the seagrasses - university of hawaiʻi
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The SeagrassesThe Seagrassesgg
Dr Kim PeytonDr Kim PeytonDr. Kim Peyton (w/ some modifications by Dr. Bruland)
University of Hawai‘i MānoaD t t f B t
Dr. Kim Peyton (w/ some modifications by Dr. Bruland)
University of Hawai‘i MānoaD t t f B tDepartment of BotanyDepartment of Botany
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Outline• Anatomy• Characteristics• Taxonomy systematics & evolutionTaxonomy, systematics, & evolution• Distribution & diversity• Habitats• Reproduction • Food sources• Annual production• Annual production• Stressors• Hawaiian seagrassesg• Seagrass research in Hawai‘i
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What is a seagrass?
•Submerged Aquatic Vegetation•Submerged Aquatic Vegetation
•Marine angiosperms
•Herbaceous monocots
•Functional grouping of plants
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Anatomy• Blades -
Photosynthesis Nutrient uptakep
• Short shoot = stem• Rhizomes -
AnchoringAnchoring Propagation Nutrient absorption Gas e changeGas exchange
• Roots -Nutrient uptake Anchoring Gas exchange
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Vegetative Morphology
• Leaves: strap-like to poval
• Leaf bundlesLeaf bundles • Short shoots
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Conveyor belt growthConveyor-belt growth
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Characteristics of Seagrasses:Functional Group
Characteristics of Seagrasses:Functional GroupFunctional Group
Arbor (1920) & den Hartog (1970)Functional Group
Arbor (1920) & den Hartog (1970)
1. Adapted ecologically to varying salinities = osmoregulation
1. Adapted ecologically to varying salinities = osmoregulation
2. Able to grow while completely submerged
2. Able to grow while completely submerged
3. Resistant to waves & tidal currents4. Adapted to pollinate underwater = 3. Resistant to waves & tidal currents4. Adapted to pollinate underwater = p p
hydrophilly5.
p phydrophilly
5.
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How extraordinary are seagrasses?How common is hydrophily?How common is hydrophily?
• 130 species of 300,000 species• Hydrophiles = 0.04%• 60 species are marine = seagrasses• Seagrasses = 0.02%• Reflects difficult evolutionary transitions
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From where did seagrassesFrom where did seagrassesoriginate?
Halophytes SAV
- emergent - freshwater
Seagrasses9
rbcL marker
• 3 lineages
(Les et al. 1998)
3 lineages• 5 families
12• 12 genera• SAV ancestry
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Seagrass DistributiongTemperate -
BorealBoreal Regions
• 4 genera28 i• ~ 28 species
Tropical -Subtropical pRegion
• 7 genera• ~ 30+ species• ~ 30+ speciesEurythermal• Ruppia• ~ 2-10 spp.
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Facultative successional sequence spans coastal wetlands (i.e., mangroves), seagrass beds, & coral reefs.
Origins of this relationship found in late Cretaceous withOrigins of this relationship found in late Cretaceous with first appearance of seagrasses & mangroves.
(Brasier 1975; McCoy & Heck 1976)
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Tropical wetlands (mangroves) -seagrass meadows -seagrass meadows coral reefs:
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Shared evolution & distribution:
Coastal wetlands (mangroves) -seagrass meadow- coral reefs
• seagrasses
• coral reef fishes co a ee s es
• decapods
• mollusks• mollusks
• manatees(McCoy & Heck 1976; Brasier(McCoy & Heck 1976; Brasier1975; Domning et al. 1982)
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Seagrass Diversity Enhalus
HaloduleZostera
PosidoniaPhyllospadix
Halophila15
Habitats: Soft Sediment
Leaves ↓ flow
Particulate matter drops outParticulate matter drops out
Rhizomes –
Roots -Roots
Habitat
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Habitats - Hard Bottom
Rocky Inner Tidal
Phyllospadix
Late s ccessional speciesLate successional species
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Seagrass Fruits & Seeds
Bird dispersed Z t &Ph ll di Zostera & Ruppia fruits
Large seeds
Phyllospadix
g
Seed bank
•Fruits with hooked barbs
•Macroalgaeg
•Roots sticky(Turner 1983) Vegetative fragments 18
Seagrass as a food source: GGrazers
Smaragdia sppSmaragdia spp.
Waterfowl
Dugongs & Manatees Green Turtles
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Seagrass as a food source: suspension & deposit feeders
• Few direct grazers• Few direct grazers
• Sequestered nutrients
Litt• Litter
• 10 tons leaves acre-1 year-1
• 50 million invertebrate infauna acre-1
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Estimated Annual Production & Bl d El ti R t Fl idBlade Elongation Rate: Florida
(Virnstein 1982)
Halodule beaudettei 182 730 g C m-2 y-1Halodule beaudettei 182 - 730 g C m-2 y-1
~3.1 mm d-1
Syringodium filiforme 292 - 1095 g C m-2 y-1
~8.5 mm d-1
Thalassia testudinum 329 - 5840 g C m-2 y-1
~2-5 mm d-1
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Anthropogenic StressorsAnthropogenic Stressors
Sewage dischargeSewage discharge
Non-point pollution
Al l i h tAlgal epiphytes
Invasive spp.
