Original paper

Morphometrical variations in two cyanoprokaryote populations from tropical streams

Branco, Luis Henrique Z.

Abstract

Two cyanoprokaryote populations (Phormidium allorgei and Porphyrosiphon martensianus) were monthly sampled from May 1998 to May 1999 in order to study the stability of specific characteristics of the populations and to evaluate the role of running water forces on the morphological expression of the specimens. 10 sampling units (15 cm diameter circles) were randomly taken in each collection and specific environmental characteristics (depth, current velocity, substratum and irradiance) of the units were measured. Selected physical and chemical variables (pH, specific conductance, dissolved oxygen, water temperature, turbidity, total nitrogen, ammonium, nitrate, nitrite, and total phosphorus) were also evaluated at each sampling. Cell diameter, cell length and cell length/diameter ratio parameters were evaluated and compared. The P. allorgei population presented high and constant statistical differences for cell diameter among sampling units of same collections as well as the P. martensianus population. Statistical differences of cell length and cell length/diameter ratio were also observed in the two populations, however they were not so constant as for cell diameter. Qualitative characteristics (constriction, necridia, granulated cross-walls) were also evaluated and their occurrence was also considered variable and related to some environmental parameters. These data indicate a reasonably morphological variability of specimens that are statistically related to microenvironmental (depth and current velocity) and macroenvironmental variables (specific conductance and turbidity). However, the ranges of variation are within the range provided by many authors for the two species, except in a few sampling units or sampling months. These deviations from the normal ranges of the species can drive to erroneous identifications. Thus, corroborating previous studies, it is demonstrated that taxonomic evaluation requires extensive observation and large samplings (considering also the microhabitat approach) for a better interpretation of the populational variation ranges that allow a more confident species identification.

Keywords

cyanoprokaryotacyanobacteriataxonomymorphological variationstreamsphormidium allorgeiporphyrosiphon martensianus