scholarly journals The role of the small planktonic communities in the diet of two Antarctic octocorals (Primnoisis antarctica and Primnoella sp.)

2003 ◽  
Vol 250 ◽  
pp. 105-116 ◽  
Author(s):  
C Orejas ◽  
JM Gili ◽  
W Arntz
Keyword(s):  
Planktonic Communities

The role of aerobic metabolism and intragel oxygen in hypoxia tolerance of three ctenophores: Pleurobrachia bachei, Bolinopsis infundibulum and Mnemiopsis leidyi

2005 ◽  
Vol 85 (3) ◽  
pp. 627-633 ◽  
Author(s):  
Erik V. Thuesen ◽  
Ladd D. Rutherford ◽  
Patricia L. Brommer
Keyword(s):  
Aerobic Metabolism ◽  
Hypoxia Tolerance ◽  
Mnemiopsis Leidyi ◽  
Survival Times ◽  
Partial Pressures ◽  
Pleurobrachia Bachei ◽  
Oxygen Measurements ◽  
Surrounding Seawater ◽  
Planktonic Communities

Ctenophores are important members of planktonic communities that are often abundant in dysaerobic environments. Previous studies have shown that ctenophores are not adversely affected by extended periods of hypoxia. The three species used in this study, Pleurobrachia bachei, Bolinopsis infundibulum, and Mnemiopsis leidyi, were all able to oxyregulate to very low partial pressures of oxygen (PO2s). These species were found to have mean critical oxygen tensions of 7.7, 10.6, and 7.2 hPa respectively. In general, ctenophores are better oxyregulators than medusae and many species of shrimps, fish and squid. Intragel oxygen was measured using a fibre optic oxygen optode. All these ctenophores have intragel subsurface [O2]s of 5–10% below that of the surrounding seawater. Intragel oxygen measurements of P. bachei showed a gradient of decreasing PO2 from surface tissues to the gut. Specimens of P. bachei over 14 mm in diameter had anaerobic guts. Survival times in anoxia ranged from 0 h for M. leidyi to up to 6 h for P. bachei. Ctenophores rely on aerobic metabolism to tolerate hypoxia.

Microbial population responses in three stratified Antarctic meltwater ponds during the autumn freeze

2012 ◽  
Vol 24 (6) ◽  
pp. 571-588 ◽  
Author(s):  
Karl Safi ◽  
Ian Hawes ◽  
Brian Sorrell
Keyword(s):  
Microbial Communities ◽  
Microbial Population ◽  
Grazing Pressure ◽  
Filamentous Cyanobacteria ◽  
Ice Shelf ◽  
Population Responses ◽  
Upper Mixed Layer ◽  
Microbial Groups ◽  
Planktonic Communities

AbstractThe planktonic microbial communities of three meltwater ponds, located on the McMurdo Ice Shelf, were investigated from the end of January 2008 to early April, during which almost the entire pond volumes froze. The ponds were comprised of an upper mixed layer overlying a salt-stabilized density gradient in which planktonic communities were primarily embedded. Plankton comprised all components of the “microbial loop”, though carnivorous protists were rare. As the ponds froze and light became increasingly limited, it was expected conditions would induce physiological changes altering the functional role of autotrophic and heterotrophic microplankton within the ponds. The results showed that microbial groups responded to the onset of winter by declining in abundance, though an exception was the appearance of filamentous cyanobacteria in the water column in March. As freezing progressed, autotrophs declined more rapidly than heterotrophs and grazing rates and abundances of mixotrophic and heterotrophic organisms increased. Grazing pressure on bacteria and picophytoplankton also increased, in part explaining their decline over time. The results indicate that stressors imposed during freezing select for increasing heterotrophy within the remaining microbial communities, although all components of the food web eventually decline as the final freeze approaches.

Comparing food-web impacts of a native invertebrate and an invasive fish as predators in small floodplain wetlands

2011 ◽  
Vol 62 (4) ◽  
pp. 372 ◽  
Author(s):  
Susie S. Ho ◽  
Nick R. Bond ◽  
P. Sam Lake
Keyword(s):  
Chlorophyll A ◽  
Trophic Cascades ◽  
Gambusia Holbrooki ◽  
Floodplain Wetlands ◽  
Poeciliid Fish ◽  
Eastern Australia ◽  
Wetland Mesocosms ◽  
Trophic Role ◽  
Planktonic Communities

Gambusia holbrooki is an invasive predatory poeciliid fish in wetlands of south-eastern Australia, where it coexists with the native waterbug Anisops thienemanni (Notonectidae). Gambusia has been shown to produce trophic cascades, leading to increased algal biomass following invasion, whereas these effects relative to the often-dominant invertebrate predator Anisops are unknown. Given its flexible diet, we predicted that Gambusia would feed more broadly than Anisops, thereby reducing the abundance of zooplankton grazers, and increasing chlorophyll a. We tested this hypothesis in experimental 110-L wetland mesocosms, using Gambusia and Anisops alone and in combination, in addition to no-predator treatments. We ran two experiments lasting 91 and 35 days, respectively. Both fish and macroinvertebrates generated weak trophic cascades, resulting in minor increases in chlorophyll a above concentrations in control treatments. Gambusia, in lowering total zooplankton abundances, triggered a larger, although still relatively small, algal response relative to Anisops. Impacts of both predators on dominant invertebrate grazers (e.g. Simocephalus spp., copepod nauplii) were similar, although Anisops was associated with an increase in ostracod (Newnhamia sp.) numbers. The similar trophic role of the two predators on algae was unexpected, given their different effects on planktonic communities and their very different taxonomic positions and zoogeographic origins.

