Hediste diversicolor

Researched ByGeorgina BuddData Supplied ByMarLIN
Refereed byMike Kendall
Taxonomy
Scientific nameHediste diversicolorCommon nameRagworm
MCS CodeP462Recent SynonymsNereis diversicolor
Nereis (Hediste) diversicolor
PhylumAnnelidaSubphylum
SuperclassClassPolychaeta
SubclassOrderPhyllodocida
SuborderFamilyNereididae
GenusHedisteSpeciesdiversicolor
Subspecies  
Additional InformationThe form and distribution of paragnaths on the pharynx can be very useful in identification and Kinberg (1866, cited in Chambers & Garwood, 1992) assigned roman numerals to eight different areas of the pharynx that bear paragnaths. However, the number of paragnaths can vary considerably both within and between populations and this variation is thought to be a result of habitat and feeding preferences (Barnes & Head, 1977).
See Chambers & Garwood (1992) for further description and detail on identification.
Taxonomy References Hayward & Ryland, 1995b, Fauchald, 1977, Barnes, 1994, Chambers & Garwood, 1992, Barnes & Head, 1977
General Biology
Growth formVermiform segmentedFeeding methodSurface deposit feeder, Omnivore, Scavenger, Sub-surface deposit feeder, Passive suspension feeder
Mobility/MovementBurrower, Swimmer, CrawlerEnvironmental positionInfaunal
Typical food typesMud, sand & detritus. Phytoplankton & plankton. Other macrofauna.HabitBurrow dwelling
BioturbatorDiffusive mixingFlexibilityHigh (>45 degrees)
FragilityFragileSizeMedium(11-20 cm)
HeightNot relevantGrowth RateInsufficient information
Adult dispersal potential1km-10kmDependencyIndependent
SociabilitySolitary
Toxic/Poisonous?No
Additional InformationFeeding
Hediste diversicolor is omnivorous and exhibits a diversity of feeding modes; carnivory, scavenging, filter feeding on suspended particles and deposit-feeding on materials in and on the surface layers of the sediment (Barnes, 1994).
Hediste diversicolor feeds using an eversible pharynx and the sensory appendages on the head, namely palps and tentacles (M. Kendall, pers. comm.).
A conspicuous difference between Hediste diversicolor and the closely related polychaete Nereis virens is the unique ability of Hediste diversicolor to satisfy its metabolic requirements from a diet of phytoplankton, like a typical obligate filter-feeder (Nielsen et al., 1995).
The filter feeding mechanism was described by Harley (1950). A funnel-shaped net consisting of fine mucous threads is drawn across the burrow and a water current is driven through the net by undulating body movements (Fauchald & Jumars, 1979). This is best observed in a tank (M. Kendall, pers. comm.). When sufficient particles have accumulated on the net, they are consumed along with the entire net (Fauchald & Jumars, 1979). After an interval, the net is replaced (M. Kendall, pers. comm.). Riisgård (1991) suspected that Hediste diversicolor is a hitherto undervalued key organism in the control of phytoplankton in shallow brackish waters. It is unknown to what extent Hediste diversicolor utilizes its potential to subsist on suspended food particles in nature but can be considered a suspension feeder when a sufficient number of algal cells are present in the water (Riisgård, 1991).
When deposit feeding, Esnault et al. (1990) recognized two main types of searching behaviour exhibited by Hediste diversicolor. The first involved the worm crawling on the surface of the substratum prospecting for food, catching it with its jaws and ingesting it immediately. The second type saw the worm depositing a string of mucous on either side of its body on the substrate surface. When the worm retreated back into its burrow the mucous was brought back and built it into a pellet which can be consumed there and then or stored for consumption later on (Esnault et al., 1990).
Olivier et al. (1995) found that juvenile Hediste diversicolor can select detritus on the sediment surface and accumulate it in their burrow. The juveniles irrigate the burrows thereby maintaining an aerobic condition that favours the decaying process of the plant debris by stimulating bacterial growth ('gardening').
Lucas & Bertru (1997) found bacteriolytic activity in the digestive system of Hediste diversicolor thus highlighting the ability of this species to feed on bacteria.

Colour
The variable colours of Hediste diversicolor approaching maturity and during spawning (see reproduction) are due to varying proportions of green (biliverdin), orange and brown (carotenoids) pigments. The green colour of mature males and females is caused by biliverdin present in the gut wall, the epidermis and coelomic cells and is formed by the breakdown of haemoglobin in the blood. In males, the white mass of sperm in the coelom gives it a lighter green colour (Dales, 1950). In mature specimens during and after spawning, the green appearance is also enhanced by a complete extraction of carotenoids from the body wall (Dales & Kennedy, 1954).

