Botanica Marina 55 (2012): 253–259 © 2012 by Walter de Gruyter • Berlin • Boston. DOI 10.1515/bot-2011-0074 Effects of temperature, salinity, irradiance, and nutrients on the development of carposporelings and tetrasporophytes in Gracilaria domingensis (Kütz.) Sonder ex Dickie (Rhodophyta, Gracilariales) Fernanda Ramlov 1, *, Jonatas M.C. de Souza 1 , André Farias 1 , Marcelo Maraschin 2 , Paulo A. Horta 3 and Nair S. Yokoya 1 1 Núcleo de Pesquisa em Ficologia, Instituto de Botânica, CP 3005, 01061-970, São Paulo, SP, Brazil, e-mail: fe_biotec@yahoo.com.br 2 Laboratório de Morfogênese e Bioquímica Vegetal, Núcleo de Produtos Naturais, Universidade Federal de Santa Catarina, CP 476, 88049-900, Florianópolis, SC, Brazil 3 Laboratório de Ficologia, Departamento de Botânica, Universidade Federal de Santa Catarina, CP 476, 88049-900, Florianópolis, SC, Brazil * Corresponding author Abstract Different environmental factors play important roles in the growth, reproduction, and distribution of marine macroalgae. We investigated the effects of temperature, salinity, irradi- ance, and nutrients on the growth of carposporelings and tetrasporophytes of Gracilaria domingensis. Carposporelings grew at temperatures of 25 °C and 30 °C, but they did not survive at 15 °C and 20 °C. In contrast, tetrasporophytes grew over a wide range of temperatures (15–30 °C) with optimum growth between 20 °C and 25 °C. Both carposporelings and tetrasporophytes tolerated a wide range of salinity (25–60 and 10–50, respectively), but carposporelings were more sensi- tive to lower salinities (10–20), while tetrasporophytes were more sensitive to higher salinities (60). The highest growth rates in basal discs of carposporelings occurred when they were grown in 25% strength von Stosch enriched medium (VSES) with an illumination of 150 μmol photons m -2 s -1 ; erect fronds grew best in 25% and 50% strength VSES with illumination of 100 μmol photons m -2 s -1 . The VSES strength did not influence the growth of tetrasporophytes of G. domingensis. Highest growth rates of tetrasporophytes occurred at 100 μmol photons m -2 s -1 . These results demon- strate very different physiological responses between carpo- sporelings and tetrasporophytes of G. domingensis and, as such, they offer guidelines for the selection of potential areas for the cultivation of the species. Keywords: Gracilaria domingensis; irradiance; nutrients; salinity; temperature. Introduction Recommendations for the cultivation of colloid-producing red algae are commonplace in the literature because there is a growing demand for biomass from the seaweed industries, while natural seaweed beds are limited (Yokoya and Oliveira 1992a). However, it is not simple to attain commercial cul- tivation of colloid-producing algae in Brazil because a clear understanding will require better knowledge of the physiol- ogy and ecology of the selected species. Gracilaria, which is harvested or cultivated worldwide, is a genus of red alga utilized for the commercial produc- tion of agar, combining a rapid growth rate and tolerance to cultivation conditions (Kain and Destombe 1995). At the same time, the increased demand for agar has brought about a depletion of natural seaweed beds along the north- eastern Brazilian coast (Oliveira and Miranda 1998). In order to provide rational support for mariculture, basic information about the biology of suitable species is under investigation. Environmental factors, including temperature, salinity, light, and nutrients, play important roles in the growth, reproduction, and distribution of marine macroalgae (Kirst 1989, Lobban and Harrison 1994). Temperature plays a sig- nificant role in the survival and growth of sporelings and adult plants of Gracilaria species (Yokoya and Oliveira 1992a, 1993, Wilson and Critchley 1997, Orduña-Rojas and Robledo 1999, Choi et al. 2006, Kakita and Kamishima 2006). Extreme salinity is another factor that interferes with biological processes and affects the concentration of ions and osmoregulation. Thus, this parameter has a significant role in the distribution of macroalgae in different environ- ments. Species of Gracilaria are generally considered to be euryhaline (Yokoya and Oliveira 1992b, 1993, Wilson and Critchley 1997, Raikar et al. 2001, Choi et al. 2006). A wide range of optimal irradiance levels for growth have been reported for Gracilaria spp. (Wilson and Critchley 1997, Kakita and Kamishima 2006). Nutrient levels may also limit the growth of seaweeds (Hanisak 1990), and some studies have shown that the growth of Gracilaria spp. is favored at low concentration of nutrients (Ursi 2005, Ferreira et al. 2006, Ferreira 2008). In this context, cultivation of seaweeds in the laboratory becomes an important tool, as the factors mentioned above can be manipulated and controlled, allowing an evaluation of their effects on vegetative and reproductive performance and, in turn, allowing us to look toward mariculture technologies Brought to you by | Takming University of Authenticated | 132.206.27.25 Download Date | 1/7/13 5:37 AM