Antarctic algae are extremophilic organisms capable of surviving harsh environmental conditions such as low temperatures and deep dehydration. Although these algae have various adaptations for life in extreme environments, the majority of the molecular mechanisms behind their resistance to dehydration and freezing are not yet fully understood. The aim of our research was to observe the behaviour of bound water freezing in the free-living Antarctic alga Prasiola crispa. One way to avoid frost damage involves deep dehydration of the algal thallus. For that reason, a detailed analysis of water freezing at different sample hydration levels was carried out. Nuclear magnetic resonance investigation revealed two types of water immobilization: cooperative bound water freezing for samples with sample hydration levels above Δm/m0 = 0.40 and non-cooperative bound water immobilization for lower thallus hydration levels. In the differential scanning calorimetry experiment, 2-h incubation at -20°C suggested the diffusion and final binding of supercooled water to the ice nuclei and a lower hydration level threshold, at which ice formation could be observed (Δm/m0 = 0.21). Our research provides a new perspective on water sorption and freezing in Antarctic algae, which may be important not only in biological systems, but also in such novel materials as metal-organic frameworks or covalent organic frameworks.

Seasonal changes in spatial structure of biomass of submerged aquatic vegetation (SAV) and environmental variables were evaluated in Celestun Lagoon, an estuarine habitat in Mexico. Geostatistical techniques were used to evaluate spatial autocorrelation and to predict the spatial distribution by kriging. The relative contribution of 11 environmental variables in explaining the spatial structure of biomass of SAV was evaluated by canonical correspondence analysis. Spatial partitioning between species of SAV was evident: the seagrasses Halodule wrightii and Ruppia maritima dominated the seaward and central zones of the lagoon, respectively, whereas the green alga Chara fibrosa was constrained to the inner zone. The spatial structure and seasonal variability of SAV biomass were best explained by organic carbon in the sediments, salinity and total suspended solids in the water column. Analysis at different spatial scales allowed identifying the importance of spatial structure in biotic and abiotic variables of this estuarine habitat.

Water microbiological and physicochemical characterizations at various depths of aquatic ecosystems are basic requirements in several fields of research. A chief difficulty in hydrobiology, limnology, biological oceanography and water environmental microbiology is that of taking accurate field collections that are representative of the natural environment and population at various depths of aquatic ecosystems. Gathering water/plankton samples in a level just below the surface of the water body upon rising in columns from various depths due to hydrostatic pressure variations provided a simple approach for water and plankton sampling. Based on this approach, several forms of simple devices for water and plankton sampling were developed for water microbiological and physicochemical characterizations at various depths of aquatic ecosystems. The described approach showed less sampling errors in comparison to Van Dorn bottle and was comparable to water pumping but requires no external source of power. The described samplers are inexpensive and can be self constructed.

La tolérance aux basses températures des gamétophytes de l'algue alimentaire Undaria pinnatifida est examinée selon différentes méthodes de cryoconservation. La conservation à -80 °C dans une solution glycérolée à 28 % et celle à −196 °C dans une solution en eau de mer de glycérol à 5 ou 10 % ne permettent que des survies de, respectivement, 9 et 4 jours. Par ailleurs, la viabilité n'est pas affectée par un refroidissement de 5 °C/min et une conservation de 15 minutes à −15 °C sans milieu de cryoprotection mais est fortement diminuée par un stockage de 15 minutes à −30 ou −196 °C, même en présence de DMSO. La réduction de la survie des gamétophytes se traduit morphologiquement par une dépigmentation et/ou une contraction des cellules.