Introduction

The global commercial perspective of seaweeds has grown tremendously in the recent era. The increasing demand for seaweeds are presently met through direct harvested directly from nature and also through seaweed farming activities (Vairappan et al. 2009). China is by far the largest seaweed producer followed by the Republic of Korea and Japan, but seaweeds are today produced in all continents (Kilic et al. 2013). The dietary incorporation of seaweeds holds strong roots in Asian countries such as China, Japan and the Republic of Korea (Tseng and Borowitzka 2003). Nevertheless, seaweeds are now integral part of cuisines worldwide (Mouritsen et al. 2018).

Seaweed industries are major economic corridor for export and import business, food security and self-employment opportunities. Seaweeds are good source of micro and macronutrients, trace elements, vitamins, proteins, carbohydrates, lipids, fattyacids (EPA and DHA) etc. (Penalver et al. 2020; Rocha et al. 2021). The varied application of seaweeds in pharmaceutical, nutraceutical, food and cosmetic industries has crossed US$ 10 billion of which food products accounts for more than US$ 5 billion (Mantri et al. 2020). Apart from this, research promoting seaweed as biofeuls to bring down energy consumption cost have lately gained immense attention (Aresta et al. 2004; Dhargalkar and Perreira 2005; Hossain et al. 2008). The sea algae also have immense ecological significance as these wide spread seaweed bed across the coastal line potentially lower global carbondioxide by trapping and sequestering atmospheric CO2 (Bunting and Pretty 2007). Additionally, it helps in removing excessive trace metals from water and seabed (Tseng and Borowitzka 2003).

Total annual use by the global seaweed industry is about 8 million tons of wet seaweed. Red and brown seaweeds are major resource for hydrocolloids; alginate, agar and carrageenan, which are used as thickening emulsifying and gelling agents (McHugh 2002). Presently, approximately one million tons of wet seaweed are harvested and extracted to produce about 55,000 tons of hydrocolloids, valued at almost US$ 600 million (Liao et al. 2021). These demands in supply of seaweeds are majorly met from cultivation rather than exploiting wild stock. Seaweed cultivation is increasingly gaining importance in both temperate and tropical countries (McHugh 2002). In terms of India, seaweed research and farming have gained huge momentum only in the recent years; however, the overall contribution to world production is almost negligible. Seaweed culture in India is being done in Tamil Nadu and Gujarat. In those places seaweed culture practices are projected towards the low-income population of coastal areas using SHG and fisher folks, particularly women. Further it also provides additional income and alternative job for the coastal people during the fishing ban seasons. It also helps in conservation of natural seaweed resources from over exploitation and depletion.

There are several potential sites in India which could be ideal for extensive seaweed farming, one such major target is the Andaman and Nicobar Islands (ANI) which is a group of 836 individual Islands including Islets and rocky outcrops. This Island boasts rich biodiversity of flora, fauna and coral reefs (Mohan and Kumari 2018). Recent estimates suggest that Indian water harbours approximately 871 seaweed species (Kaliaperumal 2017), of which about 244 species of seaweeds reported spanning these Islands (Karthick et al. 2021), however only few are commercially cultivable as the culture techniques at present are developed for these species. The algin producing alginophytes are dominant than agarophytes which contains agar in A&N Islands (Vinithkumar et al. 2018). In many tropical countries, the seaweed aquaculture is used for income generation, food security and environmental health. The methods employed for mass cultivation of seaweeds varies depending on the species of interest as well as the site selected for cultivation. Generally used methods include vegetative propagation using a smaller fragment using longline rope method (Raju and Thomas 1971), Single Raft Floating Culture Technique (Subbaramaiah and Thomas 1995) and Raft method (Ganesan et al. 2011). The present study evaluates the possibilities of initiating seaweed mass culture in South Andaman, also describes various methods adopted in this study to improve growth and overall yield.

