Physiological responses of Nodularia harveyana to osmotic stress

The effects of salinity stress on biomass yield, photosynthetic O₂ evolution and nitrogenase activity were investigated using axenic cultures of Nodularia harveyana (Thwaites) Thuret originally isolated from a salt marsh at Gibraltar Point, Lincolnshire, UK in 1971 and studied in this laboratory in 1983. Biomass yields, as chlorophyll a per culture, were highest in the 0 to 100% seawater (0 to 35 sea salt) range with negligible growth in 200% seawater; growth on NH ₄ ⁺ was greater than on N₂ and NO ₃ ^- , which did not differ significantly from each other. In short-term experiments, photosynthetic O₂ evolution remained high at salinities up to 150% seawater (52.5 sea salt); nitrogenase activity remained high at salinities up to 100% seawater (35 sea salt). The major internal low molecular weight carbohydrate which accumulated in response to increased salinity was sucrose, the levels of which fluctuated markedly and rapidly in response to salinity change.     

Factors regulating annual mating success and reproductive success in spotted sandpipers (Actitis macularia)

Summary We investigated factors affecting annual mating success (MS) and reproductive success (RS) of spotted sandpipers (Actitis macularia) from 13 years of a 17-year study at Little Pelican Island, Leech Lake, Minnesota. Analyses were restricted to ages 1–3. Mean annual female MS varied from 1.3 to 2.7 mates, and the MS pattern was indistinguishable from random. However, female MS increased with age and was affected by arrival date, territory size, and beach size. Female RS also increased with age, and number of mates and year effects were the most significant explanatory variables in each age. Older female RS was increased by priority on a territory and presence of a previous mate. Territory size and beach size varied with population density and did not predictably affect RS. The strong year affect on RS was associated with annual variation in sex ratio and predation. Males produce only one successful clutch per year, so MS greater than one is a result of nest loss and does not increase RS. Neither male MS nor RS changed with age. Male reproductive failure rate varied by year. Given that a male produced young, the degree of RS was affected by year, arrival date, priority on a territory, territory size, and beach size. In years with early-season predation, late arrivals had higher RS; territory and beach size effects varied by year. Neither the presence, nor degree, of female care was associated with male RS. Male RS was more subject to annual environmental variability than was female RS, probably because of relatively low annual potential RS among males.Offprint requests to: L.W. Oring at the current address     

Osmoacclimation in Enteromorpha intestinalis: long-term effects of osmotic stress on organic solute accumulation

The fate of the protease trypsin in intestines of individual herring larvae Clupea harengus L. was studied following digestion of the copepod Acartia tonsa. Trypsin was retained in the intestine during two consecutive pulses of feeding and defaecation of copepods. Quantification of herring trypsin in digested, defaecated copepods showed that ca. 1% of larval intestinal enzyme was defaecated along with 1 to 3 copepods. Following ingestion of a single meal, the level of intestinal trypsin post-ingestion declined to pre-ingestion levels within 1 to 2 d of starvation. All enzyme data thus indicated that trypsin, released in response to ingestion of a meal, was retained. In addition, analysis of fed subgroups of starved larvae clearly indicated that release of trypsin from the pancreas stopped after 6 to 8 d of starvation. As the fish still contained substantial amounts of trypsinogen, the underlying cause might be defective release mechanisms. Daily secretion of trypsin and processes responsible for enzyme retention in the gut are discussed. Assimilation efficiency in herring larvae was estimated for copepodite prey. Average carbon assimilation was 90%.     

The Role of Behavior in Recent Avian Extinctions and Endangerments

Abstract: Understanding patterns of differential extinction and predicting the relative risks of extinction among extant species are among the most important problems in conservation biology. Although recent studies reveal that behavior can be a critical component in many species' extinctions or endangerments, current approaches to the problem of predicting extinction patterns largely ignore behavior. I reviewed how behavior can affect population persistence and then used recent avian extinctions and endangerments to illustrate behaviors relevant to extinction risk. Behaviors that affect population persistence can be grouped as aggregation, interspecific responses, dispersal, habitat selection, intraspecific behavior, and maladaptive behavior. Behavior that can affect extinction risk is not limited to birds; for example, in many taxonomic groups (vertebrate and invertebrate) there is evidence of socially facilitated reproduction in colonial species, Allee effects on reproductive success and survival, behavioral regulation of population size, and conspecific attraction to breeding sites. Incorporating specific behaviors into models predicting extinction probabilities and patterns should improve their predictions.     