Biology References Hayward & Ryland, 1995b, Fauchald, 1977, Barnes, 1994, Dales & Kennedy, 1954, Harley, 1950, Riisgård, 1991, Riisgård, 1994, Nielsen et al., 1995, Lucas & Bertru, 1997, Esnault et al., 1990, Olivier et al., 1995, Fauchald & Jumars, 1979, Scaps, 2002
Distribution and Habitat
Distribution in Britain & IrelandWidespread along all British coasts where suitable habitat and substratum exist.
Global distributionHediste diversicolor is widely distributed throughout north-west Europe on the Baltic Sea, North Sea and along Atlantic coasts to the Mediterranean.
Biogeographic rangeNot researchedDepth rangeIntertidal
MigratoryNon-migratory / Resident
Distribution Additional Information

Distribution & density
Hediste diversicolor is an euryhaline species and can withstand great variances in salinity. Smith (1956) reported that, in the Tamar estuary, England, individuals of this species living at the upstream limit regularly experience salinities less than 0.5 ppt. In marine dominated habitats, Hediste diversicolor behaves as a brackish water animal and is found in the least saline portion of the available ground (Smith, 1956). The distribution of Hediste diversicolor in high salinity areas is likely to be reduced as result of competition in the form of interspecific aggressions (Kristensen, 1988). In a study focussing on the distribution of nereid polychaetes in Danish coastal waters, Kristensen (1988) found that Hediste diversicolor could only maintain high population densities in marginal environments when the fitness of stronger competitors such as %Nereis virens% was reduced.

In estuaries the maximum density of the Hediste diversicolor population normally occurs in the middle regions, with density decreasing both towards the head and mouth of the estuary. Smith (1956), found that the maximum population density of Hediste diversicolor in the Tamar estuary corresponded to that portion of the estuary with the greatest salinity variation. The density of worms varies between locations and throughout the reproductive cycle. Numbers of juveniles may be over 100 000 per m² (Clay, 1967(c)). In the Ythan Estuary, Scotland, the density of adult Hediste diversicolor was reported to be 961 per m² (Chambers & Milne, 1975).

Burrows
The entrance to the burrows of Hediste diversicolor are 1-2 mm wide in soft mud and are best seen when a fork is inserted into the sediment and the handle pulled towards the user (M. Kendall, pers. comm.). Short shallow depressions radiate from the opening: these are made by the anterior part of the worm's body as it searches for food around it's hole, with the tail firmly anchored within the burrow. Burrow depth increases with body size (Esselink & Zwarts, 1989). Whilst feeding at the mud surface the worm is particularly prone to predation by wading birds and fish. The burrow is thus an important refuge in which to retreat. Esselink & Zwarts (1989) found a seasonal variation in the depth of burrows of Hediste diversicolor. The deepest burrows were seen in winter and it is likely that this deeper burrowing is an adaptation to escape low temperatures. Burrow depth was seen to level off at 15 cm because at this depth the worm can retreat from the reach of most deep-probing predators including curlews and oyster catchers. The individual burrow is a well-delimited territory but this territoriality is not extended outside the burrow (Scaps, 2002).
Substratum preferencesSandy mud, Muddy sand, MudPhysiographic preferencesEstuary, Enclosed coast / Embayment, Ria / Voe
Biological zoneUpper Littoral Fringe, Lower Littoral Fringe, Upper Eulittoral, Mid Eulittoral, Lower EulittoralWave exposureSheltered, Very Sheltered, Extremely Sheltered
Tidal stream strength/Water flowWeak (<1 kn), Very Weak (negligible)SalinityLow (<18 psu), Reduced (18-30 psu), Variable (18-40 psu)
Habitat Additional InformationNone entered
AMBI Group (Borja et al., 2000)III 
Distribution References Hayward & Ryland, 1995b, Fauchald, 1977, Clay, 1967 (c.), Chambers & Milne, 1975, Esselink & Zwarts, 1989, Smith, 1956, Kristensen, 1988, Scaps, 2002, Beukema, 1990
Reproduction/Life History
Reproductive typeGonochoristic Developmental mechanismLecithotrophic, Oviparous
Reproductive SeasonSpring - summerReproductive LocationAdult burrow
Reproductive frequencySemelparous Regeneration potentialNo
Life span1 yearAge at reproductive maturity<1 year
Generation time1-2 yearsFecundityInsufficient information
Egg/propagule sizeInsufficient informationFertilization typeExternal
Larvae/Juveniles
Larval/Juvenile dispersal potentialNot relevantLarval settlement periodNot relevant
Duration of larval stageNot relevant  
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