The role of prey stratification in the predation pressure by the cydippid ctenophore Mertensia ovum in the Barents Sea

Abstract

The cydippid ctenophore Mertensia ovum occurs throughout the Norwegian arctic regions at least from the ice edge to the Arctic Circle. Using new data from the Barents and Greenland Seas, a simple model is constructed in which the upper boundary conditions for the trophic impact of Mertensia on populations of Calanus in this area are explored. Based on abundance data from MOCNES S and vertical net samples, experimental data on feeding and a range of typical values for the abundance of the principal copepod species, the range of probable predation pressure on copepods is calculated. Using typical abundances of the copepods and ctenophores in the Barents Sea, M. ovum appears to be capable of consuming a maximum of ca 1-5% d-' of the copepods in the water where it occurs. Vertical and horizontal spatial coupling probably plays a significant role in determining the extent of predation for this predator. Predation by other ctenophores may be a significant factor in its own biology.

Ctenophora in the Arctic: the abundance, distribution and predatory impact of the cydippid ctenophore Mertensia ovum (Fabricius) in the Barents Sea

“…results of the abundance of Mertensia and Beroe, including average size at stations where they were collected in both 1987 and 1988 have been presented elsewhere (Swanberg & Bimstedt 1991). Generally, the data suggest that abundances of both Mertensia and Beroe were lower in 1987 than in 1988.…”

“…This ability to store energy, and its relatively low respiration (Percy 1988) means it can survive for long periods without prey. The evidence (Swanberg & Bimstedt 1991;Ospovat pers. comm.…”

“…In 1988 considerably more effort was devoted to quantifying the distribution of Mertensia ovum and that of its principal predator, Beroe cucumis. The vertical abundance of Mertensia nearly always reached its peak in the upper 50-100m (see Swanberg & Bimstedt 1991). M. ovum was most abundant in a small group of stations (815-819) in the southwest and at a collection of copepods per ctenophore (s.d.…”

Aggregations of predators and prey affect predation impact of the Arctic ctenophore Mertensia ovum

“…In addition to the lack of historical survey data, abundance estimates of gelatinous zooplankton made from plankton surveys are widely acknowledged to underestimate both the total densities and densities in aggregations (e.g. Swanberg & Båmstedt 1991b, Båmstedt et al 2003. A good example of this inaccuracy is the high variation of Mertensia ovum abundance between samples taken with the MultiNet and MIK-net, even though the samples were taken as simultaneously as possible (see above and Table 1).…”

“…Some recent studies have incorporated spatial heterogeneity into their models (e.g. Kareiva 1990, Swanberg & Båmstedt 1991b, Nachman 2006a. But much of predator− prey theory and many of the most commonly used models assume that populations are homogeneously distributed in space (e.g.…”