Photosynthetic characteristics and C:N ratios of macroalgae from King George Island (Antarctica)

During an expedition to King George Island, the photosynthetic characteristics of 36 macroalgal species common to the South Shetland Islands (Antarctica) have been investigated. Plant material was sampled during Antarctic spring by scuba diving in the area of Maxwell Bay. Photosynthesis versus irradiance curves were obtained by determination of oxygen consumption or production of the species. Rates of maximum photosynthesis (P max) were similar to P max rates measured in earlier field and laboratory studies of Antarctic species. The present investigation shows that the photosynthetic characteristics of Antarctic macroalgae are clearly related to thallus structure, with highest rates of P max, photosynthetic efficiency (α) and dark respiration and highest Chl a contents being observed in filamentous and foliose species. The light requirements of most studied species are generally low as indicated by the high α (0.2–4.4 μmol O 2 g −1 h −1 (μmol s −1 m −2) −1) as well as low values for intial saturation of photo synthesis (Ik values) (14–49 μmol m −2 s −1) and low compensation points (Ic values) (4.5–14.7 μmol m −2 s −1), important prerequisites for survival in Antarctic waters especially with regard to the long periods of dim light. In some deep water species α was particularly high compared to species from the upper sublittoral. Some intertidal species, however, were characterised by both high α and high P max values. The C:N ratios were significantly lower in the filamentous and foliose compared to the terete and leathery species. In general, low values of between five and ten were determined reflecting the high inorganic N supply found in Antarctic waters.