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Zooplankton: who are they?

Zooplankton: who are they?. Protozoans (protists) : Include heterotrophic nanoflagellates (“HNFs”) 1- 20 m m, eat bacteria and smaller HNFs – many prefer hypolimnion Other flagellates, amoeboids (Mastigophora), some of which can migrate vertically ( Difflugia )

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Zooplankton: who are they?

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  1. Zooplankton: who are they? • Protozoans (protists): • Include heterotrophic nanoflagellates (“HNFs”) 1- 20 mm, eat bacteria and smaller HNFs – many prefer hypolimnion • Other flagellates, amoeboids (Mastigophora), some of which can migrate vertically (Difflugia) • Ciliates: (Paramecium, Stentor, Vorticella) 8-300mm, can be mixotrophic, many are epibionts, or live in sediments • Comparatively little known about ecology. One reason is difficulty in studying; note that we hardly got any of these abundant organisms Difflugia Cyclidium

  2. Rotifers (Phylum Rotifera) • Named for the rotating band of hairs called corona • 30 mm – 1mm in size, very diverse group • Parthenogenic (mostly), with short generation times • Only a small portion are planktonic, but those are often quite cosmopolitan and abundant • Many are omnivorous, feeding on flagellates, small particles, protozoans • Include Keratella, Asplanchna, Filinia, (that we caught) as well as Brachionus, Conochilus Keratella Brachionus

  3. www.spea.indiana.edu Copepods • Reproduce sexually, with longer generation times (affected also by water temperature) • Larger size: 300 – 5mm; likely to be affected by any fish-related size structuring • Sexual reproduction, generation times longer (a couple per year) in calanoids • Cyclopoid are more predaceous than calanoids, who use currents to collect and select food using modified mouthparts. • Calanoids do better than unselective cladocerans at low food quality and quantity (picky) • Juveniles of both types are herbivorous, then change in adulthood (in cyclops or large calanoids like Epischura) www.stetson.edu/~kwork/images / cyclopoid%20nauplius.jpg

  4. Interactions of total zooplankton with chlorophyll:Some trend toward greater abundances of zooplankton where phytoplankton is more abundant

  5. Onondaga, Green, and Oneida Lakes all groups: • 1) Greatest abundances in hypolimnion for all (Green monimolimnion not included) • 2) Mostly cladocerans in Onondaga and Oneida, more copepods/rotifers in Green • Copepods make up more of total in metalimnion (although actually greater • numbers in hypolimnion, as we will see) Bar charts Pie charts

  6. Arbutus, Deer, and Wolf Lakes all groups: • Greatest abundances in metalimnion (except Deer, where all laters are similar)- • However, none of these lakes appear to really be stratified anyway, so • differences may be merely chance... • 2) Mostly copepods in Arbutus and Deer, more Cladocerans in Wolf • 3) Trends for the groups different for each lake... Bar charts Pie charts

  7. Protozoans and rotifers in each lake by layer:Favor either metalimnion or hypolimnion (note Onondaga, which in all cases seems to have increasing numbers with depth)

  8. Break-down of protozoans and rotifers in layers (all lakes averaged):1) Keratella most abundant2) Trends hard to determine due to incomplete identification!

  9. Copepods in each lake by layer:1) Onondaga, Green, and Deer share trend of increase with depth2) Arbutus and Wolf have greatest in metalimnion3) Oneida shows reverse trend of 1); greatest in shallow waters

  10. Break-down of copepods in layers (all lakes averaged)1)Cyclops more abundant in epilimnion, calanoid in metalimnion2)Hypolimnion unknown due to identification problems...

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