The Effects of Hydraulic Dredging to Control Oyster Drills on Benthic Macrofauna of Oyster Grounds in Delaware Bay,New Jersey

This study describes the extent and nature of the effects of hydraulic dredging to control oyster drills (Urosalpinx cinerea and Eupleura caudata, Family Muricidae, Order Neogastropoda) on benthic macrofauna and sediments of the oyster grounds in Delaware Bay, New Jersey. The immediate effects of hydraulic dredging were reductions in numbers of species as well as in total numbers of animals on the three oyster grounds selected. However, oyster drills were most affected. Benthic populations have recovered three to ten months after dredging. The sediments of the dredged grounds can be described as muddy sands. Immediately after dredging, additional mud was brought up from subsurface layers which reduced the median grain size on Ground 154 test plot. On Ground 515 test plot, however, there was a slight loss in the mud which increased the median grain size.     

Pollution and tidal benthic communities of the James River Estuary,Virginia

Distribution of benthic communities in the estuarine portion of the James River was controlled mainly by salinity. Pollution effects were localized and difficult to assess because of a rigorous physical environment. Mesohaline and oligohaline communities were very similar to those in other estuaries of the eastern United States. Macrobenthic densities were most severely depressed in tidal freshwater habitats near Richmond & Hopewell, where the major portion of the pollution load enters the river. Cluster analysis of species distributional patterns and ordination of pollution and physical parameters produced similar results, dividing the river into mesohaline, oligohaline, and upper and lower tidal freshwater zones. Further analysis of only the tidal freshwater portion indicated the distribution of benthic communities reflected the location and concentration of pollution sources along the river. Tidal freshwater communities were dominated by the Asiatic clam, Corbicula fluminea, tubificid oligochaetes of the genus Limnodrilus and the chironomid insect larva Coelotanypus scapularis. The fauna of the freshwater zones was very eurytopic with respect to sediment type and has a great resemblance to the fauna of eutrophic lakes. The classical concept of a sharp increase in number of species occurring from oligohaline to freshwater zones was found to be misleading. This increase does not occur until free flowing (or lotic) freshwater areas of greater habitat diversity are reached.     

Influence of salinity, competition and food supply on the growth of Gobiosoma robustum and Microgobius gulosus from Florida Bay, U. S. A.

The code Gobiosoma robustum and clown Microgobius gulosus gobies were grown in the laboratory over 27 days at two salinities (5 and 35), two food levels [low (a fixed proportion of initial mass) and high (saturation)] and both with and without the presence of the other species. Both species exhibited greatest growth at the high food level and the low (5) salinity. Neither species was affected by the presence of the other species, and there were no overall differences in growth between the two species. Thus, the observed competitive superiority of G. robustum over M. gulosus does not seem to confer an advantage relative to feeding success. Furthermore, as growth of G. robustum was greater at the lower salinity, it is clear that some factor other than salinity is restricting this species from north‐eastern Florida Bay. Additional work on the importance of predation and food resources in various regions of Florida Bay is needed to further evaluate the underlying mechanisms responsible for the bay‐wide distribution of these species.     

Interim Responses of Benthic and Snag‐Dwelling Macroinvertebrates to Reestablished Flow and Habitat Structure in the Kissimmee River,Florida, U.S.A.