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Invasive SpeciesInvasive Species
Caulerpa taxifolia - cultured strainCaulerpa taxifolia cultured strain
Mediterranean Sea; California; Australia
Posidonia oceanica endemic seagrassPosidonia oceanica - endemic seagrass
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Seagrasses of Hawai‘igHalophila decipiens
Halophila hawaiiana
Ruppia maritima24
Hawaiian flora reflects isolationHawaiian flora reflects isolation
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Halophila hawaiianaHalophila hawaiianaHalophila hawaiiana Limu enenueHalophila hawaiiana Limu enenue
•Endemic species
2 3 h i ht
•Endemic species
2 3 h i ht• 2-3 cm canopy height
• Builds perennial mounds
• 2-3 cm canopy height
• Builds perennial moundsmounds (den Hartog 1970)mounds (den Hartog 1970)
Depth Distribution: 1-90 ft26
Halophila decipiensHalophila decipiensHalophila decipiensHalophila decipiens
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Invasive species & seagrasses of Hawai‘i: Displacement & Smotheringp g
Gracilaria salicorniaGracilaria sp. Florida
Halophila decipiens
Halophila hawaiiana
Ruppia maritimaAvrainvillea amadelpha
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Maunalua Bay - East Honolulu
Urbanized watershed
W t d th 1 3Water depth 1.3 m
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Methods - Removal ExperimentHalophila hawaiiana & AvrainvilleaHalophila hawaiiana & Avrainvillea
amadelpha
• Established 25 0.25 m2 fixed plots with 10 treatments, 10 controls with alga & 5 controls without alga
• Treatments - Avrainvillea is removed
• Quantified % cover and bladeQuantified % cover and blade pair densities (Morris et al. 2000)
• Monitored over 120 days• June 2004 to October 2007 +
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June 2004 to June 200831
Invasive Removal Results
100
Invasive Removal Results
80
100
Cov
er
June 2004October 2004January 2005J 2005
40
60
n Pe
rcen
t June 2005October 2005January 2006June 2006
20Mea
n October 2006June 2007October 2007
0
Seagrass(Treatment)
Seagrass(InvasiveControl)
Invasive alga(Treatment)
Invasive alga(InvasiveControl)
Seagrass(SeagrassControl)
Invasive alga(SeagrassControl)
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A line in the sand - in which direction is the invasion moving?direction is the invasion moving?
June 2004
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Avrainvillea
Seagrass
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Ruppia maritimaRuppia maritimaRuppia maritimaRuppia maritima
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Bristle-Thighed Curlew flipping t f R i M l k i
A. Dibben-Young
mats of Ruppia on Molokai
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Research Question:
Are introduced euryhaline tilapiaAre introduced euryhaline tilapia capable of eliminating Ruppia
fmaritima from Hawaiian coastal wetlands?et a ds
Observational Results:Ruppia distribution across 41 Sites inRuppia distribution across 41 Sites in
Hawai‘i
30% sites 56% sites
Experimental Results
2 experiments:• Each at 2 sites• Both tilapia generaBoth tilapia genera
1) Exclosure experiment
n = 64 Levels4 Levels
2) Cageexperiment
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Results: Cage ExptResults: Cage Expt.
C t lControl Large Tilapia Small Tilapia
Day 0 Day 0 Day 0
Day 6 Day 6 Day 640
Results: Cage Experiment
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Large tilapia consume Ruppia
40
50
60
20
30
Weig
ht
(g)
Tilapia Large
0
10
an
ge W
et
W Tilapia SmallTop Minnow LargeTop Minnow SmallNo Fish Control
-20
-10Treatments
% C
ha
-40
-30
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Waikiki Site Descriptions: Dredged Areas
1 = Impact Site 2 = Control Site
• Discontinuousmeadows of 57 m2
& 21 m2
• >3300 m2 continuous meadow
• 2.5-3.5 m water• Seagrass confined to upper portions of dredged
2
2.5 3.5 m water depth
• Occasional fragments of Gp g
slope in 2-2.5 m water depth
• G salicornia Hard bottom
fragments of G. salicornia
G. salicorniatumbleweeds at 3-3.5 m water depth
1
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Gracilaria salicornia - Negative impacts in a Halophila decipiens
meadow?
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The invasive alga Gracilaria salicorniaThe invasive alga Gracilaria salicornia
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Results, so farControl Site
• >3300 m2
Impact Site
• Discontinuouscontinuous H. decipiens meadow
3 3 5 m ater depth
meadow of H. decipiens 57 m2 & 21 m2
• 3-3.5 m water depth
• No G. salicornia • 2-2.5 m water depth
• Honu feeding area • G. salicorniapresent 3-3.5 m
t d thwater depth
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Seagrass results, so far100
60
70
80
90
100
t/m
2
n=10; n.s.
20
30
40
50
60
Mean
dry
wt
0
10
20
Control Impact
4000
2500
3000
3500
fru
its/
m2
n=10; p<0.00001
1000
1500
2000
Mean
nu
mb
er
of
f
460
500
Control Impact