Polydora hoplura

Invasion History

First Non-native North American Tidal Record: 2004
First Non-native West Coast Tidal Record: 2004
First Non-native East/Gulf Coast Tidal Record:

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General Invasion History:

Polydora hoplura was described from the Gulf of Naples, Italy in 1868, and was regarded as native from southern Britain to the Mediterranean (de Montaudouin,and Sauriau 2000; Dauvin et al. 2003). However, surveys of this worm's genetics and history of its spread suggests that it is native to the Northwest Pacific,,and Japan in particular, and spread by introductions in ship fouling, and with transfers of Pacific Oysters (Magallana = Crassostrea gigas).  Its occurrence in Japan may have been poorly known due to limited studies of shell-boring polychaetes before the 1990s  (Radashevsky et al. 2023). . Polydora hoplura is one of many spionids which burrow into the calcareous shells of mollusks, barnacles and other  organisms, and so can be transported in hull fouling. Reports of its range in Europe are somewhat spotty, possibly due to confusion with a non-boring species, P. ciliata.(Radashevsky et al. 2023). It is known from Belgium (first record 1962, establishment uncertain, Kerckhof et al. 2007); southwest England (Wilson 1928); Atlantic France (Dauvin et al. 2003), the Bay of Biscay (Galicia, Spain; Parapar et al. 2009); the Bay of Naples (Radashevsky and Migotto 2016); the Adriatic Sea (Croatia; Labura and Hrs-Brenko 1990), and the Aegean Sea (GBIF 2017). In Europe, the most common host is Ostrea edulis, the European Oyster (Wilson 1928; Labura and Hrs-Brenko 1990; Radashevsky and Migotto 2016).. However, it is often associated with Pacific Oyster (M. gigas) (Sato-Okoshi et al. 2023).

This polychaete is now widely distributed around the world, especially in culture operations for oysters and abalones, where it can damage shells, thereby affecting the condition and quality of these shellfish. Exotic occurrences are known from: the Canary Islands (Bilbao et al. 2011); South Africa (Simon 2009; Simon 2011); Australia (Blake and Kudenov 1978); New Zealand (Handley and Bergquist 1997); Chile (Moreno et al. 2006); Brazil; Japan (Sato-Okoshi et al. 1998; Sato-Okoshi et al. 2016); and California (Radashevsky and Migotto 2016).

North American Invasion History:

Invasion History on the West Coast:

In May 2004, Polydora hoplura was collected in a marina in San Diego Bay (Sato-Okoshi et al. 2023).  In 2011 it was collected at multiple sites in central and southern California: Monterey Bay, at Breakwater Cove Marina and in Dana Point Harbor, Orange County. The collections were made in 1–2 m depth, within dock fouling. The Monterey fouling community contained oysters, mussels, bryozoans, and sponges, but collection notes from Dana Point mentioned oysters and bryoliths (Radashevsky and Migotto 2016; Radashevsky et al. 2023). This polychaete is established along the coast of centrl and southern California,

Invasion History Elsewhere in the World:

Polydora hoplura was first reported from Table Bay Docks, Cape Town, South Africa, on the Atlantic side of the Cape region in 1947 (Mead et al. 2011). By 1967, this worm reached Plettenberg Bay, on the Indian Ocean side of the Cape (Day 1967, cited by Mead et al. 2011). It is now widely distributed along the southern tip of the continent, from Paternoster to Haga Haga, southwest of Durban, in oyster (Ostrea edulis, Crassostrea gigas) and abalone (Haliotus midas, H. spadaciae) (David et al. 2016; Williams et al. 2016). In 1999, it was discovered in a closed culture operation on Gran Canaria Island, infesting the native abalone Haliotis tuberculata coccinea (Bilbao et al. 2011). Wild populations are patchily distributed in the Canary Islands (Pascual and Nunez 1999, cited by Bilbao et al. 2011) and we consider it cryptogenic there.

Polydora hoplura was collected at many sites in southeastern Australia and New Zealand in the 1970s. It was found in Tiparra Bay, Gulf of St. Vincent, South Australia in 1971 (Atlas of Living Australia 2017), Port Philip Bay in 1975 (Blake and Kudenov 1978), and Simmonds Bay, on the south coast of Tasmania in 1977 (Blake and Kudenov 1978). Later collections were in northern New South Wales in 1992 (Walker 2009, Atlas of Living Australia 2017), and Albany, Western Australia in 2005 (Radashevsky and Migotto 2016). In New Zealand, P. hoplura was first found in Evans Bay, Wellington on the South Island in 1972 (Read 1975). This polychaete has been found in many sites on the North and South Islands (Read 1975; Handley 1995; Handley and Bergquist 1997; Inglis et al. 2006 a,b). It has been associated with the native pen-shell (Atrina pectinata zelandica), a native abalone (Haliotis iris), a native scallop (Pecten novaezelandiae), a native oyster (Ostrea lutaria), and the introduced Pacific Oyster (Crassostrea gigas) (Read 1975; Blake and Kudenov 1978; Handley and Bergquist 1997).

