Cultivation and Product Development Study of Commercially Important Seaweeds in South-Eastern Coast of Bangladesh

Abstract

Seaweeds are predominantly macroscopic, multicellular, and photosynthetic marine algae that grow primarily in the ocean’s rocky littoral zone. About 154 seaweed species are found in our coastal area, of which 34 belong to green (Chlorophyta), 38 brown (Phaeophyta), and 82 red (Rhodophyta). Among them, 26 species are considered economically important based on their availability, abundance, and use. Seaweeds are mainly available in St. Martin Island, Shaporir dip, Inani, Bakkhali, Kutubdia, Patowartek, Pecherdwip, Teknaf, Shaplapur, and Moheshkhali in Cox’s Bazar region of Bangladesh. They are generally found on our Cox’s Bazar coast from October to April, but the highest abundance occurs from January to March. However, in the case of mangrove forests, seaweeds are available throughout the year. Additionally, seven species are considered commercially cultivable species. Their culture techniques were developed in the long-line and net methods at different Cox’s Bazar region sites. St. Martin Island had the highest biomass yield production of seaweed due to its favorable water quality parameters. Several value-added seaweed products were developed from dried seaweed powder. Industries based on seaweed can potentially contribute to the socioeconomic upliftment of the coastal inhabitants in Cox’s Bazar.

1. Introduction

Seaweeds are an immense group of macroalgae, which refers to several macroscopic, multicellular, marine algae species. They are found in various habitats, from shallow rocky shores to deep oceanic waters [1]. Additionally, seaweed plays a vital role in marine ecosystems by providing food and habitat for many aquatic organisms. Seaweeds are the major thallophytic subdivided into three major classes: Chlorophyceae (green algae), Phaeophyceae (brown algae), and Rhodophyceae (red algae). Around 8000 different types of seaweed may be found throughout the world’s coastlines [2]. Only 150 seaweed species are edible and commonly consumed as fresh, dried, or culinary components out of 250 economically used seaweeds [3]. Seaweed is not as widely consumed in Bangladesh as in Japan and China. Seaweed, which accounts for around 25% of all food consumed in Japan and is cooked and served in various ways, has become the primary source of income for the country’s fishermen.

Natural abundances of seaweeds have been observed in Bangladesh from the south-eastern portion of the mainland and offshore islands, such as St. Martin Island, which has a stony substratum and is ideal for seaweed development. Although the seaweed floras of St. Martin’s Island in Bangladesh are extensively found, they are relatively underutilized. Fishermen, women and their children are gathering seaweeds on the island of St. Martin. The collected seaweeds were dried in the sun spreading on the open beach, whereas the people of Bangladesh did not know that seaweeds can be used as human food. In Bangladesh, the diversity of seaweed is rich, and it reported that there are 193 seaweed species belonging to 88 red (Rhodophyta), 51 green (Chlorophyta), and 54 brown (Phaeophyta) groups occurring on the Bangladesh coast [4].

2. Nutritional and medicinal values of seaweeds

Food’s nutritional value is primarily influenced by its protein content and carbohydrate reserve (or fats). Because they often include significant levels of proteins and carbohydrates, marine algae can be considered a potentially good source of nutrients. They also have a high iodine content, which explains why the population of the Asiatic Coast has a low prevalence of hypothyroidism and goiter. Additionally, some algae have high concentrations of vitamins A, B₁ (thiamin), B₂ (riboflavin), C, and B₁₂, making them a valuable source of nutrition for both humans and animals.

Seaweed consumption as a diet staple has a long history in Southeast Asia, China, Japan, and Korea. In fact, seaweed has been a mainstay of some cultures’ diets for centuries. As a sustainable and healthy ingredient, seaweed is now frequently used in salads, soups, and sushi rolls in Western cuisine. However, the most notable application of seaweed is in the pharmaceutical industry for developing drugs for Alzheimer’s disease, cancer, and gastric ulcer, phycocolloid or hydrocolloid industry, cosmetic industry, biofuel industry, wastewater treatment industry, and bioremediation [5, 6] (Figure 1). Seaweed is a versatile resource that has the potential to revolutionize various industries due to its unique properties, such as high water-holding capacity, gelling ability, and bioactive compounds. Seaweeds are also valuable sources of protein, fiber, fatty acids, vitamins, macro, and trace elements, and essential bioactive compounds. Traditionally seaweeds are rich in bioactive compounds with potent anti-inflammatory, antipain, antibacterial, antifungal, and high antioxidant properties [7]. In addition, seaweed contains different phytochemical compositions in varying concentrations, such as phlobatannins, saponins, terpenoids, phenols, and flavonoids [8, 9]. As the demand for sustainable and eco-friendly products increases, seaweed becomes an attractive alternative to traditional materials and ingredients.

Figure 1.

