reasons for this relationship are now discussed. Sediment granulometry and nematode size appear not to be directly related, but the range of nematode lengths is greater in the more heterogeneous sediments. Median particle diameter, sorting efficiency and silt/clay content are all considered to affect sediment uniformity, and an index including all three factors correlated significantly with both size diversity and species diversity. Study of the distribution of the various feeding types revealed that the relative and absolute abundances of epistratum feeders and non-selective deposit feeders correlated significantly with the sediment silt/clay content. It is concluded that sediment granulometry influences nematode distribution both directly in determining the size range of the populations (and hence, to some extent, the species diversity) and indirectly in determining, to a great extent, the type of food available. In addition, it was noted that nematodes with very ornate cuticular ornamentation tended to be associated with coarser, silt-free sediments, and it is suggested that this may be correlated both with their mode of locomotion and with the need for mechanical protection in unstable substrata.     

Diversity of free-living marine nematodes (Enoplida) from Baja California assessed by integrative taxonomy

We used morphological and molecular approaches to evaluate the diversity of free-living marine nematodes (order Enoplida) at four coastal sites in the Gulf of California and three on the Pacific coast of Baja California, Mexico. We identified 22 morphological species belonging to six families, of which Thoracostomopsidae and Oncholaimidae were the most diverse. The genus Mesacanthion (Thoracostomopsidae) was the most widespread and diverse. Five allopatric species, genetically and morphologically differentiated, were found in two localities in the Gulf of California (M. sp1 and M. sp2) and three in the Pacific coast (M. sp3, M. sp4 and M. sp5). Overall, we produced 19 and 20 sequences for the 18S and 28S genes, respectively. Neither gene displayed intraspecific polymorphisms, which allowed us to establish that some morphological variation was likely either ontogenetic or due to phenotypic plasticity. Although 18S and 28S phylogenies were topologically congruent (incongruence length difference test, P > 0.05), divergences between species were much higher in the 28S gene. Moreover, this gene possessed a stronger phylogenetic signal to resolve relationships involving Rhabdodemania and Bathylaimus. On the other hand, the close relationship of Pareurystomina (Enchilidiidae) with oncholaimids warrants further study. The 28S sequences (D2D3 domain) may be better suited for DNA barcoding of marine nematodes than those from the 18S rDNA, particularly for differentiating closely related or cryptic species. Finally, our results underline the relevance of adopting an integrative approach encompassing morphological and molecular analyses to improve the assessment of marine nematode diversity and advance their taxonomy.     

Analysis of the small-scale spatial patterns of free-living marine nematodes from tidal flats in the East Frisian Wadden Sea

Serial samples with a multiple corer were taken in order to understand the small-scale aggregation patterns in the nematode community. A total of 77 species was found in the sample. Fifteen dominant nematode species were examined by means of a dispersion analysis. Only one species (Metachromadora scotlandica) may be considered randomly distributed. A variogram analysis gave no proof of aggregation in that species, but all the other (aggregated) species displayed different spatial patterns: (1) a maximum/aggregation at the sample's margin, (2) two maxima/aggregations in the centre of the sample, (3) aggregation of individuals distributed at random over the entire sample (Metalinhomoeus typicus) and (4) aggregation of individuals distributed at random only in the centre of the sample (Paralinhomoeus ilenensis). These results allow the prognosis that distribution patterns are repetitive in five species (Microlaimus conothelis, M. marinus, Odontophora rectangula, Oncholaimellus calvadosicus, Viscosia rustica). Finally, by means of MDS-ordination (based on cosine similarity) two nematode associations were distinguished: one group represented by diatom-feeders (sensu lato), the other one comprised of DOM-users (sensu lato). Received: 13 May 1998 / Accepted: 15 January 1999     

The Mediterranean intertidal habitat as a natural laboratory to study climate change drivers of geographic patterns in marine biodiversity

