Net Production and Incerement in Stock of the Porphyra Community in the Culture Ground

Abstract

Changes in the factors controlling the growth of the Porphyra community such as photosynthesis, respiration, and the increment in stock with the progress of the culture season were investigated under natural conditions in order to elucidate the characteristics of growth of the community in the culture ground.
Net production of the Porphyra community was calculated by subtracting the respiratory loss from the total gain by photosynthesis, and was compared with the increment in stock actually observed in the culture ground. Calculated net production coincided fairly well with the observed increment in stock in earlier period of algal growth. However, in later period the remarkable discrepancy was found between the calculated net production and the observed increment in stock. This suggests that a great part of net production was lost from the community.
Gross and net primary production of the Porphyra community was estimated on net area basis (Table 2). The daily increment in stock was 2.3g dry weight/m² net area/day for the average throughout the investigated period of two months. The observed maximum standing crop was 140g dry weight/m² net area. In the present culture ground the total amount of losses during these two months was estimated to be more than twice as much as the maximum standing crop observed.