Littoral Community: Larger Plants and Benthic Animals

Wetzel

Including, but not solely:

Chs. 19, 20, 22

pp. 600-629, 665-725

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

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

Lacustrine Zonation and Terminology

Benthic Algae Terminology• Algae by attachment places:

– Rocks: epilithic– Sediments: epipelic– Plants: epiphytic– Animals: epizooic– Sand: epipsammic

Benthic Animals• Benthos defined – animals associated with

substrata• Distribution, abundance, productivity

determined by ecological processes(1) Historical events that limit an organism reaching an

environment

(2) Physiological limitations of the organism at any life stage for a specific habitat

(3) Availability of energy resources (food)

(4) Ability of species to tolerate competition from endemic organisms

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

Esrom Lake Distributions cont.

Esrom Lake Distributions cont.

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

Benthic Animals cont.• Flatworms/Turbellarians• Roundworms/Nematodes• Horsehair worms/Nematomorpha• Bryozoans• Annelids

– Oligochaets– Leeches

• Arachnids– Water mites/Hydrachnida

• Ostracods– microcrustaceans

Benthic Animals cont.

• Malocostracean Crustaceans– Mysids/Opossum Shrimp– Isopods/Sowbugs– Decapods/Crayfish, Shrimp– Amphipods/Scuds

• Mollusks– Gastropods– Bivalves

• Aquatic Insects

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

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

Types of Macrophytes

• Rooted emergent

• Rooted floating

• Floating

• Submersed

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?

Macrophyte interactions with zooplankton

• Two distinct possibilities have been proposed

(1) Zooplankton avoid macrophytes due to mechanical interference

(2) Zooplankton use macrophytes as refugia from predation

Zooplankton Avoidance of Macrophytes• Pennak (1973)

– Reasons for avoidance(i) Shadows cause zooplankton to avoid(ii) 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

Pennak cont.• Results:

– Shadowing effect was less important than repellent effect

– However, repellent effect seemed to wear off after approximately sixteen days

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

% in Central AreaControl - macrophytes - fish - fish odor 12

Macrophyte avoidance + macrophyte - fish - fish odor 73Macrophyte vs. Fish + macrophyte + fish + fish odor 34

Macrophyte vs. Chemical Fish Presence + macrophyte - fish + fish odor 46

Treatments for determining fish vs. macrophyte effects

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

% in Central AreaControl - macrophytes - fish - fish odor 12

Macrophyte avoidance + macrophyte - fish - fish odor 73Macrophyte vs. Fish + macrophyte + fish + fish odor 34

Macrophyte vs. Chemical Fish Presence + macrophyte - fish + fish odor 46

Treatments for determining fish vs. macrophyte effects

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.