News on new and recently introduced species to the Solent area

Because of the extensive shipping movements and numerous marinas welcoming boats from overseas, the Solent receives a large number of new species from other parts of the world, often attached to hulls or in ballast water. This has long been the case and many, often termed invasive species, are far from welcome. DNA analysis of water and sediment samples is now being used to detect new members of our aquatic community. Using eDNA Holman et al (2019) report the presence in a marina in Southampton Water of three newly arrived species described below:

Arcuatula senhousia (Asian date mussel) This mussel is a native of the Pacific Ocean from Siberia to Singapore, but has invaded many other regions of the world. It can live in the intertidal or shallow subtidal zones. It grows quickly and lives for only about 2 years. It prefers soft substrates and surrounds its shell in a dense mass of byssus, the beard-like threads mussels use to attach to rocks etc. This species is considered detrimental to seagrass beds which are important in the Solent region (see article in this issue). In fact, shells had been spotted prior to 2018, but the presence of DNA indicates a living population is certainly in the Solent. Readers should look out for this mollusc when walking our beaches. Barfield et al (2018) reported shells of Asian date mussel on Solent beaches.

Musculista senhousia (Asian mussel) – photo Graham Bond – Creative commons

Cephalothrix simula is a nemertean worm and is an invasive, non-native, ‘highly toxic’, species of ribbon worm. Commonly called the Pacific Death Worm, it has only physically been found in the UK at two sites, one in Cornwall and one in Dorset. Its presence in Southampton Water is only known from eDNA analysis. Do not be concerned by the name this worm currently poses little to no threat to health or the economy.

Mature male of Cephalothrix simula.- Image Hiroshi Kajihara Creative Commons

The third species was Paranais frici an oligochaete worm. The first actual specimens were recently reported from Deptford Creek. It is now probably living in brackish waters within the Solent region.

Plankton has been monitored in Southampton Water for some years and recently noted surprising numbers of two invasive species which would not normally be considered members of the plankton. The first is the North Pacific pycogonid or sea spider, Ammothea hilgendorfi. This species cannot swim so it is surprising that at some times of the year they appear in the water column.

The pycogonid or sea spider Ammothea hilgendorfi, image © P. A. Henderson

The second is the Japanese skeleton shrimp, Caprella mutica. This is also a non-swimming species which is surprisingly common in the water column possibly when reproducing or dispersing to new habitat. It was first reported in Europe in the Netherlands in 1994 now widely distributed in British waters. These are truly odd-looking animals, the head is at the right of the picture.

Japanese skeleton shrimp, Caprella mutica, image © P. A. Henderson

ARticle submitted by Dr. Peter Henderson, SPS