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Watersipora subtorquata

Rebecca Wright 2015


Watersipora subtorquata is a widespread encrusting cheilostome bryozoan. It has a cosmopolitan distribution and is found in most areas with significant shipping traffic (See Biogeographic distribution). W.subtorquata is commonly found encrusting the hulls of ships (See Ecology). Colonies are formed from a sexually produced larvae and zooids bud asexually to extend the colony (See Reproduction & Colony Formation). Colonies are orange in life and only a few centimetres in diameter (See Physical Description).  

Physical Description

Watersiporia subtorquata is a colonial encrusting bryozoan (Vieira et al., 2014). Generally unilamellar and encrusting on flat substrata it can sometimes form erect foliose colonies, which can be bilamellar or mulitlamellar (Vieira etal., 2014). It varies between orange to brownish- purple in colour (Vieira etal., 2014), the colouration comes from the colour of the polypide, with the zooecium being transparent, see figure 1. The lophophore is the tentacled feeding structure at the top of the polypide. It is everted during feeding and can be retracted inside the zooecium.  The zooecium is a calcium carbonate box like structure (Hart & Keough, 2009). The lophophore in W. subtorquata has 20-22 tentacles (Viera et al, 2014). Colonies are typically up to 4cm in diameter. Zooids are typically ~ 1mm long and ~0.3mm wide (Vieira et al., 2014) 

Figure 1


Watersipora subtorquata is the most common intertidal bryozoan in many areas of introduction (Mackie,Keough,& Christidis, 2006). It frequently outcompetes native bryozoans and other sessile organisms (Mackie et al, 2006). Copper is used in many antifouling paints (McKenzie, Brooks & Johnston, 2012). W. subtorquata is less adversely affected by copper than many other fouling organisms, giving it a competitive advantage in the presence of copper (McKenzie et al., 2012). While presence of copper increases post-settlement mortality of W. subtorquata larvae it has been demonstrated to increase overall recruitment of W. subtorquata (McKenzie et al., 2012).

Bryozoans are preyed on by a variety of taxa, fishes, gastropds, pycnogonids, echinoids,crustaceans, chitons, asteroids and turbellarians (Lidgard, 2008). Some pycnogonids, nudibranchs, and turbellarians are thought to be specialist bryozoan predators (Lidgard, 2008). Some nudibranchs have been reported to feed only on particular species of bryozoan (Lidgard, 2008). 

Life History and Behaviour


Specialised ovicells are not present in this species (Vieira, Jones, & Taylor,2014). The maternal polypide degenerates and the fertilized egg is brooded within the zooecium of the maternal zooid (Vieira et al., 2014). Unlike many species of bryozoans, polypides do not regenerate after brooding in this species (Hart & Keough, 2009). Eggs are spherical in shape and a darker, redder shade of orange than the polypides, see figure 2. A blue/pink band runs around the equator of the egg. Larvae are leciothotrophic and metamorphose within 1-2 days of release from the colony (Mackie et al, 2006). This short time to metamorphosis is likely one of the factors that has made this species so successful and widespread as a biofouling organism. Larvae metamorphose into the ancestrula (starting zooid of the colony). New zooids bud asexually from the ancestrula in a radial arrangement in this species.  

Figure 2

Colony development

Watersipora subtorquata generally forms unilamellar colonies. Colonies of this species have a radial mulitserial zooid arrangement, with deviations from this form largely in areas of the colony with obstructions such as polychaete tubes, and appear to be grow around the obstruction and then continue to bud radially. Mulitserial colonies grow in sheets of zooids without gaps between zooids, see figure . In uniserial colonies have gaps between lines of zooids, see figure 6 (McKinney & Jackson, 1989).Hart and Keough (2009) found that colonies of W. subtorquata whose growth had not been interrupted grew in a circular formation (zooids radiating from the ancestrula in a even manner), although this rarely happened in a natural setting. Figure 7 displays disruptions to the radial form, this is likely due to past damage to this area of the colony. This species exhibits multizooidal budding, see figure 8. Budding occurs on the outer edge of the colony, with new zooids forming at the frontal edge of the maternal zooid. Colonies recover more successfully from damage when the younger zooids (those towards the edges of the colony) are intact (Hart & Keough, 2009). Fragmented colonies composed of older zooids (centre of the colony) are less able to recover, as they take longer to reform a growing edge, and they also die sooner (Hart & Keough, 2009). Individual zooids have a life span of approximately 3 weeks in this species (Hart &Keough, 2009). In some species of cheilostome bryozoan it has been shown that environments with high water flow can lead to encrusting colony forms, and low water flow areas can lead to erect forms (Cocito, Ferdeghini, Morri, & Bianchi, 2000).  

