The Importance of Small Planktonic Copepods and Their Roles in Pelagic Marine Food Webs

Abstract

Jefferson T. Turner (2004) The importance of small planktonic copepods and their roles in pelagic marine food webs. Zoological Studies 43(2): 255-266. Small planktonic marine copepods (< 1 mm in length) are the most abundant metazoans on Earth. Included are adults and copepodites of calanoid genera such as Paracalanus, Clausocalanus, and Acartia; cyclopoid genera such as Oithona, Oncaea, and Corycaeus; plank-tonic harpacticoids of the genus Microsetella; and nauplii of almost all copepod species. Despite the abun-dance of small copepods, they have historically been undersampled due to the use of nets with meshes> 200-333 µm. Recent studies have shown, however, that when appropriate net meshes of 100 µm or less are used, small copepods vastly exceed the abundance and sometimes the biomass of larger ones. Failure to adequate-ly account for small copepods may cause serious underestimations of zooplankton abundance and biomass, the copepod grazing impact on phytoplankton primary production, zooplankton-mediated fluxes of chemicals and materials, and trophic interactions in the sea. The feeding ecology of small copepods is less well-known than that of adults of larger copepod species, such as members of the genus Calanus. Further, most feeding information for small copepods is for coastal genera such as Acartia, rather than for offshore taxa. Although it is generally assumed that small copepods, including nauplii, feed primarily upon small-sized phytoplankton cells, most such information comes from rearing or feeding studies on limited laboratory diets. There have