Seasonal variation of photosynthetic properties of Ecklonia cava (Laminariales, Phaeophyta) in Nabeta Bay, central Japan

Abstract

The research was carried out to quantify the photosynthetic rates of a perennial seawced Echlonia cava KJELLMAN (Laminariales, lPhaeophyta) with monthly samplings frorm April 1986 to April 1987. Photosynthesis and respiration were measured by a differential gas-volumeter in several bladelels. The photosynlhesis-light cutves were defferent among bladelets almost every month; however, in winter, when all the bladelets were new, the curves were quite similar. On a frond area basis, the youngest bladelets showed higher net photosynthesis than the older ones. with highest Pmas values (44-49 μΙO, cm -2 h -1 , ) in early spring and lowest (19--31 μΙO, cm -2 h -1) in autumn. the reproductive period. On a dry weight basis, the P mas, values showed a hierarchical order inversely relaated 1to the thickness of the bladelets. with a maximum in the 2nd bladelet and a mínimum in the 11th. On a cholorophyll a basis, the hierarchical order was similar to that on a dry weight basis, but Pmas did not show any big seasonal variation. The respiration rate of each bladelet was quite stable throughout the year, except for the 2nd bladelet with two high peaks in November and February, lhe formation periods of auturmn and winter bladelets respectively. The photosynthetic respose of E. cava blade is closely related to its growth process. The blade of this species apparently adjusts its pigment content to the prevailing light conditions in the surrounding water.