Interannual variability in Antarctic krill (Euphausia superba) density at South Georgia, Southern Ocean: 1997–2013

Abstract Antarctic krill (Euphausia superba) are a key species in Southern Ocean ecosystems, maintaining very large numbers of predators, and fluctuations in their abundance can affect the overall structure and functioning of the ecosystems. The interannual variability in the abundance and biomass of krill was examined using a 17-year time-series of acoustic observations undertaken in the Western Core Box (WCB) survey area to the northwest of South Georgia, Southern Ocean. Krill targets were identified in acoustic data using a multifrequency identification window and converted to krill density using the Stochastic Distorted-Wave Born Approximation target strength model. Krill density ranged over several orders of magnitude (0–10 000 g m−2) and its distribution was highly skewed with many zero observations. Within each survey, the mean krill density was significantly correlated with the top 7% of the maximum krill densities observed. Hence, only the densest krill swarms detected in any one year drove the mean krill density estimates for the WCB in that year. WCB krill density (µ, mean density for the area) showed several years (1997/1998, 2001–2003, 2005–2007) of high values (µ > 30 g m−2) interspersed with years (1999/2000, 2004, 2009/2010) of low density (µ < 30 g m−2). This pattern showed three different periods, with fluctuations every 4–5 years. Cross correlation analyses of variability in krill density with current and lagged indices of ocean (sea surface temperature, SST and El Niño/Southern Oscillation) and atmospheric variability (Southern Annular Mode) found the highest correlation between krill density and winter SST (August SST) from the preceding year. A quadratic regression (r2 = 0.42, p < 0.05) provides a potentially valuable index for forecasting change in this ecosystem.

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Behavioural sensitivity of a key Southern Ocean species (Antarctic krill, Euphausia superba) to p,p′-DDE exposure

Ecotoxicology and Environmental Safety ◽

10.1016/j.ecoenv.2011.09.005 ◽

2012 ◽

Vol 75 ◽

pp. 163-170 ◽

Cited By ~ 9

Author(s):

Anita H. Poulsen ◽

So Kawaguchi ◽

Catherine K. King ◽

Robert A. King ◽

Susan M. Bengtson Nash

Keyword(s):

Southern Ocean ◽

Antarctic Krill ◽

Euphausia Superba ◽

Antarctic Krill Euphausia Superba

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Circumpolar occurrence of eugregarinid protozoanCephaloidophora pacificaassociated with Antarctic krill,Euphausia superba

Antarctic Science ◽

10.1017/s0954102008001016 ◽

2008 ◽

Vol 20 (5) ◽

pp. 437-440 ◽

Cited By ~ 11

Author(s):

Kunio T. Takahashi ◽

Masaki Kobayashi ◽

So Kawaguchi ◽

Junko Saigusa ◽

Atsushi Tanimura ◽

...

Keyword(s):

Southern Ocean ◽

Antarctic Krill ◽

Geographical Location ◽

Protozoan Parasite ◽

Euphausia Superba ◽

Maturity Stage ◽

Syowa Station ◽

Frequency Distributions ◽

The Mean ◽

The Antarctic

AbstractThe geographical distribution of protozoan parasiteCephaloidophora pacificaAvdeev (Order Eugregarininda) associated with Antarctic krill,Euphausia superba, was examined in samples collected from the vicinity of the Antarctic Peninsula, near Syowa Station, and Pacific and Indian sectors of the Southern Ocean.Cephaloidophora pacificawas found at all stations around the Antarctic, with 96.4% of the euphausiids infected (n = 195). The numbers ofC. pacificaper krill ranged from 0 to 8089 krill-1, and the average was 350.0 ± 787.8 (mean ± SD). The frequency distributions ofC. pacificashowed an overdispersed parasite population (i.e. the variance was greater than the mean) at all locations. Statistical analysis showed that whilst the geographical location did not have a significant effect on intensity ofC. pacificathe maturity stage of krill did, with an increasing intensity of infection as krill matures. The infestation ofE. superbaby eugregarinid protozoan is considered to be a circum-Antarctic phenomenon, and it occurs equally throughout the Southern Ocean.