Figure 3
Figure 4
Figure 5
Figure 6
Figure 7

Feeding Behaviour

Being a sessile organism, few behaviours are observable in bryozoans. One of the few that is observable, is the presence of excurrent chimneys (McKinney & Jackson, 1989). Bryozoans are active upstream filter feeders, this means they pump water from above through the lophophore (McKinney& Jackson, 1989). In some species of bryozoan this water is expelled from the colony via excurrent chimneys (McKinney & Jackson, 1989). A chimney is simply an area in which the lophophores of the surrounding zooids bend out of the way, making a gap in the lophophore canopy which water can flow out of (McKinney& Jackson, 1989). In some species the chimney area can be raised, in others it is a temporary area, with no discernible morphological characters (McKinney& Jackson, 1989).  Studies have not yet investigated whether Watersipora subtorquata has chimneys. 

Anatomy and Physiology

Watersipora subtorquata colonies are made up of zooids. Bryozoans have no specialised gas exchange structures, gases are exchanged across the skin and in particular across the lophophore (Ruppert, Fox, & Barnes, 2004).Bryozoans have a U-shaped gut, with the mouth in the centre of the lophophore and the anus outside the ring of the lophophore (Ruppert, Fox, & Barnes, 2004).Bryozoans have no heart, they move nutrients within and between zooids via a type of circulatory system called the funicular system (Ruppert, Fox, & Barnes, 2004). The zooids are connected via the interzooidal pore and the nutrients are transferred between zooids via the rosette cells (Ruppert,Fox, & Barnes, 2004; Bone & Keough, 2010).

Evolution and Systematics

Bryozoan phylogeny is very poorly resolved at all levels of classification (Waeschenbach, Taylor, & Littlewood, 2012). Watersipora is placed within the family Watersiporidae, which includes the genera Uscia, Veleroa and Watersipora (Vieira,2014). Watersiporidae is placed within the order Cheilostomata (Class Gymnolaemata)(Vieira, 2014). Relationships within this order are very poorly resolved (Waeschenbach et al., 2012).

It is likely that the genus Watersipora contains more species than are currently described. Lack of morphological characters commonly used to differentiate between species of cheilostome bryozoans, such as avicularia and other heterozooids, makes misidentification of species within this genus common (Mackie et al, 2012; Viera et al, 2014). Genetic evidence suggests high likelihood of numerous cryptic species within this genus (Mackie et al, 2006; Mackie et al, 2012). The species Watersipora subtorquata is sometimes referred to as W. subtorquata species complex, due to it being considered likely to contain multiple species (Mackie et al, 2012).

Bryozoans have an extensive fossil record . Cheilostome bryozoans first appeared during the Jurassic and dominate the bryozoan fauna from the Cretaceous to the present day (Taylor & Ernst, 2008).Among cheilostome bryozoans, the degree of polymorphism within species has increased in the last 50 million years (McKinney & Jackson, 1989). It was believed that higher levels of polymorphism indicated higher levels of physiological connectedness among zooids (McKinney & Jackson, 1989), however more recent evidence suggests that this is not the case, at least not in all species (Bone & Keough, 2010). The only fossil of the genus Watersipora is a neogene fossil found in the southeastern USA called Watersiporagrandis (Vieira et al, 2014). 

Biogeographic Distribution

Watersipora subtorquata has a cosmopolitan distribution and is common in most areas between 0˚and 40˚ latitude (Vieira et al,2014). Although there are records of it occurring at higher latitudes (Kelso & Jackson, 2012). It is believed (although not with a great deal of certainty) to have originated in the Caribbean- Atlantic region (McKenzie,Brooks & Johnston). Its spread to other regions of the world has been recorded since approximately 1960, although spread may have preceded records by a substantial amount of time (Mackie et al, 2012). W. subtorquata was first recorded in Australia in the 1970's (Mackie et al, 2006). It has likely been spread on the hulls of ships which it commonly fouls (McKenzie, Brooks & Johnston). Low genetic divergence between widely spaced populations in Australia, Florida and Brazil support the recorded evidence of recent introductions (Viera et al,2014).

Conservation and Threats

Watersipora subtorquata is an invasive biofouling bryozoan. Consequently it is of no conservation concern. 


Bone, E.K.,& Keough, M.J. (2010) Does Polymorphism Predict Physiological Connectedness? A Test Using Two Encrusting Bryozoans. Biological Bulletin. 219. 220-230.

Hart, S.P., & Keough, M.J. (2009) Does Size Predict Demographic Fate? Modular Demography and Constraints on Growth Determine Response to Decreases in Size. Ecology.90(6).1670-1678.

Kelso, A., & Jackson, P.N.W. (2012) Invasive bryozoans in Ireland: first record of Watersipora subtorquata (d'Orbigny, 1852) and an extension of the range of Tricellaria inopinata d’Hondt and Occhipinti Ambrogi, 1985. BioInvasions Records.1(3). 209–214. doi:

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Vieira, L.M., Jones, M.S.,& Taylor, P.D. (2014) The identity of the invasive fouling bryozoan Watersipora subtorquata (d’Orbigny) and some other congenericspecies. Zootaxa. 3857 (2). 151–182.

Waeschenbach, A., Taylor, P.D., & Littlewood, D.T.J. (2012) A molecular phylogeny of bryozoans. Molecular Phylogenetics and Evolution. 62. 718–735.doi:10.1016/j.ympev.2011.11.011