Compass sea squirt
Asterocarpa humilis

Short description of Asterocarpa humilis, Compass sea squirt

Orange-red solitary sea squirt, almost spherical in shape, with a tough outer tunic, generally attached by a broad base. In GB it can be up to 4 cm in diameter and may be found singly or as dense clumps. The closed siphons and adjacent tunic are warty. When open, the siphons show four prominent cream-white stripes, with smaller pale markings in between, giving a pattern like the face of a compass; main stripes still visible in partly closed siphons.

Impact summary: Asterocarpa humilis, Compass sea squirt

Clumps could clog pipes or render submerged gear (e.g. in aquaculture) cumbersome. Potential competitor for food and space with cultured bivalves.

Habitat summary: Asterocarpa humilis, Compass sea squirt

In its introduced range, mainly found in marinas and harbours, but also in aquaculture facilities, on offshore buoys, and occasionally in the low-intertidal zone of rocky shores (Bishop et al., 2013; Wood et al., 2017; Kakkonen et al., 2019). In its putative native range (New Zealand), Asterocarpa humilis occurs across diverse habitats from the low-intertidal to <18 m subtidally, on the undersides of boulders, attached to bivalves, algae, rock walls, ship hulls, floating artificial structures such as pontoons, and aquaculture nets or ropes (Page et al., 2016; Leclerc et al., 2020). It has a wide temperature tolerance, and can survive salinities down to 20 psu (Schwindt et al., 2014; Turon et al., 2016; Trinidade de Castro et al., 2018).

Overview table

Environment	Marine
Species status	Non-Native
Native range	Australia, New Zealand
Functional type	Filter-feeder
Status in England	Non-Native
Status in Scotland	Non-Native
Status in Wales	Non-Native
Location of first record	Weymouth Harbour
Date of first record	2009

Origin

A Southern Hemisphere species, originally described from, and putatively native to, New Zealand. However, the actual native range is poorly defined, there being also early records from Tasmania, mainland Australia, Indonesia, Argentina, and the remote Chilean Juan Fernandez archipelago (Kott, 1985; GBIF 2020).

First Record

Discovered in September 2009 in Weymouth Harbour (Dorset) and the Kingsbridge-Salcombe Estuary (Devon) (Bishop et al., 2013).

Pathway and Method

Pathway and vector of introduction to N. Hemisphere unknown, possibilities include long-distance transport on hulls, or importation of commercial bivalves (Mead et al., 2011; Pinochet et al., 2017; Schwindt et al., 2020). Secondary dispersal is likely via aquaculture equipment and recreational vessels (Bishop et al., 2015b; Pinochet et al., 2017).

Species Status

Non-native, well established and rapidly spreading in GB. It was discovered in 2009 in Weymouth Harbour (Dorset) and the Kingsbridge-Salcombe Estuary (Devon) (Bishop et al., 2013). Its arrival in Plymouth marinas, which were visited regularly, was first detected in 2011, and rapid colonisation of sites on the south coast of Devon and Cornwall was documented between 2010 and 2013 (Bishop et al., 2015a; 2015b). However, it has not yet been recorded anywhere on the east coast of England. In Wales, it was present in Holyhead Marina, N. Wales in 2011 and again in 2014, it was first noted in the Milford Haven area, S. Wales in 2014; it has not yet (in 2020) been recorded from any other Welsh locations (Bishop et al., 2013; Wood et al., 2014). The first Scottish records were from Oban in 2013, and then Orkney in 2014 where it is now established (Nall et al., 2015; Kakkonen et al., 2019). Since 2017 it has also been documented in N. Ireland (NBN Atlas, 2020). In Europe it is only known from France, where it is regarded as non-native, the first documented record being at Camaret in 2005; it is now widespread and well established in Brittany, but has not been recorded from anywhere else in Europe or indeed elsewhere in the N. Hemisphere (Bishop et al., 2013). In the S. Hemisphere it has been known under many different names, including Asterocarpa cerea, Cnemidocarpa cerea and Cnemidocarpa robinsoni. Its range there includes all continents except Antarctica. It is considered non-native in South Africa (first documented in 2001) and mainland Chile (1997), and cryptogenic in the SW Atlantic (Argentina, earliest record 1882) (Clarke and Castilla, 2000; Mead et al., 2011; GBIF, 2020; Schwindt et al., 2020).