The role of environmental, geographical, morphometric and spatial variables on plankton communities in lakes of the arid Patagonian plateaus

2020 ◽  
Vol 42 (2) ◽  
pp. 173-187
Author(s):  
Sol Porcel ◽  
Griselda Chaparro ◽  
M Cristina Marinone ◽  
Juan F Saad ◽  
Julio Lancelotti ◽  
...  
Keyword(s):  
Variation Partitioning ◽  
Null Model ◽  
Taxonomic Diversity ◽  
Conservation Strategies ◽  
High Dispersion ◽  
Spatial Effects ◽  
Spatial Factors ◽  
Zooplankton Communities ◽  
Planktonic Communities

Abstract Species diversity is one of the most informative community metrics and is influenced by regional and local factors. We studied the spatial patterns of taxonomic and functional phyto- and zooplankton diversity in 33 lakes from two basaltic plateaus of the arid Patagonia. The aims of our study were to evaluate α, β and γ taxonomic diversity of phyto- and zooplankton; to assess the influence of environmental, spatial, geographical and morphometric factors on phyto- and zooplankton communities and to compare the influence of these variables on the taxonomic and functional composition. β1-diversity (within plateaus) was the major component for phytoplankton, rotifers and microcrustaceans taxonomic regional diversities. Planktonic communities were mainly constrained by macrophytes, fish, conductivity, dissolved organic carbon, altitude and spatial factors. The high dispersion of small individuals within plateaus tends to homogenize these communities, as indicated by null model results and the high explanation of fine-scale spatial factors in variation partitioning. This knowledge contributes to explaining the diversity patterns of planktonic communities of these valuable environments and to develop conservation strategies, considering both environmental heterogeneity and spatial effects.

Urea uptake and urease activity in the Chesapeake Bay

2019 ◽  
Vol 77 (2) ◽  
pp. 139-168 ◽  
Author(s):  
Caroline M. Solomon
Keyword(s):  
Environmental Factors ◽  
Chesapeake Bay ◽  
Metabolic Pathways ◽  
Urease Activity ◽  
Principal Component ◽  
Culture Studies ◽  
Urea Uptake ◽  
The Relationship ◽  
Planktonic Communities

The importance of urea in supplying the nitrogen (N) required by planktonic communities has long been recognized, notably by James J. McCarthy in studies as early as the 1970s. Utilization of urea involves a two-step enzymatic process in phytoplankton, with urea first entering the cell via transport (i.e., urea uptake), followed by the conversion of urea into ammonium by the enzyme urease. This article describes a series of field observations and experiments conducted in the Chesapeake Bay, USA, from 2001 through 2018, aimed at understanding the relationship between urea uptake and urease activity and the role of environmental factors on that relationship. Principal component analysis revealed a few patterns. Urea uptake, for example, was consistently positively related to combined variables that included urea concentrations. Similarly, urease activity was consistently positively related to combined variables that included temperature. Contrary to findings in culture studies, however, relationships with environmental factors within different phytoplankton taxa in the field were not clear. This suggests that factors other than those examined may be involved in the regulation of urea uptake and urease activity. New insights into the role of the urea cycle in phytoplankton nitrogen dynamics suggest that the regulation of urease may not be directly impacted by environmental factors, but indirectly regulated by different metabolic pathways responding to nutrient availability, light, and temperature conditions.

Role of dactinomycin in the improved survival of children with Wilms' tumor

JAMA ◽  
1966 ◽  
Vol 195 (12) ◽  
pp. 1005-1009 ◽  
Author(s):  
D. J. Fernbach
Keyword(s):  
Wilms Tumor

Role of the allergist in diagnosis and management of patients with uveitis

JAMA ◽  
1966 ◽  
Vol 195 (3) ◽  
pp. 167-172 ◽  
Author(s):  
T. E. Van Metre
Keyword(s):  
Diagnosis And Management

The power of norms to sway fused group members

2018 ◽  
Vol 41 ◽  
Author(s):  
Winnifred R. Louis ◽  
Craig McGarty ◽  
Emma F. Thomas ◽  
Catherine E. Amiot ◽  
Fathali M. Moghaddam
Keyword(s):  
Evolutionary Anthropology ◽  
Normative Systems ◽  
Violent Extremism ◽  
Identity Fusion ◽  
Group Members

AbstractWhitehouse adapts insights from evolutionary anthropology to interpret extreme self-sacrifice through the concept of identity fusion. The model neglects the role of normative systems in shaping behaviors, especially in relation to violent extremism. In peaceful groups, increasing fusion will actually decrease extremism. Groups collectively appraise threats and opportunities, actively debate action options, and rarely choose violence toward self or others.

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