BIOTIC

BIOTIC Species Information for Hediste diversicolor

Researched by

Georgina Budd

Data supplied by

MarLIN

Refereed by

Mike Kendall

Reproduction/Life History

Reproductive type

Gonochoristic

Developmental mechanism

Lecithotrophic
Oviparous

Reproductive Season

Spring - summer

Reproductive Location

Adult burrow

Reproductive frequency

Semelparous

Regeneration potential

Life span

1 year

Age at reproductive maturity

<1 year

Generation time

1-2 years

Fecundity

Insufficient information

Egg/propagule size

Insufficient information

Fertilization type

External

Larvae/Juveniles
Larval/Juvenile dispersal potential	Not relevant	Larval settlement period	Not relevant
Duration of larval stage	Not relevant

Reproduction Preferences Additional Information

Nereidae are monotelic, that is, they reproduce only once in their lifetime and then die (Olive & Garwood, 1981). Hediste diversicolor is gonochoristic (dioecious) and remains atokous throughout its life (Scaps, 2002).
In summer and autumn the sexes are externally indistinguishable being both reddish brown in colour. In any one population females are predominant, although to varying extent between localities (Dales, 1950; Clay, 1967 (c) and references therein). This observation led early workers to suggest parthenogenetic reproduction and hermaphroditism within Hediste diversicolor (Dales, 1950) but it is now acknowledged that these reproductive mechanisms are not found in Hediste diversicolor. Hediste diversicolor does not display epitoky or swarming behaviour associated with sexual reproduction like other nereid polychaetes, such as Nereis succinea and Nereis virens. The sex ratio in populations of Hediste diversicolor is heavily biased towards females. Olive & Garwood (1981) reported a ratio of females to males of approximately 4.6 : 1 in northeastern England.
Maturation & spawning
Colour differences between the sexes become more apparent upon maturation. Maturation and spawning are induced by a temperature rise in early spring to between 6°C and 11°C following a period of low winter temperatures. The male becomes bright green in colour. In contrast, the female appears darker green in colour which may be lacking on the ventral side. Reddish brown pigments may also still be visible in the female.

Coelomic germ cells may be first recognizable in females that are at least 6 months old or about 7 cm in length. Eggs mature within the coelom surrounded by a loose mass of heterogenous corpuscles which the eggs gradually displace.
Histolysis of the muscle layers and ingestion by phagocytes renders the female worm very brittle and enables the eggs to be released following rupture of the body wall, which is achieved by writhing within the burrow. In addition to a rise in temperature, the lunar cycle imposes a further synchrony on Hediste diversicolor so that spawning normally coincides with periods of new or full moon.
Mature males crawl around outside in search of a mature female and discharge sperm through the nephridia, directly outside her burrow. Direct contact between the sexes is not a necessity. Pheromones are of particular use in the final stages of reproduction for co-ordinating processes such as mate location and the synchronization of gamete release and spawning at the population level. The existence of pheromones has been demonstrated in a number of polychaete species (Bentley & Pacey, 1992). Dales (1950) supposed that owing to the low numbers of males in populations of Hediste diversicolor there may be some chemical signal detectable to the opposite sex. The observations of Bartels-Hardege & Zeeck (1990) support this supposition for the presence of chemical signals or sex pheromones, as males only released sperm outside burrows occupied by mature females.
A period of increased activity follows the release of sperm, as the female and others in surrounding burrows, perform intense ventilation movements to draw sperm into their burrow. They may also carry sperm into the burrow using the proboscis in a feeding like manner. Fertilized eggs remain inside the burrow protected by the female. Both sexes die shortly after spawning.

Environmental factors
Bartels-Hardege & Zeeck (1990) induced spawning in the laboratory, in specimens of Hediste diversicolor from tidal flats of the Jadebusen (North Sea), outside the normal spawning period of early spring. Temperatures were not lowered to simulate winter conditions but maintained at 16°C. Mature specimens appeared after four weeks and released gametes after a further four weeks according to a semilunar cycle. Reproduction was sustained for a period of four months. Such an extended spawning was witnessed on the Jadebusen following an unusually warm winter. Spawning occurred from February until May and was less synchronized. In contrast, the same population spawned within two months (February - March) following lower winter temperatures in another year. They concluded that not only a threshold temperature was important for synchronized spawning but the timing of the rise in temperature following winter was also a significant factor (Bartels-Hardege & Zeeck, 1990).
Age at maturity
Generally Hediste diversicolor is reported to reach maturity between one and three years of age. Populations appear to show local characteristics in terms of spawning periods. Spawning may be limited to a short period in spring or extend over the summer. In the Thames Estuary, Dales (1950) reported specimens growing to maturity within one year, spawning in February, with some individuals surviving up to 18 months. Mettam et al. (1982), reported that Hediste diversicolor from the Severn Estuary matured rapidly in the spring and spawned at two years old. Olive & Garwood (1981), found that females in the Blyth Estuary, Northumberland, were in their second year before eggs began to appear, so most probably spawned in their third year. However, these authors also reported that spermatogenesis was only found to take about six months in the Blyth. They therefore suggested that there is a variable age at maturity and that this could have arisen either because the population were polymorphic in terms of their genetically determined age at maturity or if the age at maturity was variable and influenced by the environmental conditions (Olive & Garwood, 1981). Golding & Yuwono (1994) showed that, although full maturation of the gametes occurred, spawning was blocked by implanting cerebral ganglia from immature donors into the body cavity of adult hosts.
In the Ythan Estuary, Scotland, Chambers & Milne (1975) witnessed two spawning peaks in the population of Hediste diversicolor, the first occurring between January and March, and another between June and August.

Reproduction References

Barnes, 1994, Clay, 1967 (c.), Chambers & Milne, 1975, Dales, 1950, Mettam et al., 1982, Olive & Garwood, 1981, Bachelet, 1987, Bentley & Pacey, 1992, Bartels-Hardege & Zeeck, 1990, Chambers & Garwood, 1992, Scaps, 2002, Golding & Yuwono, 1994,