First Record of Invasive Dwarf Surf Clam in the UK

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Eco Marine carries out regular ecological surveys in the Thames Estuary and are experts on identifying the diverse range of species found in the local marine environment. In addition to being able to classify local, native species, it is important that our staff are informed on the invasive non-native species (INNS) present in UK waters and the legislation and control measures that correspond with them.

Ecological surveys in the Thames Estuary have seen the presence of a variety of INNS throughout periods of monitoring, some of the most prominent of which are the Chinese mitten crab (Eriocheir sinensis) and the Pacific oyster (Magallana gigas) (Port of London Authority). Research has shown an increase in species invasion rates in recent decades, with a total of 96 non-native invasive species identified from 1800-2010, 53% of which became established in the last 50 years (Jackson and Grey, 2013). However, it is important to note that not all non-native species are harmful to their surrounding ecosystems.

Recently, Eco Marine reported the first record for the UK of the non-native dwarf surf clam (Mulinia lateralis). Native to the western Atlantic and Caribbean, a total of five individuals have been recorded in the Outer Thames Estuary since 2021, after first being discovered in Europe in 2017 in the Wadden Sea, where a population is now established. The dwarf surf clam is known to be highly adaptable to various ecological factors, including poor water quality, salinity fluctuations, and extreme temperatures, prompting the question of whether this will give it a competitive edge on UK native species (Craeymeersch et al., 2019).

Due to M. lateralis bearing a range of similarities to the native Spisula subtruncata, as well as other non-native bivalves found in the UK, it may go unnoticed in surveys. However, it does possess identifiable physiological features that differentiates itself from other bivalve species, with a prominent posterior radial ridge that is absent in other species. The concentric sculpture, lines along the shell marking growth, of dwarf surf clams are also finer than other similar bivalve species such as S. subtruncata, which is more rugged.

The recency of M. lateralis’ detection in European waters, including the Thames estuary, means it is not currently known whether the species will have a detrimental impact on established marine and freshwater communities. However, the presence of an established population in the Wadden Sea, despite only being first documented in 2017, indicates that the species is able to thrive and quickly colonise in these habitats. This, in addition to its tolerance for extreme habitat conditions, short generation time, and efficient exploitation of food resources, may cause the dwarf surf clam to come into competition with native species for food and space (Craeymeersch et al., 2019).

The properties that make the dwarf surf clam potentially detrimental as an invasive species, such as its small size and short generation time, make it potentially important as a model species for bivalve development and genetic studies. Also, in its natural range, M. lateralis is considered important as a source of food for birds and fish, as well as for recreational fishing, factors which could be beneficial environmentally and socio-economically (Wood et al., 2022).

Eco Marine are continuing to carry out regular ecological surveys in the Thames Estuary to provide a long-term assessment of the environmental state of the area and will continue to monitor for any further records of dwarf surf clams in UK waters to aid in understanding its distribution and impacts.

A paper detailing the findings has been published in the Journal of Conchology, available here.

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