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

Abstract

In Heterostegina depressa, the flagship species of laboratory investigations of larger benthic foraminifera (LBF) since the 70’s, the timing of reproduction, longevity and natural chamber building rates are still understudied. A recently developed method, the natural laboratory (sensu Hohenegger), has been applied on H. depressa populations from Sesoko Jima, NW Okinawa, Japan. An averaged chamber building rate and longevity of H. depressa were calculated based on 17 monthly samplings at fixed stations. All samples were collected at 20 and 50 m water depths using SCUBA. Live populations were dried and investigated by microCT. The monthly frequency distributions of chamber numbers and test diameters have been decomposed in normally distributed components. For each month, mean and standard deviations of the components were used to calculate the maximum chamber number and maximum test diameter. Based on these values, the natural chamber building rate (CBR) or diameter increase rate (DIR) could be estimated using the Michaelis-Menten function. CBR and DIR were inverted to estimate the ‘birthdate’ of all investigated individuals. Based on frequencies of these ‘birthdates’, main reproduction events could be detected and compared to the reproduction timing of other subtropical and tropical LBF taxa. Furthermore, peaks in reproduction could be linked to monsoon wet seasons (=“rainy seasons”) and winter rains.

Growth of the foraminifer <i>Nummulites venosus</i> in nature and culture

“…Pictures of each specimen were taken every four days, mostly during night when photosynthesis was inactive, to document chamber building and shell growth by size (Kinoshita et al 2017;Eder et al 2019). This interval was chosen to prevent disturbance of the chamber building process by shorter intervals.…”

“…After resting for 24 hours, living foraminifera identifiable by their complete coloring due to symbiotic microalgae were picked, put into smaller boxes and identified to the species level. Half of the species sample, washed in freshwater and dried, was sent to the Vienna University for growth investigation using the 'natural laboratory' approach (Hohenegger et al 2014(Hohenegger et al , 2019Kinoshita et al 2017;Eder et al 2019). From the remaining half put in larger petri dishes into the culture tank, the four largest and four smallest specimens were selected and separated into 4 small petri dishes combining one large and one small specimen.…”

Lunar cycles and rainy seasons drive growth and reproduction in nummulitid foraminifera, important producers of carbonate buildups

“…Using the natural laboratory approach 26 , first results on growth and reproduction based on chamber number and the largest diameter were published 27,28 . The present work presents and discusses cell volume growth of N .…”