Coral Reef Ecology

Algal reefs are formed primarily by lime-secreting green and red algae, such as Halimeda and Lithothamnion.

Accumulations of the skeletons of arious lime-secreting organisms (prim. hermatypic corals), covered by a thin layer of tissue, that lives and builds on skeletal remains of past generations.

490 Mio yrs

Ordovician

• parasitism (pathogenesis)
• amensalism
• commensalism
• mutualism

• Nutritional benefits
  • autotrophy
  • enhanced availability and retention of nutrients
• Coral skeleton formation and reef accretion
  • light-enhanced calcification
  • provision of photosynthetically fixed carbon
• Other benefits
  • fixed position in the water column
  • protection of zooxanthellae from grazers
  • de-toxificaton of coral cells
  • supplementary O₂ and CO₂
  • _{UV-filter by coral pigments}

A genus of endosymionts of cnidarians and giant clams (zooxanthellae).

The endosymbionts provide up to 100% of energy for coral survival and reef building and obligate symbionts. They are aquired by corals through:

• ingestion by planula
• transmission from mother to daughter colony
• ingestion by coral after bleaching

Coral tissue can host more than 6 million zooxanthellae per cm².

In response to light intensity pigment concentrations and algal densities can be changed.

Symbiosis is necessary for organism to survive.

p.e.: coral and zooxanthellae

The organism can survive without symbiont, but not as well.

p.e.: anemone fish and anemone

Acanthaster plancii (crown-of-thorns) feeds on live corals.

• outbreaks can destroy entire reefs
• typical: 1-20/km², outbreak: >500/km²

1. decline of predators
   • over collecting of tritons
   • overfishing
   • habitat destruction
2. increased terrestial runoff
   • denser phytoplankton
   • better larval survival
   • increased starfish populations

• direct tentacular competition
• mesenterial filament extrusion
• sweeper tentacles and polyps
• mucus secretions
• overgrowth
• overshading

• Temperature range: 25 - 31°C (Limit: 20°C minimum isotherm)
• Salinity: 34 – 37ppt
• Light level (predominantly in top 30m of water column)

• high degree of nutrient recycling (symbiotic mutualism) promotes corals
• coral diversity promotes associated species

“Biotic multiplier effect”

• predation rates/ disturbance reduce competition
• patchy environments with variable colonization

priority advantage (inhibition model)

• Habitat diversity
• small scale habitat diversity
  • fish size
  • temporal factors (day/night)
• external factors (e.g. mangroves)

• Sequential hermaphrodites: Initially male or female, later sex change to the other.
• Simultaneous hermaphrodites (e.g. corals, nudibranchs)
• Oviparous: egg-laying, either spawning in water column or deposit eggs on sea floor (mostly external fertilization)

1. Protandry
   • born as males, later sex change to females
   • clownfish
2. Protogyny
   • born as females, later sex change to males
   • wrasses, parrotfishes

differential allocation of defensive metabolites within sponges (Optimal Defense Theory)

• OTD postulates, that defenses are primarily allocated to parts of high fitness value and/or that have higher risk of predation

1. Induced defense
   • de novo production of defensive compounds
   • slow (days – weeks)
2. Activated defense
   • wound induced conversions of stored precursors to defensive compound
   • fast (seconds – minutes)

1. Coral bleaching
   • Vibrio shiloi causes coral bleaching in Oculina patagonia
2. Colored band diseases
   • Black Band
   • Brown Band
3. White Syndrome(s)

1. Asteroids
   • Acanthaster planci
2. Coral reef fishes
   • Parrotfish
   • Pufferfish
   • Damselfish
   • Blennies
   • Butterflyfish
3. Gastropods
   • Drupella spp.
   • Coralliophila violacea

• Moray eels
• Scorpian- and Lionfishes
• Anthiases, Groupers
• Jacks, travellys
• Makreles, Tunas
• Snappers, Emperors

• Damselfishes
• Butterflyfishes

• Surgeonfishes
• Parrotfishes
• Rabbitfishes
• (Damselfishes)
• (Blennies)