John H. Tietjen

Ecology of deep-sea nematodes from the Puerto Rico Trench area and Hatteras Abyssal Plain

Abstract Nematode assemblages from a bathyal silty-sand and three hadal silty-clays from the Puerto Rico Trench area were compared with that from a silty-clay from the HatterasAbyssal Plain. Fine sediments at each site were largely dominated by species belonging to three major genera: Theristus, Acantholaimus and Halalaimus . At the bathyal sand site the relative abundances of these genera were reduced and those of several others (e.g. Desmodora, Leptolaimus, Camacolaimus, Tricoma, Greeffiella, Setoplectus ) elevated. Average body weight of nematodes occurring in the sand was 0.057 μg (dry weight), approximately 20–50% that of the nematodes found in the silty-clays. It is suggested that in the deep sea, as at shallow depths, smaller nematodes are better able to move in heterogeneous, coarser sediments than in more uniform, fine ones. Deposit-feeding species were the dominant feeding type observed in all sediments, but epistrate feeders were most numerous in the bathyal sands, probably the result of increased resource partitioning by worms inhabiting a more heterogeneous sedimentary environment. Species richness in bathyal sands was also high. Normal classification of assemblages found in sediments from the Hatteras Plain, Puerto Rico Trench areas, Venezuela Basin and upper abyssal province off North Carolina suggests that deep-sea nematode families and genera are widely distributed across the Antillean Arc. However, species endemism is high: 67 and 77% of the species identified from the Hatteras Plain and Puerto Rico Trench respectively, occurred only at these sites. Affinities among species from all four sites were very low. The wide distribution of families and genera, and narrow distribution of species, suggests that current radiation of deep-sea nematodes probably occurs at the species level.

Abundance and Biomass of Metazoan Meiobenthos in The Deep Sea

Quantitative information on the abundance and biomass of deep-sea metazoan meiobenthos, gathered principally from research conducted since 1980, is summarized. Abundance and biomass in the deep Atlantic, Pacific and Indian Oceans generally range between 100 and 1000 x 103 individuals m-2 and 10 to 400 mg C m-2, respectively. Both decrease significantly with increasing water depth. Relationships between abundance and biomass of meiofauna are discussed, as are relationships between meiofaunal standing stocks and those of other benthic size groups. Available data (obtained mostly from the Atlantic deep sea) suggest that meiofaunal biomass is two orders of magnitude lower than bacterial biomass and equivalent to macroinfaunal and invertebrate megafaunal biomass. Relationships between meiofaunal standing stocks and various indices of surface-derived organic flux are generally positive, as are relationships between surface production and standing stocks. However, the functional role of metazoan meiobenthos in deep-sea food chains remains uncertain, especially the extent to which they compete with, or are food for, larger animal groups.

Meiobenthos of the hatteras abyssal plain and Puerto Rico trench: abundance, biomass and associations with bacteria and particulate fluxes

