University System of Maryland

Theoretical and empirical studies of plankton trophodynamics are usually based on some function of the relative density of predator-and-prey plankton. Such approaches based only on the relative density of predator and prey generally underestimate predator-prey contact rates because contact depends on both the relative density and the relative velocity of predator and prey. We estimate the components of predator-and-prey contact that are due to small-scale turbulence. The small-scale turbulence effect suggests reconsidering estimates of plankton food requirements, energy gain-and-loss from foraging and mechanisms associated with patch formation and dissipation.

According to many seasoned survey researchers, offering a no-opinion option should reduce the pressure to give substantive responses felt by respondents who have no true opinions. By contrast, the survey satisficing perspective suggests that no-opinion options may discourage some respondents from doing the cognitive work necessary to report the true opinions they do have. We address these arguments using data from nine experiments carried out in three household surveys. Attraction to no-opinion options was found to be greatest among respondents lowest in cognitive skills (as measured by educational attainment), among respondents answering secretly instead of orally, for questions asked later in a survey, and among respondents who devoted little effort to the reporting process. The quality of attitude reports obtained (as measured by over-time consistency and responsiveness to a question manipulation) was not compromised by the omission of no-opinion options. These results suggest that inclusion of no-opinion options in attitude measures may not enhance data quality and instead may preclude measurement of some meaningful opinions.

Nutrient enrichment and consequent alteration of nutrient biogeochernical cycles is a serious problem in both freshwater and marine systems. The response of aquatic systems to additions of N and P is generally to increase algal biomass. The partitioning of these nutrients into different functional groups of autotrophic organisms is dependent upon both intrinsic and extrinsic factors. A common response to nutrient loading in northern temperate aquatic ecosystems is an increase in diatom biomass. Because nutrient enrichment generally leads to increases in water column concentrations of total N and total P (and not Si) such nutrient loading can lead to transient nutrient limitation of diatom biomass due to lack of dissolved silicate (DSi). Increased production of diatom biomass can lead to an increased accumulation of biogenic silica in sediments, ultimately resulting in a decline in the water column reservoir of DSi. Such biogeochemical changes in the silica cycle induced by eutrophication were first reported for the North American Laurentian Great Lakes. However, these changes are not a regional problem confined to the Great Lakes, but occur in many freshwater and marine systems throughout the world. Here we summarize the effects of anthropogenic modification of silica biogeochemical cycles for the North American Laurentian Great Lakes, describe some of the biogeochemical changes occurring in other systems, and discuss some of the ecological implications of a reduction in water column DSi concentrations, including changes in species composition, as DSi concentrations become limiting to diatom growth and biomass, changes in food web dynamics, and altered nutnent-recycling processes.

