of a global ocean facing threats such as over-harvesting,
habitat destruction, marine pollution and the effects
of climate change, including ocean acidification due to
rising concentrations of carbon dioxide.
To a statistician, the questions and data generated
by the Census are both a dream and a nightmare – to
paraphrase the Breton fisherman’s prayer, Thy sea is so
large and my sample is so small. Here, we will review statistical
approaches to two fundamental questions raised
by the Census: how many species live in the ocean, and
how do we know when one of them has been lost?
Predicting the number of species in a taxonomic
group such as the fishes is a perennial problem in biology.
For most if not all groups, the taxonomic record
– that is, the list of species that have been identified in
the scientific literature – is incomplete. We are confident
of this because new species are discovered every year.
Indeed, since 2000, Census researchers have collected
and identified around 1200 new marine species, with
specimens of another 5000 awaiting identification. The
strange Yeti Crab shown overleaf is by no means the