Presently three major agarophytes are cultivated worldwide, viz., Kappaphycus spp., Eucheuma spp., and Gracilaria spp.,. Among these seaweed varieties, the Gracilaria spp., are vastly reported species from this Island. The Gracilaria / Gracilariopsis belongs to red algae are the two of the world’s most cultivated seaweeds with 3.8 million tons of annual production worth about US $1 billion (Ganesan et al. 2011; Kim et al. 2017). China and Indonesia are the top seaweed cultivating Asian countries with the production of 70% and 28% respectively in terms of global production. Gracilaria edulis (G.edulis) is already in high demand for its high agar yielding property (30—40%). This species is widely present in coastal areas of Burmanalla (South Andaman). This species has a culture harvest period of 45 – 50 days. The seaweed Acanthophora spicifera (A. spicifera) is also the locally available seaweed which has an agar yield of 15–17% of dry weight. This species grows in Andaman waters and can be harvested in a maximum period of 25 – 45 days. Mass cultivation of these two species was initiated with the vision of developing a constant and reliable source of extraction of agar for developing other byproducts. Although the agar extracted from Acanthophora spp., are below the laboratorial grades, it can be used for developing other value-added products such as bioplastics, jellys and other edible and cosmetic products. As this species is locally available and abundant at seasons, cultivation of this species would not pose a threat or endanger the survivability of other biotic communities present. Considering all these factors, the culture of A. spicifera and G. edulis was initiated at North Bay cage culture site and also at Chidiyatapu by deploying bamboo rafts or through monoline method as pre-feasibility trial.

Methodology

Survey on Potential Sites for Seaweed Farming in South Andaman

The coastal area surveys to identify the potential sites for seaweed seed bank and mass culture was carried out in South Andaman. Total of five coastal regions were surveyed for selecting appropriate site (Fig. 1). The nature and characteristics of shallow areas of the surveyed coastal locations namely, North Bay, Rangachang, Burmanalla, Badabalu, Viper Island and Chidiyatapu were recorded.

Fig. 1
figure 1

Survey sites

Full size image

Geographical Location

The locations were selected based on ease of access for successful commercial venture. The sites with enclosed coastal bay or sheltered region with moderate wave action were considered suitable. Generally, areas with 60 cm water depth even during lowest low tide with constant movement of clean seawater were specially considered as it would supply required nutrients and oxygen for seaweed culture. Another criterion was the bottom topography, the regions with sandy, rocky or a mixture of both noticeably without any other sensitive group of organisms was selected. Also, areas naturally supporting seaweed growth were taken into consideration. It was also ensured that the selected sites were well away from mangrove vegetation to avoid heavy silt deposition and organic loading. The areas with freshwater runoff, domestic discharges, harbour effluents and fishlanding centers were completely avoided.

Water Quality

The water quality parameters were measured using GPS enabled Hanna Hydrolab (Table 1). The physico—chemical constituents such as temperature, pH, salinity, total suspended solids (TSS) and dissolved oxygen (DO) of the selected sites were estimated during the low tide to select the optimal site.

Table 1 Environmental parameters recorded during survey of suitable location
Full size table

Initiative for Seaweed Cultures using Bamboo Raft

The seaweed can be cultured in various methods such as submerged sandy bottom culture, mono rope, bag net, tube net, hanging stone and bamboo raft culture etc. The present work was initiated using floating raft made of bamboo (2A, 2B, and 2C). The first three trials were carried out in NorthBay and further experiments were done in Chidiyatapu. The experiment was conducted with A. spicifera which were abundantly found and known to grow easily in these waters and with G. edulis which is highly commercially sought agrophyte. The identification of the species were done from the data available in The Seaweed site (2021). The G. edulis culture in floating rafts has been widely explored by Ganesan et al. (2011) in open sea of south eastern coast of India. Similar culture technique was adopted for this study wherein, about 50 g of seaweed bunch was collected inserted into teflon ropes, 9–12 of these ropes were tied to bamboos depending on the size of the bamboos. Rafts of two different widths were used in the study i.e. a raft size of 1.75m2 (length/breadth) with an inner frame area of 1.5m2 and another raft size of 3.0m2 having 2.5m2 inner frame area.

Results and Discussion

Site Selection

Site selection is imperative when it comes to execute any activity in the coastal zone. Setting up a commercial scale seaweed farm while abiding by CRZ rules can be highly challenging and demanding especially in Andaman Islands where most of the suitable sites falls under protected areas. Therefore, appropriate sites selected should not only be commercially feasible but also be far from violating the existing norms of coastal regulations. Hence the preliminary surveys for adequate site selection were carried out with prefixed criteria. The coasts of Badabalu were sandy with intermittent rocky outcrops, suitable for attachment and growth of seaweeds. Similar characteristics were also observed in the outskirts of Burmanalla. However, the reef area with shallow water exposes seaweed during low tide. Beyond reef area, an open sea condition with long waves prevails. The sites around Viper Island were found unsuitable for seaweed culture as the site experience higher turbidity, wide salinity fluctuations as the area is located inside the Port Blair Bay, also the close proximity to mangrove results in high organic loading. The Viper Island located near the mouth of Flat Bay is prone to salinity drop and increased turbidity during rainy seasons mainly by suspended sediment and organic matter from mangroves. While, North Bay cage culture site and the shore near to it, where the alginophytic seaweed Sargassum species growing was assessed initially as suitable site for seaweed farming. Even though the initial site selection can be done based on several criteria, the site suitability can be assessed only through trial cultivation of various species of seaweeds at different seasons.