In the coming years and decades, advanced space- and ground-based observatories will allow an unprecedented opportunity to probe the atmospheres and surfaces of potentially habitable exoplanets for signatures of life. Life on Earth, through its gaseous products and reflectance and scattering properties, has left its fingerprint on the spectrum of our planet. Aided by the universality of the laws of physics and chemistry, we turn to Earth's biosphere, both in the present and through geologic time, for analog signatures that will aid in the search for life elsewhere. Considering the insights gained from modern and ancient Earth, and the broader array of hypothetical exoplanet possibilities, we have compiled a comprehensive overview of our current understanding of potential exoplanet biosignatures, including gaseous, surface, and temporal biosignatures. We additionally survey biogenic spectral features that are well known in the specialist literature but have not yet been robustly vetted in the context of exoplanet biosignatures. We briefly review advances in assessing biosignature plausibility, including novel methods for determining chemical disequilibrium from remotely obtainable data and assessment tools for determining the minimum biomass required to maintain short-lived biogenic gases as atmospheric signatures. We focus particularly on advances made since the seminal review by Des Marais et al. The purpose of this work is not to propose new biosignature strategies, a goal left to companion articles in this series, but to review the current literature, draw meaningful connections between seemingly disparate areas, and clear the way for a path forward. Key Words: Exoplanets—Biosignatures—Habitability markers—Photosynthesis—Planetary surfaces—Atmospheres—Spectroscopy—Cryptic biospheres—False positives. Astrobiology 18, 663–708. Table of Contents1. Introduction 1.1. Requirements for life 1.2. Exoplanet biosignature definitions 1.3. Biosignature categories2. Evaluating Planetary Habitability3. Overview of Terrestrial Exoplanet Modeling Studies 3.1. Observations of earth 3.2. Spectral models 3.3. Photochemical studies of terrestrial atmospheres 3.4. Earth through time4. Gaseous Biosignatures 4.1. Gaseous biosignature overview 4.2. Earth-like atmospheres 4.2.1. Oxygen (O2) 4.2.2. Ozone (O3) 4.2.3. Methane (CH4) 4.2.4. Nitrous oxide (N2O) 4.2.5. Sulfur gases (DMS, DMDS, CH3SH) and relation to detectable C2H6 4.2.6. Methyl chloride (CH3Cl) 4.2.7. Haze as a biosignature 4.2.8. Other gases 4.3. “False positives” for biotic O2/O3 and possible spectral discriminators 4.4. Biosignatures in other types of atmospheres 4.5. Effects of the host star spectrum on photochemistry 4.6. Impacts of flares and particle events on biosignature gases5. Surface Biosignatures 5.1. Photosynthesis 5.1.1. Principles of photosynthesis 5.1.1.1. Relationship between band gap wavelength and reductant in the generation of biogenic gases and pigment color 5.1.1.2. Uniqueness of OP 5.1.2. Photosynthetic pigments and the color of phototrophs 5.1.2.1. Structure 5.1.2.2. Light absorption 5.1.3. The vegetation “red edge” 5.1.4. Speculation about photosynthesis and pigment signatures on exoplanets 5.2. Retinal pigments 5.3. Alternative surface biosignatures: nonphotosynthetic pigments and reflectance features 5.4. False positive surface biosignatures 5.5. Chiral and polarization biosignatures 5.6. Fluorescence and bioluminescence6. Temporal Biosignatures 6.1. Oscillations of atmospheric gases 6.2. Oscillations in surface signatures7. Assessing Biosignature Plausibility 7.1. Chemical disequilibrium 7.2. Biomass estimation 7.3. Applications of network theory to biosignatures8. Cryptic Biospheres: “False Negatives” for Life?9. Prospects for Detecting Exoplanet Biosignatures10. Summary

Recent determinations of high production rates (up to 30 percent of primary production in surface waters) implicate free-living marine bacterioplankton as a link in a "microbial loop" that supplements phytoplankton as food for herbivores. An enclosed water column of 300 cubic meters was used to test the microbial loop hypothesis by following the fate of carbon-14-labeled bacterioplankton for over 50 days. Only 2 percent of the label initially fixed from carbon-14-labeled glucose by bacteria was present in larger organisms after 13 days, at which time about 20 percent of the total label added remained in the particulate fraction. Most of the label appeared to pass directly from particles smaller than 1 micrometer (heterotrophic bacterioplankton and some bacteriovores) to respired labeled carbon dioxide or to regenerated dissolved organic carbon-14. Secondary (and, by implication, primary) production by organisms smaller than 1 micrometer may not be an important food source in marine food chains. Bacterioplankton can be a sink for carbon in planktonic food webs and may serve principally as agents of nutrient regeneration rather than as food.

Georges Bank, a shallow submarine plateau located off the New England coast, has supported valuable commercial fisheries for several centuries. The region is characterized by high levels of primary productivity and, historically, high levels of fish production. Within the last four decades Georges Bank has been subjected to major perturbations that have profoundly altered levels of catch, abundance, and species composition. The arrival of distant water fleets during the early 1960s resulted in dramatic increases in effective fishing effort and the subsequent commercial collapse of several fish populations. Total fish biomass is estimated to have declined by >50% on Georges Bank during the period of operation of the distant water fleets. The implementation of extended jurisdiction (the 200-mile [370.4-km] limit) in 1977 was followed by modernization and increased capacity of the domestic fleet, resulting in a second perturbation to the system that resulted in further declines in groundfish populations to historically low levels. A subsequent increase in the abundance of species of low commercial value was documented, with an apparent replacement of gadid and flounder species by small elasmobranchs (including dogfish sharks and skates). Examination of feeding guild structure suggests that this switch in species dominance may have been linked to a competitive release. The small elasmobranchs, notably dogfish sharks, also prey on species of commercial importance (primarily small pelagics, including herring and mackerel). The cumulative impacts on the groundfish populations as a result of intense exploitation and predation pressure may have been further exacerbated by effects of fishing gear on the physical structure of the habitat. Implications for the development of an ecosystem-based management approach are described.

