Simultaneous Quantitative Comparison of Planktic Crustacea in Two Newfoundland Boreal Lakes

The number, size and reproductive potential of the planktic Crustacea were compared from March to December 1973 in two Newfoundland lakes, namely Hogans Pond and Bauline Long Pond. In the first period of the study the total number of microcrustaceans was greater in the more fertile Hogans Pond, but after October all species in Hogans Pond declined catastrophically. The relative numbers of individual species are detailed, some being more abundant in one lake and some in the other. Body lengths of most copepods were the same or greater in Hogans Pond than in Bauline Long Pond, but the cladoceran Daphnia catawba was larger in Bauline Long Pond. The number of eggs carried per female was usually the same or greater in Hogans Pond, except for Diaptomus minutus and Daphnia catawba in the spring.     

Physical and Chemical Conditions in Long Pond,St. John's,Newfoundland: A Pond Receiving Both Rural and Urban Runoff

The physico-chemical environment was studied from June 1971 to May 1973 at five stations in Long Pond, St. John's, Newfoundland. This pond receives both rural and urban runoff and is characterized by a high flushing rate. Of the parameters studied, concentrations of total suspended matter, biochemical oxygen demand (BOD), total CO₂, and free CO₂ were significantly greater in a small pool prior to the main body of the pond near the entry of Learys Brook. Current speed is noticeably reduced at this point. No significant differences were found between stations with respect to pH, dissolved O₂, total dissolved solids (TDS), total hardness, Ca hardness, Mg hardness, alkalinity, ammonium-N, nitrite-N, nitrate-N, orthophosphate and polyphosphate. Water quality in Long Pond is compared with unpolluted lakes and streams in the area; nutrient levels are indicative of eutrophic conditions.     

The production of hemoglobin by small pond Daphnia pulex: intraspecific variation and its relation to habitat

SUMMARY.

• 1 Hemoglobin production was measured for two populations of Daphnia pulex, one from a temporary pond (GR Pond) and one from a permanent pond (Rash Pond). Surface water in Rash Pond remains high in oxygen, while by late summer very little oxygen remains in GR Pond. Hemoglobin synthesis was induced in the laboratory by artificial oxygen deficiency.
• 2 Reproductive state influenced the level of hemoglobin in Daphnia. Females with parthenogenesis eggs had higher total body hemoglobin than ephippial females. Clutches laid by pale Daphnia immediately before exposure to low oxygen conditions were aborted. Offspring produced by hemoglobin-rich females later in the treatment survived.
• 3 Hemoglobin production was higher for Rash Pond Daphnia. Visual predators exist in GR Pond, but are absent in Rash Pond. Also, Daphnia are smaller in GR Pond. Visual predation may have selected against high levels of hemoglobin in the temporary pond. Thus oxygen availability in nature is not necessarily a good predictor of hemoglobin production by Daphnia.
• 4 Feeding behavior was altered in low oxygen conditions. Browsing was dominant in low oxygen treatments while Daphnia in control treatments filtered algae normally. Browsing may increase access to sedimented iron necessary for hemoglobin synthesis.

     

Ecological fish production in Long Pond,a lakeshore lagoon on Long Point,Lake Erie

Synopsis Long Pond, a recently formed 2.4 ha lagoon on Long Point, Lake Erie (Canada), was treated with piscicide and found to contain 47,768 fishes of 22 species. Nine dominant species (Notropis heterolepis, Pimephales notatus, Notemigonus crysoleucas, Lepomis gibbosus, L. macrochirus, Perca flavescens, Cyprinus carpio, Micropeterus salmoides and Carassius auratus) comprised 91% and 97% of total numbers and standing crop respectively. Age, growth and production were determined giving a total fish production estimate (corrected for all species) of 87.5 kg ha^–1 y^–1 for this lagoon. Dominant species were deemed either invaders (Cyprinus carpio, Carassius auratus), which had entered the lagoon to spawn and been trapped, or residents. The invaders comprised 82% of the 277.8 kg ha^–1 total standing crop. Their successful spawning and subsequent escape of the young from the lagoon would have resulted in some 615 kg y^–1 of fish production outside the lagoon. Resident stocks were dominated by young fishes, a characteristic of exploitation or early colonization. This may have been due to the recent formation and subsequent expansion of the lagoon or high annual mortality due to extreme physical conditions but was most likely the result of excessive predation by Micropterus salmoides. Relationship between biomass and production show that the chance inclusion of the invaders produces an immediate shift from a characteristically early to a characteristically late phase of ecological development.     

