2. Tropical Reefs: Coral/Algal
Diversity and Challenges

3. Questions:
Why are tropical reefs comparable to rain forests in diversity?
Dissolved nutrients are scarce
Productivity & diversity normally go together
Why are tropical reefs disappearing?

4. Increasing threats to coral

5. Current bleaching threats

6. What are the challenges?
Low nutrients dissolved in water
Shallow habitats mean more intense wave action
Long-term: sea level changes

7. Tropical reefs are geologically important

8. Reef ecology has long challenged biologists

9. Dominant reef-building organisms
Small individuals, magnified in effect by large numbers
Phylum Cnidaria
Class Anthozoa
Subclass Zoantheria
Diverse algae, depositing CaCO3

10. Cnidaria polyps: radial symmetry

12. Cnidaria: tentacles for feeding

13. Cnidaria: stinging cells on tentacles

14. Not all corals deposit CaCO3

15. “Hermatypic” corals create reefs in symbiosis with Symbiodinium

16. Growth forms of colonies reflect tradeoffs
Access to light for symbiotic algae
Issues of depth (growth upward)
Issues of competition (shading)
Risk of damage from turbulence in shallow seas
Diverse growth forms reflect different balances

17. Fast extension: linear growth form

18. Extension + more surface area: branching

19. Lattice: a subset of “branching” form

20. Plate form: more resistant to turbulence

21. Massive form: very wave-resistant

22. Independent algae build reefs: crustose
Algae can contribute a large fraction of reef mass

23. Independent algae: Green (Halimeda)

24. Reefs: a matrix of solid coral and sand

25. Reef diversity – some examples

34. Ecological functional groups

35. A larger scale view: reef building process

36. Atoll structure

37. Habitat diversity within an atoll