Fluctuations in the abundance of fishes may be caused by episodic mortalities or by more subtle variability in the daily growth and mortality rates of eggs and larvae. Survival response surfaces are used to illustrate the relative effects of episodic and subtle mortality during early life. It is the subtle variability associated with small changes in growth or mortality rates that may exert the greater effect on recruitment. Massive advective losses of eggs or larvae, failed egg production, and acute contaminant mortalities are examples of episodic events that may impact recruitment significantly but which need not be catastrophic. Stabilization of recruitments through density‐dependent growth rate variability in early life is demonstrated to be potentially important. Whether this mechanism actually is important in the sea remains to be determined.

We address the problem of large-scale fine-grained visual categorization, describing new methods we have used to produce an online field guide to 500 North American bird species. We focus on the challenges raised when such a system is asked to distinguish between highly similar species of birds. First, we introduce "one-vs-most classifiers." By eliminating highly similar species during training, these classifiers achieve more accurate and intuitive results than common one-vs-all classifiers. Second, we show how to estimate spatio-temporal class priors from observations that are sampled at irregular and biased locations. We show how these priors can be used to significantly improve performance. We then show state-of-the-art recognition performance on a new, large dataset that we make publicly available. These recognition methods are integrated into the online field guide, which is also publicly available.

Children's and adolescents' social reasoning about exclusion was assessed in three different social contexts. Participants (N = 294) at three ages, 10 years (4th grade), 13.7 years (7th grade), and 16.2 years (10th grade), fairly evenly divided by gender, from four ethnic groups, European-American (n = 109), African-American (n = 96), and a combined sample of Asian-American and Latin-American participants (n = 89) were interviewed regarding their social reasoning about exclusion based on group membership, gender, and race. The contexts for exclusion were friendship, peer, and school. Significant patterns of reasoning about exclusion were found for the context, the target (gender or race) of exclusion, and the degree to which social influence, authority expectations, and cultural norms explained children's judgments. There were also significant differences depending on the gender, age, and ethnicity of the participants. The findings support our theoretical proposal that exclusion is a multifaceted phenomenon and that different forms of reasoning are brought to bear on the issue. This model was drawn from social-cognitive domain theory, social psychological theories of stereotype knowledge and intergroup relationships, and developmental studies on peer relationships. The results contribute to an understanding of the factors involved in the developmental emergence of judgments about exclusion based on group membership as well as to the phenomena of prejudice, discrimination, and the fair treatment of others.

User mobility in wireless data networks is increasing because of technological advances, and the desire for voice and multimedia applications. These applications, however, require fast handoffs between base stations to maintain the quality of the connections. Previous work on context transfer for fast handoffs has focused on reactive methods, i.e. the context transfer occurs after the mobile station has associated with the next base station or access router. In this paper, we describe the use of a novel and efficient data structure, neighbor graphs, which dynamically captures the mobility topology of a wireless network as a means for prepositioning the station's context ensuring that the station's context always remains one hop ahead. From experimental and simulation results, we find that the use of neighbor graphs reduces the layer 2 handoff latency due to reassociation by an order of magnitude from 15.37ms to 1.69ms, and that the effectiveness of the approach improves dramatically as user mobility increases.

The objective of this study was to review all available aquatic toxicity literature regarding the effects of salinity on the toxicity of various classes of inorganic and organic chemicals. Toxicity data for studies in which toxicity was assessed at various salinities were organized by chemical classes and trophic groups. Seventy percent of the studies were conducted with either crustaceans or fish. The other 30% were with mollusks, annelids, zooplankton, bacteria, phytoplankton, or fungi. Results from 173 data entries showed that negative correlations (toxicity increasing with decreasing salinity) were reported most frequently (55%), followed by no correlations (27%) and positive correlations (18%). The toxicity of most metals such as cadmium, chromium, copper, mercury, nickel, and zinc was reported to increase with decreasing salinity. This finding is likely related to the greater bioavailability of the free metal ion (toxic form) at lower salinity conditions. There was generally no consistent trend for the toxicity of most organic chemicals with salinity. The one exception to this was reported with organophosphate insecticides, the toxicity of which appeared to increase with increasing salinity. Physiological characteristics of the various test species were important in determining the toxicity of the various classes of chemicals at a range of salinities. Results from various studies showed that euryhaline species were more resistant to toxic conditions at isosmotic salinities due to minimization of osmotic stress. Specific examples showed that fish were more resistant to toxic chemicals at middle salinities when compared with either lower or higher extremes. Life history and ecology of test species were important factors to consider when interpreting salinity/contaminant interaction data.

