Three confirmed individuals of C. japonica were found by commercial fisherman at Outer Harbour, Gulf St. Vincent and the Port Adelaide River, South Australia, between mid-2019 and mid-2020. All three individuals were reported to Primary Regions and Industries South Australia (PIRSA) Fishwatch. After 1-2 years following a marine heatwave and strong Leeuwin Current event, C. japonica was detected in the Peel-Harvey and Swan River estuaries, WA, between 2010 – 2014 (Hewitt et al., 2018). In December 2018, a single mature female C. japonica was caught at Blackwall Reach, Swan River, Perth, by a recreational fisher. In WA and SA, media releases on the Asian paddle crab are keeping recreational and commercial fishers informed to ensure they report any sightings. Trap and eDNA surveillance are also being used to monitor the status of C. japonica in WA and SA. Currently C. japonica is not considered established in Australia and should be reported if suspected.
In New Zealand, research by Fowler and McLay (2013) found that invasive C. japonica populations in the Weiti Estuary are now considered to be established. This was based on evidence of ovigerous females and size distributions demonstrating recruitment. A New Zealand-wide marine surveillance programme is conducted bi-annually in NZ’s 11 main ports and harbours.
In 2020 a Master's Thesis investigating the continued invasion of Northern New Zealand by Charybdis japonica was published. The study discussed dispersal and distribution drivers, seasonal and sampling variations, and best methods for sampling (Hilliam, 2020).
The Asian paddle crab, Charybdis japonica, is a portunid (swimming) crab known for its aggressive behaviour. C. japonica has a carapace width of up to 120 mm (Archdale et al., 2007) and exhibits a variety of colour morphs from mottled cream and purple to pale green and off-white, through to olive-green with purplish markings (Smith et al., 2003). Most specimens found in Waitemata Harbour, New Zealand have yellow-orange markings (Smith et al., 2003). It is an aggressive marine predator that feeds on other crustaceans, cephalopods, echinoderms, molluscs and even some fish species. Native to the coastal temperate regions of the western Pacific from China to Thailand (Smith et al., 2003), C. japonica was introduced to New Zealand in 2000. It is not considered established in Australian waters but there have been a number of sporadic detections in South Australia and Western Australia.
In its native range it occurs in the intertidal and subtidal habitats to a depth of about 15 m. In Australia, individual C. japonica have been found near ports in large estuaries that comprise soft sediments, rocky shores, artificial structures and seagrass meadows. Charybdis japonica reproduce multiple times, mating and spawning numerous times throughout its ~3-year life span. This species undertakes “hard-shelled” mating which is rare among swimming crabs. On average, females spawn 200,000 – 500,000 eggs per clutch. Eggs hatch into planktonic larvae (zoea and megalopa) which can be dispersed by ocean currents and develop into juveniles after a minimum of 17 days. This species is tolerant to a wide range of temperature (4 – 34 °C) and salinity conditions (14 – 33 ppt).
Not considered established.
Detected as indivduals on several occassions in South Australia and Western Australia.
In South Australia, the first specimen of C. japonica was detected in Outer Harbour near Port Adelaide in 2000. No further specimens were detected despite surveillance efforts after this point, suggesting an isolated event in 2000 (Wiltshire et al., 2010). Then in mid-2019, a commercial fishers caught a large male C. japonica in a trap in Outer Harbour. Two more C. japonica specimens have since been confirmed near the Port Adelaide area by mid-2020. Surveillance is ongoing.
In Western Australia, C. japonica have been caught in the Peel Harvey and Swan River estuaries (Hewitt et al., 2018). Surveillance is ongoing.
Charybdis japonica is considered invasive in the following countries/regions:
Established in Northern New Zealand, with the site of introduction located at Waitematā Harbour, Auckland and neighbouring Tamaki and Weiti estuaries (Weaver, 2017). In 2010, C. japonica was found in large numbers within Whangarei Harbour ~150 km north of Waitematā Harbour. Based on sea surface temperatures in its native range, C. japonica is capable of surviving in NZ estuaries nationwide (Gust and Inglis, 2006; Weaver, 2017). In 2020 Charybdis japonica occured from Ohiwa Harbour to the Bay of Islands on the east coast of the North Island and Manukau Harbour to Hokianga Harbour on the west coast (Hilliam, 2020).
Detections and individual sightings of C. japonica have occurred in the following regions:
In 2006, a single adult male specimen of C. japonica was confirmed in Ancona Harbour, Italy, making it the first record of this species in the Mediterranean Sea (Froglia, 2012). No further records of C. japonica have been recorded in the Mediterranean Sea since.
Charybdis japonica. This crab has not recently moulted and some tube worms have settled on the shell.
C. japonica showing colour variation compared to the one above.
C. japonica in wild with claws outstretched showing colour pattern.
Underside of female C. japonica.
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