Current Problems in Marine Biodiversity Studies

This paper deals with a discussion of terminology and six proposed levels of biodiversity. Recent data and estimates were used to compare species and taxonomic diversity of terrestrial, freshwater, and marine organisms. About 1.5 million terrestrial species and 320000 aquatic species are hitherto known. In spite of a long history of research, only about 280000 marine species have been discovered, of which 180000 species are invertebrates. Of 33 metazoan phyla, 31 are found in the sea, 13 of these being exclusively marine. Seventeen metazoan phyla contain freshwater species, and only 11 phyla comprise terrestrial animals. Two phyla (freshwater Micrognathozoa and terrestrial Onychophora) possess no marine species. In this paper, we review the assessment reports on marine biological diversity in coral reefs, coastal ecosystems, macrobenthos, and meiofauna. Recent data on the number of known species are listed for each metazoan phylum; the number of anticipated new species to be discovered is estimated. Deep-sea macrobenthos are believed to comprise about 25 million species; meiofauna seems to be composed of 20 to 30 million species, ten million of whom are marine nematodes. Hypotheses are discussed that can account for the high species diversity of deep-sea macrobenthos and meiofauna.