set.seed(8)
messy <- data.frame(id = 1:4,
                          trt = sample(rep(c('control', 'farm'), each = 2)),
               zooplankton.T1 = runif(4),
                      fish.T1 = runif(4),
               zooplankton.T2 = runif(4),
                      fish.T2 = runif(4))
messy