Fragmentation of thalli and secondary attachment of fragments of the agarophyte Gelidium lingulatum (Rhodophyta, Gelidiales) Ricardo D. Otaíza 1,2 & Catalina Y. Rodríguez 1,3 & Julián H. Cáceres 4 & Álvaro G. Sanhueza 1 Received: 11 October 2017 /Revised and accepted: 2 January 2018 # Springer Science+Business Media B.V., part of Springer Nature 2018 Abstract Species of Gelidium are important sources of agar. Mass cultivation of Gelidium spp. has been elusive. Development of techniques to seed thalli in the natural environment could be used to increase in stocks and landings. Gelidium lingulatum is an important seaweed resource in central Chile, growing on the lower levels of exposed rocky intertidal shores. Experiments were done to evaluate fragmentation of the thalli and the effect of some factors on the production of secondary attachment structures (SAS). When experimentally exposed to high water flow, thalli became frequently fragmented, mainly at the level of the creeping axes. Comparisons among parts of the thallus indicated that creeping axes produced more SAS than blades and reproductive branchlets. Similar results were obtained on the three types of substrata tested (rock, barnacle shells, and mussel shells). After 7 days of incubation, more SAS were produced under low than high irradiance (8 and 80 μmol photons m -2 s -1 , respectively). Also, a small increase in dissolved calcium (0.5 mM) in the medium enhanced SAS production, but higher levels (2.0 mM) had an inhibitory effect. Higher temperature (15 °C) tended to favor SAS formation when compared to lower temperature (9 °C). For these three factors, differences in the density of SAS were reduced or disappeared after 14 days of incubation. Different seasonal series of each experiment had consistent results. Recommendations are made for the application of these results to seeding of thalli of G. lingulatum on the rocky shore. Keywords Rhodophyta . Calcium . Irradiance . Repopulation . Substratum . Temperature . Vegetative reproduction Introduction The genus Gelidium (Rhodophyta, Gelidiales) includes nu- merous species that are used as sources of agar and agarose, phycocolloids with important uses in the biotechnology and food industries, among others. They are mainly harvested in the northeastern Atlantic, from Morocco to Portugal and Spain, and also in South Korea, Japan, and Mexico, providing raw material for the agar industry (McHugh 2003; Bixler and Porse 2011; Porse and Rudolph 2017). Currently, most of the landings come from harvesting wild populations, which makes the production vulnerable to natural variations and overexploitation (Callaway 2015). Experimental cultivation trials of Gelidium spp. have been made in laboratory conditions, in tanks and at the shore (e.g., Santelices 1988; Fei and Huang 1991; Melo et al. 1991; Friedlander 2008), but mass production from cultures is not yet widespread. As an alternative, the introduction of manage- ment practices, like seeding thalli on the rocky shore, should allow the increase in the local abundance and, eventually, of landings. Different types of inocula can be used for cultivation of red seaweeds. The most commonly used are spores and fragments (e.g., Ávila et al. 1996; Alveal et al. 1997; Buschmann et al. 2001; Le Gall et al. 2004; Bulboa et al. 2005; Titlyanov et al. 2006). Nevertheless, inocula could potentially be produced by other means (see García-Reina et al. 1991), like protoplasts (Polne-Fuller et al. 1984; Chen 1989), differentiation of new individuals from calluses (Ask and Azanza 2002; Yokoya * Ricardo D. Otaíza rotaiza@ucsc.cl 1 Departamento de Ecología, Facultad de Ciencias, Universidad Católica de la Santísima Concepción, Concepción, Chile 2 Centro de Investigación en Biodiversidad y Ambientes Sustentables (CIBAS), UCSC, Concepción, Chile 3 Magíster en Ecología Marina, Fac. Ciencias, UCSC, Concepción, Chile 4 Centro de Investigación e Innovación para el Cambio Climático (CiiCC), Universidad Santo Tomás, Santiago, Chile Journal of Applied Phycology https://doi.org/10.1007/s10811-018-1391-8