An ecophysiological study of Porphyra species from Long Island Sound (USA)

Date of Completion

January 2004

Keywords

Biology, Botany|Biology, Oceanography|Biology, Plant Physiology

Degree

Ph.D.

Abstract

Several species of Porphyra occurs in LIS (U.S.A.), however, little was known about their spatial and temporal occurrence, as well as many aspects of their ecophysiology. Hence, one site at Horse Shoe Beach, Cove Island Park, Stamford, CT was chosen to be monitored from January 1999 to May 2002. Samples of P. suborbiculata (Kjellm.), P. purpurea (Roth) C. Agardh, and P. leucosticta (Thuret in Le Jol.) as well as two strains of P. leucosticta i. e Type A and Type C (sensu Neefus et al. 2000) from LIS, were used in short-term nutrient-uptake experiments. Samples were taken at specific times during the experiments to analyze content for total C, total N, phycoerythrin, phycocyanin, phycoallocyanin, FAA and dry weight. Experiments were also performed to determine each types photosynthetic characteristics. ^ At the monitoring site, only three species of Porphyra species were found. The eurythermic Porphyra suborbiculata inhabited the upper midlittoral. The winter-species Porphyra leucosticta Type A was found in lower midlittoral and the infralittoral fringe as opposed to the other winter-species P. leucosticta Type C that was found in the midlittoral, with its peak in the middle to lower part. As for several other species at the site, the abundance of the Porphyra species was correlated to change in seawater and air temperature among years. ^ At 25°C, P. suborbiculata reached a Pmax of almost 90 μmol O2·g−1DW·min −1. The efficiency coefficient (a) was twice as high in P. leucosticta Type A than in P. purpurea and P. suborbiculata and showed an increased with temperature only for P. suborbiculata. Porphyra leucosticta Type A showed signs of chronic photodamaged in temperatures above 15°C at 1650 pmol photon-m−2 ·s−1. ^ During the uptake experiments, no differences in nitrate uptake-rates were found between stenothermic and eurythermic species of Porphyra . However, average initial uptake rates by Porphyra spp. were rather high (max V0-1h30mM = 73.8μmo1 NO3·g−1DW h −1), demonstrating the ability to quickly absorb nitrate from the medium. FAA content in the summer-species Porphyra purpurea was much lower than for the winter-species and was the only species that showed an initiation of FAA synthesis during the short-term experiments. ^

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