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

Measurements of respiration rates are essential to quantify the energy requ irements of embryos and larvae. Here we describe a 'mu BOD' method that emp loys small (<1 ml) Biological Oxygen Demand (BOD) glass vials in which embr yos and larvae are incubated. A decrease in oxygen concentration is measure d by injecting seawater from each vial into the measurement chamber of a st andard polarographic oxygen sensor. This mu BOD method was used to measure respiration rates of larvae of the sea urchin Strongylocentrotus purpuratus (at 15 degrees C) and embryos and larvae of 2 Antarctic echinoderms, the s ea urchin Sterechinus neumayeri and the seastar Odontaster validus (both at -1.5 degrees C). For validation, a comparison of different methods was per formed with embryos and larvae of S. neumayeri. The mu BOD method gave resu lts for respiration rates during development that were equivalent to those obtained with either coulometric capacitance respirometry or standard Winkl er's titrations of large (300 ml) BOD bottles. Currently, the most common m ethod for measuring respiration rates of invertebrate embryos and larvae is to place them in small respiration chambers and continuously monitor oxyge n tension with a polarographic oxygen sensor (POS). However, respiration ra tes for embryos and larvae of S, neumayeri were underestimated when standar d POS measurements were compared to the measurements made with either mu BO D, Winkler's titrations or coulometric capacitance respirometry, A comparis on of the mu BOD and POS methods during early development in S, neumayeri r esulted in different estimates of 920 and 343 mu J, respectively, for the t otal energetic cost of embryogenesis to gastrulation, illustrating that the POS error can be as great as 63 %. The mu BOD method is accurate for micro -respiration measurements of invertebrate embryos and larvae as well as bei ng simple to operate and appropriate for field work.