1. Coral Reef Communities
Chapter 15
Coral Reef Communities

2. Key Concepts
Coral reefs are primarily found in tropical clear water, usually at depths of 60 meters or less.
The major types of coral reefs are fringing reefs, barrier reefs, and atolls.
Both physical and biological factors determine the distribution of organisms on a reef.

3. Key Concepts
Scleractinian (stony) corals are responsible for the large colonial masses that make up the bulk of a coral reef.
Corals obtain up to 90% of their energy from zooxanthellae, symbiotic dinoflagellates that use coral wastes, produce carbohydrates and aid in calcium carbonate deposition.
Coral reefs are constantly forming and breaking down.

4. Key Concepts
The most important primary producers on coral reefs are symbiotic zooxanthellae and turf algae.
Coral reefs are oases of high productivity in nutrient-poor tropical seas. Nutrients are stored in reef biomass and efficiently recycled.

5. Key Concepts
Inhabitants of coral reefs display many adaptations that help them to avoid predation or to be more efficient predators.
Coral reefs are huge, interactive complexes full of intricate interdependencies.

6. Coral Reef Communities
Coral reefs are highly productive, but occur in nutrient-poor waters
This is made possible by the symbiotic relationship between coral animals and zooxanthellae
These symbionts + algae form the basis of the community; other reef animals depend on these organisms
Turf algae is the other main primary producer

7. Organisms That Build Coral Reefs
Coral colonies
large colonies of small coral polyps, each of which secretes a corallite (cup of calcium carbonate)
the coral larva called a planula larva settles and attaches
a polyp develops, and reproduces by budding to form a growing colony
polyps’ gastrovascular cavities remain interconnected
a thin, usually colorful epidermis overlies the colony surface

8. Organisms That Build Coral Reefs
Coral nutrition
corals have evolved several strategies for obtaining food
symbiotic zooxanthellae
supply 90% of nutritional needs of stony coral
corals as predators
tiny zooplankton or other small animals paralyzed by the cnidocytes (stinging cells in tentacles) are passed into the digestive cavity

9. Organisms That Build Coral Reefs
Reproduction in corals
Reproduction by fragmentation
Sexual reproduction in coral
Many species of coral are hermaphroditic, some have separate sexes
mostly broadcast spawners—release both sperm and eggs into the surrounding seawater

10. Figure 15-4 FORMATION OF A CORAL COLONY.

11. Figure 15-6 CORAL POLYP FEEDING.

12. Figure 15-7 CORAL POLYP AND SYMBIONTS.

13. Types of Coral Reefs
Fringing reefs develop along shores of tropical/subtropical islands or continental landmasses
Of all reef types, most affected by human activities because of their proximity to land

14. Figure 15-11 (a) TYPES OF CORAL REEFS.

15. Types of Coral Reefs
Barrier reefs are similar to fringing reefs but separated from the landmass and fringing reef by lagoons or deepwater channels
Great Barrier Reef is the world’s largest barrier reef

16. Figure 15-11 (b) TYPES OF CORAL REEFS.

17. Figure 15 -11(d) TYPES OF CORAL REEFS

18. Types of Coral Reefs
Atolls, usually elliptical, arise out of deep water and have a centrally-located lagoon
FIGURE (c) TYPES OF CORAL REEFS.

19. Land Sea Reef Fringing reef Land Lagoon Sea Reef Patch reef
Barrier reef
Sea
Lagoon
Reef
Patch reef
Atoll
Stepped Art
Fig , p. 422

20. Types of Coral Reefs
In addition, patch reefs can occur within lagoons associated with atolls and barrier reefs
Darwin’s theory of atoll formation:
corals colonize shallow areas around newly-formed volcanic islands to form a fringing reef
the island sinks and erodes, and a barrier reef is formed about the island
the island sinks completely, leaving an atoll

21. Figure 15-12 (1) ATOLL FORMATION.

22. Figure 15-12 (2) ATOLL FORMATION.

23. Figure 15-12 (3) ATOLL FORMATION.

24. Figure 15-12 (4) ATOLL FORMATION.

25. Lagoon Active volcano Atoll Lagoon Fringing reef Barrier reef
Stepped Art
Fig , p. 423

26. Figure 15-13 9 (b) REEF CHARACTERISTICS.

27. Figure 15-14 (a) TYPES OF CORAL.

28. Figure 15-14 (b) TYPES OF CORAL.

29. Coral Reef Distribution
Major factors influencing distribution:
temperature – corals do best at 23-25o C
light availability – photosynthetic zooxanthellae need light, corals not found below 60 meters
sediment accumulation – can reduce light and clog feeding structures
salinity, corals absent from areas of massive freshwater outflow, e.g., the mouth of the Amazon
wave action – moderate wave action is beneficial, brings in oxygenated seawater, removes sediment that could smother coral polyps
heavy wave action during hurricanes can damage reef structure
duration of air exposure – can be deadly