Patterns of emergence,import of egg energy and energy export via emerging dragonfly populations in a tropical pond

The most abundant dragonflies Brachythemis contaminata, Orthetrum sabina, Diplacodes trivialis, Pantala flavescens and Trithemis festiva in the tropical pond Idumban emerged from November to April during the years 1973,1974 and 1975. The date of initiation of emergence of all the species was synchronized and tied to the events following the north west monsoon in November. During the seasons '73–74 and '74–75, as many as 10,693 and 7,910 adults emerged; females outnumbered the males in all the 5 species; male populations of B. contaminata, O. sabina, D. trivialis, P. flavescens and T. festiva represented 47, 48, 46, 49 and 44% during the '73–74 season, 48, 48, 46, 46 and 49% during the '74–75 season, respectively. The adult dragonflies equivalent to 2,442 Kcal emerged from the Pond during the season '73–74. Of this, B. contaminata contributed 30%, D. trivialis 7%, O. sabina 12%, P. flavescens 23% and T. festiva 28%. For the season '74–75, the dragonflies equivalent to 1,602 Kcal emerged from the Pond and the contribution was in the following order: B. contaminata: 31%, O. sabina: 8%, D. trivialis: 13%, P. flavescens: 27% and T. festiva: 21%. Import of energy due to inoculation of B. contaminata eggs into the Pond Idumban was 73 Kcal/ year and the output from the Pond via emerging B. contaminata population alone amounted to 620 Kcal/ year; the net energy loss from the Pond was 548 Kcal/ year. During either season, as much as 99.7% of B. contaminata eggs failed to attain adulthood due to infertility (5.8%), unhatchability (12%) and predation during the egg and nymphal stages (82.5%). During the study, the GPP of the Pond was 26,073 Kcal/m²/ year, and output of energy through emergence of 5 dragonfly species amounted to 0.0045 Kcal/m²/year, i.e. 0.00002% of the GPP is lost through the emerging carnivorous odonates; comparable values available for the emerging detritivorous chironomids, herbivorous dipterans and mayflies fall between 1.0 and 0.1%.     

Aquatic vegetation and trophic condition of Cape Cod (Massachusetts,U.S.A.) kettle ponds

The species composition and relative abundance of aquatic macrophytes was evaluated in five Cape Cod, Massachusetts, freshwater kettle ponds, representing a range of trophic conditions from oligotrophic to eutrophic. At each pond, aquatic vegetation and environmental variables (slope, water depth, sediment bulk density, sediment grain size, sediment organic content and porewater inorganic nutrients) were measured along five transects extending perpendicular to the shoreline from the upland border into the pond. Based on a variety of multivariate methods, including Detrended Correspondence Analysis (DCA), an indirect gradient analysis technique, and Canonical Correspondence Analysis (CCA), a direct gradient approach, it was determined that the eutrophic Herring Pond was dominated by floating aquatic vegetation (Brasenia schreberi, Nymphoides cordata, Nymphaea odorata), and the algal stonewort, Nitella. Partial CCA suggested that high porewater PO₄-P concentrations and fine-grained sediments strongly influenced the vegetation of this eutrophic pond. In contrast, vegetation of the oligotrophic Duck Pond was sparse, contained no floating aquatics, and was dominated by emergent plants. Low porewater nutrients, low sediment organic content, high water clarity and low pH (4.8) best defined the environmental characteristics of this oligotrophic pond. Gull Pond, with inorganic nitrogen-enriched sediments, also exhibited a flora quite different from the oligotrophic Duck Pond. The species composition and relative abundance of aquatic macrophytes provide good indicators of the trophic status of freshwater ponds and should be incorporated into long-term monitoring programs aimed at detecting responses to anthropogenically-derived nutrient loading.     

