Ecology of the Littoral Zone

Aquatic Biology
Dr. Bob Kistler
Ecology of the Littoral Zone- Chapter 11 Horn and Goldman [Plants of Lake Valentine - List]
Introduction to the littoral Zone
A. Two generalizations
1. mainly generalities
2. 2 components: aquatic macrophytes & epiphytes
B. The generalities - functions and anatomy
1. Acts as a buffer zone between the terrestrial (&watershed) & the aquatic system as all allochthonous materials must pass through
the littoral zone "filter"
2. The littoral zone is largely regulated by the geomorphology of the lake basin
- the steeper the slope, the narrower and less important the littoral zone
A/ 
b. shoreline development DL 
. Where L = shoreline perimeter; A0 = Area at zero depth [A perfect circle lake would
2 A0
have a SD of 1.0.]
Sedimentation rate: the rate of death and decomposition of organic and inorganic particles and organisms in a lake - something like
soil development in terrestrial ecosystems
Zonation of the sediments is important and is largely a result of wave action
a. sand in Eulittoral to upper infralittoral
b. gravel - plants can establish and colonize
c. boulders - difficult to colonize
d. silt - sedimentation from littoral and pelagic zones & is often anoxic
Swedish gyttja (yûtcha) or english copropel (copro= fecal+ pelos=mud) - humus on the bottom
Zonation of the littoral zone
Epilittoral zone - typically a bare zone due to use of water by aquatic macrophytes
Supralittoral zone - the spray zone - wind and wave affected
Eulittoral zone - the zone of changing water level where amphibious plants exist
Infralittoral zone
Upper Infralittoral zone - 1 meter, emergent plants, most productive
Middle Infralittoral zone - 1-3m, attached floating leaved plants
Lower Infralittoral zone - 3-10 m, limited by hydrostatic pressure at about 1Atmosphere limit
Littoral zone productivity is typically about 50% of overall lake:
An example of a lake with Zm <= 3m
a. Aquatic macrophytes 48-58%
b. Periphyton
c. Pelagic
The littoral zone is thus important to lake productivity
emergents remove 98% of light in the littoral zone depressing the contribution of other photosynthetic organisms except for those
with accessory pigments like Bluegreens and diatoms.
Emergents compete internally for nutrients, decreasing planktonic components in the littoral zone
Emergents often release "allelopathic" compounds like allyl sulfides which decrease both phytoplanktonic and periphyton
All littoral zone plants are "leaky" systems losing about 10% of their carbon and also acting as nutrient "pump" sources
Since they may rapidly change CO2 concentrations, the littoral zone plants may regulate alkalinity of the lake  use CO2 and
precipitate CaCO3
Summary - Macrophytes and the littoral zone thus are very important to the overall lake "economy"
% slope (%mean Slope = 100
Aquatic Macrophytes
A. Definition :
1. a plant that is normally found growing in association with free standing water, the level of which is at or above the soil surface.
2. A plant that is able to use both free and dissolved CO2,HCO33. Aplant that is able to complete its life cycle in water
B. There are four major "types"
1. Floating unattached
e.g. Lemna - duckweed is a plant that floats, has unattached roots, and never anchors
2. Floating attached
e.g. Nymphaea - pond lilies, roots are anchored, leaves float, may have "underwater" leaves
3. Submerged (up to 10 meters in depth)
e.g. Elodea and Ceratophyllum - entire life cycle (±flowering) occurs below the surface and these plants are usually anchored.
4. Emergent
e.g. Typha - cattails and rushes that grow in water saturated and submersed soils, from +0.5 to -1.5 m, perrenials
C. What is the origin of Aquatic plants?
1. 1300 species, 306 genera, 65 families with 12 wholly aquatic families
What this seems to indicate is that plants have moved from the land into the water and most every family of flowering plants will have at
least one aquatic member. No single group is dominant.
D. What are the problems of life in water for these "terrestrial" plants
1. Sex -pollen flow doesn't work under water
a. Hydrophily (underwater flowering) is rare
i. Coontail: males float free and shed pollen rain to attached females
b. aerial or floating is more typical
e.g. Vallisneria (wild celery)
i. Females have a very long peduncle on the flower and a very hairy stigma to keep the female flower parts dry
ii. Male flowers are in a little pocket that breaks off and floats to the surface, with 3 tepals— 2 act as rudders and
1 as a sail, and
iii. they float until they slide into the female flower depression resulting in pollination
iv. The peduncle coils following fertilization and pulls the developing zygote to the bottom and fruits and seeds
mature underwater (decrease predation)
2. Vegetative reproduction is more common
Some may never set seed
Ceratophyllum develops axillary buds which regenerate in spring from "dead" stems (seasonally)
3. Leaves - aerial, floating, submersed
a. aerial leaves are very much like terrestrial plants with a waxy cuticule and bottom stomata
b. floating leaves
i. are usually entire in shape to resist motion "stress", usually tough and leathery, with a thick upper cuticle, no
lower cuticle and a very hairy bottom leaf surface, stomata on the upper surface, often possess lacunae
ii. Petioles - are long and thin, with little to no secondary growth, are usually longer than the water depth(Why?).
(water variation, decreased shading)
iii. Etiolation occurs if leaves are submerged
c. Submersed leaves
S/V ratio increased for increased gas exchange (CO2 and O2 diffuse slowly)
Thin flexible leaves with little to no support structure (no collenchyma and schlerenchyma), no cuticle at all, and no hairs
No petioles, decreased to no stomata (why? - CO2 more abundant in H2O than air)
d. Heterophylly with floating, submersed and aerial leaves all occurring on the same plant is not at all atypical
Stems - submerged may totally lack most vascular tissue - xylem and phloem
Roots are reduced and serve more as anchors and less for nutrient uptake, but may also be highly developed to extract micronutrients
from soils.
Lacunae - the lacunae system
a. an adaptation to life in water
b. a hydrostatic skeleton to replace rigid support found in terrestrial cousins
c. increased flexibility
d. is an interconnecting system of gas filled canals and spaces for transport and storage of gases (CO2 and O2)
e. Buoyancy and leaf positioning for maximum light gain.
Aquatic and Wetland Vascular Plants of the Northern Great Plains
Gary E. Larson
Professor of Biology and Herbarium Curator
South Dakota State University
Brookings, South Dakota
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