Behaviour

Reproductive Behaviour

Polychaetes use specific behaviours during gamete release which act to enhance the synchronisation of release and increase the chance of larval survival.

Some species of Nereis release sex pheromones which are present in the coelomic fluid into the water column in order to promote synchrony in gamete release (Hardege et al., 1998)). Sexually mature individuals will leave their burrows, swim to the surface of the water and release a small amount of coelomic fluid containing the sex pheromone. The volatile pheromones are important in species recognition during this process and increase the swimming activity of other individuals (Bartels-Hardege et al., 1996). In some nereid species it has been observed that individuals of the opposite sex will swim in tight circles around each other (Zeeck et al., 1988); this results in a spawning aggregation which is thought to increase fertilisation success and acts to deter and reduce predation (Olive et al., 2000). These spawning aggregations increase the likelihood of successful gamete fertilization as there is a significant density of eggs and sperm in a small area. Individuals are most likely to release their gametes into the water during the night when there is less risk of predation.

Nereids have a planktotrophic larval phase before development occurs whereby the juvenile develops three to six segments and selects a benthic existence. This process may occur in as few as four days or as many as 40 days. As juveniles Nereis are likely to be detritovores before progressing to an omnivorous diet as they mature (Commito & Shrader, 1985). They are also likely to migrate during their growth from the high intertidal zone where the sands are muddier to the lower intertidal where there is lower mud content (Caron et al., 1993).

As gamete production, fertilization and subsequent growth of the individual are all highly synchronized, any change in the timing of a significant event in the polychaete’s life history could result in decreased fitness (Olive et al., 2000).

Different species of Nereis reproduce via different mechanisms. N. diversicolor reproduces in it’s burrow producing benthonic larvae whilst N. limnicola is a hermaphrodite and utilizes viviparity (Bartels-Hardege et al., 1996). Reproductive methods are largely a result of the environment and conditions in which the organism is exposed to (Bartels-Hardege et al., 1996).