EVPP 550 Waterscape Ecology and Management – Lecture 11

1. EVPP 550Waterscape Ecology and Management – Lecture 11 Professor R. Christian Jones Fall 2007

2. Lake Biology – BenthosProfundal Benthos • Profundal habitat can be very challenging in lakes • Cold for most of the year due to summer stratification • Anaerobic in mesotrophic and eutrophic lakes • Poor food quality: no resident primary producers, all food is imported and “stale”

3. Lake Biology – BenthosProfundal Benthos • A few groups have been able to adapt to this environment • Those which have can prosper if conditions are not too severe • Examples are chironomids (midges), chaoborus (phantom midges) and oligochaetes

4. Lake Biology – BenthosProfundal Benthos • Chironomids have been extensively studied • Some species can maintain constant respiration even at low DO • Some can withstand no oxygen for up to 4 months at 10oC • Food supply of profundal chironomids is surface sediment particles ingested in bulk with algae and bacteria selectively assimilated

5. Lake Biology – BenthosProfundal Benthos • Adaptations • Hemoglobin • Helps to bind and store limited amounts of O2 • Anaerobic glycolysis • Can split carbohydrates to produce energy with using oxygen • Similar to what happens in your muscles under strenuous activity • Accumulate an oxygen debt that must later be satisfied • Stop growth, become dormant

6. Lake Biology –Profundal Benthos • Life History of Chironomus anthrocinus in L. Esrom • Egg mass deposited at night in May on lake surface near shore • Water currents spread the eggs throughout the lake as they sink to the bottom • By June, hatching occurs, food is abundant and larvae double in size by early July • Oxygen is depleted in summer and growth stops

7. Lake Biology –Profundal Benthos • Life History of Chironomus anthrocinus in L. Esrom • Fall overturn brings oxygen to the bottom satifying the oxygen debt and allowing fresh growth to occur based on food still in the water column • Animals are quiescent during winter, but perk up again the following spring with onset of new food

8. Lake Biology –Profundal Benthos • Life History of Chironomus anthrocinus in L. Esrom • Some have grown large enough to emerge after one year, but many need a little more growth and emerge the second year • Emergence occurs at the surface, mating occurs, eggs are laid, and adults die within a few days • Highly synchronized pop’n

9. Lake Biology –Profundal Benthos • Chaoborus • Phantom midge • Alternates between plankton and benthos • Prey mostly on zooplankton and are preyed upon by fish • Migrates daily from sediment surface to photic zone • Under anaerobic conditions, may stop downward migration at the thermocline

10. Lake Biology –Profundal Benthos • Oligochaetes • Development is unsynchronized • Burrow through surface sediment, digesting bacteria, mixing sediments, and recycling nutrients

11. Littoral Zone • Portion of lake where photic zone includes the bottom

12. The Littoral Zone - Macrophytes • Macrophytes • Plants whose overall structure is visible to the naked eye • Distribution in lakes is subject to two basic constraints: • Water must be shallow enough for light to reach the bottom (= littoral zone as we have defined) • Physical stability sufficient to allow plants to grow to the bottom

13. The Littoral Zone - Macrophytes • Characteristics • General Morphology • 4 basic morphological types typically occupying “zones” of increasing depth • Emergent • Floating-leaved • Submersed • Unrooted

14. The Littoral Zone - Macrophytes • Emergent macrophytes • Occupy the transition zone between land and water • Rooted in sediment or saturated soils (anaerobic) • Shoots and leaves extend into the air so, like terrestrial plants, they must be self-supporting & get CO2 from air • Mostly angiosperms • Ex.: cattails, wild rice

15. The Littoral Zone - Macrophytes • Floating-leaved macrophytes • Root in sediment, leaves float on surface • Connections are via stems or petioles • 0.5 m < z < 3 m • Need to have some standing water, but limited by petiole or stem length • In case of water lilies, both root and stem are underwater and petioles (leaf stem) extends through water to surface leaves • A patch of water lilies may actually be one plant • Ex: yellow water lily (Nuphar), white water lily (Nymphaea)

