Abalone Growth and Development

 

Welcome to the abalone growth and development page.
Here you can find out all about how an abalone grows from gamete
(egg or sperm) to reproductive adult!

 

Fertilized egg: The males and females aggregate together and spawn simultaneously. The gametes (eggs and sperm) are released through the respiratory holes with the respiratory current. Fertilized of the egg is external (outside the body). This occurs quickly, with eggs becoming fertilized after a few minutes to a few hours latter. The egg is approximately 0.2mm across.

 

Trochophore: These microscopic (0.2mm) free-living larvae hatch from the eggs after 24 hours. This larval stage is lecithotrophic, feeding on the remains of the egg. The trochophore has a prototroch; a ciliated band, which gradually becomes unfolded into a ciliated organ called the velium, as it develops into the next larval stage. The shell first starts to form at this larval stage.

 

Veliger Larvae:

After another 24 hours the trochophore larva develops into the veliger larval stage which measures about 0.3mm. This free-swimming larva has the distinctive velium organ, which resembles two ciliated flaps. This aids in locomotion, enabling it to swim very rapidly. As a veliger, it increases in size, and the internal organs start to develop. The shell grows and the foot becomes evident. During this stage the larvae undergoes torsion where the shell twists 180 degrees.

 

Post Larval 'spat': After 2-3 weeks swimming around in the water column, the pelagic veliger larva loses its velium and metamorphoses into the post-larval stage (spat). It loses its positive phototaxis (movement towards the sunlight), moves down from the water surface, and settles on hard surfaces in intertidal and subtidal areas. Settlement is triggered by a chemical that is produced by Coralline algae and adult abalone. Abalone feed on Coralline algae and the presence of adults indicates a good habitat to live! The post-larva sheds its swimming hairs (cilia) and begins to develop the adult shell form. This is the first feeding stage where they start to feed on diatoms.

After 1-3 months after settlement the juvenile stage is fully formed and resembles the adult. After a month the juveniles are still tiny measuring about 0.5mm! Abalone are relatively slow growing and long lived. They can reach a size of 140mm and have a maximum life span of 15 years. Juveniles are cryptic, seeking refuge from predators under rocks and in crevices. They feed on diatoms, bacteria and single-celled algae.

 

After 2-4 years the abalone becomes mature, and has a shell size of about 50mm. As they grow and become less vulnerable to predation, the abalone becomes "emergent", inhabiting more open and visible locations. Abalone are dioecious, which means they have separate sexes. They are similar in size and form, and can only be distinguished by looking at their gonads (creamy white in males, greenish in females). They are broadcast spawners, so they aggregate together before releasing millions of gametes (eggs and sperm) into the water column. Forming groups ensures maximum fertilization. Therefore the "thinning out" effect of fishing which causes declines in population size, may have a negative effect on fertilization success. As adults, they feed on attached and drifting algae.


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