Initiative for Seaweed Mass Culture using Bamboo Raft

Seaweed Mass Culture Initiative at North Bay

The first field culture trial of seaweed was done in North Bay, after testing water quality parameters and preliminary assessment on site suitability. All the study attempts carried out so far has been summarized (Table 2). As the institute was already carrying out open sea cage culture activities near to the head end of North Bay, the same site was also preferred to initiate trial for seaweed mass culture due to logistic reasons and ease of maintenance Fig. 2.

Table 2 Summary of Seaweed mass cultivation trails at the study location
Full size table
Fig. 2
figure 2

A, B Raft making using bamboo for seaweed culture, C Test floating the raft to check the buoyancy

Full size image

The macroalgae, mainly A. spicifera and G. edulis were collected from intertidal regions of North Bay and Burmanalla respectively, during low tide. To initiate the field trial, the collected species were washed and separated into bunches of each around 50 gm (Fig. 3A). These fragment bunches were inserted in ropes and tied to bamboo raft deployed at North Bay, near the fish cage site (Fig. 3B, C). The rafts were monitored constantly for the growth and sustainability of cultured seaweeds. For initial trail purpose the square bamboo rafts were made with 1.75 m inner width on all four sides and deployed at North Bay during the first week of November 2018.

Fig. 3
figure 3

A Collected seedlings of Acanthophora spicifera, B Seaweed tied to Teflon rope for cultivation, C Rafts with seaweed deployed in NorthBay (cage culture site), D, E and F Destruction of rafts in cyclone Gaja and cyclone Phethai

Full size image

Due to the effect of Gaja cyclon, during the second week of November 2018, the seaweed bunches which were inserted into the rope were washed away from the rope and raft (Fig. 3D). The main cause of loss was severe wave action/loading on seaweed raft. Similar attempt with A. spicifera seaweed was made after cyclonic condition during the fourth week of November 2018. Subsequently, during the third week of December 2018 due to the effect of cyclonic storm Phethai, the bamboo rafts were damaged and were removed from the culture site to shore (Fig. 3E, F). The first trial with G. edulis and Acanthophora spicifera remained unsuccessful as the cyclone Gaja and Phethai completely damaged the bamboo rafts and washed away the seaweed from the ropes. Of the three rafts deployed in second trial, the first raft exhibited comparatively healthy growth during harvest (Fig. 4a-c). The other two rafts were afflicted with invasion of filamentous algae over the seaweeds, ropes as well as on bamboo raft even after regular cleaning and maintenance (Fig. 4d). Epiphytic fouling is one of the major problems faced during seaweed mass cultivation (Robert 1995). Though the G. edulis growth response was in these waters were positive, the overall output was hampered by uncontrollable epiphytic growth and settling of organic matter over the nets (Fig. 4e, f).

Fig. 4
figure 4

A Seed material B Pouch seeding C Monoline method. D Raft deployment E Fouling F Raft cleaning. G Initial stage H Growth in 15 days I Growth in 30 days. J Growth after 45 days K Harvest L Seaweed per pouch

