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Understanding Mangroves: Coastal Ecosystems and Their Adaptations

Learn about mangroves, dominant coastal ecosystems in subtopical and tropical regions. Explore their distribution, main genera, settings, adaptations, effects on estuaries, and hurricane resilience.

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Understanding Mangroves: Coastal Ecosystems and Their Adaptations

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  1. A. Mangroves • Or Mangal • from mangue (tree) and grove (stand of trees) • Replace salt marsh as the dominant coastal ecosystem in subtropical and tropical regions • Facultative halophytes

  2. c. Distribution • 240,000 km2 worldwide • 2,700 km2 in Florida • 68 spp worldwide • 10 spp in the Americas

  3. Distribution Continued • Found on coastlines between 25 N and 25S latitude, dependent on temperature • Rhizophora - survive 2-4 C for 24 hrs • Avicennia – survives 2-4 C for several days

  4. B. Three Main Genera • Rhizophora (red mangrove) • R. mangal and R. racemosa most common New World spp • High prop roots and dangling roots are common (Figure 11-8) • More cold tolerant

  5. b. Avicenna (black mangrove) i. A. germanaus most common in New World • ii. Can tolerate very high salinity (60 ppt) and very anoxic conditions • iii. Known for having pneumatophores

  6. Lagunicularia (white mangrove) • L. racemosa most common in New World • Affinity for lower salinity areas

  7. C. Geomorphological settings • need gentle wave/tidal action to bring nutrients • salinity allows them to out compete FW species

  8. D. Hydrodynamic settings • Fringe – protected shorelines, some canals, rivers and lagoons • Grow to 13 m tall • Accumulate organic matter • Found in S. Fla, Puerto Rico, Mexico, Texas • Avicennia found in salinity to 59 ppt, Rhizophora to 39 ppt • Overwash islands – one type of fringe mangrove • Rhizophora dominated • sensitive to ocean pollution

  9. b. Riverine – along tidal affected rivers • Grow to 21 m tall • Rhizophora dominated, but with few prop roots • Avicennia and Lagunicularia also present • Salinity 10-20 ppt

  10. c. Basin- inland depressions, behind fringe, in stagnant water • Grow to 9m tall • Soil conditions: highly anoxic, saline • Avicennia and Lagunicularia with many pneumatophores • If salinity >50ppt: Avicennia, if low: lagunicularia, 30-40ppt mixed forest

  11. d. Dwarf – isolated, low productivity, low FW, low nutrients • Grow to 2-5m shrubs • Fringe of everglades, Florida Keys • Hammock – one type • buildup of peat • Rhizophora dominated

  12. E. Understory – lacking due to variety of stressors • Mangrove ferns (Acrostichum spp) are common, 3 spp worldwide

  13. F. Salinity • Not required for mangroves • Much higher in soil than in water

  14. G. Zonation

  15. H. Adaptations • Salinity – exclusion and excretion • Prop roots and drop roots – Rhizophora • Pneumatophores – Avicennia – 20-30 cm above sediment • Lenticels found on a & b, let oxygen into plant, moves through arenchyma to root rhizosphere • Viviporous seedlings – Rhizophora – seeds germinate on tree i. Hypocotyls (seedling) drops, floats till touches sediment, roots

  16. Crabs – mangrove maintenance • Burrow, oxygenate soil, drag leaves into soil, aid in decomposition • Selectively eat dropped hypocotyls

  17. J. Hurricanes

  18. Hurricanes Continued • mangrove succession to stable community in average time between major hurricanes • Wipe out larger mangroves, small trees in gaps survive and act as a seed bank

  19. K. Mangrove effects on estuaries • Net export of organic matter and nutrients • Provides nursery areas and food sources for fisheries

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