Status and changes of water quality in typical near-city zones of three East African Great Lakes in Tanzania

Environmental Science and Pollution Research - Tanzania is the only country bordering all three transboundary East African Great Lakes, i.e., Lake Victoria, Lake Tanganyika, and Lake Nyasa (Lake...     

Social monitoring in a multilevel society: a playback study with male Guinea baboons

Keeping track of social interactions among conspecifics is a driving force for the evolution of social cognition. How social cognition, such as social knowledge, ties in with a species' social organization is, however, largely unexplored. We investigated the social knowledge of wild Guinea baboons (Papio papio) ranging in Senegal, a species that lives in a fluid multilevel society with overlapping habitat use. Using playback experiments, we tested how adult males differentiate between subjects from their own vs. a neighboring or a stranger social unit (“gang”) and assessed ranging patterns with Global Positioning System (GPS) data. While territorial species usually differentiate between group and nongroup members and often respond more strongly to strangers than neighbors (the “dear enemy” effect), subjects in this highly tolerant species should largely ignore other unit members and mainly attend to subjects from their own unit. Males responded strongly after playback of calls recorded from members of their own gang, while they attended only briefly to neighbor or stranger calls. Apparently, males benefit from monitoring the social maneuvers in their own social unit, while it remains to be resolved whether they are unmotivated or unable to keep track of the identities and actions of individuals outside their own gang. The study highlights how the allocation of social attention is tuned to the specifics of a species' social organization, while a complex social organization does not necessarily translate into the need for more elaborate social knowledge.     

Colonization and extinction in dynamic habitats: an occupancy approach for a Great Plains stream fish assemblage

Despite the importance of habitat in determining species distribution and persistence, habitat dynamics are rarely modeled in studies of metapopulations. We used an integrated habitat-occupancy model to simultaneously quantify habitat change, site fidelity, and local colonization and extinction rates for larvae of a suite of Great Plains stream fishes in the Arikaree River, eastern Colorado, USA, across three years. Sites were located along a gradient of flow intermittency and groundwater connectivity. Hydrology varied across years: the first and third being relatively wet and the second dry. Despite hydrologic variation, our results indicated that site suitability was random from one year to the next. Occupancy probabilities were also independent of previous habitat and occupancy state for most species, indicating little site fidelity. Climate and groundwater connectivity were important drivers of local extinction and colonization, but the importance of groundwater differed between periods. Across species, site extinction probabilities were highest during the transition from wet to dry conditions (range: 0.52-0.98), and the effect of groundwater was apparent with higher extinction probabilities for sites not fed by groundwater. Colonization probabilities during this period were relatively low for both previously dry sites (range: 0.02-0.38) and previously wet sites (range: 0.02-0.43). In contrast, no sites dried or remained dry during the transition from dry to wet conditions, yielding lower but still substantial extinction probabilities (range: 0.16-0.63) and higher colonization probabilities (range: 0.06-0.86), with little difference among sites with and without groundwater. This approach of jointly modeling both habitat change and species occupancy will likely be useful to incorporate effects of dynamic habitat on metapopulation processes and to better inform appropriate conservation actions.     

Seasonal and interannual variations in size,biomass and chemical composition of the eggs of North Sea shrimp, <Emphasis Type="Italic">Crangon crangon</Emphasis> (Decapoda: Caridea)

In the shrimp Crangon crangon, an important fishery resource and key species in the southern North Sea, we studied temporal variations in size, biomass (dry weight, W) and chemical composition (C, N, protein and lipid) of eggs in an initial embryonic stage. Data from 2 years, 1996 and 2009, consistently revealed that egg size and biomass varied seasonally, with maxima at the beginning of the reproductive season (January), decreasing values throughout spring, minima in June–July, and a slight increase thereafter. This cyclic pattern explains why “Winter eggs” are on average larger and heavier than “summer eggs”. Using a modelling approach, we estimated the duration of oogenesis in relation to seasonally changing seawater temperatures. According to an additive model of multiple explanatory variables, the C content per newly laid egg showed in both years a highly significant negative relationship with day length (r2 = 0.38 and 0.40, respectively; P < 0.0001), a weak positive relationship with temperature (r2 = 0.08 and 0.09; P < 0.05), and a weak negative relationship with phytoplankton biomass (r2 = 0.11 and 0.12; P < 0.05) at the estimated time of beginning oogenesis. Phenotypic plasticity in initial egg size and biomass is interpreted as an adaptive reproductive trait that has evolved in regions with strong seasonality in plankton production and periods of larval food limitation. In contrast to biomass per egg, the percentage chemical composition remained similar throughout the reproductive period. Both the absolute and percentage values also showed significant interannual variations, which caution against generalizations based on short-term studies of reproductive traits of C. crangon and other species of shrimp.     

Nitrogen turnover in the leaf litter and fine roots of sugar maple

In order to better understand the nitrogen (N) cycle, a pulse of 15NO3- was applied in 1998 to a sugar maple (Acer saccharum) dominated northern hardwood forest receiving long-term (1994-2008) simulated atmospheric N deposition. Sugar maple leaf litter and live fine-root 15N were quantified for four years prior to labeling and for 11 subsequent years. Continuous sampling of 15N following addition of the tracer enabled calculation of leaf litter and fine-root N pool turnover utilizing an exponential decay function. Fine-root 15N recovery peaked at 3.7% +/- 1.7% the year the tracer was applied, while leaf litter 15N recovery peaked in the two years following tracer application at approximately 8%. These results suggest shoots are primarily constructed from N taken up in previous years, while fine roots are constructed from new N. The residence time of N was 6.5 years in leaf litter and 3.1 years in fine roots. The longer residence time and higher recovery rate are evidence that leaves were a stronger sink for labeled N than fine roots, but the relatively short residence time of tracer N in both pools suggests that there is not tight intra-ecosystem cycling of N in this mature forest.     

