Seasonal variation in photosynthesis and biochemical composition of Caulerpa spp. (Bryopsidales, Chlorophyta) from the Gulf of Mexico

Abstract

D. Robledo and Y. Freile-Pelegrín. 2005. Seasonal variation in photosynthesis and biochemical composition of Caulerpa spp. (Bryopsidales, Chlorophyta) from the Gulf of Mexico. Phycologia 44: 312–319.Photosynthesis, pigment content, soluble carbohydrate, and protein levels of six Caulerpa species were examined on a seasonal basis from samples taken along the northern coast of the Yucatan Peninsula, Mexico, between June 1998 and August 1999. For Caulerpa ashmeadii, C. mexicana, C. paspaloides, and C. racemosa photosynthetic capacity changed depending on seasonal trends in photon flux density and water temperature in the study area. This pattern was not evident in Caulerpa prolifera and C. cupressoides. Maximum photosynthetic rates of 18.3 ± 0.8 mg O2 g dry weight−1 h−1 were obtained in C. mexicana during the cold season. Photosynthetic efficiency (α) showed a similar pattern to that of Pmax coinciding with low irradiances (photon flux density [PFD]: 151 ± 67 μmol photons m−2 s−1) and water temperature (23.8 ± 1.9°C), and the highest levels of dissolved inorganic nitrogen and dissolved reactive phosphorous in the water (9.1 μmol l−1 and 0.5 μmol l−1, respectively). Compensation (Ec) and saturation (Ek) irradiances were low and ranged from 3 to 35 and 44 to 280 μmol photons m−2 s−1, respectively. Maximum chlorophyll a and b (Chl a and b) levels occurred in C. racemosa and C. cupressoides during the cold to rainy seasons. The highest Chl b : a ratios were observed during the coldest months for all studied species. Protein and carbohydrate contents in Caulerpa spp. followed an inverse seasonal pattern. In general, high protein levels were observed in the dry season coinciding with increasing light and seawater temperatures. Photosynthesis in Caulerpa spp. from the Yucatan Peninsula coast is affected by high temperatures during the dry and rainy seasons. There is also a seasonal shift in the species proximate constituents indicative of a rapid growth period from January to May and a carbohydrate accumulation period during the rest of the year.