Is Oithona the most important copepod in the worlds oceans?
Oithona has been described as the most ubiquitous and abundant copepod in the world’s oceans. Most of our knowledge of zooplankton abundance and distribution is derived from net samples whose mesh size is often 200 µm or greater, and researchers have commented on losses of smaller organisms such as Oithona and Oncaea, as well as juvenile forms of larger copepods, from these nets. We review the literature on this subject over the last 50 years, and note that such nets remain in common use for estimating the abundance, biomass and productivity of mesozooplankton. We show that an important fraction of mesozooplankton between 200 and 800 µm in length is significantly under-represented in many current and historical data sets. A 5 year study of the abundance and size distribution of zooplankton biomass on the Atlantic Meridional Transect has produced a very large data set covering a wide range of ecosystem types across the Atlantic Ocean, from subtropical oligotrophic to areas of upwelling