Diversified uses of seaweeds.

3. Inventory of available seaweed species on the Bangladesh coast

A detailed survey was conducted in and around Cox’s Bazar (St. Martin Island, Shah Pori Dip, Teknaf, Moheshkhali, Kotubdia, Chokaria) and mangrove forest to find out the available seaweed species, their abundance, season, etc. The collection of seaweeds from the intertidal area was done during the low tide. This will give more time for collecting seaweed and observing seaweeds in their natural habitat. Description of the site location, associated flora and fauna, and other related parameters were also observed and recorded. A random sampling method was applied to assess the abundance of available seaweeds. Samples were selected at random as per requirement. This was done by selecting sampling points in the area and using a quadrant. Sampling points were chosen so that every species of the study area has a good chance of being selected. It was also employed for qualitative estimation of the seaweed.

3.1 Availability of seaweeds on the Bangladesh coast

The survey found that seaweeds are available in and around Cox’s Bazar (St. Martin Island, Shaporir dip, Inani, Bakkhali, Kutubdia, Patowartek, Pecherdwip, Teknaf, Shaplapur, and Moheshkhali). Seaweeds are generally found attaching to the rocks or sandy bottom in mid-intertidal to subtidal zones along shorelines with calm to moderate wave activity and in tidal pools. Different species of seaweeds were collected randomly by hand-picking at the time of low tide (Figure 2). Fresh samples were taken into plastic jars and kept in an icebox for laboratory work. In the laboratory, samples were gently brushed under running seawater, rinsed with distilled water, dried with paper tissue, and finally preserved by open-air drying.

Figure 2.

Seaweed species collected from Saint Martin’s island.

A survey was also conducted in different mangrove forests, i.e., Sundarbans mangrove, Sonadia mangrove, Nijhum dip mangrove, Fatrar chor mangrove, and Fakir hat mangrove area. The Sundarban mangrove forest is one of the renowned mangrove forests and a UNESCO heritage site in the Bay of Bengal. During our inventory, we observed that several seaweed species possess a decent association with mangrove species (Figure 3). Mangrove provides a substrate for the attachment of seaweed as they were found to be attached to the roots and barks of the mangrove trees (Figure 4). Some seaweed species were also found in the aerial root of mangrove trees and even in the muddy bottom of the mangrove (Figure 4). These epiphytic mangrove seaweeds are available throughout the year and can survive in adverse conditions (zero salinity).

Figure 3.

Seaweed species collected from mangrove forests.

Figure 4.

Seaweed attachment in different mangrove areas.

3.2 Abundance and seasonality of identified seaweeds in Bangladesh

A total of 154 seaweed samples were identified during the study period. Among them, 34 are Chlorophyta group, 38 are Phaeophyta group, and 82 are Rhodophyta group (Figure 5). Some photographs are attached in Figures 2 and 3. Seaweeds were abundant on St. Martin Island from October to April. However, from January to March, seaweeds were abundant in the St. Martin Island. Comparatively, more abundance of seaweeds was found on Saint Martin Island in the Western, Southern tip of Cheradip, and the Eastern part (surrounding the Coast-guard/Navy point). However, in the case of mangrove forests, seaweeds are available throughout the year, from January to December.

Figure 5.

Classwise distribution of seaweed biodiversity in Bangladesh.

3.3 Commercially important seaweeds

Aside from the export potential, the development of seaweed cultivation in the country’s coastal areas might provide an alternative source of income for the people. On the shore, there are a variety of edible seaweed species. Therefore, commercially important seaweed species were identified throughout the experimental period. Based on our country’s abundance, availability, use, and culture potentiality, 26 seaweed species were identified as commercially important. Among them, 8 were Chlorophyta, 10 were Rhodophyta, and 8 were Phaeophyta group (Figure 6). These seaweeds have multiple uses, like fodder, fertilizer, human food, industrial, biofuel feedstock, heavy metal removal from wastewater, and pharmaceutical raw materials.

Figure 6.

Commercially important seaweed species.

4. Seaweed culture practices

Seaweed farming can be described as strategically placing seaweed crops in water for growth. From there, farming ensures sustained photosynthesis at the optimal rate till harvest during the grow-out period. Though the availability of water, sunshine, and gases may typically be taken for granted when choosing a place for seaweed cultivation, appropriate nutrition supply may be a key factor. Furthermore, ropes and nets offer suitable substrates for seaweed growth; however, their performance in this capacity depends on the fabric type employed. Therefore, they are a modifiable component of farming infrastructure, allowing for altering plot lengths and widths in a range of conditions, both floating and submerged. Within collected and identified seaweed species, economically important C. racemosa, H. musciformis, P. tetrastromatica, S. ilicifolium, S. oligocystum, U. intestinalis, and U. lactuca were selected for culture experiments in Saint Martin Island and other suitable areas.

