Coastal Ecosystems in the Neotropics: Mangroves, Seagrass

and Coral Reefs

Chapter 11

What to Expect

• Questions to think about

• Introduction to coastal ecosystems and French Guiana

• Mangroves

• Seagrasses

• Coral Reefs

• Answers to Questions

Questions to Think About1. What effect does the Amazon River have on the

coastal regions of northeastern South America?

2. Globally, where is mangrove diversity and species richness the highest?

3. What are the primary morphological and physiological characteristics that true mangroves share?

4. To which group of plants do seagrasses belong?

5. What are the 3 types of coral reefs?

• Coastal Ecosystems and French Guiana

• Mangroves

• Seagrasses

• Coral Reefs

• Answers to Questions

Coastal Ecosystems

• Extremely variable and diverse habitats

• Occur on every continent and in all regions of the world

Coastal Ecosystems

• Include coastal waters, estuaries and lands that intersect these waters

• Essentially the meeting of terrestrial and marine environments

• Often harsh and variable environmental conditions (tidal fluctuation, storms, salinity, etc)

• Specialized communities and plants occupy these regions

Types of Coastal Ecosystems

• A wide variety of coastal ecosystems occur

• Highly dependent on the region of the world you are in

• Include coastal wetlands, salt marshes, lagoons, swamp forests, mangroves, etc

• In the tropical regions of the world, most coastal areas are dominated by mangrove associations

French Guiana• Circa 378 km of

coastline• Low relief coastal plain

(< 30 m elevation) made up of muddy sediments

• Undergoes seasonal flooding during the February – May rainy season

• Numerous river estuaries and inlets

French Guiana’s Coastal Plain

• Lowland rainforest in well drained areas

• Grassland and marsh with interspersed ponds elsewhere

• Intertidal zone dominated by mangroves which form an almost continuous band along the coast

• Mangroves extend inland along estuaries until salinity decreases sufficiently

French Guiana

Origin of Amazon mudbanks along the northeastern coast of

South America

Allison et al

(2000)

Amazon River Drainage• Large amounts of sediment

are carried by Amazon River and released into the Atlantic Ocean

• Amazon River contributes 2nd largest sediment discharge (2.9 X 108 tons/year) to the world ocean

• Plume of muddy, low-salinity water extends 100 to 500 km seaward

The Amazon River and French Guiana’s Coastal Region

• Amazon sediment pushed northwestward by strong east to west ocean current and trade winds

• Sediment accumulates off the Amapa-Guiana coastal region

• Amapa-Guiana mud flats are the longest mud coastline in the world

• 10-60 km long mudbanks migrate northwesterly in response to wave action

Effects of the Amazon River on French Guiana’s Coastal Region

• Coastal waters off French Guiana are high in suspended sediment and low in salinity

• Extensive mangrove forests grow along the coasts and on the exposed mudbanks

• Lack of clear, saline water prevents coral reefs from forming off the coast

• Coastal Ecosystems and French Guiana

• Mangroves

• Seagrasses

• Coral Reefs

• Answers to Questions

Mangroves

• Tropical evergreen trees restricted to intertidal and adjacent communities (brackish and marine waters)

• Not a taxonomic group – more or less unrelated plants that share certain adaptive features

Mangrove Distribution

• Restricted to the tropical and subtropical regions of the world (between 25°N and 25°S latitude)

• Occupy all but the most exposed or rockiest shorelines in tropical regions (up to 75% of the coastline in many areas)

• Often surround offshore islands - Cays

• Mangrove coverage: • 600 km2 in French Guiana

• 25,000 km2 in Brazil

• Highest species richness in the old world tropics

Mangrove Distribution (Tomlinson 1986)

Characteristics of True Mangroves (Tomlinson 1986)

1. Restricted to the mangrove environment (i.e. not found in terrestrial communities)

2. Ability to form pure stands

3. Morphological specialization including aerial roots, distinctive tropical leaf characteristics and vivipary

4. Physiological mechanisms for salt exclusion (generally excrete salt)

5. Taxonomic isolation from nearest terrestrial relatives at generic or family level

Aerial Roots and Pneumatophores• Aerial roots – roots

exposed to the atmosphere at least part of the day

• Arise from the lower branches, trunk or horizontal submerged roots

• Pneumatophores – specialized erect roots that are extensions of the subterranean root system

