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

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Abstract
Measurements of respiration rates are essential to quantify the energy requirements of embryos and larvae. Here we describe a ')_rBOD' method that employs small (~1 ml) Biological Oxygen Demand (BOD) glass vials in which embryos and larvae are incubated. A decrease in oxygen concen- tration is measured by injecting seawater from each vial into the measurement chamber of a standard polarographic oxygen sensor. This pBOD 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 echino- derms, the sea urchin Sterecbinus neumayeri and the seastar Odontasfer valiclus (both at -1S"C). For validation, a comparison of different methods was performed with embryos and larvae of S. neumayeri. The nBOD 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 inverte- brate 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 pBOD, Winkler's titrations or coulometric capacitance respirometry. A comparison of the pBOD and POS methods during early development in S. neumayeri resulted in different estimates of 920 and 343 pJ, respectively, for the total energetic cost of embryogenesis to gastrulation, illustrating that the POS error can be as great as 63 %. The yBOD method is accurate for micro-respiration measurements of invertebrate embryos and larvae as well as being simple to operate and appropriate for field work.

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