A critical component in the effort to restore the Kissimmee River ecosystem is the reestablishment of an aquatic invertebrate community typical of free‐flowing rivers of the southeastern United States. This article evaluates early responses of benthic and snag‐dwelling macroinvertebrates to restoration of flow and habitat structure following Phase I construction (interim period) of the Kissimmee River Restoration Project. Replicate benthic and snag samples were collected from remnant river channels in Pool A (Control site), and Pool C, the site of the first phase of restoration (Impact site). Samples were collected quarterly for 2 years prior to construction (baseline) and monthly or quarterly for 3 years following Phase I construction and restoration of flow. Baseline benthic data indicate a community dominated by taxa tolerant of organic pollution and low levels of dissolved oxygen, including the dipterans Chaoborus americanus (Chaoboridae) and the Chironomus/Goeldichironomus group (Chironomidae). Baseline snag data indicate a community dominated by gathering‐collectors, shredders, and scrapers. Passive filtering‐collector invertebrates were rare. Following restoration of flow, benthic invertebrate communities are numerically dominated by lotic taxa, including bivalves and sand‐dwelling chironomids (e.g. Polypedilum spp., Cryptochironomus spp., and Tanytarsini). Snags within the Phase I area support an invertebrate community dominated by passive filtering‐collectors including Rheotanytarsus spp. (Chironomidae) and Cheumatopsyche spp. (Hydropsychidae). Results indicate that restoration of flow has resulted in ecologically significant changes to the river habitat template not observed in Pool A. Observed shifts in benthic and snag macroinvertebrate community structure support previously developed hypotheses for macroinvertebrate responses to hydrologic restoration.     

The ctenophore Mnemiopsis in native and exotic habitats: U.S. estuaries versus the Black Sea basin

The native habitats of the ctenophore, Mnemiopsis, are temperate to subtropical estuaries along the Atlantic coast of North and South America, where it is found in an extremely wide range of environmental conditions (winter low and summer high temperatures of 2 and 32 °C, respectively, and salinities of <2–38). In the early 1980s, it was accidentally introduced to the Black Sea, where it flourished and expanded into the Azov, Marmara, Mediterranean and Caspian Seas. We compile data showing that Mnemiopsis has high potentials of growth, reproduction and feeding that enable this species to be a predominant zooplanktivore in a wide variety of habitats; review the population distributions and dynamics of Mnemiopsis in U.S. waters and in the Black Sea region; and examine the effects of temperature and salinity, zooplankton availability and predator abundance on Mnemiopsis population size in both regions, and the effects of Mnemiopsis on zooplankton, ichthyoplankton and fish populations, focusing on Chesapeake Bay and the Black Sea. In both regions, Mnemiopsis populations are restricted by low winter temperatures (<2 °C). In native habitats, predators of Mnemiopsis often limit their populations, and zooplanktivorous fish are abundant and may compete with the ctenophores for food. By contrast, in the Black Sea region, no obvious predators of Mnemiopsis were present during the decade following introduction when the ctenophore populations flourished. Additionally, zooplanktivorous fish populations had been severely reduced by over fishing prior to the ctenophore outbreak. Thus, small populations of potential predators and competitors for food enabled Mnemiopsis populations to swell in the new habitats. In Chesapeake Bay, Mnemiopsis consumes substantial proportions of zooplankton daily, but may only noticeably reduce zooplankton populations when predators of Mnemiopsis are uncommon. Mnemiopsis also is an important predator of fish eggs in both locations. In the Black Sea, reductions in zooplankton, ichthyoplankton and zooplanktivorous fish populations have been attributed to Mnemiopsis. We conclude that the enormous impact of Mnemiopsis on the Black Sea ecosystem occurred because of the shortage of predators and competitors in the late 1980s and early 1990s. The appearance of the ctenophore, Beroe ovata, may promote the recovery of the Black Sea ecosystem from the effects of the Mnemiopsis invasion.     

Factors Associated with Succession of Abandoned Agricultural Lands along the Lower Missouri River, U.S.A.

The 1993 flood of the Missouri River led to the abandonment of agriculture on considerable land in the floodplain. This abandonment led to a restoration opportunity for the U.S. Federal Government, purchasing those lands being sold by farmers. Restoration of this floodplain is complicated, however, by an imperfect understanding of its past environmental and vegetative conditions. We examined environmental conditions associated with the current placement of young forests and wet prairies as a guide to the potential successional trajectory for abandoned agricultural land subject to flooding. We used Bayesian mixed-effects logistic regression to examine the effects of flood frequency, soil drainage, distance from the main channel, and elevation on whether a site was in wet prairie or in forest. Study site was included as a random effect, controlling for site-specific differences not measured in our study. We found, after controlling for the effect of site, that early-successional forest sites were closer to the river and at a lower elevation but occurred on drier soils than wet prairie. In a regulated river such as the lower Missouri River, wet prairie sites are relatively isolated from the main channel compared to early-successional forest, despite occurring on relatively moister soils. The modeled results from this study may be used to predict the potential successional fate of the acquired agricultural lands, and along with information on wildlife assemblages associated with wet prairie and forest can be used to predict potential benefit of these acquisitions to wildlife conservation.     

