Mysis relicta in a eutrophic lake: Consequences of obligatory habitat shifts

Abstract

Low numbers of mysids in eutrophic lakes have usually been related to their poor tolerance to low oxygen. In eutrophic Lake Hiidenvesi, we studied the possibility that water quality indirectly affects mysids by forcing them to habitats where they are vulnerable to fish predation. Mysis relicta was absent from basins that did not stratify (water depth Ͻ 10 m). In the deep basin, as the summer progressed, M. relicta was concentrated in the deepest areas and moved upward in the water column as water temperature increased and dissolved oxygen decreased. Between mid-August and mid-September, only a thin water layer was habitable; the rest had either intolerably low oxygen concentration or too high of a temperature. M. relicta abundance decreased from 2.72 ϫ 10 8 individuals on 3 June to 3.72 ϫ 10 6 individuals on 19 October, with the sharpest decrease taking place in August. At the same time, the vertical distribution of smelts shifted downward and the percentage of mysids in the stomach contents of smelts increased steeply. The consumption rate by smelts was high enough to explain the collapse of the M. relicta population; during 18 August-2 September, smelts consumed 5.6 times the mysid production. The results suggested that unfavorable physicochemical conditions did not directly cause the drastic reduction of the population abundance of M. relicta but indirectly facilitated predation by smelts, which was the final cause of the collapse. The high predation rate by smelts was probably accelerated by the emergence of chaoborid larvae, which were important food items for smelts in early summer.

Population structure, life cycle, and trophic niche of the glacial relict amphipod, Gammaracanthus lacustris, in a large boreal lake

“…Bagge, 1992;Horppila et al, 2003;Naesje et al, 2003). are both present near the bottom where large G. lacustris reside as observed from our samples and also reported in previous studies (e.g.…”

The life history characteristics, growth and density of Mysis diluviana in Lake Pend Oreille, Idaho, USA

“…Because large lakes tend to develop thermal bars early in spring, currents near shore would be expected to differ relative to other times of the year and could influence the distribution of mysids, especially if horizontal migrations occur seasonally. The distribution of mysids could also be limited by water temperature (Horppila et al, 2003;Scharf and Koschel, 2004;Shea and Makarewicz, 1989). Thus, rapid heating of near shore area associated with thermal bars may force mysids to migrate to the pelagic zone.…”

Field observations and laboratory experiments on growth and lipid content of young-of-the-year perch

“…In addition, the lipid content of Mysis mixta Lilljeborg was found to increase considerably during the summer season (Richoux et al 2004), indicating that mysids may be a valuable food for fish (e.g. Horppila et al 2003).…”