Metabolism of Antarctic Micronektonic Crustacea as a Function of Depth of Occurrence and Season

Oxygen comsumption rates were determined on 21 species of crustaceans typical of the Southern Ocean micronektonic crustacean assemblage during spring (November), fall (March), and winter (June-August). Specimens were collected in the Scotia-Weddell Sea region in the vicinity of 60-degrees-S, 40-degrees-W in the upper 1000 m of the water column. Respiration (y, mul O2mg-1 wet mass h-1) declined with depth of occurrence (x, m) according to the equation y = 0.125 x-0.172 +/- 0.052 (p \u3c 0.05) despite the isothermal character of the water column, suggesting that lower metabolic rates are a temperature-independent adaptation to life in the deep sea. Three species of Crustacea showed a lowered metabolism during the winter season: the krill Euphausia superba and the 2 hyperiid amphipods Cyllopus lucasii and Vibilia stebbingi. Critical oxygen partial pressure (Pc) varied between 29 and 52 mm Hg, well below the lowest PO2 found in the water column. It is suggested that the long nights of the Antarctic winter decrease the effectiveness of visual predation in the epipelagic zone, allowing lowered metabolic rates to be a viable overwintering strategy for some species

Proximate Composition and Overwintering Strategies of Antarctic Micronektonic Crustacea

Proximate (protein, lipid, carbohydrate and chitin) and elemental (carbon and nitrogen) composition were determined for 18 species of Antarctic micronektonic Crustacea, representing the majority of species found in the Antarctic water column. Individuals used in the analyses were captured during fall and winter; for 8 species data were collected in both seasons. Seven of the 8 species showed some evidence that combustion of body stores were an aid to surviving the winter months; comparison with data from other investigators suggests that most of the species inhabiting shallow and mid-depths exhibit some degree of combustion of body stores during winter. Three types of overwintering strategies are proposed for Antarctic zooplankton and micronekton. Type 1, exhibited by some calanoid copepods, is characterized by accumulation of large lipid deposits and a true dormancy, or diapause, during winter. Type 2, exhibited by euphausiids and hyperiid amphipods, is characterized by a marked reduction in metabolic rate, combustion of body substance, opportunistic feeding, but no true dormancy. Type 3, \u27business as usual\u27 is exhibited by decapods and gammarid amphipods; it is characterized by an absence of a winter reduction in metabolic rate, combustion of body stores in some species but a lack of combustion or accumulation of energy in others, and opportunistic feeding. Over-wintering scenarios computed for Euphausia superba suggest that the impact of the winter season is most severe in the smaller size classes

Molecular structures of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid, obtained by gas-phase electron diffraction and theoretical calculations

The structures of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid have been determined by gas-phase electron diffraction using results from quantum chemical calculations to inform the choice of restraints applied to some of the structural parameters. The results from the study presented here demonstrate that resonance hybrids are not as helpful in rationalizing the structures of 2-, 3-, and 4-hydroxybenzoic acids as are models based upon electrostatic effects

The ecophysiology of under-ice fauna

During exposure to low salinity, the under-ice amphipods Gammarus wilkitzkii and Onisimus glacialis appeared as euryhaline osmoregulators, displaying regulation of haemolymph concentrations of sodium and chloride. Free amino acids took part in the regulation. During freezing and brine formation, the amphipods were freeze-sensitive and did not tolerate being frozen into solid ice. However, they could stay in the vicinity of the ice, conforming osmotically to the ambient brine and thus lowering the melting point of the amphipods' body fluids. This prevented internal ice formation in the absence of antifreeze agents (THF) in the haemolymph. When G. wilkitzkii, O. glacialis and Apherusa glacialis were exposed to dilute seawater, elevated rates of oxygen consumption and ammonia excretion were observed. The O:N atomic ratio was kept nearly constant during hyposmotic stress, indicating protein/lipids as metabolic substrate. Rates of oxygen consumption and ammonia excretion increased with increasing osmotic differences between the haemolymph and the medium, indicating higher energy requirements for osmotic and ionic regulation at low salinities. A minor decrease in haemolymph sodium concentrations coincided with the increased ammonia output during hyposmotic stress, indicating a possible counter ion regulation of NH+4 and Na+. An increased rate of oxygen consumption, ammonia excretion and 0:N ratio versus temperature was observed for all species