Precision of different methods used for estimating the abundance of the nitrogen-fixing marine cyanobacterium, Trichodesmium Ehrenberg.

Variances involved in estimating the abundance of the nitrogen-fixing marine cyanobacterium, Trichodesmium Ehrenberg, were evaluated by repeated sampling using bottle casts and plankton net tows at two stations in the southern East China Sea. The variance among individual samples and the variance arising from subsampling processes were separated by the method of analysis of variance, and the coefficient of variation (C.V.) of an abundance estimate based on a single subsample was calculated. For bottle-collected samples, the major source of variation came from taking subsamples from a water bottle. The C.V. of a single subsample estimate ranged from 57% to 184%. For net-collected samples, variance in abundance estimation was mainly caused by distinctive net tows, and when distributing materials in the receiving bucket into smaller containers. The C.V.s of single subsample estimates were 34% and 40%, respectively. Trichodesmium abundance estimated with bottle- and net-collected samples were further compared using data obtained from 17 stations in the East China Sea. Although a general distribution pattern was supported by both methods, the correlation coefficient between them was 0.461, not significantly different from 0.