Dispersal Mechanisms

The potential for natural dispersal is apparently very limited. Sessile as adult, fertilised eggs are brooded, and non-feeding swimming larvae may be retained by the mother after hatching, suggesting a limited subsequent period of dispersal (Brewin, 1946; Clarke & Castilla, 2000; Bishop et al., 2013). Occasional natural rafting of adults on weed etc. is possible. Spread along the coast in Europe possibly substantially assisted by leisure craft (hull fouling) (Bishop et al., 2015b).

Reproduction

Hermaphroditic, and possibly capable of self-fertilization. Fertilised eggs are brooded, and non-feeding swimming larvae may be retained by the mother after hatching. Asterocarpa humilis broods larvae throughout the year in GB waters (Lemasson, 2014; J. Bishop & C. Wood unpublished data).

Known Predators/Herbivores

When young Asterocarpa humilis may be subject to predation by urchins, crabs or gastropods (Giachetti et al., 2019).

Resistant Stages

No resistant or resting stage in life cycle.  Adult stage present year-round.

Habitat Occupied in GB

In GB Asterocarpa humilis is mainly found in marinas and harbours (e.g. on the sides and undersides of pontoon floats); but also on submerged aquaculture gear such as mussel ropes; on offshore navigation and mooring buoys; and occasionally in the low-intertidal zone of rocky shores (Bishop et al., 2013; Wood et al., 2017; Kakkonen et al., 2019).

First discovered in 2009 in Weymouth Harbour (Dorset) and the Kingsbridge-Salcombe Estuary (Devon); it rapidly colonised marinas and harbours along the south coast from Newlyn (Cornwall) to Brighton (Bishop et al., 2013; 2015a; NBN Atlas, 2020), although it is still rare in the Solent area and absent from the east coast of England. In Wales, it is present in Holyhead Marina, N. Wales and at two sites in the Milford Haven area, S. Wales, but not elsewhere (Wood et al., 2014). In Scotland, the only records are from Oban and Orkney (Nall et al., 2013; Kakkonen et al., 2019). It is also present in N. Ireland.

Environmental Impact

The proliferation of biofouling species on artificial structures has the potential to act as a reservoir that facilitates the colonisation and establishment of such species into adjacent natural habitats (Fletcher et al., 2018). Asterocarpa humilis populations might have a negative effect on the abundance and habitat occupancy of other shallow-water suspension feeding sessile invertebrates. However, it is not clear whether this would cause the local extinction of any species.

Health and Social Impact

No impacts reported or anticipated.

Economic Impact

The species’ potential abundance, coupled with the formation of clumps, means it could become a significant fouler of mussel and oyster culture gear, potentially competing for food with target species or smothering them, and rendering underwater gear and lines cumbersome. Clumps might also have the potential to block intake pipes etc. (Bishop et al., 2013).

Identification

Bishop, J. D. D., Roby, C., Yunnie, A. L. E., Wood, C. A., Lévêque, L., Turon, X., Viard, F. (2013). The Southern Hemisphere ascidian Asterocarpa humilis is unrecognised but widely established in NW France and Great Britain. Biological Invasions, 15, 253–260.

Brewin, B. I. (1946). Ascidians in the vicinity of the Portobello marine biological station, Otago harbour. In Transactions of the Royal Society of New Zealand, 76(2), 87-131.

Shenkar, N.; Gittenberger, A.; Lambert, G.; Rius, M.; Moreira da Rocha, R.; Swalla, B.J.; Turon, X. (2020). Ascidiacea World Database. Asterocarpa humilis (Heller, 1878). Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=250047 [Accessed on 2020-07-29].

Biology, ecology, spread, vectors

Bishop, J. D. D., Roby, C., Yunnie, A. L. E., Wood, C. A., Lévêque, L., Turon, X., Viard, F. (2013). The Southern Hemisphere ascidian Asterocarpa humilis is unrecognised but widely established in NW France and Great Britain. Biological Invasions, 15, 253–260.

Bishop, J. D., Wood, C. A., Yunnie, A. L., & Griffiths, C. A. (2015a). Unheralded arrivals: non-native sessile invertebrates in marinas on the English coast. Aquatic Invasions, 10(3).

Bishop, J. D., Wood, C. A., Lévêque, L., Yunnie, A. L., & Viard, F. (2015b). 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), 699-706.

Clarke, M., & Castilla, J. C. (2000). Two new records of ascidians (Tunicata: Ascidiacea) for the continental coast of Chile. Revista Chilena de Historia Natural, 73(3), 503-510.

GBIF. (2020). Asterocarpa humilis (Heller, 1878) in GBIF Secretariat (2019). GBIF Backbone Taxonomy. Checklist dataset https://doi.org/10.15468/39omei [Accessed via GBIF.org on 2020-07-28].