Hepatic biotransformation enzymes in a sentinel species,the painted turtle (Chrysemys picta), from Cape Cod,Massachusetts: seasonal-, sex- and location related differences

We report changes in biomarker enzymes (cytochrome P4501A, glutathione-S-transferase) and protein expression (cytochrome P4501A) in adult painted turtles, Chrysemys picta, as part of a study of the potential impact of contaminants originating from the Massachusetts Military Reservation on Cape, Cod, MA. In animals from both Moody Pond, a site potentially impacted by contaminants, and Washburn Pond, a nonimpacted site, rates of hepatic microsomal ethoxyresorufin-O     

Taxonomic diversity, origin, and conservation status of Bermuda killifishes (Fundulus) based on mitochondrial cytochrome b phylogenies

Sequence variation in the mitochondrialCytochrome b (Cytb) gene was assayed infour of six extant Bermuda killifishpopulations, representing two endemic species,to test taxonomic and phylogenetic hypothesesand reconstruct colonization history. Twodivergent (4.6%) haplotypes were detected; oneis identical to the Georgia 2c haplotype ofF. heteroclitus and is fixed in threeeastern populations: Lover's Lake (F.relictus), Mangrove Lake (F. bermudae),and Walsingham Pond. The second is fixed andrestricted to a western population, Evan'sPond. Likelihood and parsimony cytochrome btrees recognize a Bermuda Fundulus / F. heteroclitus clade in which the Evan's Pondhaplotype is basal. Phylogenies and haplotypedivergence indicate at least two Bermudacolonizations, the more recent involvingtransfer of the Georgia 2c haplotype. Enforcing Bermuda killifish monophyly, aspredicted from a single colonization event,does not increase tree length significantly;i.e., the trees also are consistent with asingle colonization. However, divergencebetween the Evan's Pond haplotype and the F. bermudae / F. relictus / Georgia 2chaplotype (4.6%) far exceeds the maximumdivergence among all F. heteroclitus,F. bermudae, and F. heteroclitushaplotypes (1.2%) and argues for independentcolonizations. Alternatively, recentintroduction of F. heteroclitus couldaccount for occurrence of the GA2c haplotype inBermuda but does not explain the presence ofthe genetically divergent Evans' Pondhaplotype. Cytb sequences areuninformative of the taxonomic status ofBermuda endemics, F. bermudae and F.relictus, but support recognition of theEvan's Pond population as an evolutionarilysignificant unit within the F. heteroclitus group.     

A thermal effluent as a sporadic cornucopia: effects on fish and zooplankton

Synopsis We report effects of a thermal effluent on fish and zooplankton in an impoundment in South Carolina. The effects are not directly due to heated effluent but are indirect effects on the trophic dynamics of the system and depend on the physical structure of the system, season, and geography. As effluent from a nuclear reactor cooling pond (Pond C) enters the larger Par Pond it sporadically carries with it zooplankton and/or dead fish. Pond C produces high zooplankton densities in two situations: (1) high and hot effluent flow during cold winter weather; and (2) low (cool) effluent flow during warmer seasons. High zooplankton densities attract Blueback herring, Alosa aestivalis, which attract largemouth bass, Micropterus salmoides. Dying and dead bluegills, Lepomis macrochirus from Pond C (heat killed) are eaten by Par Pond bass which swim into effluent temperatures as high as 46°C to take these easy prey. Blueback herring and largemouth bass distribution are affected by the presence of food rather than by temperature. Par Pond blueback herring appear to be available to bass mainly when herring are near the effluent from Pond C and when they spawn in spring in the littoral zone. Because Blueback herring in Par Pond live only one year and because their presence in bass habitat is seasonal there is a strong seasonal component to bass food abundance. A previously reported annual oscillation in bass condition (K), with a peak in winter, occurs throughout Par Pond but is extreme in the vicinity of the effluent. The strong seasonality of food abundance for bass at the effluent correlates the winter peak in bass condition.     

