Biology and Ecology of Algae on Tropical Reefs - PowerPoint PPT Presentation

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Biology and Ecology of Algae on Tropical Reefs

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  1. Biology and Ecology of Algae on Tropical Reefs Jennifer E. Smith, Ph.D. National Center for Ecological Analysis and Synthesis University of California Santa Barbara

  2. Slime ?

  3. Incredible Diversity • > 500 species of marine algae in Hawaii, many new species and genera collected every year • > 60 species of corals • Many exciting research opportunities • Contact me later for more info…

  4. Degraded Reef Healthy Reef

  5. Overview of Lecture • General information • Taxonomy & morphology • Importance • Ecology • The reef environment • Human impacts

  6. General Info • Algae are photosynthetic autotrophs • Through the process of photosynthesis, they convert sunlight into chemical energy—glucose, starch & other carbohydrates

  7. General Info-cont. • Kingdom Protista…not “true plants” • No real tissues or organs • Older evolutionary lines • Huge diversity • Taxonomic dumping ground

  8. General Info cont. • Air vs. water habitat, organism’s utilize different strategies Land Plants Marine Plants

  9. Importance of Algae • Primary Producers • Shelter and Habitat • Cement and Structure • Sand • Nitrogen fixation • Bioindicators • Biomedical uses • Economics

  10. Sun Light + 6H2O + 6CO2-----> C 6 H12 O 6 ("sugars") + 6O2 • Raw Materials----->   Plant Tissue + Oxygen Primary Producers • Capture energy from the sun • Chlorophyll and other photosynthetic pigments • Use this energy to fix carbon into complex carbohydrates • Serve as the base of the food web • Supply energy for entire ecosystems

  11. Shelter & Habitat • Three dimensionality • Complexity • Commercially important species (lobster, crab, fish, etc. • Endangered species • Juveniles

  12. Cement & Protection • Crustose coralline algae (heavily calcified crusts) are the glue of coral reefs…fill in the gaps and meld together • The algal ridge/reef crest continually grows upward towards the sun • Provides physical protection to islands • Prevents erosion from wave action

  13. Sand Producers • Up to 90% of the sand in the tropics is produced by algae • Halimeda • Crustose coralline algae

  14. Nitrogen Fixation • Cyanobacteria • Specialized structure: Heterocyst that fixes atmospheric Nitrogen (N2) into useable forms • Available for uptake by reef species • Important source of “new nitrogen” on reefs

  15. Medical & Other Uses • Novel Compounds • Micosporine-like Amino Acids: sun screens • Antifouling compounds • Ship hulls • Medical Supplies (contact lenses, pace makers, pins, etc.) • Antioxidants • Cure diseases: cancer • Resistance to bacteria, antibiotics …seaweeds in the ocean can avoid infection by fungi and bacteria by producing their own natural antibiotics. The seaweeds live in constant contact with potentially dangerous microbes, suggesting they are under pressure to evolve some kind of resistance…

  16. Commercial Uses & Economics • 145 species of algae are cultivated for food-Nori (Porphyra, etc.) • 101 cultivated for phycocolloids (agar and carageenan) • Each year 13 million tons of seaweed produced in farms yields an excess of $6.2 billion dollars • 50% produced in the tropics • Kappaphycus and Eucheuma

  17. Bioindicators • Algae are like all plants and require nutrients (nitrogen and phosphorous) to grow • What happens when you add fertilizer to your garden? Weeds? • Algal blooms can be the result of eutrophication-nutrient pollution, runoff, sewage etc.

  18. Taxonomy • Three major “groups” of marine algae • Division Chlorophyta-green algae • Division Phaeophyta-brown algae • Division Rodophyta-red algae • Many other obscure groups that photosynthesize but do not form large multicellular marine plants • Blue-green Algae • Bacteria-Division Cyanophyta • Dinoflagellates • Division Pyrrophyta-zooxanthellae, and many more…

  19. Chlorophyta • Most diverse group of algae-over 7000 species worldwide • Approximately 60 species in Hawaii • Range in size from a few microns to over 3 meters long • Single to multicellular • Fresh water and marine species • Very simple to very complex

  20. Phaeophyta • From less than a centimeter to over 30 meters long • No unicellular representatives • Mostly all species are marine • 3000 species worldwide • Approximately 40 species in Hawaii • Alginate and Alginic Acid are important commercial products

