BIOTIC Species Information for Nucella lapillus
|Researched by||Lizzie Tyler||Data supplied by||University of Sheffield|
|Refereed by||This information is not refereed.|
|Reproductive Season||All year but max spirng and autumn||Reproductive Location||As adult|
|Reproductive frequency||Annual protracted||Regeneration potential||No|
|Life span||6-10 years||Age at reproductive maturity||1-2 years|
|Generation time||3-5 years||Fecundity|
|Egg/propagule size||10 mm diameter||Fertilization type||Internal|
|Reproduction Preferences Additional Information||Breeding occurs throughout the year but is maximal in spring and autumn.
Adult Nucella lapillus may be seen spawning or copulating in spawning aggregations. Pre-spawning and spawning aggregations develop in early spring, sometimes summer, and may comprise 30 or (many) more individuals, dominated by adults. Pre-spawning aggregations may be difficult to distinguish from winter aggregations, except that the winter aggregations consist of all age classes. Winter and spawning aggregations occur in sheltered areas of the shore (e.g. crevices or under hangs and leeward faces), which are also perfect sites for spawning. Adults do not feed during mating and spawning, and may remain in their winter aggregation sites for 4-5 months without feeding or moving significantly (Crothers, 1985).
Nucella lapillus lays its eggs in protective egg capsules on hard substrata in damp crevices and under stones. Copulation is repeated at intervals, between which a few egg capsules are laid, one at a time (Fretter & Graham, 1994). Larger females lay larger capsules, however most capsules are vase shaped, 9 -10 mm high, 3 -4 mm across and yellow to brown in colour. Capsules are cemented to the substratum by the ventral pedal gland and foot and is sealed with a 'plug' at the opposite end. (Crothers, 1985; Graham, 1988; Fretter & Graham, 1994). The gametogenesis, ovoposition and structure of egg capsules is discussed in detail by Ankel (1937), Fretter (1941), Feare (1970a), and Fretter & Graham, (1985, 1994).
The number of capsules laid depends on the female's food reserves, age and temperature, e.g. populations in the White Sea lay ca 20-30 capsules per season, while temperate Atlantic populations may lay 5 times this number. Although each capsule may contain ca 600 eggs, 94% of the eggs are unfertilized and function as 'nurse eggs' and are fed upon by the developing embryos (Fretter & Graham, 1994; Crothers, 1985). Capsules have been reported to release 12 -15 'crawl-away' hatchlings per capsule (Crothers, 1977), 13-36 hatchlings per capsule (Feare, 1970b) or 25-30 hatchlings per capsule (Graham, 1988). Fretter & Graham (1994) estimated that each female could produce 1030 hatchling per year. Etter (1989) noted that, in Massachusetts, adults from wave exposed shore laid about twice as many egg capsules and released about twice as many hatchlings per capsule (albeit ca 20% smaller) as adults from sheltered shores. The number and size of offspring produced was dependant on wave exposure, and formed a cline across the wave exposure gradient (Etter, 1989).
Impact of TBT on reproduction
The effects of tributyl tin (TBT), used in anti-fouling paints, on Nucella lapillus have been extensively documented and represent one of the best known examples of the effects of chemical pollution (see sensitivity). The following is based upon reviews by Hawkins et al. (1994) and Bryan & Gibbs (1991) to which the reader should refer for further detail.
The equivalent of the veliger stage occurs within the capsule. Nucella lapillus larvae feed on the nurse cells in the late veliger stage, during which development is halted for about 1 week. Development is slow and temperature dependant, taking ca 4 months in temperate areas but up to seven months in the White Sea, where the eggs over-winter (Fretter & Graham, 1994). Once larvae have become miniature adults they leave the capsule via the terminal plug, although if this exit is blocked by other hatchlings they may bore through the capsule wall. Hatchlings may be termed crawl-aways (Crothers, 1985; Fretter & Graham, 1994).
Longevity and mortality
Feare (1967) suggested that a large proportion of the 69% mortality of Nucella lapillus observed on the Yorkshire coast in the winter of 1965 -66 was due to predation by oystercatchers (Haematopus ostralegus). Adults are also preyed on by gulls and eiders, which swallow the dog whelk whole. Adults dog whelks of 40mm or more long are probably safe from birds (Crothers, 1985). Juveniles are eaten by rock pipits, turnstones, and purple sand-pipers. Feare (1970b) estimated juvenile mortality to be 90% within the first year, ca. 50% in the second year and 27% in the third. Feare (1967; 1970b) reported that the purple sand-piper favoured 2-5 mm long dog whelks (occasionally 8 mm) and accounted for most of the 90% mortality in juvenile dog whelks in the winter of 1965-66 in Robin Hood's Bay. Juveniles are also susceptible to crab predation. Feare (1967) reported that most of the juvenile mortality between summer and autumn 1966-67 (Robin Hood's Bay) was due to crabs. Carcinus maenas can handle dog whelks up to 15 mm in length whereas Necora puber can handle up to 25 mm (Crothers, 1985). Crothers (1985) suggested that lobsters, which can crush any size adult, may be a significant predator below low water. Feare (1970b) estimated a life expectancy of at least 6 years, although Crothers (1985) suggested that this may be an under-estimate.
Nucella lapillus lacks a dispersive pelagic larval phase. They are relatively inactive as adults, moving mostly at night (males more than females) but rarely far. Several movement estimates have been reported, for example, an average of 100 mm /tidal cycle (Connell, 1961), or 123 mm/day over barnacles and 329 mm/day over a cockle bed (Morgan, 1972; Fretter & Graham, 1994). Crothers (1985) reported that marked specimens were recovered within 30 cm of their release site after one year, and suggested that with an abundant food supply there was little stimulus to move far from their site of birth. Castel & Emery (1981) reported that adults do not move more than 30 m in their life-time. Nucella lapillus recolonizing Watermouth Cove in north Devon, following the effects of TBT pollution (Crothers, 1998), have advanced at least 30 m in a minimum of 13 years (Crothers, in prep). Palmer (1984) also noted that few Nucella emarginata moved more than 10 m in a year in the USA. Similarly, Gosselin & Fu-Shiang Chia (1995) reported that dispersal was limited to a few meters from the egg capsules in Nucella emarginata (in the USA). Poor dispersal as adult and hatchling results in low rates of recruitment from or migration between adjacent populations, and may lead to relatively high levels of genetic isolation and variation within the population (population sub-division).
However, Martel & Fu-Shiang Chia (1991) collected two hatchling Nucella emarginata drifting in the intertidal, suggesting that dispersal by passive transport by currents can occur occasionally. Gosselin & Fu-Shiang Chia (1995) point out that occasional drifting by small numbers of hatchling, while rare, may still result in significant gene flow, and that since dislodgement increases with wave exposure, more gene flow (hence less population subdivision) may occur in wave exposed rather than sheltered shores.
|Reproduction References||Graham, 1988, Berry & Crothers, 1968, Feare, 1970a, Coombs, 1973, Moore, 1938a, Fretter & Graham, 1994, Crothers, 1985, Connell, 1961, Moore, 1938b, Etter, 1989, Palmer, 1984, Ankel, 1937, Fretter, 1941, Gosselin & Fu-Shiang Chia, 1995, Martel & Chia, 1991b, Castle & Emery, 1981, Etter, 1996, Hawkins et al., 1994, Smith, 1980, Moore et al., 2000, Feare, 1967, Bryan & Gibbs, 1991, Gibbs & Bryan, 1987, Evans et al., 1991, Evans et al., 1996b, Fretter & Graham, 1985, Crothers, 1998,|