Nylon bags containing yellow leaves of Rhizophora apiculata and Avicennia marina, were immersed for 80 days from August to October, 1996. the decomposing leaves were collected every 10 days and analysed for dry weight loss and six biochemical parameters: tannins, total amino acids, total sugars, total nitrogen, total lipids and fatty acid profile. the leaf weight initially decreased very rapidly by about 50% of the start in two species of mangroves within 10 days. Similar changes were observed with tannins, total amino acids and sugars. However, the concentration of nitrogen increased significantly with decomposition. There was no significant change in total lipid and fatty acid profile. the highest concentration of fatty acid in the decomposing leaves was palmitic acid (16:0). Unsaturated fatty acids such as, 18:1 w7c and 18:1 w9c were found to be present in decomposing leaves of both species.     

Urban marine ecology in southern California: the ability of riprap structures to serve as rocky intertidal habitat

Increasing human populations along marine coastlines has lead to increasing urbanization of the marine environment. Despite decades of investigations on terrestrial ecosystems, the effect of urbanization on marine life is not well understood. Riprap is the rocky rubble used to build jetties, breakwaters, and armored shorelines. Roughly 30% of the southern California shoreline supports some form of riprap, while 29% of the shoreline is natural rocky substrate. Astonishingly few studies have investigated this anthropogenic rocky habitat even though it rivals a natural habitat in area on a regional scale along a coastline that has been extensively studied. In this study, I compared the diversity and community structure of exposed rocky intertidal communities on four riprap and four natural sites in southern California. I ask the following questions: (1) does diversity or community composition differ between intertidal communities on riprap and natural rocky habitats in southern California, (2) if so, which organisms contribute to those differences, (3) which physical factors are contributing to these differences, and (4) do riprap habitats support higher abundances of invasive species than natural habitats? On average, riprap and natural rocky habitats in wave exposed environments in southern California did not differ from each other in diversity or community composition when considering the entire assemblage. However, when only mobile species were considered, they occurred in greater diversity on natural shores. These differences appear to be driven by wave exposure. The presence of invasive species was negligible in both natural and riprap habitats.     

Morphological and habitat divergence in the intertidal limpet Patelloida pygmaea

In the intertidal limpet Patelloida pygmaea, two distinctive morphs, the forms pygmaea and conulus, have been recorded. The former possesses a flat elongated shell, and the latter has an extremely high round shell. It has been observed in the field that pygmaea is found on oyster shells Crassostrea gigas. The form conulus uses an unusual substrate for attachment. It is found on the living shells of the intertidal gastropod Batillaria cumingi. Although conulus is normally found only on shells of Batillaria, it can also be found on oyster shells when pygmaea and Batillaria shells are not present in nature. An electrophoretic analysis of allozymes showed that these two forms are reproductively isolated from each other and coexist without gene exchange on the same mudflat. Laboratory experiments showed that pygmaea prefers oyster shells and conulus prefers Batillaria shells as substrates for attachment when both oyster and Batillaria shells are present. The form pygmaea did not attach to Batillaria shells, even when only Batillaria shells were available. However, conulus also attached to oyster shells when Batillaria shells were not available. The proportion of individuals of conulus that attached to oyster shells decreased significantly when pygmaea was attaching to the oyster shells. These results suggest that pygmaea is ecologically more specialized to living on oyster shells than conulus.     

Population distribution and structure of the free-living nematodes of Long Island Sound

