COMPARISON OF 3 TECHNIQUES FOR ESTIMATING PERIPHYTON ABUNDANCE IN BEDROCK STREAMS

Three procedures (line transect, point intercept and quadrat) for esti mating abundance of macroscopic components of periphyton (macroalgae a nd bryophytes) were compared in two bedrock streams from southeastern Brazil on the basis of frequency and percent cover. In addition, two q uadrat sizes (25 and 50 cm) were tested for best size. Samplings were all made within a 10 m length stream reach. Differences were tested by means of analysis of variance, ANOVA - one way, Student's t test and Chi-square test, whereas associations among them were evaluated by Pea rson's r correlation coefficient. Values of frequency and percent cove r varied among the different techniques and periphyton species in both sites but ANOVA, t and Chi-square tests revealed no significant diffe rence (p<0.05) for percent cover in the two sites. No consistent patte rn was observed for the different procedures between sites. Values for quadrat (25 and 50 cm) percent cover were positively correlated among distinct periphyton species. Significant differences for frequency we re found in only one site. Quadrats of 50 cm produced the highest freq uency values, whereas point intercept the lowest in both sites. In ter ms of spatial variation within the stream segment, significant differe nces were generally observed among all procedures, except between quad rats. As a rule, highly significant correlations for percent cover wer e found among the different techniques along the stream reach. The str ongest relationships were found for quadrats with the other procedures , whereas the weakest between Line and point. Pros and cons of the thr ee techniques are fully discussed.