When coral polyps settle down, they do not move around. They spread to new areas by reproduction. Surprisingly, they also battle with other species of corals for space and territory.
Corals can reproduce asexually or sexually. In asexual reproduction, coral polyps split into two halves after reaching a certain size. Each half grows to its fullest size and splits again. This process of splitting goes on and on and keeps the coral colony spreading. In another type of asexual reproduction, when a colony matures, it forms tiny young corals called planulae. These are formed asexually within one colony alone. In asexual reproduction, each planula is genetically identical to the original.
Coral Asexual Reproduction
In sexual reproduction, just like salmon reproduce, some corals release sperm and some release eggs all over a reef. The sperm fertilize the eggs and each forms a planula. Unlike asexual reproduction, each planula is genetically different from its parents. The planulae float and swim upward in the water for several days, sometimes weeks. They then become polyps. The algae zooxanthellae is also passed onto the young corals by their parents during sexual reproduction. Being fully independent, the young polyps begin building their own coral homes.
Coral Sexual Reproduction
Similarly to land animals that protect their territory, corals, even though stationary, battle each other for space. The war happens between different species or colonies of coral. They fight with their tentacles and release chemicals from their stinging tentacles to eat parts of the other coral. The injured coral may sometimes die. Just like land animals, some species of corals are more vicious than others. In labs, scientists have found that slow-growing corals attack fast and quickly. Faster-growing corals rely on their ability to grow at faster speeds to colonize the place.