Ecology
of Coastal Ecosystems:
Seagrasses and Salt Marshes
1. How are
coastal environments different from lake edges?
- Tidal variation
in water level -
- Salinity changes
daily
- Physiological
challenges to life because of osmotic gradients
- Solutions
- Plants:
internal osmotica, exclusion, excretion
- Betaines,
prolines, dimethylsulphoniopropionate (DMSP)
- Animals: skin
exudation of salt, outer mucus cover, drinking, transport across gill,
transport out by urine
- Inundation
changes daily
- Transport of
materials in and out of the coastal environment
2. How are they
the same?
- Trophic
connections: primary producer to tertiary consumer
- Plant
adaptations to inundation
- Importance of
detrital cycles to nutrient cycling
- Important
nursery functions for fish
3. Biological
components of coastal environments
- Water generally
more turbid
- More nutrients
- More sediments
- More
phytoplankton blooms - generally the major producers in the shallow
waters
- Zooplankton
& Nekton similar to ocean
- Rich sediments:
development of saltmarshes, mangrove swamps
- If photic zone
extends to the bottom: seagrasses and macroalgal communities (kelp
forests, rockweed beds, algal flats)
4. Save our SAV? = Submerged Aquatic Vegetation
- Fresher parts of
estuaries: Najas sp., Anacharis sp., Vallisneria sp., Duckweeds
- Brackish to
maritime zones: Ruppia maritima,
Zostera marina, macroalgae
(reds:
Agardhiella sp., Gracillaria sp.; greens: Ulva sp., Codium sp.; browns:
Ectocarpus sp., Fucus sp.)
5. Marine
Flowering Plants = seagrasses
- Phylum:
Anthophyta (Magnoliophyta)
- Class:
Monocotyledoneae
- Order:
Helobiae
- Families
(with some US representatives):
- Cymodoceaceae:
- Halodule
wrightii (shoal grass) - NC to Fla, G of
Mexico
- Syringodium filiforme
(manatee grass) - subtropical
- Hydrocharitaceae:
- Thalassia
testudinum (turtle grass) - subtropical
- Halophila
engelmanii,- subtropical
- H.
johnsonii, H. decipiens
- Ruppiaceae:
Ruppia maritima
(widgeon grass)- dist. ?
- Zosteraceae:
- Zostera
marina (eelgrass) - N. temperate, global
- Phyllospadix
scouleri (surf grass) - temperate, Pacific
6. Graphics from
Dawes, 1998. Marine Botany. and pictures from JJS.
Syringodium filiforme
Halodule wrightii
Thalassia testudinum
Halophila engelmannii
Zostera marina
7. Figure
3.1: World distribution of major seagrass and kelp genera from
Dawes, 1998.
8. What is a seagrass?
Seagrasses are higher
plants: separate conducting tissues, distinct leaves, stems,
roots and flowers.
A. Leaf
1. Epidermis: most
lack chloroplasts but seagrasses have
2.
Mesophyll: 2 types, spongy and palisade
Vascular tissue:
xylem and phloem
B. Stem:
not woody, typically underground = rhizome
C. Root: primary
root (radicle) stops growing soon after germination and an adventitious
root system takes over.
D. Flower: ovules are
enclosed during their development = angiospermy
9. Angiosperm Anatomy (handout given to class) with diagrams from
Dawes, 1998.
Leaf structure
A. Epidermis =
site of photosynthesis
B. Waxy cuticle
thin
C. Small,
usually unlignified veins
D. No stomates
E. Arenchyma
(air exchange or flotation?)
F. Poorly
developed, non-supportive Xylem
G. Well
developed phloem with sieve tubes and plates
10. Angiosperm
Morphology: Turtle grass (Thalassia
testudinum) Graphics from Dawes, 1998.
Leaf Development: basal
meristems
Flowering:
hydrophilous pollination
11. What are the
ecosystem services of seagrasses?
1. Sediment traps:
stabilization
2. Highly
productive
a. Direct --> herbivores
b. Indirect
--> detritus (most important)
3. Habitat and
shelter for economically important fin & shellfish
4. Substrate for
epiphytes
5. Nutrient sink
& recycling
12. What
problems would a land plant have to solve to live in the sea?
- Salinity
- Submerged growth
- Anchoring in
unconsolidated sediments
- Submerged
pollination
- Herbivory
- Biofouling
- Currents
13. How have
seagrasses adapted to the sea?
- Well developed
rhizomes
- Flat, ribbon
shaped or cylindrical, supple leaves
- Flowers which
are small and inconspicuous
- Pollen in
gelatinous strands, carried by currents.
- Antiherbivore
and anti-biofouling compounds in leaves: tannins, other phenolic
compounds.
14. From where
does a seagrass get its carbon?
- Seagrasses have
no stomates and they grow submerged.
- Their sources of
C are CO2 or HCO3-.
- Aquatic plants
develop boundary layers around their leaves due to diffusion.
- Solutions?
A. Use sediments as a source
of inorganic C.
B. Recycle CO2
through a lacunar system
15. From where
does a seagrass get N?
- N is most often
limiting
- Redfield ratio
->106 C: 16N:1P
- Sources
- Recycled from
sediments
- Water column
- Fixed by
Prokaryotes
16. From where
does a seagrass get P?
- P may be
limiting in some tropical systems.
- P enters from
roots or leaves
- P which enters
the leaves usually stays in the leaves.
- Primary source
is the sediments.
17. Handout:
Chesapeake Bay N sources
18. Handout:
Narragansett Bay N & P:Inputs + regeneration
19. Graphic: map of Great Sippewissett Marsh
20.
Handout: Massachusetts marshes:N budget
21. Handout:
Comparison of N2 fixation in marine and freshwater ecosystems
22. Graphics:
Seagrass Community Components: Epiphytes
23. Graphics:
Seagrass Restoration: tank cultures and axenic cultures