Penguindex: a Living Planet Index for Pygoscelis species penguins identifies key eras of population change

As one of the best studied components of the Southern Ocean food web, Pygoscelis penguins serve as an important window into the larger marine ecosystem, but the patchiness and heterogeneity of the census data available have made it difficult to assess trends in a policy-accessible way. Here we introduce a Pygoscelis penguin-specific biodiversity index, the ‘Penguindex,’ using the framework of the Living Planet Index (LPI), distilling 40 year population trends of pygoscelid penguins for the first time into a single pan-Antarctic indicator for use by policymakers. We also calculate species- and region-specific indices from which discrete eras of population dynamics can be identified. These indices, similar to the LPI itself, do not provide estimates of changes in absolute abundance of species but, instead, reflect comparable population trends and the relative magnitude of these changes. We find that the Adélie Penguin (Pygoscelis adeliae) index was relatively stable across the Antarctic since 1980, with declines in regional indices across the Antarctic Peninsula region being contrasted by increases in regional indices for the Ross Sea and East Antarctica. The Chinstrap Penguin (Pygoscelis antarctica) index across the Antarctic declined by 61%. In stark contrast, the index for Gentoo Penguin (Pygoscelis papua) has increased seven-fold. Our analysis also identifies several marked eras of regional pygoscelid population change that may help identify key mechanistic drivers. We expect that the Penguindex will act as a useful reference tool for policymakers and hope that, by following this example, other taxonomic groups in the Antarctic might be tracked using the Living Planet Index framework. Importantly, our development of the Penguindex should facilitate the much-needed integration of Antarctic data into global biodiversity monitoring.