Trophodynamics of the hyperiid amphipod Themisto gaudichaudi in the South Georgia region during late austral summer

Ea, Pakhomov; Perissinotto, Renzo

doi:10.3354/meps134091

Cited by 92 publications

(42 citation statements)

References 25 publications

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“…The diet and feathers from P. urinatrix have higher non-significant δ 13 C and significant δ 15 N values, and this can be related to more inshore prey and feeding at a higher trophic level, respectively, than P. georgicus. This is in agreement with the feeding habits of the diving petrels' prey, Themisto gaudichaudii and Paraeuchaeta antarctica, being carnivorous (Øresland 1991, Pakhomov & Perissinotto 1996, while Thysanoessa sp. is omnivorous and Calanoides acutus is herbivorous (Graeve et al 1994, Hagen & Kattner 1998, Falk-Petersen et al 1999.…”

Section: Dietary Segregationsupporting

confidence: 71%

Complete trophic segregation between South Georgian and common diving petrels during breeding at Iles Kerguelen

Bocher¹,

Cherel²,

Hobson³

2000

Mar. Ecol. Prog. Ser.

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Section: Dietary Segregationsupporting

confidence: 71%

Complete trophic segregation between South Georgian and common diving petrels during breeding at Iles Kerguelen

Bocher¹,

Cherel²,

Hobson³

2000

Mar. Ecol. Prog. Ser.

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“…Themisto gaudichaudi, which has been described as an opportunistic predator (Pakhomov & Perissinotto 1996), had a δ 15 N 2.41 ‰ higher than that of Calanus simillimus. As discussed earlier, Minagawa & Wada (1984) reported an average stepwise increase of 3.4 ± 1.1 ‰ between trophic levels.…”

Section: Discussionmentioning

confidence: 95%

“…Considering this, the isotope value observed for T. gaudichaudi was lower than expected. To offer a possible explanation for this, pigments from phytoplankton have been observed in the stomachs of T. gaudichaudi (Pakhomov & Perissinotto 1996) and other hyperiid amphipods (T. japonica; Sugisaki et al 1991). It is unlikely that the phytoplankton was consumed directly by the amphipod, and pigments must therefore be considered secondary in origin.…”

Section: Discussionmentioning

confidence: 99%

Trophic positions of three euphausiid species from the Prince Edward Islands (Southern Ocean): implications for the pelagic food web structure

Gurney¹,

Froneman²,

Pakhomov³

et al. 2001

Mar. Ecol. Prog. Ser.

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The relative trophic positions of Euphausia vallentini (juveniles and adults), E. longirostris (adults) and Nematoscelis megalops (adults) were investigated using samples collected in the vicinity of the Prince Edward archipelago during austral autumn (April/May) of 1998 on voyage 87 of the MV 'SA Agulhas'. Gut content analysis and stable nitrogen isotope measurements (δ 15 N) were performed on the same individuals. For comparative purposes, nitrogen isotope ratios of the copepod Calanus simillimis, the hyperid amphipod Themisto gaudichaudi and the fish Ceratoscopelus warmingi were also analysed. The results of the gut content analysis for E. vallentini juveniles showed that there was a high contribution of phytoplankton to the diet. Stable nitrogen isotope analysis supported this and indicated that E. vallentini juveniles occupied a similar trophic position to that of the copepod (mean δ 15 N values of 2.38 and 1.72 ‰ respectively). E. vallentini adults were found to be omnivorous, but the contribution of carnivory to the diet was difficult to determine. High phytoplankton and low mesozooplankton contributions to the diet from the gut content analysis suggested a predominantly herbivorous diet. However, the stable nitrogen isotope results showed that E. vallentini adults were closely grouped with T. gaudichaudi (mean δ 15 N values of 3.66 and 4.13 ‰ respectively), indicating a high degree of omnivory and a relatively large heterotrophic contribution to the diet. Irrespective of the degree of carnivory, a dietary shift with an increase in size was evident for this species. The gut content analysis of E. longirostris showed that this species consumed large amounts of both phytoplankton and metazoan prey. However, the stable nitrogen isotope analysis indicated a high degree of carnivory (mean δ 15 N = 6.88 ‰). Although the gut content analysis showed that N. megalops had a lower contribution of mesozooplankton to the diet compared to that of E. longirostris, the stable isotope analysis showed that these 2 species occupied a similar position (N. megalops mean δ 15 N = 6.83 ‰). The findings of this study support findings in the literature and show that E. vallentini juveniles are herbivorous and N. megalops adults are carnivorous. However, adults of E. vallentini and E. longirostris appear to have higher contributions of heterotrophic carbon to their diets than has been assumed and may occupy higher trophic positions than initially predicted. KEY WORDS: Sub-Antarctic euphausiids · Feeding ecology · Diet · Stable isotopes · Prince Edward IslandsResale or republication not permitted without written consent of the publisher

