BIOTIC Species Information for Bugula turbinata
|Researched by||Dr Harvey Tyler-Walters||Data supplied by||MarLIN|
|Refereed by||Dr Peter J. Hayward|
|Reproductive type||Protogynous hermaphrodite
Viviparous (No Care)
|Reproductive Season||Early summer to early autumn||Reproductive Location|
|Reproductive frequency||Annual protracted||Regeneration potential||No|
|Life span||Insufficient information||Age at reproductive maturity||<1 year|
|Generation time||<1 year||Fecundity||The colony fecundity is likely high.|
|Egg/propagule size||Insufficient information||Fertilization type||Internal|
|Reproduction Preferences Additional Information||The reproductive biology of Bugula sp. has been extensively studied and reviewed. Gametogenesis and embryology are detailed by Ryland (1976), Franzén, (1977), Dyrynda & King (1983) and Reed (1991).
The fronds of Bugula species are ephemeral, large colonies present in summer, dying back in late autumn and over-wintering as perennial, dormant, holdfasts or ancestrulae (Eggleston 1972a; Dyrynda & Ryland, 1982). Bugula species are placental ovicell brooders, producing small embryos that are brooded in conspicuous hyperstomial ovicells, increasing in size considerably during development due to nutrition derived from the inside of the ovicell, which acts as a placenta. For example, the Bugula turbinata embryo grows 33 fold in embryogenesis (Dyrynda & Ryland, 1982; Dyrynda & King, 1983).
The reproductive cycle of Bugula flabellata is summarised below and may be similar in other Bugula spp., although Eggleston (1972a) noted that the number of generations in the other species was not known.
Zooids are protogynous hermaphrodites, developing eggs then sperm. Gametogenesis begins as the new zooid has formed. Egg maturation, ovulation and transfer of a single egg to the ovicell occurs halfway through the life of the first polypide. Embryogenesis continues through to the life of the second polypide, and larvae are released prior to ovulation of the next egg, taking about 3 weeks in July at Oxwich Point, Swansea. Sperm are produced after the egg has transferred to the ovicell, during the last half of the first polypide's life, and are released through the terminal pore in the tips of the tentacles (Dyrynda & Ryland, 1982). Fertilization probably occurs at ovulation, within the zooid (internal fertilization) (Dyrynda & Ryland, 1982; Reed, 1991). Once completed the cycle is repeated. Dyrynda & Ryland (1982) reported 4 cycles of polypides within zooids, after which frond death is simultaneous. Zooids may be found at different stages all the length of the frond (Eggleston, 1972a; Dyrynda & Ryland, 1982).
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 based partly on the proximity of other colonies and genetic data, although there is evidence of self fertilization (Reed, 1991; Hayward & Ryland, 1998).
Overall, Bugula flabellata exhibits two generations of ephemeral fronds each summer. Each fronds begins to produce larvae soon after initiation, within 1 month. At Oxwich, Swansea, the first frond generation appeared in June and died in August, the second generation arising in August and dying back in late October (Dyrynda & Ryland, 1982). In the Isle of Man, Eggleston (1972c) noted rapid growth in March, with eggs and embryos by May, dying back in September, with a second generation in mid September to late October. Eggleston (1972a) also noted that offspring of the first generation grew rapidly and contributed to the second generation.
Ryland (1970) noted that in British waters bryozoan reproduction was generally maximal in late summer, declining into autumn. Dyrynda & Ryland (1982) concluded that Bugula flabellata was adapted to rapid growth and reproduction (r-selected), taking advantage of the spring/summer phytoplankton bloom and more favourable (less stormy) conditions.
While each individual zooid is not prolific, the fecundity of the colony is probably directly proportional to the number of functional zooids (Bayer et al., 1994) and is probably high.
The fronds of Bugula sp. are ephemeral, surviving about 3-4 months but producing two frond generations in summer before dying back in winter. However, the holdfasts are probably perennial (Dyrynda & Ryland, 1982). No information concerning the longevity of holdfasts was found.
The lecithotrophic coronate larva of Bugula species is free-swimming for a short period of time (<1 to 36 hrs) and colonies developing from later settling larvae (24 hr old) have significantly reduced growth and reproduction (Wendt, 1998, 2000). Therefore, dispersal is likely to be limited, resulting in poor gene flow and population subdivision( Wendt, 1998).
Bugula species are common members of the fouling community of shipping and harbour installations but are far less abundant on buoys (Ryland, 1967). Keough & Chernoff (1987) noted that post settlement mortality of Bugula neritina was high, ca 70% in the first week after settlement on a Florida seagrass bed. Populations showed substantial spatial and temporal variation and Keough & Chernoff (1987) concluded that this variation was due to poor dispersal by the lecithotrophic larvae. Similarly, Castric-Fey (1974) noted that Bugula turbinata, Bugula plumosa and Bugula calathus did not recruit to settlement plates after ca two years in the subtidal even though present on the surrounding bedrock. Ryland (1976) reported that significant settlement in bryozoans was only found near a reservoir of breeding colonies. The short larval life and large numbers of larvae produced probably results in good local but poor long-range dispersal depending on the hydrographic regime.
|Reproduction References||Hayward & Ryland, 1998, Ryland, 1967, Ryland, 1970, Ryland, 1976, Wendt & Woollacott, 1999, Wendt, 2000, Dyrynda & Ryland, 1982, Dyrynda & King, 1983, Franzén, 1977, Wendt, 1998, Keough & Chernoff, 1987, Eggleston, 1972a, Castric-Fey, 1974,|