16. The Littoral Zone - Macrophytes • Submersed Macrophytes • Whole plant is underwater • 0.5 < z < 10 m (angio-sperms), up to 100 m for mosses, Chara • No supporting tissue, rely on turgor pressure and buoyancy to maintain erect form • Underwater leaves often finely dissected, but may be laminar • May have heterophylly (different underwater vs. surface leaves) • Ex: Myriophyllum (milfoil), Potomogeton (pondweed), Chara (stonewort), Isoetes (water fern)

17. The Littoral Zone - Macrophytes • Unrooted macrophytes • Floating • Lemna (duckweed) • Eichornia (water hyacinth) • Submersed • Ceratophyllum (coontail)

18. The Littoral Zone - Macrophytes • Taxonomy • Charaphytes (stoneworts) • Algal group related to green algae • Macroscopic form • Ex: Chara, Nitella • Bryophytes (mosses, liverworts) • Plants with some tissue and reproductive specialization, but no vascular tissue (xylem, phloem) • Ex: Sphagnum

19. The Littoral Zone - Macrophytes • Taxonomy • Ferns and Fern Allies • Plants with vascular tissue, but no flowers • Ex: Isoetes (submersed macrophyte found in soft water) • Ex: Equisetum (horsetail) (emergent macrophyte)

20. The Littoral Zone - Macrophytes • Taxonomy • Gymnosperms • Vascular tissue • Reproductive: “cones” • Ex: Bald Cypress (emergent) • Angiosperms • Vascular tissue • Flowers • Ex: Cattail (Typha) • Ex: Water Lilies (White and Yellow) • Ex: Myriophyllum (milfoil) • Ex: Hydrilla • Ex: Potamogeton (pondweed) • Ex: Vallisneria (water celery)

21. Macrophytes – Factors Affecting Growth • Low oxygen levels around roots • Sediments are usually anoxic, but roots need oxygen or growth will be inhibited • Some species have vertical air tubes called lacunae which extend from the shoots down into the roots to help aerate • Root cells may be able to withstand oxygen debt

22. Macrophytes – Factors Affecting Growth • Inorganic carbon supply • Low rate of diffusion of CO2 through bulky macrophyte tissue could lead to carbon shortage • Plants can also use CO2 and in very soft water, uptake can occur through roots

23. Macrophytes – Factors Affecting Growth • Depth – Pressure • Vascular macrophytes do not grow to a depth of more than 10 m (representing 1 extra atmosphere of pressure) • This seems to be related to the effect of this extra pressure on the xylem and phloem • However, mosses have been found at up to 165 m and Chara to 64 m in Lake Tahoe, for example

24. Macrophytes – Factors Affecting Growth • Depth - Light • Two effects: Light & Pressure • Water transparency is highly correlated with depth to which macrophytes can grow • Note that maximum depth of colonization is less than photic zone depth which is about double Secchi disc depth

25. Macrophytes – Factors Affecting Growth • Depth - Light • One way that macrophyte communities respond to potential light limitation is to favor species that develop a canopy as opposed to those the grow near the sediment surface (rosettes)

26. Macrophytes – Factors Affecting Growth • Nutrients • N&P can be taken up by roots and shoots • Relative importance of root vs. shoot uptake depends on sediment vs. water concentrations • Ex: Lake Wingra, WI • 73% of P by roots • 27% of P by shoots • Root uptake is then translocated to shoots to fuel growth

27. Macrophytes – Factors Affecting Growth • Sediment Stability • Texture is important • Need fine particles: fine sand, silt or clay • Course sand, cobble, boulders are not good rooting medium • Stability is also important • If sand is moving, like on a beach plants will not become established

28. Macrophytes – Patterns of Abundance & Production • Seasonal • In temperate areas, macrophytes are very seasonal in their growth • Maximum development in late summer • However, some dieback over much of the year • In fact, plants create and shed shoots continuously

