Vergleichende ökologisch-physiologische Untersuchungen zur zellulären Kälteresistenz mariner Evertebraten

Cellular freezing and chilling resistances of different marine bivalve species have been measured comparatively, using isolated pieces of gill tissues. The species-specific resistance values correspond to the ecological behaviour and the geographical distribution of the species. Among marine animals from subarctic and boreal regions, cellular freezing resistance is significantly higher in species living, during the whole year, in the upper littoral than in bottom dwellers or sublittoral forms. Tissues of tropical littoral bivalves are very sensitive to freezing. Similar responses are obtained in deepwater species of the temperate zone. Studies on geographically separated populations of species from both sides of the Atlantic Ocean demonstrate small differences in cellular freezing resistance; no genetically fixed distinctions could be recognized. Among species within the same littoral habitat, those suffering from mass mortalities in extremely severe winters also exhibit comparatively lower cellular chilling and freezing resistances. In littoral bivalves from normal sea water, considerable seasonal variations of cellular freezing resistance occur; such variations are very small in specimens from brackisk waters. Maximum freezing resistance results from adaptation to low temperature combined with high salivity. The adaptation time required for reaching the final level of resistance depends on temperature and salinity. Also, the considerable increases in cellular freezing resistance caused by exposure to air, or to oxygen-deficient water, or by different organic compounds, are modified by temperature and salinity conditions during pretreatment. The subtropical-tropical species Chione cancellata, exhibits “meaningful” adaptation of cellular chilling resistance when the adaptation temperature is changed from 10° to 23.5°C; however, no comprehensible change in cellular freezing resistance occurs at the same time. Increased calcium contents of the external medium affect cellular chilling and freezing resistances of marine bivalves differently. Quick effluxes of aldolase (from cytoplasm) and of acid phosphatase (from lysosomes) after freezing and thawing of isolated gills indicate damage to membranes before cellular injuries are recognized by microscopical observations. Partial inactivation of acid phosphatase by exposure to freezing and thawing is only found after “death” of the tissue.