Segovia-Jara, T., H.A. Benítez, M.I. Castillo, M. La Mesa, C. Morales-Garrido, B. Rodríguez-Stepke, C.A. Cárdenas, M.F. Landaeta. (2025). Out in the Cold: The ignored influence of glacial melting on Rhincalanus gigas and R. nasutus (Copepoda, Calanoida) morphology in Antarctic waters. Marine Environmental Research. 212:1-9. nov 2025.
Segovia-Jara, T., H.A. Benítez, M.I. Castillo, M. La Mesa, C. Morales-Garrido, B. Rodríguez-Stepke, C.A. Cárdenas, M.F. Landaeta
2025
Out in the Cold: The ignored influence of glacial melting on Rhincalanus gigas and R. nasutus (Copepoda, Calanoida) morphology in Antarctic waters
Marine Environmental Research
212:1-9. nov 2025
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Environmental variability causes variations in the biological traits of marine organisms, affecting their abundance,
distribution, and morphology. By using two bio-oceanographic surveys in Maxwell Bay, King George
Island (summer 2023), and South Bay, Doumer Island, Palmer Archipelago (summer 2022), West Antarctica, the
influence of glacial meltwater was quantified on biological traits of the neritic calanoid copepods, Rhincalanus
gigas and R. nasutus. Stations were categorized as glacial-influenced (GI) when the mean temperature and salinity
were <1 ?C and <33.9 g kg- 1 (2022), and <2.2 ?C and <33.9 g kg- 1 (2023), respectively. Stations with warmer
and saltier waters were considered as non-glacial influenced (NGI) zones. The abundance of adult females was
similar for both species in the GI and NGI areas. Morphologically, both species were similar, varying from
specimens with shorter urosome, and wider 2nd somite of the prosome, to specimens with larger urosome, and
narrower 2nd somite of the prosome (PC1, 31 % of the variance). Also, copepods varied from specimens with a
narrower body and a pointed urosome to individuals with a wider body and an expanded urosome (PC2, 27 %).
The allometry was low but significant for R. gigas (3.46 %), and larger for R. nasutus (13.56 %), associated with a
widening of the base of the cephalosome and a change of the urosome’s direction. Discriminant Function
Analysis detected significant shape differences between GI and NGI areas for the endemic R. gigas, but not for
circumglobal R. nasutus. A Partial Least Squares analysis detected covariance between shape variations in
Rhincalanus gigas females and hydrographic conditions, showing that individuals with larger (shorter) urosome
were associated with warmer (colder) and less (more) oxygenated waters. These morphological variations may
pose constraints on the relevant ecological traits of local populations or represent an expression of phenotypic
plasticity in endemic Antarctic species.
