Random subsampling in R

Random subsampling in R

I am new in R, therefore my question might be really simple. I have a 40
sites with abundances of zooplankton. My data looks like this (columns are
species abundances and rows are sites)
0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 85 0 0 0 0 0 0 45 5 57 0
0 0 0 0 0 13 0 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 0 0 3 0 0 12 8 0 57 0
0 0 0 0 0 0 0 1 0 0 0 0 0 0 59 0 0 0 0 0 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 105 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 100 0 0
35 0 55 0 0 0 0 0 1 4 0 0 0 0 0 0 0 0 0 0 0 0 34 21 0 0 0 0 0 0 0 9 17 0 0
0 54 0 0 0 27 5 0 0 0 1 0 0 0 1 0 0 0 0 17 0 0 0 54 3 0 0
What I d like to is take a random subsample from each site without
replacement (e.g. 50 individuals) several times (bootstrap) in order to
calculate diversity indexes to the new standardized abundances afterwards.
I tried several commands with no success.
Every bit of help will be widely appreciated
Cheers
Paris