Background

Indonesia is one of the world's richest nations in terms of seaweed diversity, some of seaweed in indonesia have high economic value such as Eucheuma sp, Gracilaria sp, Gelidium sp, Sargassum sp, Caulerpa sp and Turbinaria spp. Methods that have been developed in seaweed cultivation such as the long line method, the floating raft method, the off-bottom method (Hendri et al., 2017; Hendri et al., 2018; Hendri et al., 2020).

These method before have a several weakness, like can’t protect fully and have potential to attacked from predators like baronang fish, sea turtle and others. Besides that, these method can’t applied in open waters who have strong current and big waves because part of seaweed (thalus) can broke, predators also can make seaweed broke and  it can be a disease for seaweed.

This problem make cultivation seaweed in Pesawaran regency, Pahawang Island is not optimal. Almost 4 years cultivation seaweed in this place are stopped. Needed new method for cultivation seaweed to handle seaweed from strong current, big waves and predators.

Pahawang waters have strong current and big waves because it near with high seas especially in dusun Jelarangan. Strong current can make thalus broke, because it very sensitive to broke. Even though if managed properly by using the right cultivation methods, strong currents and waves are actually beneficial because it can stimulate the growth of seaweed thalus, beside that strong current can preventing the attachment of the substrate to the thalus and also better for distribution of nutrients.

1 Materials and Methods

1.1 Time and place

This research has been done in July - September 2019 on Pahawang Island, Jelarangan Hamlet, Pesawaran District. The map of the research location is presented in Figure 1.

Figure 1 Map of Pahawang Island on the southeastern tip of Sumatra Island showing the research site in Jeralangan sub-village, Pesawaran District, Lampung Province, Indonesia

1.2 Tools and materials

Seaweed E.spinosum seeds used in this research came from seaweed farmers in Ketapang District, South Lampung Regency. That seeds firstly came from the Lampung Center for Fisheries and Aquaculture (BBPBL). The initial weight of seaweed used was 50 grams and was planted in 56 nets. The tools and materials in this study are presented in Table 1.

Table 1 Tools and materials

1.3 Research methods

Cultivated E. Spinosum in this research used by bag-nets, it tied to a raft. The raft was made of bamboo 10~15 cm in diameter and 4 m × 5 m in size. Every side of raft is given an anchor for make the raft stable and fixed. Every side of the raft given a polyethylene rope 2 "as a place to tied a net bag with a spacing of 40 cm. The net-bag is specially designed (Figure 2), has a length of 50 cm, is round in shape with a diameter of 40 cm. On the inside of the net bag is given a framework of wire (3 wire frame) which is circular in function as a framework so that the net can remain in the desired position. Wire made of stainless steel and given a plastic hose for avoiding sea water.

Figure 2  Design of PVC or bamboo rafts of E. spinosum culture using the bag net method

Total of net-bag planted was 56 units, and each net-bags has 40 cm distance. Cultivated E.spinosum seaweed has an initial weight of 50 grams, it placed in a net bag and given a rope to hang seaweed to remain in the middle of the net-bag. The net is cleaned every week from substrate and biota that are stuck at the net. Environmental factors are measured three (3) times during the research.

1.4 Observation variable

1.4.1 Daily growth rate

Daily Growth Rate (DGR) is the relative growth of seaweed per unit time (% / day) (Mtolera et al., 1995; Gerung and Ohno, 1997; Aguirre-von-Wobeser et al., 2001; Bulboa et al., 2007 ; Hayashi et al., 2007; Hori et al., 2009),

DGR = [(Wt / Wo) ^ (1 / T) -1] x 100% …………………………………………………… (1)

Information:

DGR: Daily Growth Rate

Wt: Weight after 1 day (gram)

Wo: Initial Weight (grams)

T: Time

1.4.2 Absolute growth rate

The absolute growth rate is the final weight (Wt) minus the initial weight (Wo) (Hendri et al., 2018), with the following formula;

