Field Document No. 4
SURVEY OF LIMU TANGA'U (Cladosiphon sp.)
IN TONGATAPU, HA'APAI AND VAVA'U ISLANDS IN TONGA:
OBSERVATIONS ON GROWTH IN DECEMBER 1996
Ed R. Lovell
Prepared for the Ministry o Fisheries,
Kingdom of Tonga
During the period of the first phase project (1986–1992), the FAO South Pacific Aquaculture Development Project (SPADP) defined that seaweed would be one of the most appropriate aquaculture commodities for the Pacific islands for export purpose, that are at present limited in number. The second phase of SPADP starting from 1994 followed the strategy of the first phase and generated awareness in exploration of seaweed farming development in the region.
Although SPADP learned through a scientific reference of the existence of useful seaweed (Cladosiphon) in New Caledonia. SPADP was thoughtlessly not aware of the distribution of a similar seaweed in Tonga until Mr.Kikutani, a JICA aquaculture expert sent SPADP Cladosiphon algae sampled from Tonga in 1995 because of its limited appearance in a certain time. No other countries reported this seaweed in the region other than Tonga and New Caledonia.
A brown algae Cladosiphon is called “Limu Tanga'u” in Tonga and is well known by the people as a seasonally edible seaweed, and it is consumed in the domestic market to a limited extent. Cladosiphon algae is being cultured extensively in Okinawa islands, Japan for domestic food market. Its production was about 10,000 tonnes annually and it was a major aquaculture commodity in volume in Okinawa. It is noted that the seaweed farming in Okinawa is contributing not only in generating income of islanders but also in protecting coastal fisheries resources from over-fishing because of observance of fishing restrictions by fishermen owing to the stabilized and increased income from the seaweed farming.
Fortunately, since the quality of Cladosiphon from Tonga was well accepted in the Japanese market and its market is still growing, two seaweed processing companies agreed to conduct a joint harvest trial with the Fisheries Division in 1996. This survey aimed to grasp the biological and ecological features of this seaweed as well as to assess the viability of its commercial harvest.
Mr.Ed Lovell is an experienced Fiji-based reef biologist. He unveiled extensive areas of natural Cladosiphon habitats in Tonga. These areas would suit its farming production in the future, and SPADP wishes Limu Tanga'u could be one of the largest national export commodities similar to that of squash.
Chief Technical Adviser
SOUTH PACIFIC AQUACULTURE DEVELOPMENT PROJECT (PHASE ii)
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
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1 EXECUTIVE SUMMARY
3-1. Field Survey
3-2. Growth Assessment
4-1. Distribution of Cladosiphon sp.
4-2. Sites of General Survey
4.2.1 Tongatapu and adjacent areas
4.2.2 Ha'apai group
4.2.3 Vava'u group
4-3. Aerial Photography of the Sites of Known Cladosiphon Occurrence
4.4 The Aerial Extent of Seagrass Habitats
4.4.1 Thalassia hemprichii and Syringodium isoetifolium as habitats for
4.4.2 Comparison of Cladosiphon habitats: Estimate of areas, known harvest and field sample
4.5 Growth Study
5-1. Life Cycle
5-2. Field Appearance
5.3.1 Potential effect of temperature on the life cycle of Cladosiphon sp.
5.3.2 El Nino - La Nina cycles and regional water temperature fluctuations
5-4. Potential Consequences of Continuous Harvest
Figure 1: Chart of the Kingdom of Tonga with its South Pacific location (inset)
Figure 2a: The area of initial harvest on Tongatapu off Navutoka (located to the right in the photo). Another site of harvest is to the right of Manima and Oneata ls. See Fig. 2b for the charted area
Figure 2b: Charted area of Fig.2a shown in the bold lined section
Figure 3a: Tonga's most extensive Cladosiphon habitat in the bay south of Atata and Toke l. See Fig. 3b for detail of the chartered area
Figure 3b: Charted area of Fig. 3a shown in the bold lined section
Figure 4a: The seagrass beds adjacent to Uiha l., Ha'apai which potentially host commercial quantities of Cladosiphon The charted area of Uiha and adjacent islands are shown in Fig. 4b
Figure 4b: Charted area of Fig. 4a shown in the bold lined box in the center of the page
Figure 5a: Aerial view of reported Cladosiphon habitats in the seagrass beds west of Koloa l. And north of Oloua l. See Fig. 5b for the charted details of the area
Figure 5b: Charted area of Fig. 5a shown in the bold lined box in the center of the page
Figure 6(a-c): Reported Cladosiphon habitats from off-shore reef areas:
Dark areas show the extent of the seagrass and mixed algal assemblage between and around Onevao and Onevai ls. on the barrier reef north of Tongatapu l. at the top of the photo. A sandy reef flat is more characteristic of the barrier reef environment.
