Only the small survive: monitoring long-term changes in the zooplankton community of an Alpine lake after fish introduction

Abstract

The zooplankton community of Alpine lake Seehornsee (1,779 m a.s.l.) was studied over a period of 13 years. In 1994, a typical high-altitude zooplankton community, consisting of two calanoid copepods (Mixodiaptomus laciniatus, Arctodiaptomus alpinus), one cladoceran (Daphnia rosea), and two rotifers (Keratella quadrata, Synchaeta pectinata) coexisted with infertile charr hybrids, which had been introduced in 1969 and again in 1974. When the aged fish were removed by intensive gill netting, they had fed predominantly on aquatic insects. After a fish-free period of 4 years, 2000 fertile juvenile Alpine charr (Salvelinus umbla) were stocked in 1998 and again in 1999. They preyed on benthic (chydorids, ostracods, cyclopoid copepods, chironomid larvae and pupae) and planktonic prey (diaptomid copepods, Daphnia). Between 2004 and 2006 charr successfully reproduced. Nine years after stocking of fertile charr, the two calanoids had virtually disappeared, and Daphnia rosea had notably declined in abundance. In concordance with the size efficiency hypothesis (Brooks and Dodson 1965), the newly appearing and smaller cladoceran Ceriodaphnia pulchella, together with the two resident, and two emerging species of rotifers (Polyarthra luminosa, Gastropus stylifer) dominated the zooplankton community.

Cascading effect of exotic fish fry on plankton community in a tropical Andean high mountain lake: a mesocosm experiment

“…These results show that young trout preyed heavily on the largest and most abundant zooplankton species (C. brandorffi), similar to that found by other authors (Hall et al, 1976;Schabetsberger et al, 2009;Tiberti et al, 2014). However, we also found that small crustaceans such as Ceriodaphnia and cyclopoid copepods were preyed upon by trout, in contrast with some other studies (Knapp et al, 2001b;Schabetsberger et al, 2009;Maclennan et al, 2015). The diets of smaller juvenile fish have not previously been characterized as they are usually not caught by gear such as gill nets.…”

Behind the impact of introduced trout in high altitude lakes: adult, not juvenile fish are responsible of the selective predation on crustacean zooplankton

“…Selective predation on more visible prey taxa, such as large zooplankton species, is the ecological mechanism driving the impact. The response of zooplankton communities to fish predation include the decrease or even the loss of large taxa (e.g., large copepods and daphnidae) favoring their smaller competitors (e.g., rotifers and chydoridae) (Schabetsberger et al, 2009;Tiberti et al, 2014). This is a well known ecological process, which has been usually studied comparing the zooplankton communities of naturally fishless and stocked lakes (Knapp et al, 2001;Tiberti et al, 2014) or before-after fish stocking or eradication (Brancelj, 1999;Knapp et al, 2001;Parker et al, 2001;Knapp et al, 2005;Schabetsberger et al, 2009).…”

Consecutive earthquakes temporarily restructured the zooplankton community in an Alpine Lake

“…Big-bodied Daphnia that appear from time to time in the Lake Krn, in contrast, are probably eliminated by the fish. Schabetsberger et al (2009) reported relatively quick shifts (2-5 years) from large bodied zooplankton (Mixodiaptomus laciniatus (Lilljeborg, 1889), A. alpinus, Daphnia rosea G.O. Sars, 1862) to small bodied (Ceriodaphnia pulchella G.O.…”

“…Such alpine lakes are mostly small and sensitive to external or internal disturbance as their biological processes are slowed by low temperatures and/ or short ice-free periods (Battarbee et al, 2002;Catalan et al, 2002Catalan et al, , 2009. Their zooplankton communities are simple, and usually consist of one or two taxa of Calanoida, one Cyclopoida, one or two Cladocera, and some Rotifera (Luger et al, 2000;Cavalli et al, 2001;Jersabek et al, 2001;Brancelj, 2002;Schabetsberger et al, 2006Schabetsberger et al, , 2009. Analyses of sediment cores have revealed some changes in the species composition of their zooplankton and benthos, but most of these were caused by fish introduction, pollution, or climate change that rapidly altered the structure of these communities (for relevant references, see below).…”

“…However, since the 15th century, most lakes in the Alps and elsewhere in Europe, and later also in North America, have been stocked with fish, predominantly with Arctic char and brown trout (Schabetsberger et al, 2009). This induced incisive changes in zooplankton, reflected in novel species compositions and/or shifts in size classes (Goyke and Hershey, 1992;Johnson et al, 1996;Schabetsberger et al, 2006).…”