Environmental niche overlap in sibling planktonic species calanus finmarchicus and c. glacialis in Arctic fjords

Knowledge of the environmental preferences of the key planktonic species,
such as Calanus copepods in the Arctic, is crucial to understand ecosystem
function and its future under climate change. Here we assessed the
environmental conditions influencing the development stages of Atlantic C.
finmarchicus and Arctic C. glacialis, and quantified the extent to which
their niches overlap by incorporating multiple environmental data. We
based our analysis on a three-year seasonal collection of zooplankton by
sediment traps, located on moorings in two contrasting Svalbard fjords:
the Arctic Rijpfjorden, and the Atlantic-influenced Kongsfjorden. Despite
large differences in water temperature between the fjords, local realized
niches of the sibling Calanus species overlapped almost perfectly. The
exception was the earliest copepodites of C. glacialis in Rijpfjorden,
which probably utilized the local ice algal bloom in spring. However,
during periods with no sea ice, like in Kongsfjorden, the siblings of both
Calanus species showed high synchronization in the population structure.
Interestingly, differences in temperature preferences of C. finmarchicus
and C. glacialis were much higher between the studied fjords than between
the species. Our analysis confirmed the high plasticity of Calanus
copepods and their abilities to adapt to highly variable environmental
settings, not only on an interannual basis, but also in a climate warming
context, indicating some resilience in the Calanus community.