长江口互花米草生长区大型底栖动物的群落特征

2005年对长江口潮滩湿地互花米草(Spartina alterniflora)生长区不同季节大型底栖动物群落特征的研究表明:长江口互花米草生长区的大型底栖动物有21种,其中甲壳纲10种、多毛纲5种、腹足纲5种、辨鳃纲1种.主要种类有拟沼螺(Assiminea sp.)、背蚓虫(Notomastus latericeus)、尖锥拟蟹守螺(Cerithidea largillierli)、中国绿螂(Glauconome chinensis)、钩虾(Gammaridae sp.)等.食性功能群均以碎屑食者和植食者为主.大型底栖动物平均栖息密度为(650.5±719.2)个/m2,标准误主要是由于北湖的拟沼螺密度很大.栖息密度从大到小的顺序为沿河口梯度从内到外分布的北湖边滩、崇明东滩、金山卫边滩.大型底栖动物群落分布不均匀,沿河口梯度变化存在明显的空间差异.栖息密度和物种多样性在夏季最高,冬季最低.大型底栖动物平均生物量为(20.8±6.1)g/m2,季相变化为夏季＞秋季＞春季＞冬季.BIO-ENV分析表明沉积物粒径和盐沼高度是大型底栖动物群落特征的主要影响因素.不同研究结果的差异除了时空因素外可能与互花米草的种群动态有关.加强不同时间尺度的研究有助于正确评价互花米草对大型底栖动物的影响.     

Benthos and zooplankton of coal strip mine ponds in the mountains of northwestern Colorado,U.S.A.

Zooplankton, benthos and associated physico-chemical conditions were sampled in coal strip-mine ponds in northwestern Colorado from June 1977 to May 1978. Two spoils ponds derived all of their drainage from the coal mine, but differed in age; one pond received only partial drainage from mine spoils; a control pond was located in an adjacent drainage basin. Acid mine drainage was not observed, although total dissolved solids (TDS), nitrate and sulfate values were higher in the spoils ponds than in the control pond. Net zooplankton were less abundant in the spoils ponds, although standing stock of benthos exhibited a progressive decrease from the youngest spoils pond to the control pond. Zooplankton and benthos species diversity values were lower in the ponds affected by mine drainage. Certain groups of zooplankters (Cladocera) and benthos (Trichoptera, Amphipoda, Hydracarina, and Sphaeriidae) were rare or absent in the youngest spoils pond. Percentage Similarity Coefficients indicate that colonization phenomena (age and distance from a source of colonizers) may be responsible, in part, for the faunal differences between ponds, since the higher levels of nitrate, sulfate, and TDS in the spoils ponds were generally within the tolerance range of aquatic organisms.     

Maturation and fecundity of a stock-enhanced population of striped bass in the Savannah River Estuary, U.S.A

The striped bass Morone saxatilis population in the Savannah River (south-eastern U.S.A.) collapsed in the 1980s, and recent eorts to restore the population have resulted in increased catch-per-unit-eort (CPUE) of striped bass in the Savannah River Estuary (SRE). The abundance of eggs and larvae, however, remain well below historic levels. The primary cause of the population decline was remedied, and environmental conditions seem suitable for striped bass spawning. Regression analysis of data derived from ultrasonic imaging of 31 striped bass resulted in a statistical model that predicted ovary volume well (r²=0.95). The enumeration of oocytes from ovarian tissue samples and the prediction of ovary volume allowed fecundity to be estimated without sacrificing the fish. Oocyte maturation in Savannah River striped bass seemed to progress normally, with oocytes developing to final stages of maturity in larger fish (>750 mm L _T). Additionally, fecundity estimates were comparable to a neighbouring striped bass population. The environmental cues needed to trigger development and release of striped bass oocytes into the SRE appeared to be present. If most of the striped bass females in the SRE are still young (<7 years), the ability to produce large numbers of eggs will be limited. As these young fish mature, egg production probably will increase and the density of striped bass eggs eventually will approach historic levels, provided suitable habitat and water quality are maintained.     