The younger pieces of seaweed were used for seeding with an average of 5 ± 0.4 grams of fresh weight in each knot and 5 cm in size in the rope twists. The density of seaweed seed was 25–28 seeds/m². The horizontal net (square net) and long-line methods were applied to cultivate seaweed when cultured between the intertidal zone. The floating raft method was applied when seaweed was cultured beyond the intertidal zone or open sea [10]. Bamboo poles anchored culture nets and kept afloat at the surface level with plastic floats. The frame was tied loosely to the poles and fixed in a submerged floating condition to facilitate it going vertically to the tide. The cultivation was attempted at slightly deeper water, i.e., 0.5–1.0 m depth on fish nets, to avoid the intensity of sedimentation and grazing by fish. No fertilizer, growth hormone, or other chemicals were used during the culture period. Partial harvesting was done after 15/20 days of seaweed reaching an average standard length. The culture period was 60/90 days. The partial harvesting took place by cutting off the algae hanging on the surface, allowing the base on the surface to expand further. Standard methods were also followed to measure different physicochemical parameters [11]. Seaweed biomass production was measured as the fresh weight of seaweed per unit culture area (kg m⁻²) and was calculated using the following formula [12]:

$$\text{Y}=\left(Wn-{\text{W}}_0\right)/\text{A}$$E1

Here, Y = seaweed biomass production; Wn = raw weight on day n; W₀ = beginning raw weight; A = culture unit’s area.

The daily growth rate (DGR %) was calculated using the following formula [13]:

$$DGR\%=\ln \left({\text{W}}_{\text{f}}/Wo\right)/\text{t}\text{x}100$$E2

Here, W_f = final raw weight (g) at t day; Wo = initial raw weight (g); t = cultivation period (days).

4.1 Seaweeds biomass production

Experimental culture sites of seaweeds were set up in sheltered intertidal zones of the Bakkhali river estuary at Nuniarchora, Chowfoldondi, Kutubdia, Pecherdwip, S.M. Para, and Saint Martin Island. Harvesting at the end of 60/90 days of the culture period in Saint Martin sites resulted in the maximum biomass yields for all seaweed species (Figure 7). Saint Martin Island has favorable environmental conditions, resulting in higher growth and maximum biomass yields for all seaweed species. Among the seven seaweed species, the most increased biomass production (30.61 ± 0.23 kg m⁻²) was observed in the case of H. musciformis, and the lowest biomass production (10.18 ± 0.45 kg m⁻²) was observed in the case of P. tetrastromatica (Figure 8). Here, total biomass production of seaweed descending sequentially as H. musciformis > U. lactuca > U. intestinalis > S. oligocystum > S. ilicifolium > C. racemosa > P. tetrastromatica, with an evident variation among them. The observed biomass yield of seaweeds was significantly higher in Saint Martin than in Nuniarchora, Chowfoldondi, S.M. Para, Kutubdia, Pecherdwip, and Inani. Generally, Bakkhali, Chowfoldondi, Nuniarchora, and Inani are allocated upstream, where water quality parameters do not remain stable like Saint Martin and have not had extensive substratum facilities to form an enormous colony of seaweeds. Again, in S.M. Para, the site was on a polyculture farm. There the surrounding water quality parameters were not satisfactory for seaweed culture. Additionally, in Pecherdwip, the site was near the Raju Khal estuary, where upstream runoff carrying heavy silt causes lower seaweed growth.

Figure 7.

Biomass productions of different cultured seaweed species.

Figure 8.

Maximum biomass production (kg m⁻²) of seaweed species at Saint Martin Island.

4.2 Seaweed daily growth rate (% day⁻¹)

Saint Martin Island possesses the highest daily growth rate for all seaweed species. Among the seven seaweed species, the highest daily growth rate (5.99 ± 0.22% day⁻¹) was observed in the case of H. musciformis, and the lowest daily growth rate (4.76 ± 0.19% day⁻¹) was observed in the case of P. tetrastromatica. Here, the daily growth rate of seaweed is descending sequentially as H. musciformis > U. lactuca > U. intestinalis > S. oligocystum > S. ilicifolium > C. racemosa > P. tetrastromatica, with an apparent variation among them (Figure 9).

Figure 9.

Daily growth rate (% day⁻¹) of seaweed species at Saint Martin Island.

4.3 Environmental parameters

The cultivation of seaweed requires appropriate physicochemical conditions. The range values of different water quality variables during the culture period at different experimental sites at Cox’s Bazar are described in Table 1. All parameters were measured every 15 days during the partial harvest following standard protocols. In our experiment, different water quality variables showed higher fluctuations throughout the culture due to the high rainfall and surface runoff.