Giachetti, C. B., Battini, N., Bortolus, A., Tatián, M., & Schwindt, E. (2019). Macropredators as shapers of invaded fouling communities in a cold temperate port. Journal of Experimental Marine Biology and Ecology, 518, 151177.

Leclerc, J. C., Viard, F., González Sepúlveda, E., Díaz, C., Neira Hinojosa, J., Pérez Araneda, K., ... & Brante, A. (2020). Habitat type drives the distribution of non‐indigenous species in fouling communities regardless of associated maritime traffic. Diversity and Distributions, 26(1), 62-75.

Kakkonen, J. E., Worsfold, T. M., Ashelby, C. W., Taylor, A., & Beaton, K. (2019). The value of regular monitoring and diverse sampling techniques to assess aquatic non-native species: a case study from Orkney. Management of Biological Invasions, 10(1), 46.

Kott, P. (1985). The Australian Ascidiacea. Part 1, Phlebobranchia and Stolidobranchia. Memoirs of the Queensland Museum, 23, 1–43.

Lemasson, A. (2014). Investigations into the reproductive biology of non-native species of ascidians in UK waters. Ascidian News Number 73. Available from http://depts.washington.edu/ascidian/AN73.html [Accessed 2020-07-28].

Mead, A., Carlton, J. T., Griffiths, C. L., Rius, M. (2011). Revealing the scale of marine bioinvasions in developing regions: a South African re-assessment. Biological Invasions, 13, 1991–2008

Nall, C. R., Guerin, A. J., & Cook, E. J. (2015). Rapid assessment of marine non-native species in northern Scotland and a synthesis of existing Scottish records. Aquatic Invasions, 10(1), 107-121.

NBN Atlas. (2020). NBN Atlas occurrence download of Asterocarpa humilis at http://nbnatlas.org. [Accessed 2020-07-28].

Page, M., Kelly, M., Herr, B. (2016). Awesome ascidians. A guide to the sea squirts of New Zealand. Version 2. [online]. Available from: https://niwa.co.nz/static/web/MarineIdentificationGuidesandFactSheets/Awesome_Ascidians_v2.0-2016.pdf [Accessed 2020-07-29].

Schwindt, E., Gappa, J. L., Raffo, M. P., Tatián, M., Bortolus, A., Orensanz, J. M., ... & Lagger, C. (2014). Marine fouling invasions in ports of Patagonia (Argentina) with implications for legislation and monitoring programs. Marine Environmental Research, 99, 60-68.

Schwindt, E., Carlton, J. T., Orensanz, J. M., Scarabino, F., & Bortolus, A. (2020). Past and future of the marine bioinvasions along the Southwestern Atlantic. Aquatic Invasions, 15(1). See Supporting Information.

Trindade de Castro, M. C., Vance, T., Yunnie, A. L., Fileman, T. W., & Hall-Spencer, J. M. (2018). Low salinity as a biosecurity tool for minimizing biofouling on ship sea chests. Ocean Science, 14(4), 661-667.

Turon, X., Canete, J. I., Sellanes, J., Rocha, R. M., & López-Legentil, S. (2016). Too cold for invasions? Contrasting patterns of native and introduced ascidians in subantarctic and temperate Chile. Management of Biological Invasions, 7(1), 77-86.

Wood, C., Bishop, J. & Yunnie, A. (2014). Comprehensive Reassessment of NNS in Welsh marinas. Report for Welsh Government Resilient Ecosystems Fund Grant GU9430, 32pp. Available from: www.nonnativespecies.org/index.cfm?pageid=597 [Accessed 2020-07-28].

Wood, C. A., Yunnie, A.L.E., Vance, T., Brown, S. (2017). Tamar Estuaries. Marine biosecurity plan 2017-2020. Species guide [online]. Available from: http://www.plymouth-mpa.uk/wp-content/uploads/2018/06/170807-Tamar-Estuary-Non-Native-Species-Guide-FINAL.docx.pdf [Accessed 2020-07-28].

Management and impact

Bishop, J. D. D., Roby, C., Yunnie, A. L. E., Wood, C. A., Lévêque, L., Turon, X., Viard, F. (2013). The Southern Hemisphere ascidian Asterocarpa humilis is unrecognised but widely established in NW France and Great Britain. Biological Invasions, 15, 253–260.

Fletcher, L. M., Atalah, J., & Forrest, B. M. (2018). Effect of substrate deployment timing and reproductive strategy on patterns in invasiveness of the colonial ascidian Didemnum vexillum. Marine Environmental Research, 141, 109-118.

General