30. Figure 15-15 DISTRIBUTION OF CORAL REEFS.

31. Comparison of Atlantic and Indo-Pacific Reefs
Pacific reefs are older and have a greater depth of reef carbonates
Buttress zone is deeper on Atlantic reefs and coral growth may extend to 100 m down
Pacific coral growth rarely exceeds 60 m
Proportion of reef covered by corals may approach 100% on some Pacific reefs, but usually less than 60% on Atlantic reefs
Algal ridges more common in the Pacific because of wind and waves

32. Comparison of Atlantic and Indo-Pacific Reefs
Hydrozoan Millipora complanata (fire coral) is dominant on Atlantic reefs
similar species never dominate in the Pacific
Gorgonians more abundant in the Atlantic
Soft corals (subclass Alcyonaria) more abundant in the Pacific
Atlantic corals nocturnal; Pacific corals diurnal

33. Comparison of Atlantic and Indo-Pacific Reefs
Atlantic corals often reproduce by fragmentation; Pacific corals by sexual reproduction
Coral diversity is far greater in the Indo-Pacific than the Atlantic
Indo-Pacific has 500 species of stony corals, only about 62 species occur in Atlantic

34. Comparison of Atlantic and Indo-Pacific Reefs
Coral reef communities also differ:
Indo-Pacific reefs have > 5,000 species of molluscs and ~ 2,200 species of ray finned fish
Atlantic reefs have ~ 1,200 species of molluscs, and 550 species of fish
Greater sponge biomass in the Atlantic
Pacific has giant clams and sea stars that prey on corals

35. Figure 15-16 (a) CORAL REEFS.
Caribbean reef

36. Figure 15-16 (b) CORAL REEFS.
Pacific reef

37. Coral Reef Ecology Source of nutrients
land runoff for reefs close to land
source of nutrients for atolls unclear
possible explanations:
nutrients accumulated over time are efficiently recycled
reef bacteria and filter feeders capitalize on nutrients from dissolved/particulate organic matter
nutrients are stored in the biomass of the community’s inhabitants

38. Coral Reef Ecology Photosynthesis on Reefs
photosynthetic organisms: zooxanthellae, benthic algae, turf algae, sand algae, phytoplankton, seagrasses
more dense than tropical ocean, with greater biomass than reef animals
associations of producers with other organisms assist in efficient recycling, e.g., zooxanthellae with corals, cyanobacteria with sponges
turf algae most abundant, process the most organic carbon

39. Table 15-1 Primary Productivity of Component Producer Communities on Coral Reefs and Their Distribution

40. Coral Reef Ecology Reef productivity
ratio of primary production to community respiration = P-R ratio
P = gross photosynthesis
C = community respiration
P-R ratio used to measure state of development of a biological community

41. Coral Reef Ecology Reef productivity (continued)
P-R ratio > 1 = primary production exceeds respiratory needs
biomass increases, excess biomass available for growth or harvesting
P-R ratio = 1 = steady state (climax)
little biomass remains available for growth
P-R ratios for coral reefs are typically close to 1
high productivity balanced by high respiration

42. Coral Reef Ecology Reef productivity (continued)
increases in productivity are often the result of eutrophication
eutrophication: nutrient enrichment
eutrophication typically manifested as a dramatic proliferation of algae
if grazing doesn’t increase, algae can grow over and smother corals

43. The Coral Reef Community
Competition among corals and other reef organisms
fast-growing, branching corals grow over slower-growing, encrusting or massive corals and deny them light
slower-growing corals extend stinging mesenterial filaments from their digestive cavity to kill faster-growing corals
fast-growing corals can also sting and kill using long sweeper tentacles with powerful nematocysts

44. The Coral Reef Community
Competition among corals and other reef organisms (continued)
Slower growing corals are more aggressive than fast growing corals
Massive corals are generally more shade tolerant and are able to survive at greater depths
as a result…
fast-growing, branching corals on many reefs dominate upper, shallower portions
larger, slower-growing corals dominate deeper portions

45. The Coral Reef Community
Competition between corals and other reef organisms (continued)
sponges, soft corals and algae can overgrow stony corals and smother them
algae outcompete corals at shallow depths unless grazers control the algae growth
massive die-off of Diadema (grazing sea urchin) in Jamaica in 1982 resulted in dramatic decline of coral cover and substantial increase in algal cover

46. The Coral Reef Community
Competition among reef fishes
coral reefs - marine habitats with greatest diversity/abundance of fishes
seems to defy competitive exclusion principle, which suggests that no 2 species can occupy the same niche
60-70% of reef fishes are general carnivores
about 15% are coral algae grazers or omnivorous

47. The Coral Reef Community
Competition among reef fishes (continued)
hypotheses proposed to explain this:
competition model: factors such as time of day or night, size of prey, position in the water column, etc. provide each species with a unique niche (hence, no competition)
predation disturbance model: assumes competition, but suggests that the effect of predation or other causes of death keep populations low enough to prevent competitive exclusion

48. The Coral Reef Community
Competition among reef fishes (continued)
hypotheses proposed to explain this:
lottery model: assumes competition occurs, but suggests that chance determines which species of larvae settling from the plankton colonize a particular area of the reef
resource limitation model: suggest that available larvae are limited and that limitation prevents fish population from ever reaching the carrying capacity of the habitat