Peat characteristics and groundwater geochemistry of calcareous fens in the Minnesota River Basin, U.S.A.

Calcareous fens in Minnesota are spring-seepage peatlands with adistinctive flora of rare calciphilic species. Peat characteristics andgroundwater geochemistry were determined for six calcareous fens in theMinnesota River Basin to better understand the physical structure andchemical processes associated with stands of rare vegetation. Onset of peataccumulation in three of the fens ranged from about 4,700 to 11,000 ¹⁴C yrs BP and probably resulted from acombination of climate change and local hydrogeologic conditions. Most peatcores had a carbonate-bearing surface zone with greater than 10%carbonates (average 27%, dry wt basis), an underlyingcarbonate-depleted zone with 10% or less carbonates (average4%), and a carbonate-bearing lower zone again with greater than10% carbonates (average 42%). This carbonate zonation washypothesized to result from the effect of water-table level on carbonateequilibria: carbonate precipitation occurs when the water table is above acritical level, and carbonate dissolution occurs when the water table islower. Other processes that changed the major ion concentrations inupwelling groundwater include dilution by rain water, sulfate reduction orsulfide oxidation, and ion adsorption or exchange. Geochemical modelingindicated that average shallow water in the calcareous fens during the studyperiod was groundwater mixed with about 6 to 13% rain water.Carbonate precipitation in the surface zone of calcareous fens could bedecreased by a number of human activities, especially those that lower thewater table. Such changes in shallow water geochemistry could alter thegrowing conditions that apparently sustain rare fen vegetation.     

An Analysis of the Biotic Community in a Kumaun Himalayan Lake,Nainital (U. P.), India

A comprehensive study of phyto- and zooplankton and macrozoobenthic components in Lake Nainital showed that species richness was high for plankton and low for macrozoobenthos. The algal biomass was dominated by greens (54 %) and blue-greens (31 %), the zooplankton population by copepods (84 %), and the macrozoobenthic community by a Tubifex-Chironomus association constituting≥95 % of the annual number of the macrobenthic invertebrates. Respiration (807.5g C m⁻² year⁻¹) surpassed gross production (630.5 g C m⁻² year⁻¹). The mean annual ratio between phyto- and zooplankton biomass is 3.3 and between phytoplankton and herbivores it is 4.6. If biomass is treated as a measure of crude production, the relationship among the three trophic levels suggests that herbivory is inefficient while carnivory is efficient, because part of the primary production remains unutilized by dominant herbivorous zooplankters, whereas Mesocyclops leuckarti, the sole carnivore, feeds efficiently on rotifers and juveniles of other copepods. The low diversity of different biotic components and the P/R ratio of less than 1 perhaps suggest that the lake is passing through the stage of heterotrophic succession.     

Contrasting Functional Performance of Juvenile Salmon Habitat in Recovering Wetlands of the Salmon River Estuary, Oregon, U.S.A.

