Identification and chemical studies of pelagic masses of Sargassum natans ( Linnaeus ) Gaillon and S . fluitans ( Borgessen ) Borgesen ( brown algae ) , found offshore in Ondo State , Nigeria

The pelagic seaweed found offshore and negatively impacting fishing activity in Ondo State Nigeria, has been identified to be a mixture of Sargassum natans and Sargassum fluitans which presumably floated from the Sagasso Sea of North Atlantic. In a bid to harness the potential uses of the seaweed biomass, the mixed Sargassum species were analyzed for the proximate composition, some minerals and phytochemical constituents using standard methods. The mixed Sargassum species contained 154 mg/100 g% protein, 86.5 mg/100 g ash content, 25.5 mg/100 g fat, 71.5 mg/100 g fibre and 573 mg/100 g carbohydrate. Thus it could be consumed by humans if cleaned. Owing to the small concentration of Nitrogen (6.3 mg/100 g), phosphorus (96.5 mg/100 g) potassium (28 mg/100 g), the percentage ratio of NP-K (1-10-3) of Sargassum spp. was recommended as fertilizer. The presence of flavonoids, tannins, terpenoids and saponins show that the species can be harnessed for their medicinal potentials.


INTRODUCTION
In July 2012, the Nigerian media reported the occurrence of an unknown seaweed floating massively off the coast of Ajegunle-Erun-Ama (Lat.06 o 19′ 32″, Long.04 o 30′ 32″E, alt 5 m) in Ondo State, Southwestern Nigeria.The fishermen in the area observed that between April and July during the wet season, their nets were often filled with the seaweed mass instead of fishes.Consequently, their fishing occupation was adversely affected.Additionally, handling the seaweed biomass resulted in skin and eye irritation.Owing to these reports, two field trips were made to the locality with a view to collecting the seaweed and getting any useful information from the fishermen.The seaweed was instantly identified by the second author as Sargassum, a brown alga.
On a global scale, Sargassum (Sargassum natans and Sargassum fluitans) has broad distribution offshore of the North Atlantic (Schneider and Searles, 1991) and outside the Sargasso Sea there are more Sargassum floating in the Gulf of Mexico than anywhere else in the world (Conver and Sieburth, 1964;Gower and King, 2008).S. fluitans has recently been added to the Global database of Invasive Species Specialist Group (ISSG) (2011).The floating S. natans and S. fluitans are taxonomically valid speciesthat dominate the algal communities of the *Corresponding author.E-mail: busik1000@gmail.com.Five Sargassum species, Sargassum acinarium, Sargassum cyniaun Sargassum filipendula, Sargassum ramifolum and Sargassum vulgare were described and reportedly found in some West African countries (John et al., 2003).Of all these species, only S. vulgare and its variety (var.foliosissimum are distributed in 12 West African countries including Nigeria.It was thought desirable to ascertain whether the features of Sargassum from Ondo State, Nigeria, resemble any of the species recorded for West Africa. Seaweeds are of economic importance.Sargassum species are used as fodder and fertilizer in China and many parts of Asia (Round, 1973).Sargassum forms about 10% of the average diet in Japan where tender parts of the plant are eaten raw as salad or cooked with coconut milk.Also in Bermuda, indigenes spread out salt free Sargassum clumps as fertilizer around the base of banana.Algin, a carbohydrate found in Sargassum is extracted for use in textile, paper and pharmaceutical industries (Chennubhotla et al., 1981).Sargassum bio-biomass is used as a potential renewable energy resource such as biogas (Wang et al., 2009, Yokoyama et al., 2007).Despite the annual invasion of Sargassum biomass and its attendant negative impact on the traditional fisheries in Ondo State, the plant material caught in the nets could be useful to humans.In view of this, the present study was undertaken to identify the invading Sargassum species and carry out chemical studies using the biomass.This is with a view to harnessing the potential uses of the seaweed.

Collection and Identification of Plant materials
Plant materials were collected into glass jar containing sea water during the two visits made to Ajegunle-Erun-Ama beach, Ondo State Nigeria Figure 1.Detailed identification of the plant material was done in the laboratory with the aid of dissecting microscope and verified with illustrations by Széchy et al. (2012), Dawes and Mathieson (2008), John et al. (2003) Littler and Littler (2000) and Schneider and Searles (1991).

