April 23rd, 2010 by Richard Lord
The Asian Shore Crab, Hemigrapsus sanguineus, has arrived on the shores of Guernsey and Jersey.
Hemigrapsus crabs can be separated from indigenous crabs by the frontal area between the eyes being straight and tooth-less. The carapace or shell of Hemigrapsus crabs also have three antero-lateral teeth rather than the five teeth on each side of the carapace in the common shore crab, Carcinus maenas.
Troy Waterman reported the first Channel Island occurrence of an Asian shore crab in Amarreurs Harbour, Grand Havre, on Guernsey’s north-west coast on 26 April 2009. The approximate location was 49.4942° north and 2.5444° west.
Crustacean specialist Dr. Jocelyne Martin from Department Ecologie et Modeles pour L’Halieutique, IFREMER, Nantes, France identified the crab from photographs.
According to a paper by Breton, Faasse, Noel and Vincent, this species of crab was introduced to European waters, probably via ballast water carried by merchant shipping, into Le Havre, Normandy in about 1998, and also in the former Oosterschelde estuary in the Netherlands.
Following Troy Waterman’s discovery in Guernsey, Dr. Paul Chambers found an Asian shore crab on 7 May 2009 in a rock pool just east of Le Hurel slipway in Jersey.
Almost a year after his initial discovery, Troy Waterman found another Asian shore crab on Guernsey’s west coast. The female crab collected on 19 April 2010 was found in Portelet (approximate grid reference 49.43 degrees north and 2.66 degrees west) at 6.30 a.m. It had a carapace width of 2.3 cm.
The two leading causes of biodiversity loss are habitat destruction and invasive species. The USGS Nonindigenous Species Information Bulletin reports that the Asian shore crab has displaced native species on the eastern seaboard of the USA.
The potential impact of Hemigrapsus sanguineus on the Channel islands inter-tidal fauna is unknown. However, if it is found in Guernsey or Jersey waters, it should be collected, and reported to the Guernsey Sea Fisheries Department or the Jersey Fisheries and Marine Resources division of the Environment Department. It should not be returned to local waters as the species could negatively impact our fisheries.
Since Troy Waterman found the second female crab on 19 April 2010, he found a male Asian shore crab on 6 May 2010 high on the shore at Perelle at 49.459157 degrees north and 2.637448 degrees west.
Another recreational angler, Damien, has also reported finding an Asian shore crab, Hemigrapsus sanguineus, in Belle Greve Bay off the Queen Elizabeth II marina during a extreme low tide on 2 March 2010. The approximate location of this discovery was 49.460789 degrees north and 2.525353 degrees west. This crab was collected but escaped back to the sea.
The female Asian shore crab, Hemigrapsus sanguineus, collected by Troy Waterman on 19 April 2010 was discovered with extruded eggs on its abdomen on 17 May 2010.
The Asian shore crab can tolerate prolonged periods out of the water, and it can tolerate near freezing conditions and make a full recovery.
Besides the introduction of Hemigrapsus sanguineus (de Haan, 1853) into Channel Island waters, it is possible that Pachygrapsus marmoratus (J.C. Fabricius, 1787) and Hemigrapsus takanoi Asakura & Watanable, 2005, could also be discovered in Channel Island waters, so the identification of any alien crab should be confirmed.
Pachygrapsus marmoratus is arriving from southern waters. It is principally a Mediterranean species. This species has already been recorded in Southampton Water and in the Teignmouth area. Hemigrapsus takanoi is native to Asia.