First record of the marine alien bryozoan Amathia verticillata (delle Chiaje, 1822) in South Africa

Résumé

This study reports on the first discovery of the marine bryozoan Amathia verticillata (delle Chiaje, 1822) from South Africa.In November 2023, an unusual soft-bodied bryozoan was observed within the Langebaan Lagoon Marine Protected Area on the west coast of South Africa.Taxonomic investigations confirmed it to be A. verticillata.In response, surveys were conducted to assess its abundance and distribution within the MPA.The tidal estuarine lagoon was divided into 15 sampling areas, with each searched for A. verticillata colonies.Additionally, colonies were collected to identify associated epifaunal assemblages.Amathia verticillata was detected in 60% of areas, with a total of 2333 colonies recorded.Colonies varied greatly in size, with some more than two meters long.Most concerning was the presence of A. verticillata within meadows of the regionally endangered seagrass Zostera capensis.A total of 33 epifaunal species were recorded within the stolonal matrices, of which three were alien and one was cryptogenic.This highlights the role that A. verticillata may play in habitat provisioning.Amathia verticillata was most likely introduced to the system via biofouling, with spread facilitated by local tidal flow regimes.It is recommended that a seasonal monitoring plan be implemented to track the spread and density of the species within the lagoon.Given the potential impacts that A. verticillata may have on vulnerable native species, it is recommended that best practice to prevent spread be established, and that areas susceptible to secondary spread be monitored, to support rapid response to additional incursions by this invader.

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