Enzymes from extremophilic microorganisms usually catalyze chemical reactions in non-standard conditions. Such conditions promote aggregation, precipitation, and denaturation, reducing the activity of most non-extremophilic enzymes, frequently due to the absence of sufficient hydration. Some extremophilic enzymes maintain a tight hydration shell and remain active in solution even when liquid water is limiting, e.g. in the presence of high ionic concentrations, or at cold temperature when water is close to the freezing point. Extremophilic enzymes are able to compete for hydration via alterations especially to their surface through greater surface charges and increased molecular motion. These properties have enabled some extremophilic enzymes to function in the presence of non-aqueous organic solvents, with potential for design of useful catalysts. In this review, we summarize the current state of knowledge of extremophilic enzymes functioning in high salinity and cold temperatures, focusing on their strategy for function at low water activity. We discuss how the understanding of extremophilic enzyme function is leading to the design of a new generation of enzyme catalysts and their applications to biotechnology.

Seasonal variations in the distribution of dissolved inorganic nitrogen, sihcon, and phosphorus along the salinity gradient of Chesapeake Bay from 1984 to 1988 suggest that dissolved silicate (DSi) controls the magnitude of diatom production during the spring bloom, causes the collapse of the spring bloom, and leads to changes in floristic composition. High sedimentation rates of chlorophyll biomass observed during this per~od could be due to Si-deficiency, suggesting that the supply of DSi may also control the flux of phytoplankton biomass to the benthos, an important parameter of seasonal oxygen depletion in the Bay.

The use of bioenergetics models in fisheries ecology and management has increased rapidly in recent years, but application-specific information on energy content of fish and their prey has lagged behind. We believe this is because the process of directly measuring energy density is very time consuming. In this paper we present and evaluate a series of general empirical models that predict energy density (J/g wet weight) from fish percent dry weight. Data were gathered from the literature, obtained from cooperating investigators, and measured directly. Least-squares models were derived for all species combined and for orders, families, and species. All models were linear; however, logarithmic transformation was necessary to normalize residuals in the combined model. All models with more than four data points were highly significant (P < 0.002) and had coefficients of determination of 0.76 or greater. The model for all species combined (N = 587, r2 = 0.95) was J/g wet weight = 45.29 DW1.507; DW is the percent dry weight of the fish. At all taxonomic levels, energy density models showed a strong positive relationship between energy density and percent dry weight. This relationship, if corroborated, should allow the estimation of seasonal and ontogenetic changes in energy density based solely on percent dry weight data.

Differences in the dynamics (growth and mortality) and energetics properties of marine and freshwater fish larvae have important implications for determining the life stages at which year-class size is established. After correcting for temperature effects, marine fish larvae, which typically weigh less at hatch, can be shown to experience mortality rates, have higher metabolic requirements, and have longer larval stage durations than do freshwater fish larvae. Growth rates and growth efficiencies are similar for the two categories of larvae. The difference in body size between typically small marine and typically large freshwater fish larvae is an important factor affecting their dynamics and energetics. Predicted mean survivorship to metamorphosis of a cohort of freshwater fish larvae is 5.30%, while that of marine larvae is only 0.12%. The probability of significant density-dependent regulation during the larval stage could be relatively high for marine species, based upon their life-history properties. The probability that episodic mortalities of larvae will have significant impacts on recruitment may be higher for freshwater fish than for marine fish. Starvation mortality is more probable for marine larvae, primarily because of their small body size, associated high metabolic demands, and possibly higher ingestion requirements. Because expected mean survivorship of freshwater larvae is 44 times higher than that of marine larvae, juvenile-stage dynamics will be relatively important in controlling/regulating recruitment levels of freshwater fishes. In contrast, properties of marine species indicate that larval-stage dynamics will have a greater influence on recruitment success.

