Vulnerability of pejerrey Odontesthes bonariensis populations to climate change in pampean lakes of Argentina.

The vulnerability of the pejerrey Odontesthes bonariensis population in Lake Chasicó was assessed under different climate change conditions. During the sampling period, the water temperature was adequate for fish reproduction and to sustain an adequate sex ratio. Climate-driven higher temperatures, however, may severely distort population structure and cause drastic reduction or local extinction of stocks. Lake Chasicó can be classified as eutrophic with clear waters and cyanobacteria that regularly cause fish mortality were identified as Nodularia spumigena and Oscillatoria sp. Global warming may strengthen the effects of eutrophication (e.g. toxic blooms or anoxia). Since many Cyanophyta species tolerate higher temperatures better than other algae, toxic blooms could increase. Furthermore, cyanobacteria have low nutritional value and could decouple the low-diversity food web. Lake Chasicó has currently the salinity optimum (c. 20) for the development of the early life-history stages of O. bonariensis. Climate change, however, is likely to amplify the intensity of droughts or inundations. Floods can endanger O. bonariensis development due to its sub-optimal growth at low salinity and droughts could increase lake salinity and also temperature and nutrient concentration. In order to reduce some of the effects of climate change on the O. bonariensis population in Lake Chasicó, integrated basin management based on an eco-hydrological approach is proposed.

New evidence of the copepod maternal food effects on reproduction.

Failure of female reproductive capacity in the copepod Calanus helgolandicus was related to number and combination of the phytoplankton species in the diets. The maternal food effects were detectable at different levels: fecundity, oogenesis and hatching. Fecundity and hatching were normal with two single (ca. Isochrysis galbana and Prorocentrum minimum) and one mixed (Phaeodactylum tricornutum+Dunaliella tertiolecta+Pavlova lutherii+I. galbana+P. minimum) diets. With the single P. lutherii diet, fecundity decreased, but hatching remained optimal. The daily egg production and hatching rates decreased significantly in females fed the other single P. tricornutum, D. tertiolecta and mixed (P. tricornutum+D. tertiolecta+P. lutherii+I. galbana) diets, or starved. The fecundity decrease coincided with gonad atresia, which was reversible when P. tricornutum and P. lutherii diets were replaced by P. minimum diet. It was irreversible when D. tertiolecta was replaced by P. minimum, leading to female sterilization expressed by the deterioration of OS3 and OS2 oocytes, as a function of the feeding duration. We assume that atresia of female gonads was caused by the limitation of essential nutrients in food, such as fatty acids, which induced catabolism and recycling of yolk reserves and thus, maintenance of gonad integrity and low spawning rates. With the D. tertiolecta diet, abnormally high increase of ornithine concentrations in eggs showed that the ornithine metabolism and polyamine pathway were affected during oogenesis, leading atresia of oocytes to be deeply disturbed and followed up by necrosis of the gonads.

Differences in the sterol composition of dominant Antarctic zooplankton.

The composition of free sterols was determined in Antarctic zooplankton species with various feeding behaviors. In the Southern Ocean, the dominant calanoid copepods Calanoides acutus, Calanus propinquus, Metridia gerlachei, and Euchaeta antarctica were investigated during different seasons and compared with the euphausiids Euphausia superba, E. crystallorophias, and Thysanoessa macrura. In addition, the Arctic copepods Calanus hyperboreus, C. glacialis, and C. finmarchicus were studied for comparison. Analyses were performed using gas chromatography and mass spectrometry. The zooplankton species exhibited a simple sterol content of up to six sterols. In the copepods, cholest-5-en-3beta-ol (22.1 to 60.5%, range of sample means), cholesta-5,24-dien-3beta-ol (22.3 to 45.2%), and cholesta-5,22E-dien-3beta-ol (4.3 to 33.4%) contributed most, while in euphausiids the sterol composition was less complex with cholest-5-en-3beta-ol always accounting for more than 75% of the total. Although sterols are membrane constituents and are expected not to vary considerably, differences in the abundance of sterols were observed between the species and the seasons. In herbivorous copepods, cholesta-5,24-dien-3beta-ol increased by a factor of 1.5 to about 45% during the main feeding period in summer; this sterol is a metabolic precursor of cholest-5-en-3beta-ol in the process of the dealkylation of dietary C-24 alkylated phytosterols. Cholest-5-en-3beta-ol decreased by the same proportion. Omnivorous and carnivorous copepods showed average levels of cholesta-5,24-dien-3beta-ol below 25%. These changes in sterol composition between copepod species seem to reflect their different feeding modes.

High-performance liquid chromatography of lignin-derived phenols in environmental samples with diode array detection.

Lignin-derived and standard phenols were successfully analyzed with reversed-phase high-performance liquid chromatography (HPLC) with diode array detection. The 11 major phenols produced by cupric oxide (CuO) oxidation were clearly and rapidly separated. Determination by diode array detection also allowed detection of interfering impurities within individual HPLC peaks. The lignin phenols were accordingly corrected and quantified. This method yields precise and reliable data for various environmental samples such as dissolved organic matter from aqueous samples and sediments and can also be applied to various particulate materials such as detritus and plant tissues. An interlaboratory method comparison with humic substance standards from the International Humic Substances Society revealed differences in lignin phenol concentrations, whereas lignin parameters better coincided.