29. Macrophytes – Factors Affecting Growth • Productivity determination • Maximum standing crop • But this ignores biomass that was shed building up to maximum • C-14 approach • Measure C-14 uptake by actively photosynthesizing parts of plant • Cohort analysis • See previous page

30. Macrophytes – Spatial Patterns • Within lake • Macrophytes generally cover only those parts of the right habitat (light, substrate, etc.) • Between lakes • Great differences between lakes

31. Littoral Zone - Periphyton • Characteristics • General Morphology • Algae: unicells, filaments, colonies • 2 general types of attachment • Adnate: cells in close contact with substrate, hard to dislodge • Loose: cells only loosely attached, easily dislodged • Taxonomy • All groups of algae represented, esp • Cyanobacteria, diatoms, greens

32. Littoral Zone - Periphyton • Factors affecting development • Substrate Availability • The amount of surface habitat obviously influences the abundance of periphyton • Could be fairly static like bottom area in photic zone or very dynamic like annual plant surfaces • Light • Have a very similar photosynthesis-light relationship as phytoplankton

33. Littoral Zone - Periphyton • Factors affecting development • Nutrients • Can periphyton get nutrients from their host substrate? • Results seem to suggest this is not a major factor • Label P in sediments, grow macrophytes, less than 5% of P in epiphytes comes from sediment • High correlation with lake water P

34. Littoral Zone - Periphyton • Patterns of Abundance and Productivity • Epiphytic periphyton vary both with depth and seasonally • These variations are a combination of: • Changes in the density of epiphytes on the macrophyte • Changes in the amount of macrophyte substrate available at different depths and times

35. Littoral Zone - Periphyton • Productivity would also need to take into account variations in light and P-I response

36. Littoral Zone - Periphyton • Resulting productivity could vary seasonally and from one year to the next • Note day-to-day variation in production (light driven) • Note different seasonal pattern (substrate availability driven) • Note rough equivalence of 10 mg C produced per mg Chl a present per day

37. Littoral Zone – Littoral Invertebrates • Characteristics • Include a much larger suite of organisms than found in the profundal benthos • Some of the dominant groups include: • Flatworms • Oligochaetes • Molluscs • Snails • Bivalves • Arthropods • Crustaceans • Insects

38. Littoral Zone – Littoral Invertebrates • Characteristics • A wide variety of feeding strategies including: • Grazers/herbivores (due to presence of primary producers in the littoral zone) • Detritivores • Predators • Littoral grazers tend to focus on periphyton as it is much more digestable • Macrophyte production tends to get utilized as detritus

39. Littoral Zone – Littoral Invertebrates • Characteristics • Type of predators • Lurking • Dragonflies • Sit in a concealed position • Attack prey as they come by • Concealed, but dependent on prey movement • Hunting • Water bugs • Actively search for prey • Often well-armoured, taste bad, and move quicky to avoid predators • Can capture both moving and stationary prey

40. Littoral Zone – Littoral Invertebrates • Characteristics • Littoral zone can be an area of great physical and chemical complexity • Allows a very high diversity, but also presents some significant sampling problems • Heterogeneous distribution • Difficulties in capturing organisms within vegetation, rocks, logs, etc.

41. Littoral Invertebrates – Patterns of Abundance • Seasonal and spatial patterns • Examine results from a study of littoral invertebrates in the tidal freshwater Potomac River • Organisms captured by dropping nets over 0.5 m2 of weedbed • Nets closed by diver at bottom and brought to surface where organisms were removed from vegetation and preserved • Study design • 3 bed types: open water, Hydrilla, mixed • 2 months (July, August) • 5 replicates each

42. Littoral Zone – Littoral Invertebrates • Results • Macrophytes harbored much higher abundance of macroinvertebrates than open water • Taxa list was similar at all sites, but relative abundance differed both with plant type and month

43. Littoral Zone – Littoral Invertebrates • Cluster analysis • Confirmed differences between veg and open water • Suggested that variation between months was more important that variation between plant types

44. Littoral Zone – Littoral Invertebrates • PCA • Reinforced importance of plants • And the effect of month over plant type