Dispersal of Shallow-Water Benthic Foraminifera – a Key to Current and Potential Future Distribution Patterns

In recent decades, climate-driven range expansions of various warm-adapted marine species have been observed, including benthic foraminifera. Distribution models predict further poleward extensions in the future, which might result in significant impacts on native faunas, habitats and entire ecosystems. The prolific expansion and colonization of benthic foraminifera is related to propagule dispersal. Foraminiferal propagules – tiny juveniles – are transported well beyond their biogeographic ranges and are able to grow and become established under suitable conditions.

Here, we focus on propagule dispersal along the southeastern coast of the United States. Sediment samples containing propagules were collected from different shallow-water locations along a latitudinal gradient from Sapelo Island (GA), Fort Pierce (FL) and the Florida Keys. We hypothesize that propagules of warm-adapted species might be transported farther to the North than their biogeographic boundaries indicate, and that their current distribution is limited.

Applying the propagule method, we are growing foraminifera from propagules collected at these three sites under constant normal and elevated temperatures (18°, 24°, 30°C) and normal and reduced salinities (15 and 35‰) with illumination on a 12-hr cycle. These set-ups cover a wide range of shallow-water habitats from intertidal to environments more proximal to the open marine realm. They also reflect the temperature gradient along the southeastern coast.

The occurrence of species typically confined to warmer regions in assemblages grown at elevated temperatures would support distribution models that predicted the further range expansion of warm-adapted species within the next decades. Thus, results of this study could provide a glimpse into the future.