Proximate analysis
The powdered Sargassum sample was analyzed for crude protein, crude fat, fibre, moisture, ash using the methods described in AOAC (2005).The carbohydrate content was calculated by using the formula below.The analyses were duplicated.

Mineral analysis
The method of Walsh (1971) was used for the digestion of dried Sargassum material.After digestion, percentage of potassium, magnesium, zinc, iron, iodine were analyzed using atomic absorption spectrophotometer (FC 210/211, VGP Bausch Scientific AAS).Nitrogen content was determined by Kjeldahl method.Phosphorus was determined using Vanadomolybdate yellow method (AOAC, 2005).Percentage transmittance was determined at 400nm using Spectronic 20 (Bausch and Lomb) Colorimeter.Analyses were duplicated.

Phytochemical analysis
Phytochemical qualitative analysis of the plant sample was carried out using standard procedures described by Sofowora (1993) and Evans (2002).

RESULTS AND DISCUSSION
The Sargassum mass is shown in Figure 1.Based on light microscopical studies, the Sargassum 'wracks' was identified as a mixture of S. natans (Linnaeus), Gaillon and S. fluitans (Borgesen) Borgesen (Figure 2).The two species were differentiated as outlined in Table 1.Of all the morphological differences, two are particularly remarkable -the usual occurrence of spines on the air bladder of S. natans and their absence in S. fluitans.The other distinguishing character is that while S. natans had long stalk bladder, the S. fluitans had short stalk with wing tissue around it (Figure 2).Several workers (Schnieder and Searles, 1991;Littler and Littler, 2000;Dawes and Mathieson, 2008;Conti, 2008;Shapiro, 2004) observed that S. fluitans is separated from S. natans by the lack of spines on the gas (H 2 S) bladder (pneumatocysts) and the presence of   winged tissue around the bladder stalk.However the two species are difficult to differentiate from one another once they have reached the shoreline (Shapiro, 2004).The present study also confirms this observation.That both S. natans and S. fluitans were mixed together in the present study, is highly suggestive of the fact that the invading seaweed must have originated from the Sargasso sea in the North Atlantic Ocean where according to Stoner and Greening (1984), both species co-exist.S. natans and S. fluitans are two most similar and common holo-pelagic brown algae (Conover and Sieburth, 1964), reproducing vegetatively by fragmentation (Awasthi, 2005;Rogers, 2011).They remain completely pelagic during their lifecycle and are never attached to the sea floor during their life cycle (Hemphill, 2005;Round, 1981).However, strong currents occasioned by several storms in May or June bump into the edges of the Sargasso Sea breaking off segments of the ecosystem (Grower and King, 2008).

