Resting stage in benthic foraminiferal propagules: a key feature for dispersal? Evidence from two shallow-water species

Abstract. Understanding dispersal mechanisms in benthic formainifera has wide implications for explaining their geological and biological distribution in space and time, including evolutionary and genetic trends. Because they lack a planktonic larval stage (although a few have a meroplanktonic life stage), their mode of dispersal in the marine environment has been subject to much speculation, and a range of alternative mechanisms have been suggested (for a review, see Alve (1999) and further discussion in Hayward et al. (1999)).

In the present note, we suggest a mechanism which is more efficient and probably more widespread than most of those previously proposed. We hypothesize that many species produce ‘propagules’ (small juveniles, perhaps just the proloculus) released in large numbers following reproduction that may enter a resting stage. Propagules can be widely dispersed by normal physical processes (currents, sediment transport) and ultimately settle over a range of habitats and conditions. Growth and reproduction commence only in those individuals and species that reach a suitable environment. We have two lines of evidence from completely different shallow-water environments (Norwegian fjord and the Florida Keys, USA) that strongly support our hypothesis.

Observations

Surface sediments from a box core were collected at 60 m water depth in the inner part of Oslofjord 10 September 1999. Some of the sediment was processed immediately after collection, and the remaining bulk sample was transferred to a transparent container with ambient seawater, sealed, and placed on a window ledge until 30 March 2000. Those sub-samples processed immediately after collection contained no live . . .