In situ respiration measurements of megafauna in the Kermadec Trench

• First measurement of hadal megafauna respiration rates made in situ are reported.
• Respiration of a large, mobile polynoid polychaete from the Kermadec Trench.
• Estimates of total megafaunal community respiration from hadal depths.

The aim of this paper is to measure metabolic rates of megafauna living in depths greater than 6000 m. Echinoderms, actinarians and a polychaete were captured by remotely operated vehicle (ROV) and inserted into respiration chambers in situ at depths of 4049 m, 7140 m and 8074 m in the region of the Kermadec Trench SW Pacific Ocean. Hadal research has moved into a new frontier as technological improvements now allow for a meticulous investigation of trench ecology in depths greater than 6000 m. The development of an in situ respirometer for use in these studies was deployed in the Kermadec Trench to obtain the first ever rates of basal metabolic rates of hadal megafauna. Typical deep-sea experiments of individual animal physiology must deal with covarying factors of pressure, temperature, light and food supply in this study investigated the effects of pressure and increased food supply on overall animal metabolism. In the Kermadec Trench, holothurian respiration rates (n=4), 0.079±0.011 (mean±SE) µmol-O2 g−1 h−1, were higher than those captured at abyssal depths (n=2), 0.018±0.002 µmol-O2 g-1 h−1, in the same region (p<0.001). When Q10 adjusted to a common temperature of 2.5 °C trench holothurian respiration rates ranged between 0.068 and 0.119 µmol-O2 g−1 h−1. Anemone respiration rates were remarkably similar between abyssal and hadal specimens, 0.110 and 0.111 µmol-O2 g−1 h−1, respectively. Our results on echinoderm respiration when corrected for temperature and mass fall below the slope regression when compared with other in situ measurements at shallower ocean depths.