Week 12: Coral reefs Flashcards
Coral reef community
Most diverse ecosystem on planet
What is a coral reef?
Consist of a living framework w internal cavities filled w sediment and a surrounding area of reef-derived skeletal grains
High energy environment- 1st to obtain nutrients
*Abiotic structure created by biotic means
Three main types of coral reefs
- Fringing reefs
- Barrier reefs
- Atolls
Fringing reefs
Non existent or shallow back reef zone, may connect directly to land
Located nearshore
Most common
ex.Ningaloo reef in west australia
Barrier reefs
Separated from land by a deep channel or lagoon
Outer edge is raised for food supply and to grow quickly
ex.great barrier reef
Atolls
Ring shaped island of coral reefs and coral debris
Encloses a shallow lagoon
Darwin and reef development
Believed it was a consistent pattern from fringing to barrier to atoll
BUT WRONG
Didnt account for sea level rise
Who builds the reef (part 1)?
Phylum Cnidaria - corals, sea anemones and jellies
All have specialized cells (cnidocytes) for protection and capturing prey
2 basic body forms of cnidaria
- Free swimming/floating medusa ex. jellies
- Sessile polyps ex. corals
How do cnidaria sting?
Their cnidocytes (stinging cells) contain nematocysts
How do cnidaria reproduce?
Sexually and asexually
Who builds the reef (part 2)?
Hermatypic corals contain tiny plant like organisms living in their tissue (zooxanthellae)
Zooxanthellae
Tiny photosynthetic algae living in tissue of most corals
Mutualism- coral supply nutrients, zooxanthellae supply food
Who builds the reef (part 3)?
Scleractinla (order)- stony or hard corals
Create a hard calcareous skeleton
Secrete aragonite
Who builds the reef (part 4)?
Coral polyp (stomach, tentacles and mouth)
Secretes CaCO3 to build hard outer skeleton
What type of organism are reef corals?
Mixotrophs
Energy needs of coral
10% from food capture
90% from zooxanthellae
What type of water is coral most efficient in?
Oligotrophic environments (nutrient poor)
Ensures adequate sunlight bc it isnt blocked
Ideal conditions for reef growth
Clear(nutrient poor), brightly lit, warm, shallow water, normal-slightly elevated salinity, strong wave activity to bring nutrients in
Ideal temp for coral growth
25-29 degrees celsius
Ideal salinity for coral growth
25-35 %
What happens if there is drastic change in conditions for coral?
Zooxanthellae leave and it causes a coral bleaching event
Horizontal zonation of coral reefs
Reef front (reef slope)
Reef crest
Reef flat
Back reef (lagoon)
Vertical zonation of coral reef
Deeper= less light , less wave energy, reduced diversity
Delicate, branching corals
Low wave energy, high sedimentationT
Thin, delicate, plate like
Low wave energy, low sedimentation
Globular, bulbous, columnar
Moderate wave energy, high sedimentation
Robust, dendroid, branching corals
Mod-high wave activity, moderate sedimentation
Hemispherical, irregular, massive corals
Mod-high wave activity, low sedimentation
Encrusting corals
Very high wave activity, low sedimentation
Tabular corals
Moderate wave activity, low sedimentation
Reef crest
Highest part of reef, exposed at low tide
Greatest wave action
Buttress zone
Reef flat
Calm shallow water
Tolerate a wide range of temp, light intensity and salinity
Adapt to low O2 levels
ex. heron island
Gorgonian corals (soft corals)
Found in reef flat
Dont produce hard CaCO3 structure
“Sea whips”
Sea cucumbers
Echinodermata- sea stars and urchins
Marine, benthic, found at all depths (reef flat)
Scavengers and deposit feeders
Deposit feeding
Ingest sediment and extract organic matter from itg
Poop out biogenous sediment
Types of organisms in the reef ecosystem
- Builders
- Dwellers
- Grazers
- Destroyers
Builders
Corals
Calcareous red algae
Dwellers
Bivalves
Calcareous green algae
Fish
Sponges
Anemones
Tunicates
Crabs
Grazers
Echinoderms
Gastropods
Some fish
Destroyers
Sponges
Bivalves
Annelids
Sponges
Sessile
Benthic filter feeders
Symbiotic relationship w algae
Calcareous algae
Imp component of reefs
Articulated- attached to substrate by calcified holdfasts
Non-articulated- crusts/encrusting
Three main classes of molluscs
All share a common ancestor
1. Cephalopoda (squid, octopuses)
2. Bivalvia (scallops, mussels, clams, oysters)
3. Gastropoda (snails, slugs, sea slugs)
Components of molluscs
Food for movement
Mantle: creates shell
Shell: protects visceral mass
Radula: tiny teeth (scraper to scrape coral)
Mobile invertebrates
Snails, limpets, abalone
80% of mollusc species
Filter (suspension) feeding
Cant move, attached to substrate (clams, oysters, molluscs)
Water passes through, filters food particles out
Parrot fish
Bioerosion
Try to break coral down using teeth
Giant clams (tridacna) - molluscs
Siphon- water flow , used for locomotion, feeding, respiration, reproduction
Symbiotic algae in mantle
How do corals provide coastal protection?
reduce shoreline erosion by absorbing energy from waves, protect coastal housing, agricultural land and beaches
Threats of coral bleaching
Climate change-water temp
Low tides- exposure
Overexposure to sunlight
Pollution
Ocean acidification threats to coral reef community
Harder for corals to create aragonite
Corals have to expend more energy to build skeletons
Slows rate at which coral reefs generate CaCO3 and build skeleton
Try to take shortcuts making their structures weaker
Threats to the coral reef community
Coral bleaching
Ocean acidification
Plastic pollution
Crown of thorns sea star
