Exploring Zooplankton Community Structure and Environmental Relationships in a Glacial-Terminating Fjord in Southeast Greenland

High-latitude oceans are among the most vulnerable regions to a warming climate. Historically covered by sea ice for much of the year, these areas are now experiencing accelerated environmental changes, such as increasing atmospheric and ocean temperatures, resulting in rapid glacial melt and calving. Sermilik Fjord, located in southeastern Greenland, is an Arctic fjord system influenced by marine-terminating glaciers and characterized by complex bathymetry and distinct water masses, including warm, saline Atlantic Water (AW), cold, saline polar water, and cold, fresh subglacial meltwater. These characteristics create a diverse and productive ecosystem, with unique physical characteristics among the inner fjord, outer fjord, shelf, and slope/off-shelf regions.

This study aims to explore and compare zooplankton community assemblages across Sermilik Fjord, specifically focusing on the presence or absence of AW in the surface waters (40-200 m depth). This research will determine relationships between zooplankton community composition and AW, define community structure for each region, and identify indicator species associated with specific regions or water masses. Field collections were conducted using 29 samples from a bongo sampler deployed to a depth of 100 m. Vertical profiles of temperature, salinity, and other parameters were collected using a CTD, providing a detailed understanding of the water column structure and the presence of different water masses.

About half of all stations that zooplankton were collected at had AW present in the surface waters. A hierarchical cluster analysis determined five key zooplankton community clusters in the fjord, and distinct separation between communities that had a presence or absence of AW in the surface waters. Zooplankton statistical analyses will be accomplished through a NMDS on community clusters. SIMPER analysis identified euphausiids and chaetognaths as key contributors (over 50%) to community dissimilarity. Diversity analysis using Shannon and Simpson indices revealed considerable variability in zooplankton community composition across samples. Low Shannon values (e.g., Upper fjord with H' = 0.032 and Mid-fjord with H’ = 0.011) and high Simpson values (e.g., Fjord Mouth, D = 0.65) indicated dominance by a single species, suggesting low community diversity. In contrast, samples near the glacier-terminus (H' = 1.10, D = 0.66) and coast (H' = 0.87, D = 0.55) exhibited higher diversity and evenness. These findings highlight areas with both high species dominance and more evenly distributed communities, reflecting spatial differences in zooplankton community structure. Preliminary results indicate potential gradients in community composition, with warmer water species and higher zooplankton abundance associated with AW presence in surface waters. Distinct communities were also observed between regions influenced by glacial meltwater and those characterized by warmer AW influx.

This work contributes to our understanding of the ecological dynamics of Greenland's fjords in response to climate change, highlighting the importance of zooplankton as key players in Arctic marine ecosystems. It further emphasizes the challenges and urgency of studying these vulnerable regions, as they undergo profound shifts in their physical and biological environments.