Depth related adaptations in symbiont bearing benthic foraminifera: New insights from a field experiment on Operculina ammonoides

Shai Oron,Jonathan Erez,Sigal Abramovich,Ahuva Almogi-Labin,Julia Woeger

doi:10.1038/s41598-018-27838-8

Abstract

Large benthic foraminifera (LBF) are marine calcifying protists that commonly harbor algae as symbionts. These organisms are major calcium carbonate producers and important contributors to primary production in the photic zones. Light is one of the main known factors limiting their distribution, and species of this group developed specific mechanisms that allow them to occupy different habitats across the light gradient. Operculina ammonoides (Gronovius, 1781) is a planispiral LBF that has two main shell morphotypes, thick involute and flat evolute. Earlier studies suggested morphologic changes with variation in water depth and presumably light. In this study, specimens of the two morphotypes were placed in the laboratory under artificial low light and near the sea floor at depths of 15 m, 30 m, and 45 m in the Gulf of Aqaba-Eilat for 23 days. Differences in growth and symbionts content were evaluated using weight, size, and chlorophyll a. Our results show that O. ammonoides exhibit morphological plasticity when constructing thinner chambers after relocation to low light conditions, and adding more weight per area after relocation to high light conditions. In addition, O. ammonoides exhibited chlorophyll content adaptation to a certain range of light conditions, and evolute specimens that were acclimatized to very low light did not survive relocation to a high light environment, possibly due to photo-oxidative stress.

Highlights

Large benthic foraminifera (LBF) are marine calcifying protists that commonly harbor algae as symbionts
Algal symbiosis is prevalent in many LBF species and they are considered as major contributors to primary production in the photic zones of shallow seas[4,5,6,7,8]
Computed Tomography (CT) scan images of selected specimens of different morphologies from the collection sites all showed megalospheric proloculus with average diameter of 59(±14) μm (Fig. 5), which indicates that the origin of those specimens is by asexual reproduction

Summary

Introduction

Large benthic foraminifera (LBF) are marine calcifying protists that commonly harbor algae as symbionts. These organisms are major calcium carbonate producers and important contributors to primary production in the photic zones. Symbiont-bearing larger benthic foraminifera (LBF) generally live in shallow oligotrophic waters of tropical and sub-tropical seas. They mostly harbor endosymbiotic algae and have complicated internal structures[1,2,3]. Symbiont-bearing larger benthic foraminifera distribution in shallow marine environments is determined by a set of parameters, of which water depth has a dominant but indirect role[5,9,10,11,12,13]. Few studies indicated that specimens found shallower than 40–60 m are mostly more involute and thicker than specimens from deeper water[5,16]

Methods

Results

Conclusion