Download Seagrasses

Switching gears from algae to angiosperms
Seagrasses
blade
holdfast
flower
leaves
stem
roots/rhizomes
• Less tissue specialization
• Happy in salt water
• More tissue specialization
• Stressed by salt water
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Algal Evolution:
Angiosperm Characteristics
3.9 bya = Cyanobacteria appear and introduce photosynthesis
2.5 bya = Eukaryotes appeared (nuclear envelope and ER thought to come
1) Pigments: chl a &chl b
cartenoids- B-carotene, violaxanthin
from invagination of plasma membrane)
1.6 bya = Multicellular algae -Rhodophyta (Red algae) &Chlorophyta
(Green algae)
2) Chloroplast structure: 2membranes
stacks of 2-6
3) Storage product: starches:amylose & amlyopectin
900 mya= Dinoflagellates & Invertebrates appear
4) Flagella: None depend of pollinators, wind, birds, bugs, bats
5) Mitosis: double fertilization
sperm cell undergoes mitosis
1 sperm fuses with egg to form zygote
1 sperm fuses with polar nuclei to form endosperm
- nutritional source for growing zygote
490 mya = Phaeophyceae (Brown algae) & land plants & coralline algae &
crustaceans & mulluscs
408mya= Insects & Fish
362 mya = Coccolithophores & Amphibians & Reptiles
290mya- Gymnosperms
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145 mya = Diatoms & Angiosperms
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Groups (Kingdom)
DOMAIN
1.Bacteria- cyanobacteria (blue green algae)
2.Archae
3.Eukaryotes
1. Alveolates- dinoflagellates
Unicellular, freshwater
Chloroplast peptidoglycan
2. Stramenopiles- diatoms, heterokonyophyta
Plantae
3. Rhizaria- unicellular amoeboids
Rhodophyta
Chlorophytes
phycoerythrin
4. Excavates- unicellular flagellates
5. Plantae- rhodophyta, chlorophyta, seagrasses
6. Amoebozoans- slimemolds
7. Fungi- heterotrophs with extracellular digestion
Chl b,
Starchamylose &
amlyopectin
Glaucophytes
Charophytes
Embryo,
cuticle
Land Plants
8. Choanoflagellates- unicellular
9. Animals- multicellular heterotrophs
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Adapted from Sadava 2014
Types of flowering plants
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Seagrass taxonomy
Mesophytes/ Glycophytes- grow where freshwater is available & lack
specialized adaptations that prevent water loss
2. Hydrophytes- live in water, partially or fully submerged (seagrass)
3. Xerophytes- have, morphological, anatomical, & reproductive
adaptations to aid in the retention of water ( mangroves & salt
marsh plants)
1.
Halophytes- adaptations to prevent water loss & can grow in
saline habitats
1. Facultative- do not require saline conditions
2. Obligate- specific requirement for sodium to complete their
life cycle
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Domain Eukaryote
Kingdom/Clade Plantae
Phylum/Division Magnoliophyta - angiosperms
Class Liliopsida - monocots
Order Najadales
y Zosteracea- eel g
grass
Family
Genus
Phyllospadix- surf grass
species
scouleri
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Evolution of Seagrasses
Seagrasses are Monocots
Monocots - one cotelydon (embryotic leaf)
- flowers petals either 3, 6, 9
- leaves with parallel blades
more closely related to lilies than grasses
- ~60 spp; present on all continents except Antarctica.
- Tropical and temperate spp; shallow, soft sediment nearshore
environments
- Initially, debate on whether seagrasses evolved from coastal plants
(salt marsh or mangroves) or freshwater plants
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Seagrass Distribution
- Recent molecular work suggests both are correct: polyphyletic
origins of seagrasses ( at least three evolutions of salt water habitat)
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SEAGRASS
1. Stabilize sediments, prevent erosion
- physically & chemically change the sediment through release of
O2, decomposition of subterranean parts, bioturbidation through
growth of roots & rhizomes
2. Improve water clarity by trapping particulates
3. Seagrass meadows = incredibly productive environments
- High Ps rate; 2000-4000 g C/m2/yr; on same order as sugar cane
-Importance of detrital food web; epiphyte productivity; use of stable
isotope analysis to identify both
- 2ndary productivity- biomass of heterotrophic organisms in a system
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4. Nursery role for many commercially important fish
and inverts
Adaptations to marine life
Hydrophytes-Ability to live completely submerged in salt water
- No stomates (osmoregulation and CO2 uptake through epidermal cells)
- Chloroplasts only in thin layer of epidermal cells
5. Important trophic linkages to other ecosystems
- Hydrophilic pollen
- Bladelike morphology with sheath  high energy environments
- Lots of things eat in one place, poop/die in another
- Lacunae & aerenchyma = air spaces
e.g., grunts in the Caribbean; hide out during the day in
coral crevices, forage at night in seagrass meadows
- Seagrass leaves
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Biomass & Productivity
Seagrass morphology
Below-ground Biomass- 50 -90% of standing stock
Upper Leaf Blades- photosynthesis
Basal Leaf Sheaths- colorless, covers
short shoot and blades, protects the apical
meristem
Short Shoots- erect stems that produce
flowers and leaves, not involved in
vegatative reproduction
Rhizome = underground primary stem,
storage of starch; transport of
photosynthate, nutrients, both horizontal
and vertical – physiological integration of
beds.
