Please cite this article in press as: de la Uz S., et al., Evaluation of tagging and substrate refuges in release of juvenile sea urchins. Regional Studies in Marine Science (2018), https://doi.org/10.1016/j.rsma.2018.02.008. Regional Studies in Marine Science ( ) – Contents lists available at ScienceDirect Regional Studies in Marine Science journal homepage: www.elsevier.com/locate/rsma Evaluation of tagging and substrate refuges in release of juvenile sea urchins Silvia de la Uz a, *, José F. Carrasco b , Carmen Rodríguez a , Jacobo López a a Centro de Experimentación Pesquera, Dirección General de Pesca Marítima, C/ El Muelle, s/n 33760 Castropol, Asturias, Spain b Centro de Experimentación Pesquera, Dirección General de Pesca Marítima, Av. Príncipe de Asturias, s/n 33212 Gijón, Asturias, Spain article info Article history: Received 27 February 2017 Received in revised form 15 February 2018 Accepted 21 February 2018 Available online xxxx Keywords: Paracentrotus lividus Tagging Juvenile release Shelter Adult conspecifics abstract 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. © 2018 Elsevier B.V. All rights reserved. 1. Introduction Sea urchins play a key role in structuring marine ecosystems due to their grazing activity, which constitutes an important con- trolling factor in benthic algal communities and over other or- ganisms (Steneck, 2013). Apart from the ecological importance, the edible species are of economic importance. Sea urchin gonads, also known as roe or uni, are considered a highly valued seafood product and a delicacy in many parts of the world. The purple sea urchin Paracentrotus lividus Lamarck, 1816 is the most important commercial species in southern European regions. This echinoid is widely distributed throughout the Mediterranean Sea and in the north-eastern Atlantic, from Scotland and Ireland to Southern Morocco, including the Azores and Canary Islands (Boudouresque and Verlaque, 2013). Nowadays, the consumption of P. lividus is mainly limited to France and Spain and, to a lesser extent, to Italy and Greece, although harvesting occurs, or has oc- curred, over a much larger area (e.g. Ireland, Portugal and Croatia) for export (Boudouresque and Verlaque, 2013). In recent decades, the exploitation of this marine resource has become increasingly intensive, causing the depletion of wild stocks and the collapse of the fishery in several countries (Byrne, 1990; Andrew et al., 2002; Fernández-Boán et al., 2012; Couvray et al., 2015). * Corresponding author. E-mail addresses: silviadelauz@gmail.com, sdelauz@tragsa.es (S. de la Uz). Restocking and stock enhancement can potentially mitigate these impacts and improve the natural stocks through the release of cultivated juveniles. But enhancement cannot be conducted effectively without pilot release experiments to identify optimal release strategies (Blankenship and Leber, 1995; Bell et al., 2006). One of the key release parameters that affects the survival of juveniles released into the wild is the selection of a suitable habitat and microhabitat (Lorenzen et al., 2010). Predation is the greatest obstacle to survival of the released juveniles and smaller sizes are the most susceptible to predators. Substrate complexity and adult abundance have been recognized as important factors determining sea urchin recruitment success (Hereu et al., 2005; Clemente et al., 2013; Oliva et al., 2016). Therefore, spatial heterogeneity and availability of physical refuges reduce mortality in juvenile sea urchins. Tagging provides the basis for distinguishing released animals from wild conspecifics and allows quantifying the release suc- cess (Blankenship and Leber, 1995). Many external and internal tags have been used for tagging sea urchins (Hagen, 1996) but it becomes more challenging for specimens of small body size (Clemente et al., 2007; Sonnenholzner et al., 2010). External tags have important advantages in field studies since they allow in- dividual identification and are easily detectable by divers. Unfor- tunately, most of them are traumatic or short lived, thus limiting their use to short-term studies, within days or weeks (Tuya et al., https://doi.org/10.1016/j.rsma.2018.02.008 2352-4855/© 2018 Elsevier B.V. All rights reserved.