Correlates of Population Recovery Goals in Endangered Birds

Abstract: Endangered species recovery plans commonly set goals for population size that are used to define the success of recovery efforts. We examined variation in these population recovery goals for bird species listed under the U. S. Endangered Species Act to determine whether there were simple predictors of recovery population size. The median population sizes that must be met for a species to be removed from the list or downlisted to the threatened category are 4000 and 1500 respectively, but the thresholds varied considerably. Most variation in population recovery goals ( ≥75%) was explained by the population size when the recovery plan was written. Species listed when their population's size was relatively large have higher population recovery goals, whereas those listed when populations were small have lower population goals. Population sizes set for recovery also increased over time and were higher for species listed throughout the United States rather than for part of the country. In combination, these three variables explained 86% of the variance in population goals for delisting and 94% of the variance in goals for downlisting. Body mass, annual fecundity, maximum lifespan, whether the population was listed as threatened or endangered, and whether a formal population viability analysis was conducted were variables not significantly associated with population recovery goals. Thus, we found that variables relating to the circumstances under which the populations were listed could explain almost all of the variance in recovery population goals, and that biological traits of the endangered birds explained little of the variance.     

Osmotic adjustment and organic solute accumulation in unicellular cyanobacteria from freshwater and marine habitats

The intracellular concentrations of low-molecular weight carbohydrates and quaternary ammonium compounds present in 26 axenic isolates of unicellular cyanobacteria have been studied over a range of external salinity from freshwater up to 300% seawater (100%=35 S). In all cases, a single carbohydrate, either sucrose or glucosylglycerol, was identified as the principal organic osmoticum, showing major variation in response to the external salt concentration; quaternary ammonium compounds were present in osmotically insignificant amounts. Glucosylglycerol was accumulated as primary osmoticum by nine of the isolates from saline habitats and by five of the freshwater isolates; trace amounts of sucrose were also prsent. The remaining twelve freshwater strains accumulated sucrose as sole osmoticum. Glucosylglycerol-accumulating strains grew over the widest salinity range (up to 200 to 250% seawater), whether isolated from saline or non-saline habitats. Sucrose-accumulating strains were more stenohaline, growing only in up to 50 to 100% seawater and showing no sustained growth in hypersaline media (>100% seawater). The data suggest that (1) glycosylglycerol accumulation is not unique to marine cyanobacteria, and (2) the upper salinity limit for growth may be linked to organic solute accumulation, rather than habitat, with glucosylglycerol-accumulating isolates having a greater potential for growth in salt-stressed conditions than sucrose accumulators.     

Regional consequences of the way land users respond to future water availability in Murcia, Spain

Agricultural development in the Murcia autonomous region, Spain, has led to overexploitation of groundwater resources, and climate change will further increase pressures. Policy options to tackle the current unsustainable situation include the development of inter-basin water transfer (IBWT) schemes from wetter regions in the north and the introduction of taxation to further control groundwater abstraction. Under these scenarios, farmers with current access to water could face higher water cost, whereas farmers in areas where water was previously not available could see first time availability of water resources. In this paper, we combine discrete choice-based interviews with farmers in the Torrealvilla catchment, in which they indicate how they would adapt their land use under different scenarios, with an input–output model to assess the aggregate effects of individual land use decisions on the economy and water consumption of the Murcia region. The paper presents steps taken in the development of an input–output table for Murcia, including disaggregation of the agricultural sector, accounting for sector water use and consideration of back- and forward linkages. We conclude that appropriate taxation can lead to better water use efficiency, but that this is delicate as relatively small changes in prices of agricultural products can have significant impacts on land use and water consumption. Although new IBWT schemes would enable water to be used more efficiently, they would considerably increase regional water consumption and the regional economy’s dependence on water. As this is not sustainable under future climate change, water saving development pathways need to be explored.     

Additional fractionation of sediment oxygen demand

Biological sediment oxygen demand was fractionated into carbonaceous and nitrogenous components. This study, in combination with previous work, provides a procedure for the complete fractionation of sediment oxygen demand for the bottom sediments of lakes and streams. The significance of this study is that this fractionation scheme sheds some lights into the physiological nature of sediments.