EFFECTS OF NITROGEN AND SEAWATER FLOW-RATE ON THE GROWTH AND BIOCHEMICAL-COMPOSITION OF GRACILARIA-FOLIIFERA VAR ANGUSTISSIMA IN MASS OUTDOOR CULTURES

The effects of nitrogen species (formula omitted and formula omitted), loading (m moles of N/day) and seawater flow rate on the growth of the red seaweed Gracilaria foliifera var. angustissima (Harvey) Taylor were investigated in outdoor culture tanks. In one experiment, cultures received seawater enriched with either (formula omitted)secondarily treated wastewater (with N as (formula omitted) but the same daily nitrogen load at four seawater turnover rates (1,7.5, 15 and 30 culture volume ex-changes/day). In another experiment, cultures were maintained at four turnover rates (1,7.5, 15 and 30 culture volume exchanges/day) with (formula omitted) at a given concentration so that nitrogen loading was proportinal to turnover rate. Below 15 m moles of N/day, algal growth was N — limited and the plants had high C/N values and appeared bleached; above 15 m moles/day, the plants had C/N values of < 10 and were a dark brown color. Above this minimal daily N loading, algal growth was highly dependant upon flow rate per se. Yield of Gracilaria was greater with (formula omitted) than (formula omitted) at nitrogen loadings just adequate to support exponential growth; however, at higher levels of nitrogen loading the maximum recorded yields (up to 44 g dry weight/m2• day-1) occurred with (formula omitted) rather than (formula omitted). Water, ash and caloric content of Gracilaria was positively correlated with C/N values in N — limited plants. Absolute levels of both phycoerythrin and chorophyll increased proportionally with decreasing C/N values of the plants. Thus the observed nitrogen-related pigment changes in Gracilaria are light intensity and not necessarily light quality adaptaons. © 1979 by Walter de Gruyter & Co.