Physiological energetics of the protobranch bivalve Yoldia hyperborea in a cold ocean environment

Molecular responses to ocean acidification in an Antarctic bivalve and an ascidian

Southern Ocean organisms are considered particularly vulnerable to Ocean acidification (OA), as they inhabit cold waters where calcite-aragonite saturation states are naturally low. It is also generally assumed that OA would affect calcifying animals more than non-calcifying animals. In this context, we aimed to study the impact of reduced pH on both types of species: the ascidian Cnemidocarpa verrucosa sp. A, and the bivalve Aequiyoldia eightsii, from an Antarctic fjord. We used gene expression profiling and enzyme activity to study the responses of these two Antarctic benthic species to OA. We report the results of an experiment lasting 66 days, comparing the molecular mechanisms underlying responses under two pCO2 treatments (ambient and elevated pCO2). We observed 224 up-regulated and 111 down-regulated genes (FC ≥ 2; p-value ≤ 0.05) in the ascidian. In particular, the decrease in pH caused an upregulation of genes involved in the immune system and antioxidant response. While fewer differentially expressed (DE) genes were observed in the infaunal bivalve, 34 genes were up-regulated, and 69 genes were downregulated (FC ≥ 2; p-value ≤ 0.05) in response to OA. We found downregulated genes involved in the oxidoreductase pathway (such as glucose dehydrogenase and trimethyl lysine dioxygenase), while the heat shock protein 70 was up-regulated. This work addresses the effect of OA in two common, widely distributed Antarctic species, showing striking results. Our major finding highlights the impact of OA on the non-calcifying species, a result that differ from the general trend, which describes a higher impact on calcifying species. This calls for discussion of potential effects on non-calcifying species, such as ascidians, a diverse and abundant group that form extended three-dimensional clusters in shallow waters and shelf areas in the Southern Ocean.

Physiological and biochemical responses of Dosinia corrugata to different thermal and salinity stressors

Temperature and salinity are major factors affecting geographic distribution, reproduction, and physiological processes of marine and estuarine organisms. In this study, the effects of different temperatures and salinity on the respiratory metabolism and physiological response were evaluated in D. corrugata by measuring oxygen consumption rate (OCR), ammonia excretion rate (AER), and glycolytic enzyme activity. An increase in the OCR of D. corrugata with increasing temperature was observed. No peak of oxygen consumption was observed in D. corrugata over the temperature range evaluated. There was an increase in AERs with increasing temperature and salinity, respectively. With increasing salinity, the enzyme activity increased until it reached a peak at a salinity of 30 ppt, while the highest HK and LDH activity was observed at a salinity of 25 ppt. Our results may be used to optimize the temperature and salinity conditions for optimal growth and survival of D. corrugata and to provide basic information for conservation management and fishing moratorium of this economically important bivalve species. The enzyme activity decreased slightly from 15 to 20°C, but when the temperature exceeded 20°C, enzyme activity increased, reaching a maximum at 30°C (tested range of 10-30°C). With increasing salinity, the enzyme activity increased until it reached a peak at a salinity of 30 ppt, but once the salinity was greater than 30 ppt, the enzyme activity began to decrease up to salinity of 35 ppt.