DefenseMechanisms
From coraldigest
Defense Mechanisms
The Importance of Defense Mechanisms
- Corals are sessile
- Fixed at a certain position, attached to a substrate (such as a rock, or between sand)
- Corals are sessile, colonial animals — remaining stationary for most of their life cycle — which makes the ocean a very dangerous place
- Their vulnerability has lead to some of the most lethal toxins found in nature today
- chemical defense is vital
- Toxicity was naturally selected for
- Corals that were often preyed upon by fish now have higher toxicity levels, for their own protection
- The low nutritional value of some corals made them less susceptible to predation, so the lower the nutritional value, the lower the toxicity level
Chemical Defense Mechanisms
- Toxins
- Harmless to humans (except fire coral – can cause pain, inflammatory effects)
- Most toxins are neurotoxins
- Interfere with signal transmission in animals’ nervous systems
- Three main types
- Saxitoxin – causes paralysis and respiratory failure
- Palytoxin - causes kidney, respiratory and heart failure
- Lophototoxin – causes muscle contractions, possibly paralysis and respiratory failure
- Symbiotic Relationships
- A close relationship between two species
- Corals often live in symbiosis with bacteria and protists that produce toxins, using them for protection
- Coral probiotic hypothesis
- Some corals maintain symbiotic relationships with small animals
- Trapeziid crabs and stony coral
- Nematocytes
- Stinging cells used to capture small prey, kill of neighboring corals in a continuous battle for space
- Most corals possess these in addition to everything else
Physical Defense Mechanisms
- Cnidocils
- Activated when a predator touches it
- Discharges a nematocyst
- Nematocysts
- Discharge by firing a barb into the predator, leaving a hollow filament through which poisons are injected to immobilize the prey
- Tentacles move the prey to the polyp mouth