Experimental sites	Range values of hydrological data
	Temperature (°C)	Salinity (ppt)	DO (mg/l)	pH	Alkanity (ppm)	Transparency (cm)
St. Martin	23.1–30.8	28–36	6.5–8.2	6.8–7.8	105–120	81.5–88
Nuniarchora	22.8–31.5	27–35	5.9–7.8	6.9–7.1	110–120	52.5–68
Inani	23.0–28.4	30–34	6.3–8.0	6.5–7.7	100–120	65–70.5
Chowfoldondi	24.1–32.5	28–35	6.1–7.9	6.8–7.5	100–120	54–70
Pecherdwip	24.2–30.1	25–32	6.6–7.7	7.0–7.4	110–120	62–67
Kutubdia	24.5–29.5	24–31	6.4–7.9	6.3–7.2	95–120	45–58.5
S.M. Para	24.8–30.5	22–32	5.7–6.8	6.3–7.0	95–110	47–59.5

Table 1.

Different water quality variables of the culture sites during the experimental period.

The salinity of seawater is a very prudent and potential factor in growing seaweeds, as it is the crucial determinator of osmotic balance. The present study recorded salinity ranged from 28 to 36 ppt in Saint Martin. So, stable and moderate salinity is the critical factor of the highest biomass yield in Saint Martin. Moreover, water salinity had a strong positive correlation with water pH, DO, and transparency; that means salinity plays a vital and influential role in these water quality parameters. Water pH is the primary factor for animals and biota in aquatic environments. pH value of the present study was found favorable at Saint Martin compared to other sites. Dissolved oxygen concentration was found in this study favorable at Saint Martin than in other culture sites. That may be the cause of higher seaweed production from Saint Martin. Water transparency is the dormant factor to govern the growth rate of seaweeds. Transparent water allows adequate light intensity to facilitate the growth of algae. This study recorded the highest average light intensity from Saint Martin compared to other sites. So, water transparency was vital in getting the highest biomass yield from Saint Martin’s.

5. Seaweed product development study

To get raw seaweed in table form, repeated screening and washing were performed to isolate nontarget seaweed species and remove the sand and other undesirable particles. Harvested seaweeds were processed, dried, powdered, and preserved for seaweed-based product development. Processed seaweeds were used to produce the products. Seaweed powder was used at different percentages to prepare Seaweed Papor (98% U. lactuca), Seaweed Piyajo (5% U. lactuca), Seaweed Beguni (5% U. lactuca), Seaweed Mango Juice (3% U. intestinalis), and Seaweed Jorda (5% H. musciformis) (Figure 10). Also seaweed soup, seaweed barfi, seaweed noodles, seaweed pizza, seaweed soap, seaweed pudding, and squid-seaweed masala were prepared. Several other value-added seaweed products were also prepared and marketed with the collaboration of local entrepreneurs Mahi Agro Industry and Jahanara Green Agro (Figure 10). The flavors and tests of these seaweed food products were good. The information about seaweed products’ nutritional value was disseminated to different hotels, motels, restaurants, and local people to build awareness of seaweed utilization as a food item.

Figure 10.

Various food products are developed from seaweed powder. (A) Seaweed pizza, (B) seaweed soap, (C) seaweed pudding, (D) seaweed Papor, (E) seaweed Beguni, (F) seaweed mango juice, (G) seaweed Piyajo, (H) seaweed Jorda, (I) squid-seaweed masala, (J) seaweed barfi, (K) seaweed soap, (L) seaweed noodles, (M) seaweed value-added product, (N) seaweed value-added product (Balachao), and (O) seaweed value-added product.

6. Conclusions

With nutritional and medicinal values, seaweeds have garnered attention for their rich content of vitamins, minerals, proteins, and fibers. These marine macroalgae also possess bioactive compounds that offer potential therapeutic benefits, such as antioxidant, antimicrobial, and anti-inflammatory properties. Along the coast of Bangladesh, about 154 seaweed species exist, varying in availability and abundance throughout the year. Notably, 26 seaweeds have been identified as commercially important due to their high demand and economic value. Cultivating seaweeds involves practices aimed at optimizing growth and productivity, resulting in the production of seaweed biomass. Environmental parameters, including temperature, light intensity, salinity, and nutrient availability, play pivotal roles in seaweed culture practices, influencing growth and development. Understanding and controlling these parameters are crucial for successful seaweed cultivation. Additionally, studies on seaweed product development aim to explore diverse applications and potential uses, incorporating seaweed extracts or biomass to create value-added products across various industries. These studies contribute to expanding their utilization beyond traditional consumption by capitalizing on seaweed’s nutritional and medicinal properties.

Acknowledgments

This research was funded by Bangladesh Fisheries Research Institute (BFRI), Ministry of Fisheries and Livestock, Bangladesh.

Conflict of interest

The authors declare no conflict of interest.