Title: Who,%20What,%20When,%20Where,%20Why,%20and%20How%20of%20Coral%20Reef%20Communities
1Who, What, When, Where, Why, and How of Coral
Reef Communities
- Who (organisms) can be found in a coral reef
community? - What is a coral reef community?
- When can you find a coral reef community (is it
seasonal)? - Where are coral reef communities found?
- Why are coral reef communities so important?
- How do coral reef communities interact with other
ecosystems in the ocean?
2Chapter 15 Coral Reef Communities
3- Lets talk about primary productivity in the
oceans - Photosynthesis by phytoplankton - Polar oceans are the most productive
- Cold water holds more gases
- Summer brings 24 hours of daylight for
photosynthesis - Temperate waters are somewhat productive
- Tropical waters are the least productive
- Thats why there are nice clear, blue water
- Coral reefs are like an oasis in the tropical
water dessert
4Coral 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
5Organisms That Build Coral Reefs
- Stony (true) corals are the primary organisms
that deposit massive amounts of CaCO3 that
compose most of the structure of coral reefs - Hermatypic coral species that produce reefs,
found in shallow, tropical waters and harbor
zooxanthellae
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7Organisms That Build Coral Reefs
- Ahermatypic corals that do not build reefs,
which can grow in deeper water from the tropics
to polar seas - most do not harbor zooxanthellae
- Coralline algae and organisms such as fire coral,
deposit lesser amounts of calcium carbonate on
reefs - fire corals important in Caribbean reefs
- coralline algae important in structure of Pacific
reefs
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11Organisms 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
12Organisms That Build Coral Reefs
- Coral nutrition
- corals have evolved several strategies for
obtaining food - symbiotic zooxanthellae
- supply 90 of nutritional needs of stony coral
- zooxanthella provide glucose, glycerol and amino
acids - coral polyp provides a suitable habitat and
nutrients, absorbed directly through the animals
tissues - zooxanthellae remove CO2 and produce O2
- need of zooxanthellae for sunlight limits depths
to which stony corals can grow
13Organisms That Build Coral Reefs
- Coral nutrition (continued)
- corals as predators
- tiny zooplankton or other small animals paralyzed
by the cnidocytes (stinging cells in tentacles)
are passed into the digestive cavity
14Organisms That Build Coral Reefs
- Coral nutrition (continued)
- other sources of nutrition
- mesenteric filaments (coiled tubes attached to
the gut wall) can be extruded from the mouth to
digest and absorb food outside the body - corals can feed off bacteria living in their
tissues, which feed on dissolved organic matter
directly from the water
15Organisms That Build Coral Reefs
- Reproduction in corals
- Reproduction by fragmentation
- in addition to budding, corals can also reproduce
asexually by fragmentation - some branching corals are fragile and tend to
break during storms - if they survive the storm, fragments can attach
and grow into new colonies
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17Organisms That Build Coral Reefs
- Reproduction in corals (continued)
- Sexual reproduction in coral
- Many species of coral are hermaphroditic, some
have separate sexes - mostly broadcast spawnersrelease both sperm and
eggs into the surrounding seawater - some are broodersbroadcast sperm, but retain
eggs in the gastrovascular cavity - spawning is usually synchronous among Pacific
reef species, but nonsynchronous among Caribbean
species
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21Reef Formation
- Involves both constructive and destructive phases
- Bioerosion the destructive phase of reef
formation - boring clams or sponges attack exposed surfaces
on the undersides of large corals - the coral stand weakens, then topples in a storm
or ocean surge - accumulating debris smothers boring organisms,
cracks are filled with CaCO2 sediments, and
coralline algae cement it together
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24- Types of reefs
- Fringing
- Barrier
- Atoll
- Patch
25Types 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,
develop right next to the land
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27Types of Coral Reefs
- Barrier reefs
- similar to fringing reefs but separated from the
landmass and fringing reef by lagoons or
deepwater channels - Great Barrier Reef is the worlds largest barrier
reef
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30Types of Coral Reefs
- Atolls
- usually elliptical, arise out of deep water and
have a centrally-located lagoon - Often eroded dead volcano
31- Darwins 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
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36Reef
Fringing reef
Reef
Patch reef
Barrier reef
Patch reef
Atoll
Stepped Art
Fig. 15-11, p. 422
37Types of Coral Reefs
- In addition, patch reefs can occur within lagoons
associated with atolls and barrier reefs
38Reef Structure
- Different reef types share common characteristics
- Reef front or forereef portion of the reef that
rises from the lower depths of the ocean to a
level just at or just below the surface of the
water, on the seaward side - drop-off a steep reef-front that forms a
vertical wall - spur-and-groove formation or buttress zone
finger-like projections of the reef front that
protrude seaward disperses wave energy and helps
prevent damage
39Reef Structure
- Reef crest the highest point on the reef and the
part that receives the full impact of wave energy - where wave impact is very strong, it may consist
of an algal ridge of encrusting coralline algae,
lacking most other organisms, and penetrated by
surge channels, grooves of the buttress zone - Reef flat or back reef portion behind the reef
crest - reef flat of fringing reefs ends at the shoreline
- reef flat of atolls and barrier reefs descends
into the lagoon
40Reef Structure
- Coral populations on reef front are massive
dome-shaped brain corals and columnar pillar
corals on intermediate slopes, below this region
coral species form plate-like formations - Higher up on reef where wave energy is greatest,
branching species of coral are found, e.g.,
elkhorn coral in Caribbean - In protected areas behind reef front, in shallow
calm waters, small species of coral occur, e.g.,
rose, flower and star corals
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45Coral Reef Distribution
- Major factors influencing distribution (corals
are sensitive) - 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
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47Comparison 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
48Comparison of Atlantic and Indo-Pacific Reefs
- Hydrozoan Millipora complanata (fire coral) is
dominant on Atlantic reefs - similar species never dominate in the Pacific
- Atlantic corals nocturnal (night) Pacific corals
diurnal (day)
49Comparison of Atlantic and Indo-Pacific Reefs
- Greater sponge biomass in the Atlantic
- Pacific has giant clams and sea stars that prey
on corals
50Coral Reef Ecology
- Source of nutrients for coral reefs
- land runoff for reefs close to land
- Thats why too much runoff can bring unwanted
nutrients - source of nutrients for atolls unclear (usually
out in the middle of the ocean) - 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
communitys inhabitants
51Coral 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
52Coral 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
53Coral Reef Ecology
- Reef productivity (continued)
- P-R ratio gt 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
54Coral Reef Ecology
- Reef productivity
- increases in productivity are often the result of
eutrophication - eutrophication nutrient enrichment
- eutrophication typically manifested as a dramatic
proliferation of algae - if grazing doesnt increase, algae can grow over
and smother corals - This will happen with too much sewage and
fertilizer runoff
55The 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
56The 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
57The Coral Reef Community
- Competition among reef fishes
- High diversity
- 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
58The 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
59The 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
60The 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
61The Coral Reef Community
- Effect of predation
- predation of sponges, soft corals and gorgonians
provides space for competitively inferior reef
corals - small invertebrates are almost all well hidden or
camouflaged, indicating the prevalence of
predation in the reef
62The 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
63Evolutionary 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
64Evolutionary 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
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66Evolutionary 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
67Evolutionary 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
68Threats 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
69Threats 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
70Threats 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
71Threats 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
72Threats 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
73Threats 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
74Threats 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
75Threats 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
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