Effects of depth and initial fragment weights of Gracilaria gracilis on the growth, agar yield, quality, and biochemical composition

Abstract

phycoerythrin is considered to be a predominant pigment in red algae. This pigment is at present used in food industry as colorant. Nevertheless, because of the spectral properties, it is used mainly in clinical and immunological analysis (Mensi et al.2012), in fluorescence microscopy and flux cytometry (Glazer and Stryer 1984;Kronick 1986). It is also reported that R-phycoerythrin and phycocyanin act as a part of protective mechanism in seaweeds in general (Sinha et al.1995) and in Gracilaria caudata particularly (Araujo et al.2014). To our best knowledge, few studies (Molloy and Bolton 1996;Mensi et al. 2009) were published regarding the effect of both depth and initial fragment weights on growth and proximate chemical composition of Gracilaria gracilis (previously known as G. verrucosa).Presently, there are neither large scale seaweed cultivation nor agar industry in Tunisia.Nevertheless, several attempts of Gracilaria farming were performed in the two last decades, using both spores (Ben Said and Aouini 2014) and cuttings/fragments (Ksouri et al.1999(Ksouri et al. , 2000 Mensi et al.2009). Four farming methods were used: ropes, sand filled plastic tubes, spade and suspended system in hoop-nets. On the other hand, some experimental agar extractions have been carried out on Gracilaria gracilis (Ben Said and Ksouri 1999; Ben Said et al.2015).This study aimed to determine the ability of Gracilaria gracilis to be cultivated at two different water depths in Bizerte lagoon, using net pockets. Additionally, relatively low initial fragment weights, compared with previously reported studies (Ksouri et al.1999(Ksouri et al. , 2000 Mensi et al.2009) were also tested in order to have an appreciable biomass with a high daily growth rate (DGR) in relation to environmental factors. The biomass could be firstly used for agar extraction and secondly for other potentially interesting compounds. Hence, agar yield, gel strength, gelling and melting temperatures were investigated because of their properties to

Effect of Lagoon and Sea Water Depth on Gracilaria gracilis Growth and Biochemical Composition in the Northeast of Tunisia

“…The higher agar yields obtained in the BB, could be due to the high salinity level, light quantity and a lower nitrate concentrations than that recorded in the BL 39 . The culture depth of G.gracilis in the BL and the BB didn't affect the agar yields in contrary to previous findings in the BL by 9 , which indicated a higher agar yields at a depth of 2 m compared to those obtained at 0.5 m. Unlike the previous work, this study was performed in the eastern part of the lagoon, characterized by a higher www.nature.com/scientificreports www.nature.com/scientificreports/ turbidity (Secchi depth <0.5 m). Consequently, the amount of light is insufficient (<70 µmol m 2 s −1 ) to interact with other factors and allowing the alga to produce higher agar yields 39,62 .…”

“…In contrast, the agar obtained in the BL is of lower quality due to the lower percentage of 3,6-AG and higher sulphate degree (23.30 ± 5.40% of 3,6-AG and 8.80 ± 0.86% of sulphate). Similar results were obtained in the BL 9 .…”

“…As a consequence, these culture methods were applied only in a depth less than 2 m, which represent a 10% of the BL surface 8 . Furthermore, agar obtained (gel strength less than 400 g cm −2 ) was of low quality compared to that extracted from Gelidium latifolium (gel strength higher than 800 g cm −2 ), which considered as the highest and used in many industrial applications 9 . Hence, no large-scale culture of G. gracilis is being developed outside the Asian region.…”

“…Hence, no large-scale culture of G. gracilis is being developed outside the Asian region. That's why suspended culture method should be an alternative to enhance biomass production in lagoon and sea 8,9 . In addition, when we move toward the lagoon depth and sea, we will look for the possibilities to improve the alga quality.…”

Seaweeds as Valuable Sources of Essential Fatty Acids for Human Nutrition

“…Previous research showed that G. gracilis biochemical composition is dependent on the depth it grows. For instance, the total lipid content was higher in the seaweed cultured at a depth of 2.5 m than the seaweed cultivated at 0.5 m [ 63 ]. Nevertheless, researchers studied G. gracilis FA profile variation during the harvesting season and found that the total content and the lipid (and fatty acid in particular) composition of this seaweed collected at the Lesina lagoon (Italy) is higher and more diverse in the spring and lower and less diverse in the autumn [ 60 ].…”