Summer distribution and size patterns of Limacina rangii (A. d’Orbigny, 1835): preliminary insights into environmental influences

Limacina rangii (d’Orbigny, 1835) is pelagic pteropod playing a key ecological and biogeochemical role in polar ecosystems, being the prey of a variety of species of higher trophic levels. They are also sensitive indicators that allow gauging environmental change. Despite their recognized ecological relevance, the influence of environmental descriptors on their biometric traits remains largely unexplored. In this study, specimens of L. rangii, including adults and larvae, were collected from the Ross Sea and Terra Nova Bay (Southern Ocean) during the XXXII Italian Antarctic Expedition (late summer 2017). Each sampling event was accompanied by in situ environmental measurements, including temperature, salinity, Chl-a concentration, and conductivity. To identify the most influential environmental drivers of body length, we employed a Random Forest machine learning algorithm. The results revealed that longitude, temperature, and conductivity were among the strongest predictors of body size, underscoring the role of both thermal regimes and oceanographic characteristics in constraining the growth and development of these pelagic gastropods. This study demonstrates that environmental variability exerts a control over the biometric traits of L. rangii, with local thermal regimes and oceanographic features acting as critical constraints on individual growth and population development. These insights are essential for forecasting the responses of pelagic calcifiers to climate-driven changes in the Southern Ocean.