Trochammina hadai is a large, benthic formaniferan, with a shell composed of spheroidal calcareous chambers, The shells foraminifera are important for micropaleontological analysis of environmental conditions in sedimentary habitats, as they are sensitive to salinity and temperature. The foraminiferan Trochammina hadai is known from northwestern Pacific, in coastal waters of China and Japan and from Chilka Lake, India, on the Bay of Bengal In its native range, it is characteristically abundant in brackish and eutrophic waters In 1990, T. hadai was discovered in San Rafael Bay, part of central San Francisco Bay. It was absent in sediment surveys from the 1970s and early 1980s. An examination of early sediment samples found it in a sample collected in South San Francisco Bay in 1983, where it was 3% of the foraminiferal fauna. By 1986-87, it was widespread in the South Bay, and dominant at many locations. In the late 1990s, it was dominant at most locations from San Pablo Bay to the South Bay . In surveys made along the West Coast in 1998, T. hadai was found to the south of San Francisco Bay, in San Diego Bay, Mission Bay, Newport Bay, Los Angeles-Long Beach Harbor, Marina del Ray, Santa Barbara Harbor, Morro Bay. To the north, it was found in Tomales, Bodega and Humboldt Bays in California, Willapa Bay, Washington, Comet and Padilla at the northern end of Puget Sound, and Prince William Sound, Alaska (McGann et al. 2000). Studies of sediment cores in Padilla Bay indicated that this foram was first present around 1958, and greatly increased in abundance around 1972 (McGann et al. 2007). The actual site of first introduction on the West Coast is not clear. Trochammina hadai is abundant in ballast water sediment but transplants of Pacific Oysters (Crassostrea gigas are also a possible vector (McGann et al. 2007). In 2005, Trochammina hadai was initially identified in sediments in Parangua Bay, Parana State, Brazil, as Portantrochammina sp., Paranagua Bay is a major shipping port, so the likeliest vecotr was ballast water. In 2014-2015, ti was found in Flamego Inlet, Ubatuba, in Sao Paulo State. Ubayuba is fishing and recreational port, so Eichler et al. (2018) suggest that mud on anchors may have been the vector for the local invasion.In 2020, Trochammina hadai was found in Leschenault Inlet and Collie River, near the port of Bunbury, Western Australia. The major export from Bunbury is woodchips, carried in small, shallow-draft Japanese-owned vessels, which are more likely to tranport sediment from smaller ports (Tremblin et AL. 2022(,in 2019, Trochammina hadai was found in Normandy, France in Le Havre and Caen-Ouistreham harbors. These are commercial harbors, rather than recreational or fihsin ports, so ballast water is considered the likeliest vector'