Abstract An abyssal station on the Hatteras Abyssal Plain (5411 m) and two hadal stations in the Puerto Rico Trench (7460 and 8189 m) were sampled to obtain quantitative information on the abundance and biomass of metazoan meiofauna and, for comparative purposes, bacteria and measurements of particulate flux rates. Average meiofauna abundance (no./10 cm2 ± 1 S.E. integrated over a sediment depth of 15 cm) was lowest at the 7460 m site (44 ± 10) and highest at the 8189 m (96 ± 15) and Hatteras sites (114 ± 26), the latter two not being statistically significant from each other. Biomasses (μg dry wt/10 cm2 ± 1 S.E., also integrated over a 15 cm depth) at the Hatteras and 7460 and 8189 m Trench sites were 38.4 ± 10.3, 3.8 ± 1.6 and 14.3 ± 5.1, respectively; all differences were statistically significant. High biomass at the Hatteras site was due to large, burrowing harpacticoid copepods that were found to depths of 10–15 cm below the sediment surface, and which were most abundant below the surface (0–2 cm) layer of sediment. Nematodes, the numerically dominant taxon, were most abundant in the upper 6 cm of sediment at all sites, as were copepods at the two Trench sites. Average abundances of bacteria (no. of cells × 109 per 10 cm2 of sediment to a depth of 15 cm), determined by epifluorescence microscopy, were 11.0, 10.5 and 5.6 at the Hatteras, 7460 and 8189 m Trench sites, respectively. Flux rates of organic carbon and total nitrogen (mg m−2 day−1) were about four times higher at the Hatteras site (e.g. 25.8 and 3.8) than at the 7460 m site in the Trench (6.3 and 0.8). An analysis of the meiofaunal and bacterial abundances obtained at the three sites revealed no significant associations between the two organismal groups, though abundances of both groups did decrease significantly and predictably with sediment depth at each station. Associations between particulate flux rates and meiofauna biomass were highly significant, suggesting that flux rates measured in near-bottom traps may be useful indicators of general resources available to the meiobenthos.

Distribution and species diversity of deep-sea nematodes in the Venezuela Basin

Abstract In three sedimentary regions in the deep (>3400 m) Venezuela Basin, nematode abundance and dry weight biomass (ean ±1 S.E.) were higher in hemipelagic sediments (94 ± 1.5 individuals, 88 ± 2.5 μg per 10 cm−2) than in pelagic (67 ± 3 individuals, 32 ±33 μg per 10 cm−2) or turbidite (36 ± 3 individuals, 30 ± 3 μg per 10 cm−2) sediments. Abundance of nematodes appears to be at least partially related to geographic position within the basin; hemipelagic sediments lie closer to an area of elevated surface production near the Lesser Antilles than do the pelagic or turbidite sediments. Abundance of nematodes is also directly correlated with macrofauna abundance and presence of sedimentary lipids. Normal hierarchical classification indicates the presence of two faunal groups in the sediments: a ‘sand’ fauna in coarser pelagic sediments (median grain size, 65 μm) and a ‘silt-clay’ fauna in the finer hemipelagic and turbidite sediments (median grain size in both, 0.65 μm). Animals among the two faunal groups differ mostly in their feeding morphology: selective deposit feeding species, unable to utilize large, pelagically derived particles (mainly foraminiferan tests) are more abundant in finer hemipelagic and turbidite sediments, whereas species capable of rasping food particles off large sedimentary particles (epistrate feeders) are more abundant in pelagic sands than in finer sediments. Species diversity is higher in the hemipelagic than turbidite and pelagic sediments. Two reasons postulated for this are (1) the possible input of relatively fresh, surface-derived organic matter that might permit a large number of species to exist in hemipelagic sediments than in the other two, and (2) an optimally heterogeneous grain size distribution that might allow the species to coexist equitably. All three sediments support more diverse nematode assemblages than those in the North Carolina slope region, probably reflecting the greater physical stability of the abyssal than bathyal sea floor.

