PHOTOSYNTHESIS AND RESPIRATION OF THE CONCHOCELIS STAGE OF ALASKAN PORPHYRA (BANGIALES, RHODOPHYTA) SPECIES IN RESPONSE TO ENVIRONMENTAL VARIABLES 1

Photosynthesis and respiration of three Alaskan Porphyra species, P. abbottiae V. Krishnam., P. pseudolinearis Ueda species complex (identified as P.  “ pseudolinearis ” below), and P. torta V. Krishnam., were investigated under a range of environmental parameters. Photosynthesis versus irradiance ( P – I ) curves revealed that maximal photosynthesis ( P max ), irradiance at maximal photosynthesis ( I max ), and compensation irradiance ( I c ) varied with salinity, temperature, and species. The P max of Porphyra abbottiae conchocelis varied between 83 and 240 μmol O 2  · g dwt −1  · h −1 (where dwt indicates dry weight) at 30–140 μmol photons · m −2  · s −1 ( I max ) depending on temperature. Higher irradiances resulted in photoinhibition. Maximal photosynthesis of the conchocelis of P. abbottiae occurred at 11°C, 60 μmol photons · m −2 ·s −1 , and 30 psu (practical salinity units). The conchocelis of P. “pseudolinearis” and P. torta had similar P max values but higher I max values than those of P. abbottiae . The P max of P. “pseudolinearis” conchocelis was 200–240 μmol O 2  · g dwt −1  · h −1 and for P. torta was 90–240 μmol O 2  · g dwt −1  · h −1 . Maximal photosynthesis for P. “pseudolinearis” occurred at 7°C and 250 μmol photons · m −2  · s −1 at 30 psu, but P max did not change much with temperature. Maximal photosynthesis for P. torta occurred at 15°C, 200 μmol photons · m −2  · s −1 , and 30 psu. Photosynthesis rates for all species declined at salinities <25 or >35 psu. Estimated compensation irradiances ( I c ) were relatively low (3–5 μmol · photons · m −2  · s −1 ) for intertidal macrophytes. Porphyra conchocelis had lower respiration rates at 7°C than at 11°C or 15°C. All three species exhibited minimal respiration rates at salinities between 25 and 35 psu.