The distribution and structure of nematode populations in 4 sedimentary environments (muds, muddy sands, fine sands and medium-coarse sands) in Long Island Sound were studied. Mean population densities were highest in muds and muddy sands. Cluster analysis suggested the presence of two basic faunistic units; a mud unit characterized by high species dominance, low species diversity and low species endemism, and a sand unit characterized by low species dominance, high species diversity and high species endemism. Species diversity in all habitats was a direct function of both species richness and equitability. Limited niche separation among deposit feeders, usually the dominant nematode trophic type in muddy sediments, is proposed as the cause for the high species dominance so often characteristic of shallow marine muds. The study afforded the opportunity to examine the quantitative and qualitative aspects of population structure in relation to environmental impact (as indicated by large differences in the heavy metal and organic carbon concentrations within each of the 4 sedimentary regimes). Within each sediment type no differences in population densities, species composition or species diversity of nematodes existed between heavily impacted and apparently non-impacted sediments, or between Long Island Sound and similar coastal regions. These findings cast doubt on (1) the use of heavy metal and organic carbon concentrations as indicators of environmental stress for marine nematodes; (2) the use of diversity indices alone as indicators of environmental deterioration; and (3) the usefulness of field monitoring studies alone for the assessment of pollution impact on marine nematodes.Contribution no. 100 from the Institute of Marine and Atmospheric Sciences, City College of New YorkCommunicated by M.R. Tripp, Newark     

The relative importance of host-plant genetic diversity in structuring the associated herbivore community

Recent studies suggest that intraspecific genetic diversity in one species may leave a substantial imprint on the surrounding community and ecosystem. Here, we test the hypothesis that genetic diversity within host-plant patches translates into consistent and ecologically important changes in the associated herbivore community. More specifically, we use potted, grafted oak saplings to construct 41 patches of four saplings each, with one, two, or four tree genotypes represented among the host plants. These patches were divided among two common gardens. Focusing first at the level of individual trees, we assess how tree-specific genotypic identity, patch-level genetic diversity, garden-level environmental variation, and their interactions affect the structure of the herbivore community. At the level of host-plant patches, we analyze whether the joint responses of herbivore species to environmental variation and genetic diversity result in differences in species diversity among tree quartets. Strikingly, both species-specific abundances and species diversity varied substantially among host-tree genotypes, among common gardens, and among specific locations within individual gardens. In contrast, the genetic diversity of the patch left a detectable imprint on local abundances of only two herbivore taxa. In both cases, the effect of genetic diversity was inconsistent among gardens and among host-plant genotypes. While the insect community differed significantly among individual host-plant genotypes, there were no interactive effects of the number of different genotypes within the patch. Overall, additive effects of intraspecific genetic diversity of the host plant explained a similar or lower proportion (7-10%) of variation in herbivore species diversity than did variation among common gardens. Combined with the few previous studies published to date, our study suggests that the impact of host-plant genetic diversity on the herbivore community can range from none to nonadditive, is generally low, and reaches its most pronounced impact at small spatial scales. Overall, our findings strengthen the emerging view that the impacts of genetic diversity are system, scale, and context dependent. As the next step in community genetics, we should then start asking not only whether genetic diversity matters, but under what circumstances its imprint is accentuated.     

Use of artificial holes in studying community development in cryptic marine habitats in a tropical rocky intertidal region

Previous studies on the rocky intertidal shores of the Bay of Panama indicate that for many sessile and mobile organisms holes and crevices are important refuges from consumers. To study the dynamics of these hole-dwelling species assemblages, we devised a method allowing repetitive, non-destructive sampling and species manipulations in artificial holes. These are fiberglass sleeves with flanges at the outer edge that are inserted into receptacles made of quick-setting concrete. Predator and herbivore manipulations include: fences excluding slow-moving benthic consumers, bars across hole mouths restricting entry of large fishes and homogeneous (shelterless) surfaces created around a treatment decreasing abundance of small crabs. This design has withstood the rigors of two wet seasons in Panama. Results from two sites in Panama indicate that colonization occurs rapidly (6–7 months) in holes established in mid dry season. Encrusting fleshy algae (Ralfsia sp.) and ephemeral green algae (Cladophora spp.) colonize first and are succeeded by encrusting species of coralline algae, bryozoans and colonial tunicates and by erect fleshy red algae. Where consumers are present, encrusting corallines predominate; without consumers, bryozoans, tunicates and erect algae are more abundant. Zonation patterns develop within the holes, with the desiccation/heattolerant Ralfsia sp. dominating at the outer edges. With increasing deph, encrusting coralline algae, bryozoans and colonial tunicates reach their respective peak abundances. In contrast to the high variability observed among naturally occurring holes, replicates of each treatment tend to be similar. Between-treatment and between-site comparisons are less so. The naturally-occurring high level of small-scale patchiness is thus presumably due to variation in recruitment and in the local (microspatial) consumer regime. Substratum heterogeneity is therefore directly and indirectly important in maintaining a high local diversity in this community. As in other studies, consumers or disturbances are key factors in regulating patterns of community structure. More experiments of longer duration are necessary to ascertain the relative importances of consumers/disturbance and competition in controlling such assemblages.     

