Alison J. Smith

Lacustrine ostracodes as hydrochemical indicators in lakes of the north-central United States

The modern ostracode distribution in lakes of the north-central United States shows how ostracode abundances are related to concentrations of major ions such as calcium, sulfate, and bicarbonate. These relationships are quantified for species living in lakes that range from fresh water (200 μS cm-1) to saline water (17 000 μS cm-1). Lakes located in the Minnesota forests have different ostracode assemblages and different water chemistry than lakes located on the prairie of North Dakota and South Dakota. These differences are attributed to differences in precipitation and rock-water interactions. Multivariate analyses of the ostracode and water chemistry data set indicate that different ostracode species are associated with different water types. For example, Limnocythere sappaensis and Heterocypris glaucus are found in bicarbonate-enriched sulfate-dominated waters, whereas Limnocythere staplini is found in bicarbonate-depleted sulfate-dominated waters. Candona ohioensis and Limnocythere itasca are found in fresh water, and Candona rawsoni is eurytopic and found in both bicarbonate-enriched and bicarbonate-depleted sulfate-dominated waters. Ostracodes can be used to identify changes in both ionic composition (solutes) and ionic concentration.

Ecology of Marine, Marginal Marine and Nonmarine Ostracodes

Ecological studies of the Ostracoda are wide ranging and have many applications. Three aspects of ostracode ecology showing recent advances are examined in this overview: biodiversity, ecotones, and spatial and temporal scale effects. By monitoring diversity hotspots where ostracode species richness is unusually high, we might better understand the subtle perturbations that mark the onset of greater environmental change. Biodiversity also serves as an indicator of the overlap of environments, and thus can be used as a tool for the exploration and mapping of ground water -surface water interaction zones. Ostracodes can be used to identify ecotones and track changes in the position of ocean water mass boundaries, tidal ranges and salinity in estuaries, solute source and solute history of a lake, and the position of the boundary between shallow ground water and surface water. Biogeographic studies at continental and higher scales indicate that cosmopolitan species show some connection to global climate patterns.

Great Lakes paleohydrology: Complex interplay of glacial meltwater, lake levels, and sill depths

The oxygen isotope record of ostracode and clam shells recovered from Great Lakes cores of known age allows definition of times when meltwaters from the Laurentide ice sheet were important components of lake water in the several lake basins since 12 ka. We find that the lowstands in Lake Huron and Georgian Bay are characterized by isotopically light waters (δ 18 O values of -20‰ to -22‰ relative to SMOW [standard mean ocean water]) and the highstands by isotopically heavy waters of more local origin. These data can be used to determine the degree of hydraulic separation among the early Holocene lakes. Southern Lake Michigan, for instance, may mix with northern-source waters only during times of rising and high water levels. Generally it is characterized by waters of local origin.

Ground-water processes controlling a prairie lake's response to middle Holocene drought

Lake response to climate forcing is commonly regarded as being controlled by within-lake processes. We present a case from the northern Great Plains in which Holocene drought response recorded in lake sediments was determined by changes in chemical characteristics of source ground water. Middle Holocene ostracode assemblages were dominated by halophylic Limnocythere staplini , indicating increased lake-water salinity, yet the oxygen isotope values in this period decreased by 2‰ to 3‰, contrary to expectations of evaporative dominance. We infer from these proxy records and ground-water flow-model results that the paleoclimatic record in the lake was mediated by changes in ground-water catchment area and by reduction in evapotranspiration accompanying desiccation of peripheral lake basins.

Younger Dryas Interval and outflow from the Laurentide Ice Sheet

A boxmodel of the Great Lakes is used to estimate meltwater flow into the North Atlantic between 8000 and 14,000 calendar years B.P. Controls on the model include the oxygen isotopic composition of meltwaters and lake waters as measured in the shells of ostracodes. Outflow rates are highest when oxygen isotopic values of the lake waters are most negative, denoting a maximum glacial meltwater component. Flow rates reach maximum values before the onset of the Younger Dryas and after it ends. These maxima appear to be correlative with the major meltwater pulses MWP 1A and 1B. Although the resumption of North Atlantic Deep Water formation may be tied to the reduction in ice sheet melting, neither the onset nor the end of the Younger Dryas, as recorded in the Greenland Ice Sheet Project (GISP2) records, appear tied to maxima in meltwater outflow from the Laurentide ice sheet.

The Ecology of Ostracoda Across Levels of Biological Organisation from Individual to Ecosystem: A Review of Recent Developments and Future Potential

Abstract Palaeoenvironmental and palaeoclimatic applications of fossil ostracods rely on a uniformitarian approach underpinned by knowledge of the biology and ecology of living species. This review reveals that in recent decades, major advances have been made in the understanding of species’ abiotic niches in relation to their preferences for different water chemistries and temperatures. However, the underlying ecophysiological mechanisms for such preferences are still largely unknown. Only a few works analyse in detail aspects of population growth or species interactions (competition, predation) in the framework of classical ecological theories. Similarly, the role of Ostracoda in the assembly and functioning of aquatic biological communities is just starting to be recognised. We finally stress the relevance of Quaternary research on ostracod palaeoecology for testing ecological theories of community succession and dynamics in the long term, which may provide answers that standard ecological studies on living communities cannot, due to an inappropriate timescale.

