Coral Ecosystem Function

Question 1

Some Coral Generalities (4)

Answer 1

Small sessile marine animals of the phylum Cnidaria, individuals are called polyps

Generally form colonies over a hard internal calcium carbonate skeleton secreted by the animals themselves (scleractinian corals)

Often have photosynthetic symbiotic zooxanthellae living within their tissues

With bacteria, they form a biological holobiont

Question 2

Coral Polyp

Answer 2

In most cases, the tentacles can retract into the security of the skeleton

The tentacle ends have nematocysts to immobilize zooplankton

Mean skeletal growth ~1cm a year

Question 3

Hermatypic vs Ahermatypic Corals

Answer 3

Hermatypic Corals: Reef-building corals, deposit calcium carbonate substructures and can form large colonies

Ahermatypic Corals: Corals that do not contribute to reef aggregation, usually solitary and form small colonies

Question 4

Coral Trick #1 (connectivity)

Answer 4

Individual polyps are connected with a tissue layer (coenosarc) allowing for chemical communication and some exchange of compounds

Question 5

Coral Colony Morphology (7)

Answer 5

Plate-like
Foliaceous (leaf-like)
Columnar
Massive 
Branching 
Encrusting
Free-living

Question 6

Coral Trick #2 (Zooxanthellae)

Answer 6

Single-celled photosynthetic algae (dinoflagellates) that live symbiotically within the coral endoderm

Feed the corals through photosynthesis (provide 40-100%)

In turn they receive protection from predation and inorganic nutrients from the host (CO2 and NH4+)

Question 7

Holobiont

Answer 7

The entire community of living organisms that make up a single healthy organism

For coral, this includes all three basic realms of life

Question 8

Symbiosis type of Coral and Zooxanthellae

Answer 8

Normally this is mutualistic
However, it is fairly fluid, when it is healthy both types benefit
When under temperature stress zooxanthellae produce toxic compounds so corals kick them out

Question 9

Heterotrophic Strategies(3)

Answer 9

Predaceous carnivores capturing zooplanktonic and phytoplanktonic prey (stinging tentacles capturing moving prey)

Utilization of dissolved organic matter from surrounding water (absorption through mesentery filaments)

Detrital and mucosal feeding (suspension feeding or trapping surficial particles with mucus)

Question 10

Asexual Reproduction (fragmentation)

Answer 10

Can create new colonies
The broken piece grows at a 25-50x faster rate
Primarily used for Acroporid conservation
Not very effective for the massive types of corals

Question 11

Issues with fragmentation (3)

Answer 11

All new colonies from fragment are genetically identical (reduces genetic diversity)

Underlying conditions for coral loss are not addressed

Does not address biodiversity loss

Question 12

Sexual Reproduction

Answer 12

Some species (brain and star) type corals are hermaphroditic

Others (such as elkhorn) are gonochoric, produce single-sex colonies

Question 13

Larvae and Settlement

What determines settlement choice?

Answer 13

Settlement is the switch from a mobile planktonic phase to a sessile one

No further moves are possible for all major hermatypic species

Determined by both biotic and abiotic conditions

Abiotic: light, currents and temperature

Biotic: composition of the biofilm on the benthos and the availability of certain crustose coralline algae

Question 14

Herbivory

Answer 14

Key process
Facilitates reef building by corals by excluding algae
Algae negatively impact coral settlement, growth and survivorship
Most important ones are Parrotfish