A method for accurate measurements of the respiration rates of marine invertebrate embryos and larvae

Abstract

Measurements of respiration rates are essential to quantify the energy requirements of embryos and larvae. Here we describe a 'μBOD' method that employs small (< 1 ml) Biological Oxygen Demand (BOD) glass vials in which embryos and larvae are incubated. A decrease in oxygen concentration is measured by injecting seawater from each vial into the measurement chamber of a standard polarographic oxygen sensor. This μBOD method was used to measure respiration rates of larvae of the sea urchin Strongylocentrotus purpuratus (at 15°C) and embryos and larvae of 2 Antarctic echinoderms, the sea urchin Sterechinus neumayeri and the seastar Odontaster validus (both at -1.5°C). For validation, a comparison of different methods was performed with embryos and larvae of S. neumayeri. The μBOD method gave results for respiration rates during development that were equivalent to those obtained with either coulometric capacitance respirometry or standard Winkler's titrations of large (300 ml) BOD bottles. Currently, the most common method for measuring respiration rates of invertebrate embryos and larvae is to place them in small respiration chambers and continuously monitor oxygen tension with a polarographic oxygen sensor (POS). However, respiration rates for embryos and larvae of S. neumayeri were underestimated when standard POS measurements were compared to the measurements made with either μBOD, Winkler's titrations or coulometric capacitance respirometry. A comparison of the μBOD and POS methods during early development in S. neumayeri resulted in different estimates of 920 and 343 μJ, respectively, for the total energetic cost of embryogenesis to gastrulation, illustrating that the POS error can be as great as 63%. The μBOD method is accurate for micro-respiration measurements of invertebrate embryos and larvae as well as being simple to operate and appropriate for field work.