Diet and feeding of Euphausia hanseni and Nematoscelis megalops (Euphausiacea) in the northern Benguela Current: ecological significance of vertical space partitioning

Abstract

Patterns of diel migration and feeding of Euphausia hanseni and Nernatoscelis rnegalops were investigated in waters of the northern Benguela (Namibia) upwelling system. N. megalops migrated to just below the thermocline at night and fed maximally in the early evening E. hanseni migrated to above the thermocline at night and fed progressively throughout the night. Although both species were omnivorous and consumed similar size ranges of copepod prey, differential prey sizefrequency with depth resulted in E. hanseni consuming mostly small-sized copepods and N. megalops preferring m e d u m size classes. At depths of overlap the 2 species appeared to partition copepod food resources on the basis of size. Verhcal spatial partitioning is examined in light of temporal and dietary separation, and overlapping horizontal distribution patterns of the species in the northern Benguela upwelling system. It is concluded that vertical space partitioning is a reflection of the structure of shelf break zooplankton communities, which is a strategy of sharing highly productive areas and avoiding competition.

Trophic position of coexisting krill species: a stable isotope approach

“…Similar trophic positions for T. longicaudata and T. inermis have been found in other studies around Svalbard in the Barents Sea and the Arctic Ocean shelf-break region (Søreide et al 2006, Tamelander et al 2006, and also agree with our results for the 2 species in the mouth of Godthåb-sfjord and in the offshore region. Based on results from the present and previous studies, we therefore conclude that the trophic position of the species might to a large extent depend on available prey, since krill can consume a wide range of prey types (Boyd et al 1984, McClatchie 1985, Barange et al 1991, Agersted et al 2011.…”

“…, and also agree with our results for the 2 species in the mouth of Godthåb-sfjord and in the offshore region. Based on results from the present and previous studies, we therefore conclude that the trophic position of the species might to a large extent depend on available prey, since krill can consume a wide range of prey types (Boyd et al 1984, McClatchie 1985, Barange et al 1991, Agersted et al 2011). …”

“…Mar Ecol Prog Ser 516: 139-151, 2014 140 Krill have a broader prey-size spectrum than copepods, and are capable of exploiting several trophic levels (Boyd et al 1984, McClatchie 1985, Barange et al 1991, Agersted et al 2011. The fact that krill are generalists could be a key trait that resolves 'the paradox' for this group as this means that interspecific food competition is reduced.…”

“…A wide prey-size spectrum can be an advantage when species feeding on the same prey coexist, since this will lower interspecific competition. Another adaptation enabling coexistence is differences in behaviour such as diel vertical migration patterns and vertical spatial partitioning (Barange 1990, Barange et al 1991. The ability of krill to utilise prey that occurs in different depth strata might also be a mechanism that reduces interspecific competition and thereby makes coexistence possible.…”

Population biology of euphausiids off northern California and effects of short time-scale wind events on Euphausia pacifica

“…They are omnivorous feeders (Ohman 1984, Barange et al 1991, Suh et al 1991, Båmstedt & Karlson 1998, Dilling et al 1998, Gurney et al 2001, Hernandez-Leon et al 2001 and are consumed by many predators including seabirds (Ainley et al 1996), pelagic fishes (Genin et al 1988, Reilly et al 1992, Tanasichuk 1999) and marine mammals (Fiedler et al 1998). Euphausiids of the California Current have been the subject of many studies (Brinton 1960, 1962, Brinton & Wyllie 1976, Youngbluth 1976, Mullin & Conversi 1988, Simard & Mackas 1989, with some focusing only on the most dominant species of the Northern California region, Euphausia pacifica (Smiles & Pearcy 1971, Brinton 1976.…”