Luquillo LTER

Snails were collected, counted, and measured within 0.5 x 0.5 m quadrats placed on the streambed as follow: snails on and under rocks were counted within 0.5 x 0.5 m quadrats (n=10) placed on the streambed on a weekly basis. Sampling quadrats were placed ˜1 m apart across the main channel (MC), and in five pairs along the side channel (SC). At SC, one quadrat of each pair was placed on the thalweg and another on the shallow part. In addition, a random sample of individuals was collected from each quadrat to measure shell size. Shell size was measured as aperture width (straight line running along the columnella from the base of the operculum to the shell shoulder on body whorl). Total length (TL, perpendicular to AW) is related to aperture width (AW) but cannot be measured in individuals with broken outer lips (TL=1.24AW+0.04, r2=0.98). Three sampling sites (reaches) in Río Mameyes near Route 3 Bridge were weekly to monthly sampled between August 2000 and December 2003. Near-bed water velocity was measured at 2 cm above the streambed using a Marsh-McBirney flowmeter. Each velocity measurement was averaged over 30 s and 3 to 5 measurements were made at each point. Ten points every 1 m were sampled across MC. Paired sampling points (thalweg vs. shallow) were measured in five cross sections along SC. Four habitats (point-bar and straight channel pools, a riffle, and a high flow pond) in Río Mameyes near Route 3 Bridge were weekly sampled between August and December 2000. Water depth and substrate type were measured within each quadrat. The three-most abundant substrates were classified as boulders, cobbles, pebbles, gravel or sand/fines. Plots covered >1/3 by Elodea were classified as “mats”. Nearbed water velocity was measured along cross-sections within each habitat as described in the data set "Neritina snails upstream migrations".. Discharge regime descriptors were calculated using data from USGS gage 50066000 located 50 m upstream of Route 3 bridge.