‍Watersipora subatra, commonly known as the red ripple bryozoan, is a marine invertebrate often referred to as a "moss animal." This species doesn’t exist as a single organism, but rather as a colony made up of dozens to thousands of tiny individuals known as zooids, which are all physically connected and functioning together. Each zooid of the red ripple bryozoan has one main function – feeding and reproducing,(both sexually and asexually), which is known as autozooids. Working together, these zooids build large, often rippled colonies, such as the red ripple bryozoan growing on rocks, harbours, sea walls and boats.

Watersipora subatra (Red ripple bryozoan) was once confused with Watersipora subovoidea (Sub-ovoid bryozoan), but a 2014study confirmed they have distinct differences in shape and colour (Vieira et al., 2014). A more recent DNA study confirmed they are genetically distinct as well and found that only the red ripple bryozoan among the Watersipora species, is currently present in the UK.

Where is the species found in the UK? How did it get to the UK?

The red ripple bryozoan is thought to have originated in Japan, spreading around the world in the 1980s. It was first observed in the UK in early 2008 in Plymouth, followed by Poole later that summer. Since then, it has moved north and reached Ireland, where it was first recorded in Dublin in2011. It likely arrived in Europe via aquaculture shipments, ferries, and/or rafting on floating seaweed and plastics. Unlike many marine species, it is often resistant to toxic copper-based antifouling paints, which are a special coating designed to prevent marine life from attaching to boats.  As a result of this, it's often first discovered in busy harbours and marinas.

Once it establishes a population of colonies, it can spread along the coast through sexual reproduction, releasing planktonic larvae (very small juveniles), that most commonly swim freely for around 12 hours before settling in shallow coastal or intertidal areas. These larvae can re-enter the water column if conditions are not right, and they are equipped with light-sensitive eyespots, touch sensors, and the ability to crawl slowly to find the ideal surface. These adaptations allow the red ripple bryozoan to colonise new locations quickly and effectively.

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Why should we track the species? What is the impact on native species?

Tracking the red ripple bryozoan is important because, as anon-native species, it has the potential to alter local marine ecosystems. So far, the effects in the UK appear to be neutral or even mildly beneficial. Areas with abundant red ripple bryozoans have been found to support a greater variety of native species, which move, especially worms, suggesting they may increase local species diversity by creating more complex habitats. Their complex structure has the potential to trap more sediment and create a greater number of habitats for other species. Although the red ripple bryozoan can form very large colonies, native species which attach to the substrate, such as barnacles, have seen no significant difference in abundance.

So, while no negative impacts have been recorded yet in UK waters, we still have a role to play in protecting future ecosystems. Non-native species can shift from neutral or beneficial to harmful roles overtime or as environmental conditions change. That’s why continued monitoring is essential, not just by scientists, but by the public too. By documenting the species you see, you are helping build a clearer picture of how our coastlines are changing. The more eyes we have on the shore, the faster we can detect negative impacts and help conservationists take action to protect marine life.

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How to spot it? Any key features?

The centres of red ripple bryozoan colonies are often dark red or orange and appear close to death (moribund). However, these seemingly dead central areas can give rise to new, active zooids through asexual reproduction, that spread outward over the dark basal layer in a red arc—hence the name 'red ripple'. These new zooids are a brighter red or orange in colour. Each zooid has a tube-like structure with a black oval opening called an operculum, with each operculum being around 1mm in size

You will commonly find them growing on hard surfaces like rocks, and harbour walls, often in rock pools at low tide or in shallow subtidal zones down to about 10m. When rock pooling check above and below rocks, as well as within seaweed.

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Sources

1.  Bishop, J.D.D., Wood, C.A, Lévêque, L.,Younie, A.L.E., and Viard. (2015). “Repeated rapid assessment surveys reveal contrasting trends in occupancy of marinas by non-indigenous species on opposite sides of the western English Channel.” Marine Pollution Bulletin 95(2), pp. 699–706. Available at: https://doi.org/10.1016/j.marpolbul.2014.11.043.

2. Feary, T.M., (2024). “Factors that influence growth in colonial bryozoans.” Otago Harbour, Aotearoa New Zealand (Doctoral dissertation, University of Otago).

3. Kelso, A. and Wyse Jackson, P. (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 OcchipintiAmbrogi, 1985.” BioInvasions Records 1(3), pp. 209–214.Available at: https://doi.org/10.3391/bir.2012.1.3.06.

4. McKinney, F.K. and Jackson, J.B.C. (1991).“Bryozoan evolution.” University of Chicago Press ed. Chicago: University of Chicago Press.

5. McLachlan, R. (2017). “The larval morphology and the effects of sound frequencies on the settlement behaviour of the biofouling Bryozoan: Watersipora subatra.” Open Access Te Herenga Waka-Victoria University of Wellington. Available at: https://doi.org/10.26686/wgtn.17068052.

6. Page, H. (2019). “Distribution and potential larval connectivity of the non-native Watersipora (Bryozoa) among harbors, offshore oil platforms, and natural reefs.” Aquatic Invasions 14(4),pp. 615–637. Available at: https://doi.org/10.3391/ai.2019.14.4.04.

7. Porter, J.S., Nunn, J.D., Ryland, J.S., Minchin. and Jones, M.E.S. (2017), “The status of non-native bryozoans on the north coast of Ireland.” BioInvasions Records 6(4), pp. 321–330.Available at: https://doi.org/10.3391/bir.2017.6.4.04.

8. Sellheim, K., Stachowicz, J. and Coates, R.(2010). “Effects of a non native habitat-forming species on mobile and sessile epifaunal communities.” Marine Ecology Progress Series 398,pp. 69–80. Available at: https://doi.org/10.3354/meps08341.

9. Vieira, L.M., Jones, M.S. and Taylor, P.D.(2014). “The identity of the invasive fouling bryozoan Watersipora subtorquata (d’Orbigny) and some other congeneric species” Zoo taxa 3857(2).Available at: https://doi.org/10.11646/zootaxa.3857.2.1.