Growth and pigmentation of juvenile Porphyra torta (Rhodophyta) gametophytes in response to nitrate, salinity and inorganic carbon

The leafy gametophytic phase of Porphyra torta Krishnamurthy(Rhodophyta), a candidate species for mariculture in Alaska, grows only inwinter and early spring and is restricted to the outer coast of southeastAlaska. To help determine specific environmental factors limiting theseasonal and geographic distribution of this species, culture experimentswere conducted using environmentally realistic levels of three physicalfactors. Growth and phycoerythrin concentration in juvenile gametophyteswere compared under combinations of nitrate, salinity, and inorganiccarbon representing the maximum and minimum levels of each factor in themarine environment. Recovery experiments were also conducted todetermine whether blades affected by low nutrient or salinity levels couldregain normal growth rates and pigment levels. To make statistically validcomparisons of growth rates among treatment groups, where repeatedmeasures were used, a two-stage analysis was tested and found to beappropriate. Low nitrate had a significant, negative effect on growth andphycoerythrin concentration. Salinity had a weak, negative effect on bladegrowth, while inorganic carbon had no observed effect on blade growth,and neither had a significant effect on phycoerythrin concentration. Bladesaffected by low nitrate were able to regain normal growth rates and higherthan normal pigment levels when nitrate was increased, after up to 6 weeksof exposure. The growth rate, modeled from the data, increased with timeinitially, dependent on nitrate level.