Investigating copepod feeding using a high throughput spectrofluorometric assay

In most aquatic ecosystems, copepod nauplii outnumber all other mesozooplankton. Although\ud thousands of studies have examined feeding by later life history stages, the feeding habits of\ud nauplii are poorly known. We investigated feeding by nauplii by comparing their feeding to\ud conspecific adults. We offered adult and naupliar stages of the current-feeding calanoid copepod\ud Pseudodiaptomus marinus and the ambush-feeding cyclopoid copepod Oithona davisae 14\ud species of phytoplankton spanning various functional and taxonomic groups. Using\ud epifluorescence microscopy, we calculated an index of pigment in the guts of copepods fed each\ud phytoplankton species. We also measured adult and naupliar feeding rates on three species of\ud phytoplankton, the cryptomonad Rhodomonas salina, the prasinophyte Tetraselmis suecica, and\ud the diatom Thalassiosira pseudonana by a gut fluorescence method using a microplate reader.\ud Despite their smaller size, weaker swimming and sensory capabilities, and rudimentary feeding\ud apparatus, nauplii fed on a large range of cell sizes and were capable of consuming many of the\ud same phytoplankton as adults. This study expands upon our formerly limited knowledge of the\ud feeding capabilities and potential trophic roles of nauplii in aquatic food webs