In 1997, a boring polychaete was found in Yamada Bay (Iwate Prefecture), Honshu, and Shironohana (Kochi Prefecture), Japan, in the shells of cultured native Pacific Oysters (Crassostrea gigas), and a native top shell (Omphalius rusticus). Sato-Okoshi (1998) described the worm as a new species, P. uncinata. Later, the Japanese specimens were found to be conspecific with P. hoplura from Europe, South Africa, Australia, and New Zealand (Radashevsky and Migotto 2016; Sato-Okoshi et al. 2017).

In 2002, Polydora hoplura, identified then as P. uncinata, was found infesting the shells of cultured Japanese abalones (Haliotis discus hannai), in land-based culture tanks in Coquimbo, Chile (Radashevsky and Olivares 2005, Moreno et al. 2006, Radashevsky and Migotto 2016). We have not found reports of this worm in open waters of Chile. However, P. hoplura has been collected from oysters (Crassostrea rhizophora) from the Atlantic side of South America, near Sao Paulo Brazil in 2015 (Radashevsky and Migotto 2016).

Polydora hoplura has a great potential for transport by humans, in the shells of transported oysters and abalones, on barnacles and bivalves fouling the hulls of ships (Radashevsky and Migotto 2016), or in ballast water. This polychaete is one of a number of invertebrates, displaying poecilogony, meaning that it is capable of switching between lecithotropic brooded development (spending about four days in the plankton at 21ºC), or planktotrophic larvae, spending ~30 days in the plankton (David et al. 2014). Planktotrophic larvae could be transported long distances in ballast water, as long as the water contained sufficient phytoplankton for sustenance.

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Description

Polydora hoplura is a shell-boring spionid polychaete, burrowing in molluscan and barnacle shells. Adults of Polydora hoplura have up to 120–160 chaeta-bearing segments (chaetigers). The prostomium has a weak anterior incision, forming two lobes and is prolonged back to chaetiger 3 as a low caruncle. A short occipital tentacle is located on the caruncle. Specimens can have up to four eyes, but can also lack them altogether. When two pairs are present, the anterior pair is further apart than the posterior. A ciliated groove runs on either side of the caruncle. The palps are long and slim and their length is the same as the total length of the first 25^th chaetigers of the worm.

Chaetiger 1 has well-formed parapodial lobes, but has short capillary chaetae only in neuropodia. The parapodial lobes are well developed anteriorly with the exception of chaetiger 5. Chaetiger 5 is enlarged, lacks parapodial lobes, and has up to four dorsal superior winged capillary chaetae, and six heavy falcate spines with lateral flanges, alternating with companion bilimbate (tipped with two wings) chaetae, and six ventral winged capillaries. Chaetigers from 7 up to 10 have hooded bidentate (double-toothed) hooks in the neuropodia, not accompanied by capillary setae. The shafts of the hooks are constricted in the middle. The notopodia in 10–15 posterior-most chaetigers each have 1–2 heavy recurved spines and a tuft of slender capillaries. Branchiae begin around chaetiger 7 and continue rearward, but diminish as the posterior spines begin. The pygidium is flared and resembles a suction cup, with a dorsal gap.

Adult worms reach a length of 25–40 mm and are pale yellow in color. Black bands are present on the pair of palps. There is some dusky pigment on the peristomium. The branchiae and the dorsal blood vessel are red. The pygidium is white. Larval morphology is described by Wilson (1928) and Radashevsky and Migotto (2016). The above description is based on Read 1975; Blake and Kudenov 1978; Walker 2009; Radashwvsky and Migotto 2016.

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Taxonomy

Ecology

General:

Polydora hoplura has two separate sexes. Eggs are laid in capsules, linked in strings attached to the interior of the burrows. In the Yealm estuary, England there were about 50 eggs per string (Wilson 1928). In South Africa, two modes of reproduction were observed: (1) a short brooded development, with release of large numbers of larvae (mean = 1544.3) at the 3-chaetiger stage followed by a comparatively long planktotrophic development (~13–40 days at 12 to 28 °C); and (2) a long brooded lecithotrophic development, with a small (mean = 19.9) brood of larvae feeding on yolky nurse eggs (adelphophagy), released at 16–18 chaetigers and spending about four to seven days in the plankton (David et al. 2014; David and Simon 2015). The two reproductive forms are conspecific, with shared haplotypes, so this appears to be a case of poecilogony or intraspecific variation in larval developmental mode, which is known in several other spionids (Levin 1984a; David et al. 2014). Larvae of both types settle at about 1 mm length (David et al. 2014).

