Reproduction
Sea anemones can reproduce both sexually and asexually, with those that are primarily asexual reproducers capable of also reproducing sexually. Asexual reproduction includes longitudinal fission, budding, fragmentation and less commonly transverse fission. For some anemones, a special form of fragmentation called pedal laceration occurs, where small pieces at the edge of the pedal disc detach with either the parent or the offspring moving away.
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The four modes of asexual reproduction in sea anemones. A. Budding, B. Transverse fission, C. Longitudinal fission, D. Basal laceration (Shick 1991)
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By undergoing asexual reproduction, offspring are genetically identical to their parents and are therefore known as clones. Clonal anemones are able to reproduce quickly and appear to be superficially dominant through mass quantities of individuals in the population, however, these species can be prone to extinction events where conditions change to fall outside their tolerance levels that are controlled by the single genotype present.
Where the sea anemone reproduces sexually, gene recombination is possible, producing genetically different offspring from the parents and as such the individual is known as aclonal. Spawning and brooding are the two main mechanisms, where spawning is subject to various factors depending on the species. Some spawning is triggered by changes in water temperature or the seasonality of plankton productivity and the duration of a spawning event can be determined by the amount of nutrition within the larva. Females can be triggered to release their eggs in response to males releasing their sperm, where some species retain their spawned eggs on the mucus of their column, which are then available for fertilization by a close male neighbour. Brooders can be internal, external or some are known to be hermaphroditic and self-fertilizing, with larva then being released into the water column once successfully brooded.
By producing planktonic larva, the initial survivability is low compared to clonal anemones. Dispersal of aclonal anemones is wide and genetic diversity potentially strong, which makes such anemones more resistant and adaptable to changes in environment and less prone to extinction events.
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