Colonization of new habitats by benthic foraminifera: a review

Colonization of new habitats, which have been established as a result of a catastrophic disturbance of the environment, is one of the characteristic r epetitive events throughout the Phanerozoic. In recent years, much attentio n has been paid to investigations focusing on biological recovery of benthi c habitats severely disturbed by human activity. In order to improve our en vironmental and stratigraphical interpretations of such events, we need a m ore thorough understanding of the processes involved in colonization by one of the most abundant and useful fossil groups, the benthic foraminifera. T he present review focuses on processes governing benthic foraminiferal disp ersion and colonization patterns in modern environments. For benthic forami nifera, the only active dispersal mechanism is through self-locomotion on o r within the sediment and this is considered to be efficient over short dis tances only. Several passive dispersal methods have been suggested but two seem to be of more general importance. These are dispersal through release and transport of embryonic juveniles and passive suspension and transport o f various growth stages. Both are probably important for most benthic foram inifera but the former is likely to be the main mechanism for attached, tub ular and larger foraminifera, which are not easily entrained at a later lif e stage. The latter seems to be a more important dispersion mechanism for b enthic foraminifera than previously realized. The colonization rate of soft -bottom substrates is closely related to the hydraulic regime in, and the t ransit time from, the source area inhabited by species capable of colonizin g the new habitat las long as food and other environmental characteristics are not limiting factors). The transit time depends on the speed of the tra nsporting medium and the distance from the source area. There seems to be t wo end-processes which can operate during the colonization, depending on wh ether physically induced or biological processes are allowed to dominate. T hey are characterized by different colonization patterns. In high energy en vironments (bottom current velocities often > 20 cm/s), a short transit tim e may cause the major components of the nearest ambient seafloor assemblage s to colonize the new habitat within days. In this case the colonization is simply through a physical transfer of parts of the source community to the new habitat, allowing no time for pioneer, opportunistic assemblages to de velop. In low energy environments (bottom current velocities generally < 10 cm/s), the transit time is long for most species. Here, colonization follo ws the classic metazoan successional pattern with an initial, high abundanc e pioneer assemblage strongly dominated by small opportunists followed by d evelopment of assemblages with increasing numbers of specialized species an d recovery can take from one to several years. Initial lack of food (e.g., volcanic ash) or 'hostile' substrate properties (e.g., recently reoxygenate d or severely contaminated sediments) may delay colonization by months or e ven years. Small, infaunal species (both calcareous and agglutinated) are a mong the first and most successful colonizers of soft bottom habitats from shallow waters to the deep sea. Throchospiral agglutinated taxa are among t he most abundant colonizers on deep sea hard substrates. (C) 1999 Elsevier Science B.V. All rights reserved.