For an estuarine restoration project to be successful it must reverse anthropogenic effects and restore lost ecosystem functions. Restoration projects that aim to rehabilitate endangered species populations make project success even more important, because if misjudged damage to already weakened populations may result. Determining project success depends on our ability to assess the functional state or “performance” and the trajectory of ecosystem development. Mature system structure is often the desired “end point” of restoration and is assumed to provide maximum benefit for target species; however, few studies have measured linkages between structure and function and possible benefits available from early recovery stages. The Salmon River estuary, Oregon, U.S.A., offers a unique opportunity to simultaneously evaluate several estuarine restoration projects and the response of the marsh community while making comparisons with a concurring undiked portion of the estuary. Dikes installed in three locations in the estuary during the early 1960s were removed in 1978, 1987, and 1996, creating a “space‐for‐time substitution” chronosequence. Analysis of the marsh community responses enables us to use the development state of the three recovering marshes to determine a trajectory of estuarine recovery over 23 years and to make comparisons with a reference marsh. We assessed the rate and pattern of juvenile salmon habitat development in terms of fish density, available prey resources, and diet composition of wild juvenile Oncorhynchus tshawytscha (chinook salmon). Results from the outmigration of 1998 and 1999 show differences in fish densities, prey resources, and diet composition among the four sites. Peaks in chinook salmon densities were greatest in the reference site in 1998 and in the youngest (1996) site in 1999. The 1996 marsh had higher densities of chironomids (insects; average 864/m²) and lower densities of amphipods (crustaceans; average 8/m³) when compared with the other sites. Fauna differences were reflected in the diets of juvenile chinook with those occupying the 1978 and 1996 marshes based on insects (especially chironomids), whereas those from the 1987 and reference marshes were based on crustaceans (especially amphipods). Tracking the development of recovering emergent marsh ecosystems in the Salmon River estuary reveals significant fish and invertebrate response in the first 2 to 3 years after marsh restoration. This pulse of productivity in newly restored systems is part of the trajectory of development and indicates some level of early functionality and the efficacy of restoring estuarine marshes for juvenile salmon habitat. However, to truly know the benefits consumers experience in recovering systems requires further analysis that we will present in forthcoming publications.     

Managing Non-Native Plant Populations Through Intensive Community Restoration in Cades Cove, Great Smoky Mountains National Park, U.S.A.

Abstract Cades Cove, Great Smoky Mountains National Park, U.S.A. was historically cleared largely for pastoral purposes; it is now comprised of recently abandoned pastures dominated by non‐native pasture species. To investigate the potential for reducing non‐native species relative to native species, park managers initiated an experiment in 1995 that included mowing, herbicide application, planting of seed, and burning of replicate 20 × 50–m plots at each of two sites within Cades Cove. Between 1995 and 2001 we evaluated the response of the plant community (i.e., species‐specific cover and frequency, biomass, diversity) to this suite of treatments and compared it with unmanipulated control plots at each site. Four years after treatment initiation abundance measures of Plantago lanceolata, Setaria geniculata, and Trifolium spp. averaged one‐third lower in treated than control plots. Frequency of Festuca pratensis was lower in treated than in control plots for 2 years, but after 4 years its frequency, cover, and biomass did not differ between treated and control plots. By 2000 the cover of Sorghastrum nutans in treated plots increased to 23–47%, depending on the site. Total biomass and diversity increased in treated plots. The dominance of Lespedeza cuneata at one site apparently reduced planting success, biomass production, and diversity and evenness. Post‐treatment lags in response for several species, coupled with interannual variation in response to environmental conditions, suggest that evaluations of treatment success would differ greatly depending on when the evaluation was conducted.     

The Kissimmee River Restoration Project and Evaluation Program,Florida, U.S.A.

Over the past decade, restoration of the Kissimmee River in central Florida has received considerable attention from local, state, national, and international media. In terms of areal extent, project cost, and ecological evaluation it is one of the largest and most comprehensive river restoration projects in the world. The goal of reestablishing ecological integrity involves restoring the physical attributes and the hydrologic processes that were lost after channelization of the river in the 1960s. The project is expected to restore over 80 km² of floodplain wetlands and reestablish over 70 km of river channel. Restoration construction began in 1999; to date, three construction phases have been completed, with the final phase of construction slated for completion in 2019. Restoration evaluation is widely viewed as a critical component of any restoration project. Equally important is the dissemination of information gained from restoration evaluation programs. This introductory article presents a brief overview of project history and outlines the approach and logic of the Kissimmee River Restoration Evaluation Program. The following papers present the results of ecological studies conducted before and after completion of the first phase of restoration construction. This first phase reestablished flow through 23 km of reconnected river channels and seasonally inundated a large portion (approximately 2,900 ha) of the floodplain within the Phase I project area. Although these studies present interim responses prior to full hydrologic restoration, results suggest that the ecosystem is responding largely as predicted by performance measures developed prior to restoration construction.     

