Growth, chamber building rate and reproduction time of Palaeonummulites venosus (Foraminifera) under natural conditions

Abstract

We investigated the symbiont-bearing benthic foraminifer Palaeonummulites venosus to determine the chamber building rate (CBR), test diameter increase rate (DIR), reproduction time and longevity using the 'natural laboratory' approach. This is based on the decomposition of monthly obtained frequency distributions of chamber number and test diameter into normally distributed components. Test measurements were taken using MicroCT. The shift of the mean and standard deviation of component parameters during the 15-month investigation period was used to calculate Michaelis-Menten functions applied to estimate the averaged CBR and DIR under natural conditions. The individual dates of birth were estimated using the inverse averaged CBR and the inverse DIR fitted by the individual chamber number or the individual test diameter at the sampling date. Distributions of frequencies and densities (i.e., frequency divided by sediment weight) based on both CBR and DIR revealed continuous reproduction throughout the year with two peaks, a stronger one in June determined as the onset of the summer generation (generation 1) and a weaker one in November determined as the onset of the winter generation (generation 2). This reproduction scheme explains the presence of small and large specimens in the same sample. Longevity, calculated as the maximum difference in days between the individual's birth date and the sampling date, is approximately 1.5 yr, an estimation obtained by using both CBR and DIR.

Strategies in times of crisis—insights into the benthic foraminiferal record of the Palaeocene–Eocene Thermal Maximum

“…Many foraminifers grow by sequentially adding chambers and hence preserve their entire ontogeny in their morphology [ 27 ], which can be revealed by tomography [ 28 , 29 ], a technique using X-rays to reveal the internal features of objects. Some benthic foraminifers can alternate between sexual and asexual reproduction, as recorded in the size of the first chamber (proloculus) [ 30 ]: the asexually produced, haploid generation generally has a large proloculus and is called megalospheric, whereas the sexually produced diploid generation usually has a smaller proloculus and is called microspheric [ 31 ].…”

Growth estimation of the larger foraminifer Heterostegina depressa by means of population dynamics

“…This is very similar for both water depths starting at 20 m with 1.82 chambers/day (Generation 2) and 1.90 chambers/day (Generation 3); at 50 m this is 1.84 chambers/day (Generation 2) and 1.84 chambers/day (Generation 3). Interestingly, the initial growth of H. depressa is thus much faster than of P. venosus (Kinoshita et al, 2017), which may be caused by the smaller proloculus (∼1/3) and initial chambers size of H. depressa . Furthermore, it should be remarked that according to Eder, Hohenegger & Briguglio (2017) only schizonts of Heterostegina depressa can be found ∼20 m water depth around Sesoko Jima.…”

“…The estimation of longevity have not been calculated in accordance to Hohenegger, Briguglio & Eder (2014), but rather by computing the maximum difference in days between individual reproduction date and sampling date (Kinoshita et al, 2017) …”

“…For the study of reproduction timing, growth and life expectancy of LBF under natural conditions, the ‘natural laboratory’ (Hohenegger, Briguglio & Eder (2014) has been developed. This methodology has been already applied on some porcelaneous eulittoral species (e.g., Peneroplis antillarum , Hohenegger, 2006) and the sublittoral P. venosus (Kinoshita et al, 2017). Apart from that, a similar methodology has been applied on biostromes of the shallow-marine brachiopod Magellania venosa (Baumgarten et al, 2014).…”

“…By observing the mean size of population over one to one and half years in monthly intervals, a growth rate for test diameter and chamber number for the larger benthic foraminifera H. depressa has been modelled. The results are compared with known long-term cultures, especially Röttger (1972b), and Krüger (1994), as well as results of P. venosus (Kinoshita et al, 2017).…”