Leaf Area Indices- amount of leaf available for
photosynthesis expressed relative to ground cover
broad leaf trees- 4-6
grasses- 9-10
rainforest leaves- 20
seagrasses- 4.9-21
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LAI of seagrass reflect the high density of blade cover
in relation to ground cover, adaptation to submarine
irradiance, need for water movement to enhance
nutrient and gas diffusion
Roots = adventitious, thick to fibrous, have
root cap & root hairs
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Seagrass morphology
Seagrass Leaf Diagram
Bundle sheath- containing phloem & xylem
lacunae
aerenchyma
Leaves - flat and flexible
-strong due to internal fiber bundle
-reduced vascular bundle with xylem and phloem
- epidermal cells lack stomata & guard cells
- covered by a thin porous cuticle
Fb b
Fiber
bundles
dl
Wheat
Bundle sheath- containing phloem & xylem
stomata
lacunae
aerenchyma
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Fiber bundles
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Seagrass morphology
Seagrass morphology
Lacunae- gas exchange
- air spaces formed by the breakdown of cells
- continuous through the blades, short shoots,
rhizomes, & roots
- provide gas exchange through plant
- storage of CO2
- diffusion of O2 into the rhizome & roots
- have septae (diaphrams) with pores allow air
exchange but block water to prevent flooding
Aerenchyma tissue- gas exchange
- Formed by cell separation
- Specialized parenchyma tissue
with air spaces
- Mechanism
M h ism for
f roott aeration
ti iin llow
oxygen concentrations
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Seagrass Habitat Requirements
Seagrass Reproduction
- Shallow water (above 20m)
- 2 kinds of reproduction: sexual and clonal
- Genets – (genetic individual) consists of a series of ramets
(physical individual)- short shoots
- majority dioecious whereas only 5% of all angiosperms dioecious
- Very susceptible to turbidity 
require clear water
- Higher Ec (photosynthesis =
respiration) than algae due to below
ground biomass
- Lower photosynthetic capacity than
terrestrial p
plants
- Less carbon available for Ps in
water than in air
- Macroalgae are better at using
HC03- than seagrasses.
- When seagrasses evolved  higher
atmospheric C02, more inorganic C02
available in sea water.
- Seagrasses have lower nutrient
requirements than algae
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Seagrass Reproduction
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Seagrass Reproduction
Clonal- ability to carry out vegetative expansion via a rhizome
that produces short shoots or ramets
- sharing of resources btw ramets in areas of stress or
low nutrients
• Zig-zag pattern
of flowers in the
spadix (spadices)
• Male flowers
release long,
stringy pollen (~2
mm long!) in
clumps, typically
on an incoming
i
i
tide, dispersed by
water motion
Hydrophily = water-mediated pollination
Posidona meadows in Mediterranean and Australia
- one individual may cover 10 m2!
- Genetic work to ID individual genets
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Anthers and pollen
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Seagrass Reproduction
Seeds developing in spadix
Vivipary- bearing live young
- germination occurs while seed is still attached to flower
- mangroves also do this
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Seagrass Reproduction
• Fertilization occurs
between pollen and stigma
of female flowers, both are
coated with a strongly
adhesive substance
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Seagrass Reproduction
• Sexual reproduction not nearly as common as clonal
• Often high rates of seed predation
• Positive density-dependence (facilitation by adult surfgrass) and
facilitation by coralline alga for recruitment
mm
• Ripe fruits are released
from the spadix; pericarp
erodes away, leaves two
bristly arms
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Shelton Ecology 200830
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Shelton Ecology 2008
Surfgrasses
Zostera marina
eel grass
• Monoecious
• Mediterranean & Temperate
• Common locally in bays and estuaries
• Wide blades (3-10mm)
• Protogynous (female first, then male)
Thalassia testudinum
Phyllospadix scouleri
turtle grass
• Dioecious
• Tropical – common in Caribbean
• Food for sea turtles, manatees,
dugongs
• roots for nutrient uptake
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Flatter, wider blades (2-4 mm)
• Higher, lower wave action
Phyllospadix torreyi
Rounder, thinner blades (1-3 mm)
• Lower, higher wave action
• Dioecious, long-lived perennial
• Only genus to occur on rocky substrate
•roots for attachment only
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Surfgrass Removal Experiments
Removal pools 10-150 C higher
Temperature difference are
biologically significant
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34Shelton 2009
Seagrass Community Ecology
Seagrass Community Ecology
Lots of grazers, especially in the tropics
epiphytes
Urchins, manatees, dugongs, green turtles
Smithora
Water fowl, fish
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Seagrass Community Ecology
Major (ongoing) loss of seagrass habitat worldwide
associated mesograzers- feed on associated epiphytic algae
declines reported since 1970
from: Heminga and Duarta, 2000
anthropogenic
natural
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Seagrasses Habitat Restoration
Major (ongoing) loss of seagrass habitat worldwide
Mitigation for seagrass loss:
- Protected under Clean Water Act &
Magneson-Stevens Act (fisheries focus, “essential fish habitat”)
1) Coastal development: dredging
and filling
2) Eutrophication
3)) Oilspills
p
4) Thermal pollution from power
plants
5) Invasive species – Caulerpa
taxifolia
6) Anchors & prop scars
- Test of ecological understanding: SEAGRASS RESTORATION
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Caveats to doom and gloom scenario?
Things we’ve learned so far:
1.
Building a seagrass meadow is really hard
Historical losses: “wasting disease” on East Coast, 1931-1950s
2. We don’t even really have a good metric for success
Blackish-brown spots, loss of leaves. ~90% SG lost on Atlantic
coast, within a year or so
3. Subtle things may make a big difference in “quality” of a
seagrass bed
e.g. Genetic
G
ti diversity
di
it of
f ttransplanted
l t d vs. natural
t
l seagrass meadows
d
Unclear what caused death or recovery (Labyrinthula slime mold?
Bacteria? Ascomycete fungus? Temperature spike?)
Did fisheries collapse? Not really.
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