Transcript Tropical reef diversity

Coral/algal Reefs II
What forces maintain reef
diversity?
Planet Earth video
Ecological functional groups
A larger scale view: reef building process
Atoll structure
Habitat diversity within an atoll
Niche dimensions enhancing reef fish
diversity
• Defensive tactics
• Feeding
– Food type
– Food location
– Timing of foraging
• Life-history and social structure
Physical defenses: Spines of Porcupine fish
Physical defenses: misdirection, Butterfly fish
Territoriality: Pomacentrus
Poisons: Purple trunk fish, lionfish
Feeding: >50% feed on other fish
• Variation by size, location, timing
Feeding: coral (Triggerfish)
Feeding: “inverts” by probing (file fish)
Feeding: marine worms (butterfly fish)
Feeding: plankton (purple queen)
Feeding: algae (surgeon fish)
Feeding: other fish/ cleaning symbiosis
–Pacific Cleaner
Wrasse
–Moray Eel
–Saber Tooth
Blenny
External factors influencing diversity
• Proximity to mangrove nurseries
– Mumby et al. 2004, Nature 427:533
– Compare fish biomass from reefs near mangroves and
where mangroves scarce
Species
Scarce mangrove
Rich mangrove
H. sciurus
1,205
33,349
H. pumieri
5,174
16,280
Haemulidae
11,636
67,370
739
6,192
L. apodus
How can coral/algal reefs support so many
species?
• “Bottom-up” hypotheses
– High degree of nutrient recycling (symbiotic
mutualism) promotes corals
– Coral diversity promotes associated species
– “Biotic multiplier effect”
• “Top-down” hypotheses
– Predation rates/disturbance reduce competition
– Patchy environments with variable colonization
– Priority advantage (inhibition model)
Utilitarian justification for reef conservation
• Therapeutic compounds from marine
species
– Anti-virals from sponges, seagrass
– Anti-tumor compounds from tunicate, dogfish,
bryozoan, sea hares, cyanobacteria, sponge
– Compounds to promote bone grafts from stony corals
• Tourism
• Food
• Impact on global climate, carbon exchange
• Models for scientific study
Processes important in reef dynamics –
what maintains the reef structure?
• Symbiosis (and dissolution of associations)
• Competition
• Predation and grazing
• Disturbance & recovery
Competitive dynamics
• Exploitation competition (for light)
– Upright, branching corals can shade massive
corals
– Encrusting algae can spread over corals
• Interference competition (for space)
– External digestion by some corals
– “Sweeper” tentacles for some species
• Hierarchy of competitive dominance
– Algae easily overgrow most corals
– Among corals Pocillopora is nastiest
Dynamics of predation on coral reef species
• Coral-feeding fish are present but usually
not devastating
– Territorial damselfish create safe zones (up to
60% of surface area)
– Coral-feeders have their own predators
• Starfish, such as “Crown-of-Thorns” can
be problematic
– Population “outbreaks” can damage living
corals
Dynamics of grazing on algal reef species
• Urchins are major
•
•
•
consumers (e.g., Diadema
antillarum)
Grazing by herbivorous fish
can be specialized on algae
(more impact than fish
feeding on corals)
Grazing can suppress
competitively dominant
algae
Indirect effects can become
important