Evaluation of tagging and substrate refuges in release of juvenile sea urchins

Pilot experiments are required and helpful to identify optimal release strategies in restocking and stock enhancement programs. The selection of a suitable habitat has been identified as an important factor determining sea urchin recruitment success. Substrate complexity and adult abundance offer physical refuges and reduce mortality of juvenile sea urchins. The present study evaluated the effect of substrate shelters on the survival of Paracentrotus lividus juveniles released in the field. Previously, the reliability of an internal tag (coded wire tag) was assessed during four months under laboratory conditions. No significant effect of tagging was detected on survival (≥96%) and growth (p<0.05) between tagged and control groups in the different size-classes. However, there were differences among size-class 1 (62%) and size-classes 2 and 3 (80%) in terms of retention rate. In the field, 100% and 80% of recaptured individuals were tagged after 6 and 14 weeks, respectively. All juveniles released on substrates with burrows did not survive the first few weeks, and only those that were released on substrates with adults successfully settled (12%). In conclusion, the present study provided a useful tag for sea urchin and identified a suitable habitat for releases of cultivated juveniles.