Search

To evaluate the thermal resistance of marine invertebrates to elevated temperatures under scenarios of future climate change, it is crucial to understand parental effect of long acclimatization on thermal tolerance of offspring. To test whether there is parental effect of long acclimatization, adult sea cucumbers (Apostichopus japonicus) from the same broodstock were transplanted southward and acclimatized at high temperature in field mesocosms. Four groups of juvenile sea cucumbers whose parents experienced different durations of high temperature acclimatization were established. Upper thermal limits, oxygen consumption and levels of heat shock protein mRNA of juveniles was determined to compare thermal tolerance of individuals from different groups. Juvenile sea cucumbers whose parents experienced high temperature could acquire high thermal resistance. With the increase of parental exposure duration to high temperature, offspring became less sensitive to high temperature, as indicated by higher upper thermal limits (LT50), less seasonal variations of oxygen consumption, and stable oxygen consumption rates between chronic and acute thermal stress. The relatively high levels of constitutive expression of heat-shock proteins should contribute to the high thermal tolerance. Together, these results indicated that the existence of a parental effect of long acclimatization would increase thermal tolerance of juveniles and change the thermal sensitivity of sea cucumber to future climate change. [ABSTRACT FROM AUTHOR]

Abstract: The mortality of juveniles of the sea cucumber Apostichopus japonicus and related physiological responses (osmoregulation and heat-shock protein 70 (Hsp 70) gene expression) were studied in a simulated field salinity decrease after a heavy rainfall in summer. Salinity firstly decreased gradually from 30psu to 20psu (S20) or 25psu (S25) at a rate of 2.5psu every 6h, and then was maintained at 20psu or 25psu. After 96h at the low salinities, salinity was increased gradually to 30psu at a rate of 2.5psu every 6h, and then was maintained at 30psu for 96h. There was no mortality during salinity decreases, but 40%–50% mortality occurred when salinities were maintained at low levels. The osmotic pressure of the coelomic fluid changed with decrease in ambient salinity but stabilized within 6h after the salinity change. In both S20 and S25 treatments, expression of hsp70 mRNA increased initially after salinity decrease, reached a maximum value at the lowest salinity and returned to the control level (without salinity decrease) after 72-h low-salinity exposure. These data suggest that low salinity can cause large-scale mortality of juvenile A. japonicus, which may be partly due to the rapid decrease of osmotic pressure in the coelomic fluid during hypo-osmotic stress. Furthermore, cellular level stress is indicated by up-regulation of mRNA for the molecular chaperone Hsp70, but this adaptive response can only provide temporary protection against salinity decrease. [Copyright &y& Elsevier]