Polydora hoplura is known from cold-temperate Southwest England and Brittany, to subtropical climates (Sao Paulo, Brazil and Canary Islands) (Bilbao et al. 2011; Radashevsky and Migotto 2016). Its salinity range is unknown, but it appears to be absent from low salinity waters. This worm is associated with a wide range of calcareous habitats, most frequently mollusk shells, but also barnacles, coralline algae, and sponges (Bilbao et al. 2011; David and Simon 2014; Radashevsky and Migotto 2016). It was found on pen shells (Atrina pectinata zelandica) protruding from soft subtidal sediment in New Zealand (Read 1975), but is also found in rocky areas and pilings, on mussels, abalones, other mollusks, barnacles, and coralline algae (Radashevsky and Migotto 2016; David et al. 2016). Polydora hoplura is known to be especially abundant in cultivated oyster beds and in onshore culture tanks for oysters and abalones (Wilson 1928; Handley and Bergquist 1997; Bilbao et al. 2011; Simon 2015). At the same time, its occurrence on barnacles and mussels gives it the potential for transport in ship fouling (Walker 2009). Adults are suspension-feeders, and feed by extending beyond their burrows to capture phytoplankton and detritus on their long palps (Blake 1971).

Food:

Phytoplankton, detritus

Consumers:

Competitors:

Other shell-boring spionids

Trophic Status:

Suspension Feeder

SusFed

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Habitats

General Habitat	Oyster Reef	None
General Habitat	Marinas & Docks	None
General Habitat	Unstructured Bottom	None
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Tidal Range	Low Intertidal	None
Vertical Habitat	Epibenthic	None

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Life History

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Tolerances and Life History Parameters

Minimum Reproductive Temperature	12	Lowest tested (David and Simon 2014, South Africa).
Maximum Reproductive Temperature	28	Highest tested (David and Simon 2014, South Africa).
Minimum Duration	7	Polydora hoplura produces either lecithotrophic or planktotrophic larvae. At 28 °C, planktotrophic spend about 13 days in the plankton after release from the egg capsule, while lecithotrophic larvae take about 7 days (David and Simon 2014).
Maximum Duration	40	Polydora hoplura produces either lecithotrophic or planktotrophic larvae. At 12 °C, planktotrophic spend about 40 days in the plankton after release from the egg capsule, while lecithotrophic larvae take about 7 days (David and Simon 2014).
Minimum Length (mm)	25	Radashvesky and Migotto 2015, Brazil
Maximum Length (mm)	40	Read 1975, New Zealand
Broad Temperature Range	None	Cold temperate-Subtropical
Broad Salinity Range	None	Polyhaline-Euhaline

General Impacts

Polydora hoplura is a spionid polychaete which bores into calcareous substrates, usually the shells of mollusks, but also barnacles, coralline algae, sponges, and limestone (Wilson 1928; Read 1975; Simon 2015). In cultivated oyster beds and onshore abalone culture systems, P. hoplura heavily infests shells, producing frequent mud-blisters and riddling the shells with burrows, producing deformations, shell breakage, and lowering the commercial quality of the shellfish (Simon 1995; Handley and Bergquist 1997; Radashevsky and Olivares 2005; Bilbao et al. 2011). The species enters abalone shells through the leading edge and is also capable of burrowing directly through the shell (Lleonard et al. 2003). In open-water culture and natural ecosystems, impacts of P. hoplura are difficult to assess because of the presence of native and cryptogenic shell-boring spionids, including other worms of the P. websteri/ciliata complex (Read 1975; Simon 1995; Sato-Okoshi et al. 2023).

Economic Impacts

Fisheries- Impacts of P. hoplura seem to be concentrated in cultivated oyster beds and closed aquaculture systems, probably because of the high densities of mollusks. Studies found that this polychaete had little effect on condition or survival of the European Oyster (Ostrea edulis) in the Adriatic Sea, Croatia (Labura and Hrs-Brenko 1990), or on Pacific Ooysters (Crassostrea gigas) in New Zealand (Handley and Bergquist 1997). However, more serious infestations of Pacific Oysters by P. hoplura have been reported from South Africa and Tasmania (Lleonard et al. 2003a; David et al. 2015; Simon 2015). Polydora hoplura has had severe impacts on cultured abalones in closed culture, including Japanese abalones (Haliotis discus hannai) in Chile (Radashevsky and Olivares 2005), and in native abalones in the Canary Islands (H. tuberculata coccinea). In South Africa, this polychaete infests cultured native H. midas and H. spadaciae (Simon 2011).

Treatment of commercially reared Crassostrea gigas with fresh water or heated sea water seems to be a practical means to reduce Polydora infestation (Nel et al. 1996) and also air drying was found to be a promising spionid treatment in abalone culture (Lleonard et al. 2003b). The authors recommended about 2–4 h exposure time at greater than approximately 16 °C for treatment of relatively recent infestations, but they mentioned that has to be done prudently to avoid potential suppression of abalone growth. Other chemicals were investigated, but none seems to be the best treatment for both the host and the parasite (Simon et al. 2010).

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