Diet of Mysis relicta in Lake Ontario as revealed by stable isotope and gut content analysis

Abstract

Stable isotope analysis of the potential prey and predator can be combined with gut content analysis to quantify the diet. This dietary knowledge allows the quantitative assessment of the role of key species in energy and contaminant transfer, their impact on prey communities, and their susceptibility to perturbation. The diet of Mysis relicta was examined in Lake Ontario in spring, summer, and autumn using both techniques. Mysids fed on the bottom during the day and in the pelagia and on the bottom at night. A trophic fractionation of 2.2‰ N between mysids and their prey provided the best correspondence between the observed stable isotope signature of mysids and that estimated from their diet. Tissue turnover rate of d 13 C was slow compared with that of d 15 N. Diatoms formed 50% of the assimilated diet in May. In September, 25% of large mysids feeding on the bottom contained amphipod parts and 20% contained phytoplankton. The remainder of the diet consisted of zooplankton and rotifers. The contribution of amphipods and phytoplankton could not be quantified. Revised daily consumption estimates, based on this new diet information and clearance rate estimates of consumption, gave daily consumption estimates similar to those estimated from previous bioenergetic modelling.

Plankton development in Lake Jonsvatn, Norway, after introduction of Mysis relicta: a long-term study

“…was decimated by Mysis relicta predation in Lille Jonsvatn, although it might be a difficult prey as it forms colonies of considerable size. Rotifers have been paid less attention than cladocerans and copepods, but in some studies are reported to be part of the mysid diet (Lasenby & Langford 1973, Bowers & Grossnickle 1978, Johannsson et al 2001, Ikonen et al 2005. Lasenby & Langford (1973) reported Kellicottia to be an important prey in Stony Lake, Ontario.…”

“…Although phytoplankton may be an important part of the Mysis spp. diet (Grossnickle 1982, Johannsson et al 2001), it has not been shown that M. relicta by its herbivory has influenced phytoplankton biomass in lakes. As the total P content in Lille Jonsvatn showed a significant decrease from ~11 µg l -1 in 1989-1990 to 5 µg l -1 in 2006 (Fig.…”

“…Grossnickle (1982) showed in an overview that M. relicta is capable of both filterfeeding and raptorial feeding, eating phytoplankton, zooplankton, benthos, detritus and sediments. More re-cent studies have added nuanced information to the omnivorous feeding habits of M. relicta (Branstrator et al 2000, Johannsson et al 2001, Lasenby & Shi 2004, Ikonen et al 2005, Scharf & Koschel 2005. After introductions both in North America and Scandinavia, it gradually became evident that M. relicta had the ability to reduce zooplankton abundance and change species composition through its predatory behavior (Lasenby & Langford 1973, Threlkeld et al 1980, Kinsten & Olsén 1981, Lasenby et al 1986, Nero & Sprules 1986a, Spencer et al 1999.…”

Molecular identification of the invasive cladoceranCercopagis pengoi(Cladocera: Onychopoda) in stomachs of predators

“…Despite its rarity in plankton (<1% of total zooplankton abundance and biomass; Gorokhova et al, 2004), C. pengoi seems to be ingested with a relatively high frequency by mysids (≥23% of analyzed individuals), indicating that this prey is accessible to a significant part of the mysid population. The fact that mysids are able to consume C. pengoi has significant implications for pelagic food web structure in the Baltic and possibly also in the Great Lakes, where mysids are also important zooplanktivores (Johannsson et al, 2001), co-occurring with increasingly abundant C. pengoi (Vander Zanden et al, 2004). Indeed, if C. pengoi is or can become a competitor with zooplanktivorous fish, then an additional predation pressure exerted by mysids might mediate the strength and the net trophic outcome of this competition.…”

“…The species is a cyclic parthenogen producing diapausing eggs that sink down and overwinter in the sediment (Rivier, 1998). Mysids, on the other hand, are known to perform vertical migrations (Rudstam et al, 1986;Johannsson et al, 2001), and it is possible that they feed on the benthic material, including the diapausing eggs, while staying close to the bottom. If this is the case, the consumption of diapausing eggs by mysids could potentially affect the recruitment of C. pengoi the following year.…”