PHOSPHORUS AND NITROGEN NUTRITION IN CHONDRUS CRISPUS (RHODOPHYTA): EFFECTS ON TOTAL PHOSPHORUS AND NITROGEN CONTENT, CARRAGEENAN PRODUCTION, AND PHOTOSYNTHETIC PIGMENTS AND METABOLISM 1

The existence of a phenomenon in phosphorus (P) nutrition comparable to the “Neish effect” in nitrogen (N) nutrition (an inverse relation between seawater N enrichment and carrageenan content) was investigated in the temperate red alga Chondrus crispus Stackhouse. Plants were preconditioned for 17 d and then cultured under varying enrichments of P (0, 3, 6, 10, 15 μM P·wk −1 ) and a constant N enrichment (53.5 μM N·wk −1 ) for 5 wk. Tissue total P, tissue total N, and carrageenan contents were then determined. Identical experiments were performed using C. crispus collected during the fall, winter, spring, and summer seasons. The procedure was repeated using material collected during the following fall season and cultured under constant P (6 μM P·wk −1 ) and varying N enrichments (0, 3, 6, 10, 25 μM N·wk −1 ). In the fall (P) experiment, carrageenan content was the highest [53.1 ± 0.3% DW (dry weight)], and tissue total P content was the lowest (1.71 ± 0.27 mg P·g DW −1 ) in plants that received no P enrichment. Carrageenan content was stable (46.1 ± 1.8% DW) for plants given enrichments of 3 μM P·wk −1 and greater. Thus, a decrease in carrageenan content, concomitant with an increase in tissue total P content, was observed, but only at tissue total P levels below 2 mg P·g DW −1 . As these levels were always higher than 2 mg P·g DW −1 in the winter, spring, and summer experiments, carrageenan content remained constant within each season at 46.2 ± 1.3, 43.1 m 0.7, and 44.5 ± 0.6% DW, respectively. Nitrogen enrichment of plants collected in the fall did not affect carrageenan content, which was stable at 49.3 ± 0.9% DW. When these plants were compared with those of the previous fall experiment (6 μM P·wk −1 and 53.5 μM N·wk −1 ), a slight increase in carrageenan content was noted. Thus, at sufficiently high concentration, N also decreased carrageenan content in C. crispus. Phosphorus nutrition had no significant effect on photosynthesis versus irradiance parameters (P max , α, R d , I c , and I k ), the contents of the photosynthetic pigments chlorophyll‐ a , phycoerythrin (PE), phycocyanin (PC), and allophycocyanin (APC), and the ratios PE:APC and PC:APC. In contrast, N nutrition affected both P max and the photosynthetic pigment contents. The data indicate that N limitation reduces the number of phycobilisomes but not their size. The greater reduction in phycobiliprotein than chlorophyll ‐a content corroborates the natural bleaching phenomenon regularly observed in C. crispus populations during summer when N levels are generally low in seawater. These results suggest that C. crispus in the temperate waters of the Bay of Fundy may experience N limitation, but P limitation is unlikely .