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This study is concerned with the occurrence and growth of the brown algae, Cladosiphon sp. (Phaeophyceae, Chordariales). It is locally known as Limu Tanga'u. It is consumed in the domestic market to a limited extent but recently commercial interest in the export of Cladosiphon (Mozuku) to Japan has prompted a need for a more complete understanding of the algae.

The presence of the algae is noted in a fisheries resource profile for Tonga (Bell et al. 1994) but was not discussed separately from other seaweeds. A preliminary survey of the occurrence of the algae in the Tongatapu region was conducted during the gametophyte phase of the algae to assess its general occurrence (Billings 1996). This was largely based on anecdotal information due to the cryptic nature of the algae at that time of the year. The present study, conducted between December 1–20, 1996, was an extension of this work in which a broader understanding of the algae's occurrence throughout Tonga was made. The period of survey coincides with the end of the macroalgal or sporophyte phase of growth. The presence or absence and an estimate of the biomass of material in the field was made. The area of habitat suitable for Cladosiphon colonisation was made. Finally, the rate of growth for the algae at the late stage of its sporophyte generation was determined.

This survey was conducted at the end of the period of the specie's vegetative growth. Field and growth observations were made during a period of general senescence.

Environmental conditions such as a seasonal change in the wind pattern and the elevation of temperature have influenced the presence of Cladosiphon in December.

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