Abstract
Until recently, polar night constituted truly a “mare incognitum” of our times. Yet, the first records from this very little-explored period showcased a surprisingly rich and active ecosystem. This investigation aims to reveal the level of scavenger activity during both Arctic polar night and day. It compares the shallow-water scavenging fauna observed during two contrasting seasons (winter vs. summer) in a high Arctic fjord (Kongsfjorden, 79° N, Spitsbergen, Svalbard Archipelago). In each of January and July 2015, two different bait types – Atlantic cod (Gadus morhua) and a bird carcass (chicken meat) were deployed at a depth of 12 m. Fauna were monitored remotely using time-lapse cameras equipped with bait traps, with photographs taken every 15 min over a period of 4 days. Thirty taxa were recorded at baits, dominated by lysianassid amphipods (Onisimus sp. 88%, Anonyx sp. 2%, but only during winter), and buccinid gastropods (B. undatum 5%, B. glaciale 1%, Buccinum sp. 3%, in both seasons). In most cases, buccinids were the first animals to appear at bait. The total number of recorded taxa, mean species richness per sampling unit, total abundance and associations among taxa were higher, on average, in winter than in summer deployments, while Pielou’s evenness index showed the opposite pattern. Scavenger assemblages differed significantly between the two seasons and also in response to the two different bait types, with seasonal effects being strongest. Contrary to expectations, bait consumption rates differed very little between the two seasons, being slow in general and only slightly faster in summer (0.05 g of cod bait consumed in 1 min) compared to winter (0.04 g min–1), yielding novel insights into ecological interactions and functions in shallow marine ecosystems during Arctic polar nights.
Highlights
Scavengers play an important role in benthic nutrient and energy circulation essential for ecosystem functioning (Benbow et al, 2020)
We observed similar patterns of abundance for these species in winter and in summer cases, which does not support this phenology in the Arctic (79◦ N), but rather suggests a high level of physiological plasticity for B. undatum (UK 50◦ N, Iceland 65◦ N, Thatje et al, 2019)
High densities of buccinids in the shallow waters of Kongsfjorden and their relatively rapid movement (15 cm per minute, Lapointe and Sainte-Marie, 1992) may explain why, in most cases, buccinids were the first species at the bait, appearing only 15 min after its placement on the seabed
Summary
Scavengers play an important role in benthic nutrient and energy circulation essential for ecosystem functioning (Benbow et al, 2020). The fact that most organic carbon is produced during intense spring phytoplankton blooms, after the return of the sun, ice-cover breakdown and the stabilization of the upper water column (Sakshaug et al, 2009; Hodal et al, 2012) might suggest that benthic consumers in the Arctic are resource-controlled or food-limited and, depend on seasonal vertical fluxes of phytodetritus to the sea floor (bottomup control; Presler, 1986; see Piepenburg, 2005 and references therein) This classic perception of depleted life during the harsh polar night has been questioned recently, by Berge et al (2015a,b) who documented not a dormant but a surprisingly rich and active winter ecosystem across most of its components, including benthic invertebrates and scavengers, indicating a greater top-down influence on ecosystem structure and function during winter than was previously assumed. In such a system, opportunistic omnivores capable of deriving nutrition from a variety of sources, especially those available year-round, are favored (Renaud et al, 2020)
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