> gros.degat.long <- gather(gros.degat, taxa, count, -id, -trt)
> head(gros.degat.long)
  id      trt           taxa     count
1  1 controle zooplancton.T1 0.3215092
2  2 controle zooplancton.T1 0.7189275
3  3  culture zooplancton.T1 0.2908734
4  4  culture zooplancton.T1 0.9322698
5  1 controle     poisson.T1 0.7691470
6  2 controle     poisson.T1 0.6444911