Seasonal changes in the structure of an intertidal community

Quantitative (0.25 m²) samples of macrofaunal (>1.0 mm) invertebrates were taken in each season from one habitat of an intertidal sandbar in the North Inlet estuary near Georgetown, South Carolina, USA. During all seasons the community inhabiting the sample site was numerically dominated by two species of haustoriid amphipods (Acanthohaustorius millsi and Pseudohaustorius caroliniensis). Seasonal changes at the community level were clearly controlled by the population dynamics of the numerically dominant species, and qualitative information on life histories was important to the interpretation of analyses' results.This work was supported by the Environmental Technology Center of Martin Marietta Corporation and the Belle W. Baruch Institute for Marine Biology and Coastal Research. It is Contribution No. 138 of the Belle W. Baruch Institute for Marine Biology and Coastal research.     

海洋滩涂贝类养殖环境的研究现状

随着海洋滩涂贝类养殖业的发展，滩涂贝类养殖环境日趋恶化，生物病原大量滋生，养殖生产受到了严重的阻碍。文章介绍了我国滩涂的分布、类型和资源开发利用状况；结合滩涂贝类养殖生产和发病状况，从微生物学、底栖生态学和污染生态化学等角度，对我国在海洋滩涂贝类养殖环境方而取得的研究成果进行了综述；提出了滩涂贝类养殖环境方面亟需解决的问题。这些问题包括养殖容量的确定、底栖生物生态的研究、健康养殖模式的确立和污染环境的生物修复等。     

Studies on the sublittoral free-living nematodes of Liverpool Bay. I. The structure and distribution of the nematode populations

Data collected from a survey of the benthic fauna of Liverpool Bay (UK) have been used to study the distribution and structure, in terms of percent age dominance and percent age frequency, of the nematode populations. Cluster analysis of the faunistic data from individual stations has shown that the populations are not sharply delimited. The relative proportions of their characteristic genera are extremely variable, and apparently influenced by small differences in sediment composition. It is, thus, considered more logical to think in terms of a number of different habitats, each with certain characteristic genera, rather than in terms of a series of discrete associations. Six types of habitat are distinguished on the basis of sediment granulometry: (1) mud and sandy mud; (2) very muddy sand; (3) muddy sand; (4) muddy sand-gravel mixtures; (5) clean sand-gravel mixtures; (6) clean sand. Habitats 1, 2 and 3 were dominated by Sabatieria spp., the degree of dominance apparently being related to the percentage of silt-clay. Habitat 4 was dominated by Neochromadora sp. and Sabatieria spp. and Habitats 5 and 6 by Desmodora sp. Both generic and dominance diversity were very much lower for Habitats 1 and 2 than elsewhere.     

Acetate uptake from ambient water by the free-living marine nematodeAdoncholaimus thalassophygas

Nematodes belonging to the family Oncholaimidae are known to aggregate at sites of organic pollution. The oncholaimidAdoncholaimus thalassophygas (De Man, 1876), collected from the Weser Estuary, FRG, in 1989, has the capability to take up acetate at naturally occurring concentrations. Under almost axenic conditions, ca 2.3 to 3.0 ng sodium acetate was taken-up per worm within 24 h, when an ambient concentration of 0.33 mmol was offered. The concentration factor was ca 8.5 to 11.1. The results suggest that a highly motile oxybiotic nematode may benefit from the fermentation products of anoxic habitats.Contribution No. 251 of the Alfred-Wegener-Institute for Polar and Marine Research     

