Worldwide, about 91% of agar was manufactured from Gracilaria spp. and 9% obtained from Gelidium, Gelidiella and Pterocladia (Porse and Rudolph 2017). Gracilaria is being farmed mainly through vegetative propagation in pond co-cultured with other animal species mostly with shrimps and abalone with floating raft and off-bottom long line method with a growth rate reported from 1.21 to more than 10% (Cirik et al. 2010; Baloo et al. 2011; Yang et al. 2015; Diatin et al. 2020). In India, the experimental cultivation of Gracilaria species namely, G. debilis, G. dura, G. edulis and G. verrucosa was attempted by using various methods which includes off-bottom long line method, single rope floating technique, spore culture technique, floating bamboo raft method, polypropylene net method, hanging rope technique, net bag method and net pouch method (Table 2) (Subbaramaiah and Thomas 1990; Jayasankar and Varghese 2002; Padhi et al. 2011; Veeragurunathan et al. 2015a,b, 2016, 2019; Mantri et al. 2020).
Table 2
DGR recorded in cultivated Gracilaria species in India
Name of the species | Method of cultivation | Culture period | DGR | Name of the place | Reference |
Gracilaria dura | Spore-based seedling through bamboo raft method | 45 days | 4.67% day− 1 | Port Okha, Gujarat | Mantri et al. 2009 |
G. dura | Polypropylene net method | 45 days | 3.75% day− 1 | Mandapam, Tamil Nadu | Veeragurunathan et al. 2015a |
G. dura | Floating Bamboo Raft method | 45 days | 2.61% day− 1 | Mandapam, Tamil Nadu | Veeragurunathan et al. 2015a,b |
G. dura | Net bag method | 45 days | 3.17% day− 1 | Mandapam, Tamil Nadu | Veeragurunathan et al. 2015a |
G. dura | Net pouch | 45 days | 0.985% day− 1 | Mandapam, Tamil Nadu | Veeragurunathan et al. 2015a |
G. dura | Hanging Rope Technique | 45 days | 0.726% day− 1 | Mandapam, Tamil Nadu | Veeragurunathan et al. 2015a |
G. dura | Tube-net method | 45 days | 1.88–3.30% day− 1 | Simar, Gujarat | Mantri et al. 2020 |
G. debilis | Floating Bamboo raft | 60days | 3.59–4.17% day− 1 | Mandapam, Tamil Nadu | Veeragurunathan et al. 2019 |
G. edulis | Single Rope Floating Technique (SRFT) | 90–120 days | 5.48% day− 1 | Krusadai island, Tamil Nadu | Subbaramaiah and Thomas 1990 |
G. edulis | Bamboo raft method | 60days | 5.82% day− 1 | Thonithurai, Tamilnadu | Veeragurunathan et al.2016 |
G. edulis | Through spores in nylon bag | 22 days | 7.73% day− 1 | Narakkal, Kochi, Kerala | Jayasankar and Varghese 2002 |
G. verrucosa | Bamboo Raft method | 30 days | 8.65–8.96% day− 1 | Chilika Lake, Odisha | Padhi et al. 2011 |
For G. dura the maximum DGR (3.17% day− 1) was recorded by Veeragurunathan et al. (2015a) through polypropylene net method from south east coast of India; while Mantri et al. (2009; 2020) reported 4.67% day− 1for bamboo raft method and 1.88 ± 0.23% day− 1 to 3.30 ± 0.25% day− 1 from tubular net method along the west coast of India (Table 3). The DGRs in the present study (1.74 ± 0.44 to 12.22 ± 2.05% Day− 1) were either similar or higher than the DGRs reported for various Gracilaria species in India as well as in the foreign countries. Ganesan et al. (2011) noted that the methods of cultivation had spacial and temporal variation affect on the biomass yield and growth rate in red algae. In the present study, the highest biomass yield was found in 35 days culture period followed by 15 and 45 days. The lowest biomass yield was recorded in 55 days of culture period in the month of April. The probable reason for loss of biomass is the drifting, prone to strong wind and wave action of pre-monsoon conditions. There was no specific trend observed among DGR and biomass yield with respect to the growth cycles. Temperature is the crucial factor for growth of various Gracilaria spp. The ambient temperature recorded during culture period (December 2019 to April 2020) was ranged from 17.9–34°C (minimum to maximum) with an average range of 22.4–27.6°C. During 5 months of cultivation experimental period the highest biomass yield and DGR were observed in the range of February > January > December where the average ambient temperature was 22.4–23.7°C while the lowest biomass yield and DGR was recorded April > March at 25.9–27.6°C.