Ecology and distribution of deep-sea meiobenthos off North Carolina

Abstract Observations on the ecology and distribution of meiofauna occurring on the outer continental shelf and continental slope at depths from 50 to 2500 m in the region where the Blake Plateau cuts across the North Carolina slope are reported. Total numbers of meiofauna ranged from 151/100 cm 3 of sediment at 400 m to 1196/100 cm 3 of sediment at 250 m. Sediments of the upper region (50–500 m) consisted of medium-sized calcareous sands with relatively low organic carbon contents, while the deeper sediments (600–2500 m) consisted of sandy silts and silts with organic carbon contents 6–10 times that of the shallower sediments. Two basic faunas appear to be present in the areas investigated; a shallow-water fauna extending from 50 to 500 m and a deep-water fauna from 800 to 2500 m. The shallow-water fauna consists of nematodes (the dominant taxon) and relatively large numbers of harpactacoid copepods, ostracods, benthic foraminifera, polychaetes, gastrotrichs and several other groups, while below 500 m only nematodes and foraminifera are present in large numbers, the latter being especially abundant between 800 and 2000 m. A major change in the meiofauna occurs on the Blake Plateau between the depths of approximately 400–500 m and 600–750 m where the composition of the sediment changes from sand to silty sand. From 50 m to 400–500 m gastrotrichs, turbellaria, tardigrades, kinorhynchs, halicarids, hydrozoans, gnathostomulids, lamellibranchs and cumaceans are commonly encountered; these groups are absent below 500 m. In addition, there are significant reductions in the numbers of harpactacoids, ostracods, nemerteans and polychaetes below 500 m. Examination of the nematode population also show faunal differences between the shallower sediments (50–500 m) and the deeper sediments (600–2500 m). High indices of affinity exist among the faunas between 50 and 500 m and among the faunas between 800 and 2500 m; the fauna at 600–750 m represents a transition between these two regions, but it is more closely related to the deep-water fauna. Changes in the distribution of both the total meiofuna and also the nematodes are highly correlated with changes in sediments composition and bottom water temperatures. It is suggested that changes in grain size and accompanying changes in sources of nutrition, which are the results of Gulf Stream and other current activity, are the dominant environmental factors influencing the meiofauna of the area.

Life history and feeding habits of the marine nematode, Chromadora macrolaimoides steiner

SummaryChromadora macrolaimoides Steiner, a free-living nematode present in the aufwuchs assemblages of several marine macrophytes located in North Sea Harbor, Southampton, New York, was isolated from Enteromorpha intestinalis and established in laboratory culture, where its life history and feeding habits were studied. Under the experimental conditions (25 C and 26‰ S) the worm has an average generation time (22 days) and average life span (45 days) similar to other chromadorids which have been studied in the laboratory.Tracer-feeding experiment with 32P-labelled bacteria, diatoms and chlorophytes indicate selectivity by the worm in both the ingestion and apparent digestion of potential food organisms, with the diatoms and chlorophytes being the preferred foods. Out of a total of 20 species of algae and 14 species of bacteria, two species of diatoms (Nitzschia acicularis and Cylindrotheca closterium) were found which are capable of sustaining indefinite growth. Bacteria-free culture has not been established, however, due to the extreme sensitivity of the worm to antibioties.A comparison of the feeding habits of C. macrolaimoides with Rhabditis marina, another marine nematode fed the same potential food organisms is made, and the influence of selective feeding on the spatial and temporal distribution of marine nematodes is discussed.

Distribution and species diversity of deep-sea nematodes off North Carolina*

Abstract In four sedimentary environments off North Carolina 209 species of free-living marine nematodes were identified. Of these, 106 were restricted to one of four habitats. Clayey-silts (800 to 2500 m) contained the most stenotopic species (49). Quartz-algal sands (50 to 100 m) contained 35, foraminiferan sands (250 to 500 m) 17, and sandy silts (500 to 800 m) only 5 stenotopic species. A sand zone (50 to 500 m) and a clayey-silt faunistic zone (800 to 2500 m) are recognized, separated by a transition zone (500 to 800 m) characterized by little endemism. There may be zonation of the fauna within these major zones. Species diversity decreased with increasing water depth, attributable to the decreased number of microhabitats available in the clayey-silts. Diversity is largely a function of species richness. Withinhabitat diversity in the North Carolina sediments is higher than in Long Island Sound (a shallower, temperate body of water).

