Species-Specific Settling Behaviors of Benthic Foraminifera: Size, Density and Structure

ABSTRACT Settling velocity is a key hydrodynamic parameter to understand the transport behavior of benthic foraminiferal tests. Both size and density are fundamental in predicting settling velocity, but their relative importance is unclear. We used specimens of four benthic foraminiferal species from a carbonate-sand sample collected from Xisha Qundao, South China Sea, to investigate this question. Measurements on foraminiferal test size, shape, and density were combined with settling velocity observations using a laboratory settling tube. In addition, a micro-Computed Tomography (CT) Scanner was used to extract the internal-structure patterns of the tests of four representative specimens. Our study revealed that both size and density are important in affecting settling velocity, but the relative importance is species-specific. Size is more important than density for Amphistegina lobifera and Heterostegina depressa; these two factors are equally important for Peneroplis pertusus, but the settling velocity of Sorites orbiculus is also considerably controlled by their unique structure, besides size and density. This species-specific pattern was further compared with test development to reveal the associated biological mechanisms. As a result, a novel parameter, DT (density*TND2), is proposed as a better variable for predicting the species-specific settling behaviors.

Seascape ecological view as a new insight of benthic foraminiferal community

<p>Foraminifers secrete various chemicals for chamber walls. They are calcium carbonates such as calcite, aragonite, Mg-calcite, organic compounds for agglutinated chambers and/or organic cemented test walls.  Foraminiferal test walls basically form according to genetic information.  However, same test group is tended to gather at specific microenvironments.  For instance, turf shaped algal microhabitat such as coralline algae at rocky shore is composed of both frond and thallus parts as microhabitat.  Frond part is open space where fresh seawater moves inbetween one frond and the other.  <em>Elphidium crispum</em>, <em>Pararotalia nipponica</em> and <em>Patellina corrugate</em> and other calcareous foraminifers dwell at frond surface.  In contrast, thallus part is muddy and high concentration of organic matters.  The thallus part shows less oxygenated than frondal part as the space is close.  Microbial cascades are developed at thallus part.  Minor elements such as Mg or Sr are relatively high in sediment.  Soft-shelled forms such as <em>Allogromia</em>, gromiid, agglutinated forms and miliolids groups with high magnesian calcite tests flourish at the thallus part.</p><p>Microhabitat segregation and microenvironmental differences may cause similar biomineralization of benthic foraminiferal tests.  I would like to stress that micro-seascape should be important to characterize benthic foraminiferal assemblages.</p>

Investigating crystal orientation patterns of foraminiferal tests by electron backscatter diffraction analysis

We studied the crystallographic orientation of calcite crystals in benthic foraminifers by electron backscatter diffraction (EBSD). Individuals of two species, Gyroidinoides soldanii and Cibicidoides grimsdalei, featuring different test structures, were investigated for a time span covering 43 Myr. The aims of this study are to visualize test structure differences in foraminifers and to reveal potential changes in crystal orientation and grain size over time caused by diagenetic reactions such as recrystallization. Such recrystallization effects over time may aid in the interpretation of time-resolved geochemical data obtained on foraminiferal samples for paleo-environmental reconstructions. The EBSD patterns clearly resolve the different test structures of the two species. Cibicidoides grimsdalei has the c axes perpendicular to the test surface. An apparent shift in the preferred crystal orientation can most likely be attributed to a mismatch between the equatorial plane and cutting plane of the foraminiferal test, highlighting the importance of reproducible preparation techniques. In Gyroidinoides soldanii, the c axes of the calcite crystals show a broader distribution of the crystals with no preferred orientation. The specimens show no change in crystal sizes over time, with a frequency maximum corresponding to the spot size of the electron beam. Overall, the differences between the two species demonstrate that EBSD is a powerful tool to visualize and differentiate between foraminiferal test structures.

