LIFE HISTORY AND DISPERSAL IN FORAMINIFERA

Foraminifera have complex life cycles with different dispersal aims and mechanisms for each part of the cycle. Adult benthic foraminifera usually do not disperse far on their own, unless they are associated with some other mechanism such as rafting, ingestion by other larger organisms, or water turbulence among others. Planktic species, on the other hand, are carried in currents for many km and vertically for hundreds of m during their life cycles. Asexual reproductions do not enhance dispersal of benthic individuals although populations may expand in range under favorable environmental conditions. During sexual reproduction, most benthic species undergo a process broadly analogous to spawning found in many marine invertebrates. That is, they release thousands of tiny flagellated gametes directly into the surrounding water column. Since gamete production is limited by the amount of cytoplasm available to form gametes, each gamete must have a high probability of fertilization controlled chiefly by dispersal mechanisms. Gametes are concentrated on the substrate, at the air-water interface or at particular depth ranges or habitats. Gamete fertilization results in propagules that can disperse widely, commonly waiting on the bottom for appropriate conditions to appear. They then may find suitable habitats for growth by further dispersal. This mode of sexual reproduction is broadly shared across most of the extant clades, suggesting that dispersal may have played a significant role in the evolution of the foraminiferal life cycle.Although these dispersal mechanisms provide opportunity for wide geographic distributions, and indeed propagules may disperse beyond the natural range of the species, foraminifera like other marine organisms, are restricted to habitats and/or specific regions to which the species have been long adapted.