Variability inCalanusspp. abundance on fine- to mesoscales in an Arctic fjord: implications for little auk feeding

Abstract

We studied the abundance of calanoid copepods of the genus Calanus in a high-resolution sampling grid located in the vicinity of a breeding colony of an avian Calanus predator, the little auk (Alle alle) in an Arctic fjord (Isfjorden, Svalbard) in July 2007. Within diving reach of little auks, all copepodite stages of C. finmarchicus, as well as stages CIIIÁCV of C. glacialis, were recorded in all 26 stations sampled. Spatial autocorrelation analysis was used to detect spatial heterogeneity (patches) in the distribution of Calanus spp. Positive spatial autocorrelation was detected on scales up to 1.2 km for C. finmarchicus stages CIIIÁCV and for C. glacialis CIV and CV, but was rarely detected for the younger stages. This suggests that the tendency to form patches varies with ontogeny in Calanus spp. At an adjacent little auk colony, the diet prey composition from 30 gular pouches of little auks returning from feeding trips was investigated. Calanus glacialis CIV and CV were numerically dominant in the prey samples, while C. finmarchicus CIV which was dominant in the net samples did not contribute to the little auk diet. This could suggest selective feeding, a detection of patches beyond the scale of our survey, feeding beyond the sampling area or a combination of these factors. Large Calanus abundance differences within the sampling grid underline the necessity of a proper choice of grid size, in this case 2 km between stations.

Plankton patchiness in the Polar Front region of the West Spitsbergen Shelf

“…According to Pinca & Huntley (2000), patches of this size are considered small. However, Vogedes et al (2014) found that in Svalbard fjord the zooplankton patches can be even smaller (1.2 km). In contrast, patches of large size are known to spread horizontally over many kilometres, that is between 30 and 60 km (Huntley et al 1995) or even >100 km in case of the largest patches (Pinca & Huntley 2000).…”

“…by net sampling (Wiebe 1970, Vogedes et al 2014, continuous water pumping (Piontkovski et al 1997, Molinero et al 2008, acoustics (Zhou & Huntley 1996, Genin et al 2005, optical counters (Basedow et al 2006, Trudnowska et al 2012, video recording (Benfield et al 1996, laboratory experiments (Dagg 1977) or modelling (Riley 1976, Woodson et al 2005. Nevertheless, this phenomenon remains more a topic of speculation than one of actual measurements and documentation.…”

Zooplankton in Svalbard fjords on the Atlantic–Arctic boundary

“…Despite the differences in hydrography, the abundance of Arctic holoplankton was comparable along the WSS and was in the same range as that reported in previous studies (Scott et al 2002;Kwasniewski et al 2003Kwasniewski et al , 2010Basedow et al 2004;Hop et al 2006;Weydmann and Kwasniewski. 2008;Piwosz et al 2009;Vogedes et al 2014). Thus, it seems that in 2007, the west Spitsbergen fjords still contained reservoirs of cold ArW in the bottom layers or in basins separated by sills, offering refugia for Arctic species (Arnkvaern et al 2005;Weydmann and Kwasniewski 2008) and making it possible for Arctic C. glacialis to survive in the face of climate warming.…”

Marine birds and mammals foraging in the rapidly deglaciating Arctic fjord - numbers, distribution and habitat preferences

“…Little auks avoid areas with turbid water and/or with high abundance of small-sized copepods (e.g. Calanus finmarchicus) making selection of their staple prey (C. glacialis) difficult Vogedes et al 2014). Kittiwakes feeding efficiently on the surface of the water, including Bbrown zones^, seem not to be affected by this problem.…”