Cryptic Species in Putative Ancient Asexual Darwinulids (Crustacea, Ostracoda)

Background Fully asexually reproducing taxa lack outcrossing. Hence, the classic Biological Species Concept cannot be applied. Methodology/Principal Findings We used DNA sequences from the mitochondrial COI gene and the nuclear ITS2 region to check species boundaries according to the evolutionary genetic (EG) species concept in five morphospecies in the putative ancient asexual ostracod genera, Penthesilenula and Darwinula, from different continents. We applied two methods for detecting cryptic species, namely the K/θ method and the General Mixed Yule Coalescent model (GMYC). We could confirm the existence of species in all five darwinulid morphospecies and additional cryptic diversity in three morphospecies, namely in Penthesilenula brasiliensis, Darwinula stevensoni and in P. aotearoa. The number of cryptic species within one morphospecies varied between seven (P. brasiliensis), five to six (D. stevensoni) and two (P. aotearoa), respectively, depending on the method used. Cryptic species mainly followed continental distributions. We also found evidence for coexistence at the local scale for Brazilian cryptic species of P. brasiliensis and P. aotearoa. Our ITS2 data confirmed that species exist in darwinulids but detected far less EG species, namely two to three cryptic species in P. brasiliensis and no cryptic species at all in the other darwinulid morphospecies. Conclusions/Significance Our results clearly demonstrate that both species and cryptic diversity can be recognized in putative ancient asexual ostracods using the EG species concept, and that COI data are more suitable than ITS2 for this purpose. The discovery of up to eight cryptic species within a single morphospecies will significantly increase estimates of biodiversity in this asexual ostracod group. Which factors, other than long-term geographic isolation, are important for speciation processes in these ancient asexuals remains to be investigated.

Dry Climate Disconnected the Laurentian Great Lakes

Recent studies have produced a new understanding of the hydrological history of North Americas Great Lakes, showing that water levels fell several meters below lake basin outlets during an early postglacial dry climate in the Holocene (younger than 10,000 radiocarbon years, or about 11,500 calibrated or calendar years before present (B.P.)). Water levels in the Huron basin, for example, fell more than 20 meters below the basin overflow outlet between about 7900 and 7500 radiocarbon (about 8770–8290 calibrated) years B.P. Outlet rivers, including the Niagara River, presently falling 99 meters from Lake Erie to Lake Ontario (and hence Niagara Falls), ran dry. This newly recognized phase of low lake levels in a dry climate provides a case study for evaluating the sensitivity of the Great Lakes to current and future climate change.

Hydrologic and climatic implications of a multidisciplinary study of late Holocene sediment from Kenosee Lake, southeastern Saskatchewan, Canada

Sediment lithology and mineralogy, as well as ostracode, plant macrofossil and stable isotope stratigraphies of lake sediment cores, are used to reconstruct late Holocene hydrologic changes at Kenosee Lake, a relatively large, hyposaline lake in southeastern Saskatchewan. Chronological control is provided by AMS radiocarbon ages of upland and shoreline plant macrofossils. All indicators outline an early, low-water, saline phase of lake history (4100–3000 BP), when the basin was occupied by a series of small, interconnected, sulfate-rich brine pools, as opposed to the single, topographically-closed lake that exists today. A rapid rise in lake-level (3000–2300 BP) led to the establishment of carbonate-rich, hyposaline lake conditions like those today. Lithostratigraphic data and ostracode assemblages indicate peak salinities were attained early in this period of lake infilling, suggesting that the lake-level rise was initially driven by an influx of saline groundwater. Lake-level and water chemistry have remained relatively stable over the last 2000 years, compared to earlier events. Because of a lack of datable organic material in sediments deposited during the last 2000 years, the chronology of recent events is not well resolved. Plant macrofossil, lithostratigraphic and ostracode evidence suggests that lake draw-down, accompanied by slightly higher than present salinites, occurred sometime prior to 600 BP, followed by peak lake-level and freshwater conditions. This most recent high lake stand, indicative of a high water table on the surrounding upland, may also have led to the establishment of an extensive cover of Betula in the watershed, possibly in response to paludification. Ostracode assemblages indicate that peak freshwater conditions occurred within the last 100 years. Since historically documented lake-level fluctuations correlate with decadal scale climatic fluctuations in the meteorological record, and late-Holocene hydrologic dynamics correspond to well documented climatic excursions of the Neoglacial and Little Ice Age, Kenosee Lake dynamics offer insight into the susceptibility of the regions water resources to climate change.

Chapter 19 – Ostracoda

Publisher Summary This chapter introduces the general biology, morphology, phylogeny, evolution, ecology, physiology, and classification of members of the class ostracoda of Crustacea. About 420 species of seed shrimps (ostracodes) are found in North America. Ostracodes are easily distinguished from other crustaceans by the typical, bivalved carapace enveloping their bodies. This protective covering is composed of chitin and calcite. Ostracodes occur within the benthos of nearly every conceivable aquatic system, from temporary ponds to large rivers to groundwater habitats, but they rarely enter the plankton even though many species are good swimmers. They are more commonly found in lentic systems than flowing-water habitats. Almost all are free living, and most consume attached algae or detritus. In turn, they are, preyed upon by fish, waterfowl, and various benthic and planktonic invertebrates.