Regional Variability in Food Availability for Arctic Marine Mammals

Abstract

Abstract. This review provides an overview of prey preferences of seven core Arctic marine mammal species (AMM) and four non-core species on a pan-Arctic scale with regional examples. Arctic marine mammal species exploit prey resources close to the sea ice, in the water column, and at the sea floor, including lipid-rich pelagic and benthic crustaceans and pelagic and ice-associated schooling fishes such as capelin and Arctic cod. Prey preferred by individual species range from cephalopods and benthic bivalves to Greenland halibut. A few AMM are very prey-, habitat-, and/or depth-specific (e.g., walrus, polar bear), while others are rather opportunistic and, therefore, likely less vulnerable to change (e.g., beluga, bearded seal). In the second section, we review prey distribution patterns and current biomass hotspots in the three major physical realms (sea ice, water column, and seafloor), highlighting relations to environmental parameters such as advection patterns and the sea ice regime. The third part of the contribution presents examples of documented changes in AMM prey distribution and biomass and, subsequently, suggests three potential scenarios of large-scale biotic change, based on published observations and predictions of environmental change. These scenarios discuss (1) increased pelagic primary and, hence, secondary production, particularly in the central Arctic, during open-water conditions in the summer (based on surplus nutrients currently unutilized); (2) reduced benthic and pelagic biomass in coastal/shelf areas (due to increased river runoff and, hence, changed salinity and turbidity conditions); and (3) increased pelagic grazing and recycling in open-water conditions at the expense of the current tight benthic-pelagic coupling in part of the ice-covered shelf regions (due to increased pelagic consumption vs. vertical flux). Should those scenarios hold true, pelagic-feeding and generalist AMM might be advantaged, while the range for benthic shelf-feeding, ice-dependent AMM such as walrus would decrease. New pelagic feeding grounds may open up to AMM and subarctic marine mammal species in the High Arctic basins while nearshore waters might provide less abundant food in the future.

Spring-to-summer changes and regional variability of benthic processes in the western Canadian Arctic

“…At one site (A-NE), we did observe a seasonal transition from juvenile to adult individuals in polychaete species between the two sampling events, but a quantification of such growth processes is difficult due to the small size of the encountered infauna. The influence of predation has neither been investigated in our study area nor suggested to limit the increase in biomass in other polar regions Renaud 1997, Bluhm andGradinger 2008). Moreover, faunal composition also responds to environmental changes on time scales greater than 1 year (Cusson et al 2007;Piepenburg et al 2010) and does, therefore, integrate the effects of past processes that have not been covered during our sampling.…”

“…There is still controversy about the actual scope and direction of future changes in primary production and vertical flux patterns (Wassmann et al 2008). Regardless, shifts in benthic community metabolism and composition are expected (ACIA 2004;Grebmeier et al 2006b;Carroll et al 2008;Sun et al 2009;Archambault et al 2010) and are likely to influence the ecosystem at higher trophic levels (Bluhm and Gradinger 2008). Our incomplete knowledge about spring-to-summer dynamics of benthic processes makes it difficult to reliably predict their response to climate-induced changes in the abiotic environment and to concurrent changes in the timing and magnitude of primary production, the quality of organic material deposited on the seafloor, and the composition of benthic communities.…”

Advection in polar and sub-polar environments: Impacts on high latitude marine ecosystems

“…Early ice retreat and thinner ice will lead to an increase of irradiance in the water column and under the ice, which may shift the onset of ice algal and phytoplankton production to earlier in the season (Arrigo and van Dijken, 2011;Frey et al, 2011;Ji et al, 2013). Conversely, expanded areas of open water may delay the phytoplankton bloom due to wind-induced mixing delaying the formation of the seasonal pycnocline, as is apparently the case in the eastern Bering Sea (Baier and Napp, 2003;Bluhm and Gradinger, 2008;Hunt et al, 2011). Changes in timing of bloom events may have repercussions for herbivorous zooplankton and ice fauna species as the probability for a ''mismatch" increases if the sequential timing is altered for primary production blooms relative to life history events of herbivores that rely on energetic input from the blooms (e.g., for reproduction and recruitment; Baier and Napp, 2003;Søreide et al, 2010;Varpe, 2012;Daase et al, 2013).…”

Biological Response to Recent Pacific Arctic Sea Ice Retreats

“…While temporally constrained models indicate that primary production has increased over the Chukchi Sea shelf [Arrigo et al, 2008], recent 6-year time series show that chlorophyll a concentrations are not increasing throughout the region as a whole (Figure 1). Thus, researchers must exercise caution before summarily assuming that increased primary production accompanies an extended open-water season-biological processes vary greatly with seasonal solar input, timing of sea ice retreat, effects of open-water storm events on mixed-layer depth, increased freshwater runoff, and nutrient limitation [Bluhm and Gradinger, 2008]. A shift to smaller algal species sizes with Arctic Ocean freshening [Li et al, 2009] may affect food web structure and carbon cycling with continued warming.…”