| Abstract: | A planktonic alga similar in general morphology and pigments to Aureococcus anophagefferens Hargraves and Sieburth has caused persistent and ecologically damaging blooms along the south Texas coast. Experiments using 100 μM NO3?, NO2?, and NH4+ demonstrated that the alga could not use NO3? for growth but could use NO2? and NH4+. Doubling iron or trace metal concentrations did not permit growth on NO3?. Chemical composition data for cultures grown in excess NO3? or NH4+, respectively, were as follows: N·cell?1 (0.88 vs. 1.3 pg), C:N ratio (25:1 vs. 6.4:1), C:chlorophyll a (chl a) (560:1 vs. 44:1), and chl a·cell?1 (0.033 vs. 0.16 pg). These data imply that cells supplied with NO3? were N-starved. Culture addition of 10 mM final concentration chlorate (a nitrate analog) did not affect the Texas isolate while NO3? utilizing A. anophagefferens was lysed, suggesting that the NO3? reductase of the Texas isolate is nonfunctional. Rates of primary productivity determined during a dense bloom indicated that light-saturated growth rates were ca. 0.45 d?1, which is similar to maximum rates determined in laboratory experiments (0.58 d?1± 0.16). However, chemical composition data were consistent with the growth rate of these cells being limited by N availability (C:N 28, C:chl a 176, chl a·cell?1 0.019). Calculations based on a mass balance for nitrogen suggest that the bloom was triggered by an input of ca. 69 μM NH4+ that resulted from an extensive die-off of benthos and fish. |
