Abstract:
The accumulation of greenhouse gases in the atmosphere has led to an increase in global temperature, with a consequent increase in ocean temperature. Marine ectotherms are more likely to be affected by this increase in seawater temperature. Thermal limits are species-specific, with early life history stages having narrower limits than adults, and therefore being more vulnerable to changes in seawater temperature. This study demonstrated the biological effects that an increase in seawater temperature has during early development of the ecologically and economically important New Zealand sea urchin, Evechinus chloroticus. The early development of E. chloroticus was evaluated at different temperatures (from 15 to 24°C), which included the optimum temperatures for fertilization as well as the highest temperature predicted for the Auckland region due to global warming. Development rate of E. chloroticus increased with an increase in seawater temperature; however, at temperatures higher than 21.5°C the proportion of abnormal development was ~30%. The optimum temperature during early development of this species was between 15-21°C, whereas the upper thermal limit was 24° C as more than 50% of abnormal development was observed at this temperature. Respiration rate and consumption of lipid reserves were measured in different developmental stages of E. chloroticus at three different temperatures (15, 18 and 21° C). Respiration rate increased with temperature after hatching, especially in larval stages in which the respiration rate doubled from 15 to 21° C. The amount of the different lipid classes changed with temperature, with lower amounts at higher temperatures. In addition, development until the 4-arm larvae was observed to use more of the initial energy in the eggs at higher temperatures. The integration of the results of this research lead to the conclusion that the overall performance during early development of E. chloroticus will be negatively affected by an increase in seawater temperature of ~3-4° C above current seawater temperature levels in northern New Zealand. This could have dramatic effects on the survival and performance during early development of this species in a global warming scenario. This could impair recruitment in northern population, leading to possible distributional shifts. Thus, the reduction of the north-eastern populations of this species due to global warming may have both, ecological and economic consequences in the region.