Microtiter plate, optode respirometry, and inter-individual variance in metabolic rates among nauplii of Artemia sp.

Understanding the potential metabolic lifespan of a cohort of marine invertebrate embryos or larvae requires not just precise measurements of respiration rates, but also requires a large number of individual-level measurements to accurately describe the distribution of metabolic rate potentials within that cohort. To this end, we have developed a simple protocol for converting a 384-well microtiter plate into a 384-chamber, microrespirometer, optode using a plate-reading fluorometer for continuous, real-time data acquisition. We have ground-truthed this high-throughput technique using Artemia sp. nauplii at -48 h post-hydration. In this paper we present > 1000 separate respiration rate measurements on nauplii, providing a novel look at the distribution of metabolic rates within a cohort of larvae. At this high level of individual sampling, we have applied a Shannon-Weaver information entropy statistic to describe the 'complexity' of these rate distributions and to show that the range of metabolic phenotypes expressed in a group of nauplii is responsive to the salinity in which they are rehydrated. Understanding the nature and mechanisms by which variations in metabolic rate intensities can be so large within a cohort and can be responsive to environmental parameters represents a real challenge in larval biology, which will require high-throughput methodologies at both molecular and biochemical levels to decipher.