Life history of a free-living marine nematode Daptonema normandicum reared in laboratory

Life history of a free-living meiobenthic nematode Daptonema normandicum (DeMan, 1890) was studied in the laboratory. Live specimens were primarily collected from the sewage outlet site near the mouth of the Mandovi estuary, Goa This species was the most dominant (> 67%) among the meiobenthic nematodes. Vertically, nematode abundance was highest at the surface sediment and correlated with the organic carbon and sediment chlorophyll-a. Considering their dominance in the meiofauna, attempts were made to rear D. normandicum in laboratory. Salinity of the culture medium was maintained at 14 to 17 PSU (same as the collection site). All the culture experiments were conducted in semisolid nutrient agar media at 27 +/- 2 degrees C temperature for 12 hr dark: 12 hr light conditions. The food consists primarily of an unidentified bacterium and mixed algae, but diatom and ciliates were also observed in culture. Females produced first batch of eggs at the age of 23 days. Gravid female normally carry 8-10 eggs. Embryonic development is completed in -72 hr and entire life cycle (egg to adult) was completed in 22-24 days. Average size of juveniles at the hatching was 0.189 mm. Young individuals attains a maximum size of 1.23 mm (male) and 1.04 mm (female) in -21-23 days. Growth, in terms of length was augmented upto 23rd day and ceased thereafter. The daily growth increment for the first 5 days was 0.01-0.04 mm which increased upto 0.05-0.08 mm d(-1) during the maturation (10-18 days). Male : female ratio was 1:2. In this laboratory study, we provided information on the embryonic development, the life cycle and ecology Our results demonstrated that D. normandicum can be reared successfully under the controlled conditions, suggesting possible use of this species in toxicological and aquaculture studies. The culture method described is very handy and can be applicable for rearing other meiobenthic species particularly the nematodes with comparable feeding habits.     

Distribution and abundance of marine nematodes on the kelp Macrocystic integrifolia

The species and distribution of nematodes on the kelp Macrocystic integrifolia Bory, in the Bamfield region of Barkley Sound, British Columbia, Canada were examined. Nine species (belonging to six families) of nematodes were found on the kelp blades. Three species (Monhystera disjuncta, M. refringens and Prochromadorella neapolitana) comprised 91–99% of the nematode fauna and occurred in all monthly samples from July 1978 to November 1979. The three dominant species exhibited seasonal density differences. P. neapolitana occurred mostly in the summer, M. refringens abundance peaked from July to October and M. disjuncta was relatively abundant throughout the year. The other species contributed little to the overall abundance and distribution patterns. All three species occurred in greatest abundance on the lower and middle blades of M. integrifolia in the deep end of the kelp bed. Very few individuals occurred on the upper blades. Nematode distribution on M. integrifolia appeared to be related to blade age and the associated food sources on the blade.     

The role of habitat disturbance and recovery in metapopulation persistence

Classical metapopulation theory assumes a static landscape. However, empirical evidence indicates many metapopulations are driven by habitat succession and disturbance. We develop a stochastic metapopulation model, incorporating habitat disturbance and recovery, coupled with patch colonization and extinction, to investigate the effect of habitat dynamics on persistence. We discover that habitat dynamics play a fundamental role in metapopulation dynamics. The mean number of suitable habitat patches is not adequate for characterizing the dynamics of the metapopulation. For a fixed mean number of suitable patches, we discover that the details of how disturbance affects patches and how patches recover influences metapopulation dynamics in a fundamental way. Moreover, metapopulation persistence is dependent not only on the average lifetime of a patch, but also on the variance in patch lifetime and the synchrony in patch dynamics that results from disturbance. Finally, there is an interaction between the habitat and metapopulation dynamics, for instance declining metapopulations react differently to habitat dynamics than expanding metapopulations. We close, emphasizing the importance of using performance measures appropriate to stochastic systems when evaluating their behavior, such as the probability distribution of the state of the metapopulation, conditional on it being extant (i.e., the quasistationary distribution).