  21. Rhodophyta • Single to multicellular • Few millimeters to few meters • Fresh water and marine • Approximately 5000 species, 360 in Hawaii • Carrageneen and agar are important commercially • Deepest alga ever found at 364 meters was a red crust

  22. Taxonomic Divisions and Photosynthetic Pigments

  23. Light in the Marine Environment

  24. Morphology

  25. Morphology Cont. Branching Patterns

  26. Algal Functional Form


  28. Factors necessary for growth Light Nutrients Factors that can influence growth Water motion Disturbance Temperature Salinity Substrate Competition Predation Algal Ecology Physical factors Biological interactions

  29. Temperate (cold water) High nutrient levels-upwelling, cold nutrient rich seawater Dominated by producers Algae form the ecosystem Productive High herbivory High net export of energy Tropical (warm water) Low nutrient levels-no upwelling High herbivory Corals form the ecosystem Highly productive Low algal abundance Low export of energy from system Coastal Marine Ecosystems

  30. Where are all the producers???

  31. The Paradox of Tropical Reefs Extremely diverse and highly productive ecosystems thriving in nutrient poor seas…how does this work??? …and where are all of the algae???

  32. The Coral/Algal Symbiosis • Self-contained unit • Highly efficient nutrient cycling • Coral fertilizes the zoox (with NH4 as excretion) and the zoox “feeds” the coral (translocation of complex sugars-photosynthate) • Evolved to thrive in nutrient poor waters • Very little “outside” energy needed

  33. The solution for other algae… Nitrogen & Phosphorus-low • Low Nutrients • Slow growth rates, high efficiency (high surface to volume ratio), grow in areas where nutrients are relatively high • Herbivory • Intense & diverse-keeps “standing stock” low • Avoid consumption by herbivores • Chemical (toxins) or physical defense (calcium carbonate, or cryptic growth form), • Grow fast

  34. Relationship between functional form and ecology

  35. Functional Forms & the Reef

  36. The Reef Flat • Refuge from herbivory • Intense solar radiation • Shallow, nutrient rich, moderate hydrodynamic forces • Substrate: basalt, limestone, rubble, sand and mud • Macroalgae dominate

  37. Reef Flat Algae

  38. The Reef Crest: Algal Ridge • Extreme hydrodynamics • High Flux-nutrient delivery • Intense herbivory • Severe physical conditions: light, temp., desiccation • Crustose coralline algae

  39. Reef Crest Algae

  40. Reef Slope • Intense herbivory • Low hydrodynamic forces • Low nutrients, mild fluctuation in physical factors • Corals dominate • Algae are cryptic, fast growing (turfs) or chemically defended

  41. Reef Slope Algae

  42. Keeping the Balance on Reefs • Intense grazing of algae by fish and invertebrates keeps algal standing stock low-helps to maintain the competitive dominance of corals • Clear, low nutrient water prevents algae from growing overly fast; favors the abundance of nutrient efficient species-symbioses

  43. Coral Reefs are Fragile Ecosystems • Because these unique ecosystems have evolved under specific conditions they are susceptible to small changes • Global population: 6.3 billion • 3.8 billion live within 100 km of the ocean, > 60% of total • This number is expected to double in the next 30 years • Tremendous pressure on marine resources & associated ecosystems

  44. Natural Storm disturbance, hurricanes, tsunamis Predation: COT Changes in sea level Disease Anthropogenic Overfishing Eutrophication Sedimentation Pollution Global warming Destructive fishing practices Trampling Exotic species Coral Reef Loss: Causes

  45. Phase-Shifts • Phase shifts can be the result of coral death where algae simply settle on “open space” • Or the algae may actually kill coral as a result of overgrowth, shading and smothering • Reduced herbivory & increased nutrients

  46. Things that kill coral • Localized • Sedimentation (smothering), disease outbreaks (coral death), Acanthaster blooms, trampling (abrasion) etc. • Global • Global warming-increased temperature (coral bleaching) and carbon dioxide (reduced calcification)

  47. Things that enhance algal growth/abundance • Nutrient addition: Eutrophication • Overfishing or loss of grazers

  48. Nutrient Pollution

  49. Overfishing & Reduced Herbivory