Event Abstract

The influence of light and culture media on the growth of the red seaweed Gracilaria gracilis (Rhodophyta, Gracilariales) under laboratory conditions

  • 1 Escola Superior de Turismo e Tecnologia do Mar, Politécnico de Leiria, MARE – Marine and Environmental Sciences Centre, Portugal

Seaweed culture systems worldwide aim to achieve high biomass production and profitable yields, by adopting methodologies specifically designed for a target species. In this sense, research aimed at improving the growth conditions of the red seaweed Gracilaria gracilis , a gracilarioid widely cultivated worldwide, is of utmost importance, mainly due to the importance of this genus as an agarophyte, but also as a food and feed component (Abreu et al. 2015). Therefore, the present work aims to assess the influence of light and culture media on the vegetative growth of the red seaweed G. gracilis, performed at a small-scale and under laboratory conditions. Specimens of G. gracilis were harvested from Lagoa de Óbidos (39°24’18.93’’N, 9°11’13.05’’W) and Figueira da Foz (40°07’56.5’’N, 8°50’35.9’’W), Portugal, during low tide. In the lab, only the healthiest individuals were chosen, thoroughly washed and cleaned for culture purposes. Specimens were then placed under acclimatization for one week, and afterwards distributed in three 50 L tanks (2 g seaweed/L), Petri dishes (4 tips each), and 250 mL flat-bottom flasks (8 tips each). The seaweed were placed at 20°C, 35 ‰ seawater, under low-light photoperiod of 16:8 L:D and natural light and supplemented with one of the following culturing media: Von Stosch Enriched (VSE) medium modified for red seaweeds (Redmond et al. 2014), F/2 medium, and the fertilizer Complesal 12-4-6 (Bayer Cropscience), supplied on a weekly basis. The Petri dish and flat-bottom flask cultures were also placed at 20°C, VSE seawater (35 ‰), photoperiod 16:8 L:D and distributed by shelves under the following light conditions each: grolux and daylight combo (GL+ DL 3000 lux), grolux and daylight combo (GL + DL 1500 lux), and white cool light (WCL 1500 lux). Media renewal was performed on a weekly basis for Petri dishes and on a fortnight basis for flat-bottom flask cultures. Weight was registered for all individuals whenever media was renewed and all assays were performed in triplicate, for each of the populations studied (FF = Figueira da Foz, LO = Lagoa de Óbidos). Daily growth rates were calculated according to Hayashi et al. (2011). G. gracilis presented a distinct behaviour according to (1) the type of container chosen (tank, Petri dish, or flat-bottom flask), (2) the chosen nutritional media, and (3) the distinct light sources and intensities studied. Among the seaweed kept growing in tanks, G. gracilis seems to perform well in seawater supplied with VSE medium, whereas individuals placed in F/2 or Complesal medium died within the first and second week of assays, respectively. The highest growth rate for tips growing in Petri dishes was obtained under WCL (32.75 % day-1) during the first week, while those growing in flat-bottom flasks achieved the highest value under GL+DL 1500 lux (15.41 % day-1) during the first fortnight. While this value decreased after the second fortnight, it remained higher than those obtained for any other assay did. Tips growing in the highest light intensity (GL+DL 3000 lux) did not perform so well in either Petri dish or flask assays, confirmed by the discoloration visually observed in most tips. This particular result stands in agreement not only with the knowledge that prolonged exposure to strong light intensities is harmful to Gracilaria spp., especially regarding young individuals (Raikar et al. 2001), but also in agreement to the natural light-sheltered conditions where this species has been usually found thriving. The development and fine-tuning of these assays will be undoubtedly interesting in the context of pigment production achieved by wavelength manipulation. In addition, in all assays the daily growth rate values showed a decreasing progression, especially in tips growing in Petri dishes, after the first two weeks in culture, regardless of the light source, leading to the hypothesis that the nutrient supply routines adopted were the limiting factor for the G. gracilis growth after the first two weeks of culture. Current assays to overcome this issue include an increasing in the frequency of nutrient changes, up to one week of interval between media changes, after the first two weeks in culture. This will cover the nutrient demands that come with increasing growth rates, to ultimately manipulate G. gracilis biomass growth while keeping an economically feasible culture system.


This study had the support of Fundação para a Ciência e Tecnologia (FCT), through the strategic project UID/MAR/04292/2013 granted to MARE, and the project Operational Programme MAR2020 through the project 16-02-01-FMP-84 - Seaweedfeeds.


Abreu MH, Pereira R, Sassi J-F. (2015) Marine Algae and the Global Food Industry. In: Pereira L, Neto JM (eds) Marine Algae: Biodiversity, Taxonomy, Environmental Assessment, and Biotechnology, Chapter 9, 1st edition. CRC Press, Boca Raon FL, 300-319.

Hayashi L, Faria GSM, Nunes BG, Zitta CS, Scariot LA, Rover T, Felix MRL, Bouzon ZL (2011) Effects of salinity on the growth rate, carrageenan yield, and cellular structure of Kappaphycus alvarezii (Rhodophyta, Gigartinales) cultured in vitro. Journal of Applied Phycology 23(3): 439-447.

Raikar SV, Iima M, Fujita Y. (2001) Effect of temperature, salinity and light intensity on the growth of Gracilaria spp. (Gracilariales, Rhodophyta) from Japan, Malysia and India. Indian Journal of Marine Sciences 30: 98-104.

Redmond S, Green L, Yarish C, Kim J, Neefus C (2014) New England Seaweed Culture Handbook. Connecticut Sea Grant CTSG-14-01, Connecticut, 92 p.

Keywords: Gracilaria gracilis, Seaweed cultivation, growth rates, light intensity, Nutrient medium

Conference: IMMR'18 | International Meeting on Marine Research 2018, Peniche, Portugal, 5 Jul - 6 Jul, 2018.

Presentation Type: Poster Presentation

Topic: Aquaculture

Citation: Freitas M, Correia AP, Pereira CR, Santos JR, Baptista TM, Afonso CN, Gil MM, Pombo A, Tecelão C, Mendes SL and Mouga TM (2019). The influence of light and culture media on the growth of the red seaweed Gracilaria gracilis (Rhodophyta, Gracilariales) under laboratory conditions. Front. Mar. Sci. Conference Abstract: IMMR'18 | International Meeting on Marine Research 2018. doi: 10.3389/conf.FMARS.2018.06.00116

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Received: 26 Apr 2018; Published Online: 07 Jan 2019.

* Correspondence: Prof. Teresa M Mouga, Escola Superior de Turismo e Tecnologia do Mar, Politécnico de Leiria, MARE – Marine and Environmental Sciences Centre, Peniche, 2520-641, Portugal, mougat@ipleiria.pt