The Effects of Phragmites Removal on Nutrient Pools in a Freshwater Tidal Marsh Ecosystem

Selected nitrogen and phosphorus pools in two freshwater tidal marsh ecosystems on the lower Connecticut River were measured relative to Phragmites, Typha and mixed native wetland plant cover types. For both the Chapman Pond Preserve and Chester Creek Marsh, significant differences were found between plant cover types in porewater ammonium and phosphate for some months during the 1998 growing season; porewater nitrate was always below the detection limit. At Chapman Pond, no significant differences were detected between Phragmites and Typha for plant tissue N concentrations. The standing stock of nitrogen was higher in Phragmites stands, however, owing to its greater aboveground biomass. No significant difference was found between plant cover types for total soil N at Chapman Pond, but KCl extractable ammonium was higher in the mixed cover type than Phragmites or Typha. The results of this study suggest that Phragmites is affecting nutrient pools in freshwater tidal marshes, a result that should be considered in future management design.     

Chemical and isotopic composition of karstic lakes in Jamaica,West Indies

Lakes in the limestone region of Jamaica exhibit a range of chemical characteristics that reflect varying inputs from precipitation, surface runoff and groundwater, together with the subsequent evolution of the water within the limnic environment. Detailed spatial and temporal sampling was conducted on one lake, Wallywash Great Pond. Chemical data, together with D/H, ¹⁸O/¹⁶O, ¹³C/¹²C and ⁸⁷Sr/⁸⁶Sr ratios confirm that the karstic spring waters entering the lake evolve chemically through degassing, mixing with rainfall and runoff, biogenic decalcification (resulting mainly from bicarbonate assimilation by the high biomass of submerged macrophytes), and evaporation. Modern carbonate sedimentation in Wallywash Great Pond is largely of high-Mg calcite. This is consistent with Mg/Ca molar ratios >2 within much of the lake. However, aragonite forms on the adaxial leaf surfaces of Potamogeton spp. This may be explained either as a result of locally elevated Mg concentrations or a high degree of supersaturation favouring very rapid carbonate precipitation. Two small lakes to the north of Wallywash Great Pond show minor influence of the Na-Cl dominated coastal aquifer, suggesting that coastal lakes are sensitive to variations in the boundary between fresh and brackish groundwater caused by changes in climate or sea level. Their ¹³C/¹²C ratios are strongly influenced by biogenic CO₂ derived from plant respiration or decay.     

Biomanipulation by introduction of herbivorous zooplankton. A helpful shock for eutrophic lakes?

In 1988 and 1989Daphnia magna were introduced into the Gewerbepark Pond and into the University Pond, and also into a limnocorral (10 m diameter, 5 m deep) in Postfelden Reservoir. Limnological parameters were regularly monitored in all the three water bodies over three months or longer. The objective of the experiments was to induce a clear-water period in turbid eutrophic waters by direct manipulation of the zooplankton community. Introduction of four million individuals ofD. magna (10 ind. 1⁻¹) caused a long lasting clear-water period in the limnocorral. While Secchi-disc transparency in the reservoir decreased from 1.3 m to<1 m during summer, transparency increased to a stable level of about 4 m in the corral. Despite very low phytoplankton biomass,D. magna was still abundant. The experiment was terminated after three months because of oxygen depletion in the corral. In the Gewerbepark Pond 3.3 million individuals ofD. magna (0.6 ind. 1⁻¹) were introduced at the beginning of August. The daphnids soon increased 60-fold in their density causing a persistently high water transparency and low phytoplankton biomass up to November. Ammonia concentration rose steeply, whereas that of nitrate and oxygen decreased. Subsequently in summer, concentrations of chlorophyll as well as of inorganic phosphorus and nitrogen were extremely low. Instead of the phytoplankton,Elodea canadensis grew enormously and covered 12% of the pond surface. The biomanipulation experiment in University Pond failed, probably due to predation by carp.     

