JA Mortimer: Seagrass Ecosystems. Coral 8/22/2019 Facility - - PDF document

JA Mortimer: Seagrass Ecosystems. Coral Facility Inauguration 16 July 2019 8/22/2019 1

Seagrass Ecosystems: Beyond the Confines of the Meadows

• Dr. Jeanne A. MORTIMER

Island Conservation Society (ICS)

Seagrass v Seaweeds (Algae)

 Kreol: both = “Gomon”  Seagrass = Flowering plants (~55 species worldwide)  Flowers & seeds  Vascular plants with roots, stems, leaves  Seaweeds = Multi-cellular algae (~5,000-6,000 spp worldwide)  Little or no vascular tissue

Seagrass or Algae? Seagrass or Algae? What is a seagrass?

 Flowering plants  Not true “grasses”  Special features:  Grow underwater  Disperse pollen & seed underwater (most plants, even aquatic plants, disperse above water)  4 families worldwide:  Seychelles: 2-3 families  ~60 species worldwide:  Seychelles: 9-12? species

Seagrass Map of the World

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JA Mortimer: Seagrass Ecosystems. Coral Facility Inauguration 16 July 2019 8/22/2019 2

Seagrasses of Seychelles: Most common species

Thalassodendron ciliatum Thalassia hemprichii Cymodocea rotundata Cymodocea serrulata

Seagrasses of Seychelles: other species

Syringodium isoetifolium Halodule uninervis Halophila

• valis

Halophila decipiens

Seagrasses of Seychelles: most endangered

Enhalus acoroides = “Tape Seagrass”

Only in the Inner Islands:

• - Praslin
• - Mahé

Ecological Services of Seagrass Ecosystems

Food for Sea Turtles



Green turtles (Chelonia mydas)

Habitat for Sea Turtles



Hawksbills (Eretmochelys imbricata)

Habitat for Commercially Important Fishes

• e.g., Rabbit fish

Ecological Services of Seagrass Ecosystems Good for corals

 Bind sediments (esp. during storms) – good for corals  Protect coastlines from erosion  Below ground biomass > Above ground biomass  Blades baffle currents, encourage sediment settlement



Tropical seagrasses may tolerate higher temperatures, so may

remain productive even as climate warms

Ecological Services of Seagrass Ecosystems Good for corals

 Produce lots of organic carbon: take up CO2 & give off O2 - good

for corals

 Bind organic pollutants  Remove carbon dioxide from ocean-atmosphere system =

“Blue Carbon Sinks”

• Reduce impact of climate change
• Increases pH levels in vicinity – makes H2O less acidic -

good for corals

• Coral calcification can be 20% greater downstream of

seagrass

• Seagrass conservation enhances resilience of coral reef biodiversity

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JA Mortimer: Seagrass Ecosystems. Coral Facility Inauguration 16 July 2019 8/22/2019 3

Seagrass Survey Protocol:



Quadrat sampling: 50 cm x 50 cm square



Thrown randomly at intervals



Record:

 GPS location  Photo  Sediment type  T

• tal seagrass over (% of total)

 % Contribution per seagrass spp  % Macro-Algal cover  Associated Fauna  Canopy Height (cm)

Poivre Atoll: shallow water surveys

• -early Dec 2017
• -low spring tides
• - 3 spp seagrass
• - evidence of turtle

cropping

Poivre reef-flat seagrass survey Beautiful seagrass pastures in Seychelles

Thalassodendron ciliatum

• - among the tallest canopies in world
• - > 100 cm tall

Washes up on beach, fertilizes vegetation Nekton Expedition

Seagrasses & Algae

• - to what depth?

Differences among island groups? Previous records ~37m

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JA Mortimer: Seagrass Ecosystems. Coral Facility Inauguration 16 July 2019 8/22/2019 4

Nekton Expedition Activities Relevant to Seagrass & Algae study:

 Snorkel & SCUBA surveys (including in

seagrass meadows)

 Neuston Sampling of the surface waters  Deep sea Surveys

Neuston Sampling Neuston Sampling Neuston Sampling Deep Sea Surveys

Submersibles:

• Operated

from 30 m to 250 m

• Video records of all

dives using several cameras

Deep Sea Surveys

ROVs operated up to 450m

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JA Mortimer: Seagrass Ecosystems. Coral Facility Inauguration 16 July 2019 8/22/2019 5

Dead Seagrass Leaves at all depths:

ROV screen shot ~300 m

Blue Carbon Sink: Carbon Sequestration: i.e., keeps Carbon out

• f the atmosphere

In Summary:

 Seagrass important to most marine ecosystems in

Seychelles:

• Seagrass meadows themselves (& associated species)
• Beach vegetation (prevents erosion; provides nutrients)
• Coral reefs (binds sediments; less acidity; adds O2)
• Surface waters (habitats for small organisms)
• Deep sea (provides nutrients)

Serves as Blue Carbon Sink that keeps Carbon out of Atmosphere

Thank you!

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