Comparison of sampling methods for semipelagic animals in two deep basins of Lake Saimaa

Abstract

The efficiency of different methods for sampling semipelagic animals was compared in the deep basins of Lake Paasivesi and Lake Puruvesi of the complex Lake Saimaa, Finland, during 1990-92. Certain semipelagic animals, such as Mysis relicta, amphipods and larvae of ChaoborusJlavicans, are important bioindicators of water and benthic quality. However, owing to their high mobility and vertical migrations they are difficult to sample quantitatively with traditional benthic methods.The equipment used for sampling was comprised of: 1. Vertical nets (0.56 and 0.13 m2) placed on the bottom for 5 minutes or 12 hours and hauled up vertically. 2. Plexiglass traps placed on the bottom for 12-14 hours. 3. Mysis-trawl hauled horizontally c. 250-300 metres on the bottom. 4. Ekman-grab.In 1992, parallel samples were taken with vertically hauled nets (12 h and plexiglass traps baited with fish or liver or provided with a chemical light. Large vertically hauled nets were the most efficient equipment for catching Gammaracanthus lacustris, M. relicta and larvae of Ch. Jlavicans whilst baited or lighted nets were less effective. Lighted plexiglass traps were most effective in catching Pallasea quadrispinosa and water mites, but baited and control traps sampled inefficiently. The trawl sampled M. relicta and P quadrispinosa relatively well, but was less efficient in sampling other groups. The Ekman-grab was effective only for sampling Monoporeia aflnis.The semipelagic community differed between the studied basins. The dominant semipelagic animals in the humic, deep L. Paasivesi were M. relicta, amphipods and larvae of Ch. fivicans whilst the number of water mites was low in the catches. In the shallower, clear-water L. Puruvesi the densities of crustaceans and Chaoborus-larvae were low whilst some water mites, such as Pionapusilla, occurred in high numbers. Nocturnal sampling was more effective, especially for M. relicta.

Habitat shifts of Mysis relicta (Decapoda, Mysidacea) in the lakes Breiter and Schmaler Luzin (NE Germany)

“…Song & Breslin (1999) observed the occurrence of mysids in Lake Ontario both on mud and on anthropogenic sediments formed by coal mining. Bagge et al (1996) also caught Mysis on mud.…”

“…That is why Morgan & Beeton (1978) used a submarine for visual observations of M. relicta at greater depths. Bagge et al (1996) could not effectively catch mysids on the bottom of two Finnish lakes with plexiglass traps or Eckman-grabs. Their epibenthic dredge catches at depths of 250-300 m were also much poorer than the comparable vertical haul catches (0.5 ± 0.5 to 119.5 ± 111.1 ind./m 2 in lake Paasivesi and 0.8 ± 1.0 to 4.4 ± 14.7 ind./m 2 in lake Puruvesi).…”

“…Therefore, different methods are necessary to study its population structure and dynamics, as well as its density and movements in the water column and on the bottom. Densities of M. relicta were recorded effectively with vertical nets at night (Grossnickle & Morgan, 1978;Bagge et al, 1996). Scharf & Koschel (2004) successfully used these methods in the Luzin lakes.…”

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

“…There is no detailed research on the vertical occurrence of this species, although it is generally suggested to prefer the deepest zones of lakes with temperatures <8°C (Bagge, 1992;Bagge, Liimatainen, & Liljaniemi, 1996;Hill, Fürst, & Hammar, 1990;Särkkä et al, 1990). However, the ecology of G. lacustris and their role in lake food webs and ecosystems are poorly understood.…”

Recovery from acidification in boreal lakes inferred from macroinvertebrates and subfossil chironomids

“…Water mites (Acari, Hydrachnellae) and Nematoda were not identified to species. The Ekman grab used in this study is not effective for sampling water mites (Bagge et al, 1996), but they can be caught more effectively by traps baited with fish or provided with chemical light. Because of this, the abundance of Trichoptera 11…”