Response of Intertidal Foraminiferal Assemblages to Salinity Changes in a Laboratory Culture Experiment

This study explored the response to salinity of intertidal foraminiferal assemblages from the Yellow Sea by culturing them for 100 days at six constant salinity levels (17, 22, 27, 32, 37, and 42 psu) in laboratory microcosms with four replicates each. A total of 7,471 live (stained) foraminiferal specimens were obtained and analyzed. The diversity parameters of foraminiferal assemblages (species richness, Margalef index, Shannon-Wiener index, and Fisher's alpha) declined significantly when the salinity was increased or decreased from the field value, but foraminiferal abundance was highly resistant to salinity. In addition, salinity exerted different effects on foraminifera from different orders. Specifically, the proportion of species from Order Miliolida significantly increased whereas that of species from Order Rotaliida decreased with increasing salinity. High salinity-tolerant species Ammonia aomoriensis, Cribrononion gnythosuturatum, Ammonia tepida, and Quinqueloculina seminula could fill unoccupied ecological niches when the proportion of salinity-sensitive species has declined. Furthermore, our morphometric results showed that foraminiferal test size was significantly negatively correlated with salinity, and numerous abnormal specimens appeared in foraminiferal assemblages when salinity deviated from the field value. Our study revealed that intertidal foraminiferal assemblages had high adaptability at different salinities because of the existence of high salinity-tolerant dominant species. In addition, salinity variation can significantly alter foraminiferal morphology in test size and abnormality.

Size variations in foraminifers from the early Permian to the Late Triassic: implications for the Guadalupian–Lopingian and the Permian–Triassic mass extinctions

The final 10 Myr of the Paleozoic saw two of the biggest biological crises in Earth history: the middlePermian extinction (often termed the Guadalupian–Lopingian extinction [GLE]) that was followed 7–8 Myr later by Earth's most catastrophic loss of diversity, the Permian–Triassic mass extinction (PTME). These crises are not only manifest as sharp decreases in biodiversity and—particularly for the PTME—total ecosystem collapse, but they also drove major changes in biological morphological characteristics such as the Lilliput effect. The evolution of test size among different clades of foraminifera during these two extinction events has been less studied. We analyzed a global database of foraminiferal test size (volume) including 20,226 specimens in 464 genera, 98 families, and 9 suborders from 632 publications. Our analyses reveal significant reductions in foraminiferal mean test size across the Guadalupian/Lopingian boundary (GLB) and the Permian/Triassic boundary (PTB), from 8.89 to 7.60 log10 μm3 (lg μm3) and from 7.25 to 5.82 lg μm3, respectively. The decline in test size across the GLB is a function of preferential extinction of genera exhibiting gigantism such as fusulinoidean fusulinids. Other clades show little change in size across the GLB. In contrast, all Lopingian suborders in our analysis (Fusulinina, Lagenina, Miliolina, and Textulariina) experienced a significant decrease in test size across the PTB, mainly due to size-biased extinction and within-lineage change. The PTME was clearly a major catastrophe that affected many groups simultaneously, and the GLE was more selective, perhaps hinting at a subtler, less extreme driver than the later PTME.

TAXONOMIC CONSIDERATION AND STRATIGRAPHIC IMPLICATION OF THE ACCELERATED EVOLUTION OF THE MAASTRICHTIAN-EOCENE TRANSITION OF TWENTY BENTHIC FORAMINIFERAL SPECIES IN THE TETHYS

Within the Maastrichtian-Eocene transition in some localities in the Tethys, ten trends of accelerated evolution are recognized within twenty species belong to eight benthic foraminiferal genera: Siphogaudryina, Textularia, Pseudoclavulina, Pyramidulina, Frondicularia, Hopkinsina, Gyroidinoides and Angulogavelinella. Three out of the identified species are treated here to be new: Textularia haquei, Pyramidulina leroyi and Hopkinsina haquei. These lineages marked by changes in the morphology of the foraminiferal test, throughout the number, size and shape of chambers, ornamentation, size and position of aperture, suture and umbilicus. The identified Maastrichtian-Eocene species in this study are recognized in different localities in the Tethys: USA, France, Italy, Tunisia, Egypt, Jordan, UAE, Qatar and Pakistan.