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

1

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

2

What is a seagrass?

•Submerged Aquatic Vegetation•Submerged Aquatic Vegetation

•Marine angiosperms

•Herbaceous monocots

•Functional grouping of plants

3

Anatomy• Blades -

Photosynthesis Nutrient uptakep

• Short shoot = stem• Rhizomes -

AnchoringAnchoring Propagation Nutrient absorption Gas e changeGas exchange

• Roots -Nutrient uptake Anchoring Gas exchange

4

Vegetative Morphology

• Leaves: strap-like to poval

• Leaf bundlesLeaf bundles • Short shoots

5

Conveyor belt growthConveyor-belt growth

6

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.

7

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

8

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

16

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

19

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

60

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

41

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

42

Gracilaria salicornia - Negative impacts in a Halophila decipiens

meadow?

43

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

45

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