Table 3
Comparison of present study data with other Indian agarophytes
Sr. No. | Name of Algae | Area of cultivation | Method of cultivation | Agar Yield (%) | Gel Strength (g cm− 2) | Gelling Temperature (°C) | Melting temperature (°C) | Ash Content (%) | References |
1 | Gelidium pusillum | Thonithurai Palk Bay, Tamil Nadu | Bamboo Raft | 6.9 | 1800 | 36 | 88 | ≤ 1 | Veeragurunathan et al. 2018 |
Net bag | 9.5 | 2100 | 35 | 88 | ≤ 1 |
2 | Gelidiella acerosa | Krusadai island Gulf of Mannar, Tamil Nadu | Suspended stone | 16 | 2400 | 41 | 86 | - | Ganesan et al. 2015 |
3 | Gracilaria dura | Simar, Gujarat | Tube net | 15.50-19.15 | 1507.67 -2087.67 | - | - | - | Shah et al. 2021 |
4 | Gracilaria dura | Rajpara, Gujarat | Monoline | 26–34 | 1367.5-1606.5 | 39 | 89 | 1.11–1.14 | Present study |
The quality of agar is depending upon the species used for farming, season, habitat, nutrient availability, environmental parameters, methods of cultivation and extraction (Marinho-Soriano and Bourret 2003, Rejeki et al.2018). In the present study, culture period was optimised based on agar characteristics of various culture period from 15–55 days. According to the agar data shown in Table 2, it was confirmed that the culture period of 25 and 35 days showed the highest gel strength and agar yield. It was observed that the agar gel strength was not significantly affected by duration of culture period however, agar yield showed significant difference. The culture period of 15 days showed highest DGR and lowest agar yield. There was no significant difference in agar yield of culture period of 25, 35 and 55 days. Therefore, for the commercial farming the growth cycle of 25 to 35 days should be preferable. Veeragurunathan et al. (2015b) observed increase in period of cultivation resulted in decrease in DGR in G. dura cultivated along the south east coast of India. Further, he also notated that 15 days of cultivation period showed highest DGR. Although our results corroborate with Veeragurunathan et al. (2015a,b) observations in G. dura cultivation, the agar yield was significantly lower for 15 days of culture period than 25–35 culture period. It was apparent from various research communications that season, habitat, species, geography and environmental parameters, methods of cultivation could influence the agar yield and gelling properties. However, in addition to these factors, duration of growth cycle also proved to be one of the imperative factor.
In India, 32 Gracilaria species reported however, there were limited reports available among Indian agarophytes for higher quality agar where hydrocolloid characterisation was made with respect to methods and culture periods (Table 2). Higher quality agar was reported from cultivated material of Gelidium pusillum (Veeragurunathan et al. 2018), Gelidiella acerosa (Ganesan et al. 2015), Gracilaria dura (Shah et al. 2021). The present study result demonstrated that the higher agar yield of 26–34% as compared to previous reported value in G. dura (Shah et al. 2021), Gelidiella acerosa (Ganesan et al. 2015) and Gelidium pusillum (Veeragurunathan et al. 2018). However, gel strength was comparatively lesser than G. dura reported by Shah et al. (2021) which cultivated by tube net method at Simar, Gujarat and Gelidiella acerosa by Ganesan et al. (2015), cultivated by suspended stone method and Gelidium pusillum by Veeragurunathan et al. (2018), and cultivated by net bag and bamboo raft method. In this present study, agar yield was significantly differed with different culture periods. Variations in agar yield and gel strength was depended on species variation and aging and reproductive stages of the selected algae (Kim and Henriquez 1979; Yao et al. 1984; Marinho-Soriano et al. 1999; Mantri et al. 2009)