The tropical Atlantic Ocean and Caribbean Sea have been isolated from other tropical oceans for the past three million years since the closure of the connecting seaway by the formation of the Isthmus of Panama. The investigation of how tropical marine organisms are able to get from one ocean to the other since that closure is of considerable biogeographic interest. 

The larger benthic foraminifera (LBFs) are a group of millimeter-sized shelled marine protists, harbouring symbiotic microalgae such as diatoms, that are commonly found in tropical coral reef communities. Like corals, they are environmentally confined to warm shallow tropical and subtropical waters. This control on their choices of habitat, as well as their small size and ease of collection make the LBFs useful proxies in the study of how invasive marine species are transported involuntarily, through attachment to ship hulls or through contamination of ballast water in modern commercial shipping. 

There is abundant literature on the subject for the Mediterranean and Indo-Pacific regions, especially since the opening of the Suez Canal. However, there is very little published information on the importance of these dispersal mechanisms, as well as possible natural alternatives, such as transport by ocean currents or inadvertent transport by attachment on other pelagic organisms like migratory fish, in the pre-1850 era of sailing ships and earlier historical times. 

Emeritus Professor Edward Robinson and Dr. Thera Edwards, Department of Geography and Geology, Faculty of Science and Technology, The University of the West Indies, Mona examined the likely constraints and vectors controlling the invasion of recent cosmopolitan foraminifers from the Indo-Pacific region to the Atlantic and Caribbean using the species _Heterostegina depressa_ as a test case. This species originally evolved in the Indo-Pacific but was first described in 1826 from St Helena, a remote island in the South Atlantic, before the Suez and Panama Canals were opened. The authors provide reasons for discounting an invasion through natural range expansion or ocean currents along the possible routes available around South America or South Africa due to low temperatures and adverse ocean currents. The authors hypothesise that anthropogenic vectors such as sailing ships were the only likely means of transport because of their relatively high speeds and non-reliance on ocean currents. They concluded that the invasion of the Atlantic by _H. depressa_ was accomplished within the Little Ice Age (1350-1850 C.E.) when trans-Atlantic shipping first started to populate what had previously been an ocean devoid of shipping, between the start of Portuguese marine trade via South Africa with East Africa, India and the Far East in 1497 and the first description of _H. depressa_ in 1826. 

The authors’ hypothesis is potentially applicable to other foraminifers as well as other biota currently resident in the ACR. Their model provides well defined parameters that can be tested using methods such as isotopic dating of foraminiferal assemblages or associated sediments.

Reference: Robinson, E.; Edwards, T. Invasion of the Atlantic Ocean and Caribbean Sea by a Large Benthic Foraminifer in the Little Ice Age. Diversity 2025, 17, 110. https:// doi.org/10.3390/d17020110