Bacterivory by tropical copepod nauplii: extent and possible significance

Abstract

Copepod nauplii may be an important intermediary between the 'microbial' and 'classical' pelagic marine food webs. In studies of planktonic food webs, along a trophic gradient from eutroph~c harbour through coastal to oligotrophic oceanic waters off Jamaica, West Indies, we investigated bacterivory by nauplii of 11 representative copepod taxa (n = 176 total nauplii) using fluorescently labelled bacteria (FLB) of 0.7 pmholume at concentrations of 1.5 to 2.5 X 10"ells ml-l Seven taxa consistently ingested FLB: Acartia liljeborgii, Paracalanus spp., Temora stylifera, T turbinata, Oncaea spp., Undinula vulgaris, Oithona spp.; 4 taxa consistently did not: Centropages velificatus, CJausocalanus spp., Euchaeta marina, and Corycaeus spp. These data, and the observations that naupliar moulting and growth rates were uncoupled from chlorophyll a concentrations in any size fraction over the range 0.09 to 4.7 mg m-3, suggest that nauphi are not food limited even in oceanic waters. Calculations indicate that daily food requirements of oceanic nauplii can be met from a diet of bacteria and picoplankton, but not from a diet of nano-and net-phytoplankton. Naupliar production in oceanic waters is at least 50 to 60% of copepodite production; it appears therefore that the ecological importance of copepod nauplii in oceanic waters has been greatly underestimated.