Census of Marine Life, the global project I'm involved in, released a collection of research papers on marine species and biodiversity on PLoS ONE. It is safe to say that they are the most comprehensive assessments of marine species and biodiversity in the human history. The researches were conducted by region.
A news article published on Nature is a good summary of the collection. It reports that while discoveries of new species will continue, the species and biodiversity in oceans are under threats such as overfishing, habitat loss, endemic species, and pollution along with emerging sea temperature rise and acidification due to the global warming.
Please refer to the Census press release, too.