• Stilt roots – looping aerial roots arising from the branches or trunk

Stilt/Prop Roots of Rhizophora

Characteristics of Mangrove Leaves

• General uniformity in size and shape (more pronounced toward the seaward side of the community)

• More variation at interface with terrestrial forest (generally because there are significantly more species present in the transition zone)

• Leaves generally ovate to elliptic, entire margined, firm to coriaceous, glabrous and with a thick, waxy cuticle

Mangrove Leaf Shapes

Vivipary

• Embryo development in seed plants where no seed dormancy occurs

• Tropical plants often have very short seed dormancy - taken to an extreme in some mangroves

• No consensus on the adaptive value of vivipary

Vivipary in Rhizophora

• In the family Rhizophoraceae, true vivipary represents the most advanced state

• Seeds germinate while still attached to the parent plant

• Seedlings break free from parent plant and become established in suitable habitat

Common Mangrove Species in the Neotropics

The new world tropics has the fewest mangrove species of any tropical region of the world (ca. 8 species)

• Rhizophora mangle• Avicennia germinans• Laguncularia racemosa• Conocarpus erectus

Rhizophora mangle – Red Mangrove

• Rhizophoraceae• Distributed from

western Africa to the American tropics

• Very abundant• Found as a small tree

(ca. 10 m) or a small shrub

• Typically found on exposed flats (hence the abundant prop roots)

Rhizophora Saplings Established on a Mud Flat – High Tide

Avicennia germinans – Black Mangrove

• Avicenniaceae• Restricted to and

widespread in the American tropics

• Large trees (>20 m) in mature stands to much-branched shrubs in depauperate areas

• Grow in somewhat less exposed areas than red mangrove

Laguncularia racemosa - White Mangrove

• Combretaceae

• Distributed from western Africa to the American tropics

• Trees up to 18 m tall

• Found on the landward side of mangrove communities

• Less tolerant of immersion in salt water than the previous 2 species

Conocarpus erectus - Buttonwood

• Combretaceae• Widely distributed

from western Africa to tropical America

• Grows as a small tree or shrub

• Not considered to be a true mangrove by some – lacks a number of the specialized features

Fregata maginificens – Man-o’war Birds

Structure, above-ground biomass and dynamics of mangrove ecosystems: new data from

French Guiana

Fromard et al

(1998)

Summary of article

• Previous studies of mangroves (specifically in French Guiana and Brazil) have been primarily descriptive in nature

• Widely accepted that mangroves are extremely important components of tropical coastal ecosystems

• They are highly productive ecosystems and play a crucial role in the trophic cycling of nutrients and organic matter in coastal marine systems

• No previous studies have reported data on mangrove primary productivity and/or biomass

Summary of Article

• Nine mangrove stands were studied• Four characteristic mangrove stages were recognized:

sea edge pioneer or young, mature coastal or pure, mature riverine or mixed, and declining or dead

• Density and importance values were calculated for the various species present

• Looked specifically at Avicennia germinans, Rhizophora spp., and Laguncularia racemosa

• Representative trees (from above) were felled and biomass estimates for the stands were calculated using allometric relationships

Mangrove Stand Structure

Comparisons of Mangrove Biomass

• Coastal Ecosystems and French Guiana

• Mangroves

• Seagrasses

• Coral Reefs

• Summary

Seagrasses

• Sole marine representatives of the angiosperms

• Believed to have evolved from terrestrial plants

• Commonly found in shallow marine waters, salt marshes and estuaries

• Associated with mangroves and coral reefs if the tropics

Seagrasses

• Seagrasses have an extensive underground root/rhizome systems

• Anchors them securely to the substrate while at the same time stabilizing it

• Often form extensive beds which are often monotypic

• Predominantly submerged and their flowers are pollinated underwater

Seagrass Diversity

• Seagrasses occur in 2 families

• Potamogetonaceae

• Hydrocharitaceae

• Approximately 58 species in 12 genera

• Greatest diversity of seagrasses is in the Indo-Pacific region

Thalassia testudinum

• Coastal Ecosystems and French Guiana

• Mangroves

• Seagrasses

• Coral Reefs

• Summary

Coral Reefs

• Restricted primarily to tropical waters in the Indo-Pacific and Caribbean regions

