Review: the energetic value of zooplankton and nekton species of the Southern Ocean.

Understanding the energy flux through food webs is important for estimating the capacity of marine ecosystems to support stocks of living resources. The energy density of species involved in trophic energy transfer has been measured in a large number of small studies, scattered over a 40-year publication record. Here, we reviewed energy density records of Southern Ocean zooplankton, nekton and several benthic taxa, including previously unpublished data. Comparing measured taxa, energy densities were highest in myctophid fishes (ranging from 17.1 to 39.3 kJ g DW), intermediate in crustaceans (7.1 to 25.3 kJ g DW), squid (16.2 to 24.0 kJ g DW) and other fish families (14.8 to 29.9 kJ g DW), and lowest in jelly fish (10.8 to 18.0 kJ g DW), polychaetes (9.2 to 14.2 kJ g DW) and chaetognaths (5.0-11.7 kJ g DW). Data reveals differences in energy density within and between species related to size, age and other life cycle parameters. Important taxa in Antarctic food webs, such as copepods, squid and small euphausiids, remain under-sampled. The variability in energy density of was likely regional rather than seasonal, although for many species with limited data it remains difficult to disentangle regional and seasonal variability. Models are provided to estimate energy density more quickly using a species' physical parameters. It will become increasingly important to close knowledge gaps to improve the ability of bioenergetic and food web models to predict changes in the capacity of Antarctic ecosystems to support marine life.