Coastal communities: Seagrass beds

Dr. Loretta Roberson, UPR-RRP and Institute of Neurobiology

OUTLINE

• What is seagrass?• Associated flora and fauna• Seagrass ecosystem function

– Habitat connectivity• Disturbances and threats

What is seagrass?

What is seagrass?Leaf

Sheath

Rhizome

Root

What is seagrass?

• True flowering plant (angiosperms)– Monocots (lily, corn, rice)– Not a true grass

• Wholly submerged in salt or brackish water

• Can reproduce sexually and asexually– developed a submarine pollination

mechanism– can produce large, old clones

(600 m2 and >1,000 years old)

What is seagrass?

• Aerenchyma– specialized parenchyma with regularly arranged air

spaces (gas exchange, buoyancy)

• Chloroplasts in the leaf epidermis

• Require high light levels– 25% of incident radiation (compared to 1% in other

plants)– supports large amount of nonphotosynthetic tissue– must provide oxygen to roots and rhizomes

(toxic sulfide sediments)

What is seagrass?

• 59 species worldwide in 12 genera• Abundant in Australia, Alaska, S. Europe,

India, E. Africa, SE Asia, Caribbean, Gulf of Mexico

• 7 species found in Caribbean:Thalassia, Syringodium, Halodule, Ruppia, Halophila engelmanni, H. decipiens, and H. baillonii

What is seagrass?

• 7 species found in Caribbean:Thalassia, Syringodium, Halodule, Ruppia, Halophila engelmanni, H. decipiens, and H. baillonii

Thalassia Syringodium

World Seagrass Distribution

From: World Atlas of Seagrasses 2003

Coral distribution

World Seagrass Distribution

Florida

Gulf of Alaska

Factors affecting distribution

Physiology– Temperature– Salinity– Waves– Currents– Depth– Substrate – Day length

Photosynthesis– Light– Nutrients– Epiphytes– Disease

General Habitat Characteristics

• Shallow, soft bottom• Clear water• Protected from wave action• Monospecific or mixed stands• Patchy

Associated flora and fauna

Associated flora and fauna

BacteriaFungiDiatomsAlgae (green, red, brown)Protozoa (slime mold, forams)SpongesCnidarians (corals)PolychaetesRibbon wormsSipunculid wormsFlatworms

Crustaceans (shrimp, lobster)Bivalves (oysters, scallops)Gastropods (Conus, Strombus)Cephalopods (squid, cuttlefish)BryozoansEchinoderms (sea cucumbers)TunicatesFish (snapper, sea horses)Reptiles (green turtles)Birds (Brant geese)Mammals (dugong, manatee)

Functions of seagrass – An ecosystem perspective

• Primary production• Canopy structure• Below-ground structure • Wave and current energy damping• Nutrient, contaminant and sediment filtration and

trapping• Nutrient regeneration and recycling• Epiphyte and epifaunal substratum

Primary production – Photosynthetic organisms

• Cyanobacteria• Diatoms and Coccolithophores• Algae – includes zooxanthellae• Plants – seagrass

Primary Production

·  primary production = rate of photosynthesis or chemosynthesis

·  utilize sunlight or chemical nutrients as a source of energy (autotrophy)

·  the lowest level of the food chain

Primary producers serve as the basis for nearly all life in the ocean

Factors Affecting Primary Productivity

• Light• Nutrients• Hydrographic conditions

– Currents– Upwelling– Vertical mixing

Estimates of primary production

Pelagic zone = 50-600

Grasslands = 2,400

Tropical forests = 5,000

Mangroves = 2,700

Coral reefs = 1,200-8,000

Seagrass beds = 800-10,000

(measured as g C/m2/yr )

Ecosystem function – Canopy structure

Ecosystem function – Canopy structure

Ecosystem function – Below-ground structure

Ecosystem function – Epiphyte and epifaunal substratum

Ecosystem function – Epiphyte and epifaunal substratum

Ecosystem function – Epiphyte and epifaunal substratum

Ecosystem function – Wave and current energy damping

Ecosystem function – Wave and current energy damping

Ecosystem function – Nutrient, contaminant and sediment

filtration and trapping

Ecosystem function – Nutrient regeneration and recycling

Habitat connectivity

Habitat connectivity

N

Habitat connectivity

Habitat disturbances

• Natural– Waves– Hurricanes– Animal foraging

• Anthropogenic– Eutrophication– Sedimentation– Habitat destruction– Overfishing

Natural disturbances – Waves

Natural disturbances – Waves

Natural disturbances – Hurricanes

Blow outs

Natural disturbances – Animal Foraging

Natural disturbances – Animal Foraging

Natural disturbances – Animal Foraging

Natural disturbances – Animal Foraging

Natural disturbances – Animal Foraging

Anthropogenic disturbances – Eutrophication

The process by which a body of water becomes enriched in dissolved nutrients that stimulate the growth of aquatic plant life

Eutrophication – HABs [ Harmful Algal Blooms ]

Eutrophication – HABs

Anthropogenic disturbances – Sedimentation

Anthropogenic disturbances – Sedimentation

Anthropogenic disturbances – Urbanization

Anthropogenic disturbances – Urbanization

1963 2000

From: Planning Commission of Puerto Rico, Office of Land Use

Shading = >1,000 persons/mi2

10 km

Other anthropogenic disturbances -

Propeller scarring

Other anthropogenic disturbances - Harvesting

Other anthropogenic disturbances - Invasive species

Caulerpa

Ballast water

Anthropogenic disturbances – Overfishing

Jackson et al., Science 293, 629 -637 (2001)

Before Fishing After Fishing

Anthropogenic disturbances – Overfishing

>3.3 × 107 adult turtles historically 1.1 × 106 50-kg turtles today

Jackson et al., Science 293, 629 -637 (2001)

Current research

Orth et al. 2006 Bioscience 56(12): 987-996

More seagrass research!!

Current researchEffects of water quality on seagrass community

productivity and biodiversity in NE Puerto Rico

USGS Water Resources Data 2004

Study sites – Fajardo

“Non-impacted” - 7S Impacted - LC

Biodiversity - Fish

Impacted“Non-Impacted”

CG 7S CGR LC0

5

10

15

20

25

30Indicator spp

Total

Nu

mb

er o

f S

pec

ies

Biodiversity - Fish

CG 7S CGR LC Guadalupe-5

5

15

25

35

45

55

65

75N

um

ber

of

Sp

ecie

s

* From Kopp et al. 2007 Aquatic Botany

*

Conclusions:

• Nearshore and watershed water quality are poor,

mainly due to sediment not nutrients• More stable communities may

protect biodiversity (and vice versa)

• Higher frequency measurements are needed, especially light

• Long-term studies are needed (study is ongoing) i.e., SeagrassNet.org

• Seagrass conservation areas and nearshore water quality management

are needed in Puerto Rico!