RESUMO
Biovolume variation of twelve centric diatom species from eight natural habitats of the northeastem continental shelf of Venezuela were analyzed. Also, the morphometric variable that exerts the greatest influence on the biovolume was determined. Samples were collected with a net (mesh 36 microns), or with a Niskin bottle (5 l) and fixed with neutralized formaldehyde (4 per cent). Water temperature and salinity were measured. The species studied were: Detonula sp., Skeletonema costatum, Lauderia annulata, Pseudoguinardia recta, Cerataulina pelagica, Helicotheca tamesis, Rhizosolenia styliformis, Proboscia alata, Guinardia flaccida, G. striata, Dactyliosolen fragilissimus y Leptocylindrus danicus. Forty individuals of each species from each locality were isolated and measured with a Leitz Wetzlar binocular microscope with an ocular micrometer, magnified 400X. A one-way ANOVA showed the existence of highly significant differences (p < 0.001) in the biovolume of the species regarded with its locality. These differences could be due to: (a) temporal differences in sample collection: (b) the existence of populations in different phases of their vital cycles; (c) genetic differences; (d) and differences in the physical-chemical environment at each locality. The diameter was the morphometric variable exhibiting the largest positive correlation (r > or = 0.77, p < 0.001) with biovolume for all species, except for H. tamesis. In the latter, the apical axis (or side) exhibited the best correlation with biovolume (r = 0.94, p < 0.001). The high correlation between the diameter and/or the apical axis with the biovolumen suggests that the latter could be predicted from these morphometric variables with great reliability in these species.