Full size image

Seaweed Mass Culture Initiative at Chidiyatapu

The failed seaweed mass culture attempts experienced during the trial study at North Bay, prompted initiation of seaweed culture in Chidiyatapu. The average water temperature in this site was 28.33 °C, with an average salinity of 32.13 and pH of approximately 8.15 units (Table 3). The overall nutrient content suggested that the region contains oligotrophic waters (Table. 4). Three types of culture method were tried viz., floating raft method with direct seeding on ropes, filling G.edulis in small nylon pouches before tethering onto ropes and last one as monoline ropes without rafts (Fig. 4A-L). About, 2.5 kg of G.edulis, depending on the raft size was tied and deployed at 100 m from the shore. The rafts were regularly cleaned and monitored to avoid biofouling and sediment settlement over the seaweeds, bamboo and net. This was practiced to ensure that growth of seaweed was not hampered by attachment of undesirable algae and epifauna on G.edulis culture fragments. The epiphytes such as Enteromorpha spp., Padina spp., Acanthophora spp., are some of the species found to be attached to rafts and seaweed pouches in this study. Some of these species are also reported in seaweed cultivation studies elsewhere (Kim et al. 2017). These epiphytes compete for light and nutrients supplement against our culture of interest, thereby inflicting their growth (Kim et al. 2017; Ingle et al. 2018). Apart from this faunal association over rafts and seaweeds were also note in the study. This group largely consisted of crustaceans, nudibranchs and barnacles, along with microbial load. Earlier reports have suggested some of these epifaunal species are pests that feed on seaweed (Shacklock and Croft 1981; Ingle et al. 2018). However, regular cleaning of rafts minimizes epiphytes and epifaunal attachment and improves seaweed quality (Vairappan et al. 2009). The variation in seawater temperature, pH, and salinity are recorded on daily and total suspended solids on weekly basis and nutrients on monthly basis (Table 3). The seaweeds inserted directly onto ropes exhibited slower growth and were also, prone to grazing. High wash off seaweed bunches were noted in periods of strong winds. In the case where the G.edulis fragment bunches are inserted into the nylon pouches, these pouches acted as barriers against grazing and also prevented loss by wave action to a great extend. Thus, pouch tying method was found to be suitable method for culturing seaweeds in this location. Approximately, 160-180 kg of seaweeds were harvested through floating raft technique at Chidiyatapu from 7 rafts with a seed amount of 2.5 kg/raft during December 2019 to March 2020 from (Fig. 5). The PCA results suggested that salinity and pH are closely interlinked to seaweed growth than other observed parameters. While, total suspended solids and temperature share a negative correlation. This could be mainly from the influence of rain and concurrent fresh water discharge from land that decrease surface temperature and increase suspended solid loads. The G. edulis culture using rope technique/monoline method, is although less labour intensive and minimises the overall input cost, it faces the risk of grazing. Heavy grazing by sea turtles, dugong, and other reef fishes was noted in this study (Fig. 6).

Table 3 Mean of physico chemical properties at Chidiyatapu during the study period
Full size table
Table 4 Mean nutrient condition at Chidiyatapu during the study period
Full size table
Fig. 5
figure 5

Total seaweed biomass obtained per raft on seasonal basis during the study period. *MS—Monsoon, PMS—Post-Monsoon, PRMS—Pre-Monsoon

Full size image
Fig. 6
figure 6

PCA biplot depicting influence of environmental factors on G.edulis growth at Chidiyatapu

Full size image

Daily Growth Rate (DGR)

The daily growth rate was calculated using the formula.

$${\mathrm O}_{\mathrm a}={\mathrm I}_{\mathrm a}/{\mathrm T}_{\mathrm d}$$

where,

Ia is Input amount, Oa is Output amount and Td is the total number of days.

Generally, the seaweeds were harvested between 45–50 days period based on growth, however, at few occasions, prevailing turbulent sea conditions delayed the harvest period. The growth was evidently higher in 60 days interval, but risk of loss and maintenance was also undoubtedly high. The DGR was 0.135 kg (± 0.085 kg) approximately per kg and about 0.405–0.581 kg(± 0.126 g) per raft (Fig. 7). However, depending on the wave action, turbulence and biofouling the daily average growth rates can vary significantly. Unexpected changes in climate and periodic cyclonic events also lead to heavy loss of culture as observed in present study.

Fig. 7
figure 7

Daily growth rate recorded per raft at Chidiyatapu on seasonal basis

Full size image

Conclusion

The seaweed culture in Andaman is possible with selection of appropriate site. Not all sites in the present study supported seaweed culture, owing to various reasons such as tidal activities, current pattern, water quality, turbidity and sediment deposition from adjacent mangroves etc. However, the coastal region of Chidiyatapu has been proved to be a promising site for seaweed growth and culture, among the surveyed sites. The cultured seaweeds exhibited stable growth despite filamentous algae invasion. The method employed to culture seaweeds also has significant importance. In this study, pouch method had given better results with both attempted species than directly inserting into ropes tied in bamboo rafts or open monocline method. The period of executing seaweed farming also needs to be considered. Culturing seaweeds during southwest monsoon can bring heavy loss in these regions due to recurring depressions, cyclone and extremely rough sea conditions. The best suitable period is from November to May, during which the sea is fairly calm to support raft culture. The studied species both Acanthophora spicifera and Gracilaria edulis exhibited good growth in Chidiyatapu coastal region and also these being a native species would not create an environment concern. The seaweed growth performance is site, season and species specific. Hence many trial cultures with different commercially useful seaweed species should be done in various coastal areas to select the best suitable site and also to optimize the culture conditions for maximum output. The major bottleneck in expanding the culture is non-availability of required quantity of seaweed for seeding of rafts which needs be overcome by setting seed developing units either in door or in the coastal waters.