What are the different types of defense mechanisms seen in marine animals?
A lot of sea animals use venomous spines. Examples of this include the urchin and puffer fish.
When in danger, puffer fish will inflate up. This makes them look more threatening stopping predators from eating them. If they do get attacked while in this form, they have venomous spines which will pierce the predator and damage them.
Sea urchins also use a similar technique. They have a strong hard shell covered with hundreds of venomous spines. This makes them hard to hunt (for predators). They are also a nuisance when people accidentally step on them. As the urchins are hard to get rid of due to their spines, it makes urchin armies dangerous to environments. Urchin armies are destructive to habitats, mainly "kelp forests". As they are hard to stop due to their spines, it makes the urchins destructible to "kelp forests".