Littoral Community: Larger Plants and Benthic Animals

1. Littoral Community: Larger Plants and Benthic Animals Wetzel Including, but not solely: Chs. 19, 20, 22 pp. 600-629, 665-725

2. Lacustrine Zonation and Terminologyp. 42 class notes, Fig. 8-2 Wetzel • Epilittoral – above water, not subject to spray • Supralittoral – above water, subject to spray by waves • Littoral • Eulittoral – between highest and lowest seasonal water levels, subject to disturbances of waves

3. Lacustrine Zonation and Terminology cont. • Littoral cont. • Infralittoral – 3 regions based upon distribution of macrophytic vegetation • Upper Infralittoral – emergent rooted vegetation • Middle Infralittoral – floating-leaved rooted vegetation • Lower Infralittoral – submerged rooted vegetation • Littoriprofundal – transitional zone of attached algae and bacteria; cyanobacteria important in this zone • Profundal – free of vegetation

4. Lacustrine Zonation and Terminology

5. Benthic Algae Terminology • Algae by attachment places: • Rocks: epilithic • Sediments: epipelic • Plants: epiphytic • Animals: epizooic • Sand: epipsammic

6. Benthic Animals • Benthos defined – animals associated with substrata • Distribution, abundance, productivity determined by ecological processes • Historical events that limit an organism reaching an environment • Physiological limitations of the organism at any life stage for a specific habitat • Availability of energy resources (food) • Ability of species to tolerate competition from endemic organisms

7. Esrom Lake diagrams from Berg, 1938 – distributions from 0.2-20m

8. Esrom Lake Distributions cont.

9. Esrom Lake Distributions cont.

10. Benthic Animals cont. • Major groups: • Protozoa • Diverse group • Ciliate and flagellate protozoans important • Little known about productivity • Porifera • Freshwater sponges • Few, but some occur in Lake Erie • Hydrazoans • Freshwater hydras

11. Benthic Animals cont. • Flatworms/Turbellarians • Roundworms/Nematodes • Horsehair worms/Nematomorpha • Bryozoans • Annelids • Oligochaets • Leeches • Arachnids • Water mites/Hydrachnida • Ostracods • microcrustaceans

12. Benthic Animals cont. • Malocostracean Crustaceans • Mysids/Opossum Shrimp • Isopods/Sowbugs • Decapods/Crayfish, Shrimp • Amphipods/Scuds • Mollusks • Gastropods • Bivalves • Aquatic Insects

13. Benthic invertebrates as indicators of lake health • Just as fish can be indicators, so can benthic invertebrates • These organisms have high oxygen demands • As the lake becomes more eutrophic, decomposition in profundal waters increases • Decreases oxygen concentration, more tolerant organisms become more abundant in benthos • In Lake Erie, as lake became more eutrophic, lost Hexagenia sp. (burrowing mayfly); as lake became less eutrophic due to nutrient controls, Hexagenia has come back

14. Aquatic Macrophytes • Net productivity does not overlap with max biomass due to high respiration and death • Fig 18-8 • Macrophytes can significantly contribute to oxygen concentration • Fig 18-3

15. Types of Macrophytes • Rooted emergent • Rooted floating • Floating • Submersed

16. Macrophytes and Primary Productivity • Table 18-10 • Compare macrophytes to phytoplankton • Macrophytes as productive as a rain forest? • How much of this productivity is transferred to higher trophic levels?

17. Macrophyte interactions with zooplankton • Two distinct possibilities have been proposed • Zooplankton avoid macrophytes due to mechanical interference • Zooplankton use macrophytes as refugia from predation

18. Zooplankton Avoidance of Macrophytes • Pennak (1973) • Reasons for avoidance • Shadows cause zooplankton to avoid • Macrophytes release substance that repels zooplankton • Used a tank with divider to measure zooplankton preference • Four treatments • Control – both sides empty • One side had vegetation • One side had plastic vegetation • One side vegetation, other side plastic vegetation • Response was % Daphnia on vegetated side

19. Pennak cont. • Results: • Shadowing effect was less important than repellent effect • However, repellent effect seemed to wear off after approximately sixteen days

20. Macrophytes as Refugia • Lauridsen and Lodge (1996) • Hypothesis: macrophytes can serve as both a refuge and an impediment for Daphnia depending upon the presence/absence of fish • Response: % of Daphnia in central area of tank • Central area was near fish but had no macrophytes

21. Lauridsen and Lodge results • Zooplankton also avoid macrophytes when no fish are present • Zooplankton avoid the open area when fish or fish odor is present • Therefore, behavioral avoidance of fish supercedes behavioral avoidance of macrophytes • Consequently, macrophytes may serve as refugia in shallow lakes with fish where diel vertical migration (DVM) is not possible, but zooplankton still avoid macrophytes

22. Conclusions • Spatial heterogeneity occurs and is of importance in lakes – i.e. Esrom lake • Macrophytes are not just simple, non-interactive plants in the water • Organisms specialize to all sorts of different habitats – kinds of benthic algae, different kinds of plants, etc.