To cite package 'BENMMI' in publications use:

  Dennis Walvoort [aut, cre], Willem van Loon [aut, cph] (2020).
  Benthic Multi-Metric Index. R package version 4.3-7.
  https://CRAN.R-project.org/package=BENMMI

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {Benthic Multi-Metric Index},
    author = {Dennis Walvoort and Willem {van Loon}},
    year = {2020},
    note = {R package version 4.3-7},
    url = {https://CRAN.R-project.org/package=BENMMI},
  }

  Willem van Loon, Dennis Walvoort, Gert van Hoey, Christina
  Vina-Herbon, Abigayil Blandon, Roland Pesch, Petra Schmidt, Jorg
  Scholle, Karin Heyer, Marc Lavaleye, Graham Philips, Gerard
  Duineveld, Mats Blomqvist, 2018.  A regional benthic fauna assessment
  method for the Southern North Sea using Margalef diversity and
  reference value modelling Ecological Indicators 89:667-679.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {A regional benthic fauna assessment method for the Southern North Sea using Margalef diversity and reference value modelling},
    author = {Willem {van Loon} and Dennis Walvoort and Gert {van Hoey} and Christina Herbon and Abigayil Blandon and Roland Pesch and Petra Schmidt and Jorg Scholle and Karin Heyer and Marc Lavaleye and Graham Philips and Gerard Duineveld and Mats Blomqvist},
    journal = {Ecological Indicators},
    year = {2018},
    volume = {89},
    pages = {667-679},
  }

The first citation refers to the BENMMI-package, the second citation to
the methodology implemented in the BENMMI-package.