Sheltering behavior of the abalone, Haliotis tuberculata L., in artificial and natural seawater: The role of calcium Federica Cenni a , Giuliana Parisi b , Felicita Scapini a , Francesca Gherardi a, ⁎ a Dipartimento di Biologia Evoluzionistica “Leo Pardi”, Università di Firenze, Via Romana 17, 50125 Firenze, Italy b Dipartimento di Scienze Zootecniche, Università di Firenze, Via delle Cascine 5, 50144 Firenze, Italy abstract article info Article history: Received 8 September 2009 Received in revised form 16 November 2009 Accepted 17 November 2009 Keywords: Artificial seawater Calcium Haliotis tuberculata L. Sheltering behavior There is an increased interest worldwide in developing land-based closed systems to cultivate the abalone, Haliotis tuberculata L. Here, we analyzed whether artificial conditions, and particularly the use of artificial seawater, might affect sheltering, a critical behavior of this species. The study was composed of two experiments. In the first, we compared sheltering between two groups of 100 individuals each reared in either natural or artificial seawater. For 15 days, a score was assigned every day to the position occupied by each individual, i.e. “0” when it was out of the hide, “1” when it was on the bottom of the maintenance tank underneath the hide, and “2” when it occupied the inner spot of the hide. Our results show that artificial seawater significantly affects sheltering: only the individuals reared in natural seawater were able to reach the hide and maintain a position in it. Chemical analyses revealed that artificial seawater differed from natural seawater for a relatively low concentration of Ca 2+ . In the second experiment we compared H. tuberculata's sheltering behavior in three media, natural, artificial, and calcium-enriched artificial seawater. Sheltering was restored in enriched artificial seawater, which supports the hypothesis that calcium has an effect on this species' behavior. However, calcium concentration both in the artificial and “natural” water showed a progressive decrease with time likely due to the absorption by abalones, which suggests that in closed systems calcium supply is constantly required, even when the used medium is natural seawater. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Natural stocks of the abalone, Haliotis tuberculata L. (Mollusca: Haliotidae), are worldwide overexploited and in a state of serious decline (Guzmán del Proó, 1992; Parker et al., 1992; Tegner et al., 1992; Shpigel et al., 1999). Decreased fisheries, combined with the increasing demand for this species and its high market value, have resulted in accelerating the spread of abalone aquaculture (e.g. Oakes and Ponte, 1996) and the development of new projects that look into land-based closed or semi-closed systems (Basuyaux and Mathieu, 1999) to support traditional farming in natural environments. In order to maximize production, research has been mostly directed to understand the biology of the species (Mgaya and Mercer, 1994). Conversely, little is known about the environmental factors that are likely to influence the abalone's growth in closed systems (Basuyaux and Mathieu, 1999). Here, we analyzed whether the use of artificial seawater may alter the behavior of H. tuberculata. The rationale underlying this pivotal study is that, in farm settings, rearing techniques should be adjusted to it so as to maximize the health and growth performance of the animals (Huchette et al., 2003). This implies a good knowledge of the behavior of the reared species. Changes in behavior may in fact be used as early warning indicators of suboptimal rearing conditions. On the basis of the information about this species' biology in nature (e.g. Momma and Sato, 1969) and in the laboratory (Cenni et al., 2009), we used sheltering behavior as a proxy of the individuals' wellbeing. In the inhabited reefs, abalones take refuge during the day under rocks or in crevices, from which they emerge in the evening to hide again at dawn (Stephenson, 1924). As observed in several species of Haliotis, some spots of the reef are most often occupied as shelters possibly because of the better protection from predators they offer (Momma and Sato, 1969; Shepherd, 1973; Tarr, 1995). Laboratory studies on H. rubra (Leach) (Huchette et al., 2003) and H. tuberculata (Cenni et al., 2009) showed that abalones do not distribute evenly on the provided sheltering space in the tanks, but rather aggregate in particular spots, suggesting that this phenomenon, i.e. sheltering in the most suitable spots, also occurs in artificial environments. Based on these premises, firstly we compared sheltering behavior in H. tuberculata reared in either natural or artificial seawater; secondly, having found a significant difference between the two treatments, we analyzed the possible effect of calcium on this species' sheltering behavior, since natural and artificial seawater differed in calcium content. Aquaculture 299 (2010) 67–72 ⁎ Corresponding author. Tel.: +39 055 2288216/215; fax: +39 055 222565. E-mail address: francesca.gherardi@unifi.it (F. Gherardi). 0044-8486/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2009.11.016 Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online