The Grass is Always Greener: Seagrass Ecology in South Florida

R.P

. van D

am

James W. Fourqurean Biological Sciences and Southeast Environmental Research Center, Florida International University

Ocean Life Lecture Series, Florida Keys Cultural Center, Ley Largo February 17, 2012

Outline

• What are seagrasses?

• What is the global status of seagrass ecosystems?

– Seagrass services

– Seagrass history

– Seagrass pressures

– Seagrass response

– Human response

• What is the local status of the seagrasses in south Florida? – signs of trouble in paradise

Seagrasses are flowering plants that live submerged in the sea

The seagrasses are an ecological group, NOT a taxonomical unit

A plant is called a seagrass if it: 1. Grows when fully submerged 2. Is securely anchored by a root system 3. Is adapted to live in salt water 4. Has flowers that are pollinated under water 5. Can compete with other organisms in the sea

Seagrass or seaweed?

300 BC: Seagrasses are a type of “seaweed”

- Theophrastus (300 BC), Enquiry into Plants

No. Species Seagrasses •50-60 spp. Flowering plants •235,000 spp. Marine plants •60,000 spp. Phytoplankton • 50,000 spp. Macroalgae - seaweeds • 10,000 spp. Seagrasses (No. Genera) •7 tropical (Halodule, Cymodocea, Syringodium, Thalassodendron, Enhalus, Thalassia, Halophila), •5 temperate (Zostera, Phyllospadix, Heterozostera, Posidonia, Amphibolis) •1 cosmopolitan (Ruppia)

Evolution

Seed

Male flower

Female flower Juvenile

Juvenile

Fruit

LIFE CYCLE of

Thalassia testudinum

Male clone

Female clone

Seagrasses are abundant in tropical and temperate regions

Halophila:

Bocas del Toro, Panama

Thalassia:

Kuna Yala, Panama

Ruppia:

Morro Bay, USA

Zostera:

Ria Formosa, Portugal

Seagrass provides critical food source in tropical regions

R.P

. van D

am

J. K

enw

ort

hy

Manatee (Trichechus)

In Thalassia meadow,

Puerto Rico

Green Sea Turtle (Chelonia)

In Thalassia and

Syringodium meadow,

Yucatan, Mexico

Seagrass provides critical habitat in temperate regions

G. K

endrick

G. P

erg

ent

Seahorse (Hippocampus)

In Cymodocea meadow,

Mediterranian Sea

Zebra fish (Girella)

In Posidonia meadow,

Perth, Western Australia

Seagrass provides valuable fisheries resources

Nutrient processors: Seagrass beds absorb and transform nutrients in the marine environment

Sediment stabilizers: seagrasses efficiently hold

sediments in place, preventing resuspension and

movement of sediment deposits-

They reduce shoreline erosion and keep the water

clear!

Seagrasses need:

• Clear water!

• Sandy or muddy bottom

• Stable salinity

• Moderate waves and currents

Seagrasses are valuable and threatened compared to other major marine habitats

Seagrasses evolved in a very different marine environment from today

Hydorcharitaceae

Cymodoceacea

Posidoniaceae

Zosteraceae

Seagrasses evolved in a very different marine environment from today

Hydorcharitaceae

Cymodoceacea

Posidoniaceae

Zosteraceae

“An inconvenient truth” timeline

Seagrasses evolved in a very different marine environment from today

Hydorcharitaceae

Cymodoceacea

Posidoniaceae

Zosteraceae

Pressures to seagrass: human population

Egypt ca. 10 000 years ago

Pacific northwest, seagrass use

Washington DC, 2006

Pressures to seagrass: human population

Egypt ca. 10 000 years ago

Pacific northwest, seagrass use

Washington DC, 2006

Pressures to seagrass: human population

Egypt ca. 10 000 years ago

Pacific northwest, seagrass use

Washington DC, 2006

Pressures to seagrass: increased invasive species

Panama Canal, 1907 Ballast pumping

Caulerpa

taxifolia

Pressures to seagrass: increased invasive species

Panama Canal, 1907 Ballast pumping

Caulerpa

taxifolia

Pressures to seagrass: increased nutrient input (Fertilizer and sewage)

Fertilizer applied in agriculture Fertilizer applied to lawns Wastewater Treatment Plant

Fishing practices may also be changing seagrass meadows around the world

Reports of seagrass losses and the rates of decline are increasing dramatically

Waycott et al. 2009 PNAS

Drivers of seagrass loss

1. Water quality degradation from poor land use practices

3. Invasive species

2. Dredging and filling

Research effort on seagrasses increasing, but lagging behind other coastal habitats.

