Journal of Applied Phycology 16: 227–235, 2004. C  2004 Kluwer Academic Publishers. Printed in the Netherlands. 227 Photosynthetic performance of transplanted ecotypes of Ecklonia cava (Laminariales, Phaeophyta) Yukihiko Serisawa 1,∗ , Yasutsugu Yokohama 2 , Yusho Aruga 3 and Alecia Bellgrove 4 1 Marine Biosystems Research Center, Chiba University, Amatsu-kominato, Awa-gun, Chiba 299-5502, Japan (JSPS Research Fellow); 2 Shizugawa Nature Center, Shizugawa, Motoyoshi-gun, Miyagi 986-0781, Japan; 3 Department of International Agriculture Development, Tokyo University of Agriculture, Sakuragaoka 1-1-1, Setagaya-ku, Tokyo 156-8502, Japan; 4 School of Ecology & Environment, Deakin University, PO Box 423, Warrnambool, Victoria 3280, Australia ∗ Author for correspondence (e-mail: yukihikoserisawa@mail.goo.ne.jp) Received: 20 August 2003; accepted in revised form 6 April 2004 Key words: artificial reef, Ecklonia cava, ecophysiology, ecotype, Laminariales, photosynthesis, respiration, transplant experiment Abstract Young sporophytes of short-stipe ecotype of Ecklonia cava from a warmer locality (Tei, Kochi Pref., south- ern Japan) and those of long-stipe ecotype from a cooler locality (Nabeta, Shizuoka Pref., central Japan) were transplanted in 1995 to artificial reefs immersed at the habitat of long-stipe ecotype in Nabeta Bay, Shizuoka Pref., central Japan. The characteristics of photosynthesis and respiration of bladelets of the trans- planted sporophytes of the two ecotypes were compared in winter and summer 1997; the results were as- sessed per unit area, per unit chlorophyll a content and per unit dry weight. In photosynthesis-light curves at 10–29 ◦ C, light saturation occurred at 200–400 μmol photon m –2 s –1 in sporophytes from both Tei and Nabeta. The maximum photosynthetic rate ( P max ) at 10–29 ◦ C and the light-saturation index ( I k ) at 25–29 ◦ C in sporophytes from both localities were generally higher in winter than in summer. P max at 25–29 ◦ C (per unit area and chlorophyll a) were higher in sporophytes from Tei than those from Nabeta in both seasons. The optimum temperature for photosynthesis was 25 ◦ C in winter and 27 ◦ C in summer at high light intensities of 100–400 μmol photon m –2 s –1 . However, at lower light intensities of 12.5–50 μmol photon m –2 s –1 , it was 20 ◦ C in winter and 25–27 ◦ C in summer for sporophytes from both locations. Dark respiration increased with temperature rise in the range of 10–29 ◦ C in sporophytes from both locations in summer and winter. The sporophytes transplanted from Tei (warmer area) showed higher photosynthetic activities than those from Nabeta (cooler area) at warmer temperatures even under the same environmental conditions. This indicates that these physiological ecotypes have arisen from genetic differentiation. 1. Introduction Sporophytes of Ecklonia cava Kjellman form dense kelp bed called “marine forest” on subtidal rocky sub- strata from central to southern Japan (Kawashima, 1993; Terawaki, 1993). Marine forests play important roles as nursery and breeding grounds for commer- cial fish, shellfish and other animals (Ohno, 1985) as well as being significant primary producers (Tominaga et al., 2004; Yokohama et al., 1987). Intraspecific morphological variations have been described for several brown algae with a number of different ecotypes described for some species (e.g., Hormosira banksii (Clarke and Womersley, 1981; Ralph et al., 1998)). Two ecotypes of E. cava have been reported: sporophytes occurring in warm waters along the coasts of Shikoku and Kyushu (southern Japan) usually have short stipes (10–30 cm) (Tsukidate et al., 1991; Tominaga et al., 1999; Serisawa et al., 2002a, b), whereas those growing in cooler waters along the