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Natural age-dependent mortality rates of Antarctic krill Euphausia superba Dana in the Indian sector of the Southern Ocean

Polar Biology ◽

10.1007/bf00236127 ◽

1995 ◽

Vol 15 (1) ◽

Cited By ~ 7

Author(s):

E.A. Pakhomov

Keyword(s):

Southern Ocean ◽

Antarctic Krill ◽

Euphausia Superba ◽

Mortality Rates ◽

Age Dependent ◽

Indian Sector ◽

Antarctic Krill Euphausia Superba ◽

Dependent Mortality

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Spatial and temporal variability in the structure of aggregations of Antarctic krill (Euphausia superba) around South Georgia, 1997–1999

ICES Journal of Marine Science ◽

10.1093/icesjms/fsq202 ◽

2011 ◽

Vol 68 (3) ◽

pp. 489-498 ◽

Cited By ~ 15

Author(s):

Martin J. Cox ◽

Jonathan L. Watkins ◽

Keith Reid ◽

Andrew S. Brierley

Keyword(s):

Temporal Variability ◽

Antarctic Krill ◽

Marine Ecosystem ◽

Euphausia Superba ◽

Spatial And Temporal Variability ◽

Dual Frequency ◽

South Georgia ◽

Estimation System ◽

Antarctic Krill Euphausia Superba

Abstract Cox, M. J., Watkins, J. L., Reid, K., and Brierley, A. S. 2011. Spatial and temporal variability in the structure of aggregations of Antarctic krill (Euphausia superba) around South Georgia, 1997–1999. – ICES Journal of Marine Science, 68: . Antarctic krill are important in the South Georgia (54°S 35°W) marine ecosystem. They form aggregations that vary widely in packing density (<1 to 1000 s of individuals m−3), length (tens to thousands of metres), and height (tens of metres). Acoustic surveys are often used to estimate krill biomass and provide data that give insight into aggregation structure. Using dual-frequency (38 and 120 kHz) acoustic data collected during six surveys conducted around South Georgia during the 1997, 1998, and 1999 austral summers, we isolated 2990 aggregations by applying the Shoal Analysis and Patch Estimation System algorithm in Echoview and a krill-length-dependent acoustic identifier (ΔSv120–38). Multivariate cluster (partition) analysis was applied to metrics from each of the aggregations, resulting in three aggregation types with an overall proportional split of 0.28:0.28:0.44. Types 1 and 3 had low mean densities (<2 g m−3), whereas Type 2 had a mean density of 94 g m−3. Intersurvey differences were found between the effort-corrected numbers of aggregation types (p = 2.5e−6), and between on- and off-continental shelf areas (p = 1.5e−7), with a greater number of Type 2 aggregations being found on-shelf. The findings suggest intersurvey variation in krill catchability, with krill being more likely to be caught on-shelf.

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Demography and life cycle of Antarctic krill, Euphausia superba, in the Indian sector of the Southern Ocean: long-term comparison between coastal and open-ocean regions

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f00-175 ◽

2000 ◽

Vol 57 (S3) ◽

pp. 68-90 ◽

Cited By ~ 24

Author(s):

E A Pakhomov

Keyword(s):

Southern Ocean ◽

Life Span ◽

Antarctic Krill ◽

Age Groups ◽

Substantial Reduction ◽

Euphausia Superba ◽

Age Composition ◽

Indian Sector ◽

Antarctic Krill Euphausia Superba

Size/age composition and reproductive status of Antarctic krill, Euphausia superba, in the central part of the Indian sector of the Southern Ocean, e.g., the Cooperation Sea (Prydz Bay region) and the Cosmonaut Sea, during austral summers 1977-1990 were summarized to estimate growth rates, longevity, reproduction, recruitment, life span, and mortality rates. The life span of Antarctic krill exceeds 5 years in both the Cosmonaut and Cooperation seas. The age composition of the southern and northern groupings differs markedly, with substantial reduction in numbers of early age groups in the northern grouping. Long-term observations of spawning success, recruitment, and age composition suggest that a self-sustained grouping of krill persists in the Cooperation Sea south of the Antarctic Divergence. However, periodic gene flow via recruits from surrounding regions most probably accounts for the lack of spatial genetic differences between the Cooperation Sea and adjacent areas, thus preventing the establishment of an isolated subpopulation in the region investigated. The major factor responsible for the substantial interannual variability in krill dynamics appears to be macroscale oceanographic and atmospheric circulations, which determine a level of environmental isolation of the Cooperation Sea from adjacent waters.

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