Within widely accessed media, reports of seagrass are lacking

Bottom line: less seagrass research done AND it isn’t broadly publicized

Seagrasses on a global scale

• Extensive seagrass losses have occurred in

temperate and tropical regions

• Nutrients and sediment inputs are the primary

pressures

• Research and understanding of seagrass

communities is increasing…

• BUT – despite a lot of effort, the importance

and issues of seagrass habitats are still

lagging behind other coastal communities in

effective communication to the public and

ultimately policy makers

A broad variety of seagrass habitats in south Florida

Thalassia testudinum Turtle grass

Many (most) seagrasses are dioecious

Syringodium filiforme Manatee grass

Halodule wrightii Shoal grass

Halophila decipiens

A monoecious seagrass

Halophila engelmanni

Halophila johnsonni

Ruppia maritima Widgeon grass

Synoptic Benthic Habitat Surveys

Synoptic Surveys: Species distributions

Thalassia testudinum

Halodule wrightii Syringodium filiforme

Halophila decipiens

As nutrient inputs to seagrass beds increase, species shifts occur and seagrasses get displaced by seaweeds, then by phytoplankton

Long-term changes in seagrass bed composition suggest nutrients are becoming more plentiful

1996 1998 2000 2002 2004 2006 2008 2010

Bra

un

Bla

nq

uet

Den

sit

y

0.0

1.0

2.0

3.0

4.0

5.0Site 273 Thalassia

SyringodiumHaloduleCalcareous Green*

1996 1998 2000 2002 2004 2006 2008 2010

Bra

un

Bla

nq

uet

Den

sit

y

0

1

2

3

4

5 Site 260

Changes in relative abundance of primary producers At 19 of 30 sites, species composition has shifted in a manner

consistent with increased nutrient availability

Green: Thalassia getting denser

Red: Thalassia decreasing in relative

importance

Progressive eutrophication or light reduction

Sea

gra

ss L

eaf

N:P

20

30

40

50

60

0.05 0.10 0.15 0.20 0.25

0.5

1.0

1.5

2.0

2.5

3.0

Nutr

ient-

reple

te

Oligotrophic

P-limited

Oligotrophic

N-limited

Eutrophication

Eutrophication

N:P

= 3

0:1

Leaf tissue P content (% of dry weight)

Lea

f ti

ssu

e N

con

ten

t (%

of

dry

wei

gh

t)

As nutrient inputs increase, the amounts of important plant nutrients in the seagrass leaves

changes – providing a sentinel for nutrient addition

N:P of leaves

Thalassia testudinum

10 20 30 40 50 60 70 80 90 100

P-limitedN-limited

The relative importance of the two important plant nutrients nitrogen and phosphorus change across the

landscape in south Florida

Some seagrass meadows in south Florida are changing in ways that indicate nutrient pollution

1996 1998 2000 2002 2004 2006 2008 2010

N:P

of T

ha

lassia

20

25

30

35

40

45

50

Site 267 Y=1032.6-0.5x

r2=0.171, p=0.002

Long-term changes in N:P consistent with increases in nutrients

Changes in water management in south Florida will cause a change in the distribution of seagrass species – and the animals that live in the seagrass beds

0 1 2 3 4 5

Kilometers

Organic C content (% of dry wt)

0 1 2 3 4 5 6

Dep

th (

cm

)

0

50

100

150

200

250

Organic C content (% of dry wt)

0 1 2 3 4 5 6

Dep

th (

cm

)

0

50

100

150

200

250

Trout Cove

Russel Bank

Organic C content (% of dry wt)

0 1 2 3 4 5 6D

ep

th (

cm

)

0

50

100

150

200

250

Organic C content (% of dry wt)

0 1 2 3 4 5 6

Dep

th (

cm

)0

50

100

150

200

250

Nine Mile Bank

Bob Allen Keys

Corg generally

decreases

downcore in

Florida Bay

seagrass soils.

Buried peats

have high Corg

Deep, C-rich soils underlay seagrass meadows

Ec

os

ys

tem

C s

tora

ge

(Mg

Co

rg h

a-1

)

0

200

400

600

800

1000

1200

**

*

**

*******

**

***

*

*

*

*

*

*

*

*

*

**

*

*

*

*

*

**

**

**

*

*

**

****

*

*

*

**********************

************

***

**

Boreal

Temepra

te

Tropic

al

Upland

Oceanic

Mangro

ve

Seagrass

Living Biomass

Soil Corg

Seagrasses store about as much C as forested ecosystems

There are about 18,000 km2 of seagrass beds in south Florida

A very rough estimate of carbon stored in the top meter of seagrass soils in south Florida: 18,000 km2 of seagrasses 594 tons CO2e ha-1

1 x 109 tons CO2e stored in the soils!

Anthropogenic CO2e flux is about 29 x 109 tons y-1

Summary points – Seagrasses in south Florida •The Keys are home to some of the most expansive and important seagrass beds on earth

•Rapid population increases adjacent to oligotrophic marine ecosystems in south Florida may have deleterious effects on those ecosystems, as in so many other places in the world •Changes are occurring in south Florida seagrass beds that are consistent with increased nutrient availability in the system. •These changes are relatively subtle, we have not witnessed large-scale permanent loss of seagrass beds in the Keys. There is time to act!

Are we describing locally-

induced changes, responses to

larger-scale processes, or

natural cycles?

• Sister taxa in Atlantic and Indopacific