49. The Coral Reef Community
Effect of grazing
reef is a mosaic of microhabitats with different levels of grazing and different algal communities
grazing of larger, fleshier seaweeds permits competitively inferior filamentous forms or coralline algae to persist
herbivory decreases with depth
damselfish form territories where they exclude grazers and permit abundant algal growth
provides habitat for small invertebrates
overgrows corals; fast-growing, branching corals are most successful near damselfish

50. The Coral Reef Community
Effect of predation
predation of sponges, soft corals and gorgonians provides space for competitively inferior reef corals
species that feed on fast-growing coral assist slower-growing species to remain
corallivores seldom destroy reefs
small invertebrates are almost all well hidden or camouflaged, indicating the prevalence of predation in the reef

51. The Coral Reef Community
Symbiotic relationships on coral reefs
cleaning symbioses
cleaner wrasses, gobies, etc. feed on parasites of larger fishes
cleaning organisms set up a cleaning station
Other symbiotic relationships
clownfishes and anemones
conchfish and the queen conch
gobies and snapping shrimp
crustaceans and anemones

52. Figure GIANT CLAM.

53. Evolutionary Adaptations of Reef Dwellers
Adaptive behaviors to avoid predation
invertebrates hide during the day and forage at night
producing a poisonous coating of mucus
burying the body in sand to hide
inflating to appear larger
hiding at night when nocturnal predators are active

54. Evolutionary Adaptations of Reef Dwellers
Structural adaptations for feeding
cnidocytes (stinging cells) of cnidarians aid in prey capture
radioles (hair-like) appendages of Christmas tree worms are used to capture phytoplankton
non-bivalve mollusks use radula to graze algae
mantis shrimp have extremely sharp forward appendages
snapping shrimp use sound to defend territory and stun prey
crinoids (feathers stars) use basket of mucus to feed

55. Figure 15-25 REEF FILTER FEEDERS.

56. Evolutionary Adaptations of Reef Dwellers
Protective body covering
tough, defensive exteriors help animals avoid predation, but can limit mobility and growth
Role of color in reef organisms
color for concealment and protection
Many invertebrates have colors and stripes that allow them to blend in with the environment

57. Evolutionary Adaptations of Reef Dwellers
Role of color in reef organisms (continued)
brilliant color of many fish actually helps them to blend in with colorful background of the reef
other types of camouflage
body shape
warning coloration
e.g., lionfish
other roles of color
defending territories
mating rituals

58. Threats to Coral Reef Communities
Effect of physical changes on the health of coral reefs
hurricanes and typhoons topple and remove coral formations
El Niño Southern Oscillation (ENSO)
changes winds, ocean currents, temperatures, rainfall and atmospheric pressure over large areas of tropical and subtropical areas
can cause massive storms

59. Threats to Coral Reef Communities
Why are coral reefs important?
protect coast from high surf conditions
remove large amounts of carbon dioxide from water and air
provide habitat for a huge diversity of invertebrates and fish
economical value, many people earn living by collecting and processing reef products
important place of recreation
have potential for harvesting pharmaceutical products

60. Threats to Coral Reef Communities
Effects of human activities
Destructive fishing practices
overfishing, i.e., eliminating grazers, allows algae to overgrow reefs
poisonous chemicals used to capture fish also poison corals
explosives used to stun and capture fish can cause massive destruction to coral
bottom trawling for fish also destroys coral structures

61. Threats to Coral Reef Communities
Effects of human activities (continued)
Coastal development
produces runoff containing nutrients, pesticides, toxic wastes
increases sedimentation and changes patterns of water flow

62. Threats to Coral Reef Communities
Effects of human activities (continued)
Other human activities
coral mined for use as bricks, road-fill, cement component
removed to make jewelry
inexperienced snorkelers and boaters damage reefs

63. Threats to Coral Reef Communities
Effects of human activities (continued)
effects of human-induced climate change in atmosphere
increased levels of carbon dioxide from burning of fossils fuels primary cause of ocean warming
causes corals to become stressed and more susceptible to coral bleaching and disease

64. Threats to Coral Reef Communities
Effects of human activities (continued)
coral bleaching
a phenomenon by which corals expel their symbiotic zooxanthellae
most often associated with warming of the ocean water by ENSO or global warming
if the stress is not too severe, corals may regain zooxanthellae and recover
if the stress is prolonged, corals may fail to regain zooxanthellae and die

65. Threats to Coral Reef Communities
Effects of human activities (continued)
coral diseases
black band disease: a distinct dark band of bacteria migrates across the living coral tissue, leaving behind a bare white skeleton
white pox: characterized by white lesions and caused by Serratia marcescens
other coral diseases:
white band disease
white plague
CYBD (Caribbean yellow band disease) or yellow blotch disease

66. Figure 15-31 (a) CORAL BLEACHING AND DISEASE.

67. Figure 15-31 (c) CORAL BLEACHING AND DISEASE.