Shipping live sea urchins: Effects of temperature and exposure time on survival

Sea urchin aquaculture could offset declines in wild fisheries. The economic feasibility of sea urchin aquaculture may depend on farmers receiving premium prices for product transported live internationally to markets or processing facilities. Research into cost-effective methods of transporting live sea urchins out of water is scarce. In this study, to get a baseline of the temperatures experienced by sea urchins transported by air in the Indo-Pacific region, temperature loggers recorded temperatures in 'cooler boxes' containing the sea urchin, Tripneustes gratilla, packed and shipped in seawater or dry. We then examined the effect of time kept out of water (6, 12, 24, 48 h) and air temperature (chilled ~4 °C, cooled ~12 °C, or ambient ~27 °C) on mortality, change in wet weight, and fitness (as measured using righting behaviour) of two sea urchins, T. gratilla and Heliocidaris erythrogramma. For both species mortality (15 days after the treatment) was low (0–20%) when held out of water for up to 24 h at 12 °C, but 100% died within 15 days when held out of water at 4 °C and 27 °C. Mortality increased (~60%) for T. gratilla held out of water for 48 h at 12 °C, but remained at ~20% for H. erythrogramma in the same treatment. Righting times were faster for urchins exposed to air at 12 °C than at 4 or 27 °C. The mass (fluid) lost by urchins was a key predictor of mortality with urchins losing a higher percentage of their mass during longer exposure periods at higher temperatures. T. gratilla frequently spawned after being out of water. To test packing strategies that could influence sea urchin health, T. gratilla were packed out of water at 28.6 °C for 12 h in sealed or open containers and in containers that drained off excreted fluid or retained fluid around the urchins. None of these treatments had an impact on mortality to 15 days, the amount of fluid lost, or righting activity. Our results indicate producers may be able to transport T. gratilla and H. erythrogramma dry for up to 24 h with little mortality as long as temperatures are maintained at ~12 °C. Additional research into limiting the fluid loss of sea urchins while being shipped dry may improve survival during longer shipping periods.