Abstract

SANCHEZ¹, Gloria E; MORALES², Ever; GUILLOT³, Gabriel  and  VIDAL¹, Luis A. RESPONSE OF THE DIATOM ACTINOCYCLUS NORMANII HUSTEDT TO VARIATIONS IN INITIAL CELLULAR DENSITY, SALINITY, SILICATE, AND PHOSPHATE CONCENTRATIONS IN LABORATORY CONDITIONS. Bol. Invest. Mar. Cost. [online]. 2003, vol.32, n.1, pp.169-181. ISSN 0122-9761.

Microalgae are important for the restoration of coastal lagoon ecosystems affected by human activities because they are useful indicators of variations of salinity and levels of nutrients such as silicate and phosphate in the water column. With the centric diatom Actinocyclus normanii from Ciénaga Grande de Santa Marta (Colombian Caribbean) we conducted several experiments to evaluate the responses of this species at three levels of salinity (0, 15 and 25) and two initial densities (100 and 800 cells·ml^-1) to nine treatments combining several concentrations of phosphate (0, 1,5 and 3,0 μmol·l^-1) and silicate (10, 150 and 300 μmol·l^-1). All treatments were maintained with light intensity of 57,9 mE^-2·seg^-1, photoperiod of 12:12 hrs, temperature between 22 and 24 ^oC and constant aeration.  Results show that A. normanii grows in function of silicate, phosphate and salinity but silicate exerts a more important effect than phosphate while high salinity reduced the density of cells.  The treatment that combined concentrations of 300 µmol·l^-1 silicate and 3 µmol·l^-1 phosphate achieved the highest density (11.700 cells·ml^-1) at salinity 0. This density is 12 fold than the obtained with the lowest silicate and phosphate concentrations in non-saline medium. Growth of A. normanii decreases with salinity, despite that the species exhibit certain degree of halotolerance, thus this species can be considered as indicator of non saline and (at least) silicate enriched conditions.

Keywords : Actinocyclus; Bioindicator; Culture; Phosphate; Salinity; Silicate.

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