• Require sea temperatures generally between 20°C and 33°C

• Tolerate salinity ranging somewhere from 30 to 40 parts per thousand

• Very sensitive to increased turbidity and nutrient runoff from coastal regions

• Very sensitive to other sources of pollution as well

World Coral Reef Distribution

Species richness is highest in the Indo-Pacific region

Western Hemisphere Coral Reef Distribution

Manoel Luis Reefs

Coral Reefs

• Diverse assemblages of sclerectinian hermatypic (stony) corals, algae and numerous other organisms

• Corals are made up of tiny organisms (animals) called polyps (phylum Coelenterata)

• The polyps secrete the calcium carbonate that creates the reef

• Photosynthesis in reefs is carried out by single-celled algae (zooxanthellae) that live in symbiotic association with the coral polyps

• This symbiotic relationship supports all life on the reefs

• Coral reefs rival rainforests in their productivity

Acropora cervicornus – Staghorn Coral

Acropora palmata – Elkhorn Coral

Colpophyllia natans – Brain Coral

Types of Coral Reefs

• Barrier Reefs

• Fringing Reefs

• Atoll Reefs

Barrier Reefs

• Long, continuous reefs that parallel coastlines (continents or islands)

• Separated from the shore by a deep lagoon

• Belize’s barrier reef is the longest barrier reef in the Caribbean

Fringing Reefs• Found in shallow

waters bordering the coast

• Not separated from the coast by a deep lagoon, but may have shallow channels between the coast and reef flat

Atoll Reefs

• Reefs occurring around the perimeter of sunken islands

• Usually asymmetric is shape with a central lagoon

Sea surface temperature and coral bleaching off La Parguera, Puerta

Rico (northeastern Caribbean Sea)

Winter et al

(1998)

General Summary of the Article

• Coral reef bleaching is the death of reef corals due to the loss of the endodermal symbiotic algae

• Outbreaks of coral reef bleaching have been on the rise since the mid 1980’s

• Winter et al used sea surface temperature data (1966-1995) off of Puerto Rico and examined the association between temperature and coral reef bleaching

General Summary of the Article

• No single factor can be used to predict the onset of coral bleaching off of Puerto Rico

• Prolonged heat stress is a possible precondition with sharp temperature changes acting as an immediate trigger

Answers to Questions

1. What effect does the Amazon River have on the coastal regions of northeastern South America

• Large amounts of sediment lead to muddy and nutrient rich coastal waters

• Extensive mudbanks occur along the Guianan coast

• Enormous volume of fresh water discharged from the river produces coastal waters that are low in salinity

2. Globally, where is mangrove diversity and species richness the highest?

• The old world tropics (Indo-Pacific region)

Answers to Questions3. What are the primary morphological and

physiological characteristics that true mangroves share?

• Aerial roots (stilt/prop roots and/or pneumatophores)

• Distinctive tropical leaf morphology

• Vivipary

• Physiological adaptations for salt exclusion

4. To which group of plants do seagrasses belong?• Angiosperms

5. What are the 3 types of coral reefs?• Barrier

• Fringing

• Atoll

References

Allison, M. A., M. T. Lee, A. S. Ogston and R. C. Aller. 2000. Origin of Amazon mudbanks along the northeastern coast of South America. Marine Geology 163: 241-256.

Fromard, F., H. Puig, E. Mougia, G. Marty, J. L. Betoulle and L. Cadamuro. 1998. Structure, above-ground biomass and dynamics of mangrove ecosystems: new data from French Guiana. Oecologia 115: 39-53.

Guilcher, A. 1988. Coral Reef Geomorphology. John Wiley and Sons, Chichester. Kricher, J. 1997. A Neotropical Companion. Princeton University Press, Princeton. Phillips, R. C. and C. P. McRoy (eds). 1990. Seagrass research methods. Unesco,

Paris.Robertson, A. I. and D. M. Alongi (eds.). 1992. Coastal and Estuarine Studies:

Tropical Mangrove Ecosystems. American Geophysical Union, Washington DC.Tomlinson, P.B. 1986. The Botany of Mangroves. Cambridge University Press,

Cambridge. Wells, S. M. (ed). 1988. Coral Reefs of the World. Volume 1: Atlantic and Eastern

Pacific. UNEP/IUCN, Cambridge.Winter, A., R. S. Appeldoorn, A. Bruckner, E. H. Williams and C. Goenaga. 1998.

Sea surface temperature and coral bleeching off La Parguera, Puerto Rico (northeastern Caribbean Sea). Coral Reefs 17: 377-382.