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

Abstract

Quantitative sampling of phyto-and zooplankton has been carried out for 25 yr in Lake Jonsvatn, Norway, in order to assess changes after the introduction of Mysis relicta. In Lille Jonsvatn, the outlet basin, the cladoceran populations collapsed 7 yr after the mysid introduction. The mean cladoceran biomass was reduced by 95 to 99% for a decade before Bosmina longispina, Holopedium gibberum and Daphnia galeata developed new populations. B. longispina and H. gibberum almost disappeared again after a few years, while D. galeata was replaced by D. longispina, which unexpectedly maintained a relatively dense population in the presence of high mysid abundance. Rotifers declined significantly in Lille Jonsvatn after the mysid establishment, whereas copepod biomass did not change. Phytoplankton biomass increased during the first years after the cladoceran collapse, but declined later to levels lower than in pre-mysid years. The changes were probably a combined effect of reduced nutrient loads and grazing pressure. In the main basin, Store Jonsvatn, there were no detectable effects on the zooplankton community during the first 10 to 15 yr after the introduction, in spite of development to common densities of mysids within 8 yr. Over time, cladocerans decreased significantly, however, and mean biomass for the last 5 yr showed a 60% reduction compared with the first 10 yr. No significant long-term changes were detected in copepods, rotifers or phytoplankton biomass in Store Jonsvatn. Differences in temperature, stratification, light transmission and depth may partly explain the different plankton development in the 2 basins.KEY WORDS: Mysis relicta · Long-term study · Phytoplankton biomass · Zooplankton biomass Resale or republication not permitted without written consent of the publisher Contribution to the Theme Section 'Advances in the ecology of freshwater mysids'OPEN PEN

Forecasting the ecological impacts of the Hemimysis anomala invasion in North America: Lessons from other freshwater mysid introductions

“…There are virtually no published studies on its longterm dynamics, but strong temporal fluctuations are expected (as observed for other mysids, cf. Bowles et al, 1991;Koksvik et al, 2009;Langeland et al, 1991b;Spencer et al, 1991). A once abundant and expanding H. anomala population subsequently disappeared from a Dnieper River reservoir, apparently in response to water quality degradation (Pligin and Yemel'yanova, 1989).…”

“…Enhanced phytoplankton production has been observed in some lakes during the development of dense mysid populations, although such effects vary greatly over time (Kinsten and Olsen, 1981;Koksvik et al, 1991;Koksvik et al, 2009). A few years after the introduction of Mysis relicta to a Scandinavian lake, the phytoplankton biomass nearly doubled (Koksvik et al, 1991), likely in response to the reduction of large-sized cladocerans and to benthic feeding activities that release phosphorus from sediments (Northcote, 1991).…”

“…1; Table 2), upon which Mysis feeds preferentially (Lasenby and Fürst, 1981;Spencer et al, 1999). Cladoceran biomasses have been reduced by 55-99% following Mysis invasions (Koksvik et al, 1991;Koksvik et al, 2009;Langeland et al, 1991b). Although cladocerans are preferred prey, copepods may also be severely reduced in abundance (Spencer et al, 1999).…”

Heterocope borealis in Norway - A copepod on the move, or on the edge of its natural distribution?

“…There is evidence for dispersal of invertebrates between watercourses through tunnels built in connection with hydroelectric development in Norway, e.g. Mysis relicta (Koksvik & Reinertsen 2009, 2012. There is no zooplankton data from other lakes in the drainage area of Lake Fustvatn.…”

Advances in the ecology of freshwater mysids

“…In Lake Lille Jonsvatn, the cladocerans returned after a period of 11 yr with depressed Daphnia abundance. Koksvik et al (2009) think that this may be due to increased water clarity, which limits mysid migration into shallower water and provides a refuge for cladocerans in the epilimnion. This study highlights the importance of longterm studies.…”