Aerial photo of the reef flat habitat around Fukave and Nuku ls. which is representative of the remainder of the barrier reef area to the east of Fig. 6a.
The reported occurrence of Cladosiphon sp. At Nukupule l., Ha'apai group, shows the limited nature of the seagrass habitat by the dark area to the west of the island.
Figure 6d: Areas shown in Fig. 6 a, b on the barrier reef north of Tongatapu l.
Figure 7(a-o): Cladosiphon lifecycle, habitat and experimental design
(a,b) Dispersal of Cladosiphon involves two modes:
Vegetative propagation whereby grown filaments travel by current and are subsequently entangled by bottom relief such as a clump of hard coral (Pocillopora damicornis) or a stiff upright algae such as Halimeda spp. and subsequently colonise the surrounding area.
The settlements of spores on hard surfaces such as the skeletal material of Halimeda spp.
Settlement of the gametophyte stage on a glass surface induced by the collection of sample material indicating sporulation in October.
Cladosiphon sp. In a common association of Syringodium isoetifolium and Galaxeura sp. This specimen has a clear, smooth outer sheath and golden brown colour characteristic during a period of vital growth. This condition is less common late in the season.
A more translucent nature of the outer sheath with an irregular surface is characteristic of colonies late in the season.
Late in the development of Cladosiphon, the sheath becomes ragged and more opaque with a light appearance.
The Cladosiphon colony is often matted amongst the Syringodium seagrass forming dense layers.
Mounds of Cladosiphon are rolled up in the sandy areas within the seagrass meadows as well as on the beach following strong westerly winds. This seasonal feature heralds the end to the algaes presence and the end of the sporophyte phase.
Generally, the seagrass Syringodium with its stiff blades provides the habitat for Cladosiphons intertangling growth. In mixed seagrass beds and on the periphery of the intertangling growth. In mixed seagrass beds and on the periphery of the Syringodium patches in deeper water, Thalassia hemprichii is also colonised.
In deeper water (5–7 m), the detached pieces of Cladosiphon become entangled on the upright thalli of algal colonies. The migration of this material into deeper water is the result of strong winds causing the material to remove the algae from the seagrass beds.
The tank culture of the algae was conducted at the Ministry of Fisheries aquaculture unit. The design was unsuccessful presumably due to high temperatures and/or caused by unshaded conditions.
Tank culture in trays.
The rope culture design in the field at Navutoka, Tongatapu.
The irregular fringing reef coast line along the western shore of Foa l., Ha'apai. This area is characteristic of the unsuitable habitats for seagrasses and Cladosiphon in all but a small area of the Ha'apai Group.
Intertidal seagrasses adjacent to Koloa l, Vava'u Group. In deeper water, this habitat is reported to host the Cladosiphon algae.
Figure 8a: Life Cycle of Cladosiphon okamuranus (adapted from Okanamura 1936; Shimura, 1977; and Okinawa Pref. Fish. Exp. Station, 1978)
Figure 8b: Seasonal diagram of Cladosiphon okamuranus rectified for Tonga for comparison
Figure 9: Comparative temperature data from Tongatapu and Vava'u l.
Figure 10: Equatorial Pacific sea surface temperature anomaly (C°) for the area between 160°E and 150°W and 5°N&S of the equator for a 20 year period
Figure 11: El Nino and La Nina periods - variation in the standard deviation for the Southern Oscillation Index as a five month running mean for the last twenty years
Figure 12: Time/longitude sections of sea surface temperature (C°) for the past 24 months. Data derived from moored time series sample between 2° N/S Latitude
Figure 13: Predicted sea surface temperature anomalies at 6, 9 and 12 month lead times
Table 1: Summary of information on the sites surveyed
Table 2: Comparison of Cladosiphon habitats
Table 3: Growth rate assessment: Rope and tray culture