S. natans
In the process, the sea currents and winds carry the Sargassum fragments along, eventually sweeping it into West African coastal regions of countries like Nigeria and Gabon (Colombini and Chelazzi, 2003).Sargassum, being highly tolerant of variations in environmental parameters like desiccation, sunlight, salinity and temperature occupies a broad range of habitats (Abbott andDawson, 1978, Fritsch, 1965).
The proximate analysis of mixed Sargassum sample is shown in Table 2. Crude protein (154 mg/100 g) was relatively higher when compared with the crude protein of two commonly consumed Nigerian vegetables.Idris (2011) reported that Telfairia occidentale had 87.3 mg/100 g protein and Adeboye (2004) obtained 116-123 mg/100 g protein for two varieties of Senecio biafrae.Proteins are required for growth and body building.In this study, ash content in Sargassum sample was 86.5 mg/100 g but Gbadamosi et al. (2012) reported 87.2 mg/100 g for S. biafrae.The crude fat (25.5 mg/100 g) of the seaweed is lower than that of T. occidentale (35.7 mg/100 g) obtained by Gbadamosi et al. (2012).All these show that S. natans and S. fluitans have nutritional potentials.
Seaweeds and their products are used in coastal Asia to enhance growth and productivity, however, horticultural uses of Sargassum are limited (Eyras et al., 2008;Klock-Moore, 2000;Win and Saing, 2008).Although using Sargassum biomass as fertilizer is another way of harnessing its potentials, Sargassum is natural fertilizer for Panicum amarum, a saline habitat grass (Williams, 2008).Ocean algae consistently have lower nitrogen content when compared to compost from traditional feed stocks (Eyras et al., 1998;Maze et al., 1993).As shown in Table 3, the percentage ratio of N-P-  K (1-10-3) was relatively small.However, high N-P-K percentage does not necessarily mean a better fertilizer.
Besides, N-P-K percentage ratios of organic fertilizers are typically smaller compared to inorganic ones.Organic fertilizers are not water soluble and thus release nutrients slowly over time, especially when enhanced by a soil pH 6.5-6.8,thus increasing soil fertility capacity (Granstedt and Kjellenberg, 1997).Since nitrogen generally promotes foliage growth, phosphorus promotes root growth and fruit production and potassium promotes overall health of the plant, the percentage ratio (1-10-3) of Sargassum in the present study is recommended as fertilizer for a new lawn and for seedling establishment.
The low concentration of iodine (0.04 mg/100 g) in this study agrees with the view of Liu et al. (2012) that the contribution of iodine in Sargassum for treating thyroid and related diseases seems to have been over estimated.
The quantitative phytochemical analysis of the mixed Sargassum species is shown in Table 4. Sargassum seaweeds have been used in more than 226 prescriptions to treat various diseases in China (Liu et al., 2012).The uses in traditional Chinese medicine presumably depend on the phytochemical compounds in the seaweed.Although Liu et al., (2012) listed 80 Sargassum species that have been analyzed for their phytochemical constituents, S. natans and S. fluitans are not included.Liu et al. (2009) isolated two flavonoids from Sargassum pallidum, but in low concentrations.The occurrence of relatively high flavonoid constituents (750 mg/100 g) in the mixed Sargassum (S. natans and S. fluitans) shows that the biomass is a rich source of flavonoids hence useful medicinally.Flavonoids are known to have antiviral, antineoplastic, antithrombotic and vasodilatory activities (Alan and Miller, 1996).The occurrence of tannins in appreciable amount (122.5 mg/100 g) is significant.According to Okwu and Okwu (2004), tannins hasten the healing of wounds and inflamed mucous membrane.Phlorotannin fractions from mixed Sargassum species showed anticoagulant and antioxidant activities (Wei et al., 2007).
The mixed Sargassum sample had 66.5 mg/100 g of terpenoids.
Terpenoids have antimicrobial and antiamoebic activities (Amaral et al., 1998).The present study supports the report of Liu et al. (2012) that meroterpenoids (class of compounds containing terpenoid elements) are particularly abundant in Sargassum.Meroterpenoids are antioxidant, anticancer, antimalarial, and antiviral and neuroprotective agents (Tsang and Kamei, 2004).Saponin constituent (525 mg/100 g) was relatively high in the mixed Sargassum sample.Saponins are used in manufacturing insecticides, shampoos and in the synthesis of steroid hormones (Okwu, 2003).That alkaloid (77.5 mg/100 g) occur in the Sargassum sample may explain the usefulness of the seaweed in the management of high blood pressure.Harborne (2000) reported that alkaloids such as rynchosphylline help in improving cardiac conditions by reducing blood pressure, increasing circulation and inhibiting deposition of arteriosclerosis plaque and blood clots.
The Nigerian traditional fishermen reported that the invading Sargassum mass caused skin and eye irritation when handled.This effect might be due to the production of some chemical substances as the seaweed decomposed.As observed by the present study, Sargassum was harmless when dry but decomposed very fast in wet conditions on the beaches, emitting foul odor (poisonous hydrogen sulphide).The inhalation of the gas could trigger irritation of the eyes and the respiratory system.

Conclusion
It was evident that the features of Sargassum from Ondo State, Nigeria, did not resemble any of the species recorded for West Africa.In consideration of seasonal appearance on coastal beaches, Sargassum constitutes a nuisance to both the fishermen and the beach lovers.Since biological, chemical and mechanical removal approaches may not be effective, attention should be focused on how the pelagic masses can be economically useful.

Flat
range; b, length range.

Table 2 .
Proximate analysis of mixture of Sargassum natans and S, fluitans powder.
a, Mean of two readings + SD.

Table 3 .
Mineral analysis of mixture of Sargassum natans and S. fluitans powder.

Table 4 .
Quantitative phytochemical analysis of mixture of Sargassum natans and S. fluitans powder.
a, Mean of two readings + SD.