Abstract It appears that living communities serve to augment the rate of entropy production over what it would be in the absence of biota. This hypothesis might be tested by comparing the spectra of electromagnetic fluxes incident to and emanating from the surface of the Earth. An added measure of the value of stored energy to ecosystems is derived by using the economic theory of discounting.

Mixed distearoylphosphatidylethanolamine (DSPE) and dioleoylphosphatidylethanolamine (DOPE) monolayers and bilayers have been deposited on mica using the Langmuir−Blodgett (LB) technique, as a model system for biomembranes. Investigation with atomic force microscopy revealed phase-separation for both monolayers in air and bilayers in water in the form of microscopic DSPE domains embedded in a DOPE matrix. For the monolayers in air, the step height measured between the higher DSPE phase and the lower DOPE phase was larger than expected from the molecular lengths, and a significant contrast in adhesion and friction was observed despite identical lipid end groups. This unexpected behavior resulted primarily from a difference in the film mechanical properties, the DOPE phase being inelastically deformed by the probe. For the bilayers in water, similar trends were found in terms of height, adhesion, and friction, but an additional short-range repulsive hydration/steric force over the DSPE phase contributed to the observed differences.

The bottom waters of the mesohaline portion of Chesapeake Bay become depleted in oxygen in summer. We found that copepods and nauplii were in low abundance or absent from bottom waters when oxygen concentrations were &lt;1 mg O 2 liter −1 . In contrast, when oxygen concentrations were higher in bottom waters in spring or summer due to episodic mixing events, the highest copepod abundances were often found in bottom waters. Laboratory experiments confirmed that oxygen concentrations &lt;1 mg O 2 liter −1 resulted in reduced survival of the copepods Acartia tonsa and Oithona colcarva and inhibited the hatching of A. tonsa eggs. The decrease in Chesapeake Bay copepods in May–June parallels the decline of oxygen in bottom waters. Our field and laboratory data suggest that this decline in copepods could result from reduced recruitment as a consequence of egg mortality in the low‐oxygen bottom waters. In summer this source of mortality would be reduced because warmer water temperatures would allow the eggs to hatch in the upper water column above the low‐oxygen bottom waters.

A comprehensive study of the strongly wind driven midlatitude buoyant plume from the Columbia River, located on the U.S. west coast, demonstrates that the plume has two basic structures during the fall/winter season, namely, a thin (∼5–15 m), strongly stratified plume tending west to northwestward during periods of southward or light northward wind stress and a thicker (∼10–40 m), weakly stratified plume tending northward and hugging the coast during periods of stronger northward stress. The plume and its velocity field respond nearly instantaneously to changes in wind speed or direction, and the wind fluctuations have timescales of 2–10 days. Frictional wind‐driven currents cause the primarily unidirectional flow down the plume axis to veer to the right or left of the axis for northward or southward winds, respectively. Farther downstream, currents turn to parallel rather than cross salinity contours, consistent with a geostrophic balance. In particular, during periods when the plume is separated from the coast, currents tend to flow around the mound of fresher water. At distances exceeding about 20 km from the river mouth, the along‐shelf depth‐averaged flow over the inner to midshelf is linear, and depth‐averaged acceleration is governed to lowest order by the difference between surface and bottom stress alone. In this region, along‐shelf geostrophic buoyancy‐driven currents at ∼5 m (calculated from surface density) and along‐shelf geostrophic wind‐driven currents (computed from a depth‐averaged linear model) are comparable in magnitude (∼10–25 cm s −1 ).

Biotechnology has almost unlimited potential to change our lives in very exciting ways. Many of the chemical reactions that produce these products can be fully optimized by performing them at extremes of temperature, pressure, salinity, and pH for efficient and cost-effective outcomes. Fortunately, there are many organisms (extremophiles) that thrive in extreme environments found in nature and offer an excellent source of replacement enzymes in lieu of mesophilic ones currently used in these processes. In this review, I discuss the current uses and some potential new applications of extremophiles and their products, including enzymes, in biotechnology.