BIOTIC

BIOTIC Species Information for Nephtys hombergii

Researched by

Lizzie Tyler

Data supplied by

University of Sheffield

Refereed by

This information is not refereed.

Reproduction/Life History

Reproductive type

Gonochoristic

Developmental mechanism

Planktotrophic
Lecithotrophic

Reproductive Season

See additional information

Reproductive Location

Sediment surface

Reproductive frequency

Annual protracted

Regeneration potential

Life span

3-5 years

Age at reproductive maturity

1-2 years

Generation time

1-2 years

Fecundity

>10,000 eggs per year

Egg/propagule size

150 µm diameter

Fertilization type

External

Larvae/Juveniles
Larval/Juvenile dispersal potential	Insufficient information	Larval settlement period	Insufficient information
Duration of larval stage	1-2 months

Reproduction Preferences Additional Information

Spawning
Sexes are separate. Nephtys hombergii remains in the sediment during spawning and eggs and sperm are released on to the surface of the sediment during low tide. Bentley (1989) gives an ultrastructural description of oogenesis in Nephtys hombergii. Mean size of oocytes was reported to be between 140 and 160 µm in Arcachon Bay, France, 200 µm in Southampton Water and between 100 to 140 µm on the Northumbrian coast (Mathivat-Lallier & Cazeau, 1991; Oyenenkan, 1986). The animals spawn via the anus. Histological examination by Bentley et al. (1984) revealed the development of a cleft in the central part of the gut in the prepygidial segment which serves to deliver the mature gametes to the anus for spawning. This system is developed only in mature worms of both sexes. Bentley et al. (1984) suggested that this represents the normal pathway for the discharge of gametes in the Nephtyidae, which lack functional coelomoducts. A spawning hormone (SH) released from the supraoesophageal ganglion brings about spawning in mature individuals (Olive, 1976; Olive & Bentley, 1980). Nephtys hombergii is a broadcast spawner, so it is advantageous that the spawning of a given individual coincides with that of several others of the same species. In addition to endocrine control, environmental factors, such as temperature, day-length, and tidal or lunar cycles, have been implicated in the timing of spawning of the Nephtyidae, in particular the spring tide phase of the lunar cycle (Bentley et al., 1984).
Developmental mechanism
The planktonic cycle of Nephtys hombergii was described by Cazaux (1970), who defined five stages: two trochophore stages (2-3 days) and three metatrochophore stages. The first trochophore stage is lecithotrophic and successive four other stages are planktotrophic. The pelagic life cycle of Nephtys hombergii lasts seven to eight weeks at the end of which larvae metamorphose into benthic juveniles. Newly metamorphosed juveniles have an average width of 0.2 mm and eight or nine segments (Mathivat-Lallier & Cazaux, 1991).
Reproductive cycle
Observation of the reproductive patterns of the Nephtyidae suggest that they are related to environmental conditions in central parts of the range of each species, marginal populations of some species exhibit occasional reproductive failures, e.g. Nephtys cirrosa, whose reproductive physiology is not sufficiently well adapted to conditions experienced in the northern limit of its range (Olive & Morgan, 1991). In the British Isles Nephtys hombergii has been observed to spawn in May and June in northern Britain, sometimes successfully but also unsuccessfully, to be followed by a period of oosorption (internal breakdown of gametes) overlapping with the subsequent cycle of gamete production. Olive & Morgan (1991) found reproductive failure in this species difficult to explain, as distribution records inferred Nephtys hombergii to be in the centre of its range in northeast England. They suggested for the relatively long-lived Nephtys hombergii that spawning failure could be part of an adaptive response in which adult survivorship is maintained at the expense of reproductive output (see Lewis et al., 1962; Grémare & Olive, 1986). The endocrine system of Nephtys hombergii (see Bentley & Pacey, 1992) is able to control spawning by failing to secrete gonadotrophic hormone (GH), withdrawing GH secretion during the vitellogenic phase, or failing to secrete spawning hormone. Such endocrine responses may result from the receipt of inappropriate environmental signals from the soma (Bentley & Pacey, 1992). Olive et al. (1985) suggested that when energy levels of the soma fall below some critical level (which may reduce survival chances of the individual) then reproductive failure through GH withdrawal may result.
In the Tyne Estuary spawning of Nephtys hombergii occurred in May and September, whilst in Southampton Water the species spawned throughout the year with peaks in July and November (Wilson, 1936; Oyenekan, 1986). In Århus Bay, Denmark, Nephtys hombergii spawned in August and September, but a decrease in the number of individuals bearing gametes in May and June suggested that at least part of the population spawned in early summer (Fallesen & Jørgensen, 1991).

Reproduction References

Cazeau, 1970, Mathivat-Lallier & Cazaux, 1991, Oyenekan, 1986, Olive & Morgan, 1991, Grémare & Olive, 1986, Lewis et al., 1982, Fallesen & Jørgensen, 1991, Olive, 1976, Olive & Bentley, 1980, Bentley & Pacey, 1992, Bentley et al., 1984, Bentley, 1989, Eckert, 2003, Julie Bremner, unpub data, Olive, 1977,