Ecological studies of Euglenineae in certain polluted and unpolluted environments

Summary The ecology of Euglenineae was investigated for two years in certain polluted and unpolluted environments of Hyderabad, India. The paper includes discussions regarding the distribution and periodicity of euglenoid population in relation to the physicochemical complexes which existed in the three ponds during the period of investigation. Sewage and Garden Ponds were found to be considerably polluted, whereas, the Typha Pond was comparatively pure and less polluted. Sewage Pond exhibited the highest percentage of Euglenineae harbouring 13 species and Garden Pond harboured 2 species in large numbers. Typha Pond harboured typically Trachelomonas hispida and Euglena Sp. which were totally absent in the other two ponds. It seems that high average concentrations of free CO₂ were favourable for euglenoid growth in Sewage Pond and the oxygen deficiency was helpful to trigger the oxygen-iron-phosphate complex, releasing larger quantities of phosphorus and iron. Higher average values of percent Cl + NO₃ ratio were found to be responsible for the luxuriant growth of these flagellates and it was suggested that inorganic sources of nitrogen might be more important in their ecology as fluctuations of nitrate coincide closely with those of Euglenineae in all ponds. These flagellates were found to be abundant during the periods when water was not rich in total sulphides and concentrations higher than 2.0 ppm adversely effected the euglenoid development. These flagellates were found to develop usually after rains or during intermittent showers experiencing comparatively higher temperatures. A temperature range of 27° – 39°C was observed to be favourable for their growth. Higher concentrations of oxidizable organic matter showed a direct relationship to euglenoid population in Sewage Pond. It is suggested that certain species of Euglenineae, which very often developed in the polluted waters of Sewage Pond, could be used as biological indicators of pollution in the present investigation.Part of the thesis approved by Osmania University, Hyderabad, India for the award of the degree of Ph. D.     

COMPARISON OF TOXINS IN THREE ISOLATES OF GONYAULAX TAMARENSIS (DINOPHYCEAE)1

Toxicity levels and profiles of three isolates of Gonyaulax tamarensis Lebour grown under the same conditions were compared. One isolate was collected from Ipswich, Massachusetts, during the massive red tide of 1972 along the New England coast. The other two isolates were obtained from Perch Pond (Falmouth, Massachusetts) and Mill Pond (Orleans, Massachusetts) located in the southwest and south of Cape Cod, Massachusetts, respectively. All the three cultures produced toxins with variation in their toxicity levels. Toxin contents were highest in the Ipswich isolate, followed in an order by Mill Pond and Perch Pond cultures. Morphological similarity existed between Ipswich and Mill Pond cells, whereas the Perch Pond cells possessed an additional ventral pore on the l' epithecal plate.     

CLONAL INHERITANCE OF A DIPLOID NUCLEAR GENOME BY A HYBRID FRESHWATER MINNOW (PHOXINUS EOS-NEOGAEUS,PISCES: CYPRINIDAE)

Hybrids between the minnows Phoxinus eos and Phoxinus neogaeus coexist with a population of P. eos in East Inlet Pond, Coos Co., New Hampshire. Chromosome counts and flow cytometric analysis of erythrocyte DNA indicate that these hybrids include diploids, triploids, and diploid-triploid mosaics. The mosaics have both diploid and triploid cells in their bodies, even within the same tissues. All three hybrid types are heterozygous at seven putative loci for which P. eos and P. neogaeus are fixed for different allozymes, indicating that the hybrids carry one eos and one neogaeus haploid genome. The diploid hybrids are therefore P. eos-neogaeus, whereas the triploids and mosaics are derived from P. eos-neogaeus but have an extra eos or neogaeus genome in all or some of their cells. Diploid, triploid, and mosaic hybrids accept tissue grafts from diploid hybrids, indicating that all individuals carry the identical eos-neogaeus diploid genome. Thus, one P. eos-neogaeus clone exists at East Inlet Pond. Grafts among the triploids and mosaics or from these individuals to diploid hybrids are rejected, indicating that the third genome is different in each triploid and mosaic individual. In this study, diploid and mosaic hybrids, carrying the clonal eos-neogaeus genome, were bred in the laboratory with males of P. eos or P. neogaeus. Both diploid and mosaic hybrids produced diploid, triploid, and mosaic offspring, revealing the source of the three hybrid types present at East Inlet Pond. These offspring accepted grafts from P. eos-neogaeus individuals, indicating that they all had inherited the identical eos-neogaeus genome. Most grafts among triploid and mosaic progeny, or from these individuals to their diploid broodmates, were rejected, indicating that the third genome was different in each triploid and mosaic (as was observed in the wild hybrids) and was contributed by sperm from males of P. eos or P. neogaeus. Diploid progeny are produced if sperm serves only to stimulate embryogenesis; triploid or mosaic progeny are produced if the sperm genome is incorporated. Although based on a mode of reproduction that by definition results in a genetically identical community of individuals, i.e., gynogenesis, reproduction in hybrid Phoxinus results in a variety of genetically distinct individuals by the incorporation of sperm into approximately 50% of the diploid ova produced.     