Benthic microbial respiration in Appalachian Mountain, Piedmont, and Coastal Plains streams of the eastern U.S.A.

1. Benthic microbial respiration was measured in 214 streams in the Appalachian Mountain, Piedmont, and Coastal Plains regions of the eastern United States in summer 1997 and 1998. 2. Respiration was measured as both O₂ consumption in sealed microcosms and as dehydrogenase activity (DHA) of the sediments contained within the microcosms. 3. Benthic microbial respiration in streams of the eastern U.S., as O₂ consumption, was 0.37 ± 0.03 mg O₂ m^–2 day^–1. Respiration as DHA averaged 1.21 ± 0.08 mg O₂ m^–2 day^–1 4. No significant differences in O₂ consumption or DHA were found among geographical provinces or stream size classes, nor among catchment basins for O₂ consumption, but DHA was significantly higher in the other Atlantic (non‐Chesapeake Bay) catchment basins. 5. Canonical correlation analyses generated two environmental axes. The stronger canonical axis (W₁) represented a chemical disturbance gradient that was negatively correlated with signatures of anthropogenic impacts (ANC, Cl^–, pH, SO₄²), and positively correlated with riparian canopy cover and stream water dissolved organic carbon concentration (DOC). A weaker canonical axis (W₂) was postively correlated with pH, riparian zone agriculture, and stream depth, and negatively correlated with DOC and elevation of the stream. Oxygen consumption was significantly correlated with W₂ whereas DHA was significantly correlated with W₁. 6. The strengths of the correlations of DHA with environmental variables, particularly those that are proven indicators of catchment disturbances and with the canonical axis, suggest that DHA is a more responsive measure of benthic microbial activity than is O₂ consumption.     

Limnology of a desertic terminal lake,Walker Lake,Nevada, U.S.A.

Walker Lake, a large terminal lake in west-central Nevada, is rapidly desiccating and becoming more saline. From 1937 to 1977, total dissolved solids increased from 5 650 to 10 650 mg l^–1. Ionically, the lake is a chlorocarbonate one; however, as desiccation continues it should eventually have about equal amounts of chloride, sulfate and carbonate. With regard to algal nutrients, the lake appears to be nitrogen limited. The phytoplankton is currently dominated by Nodularia spumigena; at times this produces noxious blooms. The zooplankton community is depauperate and composed of three species. The fish fauna is limited to three endemic fishes, with tui chub, Gila bicolor, dominant. Lahontan cutthroat trout, Salmo clarki henshawi, is restricted during summer to a narrow mid-water zone low enough in temperature and high enough in dissolved oxygen to meet physiological requirements.Dr. Koch passed away in October 1983.     

Weather and landscape factors associated with adult mosquito abundance in southwestern Georgia, U.S.A

Mosquito community composition and population dynamics were compared to weather variables and land use/cover data during 2008 to determine which variables affected population dynamics at the J.W. Jones Ecological Research Center in southwestern Georgia. Models relating adult mosquito distributions to weather variables and time of year were compared using Akaike's Information Criterion (AIC) model selection. Precipitation, temperature, humidity, and Keetch-Byram Drought Index were important factors correlated with mosquito abundance or presence/absence for the species considered. A cluster analysis, which grouped eight sites based on the percentages of land use/cover and hydric soils located in a 1-km radius surrounding collection sites, and an indicator species analysis were used to investigate the associations among 11 mosquito species and sites with similar land use/cover. Aedes albopictus (Skuse), Culex coronator Dyar & Knab, Culex quinquefasciatus Say, and Culex salinarius Coquillett were associated with sites that had the most anthropogenic influence, while Coquillettidia perturbans (Walker) and Psorophora ferox (von Humboldt) were associated with natural land cover such as wetlands and forested land. This study demonstrates that regional climate and land use/cover data can be predictive of the population dynamics of certain mosquito populations and is the first to examine how the distribution of Cx. coronator adults relate to land use/cover in the southeastern United States.     