AG = Wt-Wo …………………………………………………… (2)

Information:

AG: Absolutely Growth

Wo: Weight of the test plant at the start of maintenance (grams)

Wt: Weight of the test plant at the end of maintenance (grams)

2 Results

2.1 Aquatic quality parameters

The quality of the waters are determining success of seaweed cultivation. The quality of waters including physical, chemical and biological, that factor can inhibit and can also accelerate the growth of seaweed itself. Each parameter has a different value in seaweed growth. If the water parameters meet the criteria of seaweed growth, the growth of seaweed will be good and the carrageenan content in seaweed will be better too. The results of measurement of environmental parameters can be seen in Table 2.

Table 2 Measurement of Pahawang Island Waters Quality (Jelarangan village)

The temperature of the waters at the study site is very suitable to support the optimum growth of seaweed. This is same with the opinion of WWF (2010) seaweed growth in the temperature range of 26°C~32°C.

The optimum water temperature seaweed metabolism process will be in optimum conditions too. Sources of nutrients come into thalus will be relatively used optimally to spur growth. Temperatures that are too low or too hot can stress the seaweed. Thalus will break easily and attack diseases such as ice-ice will attack easily.

The depth of the waters of the study is 9 m and is on the edge. The transparance of water is 100% and sunlight reaches the bottom of the water properly. This condition is supported by a substrate of water in the form of coral and sand fragments. So that the substrate stirring process at high tide or low tide and by currents or waves does not have a big effect on the brightness of the waters at this location. Good transparance and penetrate the bottom of the water will support the process of photosynthesis to be more optimal. Seaweed that will carry out photosynthesis and this process will be disrupted if the penetration of sunlight is blocked by sediment or susbtrat which is stirred and floated in the water column.

Relation of water depth on the growth rate of seaweed research has been done quite a lot, according to Hendri et al. (2017), Gracilaria Sp can still grow well to a depth of 630 cm with a DGR of 2.15% / day (0 cm) and the lowest of 1.84% / day (630 cm). While the type of E.cottoni growth rate is smaller with the highest DGR value 1.59% / day (0 cm) and the lowest 1.33% / day (630 cm) (Hendri et al., 2018). While in other studies on the type of E.cottonii, the growth rate at a depth of 25 cm has the highest growth rate with a value of 5.12% and the lowest at a depth of 75 cm with a value of 3.13% (Susilowati et al., 2012).

E. spinosum is a type of marine plant that really needs salinity. Salinity is one of the parameters that is closely related to osmotic pressure in the thalus of seaweed, this condition will affect its balance. Aquatic salinity for marine organisms is an important environmental factor. Each marine organism has a different tolerance to salinity for survival.

Salinity at this location is in very good condition to support the growth of seaweed. According to Lüning (1990) Gracilaria sp lives well at 15~22 ppt salinity, except the Fucus vesiculosus species has a wider tolerance with a range of 8~34 ppt. Different with the Euchemic species have a much narrower tolerance range of 30~35 ppt (Dawes, 1981). Low or high salinity will inhibit the growth of seaweed and can even make seaweed die. According to Yuliyana et al. (2015) salinity affects the growth (DGR) of latoh seaweed (C. lentillifera). The best growth at salinity was 30 ppt (3.53%/day), 35 ppt (2.82% / day), 25 ppt (1.84% / day) and the lowest was 20 ppt (1.42% / day) on a laboratory scale.

Low and high salinity will affect the growth of seaweed. Seaweed (E.spinosum) can die and be damaged by bad salinity. Salinity can make plasmolysis in cell walls seaweed. According to Xiong and Zhu (2002) the effect of salinity on plants is very complex, it can cause ionic, osmotic and secondary. Seaweed from the Euchema sp need high salinity in the range of 31~35 ppt, with an optimum salinity of 32~33 ppt. Higher or lower salinity will cause growth to be disrupted and can cause damage to the thalus (death). This is in accordance with the opinion of Beveridre (1987) in Iksan (2005) stating that salinity is closely related to osmotic pressure, the higher the salinity, the greater the osmotic pressure this condition is related to the osmoregulation process in the body of an organism. Seaweed Eucheuma sp grows well in high salinity.

