Methods

Site Description:

The study was conducted at Rancho Mastatal in the tropical rainforest of Costa Rica (latitude 9 45'N, longitude 84 18' W, altitude 250 m). Data was collected at two randomly selected sites of the adjacent riverbanks of the Rio Quebrada Grande and Rio Negro streams.

The site at Rio Q. Grande is 25 m long and 5 m wide. The Rio Negro site is 21.4 m long and 6 m wide.

Data Collection:

Fieldwork was carried out during July 10-21, 2005. The size of the individual rocks and patches was measured. The biomass was estimated by ocular approximation of percent coverage. The overstory density of the sites was measured with a densiometer in all four directions. Water velocity was measured with a timer and a ping pong ball. Five trials were recorded at each site and the average river velocity was obtained.

Data Analysis:

The data was analyzed with Excel. T-tests were performed for each of the factors in order to determined whether the perceived differences are statistically significant.