|Reproduction Preferences Additional Information||Reproduction
Bryozoan colonies are hermaphrodite, however, zooids may be monoecious, dioecious, protandrous or protogynous, depending on species (Hayward & Ryland, 1998). Flustra foliacea bears both male and female zooids and is presumably hermaphrodite.
- Male zooids of Flustra foliacea in the Isle of Man were reported to be full of sperm in September, giving the entire colony a white appearance. Sperm were absent by October. Orange eggs were visible in August and the yellow coloured embryos had entered the ooecia (ovicells) by October (Eggleston, 1970; 1972a). Sperm are shed from pores in the polypide tentacles of male zooids.
- Fertilization in brooding species such as Flustra foliacea is probably internal (Hayward & Ryland, 1998). In bryozoans, released sperm are entrained by the tentacles of feeding polypides and may not disperse far, resulting in self-fertilization. However, genetic cross-fertilization is assumed in oviparous and brooding bryozoans, although there is evidence of self fertilization (Hayward & Ryland, 1998).
- Eggleston (1972a) reported that about one third of zooids produced a single embryo in their first and second years, but that older zooids were infertile. Embryos were brooded over winter and larvae released between February and April.
Dalyell (cited in Hincks, 1880) stated that ca 10,000 larvae were released from a specimen of Flustra foliacea within 3 hrs. Eggleston (1972a) reported that each zooid produced a single embryo, so that fecundity is probably related to the number of sexual zooids and hence size of the colony.
Flustra foliacea colonies regularly reached 6 years of age, although 12 year old specimens were reported off the Gower Peninsula (Stebbing, 1971a; Ryland, 1976).
- Larvae are positively phototactic on release, and swim for only short periods, although in species in which light stimulus is un-important, larvae may delay metamorphosis for 12 hrs of more (Hayward & Ryland, 1998). Daylength is an important cue for larval release in some species of bryozoa, and Flustra foliacea releases larvae in spring (February- April) (Eggleston, 1972a; Hayward & Ryland, 1998), however, at the depths Flustra foliacea can occur light may not be important.
- Larvae are probably sensitive to surface contour, chemistry and the proximity of conspecific colonies. However, Hayward & Ryland (1998) suggested that larval behaviour at settlement is only of prime importance to species occupying ephemeral habitats. Eggleston (1972b) demonstrated that the number and abundance of species of bryozoan increased with increased current strength, primarily due to a resultant increase in the availability of stable, hard substrata (Eggleston, 1972b; Ryland, 1976). Dyrynda (1994) noted that the abundance of Flustra foliacea was greatest in the deepest, and most current scoured, mouth of Poole Harbour due to the presence of circalittoral boulders not commonly found in other parts of the harbour, although reduced salinity probably also restricted its distribution within the harbour. Therefore, recruitment is probably dependant on the availability of suitable substratum.
- The short larval life probably results in good local but poor long-range dispersal. Ryland (1976) reported that significant settlement in bryozoans was only found near a reservoir of breeding colonies. However, the hydrographic regime probably strongly influences potential dispersal, and in the strong currents tolerated by Flustra foliacea, larvae may be transported some distance in a short time, unless constrained within eddies between faunal turf forming species. The sand abrasion tolerated by Flustra foliacea may remove other species, providing Flustra foliacea with space to colonize.