Map showing countries having commercial maritime routes with the Norman harbors of Le Havre harbor and Caen-Ouistreham in France (in black, red and green, sources: Le Havre harbor website: https://www.haropaport.com/fr/havre/offre-maritime, grey countries does not have maritime trade with Normandy). Red and green countries are known for the presence of Trochammina hadai, invasive or natural range of distribution, respectively. Places where T. hadai was introduced are also indicated (filled grey circles).