Redescription of Ilyocryptus brevidentatus Ekman, 1905 (Anomopoda,Cladocera, Branchiopoda)

During the wet season of 1999–2000, we studied the effects of the hydroperiod and other physical and chemical variables on planktonic copepod communities from six stations in Everglades National Park. Two stations were located in a slough (Taylor Slough 1, Taylor Slough 2) and four stations in the marl prairies of the Rocky Glades (Long Pine Key 7, Long Pine Key 8, Pa-hay-okee, Chekika). During the period of investigation, Taylor Slough sites had the longest hydroperiods, together with Pa-hay-okee, which is located near the eastern edge of Shark River Slough. Long Pine Key 7 and Long Pine Key 8 had the shortest hydroperiods, and Chekika had an intermediate hydroperiod. The pineland edge sites in the southern Rocky Glades (Long Pine Key) had higher numbers of individuals, and high percentages of larval stages, especially at the end of the wet season. The pineland ecotone is morphologically very heterogeneous, with solution holes in the limestone bedrock that provide below-ground refugia when there is no water on the marsh surface. The slough stations had the lowest numbers of individuals, as well as Chekika in the Rocky Glades, probably as a consequence of the altered water quality and hydropatterns caused by water management structures and operations We collected two species of calanoids, 18 cyclopoids, and three harpacticoids. The most abundant species were Acanthocyclops robustus, Tropocyclops prasinus mexicanus, Arctodiaptomus floridanus, Mesocyclops americanus, Macrocyclops albidus, Osphranticum labronectum, Microcyclops varicans, Microcyclops rubellus, Eucyclops conrowae, and Mesocyclops edax. Of these species, T. prasinus mexicanus and A. floridanus seemed to be adapted to short-hydroperiod habitats, M. rubellus and M. varicans to longer hydroperiod habitats, and E. conrowae to high conductivity habitats. Acanthocyclops robustus, M. albidus, and O. labronectum were dominant regardless of hydroperiod. As regards the temporal distribution, A. robustus was abundant throughout the entire wet season, M. edax, M. rubellus, M. americanus and M. varicans were most abundant in mid-wet season, in September–October, and T. prasinus mexicanus, M. albidus, and E. conrowae were abundant late in the wet season, in winter. The two calanoids only slightly overlapped in time: A. floridanus was abundant at the beginning of the wet season, in July–August, and O. labronectum was abundant at the end of the wet season, in December.     

Aspects of the biology of Xanthocnemis zealandica and Austrolestes colensonis (Odonata: Zygoptera) at three ponds in the South Island,New Zealand

Abstract

Both Xantnocnemis zealandica McLachlan and Austrolestes colensonis White were univoltine, and emerged asynchronously. At Woodend Pond, in 1971, larval growth was divided into cohorts by the drying up of some larval habitats in summer and autumn. Larval development was continuous in the other (permanent) habitats. A. colensonis differed from X. zealandica in its oviposition sites and its ability to survive the winter in the egg stage. There were differences in the larval food of the two species reflecting their differing agility.     

