Contrasting copepod community composition in two Greenland fjords with different glacier types

Greenland's fjord ecosystems are strongly influenced by meltwater discharge from glaciers. Marine-terminating glaciers can significantly enhance primary production during the melt season (compared to land-terminating glaciers), but their impact on secondary producers is not well understood. Here, we study seasonal changes in the zooplankton community (>50 µm) and grazing rates along two fjord transects in southwest Greenland influenced by different glacier types. Zooplankton biomass was comparable between the fjords, but community composition differed during summer. Nuup Kangerlua, a predominantly marine-terminating system, was characterised by large, herbivorous copepods and a longer summer grazing period in connection with the summer bloom. Ameralik, influenced by a land-terminating glacier, was characterised by small, omnivorous copepods, particularly Microsetella norvegica and Oncaea spp., and indicated a faster post-bloom transition towards regenerated production. Local hydrographic conditions also impact copepod biomass. A station with high biomass was found in Ameralik, potentially linked to a frontal zone where fjord water masses meet, providing favourable grazing conditions. We hypothesise that a future transformation from marine- to land-terminating glaciers could result in an increased abundance of smaller copepods, as observed in Ameralik. Such a community would constitute a less lipid-rich food source for higher trophic levels.

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