Life cycles of marine nematodes

SummaryMonhystera denticulata Timm, a free-living nematode present in the aufwuchs assemblages of several marine macrophytes located in North Sea Harbor, Southampton, New York, was isolated from Zostera marina and established in laboratory culture in order to study the influences of temperature and salinity on its life history. Under experimental conditions, M. denticulata has a generation time (Measured as the time elapsing between the first egg depositions of consecutive generations) of 10–12 days at 25° C and 26‰ S, which represent optimal growth conditions in the laboratory. The organism has a generation time of 20 days at 25° C and 13‰, 17 days at 25° C and 39‰, 18 days at 15° C and 26‰, 36 days at 15° C and 13‰ and 34 days at 15° C and 39‰. As conditions vary from the optimum of 25° C and 26‰ S, a decrease in temperature of 10° C and an increase or decrease in salinity of 13‰ results in a doubling of the generation time. At 5° C the generation time is about 180–197 days.Assuming optimum conditions and average generation time, about 15 generations of M. denticulata could occur in North Sea Harbor during the year. The number of generations occurring in reality is probably less, however, due to the fact that the females deposit their eggs over a period of several days.

The use of free-living nematodes as a bioassay for estuarine sediments

Abstract A bioassay technique using free-living nematodes has been developed to assess the environmental quality of estuarine sediments. Nematodes offer the advantages of (a) generally being the most abundant metazoan in sediments; (b) having short life histories and no pelagic larvae; and (c) being relatively easy to maintain in laboratory culture. Small individual body size and rapid generation time (two weeks) render nematodes especially useful in evaluating effects of potential toxicants on populations, rather than on single individuals. The bioassay technique was developed using two species, Chromadorina germanisa and Diplolaimella punicea, and sediments from the Hudson-Raritan estuarine area. The life histories and feeding habits of both species are known. Test sediments were taken from eight stations that represent a gradient from lightly to heavily impacted. Concentrations of potential toxicants measured in these sediments included polychlorinated hydrocarbons, polynuclear aromatic hydrocarbons, and heavy metals. Control sediments, taken from 100 km distant, were almost totally toxicant-free. Nematodes were incubated in the dark at 25°C for two weeks at 1:1 and 1:10 concentrations (volume/volume) of sediments prepared with sterile sea water. Food consisted of bacteria from nematode stock cultures. Intrinsic rate of natural increase (r) of the nematodes was used as the indicator of sediment quality; r has units (daily increase in number of generations), is easily computed, and can be treated statistically. Both species grew better in control and other sediments containing low concentrations of PCBs, PAHs, and heavy metals. In sediments having TIF PCB and PAH concentrations (ppb) of more than 270 and 8700, respectively, population growth of both species tended to be less than half that found at lower concentrations. Significant inverse correlations between r and toxicant concentration occurred at 1:1 sediment-water concentrations. At 1:10 concentrations the correlations remained negative, but not at the 0·05 level of significance. Use of the nematodes Chromadorina germanica and Diplolaimella punicea offers a quick, easy and statistically testable means of assessing the quality of marine sediments on populations, rather than single individuals, of marine benthic invertebrates.

Horizontal and vertical distribution of meiofauna in the Venezuela Basin

Abstract Benthic samples collected in three sedimentary regions of the Venezuela Basin indicated differences in abundance and distribution of meiofauna among sediments. Abundance (mean ± 1 s.e.) was greatest in hemipelagic sediments (131.9 ± 14.3 individuals 10 cm−2) less in pelagic (81.2 ± 9.5) and least in turbidite (49.4 ± 8.5) sediments. Significant differences in abundance between hemipelagic and turbidite sediments were related to percent organic carbon and silt-clay. Significantly more organisms occurred in the upper than lower layer of sediments at all stations, with greatest differences occurring between the 0–2 and 2–4 cm layers. On a horizontal scale, no heterogeneity in meiofauna dispersion at centimeter or kilometer distances was detected for the turbidite and pelagic sediments. Homogeneity of dispersion was attributed to sediment homogeneity at the turbidite station and small sample size at the pelagic station. Heterogeneity in meiofauna dispersion at the centimeter scale in hemipelagic sediments was attributed to sediment heterogeneity and high organic input derived from surface production.