Polymorphism and Food Limitation in Three Daphnia carinata Populations

The annual cycles of Daphnia carinata in three fish-free ponds in southern New Zealand (Quarry, Taieri and Raupo Ponds) are described. Although breeding was continuous, the populations were frequently dominated by distinct cohorts and there was a sexual phase in spring. Growth rates, particularly in Quarry Pond, were often slow, and clutch sizes generally small. Egg and neonate sizes changed seasonally, but changes were not closely related to clutch sizes and body lengths. In Taieri Pond and Raupo Pond some D. carinata grew to 6.14 mm and carried clutches of up to 154 eggs. The potentially high fecundity associated with large size makes D. carinata a good coloniser, but our studies showed that it also survives well in poor food conditions by growing slowly and producing only 1–2 eggs per clutch. D. carinata showed marked seasonal polymorphism in tailspine length and development of head crests. In winter, crests were absent and tailspines were short and varied little with body length. Crests were first apparent, and tailspines began to elongate, in early spring, before the first appearance of a notonectid, Anisops wakefieldi. By midsummer, tailspines had increased markedly with body length but the slope of the relationship declined in autumn. Laboratory trials showed that both tailspine length and crest development increased in the presence of Anisops. These increases may be due to water-soluble factor(s) produced by Anisops.     

BIOCHEMICAL GENETICS OF MOSQUITOFISH. IV. CHANGES OF ALLELE FREQUENCIES THROUGH TIME AND SPACE

Gene frequency data from samples of Gambusia affinis populations at 76 localities across the Savannah River drainage were used to investigate temporal and spatial patterns in population genetic structure. Localities in the Par Pond system on the Savannah River Plant were sampled in 1971, 1977, and 1979. Allelic frequencies in these populations were generally stable through time, although significant temporal changes were observed among samples from Pond C, an impoundment receiving thermal effluent. Significant spatial heterogeneity in allele frequencies was observed on both microgeographic and regional scales. Populations within the Par Pond system were spatially subdivided at four of the five loci surveyed (mean F_ST = 0.051). Subdivision was even more pronounced when samples from across the Savannah River drainage were compared (mean F_ST = 0.196). A hierarchial analysis of gene diversity (G_ST) demonstrated that most of the genic diversity across the drainage exists as within-subdivision diversity. Even when populations from such contrasting habitats as rivers, creeks, ponds, and reservoirs are compared, an average of only 13% of the total gene diversity was attributed to between-group diversity. Greatest between-group gene diversity was observed when reservoirs were compared with one another. This general pattern of low between-habitat diversity suggests that differential selection pressures are not playing a major role in producing the observed levels of subdivision. In the Par Pond system, neither single locus nor multilocus genetic distances were significantly associated with geographic distance or with its reciprocal. For samples from over the Savannah River drainage, significant correlations between genetic and geographic distance were observed only for the Gpi-2 and Pgm-2 loci. Thus, there was a general lack of concordance between genetic and geographic distances. Spatial autocorrelation demonstrated patterns consistent with Wright's isolation by distance model. Significant positive correlations in allelic frequencies among neighboring populations were observed for five of six alleles; allelic frequencies in more distantly separated populations were typically not correlated.     

A Seasonal Quantitative Study of the Littoral Cladocera and Copepoda in a Bog Pond and an Acid Marsh in Newfoundland

A quantitative study was made of the littoral microcrustaceans in a bog pond and an acid marsh located on the Avalon Peninsula, Newfoundland, from May, 1972 to May, 1973. A total of 17 species of Cladocera and 7 species of Copepoda were found in La Manche Marsh, while 21 species of Cladocera and 5 species of Copepoda were collected in Round Pond. The maximum standing stocks were similar in the two localities. The dominant forms in the summer and fall in La Manche Marsh were Cladocera: Acantholeberis curvirostris, Biapertura intermedia, Chydorus sphaericus, and Ilyocryptus spinifer. In the winter the copepod, Macrocyclops albidus, was dominant, while Cyclops varicans rubellus was the most abundant species in the spring. Round Pond also was dominated by Cladocera in the summer and fall; namely, Acroperus alonoides, Alona rustica, Alonella excisa, Chydorus sphaericus, and Sida crystallina. The copepods, Eucyclops agilis and Macrocyclops albidus, were dominant in the winter and early spring.