The effect of elevated temperature on roe enhancement of Evechinus chloroticus collected from two latitudes

An experiment testing the effects of elevated temperatures on roe enhancement of sea urchins Evechinus chloroticus collected from two widely separated sites in New Zealand was conducted over a 10 week period between September and December 2007. Groups of urchins from Central and Northern Populations were held at 18 °C, 20 °C, 22 °C and 24 °C and fed ad libitum a formulated moist feed. After 10 weeks there were no significant differences in GI between urchins held at 18 °C (15.32±0.47) and 20 °C (15.02±0.45) but the GI of urchins held at 22 °C were significantly lower (11.91±0.42) and those held at 24 °C were significantly lower again (8.69±0.33). The increase in GI from the initial GI followed the same pattern, with urchins held at 18 °C and 20 °C having a significantly greater increase than those held at 22 °C, which in turn had a significantly greater increase than those held at 24 °C. There was no significant difference in GI after 10 weeks between the urchins held at 24 °C and urchins that remained in the wild during the experimental period. Urchin survival was also significantly lower at higher temperatures and it was lower in the Central Population compared to the Northern Population, probably because the experimental temperatures exceeded the natural temperature range of the former. There were no significant differences between the increases in GI of the urchins collected from the two populations and held at each of the different experimental temperatures. The benefits from increasing the holding temperature for roe enhancement must be weighed against the increased cost of holding urchins at the higher temperatures. Roe enhancement of E. chloroticus should be carried out at temperatures less than 22 °C and the higher survivorship of urchins taken from populations with higher ambient seawater temperatures, compared with those collected from populations exposed to lower ambient seawater temperatures, must also be taken into consideration.