Marine fish begin as eggs, hatch as larvae and go through further phases to adulthood. Once the eggs hatch, the larvae are entirely on their own, with no parental care or training. Knowledge of the larval phase for each species is vital to our understanding of the connectivity of fish populations along the Great Barrier Reef. It also informs policy and management decisions on conservation and sustainable fishing.
No larger than the tiny egg from which they come, newly-hatched larvae are unable to propel themselves. As these tiny larvae develop, for them swimming through the sea is like swimming through honey. Some stay close to where they were spawned, but most new larvae from marine species are dispersed by ocean currents as plankton – the collective name for multitude of tiny passive organisms found mainly in the pelagic open-water part of the ocean. As their sensory, swimming endurance, navigation and feeding capabilities increase, larval fish gradually develop the ability to swim towards a suitable adult habitat, such as a nearby coral reef.
Dr Jeff Leis, Amanda Hay and their collaborating scientists have undertaken extensive investigation of the complex behaviour of pelagic larvae of coral reef fishes at the Australian Museum’s Lizard Island Research Station. Among their findings:
- Tiny 1 cm long Damselfish (Blackaxil Puller Chromis atripectoralis) larvae can swim at more than 1 km per hour, or 28 body lengths per second. Swimming at half this speed, they can travel around 15 km without food or rest. This is faster than the average currents around Lizard Island.- See Hey Little Damsel Where Are You Heading?
- Damselfish larvae Chromis atripectoralis are faster and better navigators when they swim in groups rather than as solitary individuals – see With a Little Help From My Fishy Friends.
- Larvae of some species use sound to navigate. Others can use odour to find settlement habitat. – See Swimming with the big fish studying the small.
- Sun position may aid swimming orientation – See Which way home from the big blue?
- Larvae in warm (tropical) seas swim sooner and more efficiently than those in cooler seas – see Behaviour in Relation to Dispersal
These tiny Damselfish larvae are approximately 9 mm in length. Mature adults range up to 12 cm.