1Akita Prefectural Fisheries Promotion Center, Oga, Akita 010-0531, 2Laboratory of Applied Aquatic Botany, Graduate School of Agricultural Science, Tohoku University, Sendai, Miyagi 981-8555, Japan
Seasonal changes and productivity of the Coccophora langsdorfii population at depths of 1-3m off the coast of Oga Peninsula were studied from August 1993 to August 1994. The new thalli with filamentous leaves which were germinated from perennial holdfasts appeared in September and grew gradually in winter. Then, they grew rapidly in spring. In June, their length and biomass reached the maximum values of 52cm and 5,974gwet/m2, respectively. Filamentous leaves shed remarkably from July to September. On the contrary, numerous new branches with ramentacious leaves on thalli grew from September to December. In January, maximum length of 53cm and biomass of 6,503gwet/m2 were recorded in thalli of one year old, and receptacles began to form at the tips of the branches. Eggs were released from receptacles when the sea surface temperature exceeded 8°C in April. After maturation, the thalli gradually withered and shed in spring and summer, and decayed away in November, two years after appearance. The annual net production of C. langsdorfii was calculated to be 10,478.8gwet/m2 by using the stratified clip technique.