Other researchers have the same opinion about the salinity range for Euchema sp, Soegiarto et al. (1978) a good salinity range of 32~35 ppt, Dawes (1981) argues, a good salinity range of 30~35 ppt while Zatnika and Angkasa (1994) ranged from 28 to 34 ppt. Low salinity (<30 ppt) will damage the seaweed (thalus) which is characterized by the emergence of white at the tips of the thalus (Collina, 1976 in Iksan, 2005). 33.5 ppt salinity at the research location is very suitable and is in the optimum range for growth E. spinosum.

Current speed at the research is quite strong 49.5 cm/sec. The recommended current speed for seaweed cultivation ranges from 20~40 cm/sec (Hendri et al., 2017; Hendri et al., 2018). Strong current speeds coupled with large waves (> 2m) can break the thalus. A broken talus will be washed away and carried by the current. However, strong currents and large waves can also have a positive impact, especially on the distribution of nutrients and air exchange (oxygen and CO₂). Even strong currents can prevent the attachment of the substrate to the thalus. Substrate attachment can disrupt the entry of nutrients into the thalus and block sunlight during photosynthesis.

Current speed and wave at this research did not have big impact for thalus fracture. The netting protects the thalus broken by the waves and currents. Factually,  currents and waves have a positive impact that can be obtained seaweed optimally. Good nutrient distribution, thalus washing (flushing) from the substrate attachment and optimum photosynthesis are important factors for the growth of E. spinosum at this research.

The dissolved oxygen and pH values at this study site are already in good condition to support the growth rate of seaweed. The value of pH and dissolved oxygen which is sufficient will help the process of metabolism and accelerate the rate of growth.

3 Discussion

3.1 Growth of seaweed

The net-bag used in this study are designed to protect E.spinosum from its predators (Baronang Fish and Turtles). The net is made from a kind of nylon rope that is strong enough. In addition, the bag nets are expected to protect the thalus from being hit by strong currents and waves. Even if it is broken, the fracture remains in the net. The visual observation result shows that the predator cannot touch the seaweed in the net (Figure 3; Figure 4).

Figure 3 E. spinosum net and its predatory fish

Figure 4 The E. spinosum net and its predatory fish

Based on the results of the study, the average weight gain of E. spinosum, measured for five (5) weeks, showed quite good growth. Observation and weighing results are seen in Figure 5 and Table 3.

Figure 5 Weighing E.spinosum seaweed

Table 3 Growth of E. spinosum in a net bag (35 days)

Growth of E. spinosum weight during the study (35 days) look in Table 3.

The total final weight of E.spinosum from 56 planted nets is 19875 grams with an average of 354.91 grams per bag net. The highest weight in the 1^st and 16^th bag nets weighing 411 grams and the lowest in the 50^th bag nets weighing 302 grams. On average there is an addition of 6-8 times the initial weight which has an initial weight of 50 grams. For more final weight E. spinosum in this study can be seen in Table 3 and Figure 6.

Figure 6 Absolute Growth Rate (AGR) of E. Spinosum

Daily growth rate (DGR) in this study ranged from 5,138% / day to 6,018% / day. The DGR value is very good for seaweed cultivation because it has a value of > 2% / day. According to Ask and Azanza (2002) the value of DGR is good for growth> 2% / day. Other studies mention the same good DGR value> 2% days (Indriani, H., dan Sumiarsih, 1995; Hendri et al., 2017; Hendri et al., 2018). The value of this daily growth rate is much better than previous research Hendri et al. (2017) 1.5%~2% / day, Wijayanto et al. (2011) <2% / day.