The relationship between pH and community structure of invertebrates in streams of the Shenandoah National Park, Virginia, U.S.A.

1. A replicated natural experiment was used to assess the influence of pH and low alkalinity on abundance and richness of invertebrate families in streams draining catchments that receive acid deposition. Individual streams were used as the unit of replication, allowing conclusions to refer to a class of streams rather than to particular streams. 2. We also controlled for several factors other than pH and alkalinity, including flow and temperature, that are recognized as determinants of invertebrate distribution. Samples were from indigenous rocks, standardized for size, surface area, and geology. 3. Repeated measures analyses of variance (ANOVA) revealed that invertebrate abundance and richness were significantly lower at pH 5.8 than at pH 7.1 for the total community. Thirty per cent of the forty-seven families exhibited significantly lower abundance at pH 5.8; thirteen families were absent at pH 5.8. Differences were greatest for Ephemeroptera: species richness was significantly lower at pH 5.8, and 71% of the twenty-four species were either absent (seven) or found in reduced abundance (ten) in the acidic streams. 4. Stream alkalinity is projected to continue to decrease with continued acid deposition in the Shenandoah National Park. Concurrent decreases in pH may lead to the absence or continued numerical decline of certain Ephemeroptera species in streams that acidify to less than pH 6.0 and/or 50μEql^?1 alkalinity.     

Distribution of puimonate snails in the New River of Virginia and North Carolina, U.S.A.: interaction between alkalinity and stream drainage area

SUMMARY. The distribution and abundance of five species of pulmonate snails over 87 sites in the New River seem to be related to two variables, alkalinity and drainage area of the stream. The snails were generally found in the more alkaline streams regardless of stream drainage area and in the larger streams regardless of alkalinity. Considering only the 26 sites where at least one species of the five pulmonates occurred, rank snail abundance is significantly correlated with rank alkalinity, rank drainage area, and the alkalinity/area interaction. But the correlations between abundance and both alkalinity and drainage area drop to low levels when interaction is partialled out, while the correlation between abundance and interaction remains high upon partialling out alkalinity or area. This suggests that the apparent correlation between puimonate abundance and alkalinity is secondary and that neither alkalinity nor water chemistry variables correlated with it directly limit the distribution and abundance of pulmonates in the New River. Both alkalinity and stream drainage area may influence the abundance of pulmonate food.     

Evidence of non-vascular land plants from the early Silurian (Llandoverian) of Virginia,U.S.A.

Evidence is presented for the earliest known occurrences of non-vascular land plants and of higher, septate fungi. Macerates of carbonaceous silstone lenses from the lower Massanutten Sandstone, early Silurian (Llandoverian) of Virginia, have yielded a diverse assemblage of microfossil elements. Parallel aligned, banded tubes with annular to spiral ribbing and rounded to papilliform ends, membranous cellular sheets, cuticles, trilete spores, small spore tetrads, and septate higher filamentous fungi were recovered from the macerates. The banded tubes are probably a significant analogue with supportive or conductive cell types, but are not considered tracheidal. The heterogeneous plant assemblage may represent a thalloid, non-vascular land plant, in part, with a tubular-filamentous (nematophytic) organization associated with a membranous cellular layer and cuticular covering. While no spores were established as nematophytic, the presence of trilete spores adds to the indirect evidence of multiple evolutionary convergence toward land-plant characters. This assemblage is interpreted as of land-plant origin, based on the inferred fluvial depositional model of the fossiliferous rocks. A glacio-eustatic sea-level drop in the late Ordovician is suggested as a stimulus to the advent of land plants in the early Silurian.