SURVEY OF LIMU TANGA'U (Cladosiphon sp.) IN TONGATAPU, HA'APAI AND VAV'AU ISLANDS IN TONGA: OBSERVATIONS ON GROWTH IN DECEMBER 1996
The presence of the Cladosiphon sp. has been reported throughout the Kingdom of Tonga. However, inspection of known areas and a more complete understanding of the ecology of algae have led to the realisation that the main area of abundance is on the north side of Tongatapu I., particularly in the bay margins south of Maria Bay and Toke I. Though there are substantial quantities in Felemea Bay, Hapa'ai Group, the area suitable for growth is limited compared to Tongatapu I. and this year the season was shorter. Again in the Vava'u Group, the suitable habitat is relatively limited and the season was shorter still with no Cladosiphon found in December. Presuming that temperature was limiting, this may be as short as 4 months as compared to 9.5–10 months on Tongatapu I.
An estimate of Cladosiphon habitats and the biomass present have been assessed by the use of aerial photographs and field sampling. This technique needs to be refined through more extensive ground truthing and increasing the frequency of field material sampled.
The growth of Cladosiphon sp. was in decline during the month of December. The growth rates of cultured species in the field and in tank, indicated a reduction in biomass with a negative measured weight of -56.9% and -47.9%, respectively. In the field, the standing stock generally had an moribund appearance. Substantial matting of the algae had occurred in some areas (3.75 kg/m2).
The seasonality of the sporophyte generation is determined both by the advent of high water temperature and the occurrence of wave action caused by contrary winds. This latter effect was important in Felemea Bay with winds of greater than 25 kts. dislodging the algae from the seagrass beds. It is important in shallow areas such as the reef flat at Navutoka but they remained unaffected with northerly winds of 15 kts for an 8 day period. Wind is less a factor in the deeper areas where the Cladosiphon is most abundant south of Maria Bay.
1 Project Consultant, Biological Consultants, Lami, Fiji