Better DGR value happen because of several factors. The current speed at the research is quite large (49.5 cm.det) which has a positive effect on preventing the attachment of the substrate to the thalus so that photosynthesis can proceed well and the distribution of nutrients is well. The designed bag-nets are quite effective in preventing predation from predatory fish (baronang/samadar) and turtles. The broken thalus is still in the net and does not drift along with the current. The full DGR values are presented in Figure 7.

Figure 7 Daily Growth Rate (DGR) of E. spinosum

Beside a good flow, optimum salinity is also one of the environmental parameters that are having effect of the high growth rate (DGR) in this study. Salinity 33.5 ppt is the optimum value for the growth of seaweed species Euchema sp. This is consistent with the results of research by Soegianto et al. (1978) 32~35 ppt, Dawes (1981) 30~35 ppt and Zatnika and Angkasa (1994) 28~34 ppt. Low salinity will trigger slow growth and cause white spots on the thalus. This condition can make the thalus to become brittle and broken. This high DGR value is highly recommended for seaweed farming. DGR value> 2% / day is a good value for seaweed cultivation business.

4 Conclusions and Suggestions

4.1 Conclusion

Based on the results of research that has been observed in the cultivation of seaweed Eucheuma spinosum which has been conducted for 5 weeks using the bag net method, the following conclusion are:

1) Daily growth rate (DGR) in this study ranges from 5,138% / day to 6,018% / day.

2) The total final weight of E.spinosum from 56 planted nets is 19875 grams with an average of 354.91 grams per bag net. The highest weight in the 1st and 16th bag nets weighing 426 grams and the lowest in the 50th bag nets weighing 302 grams

3) The absolute growth rate or absolute growth (AG) of a total of 56 bag nets is 17075 grams with an average of 304.91 grams. The highest absolute growth rate is 426 grams and the lowest is 302 grams.

4.2 Suggestion

Suggestions can be given from the results of research that has been done:

1) The framework of the bag net needs to be strengthened and ensured not to leak (plastic hose) so as not to damage the wire (corrosive).

2) It is necessary to design a better one at the top of the bag net so that sunlight can more easily enter and make easy binding.

Acknowledgments

Thanks to, Yoga Pebrian Firmansyah, S. Kel, Adi Murdianto, S. Kel, Tri Rizky Oktariansyah, Mas Ebiet and Mas Kacong (Pahwang) for their contributions during the research. Thank to Sriwijaya University for supporting and assistance.

Reference

Aguirre-von-Wobeser E., Figueroa F., and Cabello-Pasini A., 2001, Photosynthesis and growth of red and green morphotypes of Kappaphycus alvarezii (Rhodophyta) from the Philippines, Marine Biology, 138(4): 679-686

https://doi.org/10.1007/s002270000506

Ask E.I., and Azanza R.V., 2002, Advances in cultivation technology of commercial Eucheumatoid species: a review with suggestions for future research, Aquaculture, 206(3): 257-277

https://doi.org/10.1016/S0044-8486(01)00724-4

Bulboa C.R., de Paula E.J., and Chow F., 2007, Laboratory germination and sea out-planting of tetraspore progeny from Kappaphycus striatum (Rhodophyta) in subtropical waters of Brazil, Journal of Applied Phycology, 19(4): 357-363

https://doi.org/10.1007/s10811-006-9142-7

Dawes C.J., 1981, Marine Botanv, John Wiley & Sons, pp.627

Gerung G.S., and Ohno M., 1997, Growth rates of Eucheuma denticulatum (Burman) Collins et Harvey and Kappaphycus striatum (Schmitz) Doty under different conditions in warm waters of Southern Japan, Journal of Applied Phycology, 9(5): 413-415

https://doi.org/10.1023/A:1007906326617

Hayashi L., de Paula E.J., and Chow F., 2007, Growth rate and carrageenan analyses in four strains of Kappaphycus alvarezii (Rhodophyta, Gigartinales) farmed in the subtropical waters of São Paulo State, Brazil, Journal of Applied Phycology, 19(5): 393-399

https://doi.org/10.1007/s10811-006-9135-6

Hendri M., and Apri R., 2017, Optimization of cultivated seaweed land gracilaria sp using vertikultur system, International Journal of Marine Science, 7(43): 411-422

https://doi.org/10.5376/ijms.2017.07.0043

Hendri M., 2018, Untung berlipat dari budidaya rumput laut rumput laut tanaman multi manfaat, Yogyakarta: Andi Publisher-Lily Publisher, ISBN: 978-979-29-6770-8, Edisi 1. Hal.180

