MEPS 751:23-36 (2024)  -  DOI: https://doi.org/10.3354/meps14749

ABSTRACT: This study examines the dispersal ability of megalospheric (haploid) and microspheric (diploid) foraminiferan generations in their natural soft bottom habitat. Foraminiferans typically exhibit an alternation between microspheric and megalospheric generations. Both generations display similar shapes, sizes, habitat preferences, and lifestyles. However, subtle morphological differences exist, particularly in their test (= shell) details, allowing for their differentiation. Colonization experiments were conducted along the Swedish west coast where a container with soft-bottom sediment was suspended 2.5 m above the sea bottom at 40 m water depth. They demonstrated that sublittoral benthic foraminiferans possess the capability to disperse planktonically. Reproduction and settling activities were observed year-round, peaking in the late autumn and showing a smaller second peak in April-May, coinciding with the seasonal sedimentation of algal plankton blooms. The lowest settling numbers were recorded during winter (January-March). Notably, various species reproduced at different times throughout the year, with the microspheric stage (the growing zygote) identified as the primary dispersal stage, following a pattern observed in many organisms where dispersal follows sexual reproduction. Post-dispersal, the microspheric stage undergoes growth and asexual reproduction through schizogony (meiosis and fission). In contrast, haploid offspring (megalospheric schizozoites) generally exhibit limited dispersal (cm to dm), remaining within established habitats to exploit available resources. This research sheds new light on foraminiferan dispersal patterns. It highlights that attached littoral foraminiferans in turbulent environments commonly engage in gamontogamy (aggregation between haploid gamonts) to ensure fertilization, while soft-bottom species often release flagellated gametes into the sediment or near-bottom water.

KEY WORDS: Planktonic dispersal · Diploid juvenile · Benthic foraminiferans