Foraminifera as indicators of species invasion: <i>Ammonia confertitesta</i> in Long Island Sound

Resolving timing of the invasion of nonindigenous species is difficult in estuarine settings, due to their pervasive history of anthropogenic disturbance. Many non-native marine taxa are not documented until after they have become invasive, leaving questions about invasion timing (first introduction and lag period), geographic origin, vectors and pathways, and cause(s) of success. Foraminifera, unicellular, calcareous-shelled eukaryotes, offer a unique way of analyzing past ecosystem structure because their fossilized shells provide a window into the past, and small size and abundance enable us to document distribution over time in core samples. We use records of Foraminifera to document the timing and history of establishment of an invasive species (<i>Ammonia confertitesta</i>) in Long Island Sound, east of New York City (USA). <i>A. confertitesta</i> was rare from the mid-19th century but did not proliferate until the mid-1970s. We hypothesize that increasing propagule pressure from the rapid increase in global ship traffic and ballast water was the main factor for its success.