The South Pacific freshwater ecosystems have never been investigated systematically. Although their ecological value has long been recognized and recommended for protection, little action has been taken so far. Here, we present results of 39 lentic water bodies on 18 islands belonging to seven countries. Temperature, conductivity, and pH were measured and samples of aquatic organisms were collected. Freshwater algae, nematodes, rotifers, ostracods, copepods, cladocerans, and aquatic oribatid mites were identified to genus or species level. Sixty-six percent of all taxa recorded have a cosmopolitan distribution, 14% are circumtropical/tropicopolitan species, and for 20% a restricted distribution predominantly in Australasia has previously been reported. Eleven new copepod and three new ostracod taxa were discovered. Out of 39 water bodies we found at least 17 stocked with nonindigenous fish species. Salinization and uncontrolled introduction of alien fish species may lead to reduced species richness in these remote freshwater ecosystems. The highest species richness was recorded in old, shallow, fish-free softwater lakes at high altitude.

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.

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Abstract. The waters surrounding the Pribilof Islands are an important nursery ground for juvenile walleye pollock (Theragra chalcogramma), an important forage fish in the pelagic food web of the productive Bering Sea shelf region. The diet of juvenile pollock was studied in two consecutive years along a transect line crossing from a well‐mixed coastal domain, through a frontal region to stratified water farther offshore. Variability in stomach fullness was high and evidence for increased feeding intensity in the front was weak. Prey diversity and prey size generally increased with increasing fish size, shifting from predominantly small copepods to larger, more evasive prey items such as euphausiids, crab megalopae and fish. The diet of the fish reflected changes in the relative abundance of copepods and euphausiids in the prey fields between years. Juvenile pollock showed increased feeding rates at dusk, and stomach fullness as well as prey condition were generally lowest just before sunrise; however, the proportion of euphausiids increased in the diet of pollock caught at night, suggesting that some food was also ingested during darkness. Juvenile pollock and their euphausiid prey both vertically migrated above the thermocline at night, although each had a different daytime depth.