Hendri M., Rozirwan R., Apri R., and Handayani Y., 2018, Intensification of seaweed cultivation Euchema cottonii with verticulture method in the water of Kelagian Island, Lampung Bay, International Journal of Marine Science, 8(14): 114-126

https://doi.org/10.5376/ijms.2018.08.0014

Hendri M., 2020, Growth of Eucheuma denticulatum (spinosum) cultivated with a net bag verticulture method, AACL Bioflux, 13(4): 2032-2040

Hori K., Nang H.Q., and Kha T., 2009, Seasonal changes in growth rate, currageenan yield and lectin content in the red alga Kappaphycus alvarezii, Journal of Applied Phycology, 21(3): 265-272

https://doi.org/10.1007/s10811-008-9360-2

Iksan K.H., 2005, Kajian Pertumbuhan, Produksi Rumput Laut (Eucheuma cottonii), dan kandungan Karaginan pada berbagai Bobot Bibit dan Asal Thallus di perairan desa Guraping Oba Maluku Utara, Tesis (tidak dipublikasikan), Sekolah Pascasarjana, Institut Pertanian Bogor. Bogor

Indriani H., and dan Sumiarsih E., 1995, Budidaya, Pengolahan dan Pemasaran Rumput Laut, Penebar Swadaya, Jakarta

Lüning K., 1990, Seaweeds:Their Environment, Biogeography and Ecophysiology, John Wiley and Son. Inc., ISBN: 0-471-62434-9

Mtolera M.S., Collén J., Pedersén M., and Semesi A.K., 1995, Destructive hydrogen peroxide production in Eucheuma denticulatum (Rhodophyta) during stress caused by elevated pH, high light intensities and competition with other species, European Journal of Phycology, 30(4): 289-297

https://doi.org/10.1080/09670269500651071

Soegianto S., Atmadja W.S., and Mubarak H., 1978, Rumput Laut (Algae) Manfaat, Potensi dan Usaha Budidayanya, Lembaga Oseanologi Nasional, LIPI. Jakarta

Susilowati T., Rejeki S., Nurcahya E., and dan Zulfitriani, 2012, Pengaruh kedalaman terhadap pertumbuhan rumput laut (Eucheuma cottonii) yang dibudidayakan dengan metode longlinedi Pantai Mlonggo, Kabupaten Jepara, Jurnal Saintek Perikanan, Volume 8 Nomor 1.Tahun 2012

Xiong I., and Zhu J.K., 2002, Salt Tolerance in The Arabidopsis, American Society of Plant Biologists

https://doi.org/10.1199/tab.0048

PMid:22303210 PMCid:PMC3243379

Yuliyana A., Rejeki S., and Widowati S.L., 2015, Pengaruh salinitas yang berbeda terhadap pertumbuhan rumput laut latoh (Caulerpa lentillifera) di Laboratorium Pengembangan Wilayah Pantai (LPWP) Jepara, Journal of Aquaculture Management and Technology, 4(4): 61-66

Zatnika A., and Angkasa W.I., 1994, "Teknologi budidaya rumput laut." Makalah pada seminar pekan akuakultur V. Tim rumput laut Badan Pengkajian dan Penerapan Teknologi (BPPT), Jakarta

Wijayanto T., Hendri M., and Aryawati R., 2011, Studi pertumbuhan rumput laut Eucheuma cottonii dengan berbagai metode penanaman yang berbeda di perairan Kalianda, Lampung Selatan, Maspari Journal: Marine Science Research, 3(2): 51-57