Seagrass lecture
Transcript of Seagrass lecture
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!