Abstract:
Acclimation of adult E. chloroticus for 90 days at projected seawater temperature for the next century (i.e., 24ºC) resulted in decreased feeding, respiration, negative growth and complete loss of reproductive output. The thermal limits (median lethal temperature (LT50) and lethal temperature) of adult E. chloroticus were not affected by duration of acclimation at 18 and 24ºC (i.e., one or four weeks) or by acclimatization summer (21ºC) seasons. However, acclimatization of animals to winter season resulted in lower thermal limits. Expression of hsp70 mRNA in adult E. chloroticus increased with temperature during a thermal shock (1ºC day-1) with a maximum expression at ca. 27-28ºC regardless of the acclimation/acclimatization temperature. Performance of early development at different temperatures (18, 21, 24ºC) was evaluated using gametes obtained from acclimated and non-acclimated wild adults. Development was successful in all treatments, and larvae raised at 24ºC developed faster and were larger compared to larvae cultured at 18 and 21ºC. Culture temperature did not affect respiration rate, lipid and protein content of the gastrulae, 2- and 4-arm larvae. Whereas for the 8-arm larval stage, larvae cultured at 18ºC had more lipid compared to those from 24ºC, and larvae cultured at 24ºC had more protein compared to those from the 18ºC treatment. When cultured at 24ºC, both gastrula and 2-arm larvae showed higher LT50. Thermal shock had an effect on the hsp70 mRNA expression of gastrulae, 2- and 4-arm larvae. The genotype-by-environment (GxE) interactions during early development of E. chloroticus were evident, with some genotypes performing better than others at higher temperatures. In addition, including a second stressor (i.e., low salinity, 29 ppt) during the first 24 hours of development affected fertilization, development rate, gastrulation success and normal development, with seawater temperature only affecting development rate and gastrulation. Nonetheless, an increase in temperature from 18 to 21ºC minimized the negative effect of low salinity (≤31 ppt) on development rate and gastrulation of E. chloroticus. Overall, the sea urchin E. chloroticus may have the potential to adapt to warmer seawater conditions induced by climate change due to the presence of developmental plasticity in the early life stages to withstand higher seawater temperatures and lower salinities. However, adaptation would require the presence of competent reproductive adults able to carry on plasticity through generations. Considering the total loss of reproductive output observed at higher temperatures, an increase in seawater temperature could dramatically influence the persistence of northern populations of E. chloroticus, leading to flow-on effects in the subtidal ecosystem. Finally, the results obtained in this research provide detailed information on the physiological and molecular responses of both adults and early life stages of E. chloroticus under current and projected seawater temperatures in a climate change scenario.