Effect of dissolved oxygen level on respiratory metabolism, nutritional physiology, and immune condition of southern king crab Lithodes santolla (Molina, 1782) (Decapoda, Lithodidae)

Episodes of hypoxia are common in the marine environment, and their ecological effects depend, in part, on their severity and duration. Many species of decapod crustaceans reside in areas with fluctuating oxygen regimens. Physiological mechanisms enhance the ability of these crustaceans to cope with acute episodes of hypoxia. Southern king crab, Lithodes santolla, fishery is important in the south of South America, and some data describe fishing zones with low dissolved oxygen (DO) levels (3.5 mgO₂ l⁻¹, i.e., 8.3 kPa). Our main objective was to evaluate the effect of dissolved oxygen level on respiratory metabolism, nutritional physiology, and immunological condition of L. santolla juveniles. Individual animals were exposed for 10 days to different oxygen tensions (2.1, 4.2, 8.5, 12.7, and 21.1 kPa) to quantify the oxygen consumption rate; thereafter, blood oxyhemocyanin (Hc), protein concentration, as well as hemocytes, were sampled. Freeze-dried animals were dissected, and digestive gland metabolites (glycogen, protein, glucose, cholesterol, acylglycerol, and lactate) and digestive enzyme activity (general protease, trypsin, and chymotrypsin), as well as gill lactate dehydrogenase (LDH) activity, were quantified. In the present study, Lithodes santolla showed a critical oxygen tension between 4 and 9 kPa, indicating that this crab species is more sensitive to DO than other crustacean species. Protein and Hc concentrations followed a similar pattern to that of oxygen consumption. Digestive gland glycogen and protein concentration did not change after 10 days at different oxygen exposures, but glucose, cholesterol, and acylglycerol concentrations decreased linearly and proportionally to the available oxygen in the water. As in other decapods, chymotrypsin showed over 90% of the total quantified proteases activity. Chymotrypsin activity together with total proteases and trypsin was not affected by the environmental oxygen tension. Gill LDH and digestive gland lactate followed a similar increase at lower environmental oxygen tension but dropped sharply at the lowest tension (2.1 kPa). Dissolved oxygen affected also the immune system through reduction of hemocytes. This could provide a critical window for opportunistic pathogens to become established when crabs are exposed to hypoxic conditions. L. santolla juveniles show a moderate tolerance to low oxygen availability by modifying the concentration of hemolymph proteins, mainly OxyHc, some digestive gland metabolites, and by activating the anaerobic metabolism. This allows L. santolla juveniles to inhabit temporarily low oxygen zones in the deep ocean and suggests an advantage for culture conditions.     

Simulation of cumulative effects of nearshore restoration projects on estuarine hydrodynamics

Many nearshore restoration projects are currently underway at coastal locations where human influence and development have disrupted natural habitat and coastal ecological systems. The objectives of these projects in general are to restore the lost estuarine functions to the tidal marshland. Often these projects are conducted with little understanding of the potential effects of other nearby projects within the ecosystem, and similarly, it is easy to neglect the effect of the local project on the larger estuarine scale. In this paper, a modeling study is presented to evaluate the hydrodynamic responses of multiple restoration projects and their cumulative effect in the Snohomish River estuary in Washington, USA. The concept of absolute mean tidal transport is introduced and used to measure the cumulative effect of the proposed restoration projects on the estuarine hydrodynamics. The results show that the hydrodynamic responses due to multiple restoration projects are additive in the estuary, and the effect is nonlinear. The hydrodynamic response under restoration conditions depends on the size of the restoration area and the geometric configuration of the existing river channels. Within a complex braided estuary such as the Snohomish, the influence of a specific restoration project is not only experienced locally, but also found to significantly affect tidal transport in all distributary branches within the system.     

Allelochemicals of the invasive neophyte Polygonum cuspidatum Sieb. & Zucc. (Polygonaceae)

Polygonum cuspidatum Sieb. and Zucc., a traditional Chinese medicine is now a wide-spread invasive neophyte in Europe and America. The novel weapon hypothesis states that some invasive weed species owe part of their success as invaders to allelopathy mediated by some allelochemicals. Previous HPLC/UV/ESI-MS analysis showed that the constituents of the roots of P. cuspidatum from China were obviously different from the species collected in Switzerland (present as an invasive neophyte) with respect to piceatannol glucoside, resveratroloside and some proanthocyanidin. This work isolated these special constituents from the invasive plant and studied their allelopathy effect, as well as the related structures by the seedling and growing model of Lepidium sativum (garden cress, Brassicaceae). The results revealed that stilbenes as piceatannol glucoside, resveratroloside and proanthocyanidins as catechin, epicatechin from this plant were comparatively stronger allelochemicals than the reported allelochemical (−)-catechin, which may partly explain the invasive behavior of this plant in Europe.