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“…These include vertebrates, such as prions and diving petrels (Goss et al 1997, Reid et al 1997a, as well as fish larvae (North & Ward 1989,1990) and a wide range of invertebrates. The latter include euchaetiid copepods (Øres-land & Ward 1993), the amphipod Themisto gaudichaudii (Pakhomov & Perissinotto 1996), and also krill. Krill are known to be omnivorous (Price et al 1988, Hopkins et al 1993a but are considered to be mainly herbivorous in summer (see Miller & Hampton 1989, Quetin et al 1994.…”

Section: Mortalitymentioning

confidence: 99%

South Georgia, Antarctica: a productive, cold water, pelagic ecosystem

Atkinson¹,

Whitehouse²,

Priddle³

et al. 2001

Mar. Ecol. Prog. Ser.

255

188

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The South Georgia region is characterised by high biomass and productivity of phytoplankton, zooplankton and vertebrate predators. Important commercial fisheries have been based at the island since the late 1700s, initially exploiting seals and whales, and currently taking krill Euphausia superba and finfish. Despite studies dating from the beginning of the last century, the causes of the high productivity remain unclear. The island lies within the Antarctic Zone of the Antarctic Circumpolar Current, to the south of the Polar Front. The offshore waters to its north and east are affected by a northwards deflection of the Southern Antarctic Circumpolar Current Front, together with waters from the Weddell-Scotia Confluence. Despite a retentive circulation over the shelf, the high productivity of phytoplankton and copepods is widespread, occurring far downstream and possibly extending to the Polar Front. High phytoplankton concentrations (>20 mg chlorophyll a m , equally dominated by krill and copepods. This greatly exceeds typical values for Antarctica, and is high compared to productive northern shelves. Zooplankton, and in particular krill, appear to have a pivotal role in regulating energy flow in this food web, through selective grazing and possibly also through nutrient regeneration. Abundances of krill and copepods are negatively related across a wide range of scales, suggesting direct interaction through competition or predation. Evidence suggests that when phytoplankton stocks are low, energy flow through krill is maintained by their feeding on the large populations of small copepods. Metazoans and higher predators at South Georgia can feed across several trophic levels according to prey abundance, and they regenerate substantial quantities of reduced nitrogen. Therefore we suggest that these groups have a controlling influence on lower trophic levels, both stabilising population sizes and maintaining high rates of energy flow. Hydrography, nutrient concentrations, phytoplankton, copepod, and krill biomasses fluctuate between years. Periodically (once or twice a decade), shortages of krill in summer result in breeding failures among many of their predators. This appears to be a downstream effect from wider scale, Scotia Sea phenomena, although the processes involved are unclear. The elevated biomass and energy flows at South Georgia appear to be caused by locally enhanced growth rates; there is no evidence so far for any physical concentration mechanism. Even for krill, which do not breed there, local growth rates are probably of a similar order to the biomass removed by their main land-based predators in summer. Thus the transfer of energy to higher predators depends on local enhancement of fluxes through the food web as well as the supply of plankton to the island by the Antarctic Circumpolar Current.

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Trophodynamics of the hyperiid amphipod Themisto gaudichaudi in the South Georgia region during late austral summer

Cited by 92 publications

References 25 publications

Complete trophic segregation between South Georgian and common diving petrels during breeding at Iles Kerguelen

Complete trophic segregation between South Georgian and common diving petrels during breeding at Iles Kerguelen

Trophic positions of three euphausiid species from the Prince Edward Islands (Southern Ocean): implications for the pelagic food web structure

South Georgia, Antarctica: a productive, cold water, pelagic ecosystem

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