the biomineralisation model of Elderfield et al. (1996). Elderfield et al. (1996)
observed that precipitation occurs at the mineralisation site, which is isolated from the
outside medium, however, the medium supplies the extraneous ions for precipitation.
The biomineralisation reservoir is similar but not necessarily identical to sea water in
composition. Sea water provides chemicals for calcification and controls the diffusion
gradient, and thus influences the test composition. Organisms probably extract calcium from vacuoles with sea water into the storage organelles (Elderfield et al. 1996).
According to Hottinger 2000) new chamber formation in Foraminifera includes
two processes: rhizopodial extrusion and biomineralisation. It seems that the rhizopodia play a key role in a test formation. A new chamber is built on a rhizopodial
skeleton formed by microtubules. In the next stage rhizopodial skeleton is saturated
with skeleton elements in a biomineralisation process (Hottinger 2000). Most
probably in a low mineralisation environment they cannot complete the precipitation of new test, but the naked rhizopodial skeleton is not hard enough to protect
them against predators and other unfavourable environmental conditions.
The following parameters seem to be involved in the control of foraminiferal
Mg/Ca and Sr/Ca ratios: water temperature, salinity, calcite saturation, carbonate
ions concentration, water pressure, ontogeny and growth rate (Elderfield et al. 1996;
Lea 2003; Dueñas-Bohórquez et al. 2009, 2011). An impact of salinity on foraminiferal calcification has been observed in several studies (e.g. van Raden et al.
2011). According to Dueñas-Bohórquez et al. (2009) the average Mg/Ca values of
planktonic Foraminifera Globigerinoides sacculifer increase in higher salinities
despite the relatively large inter-individual variability. Ferguson et al. (2008) suggested that salinity is the most likely environmental factor to explain unusually high
Mg/Ca ratios of Mediterranean Foraminifera. They recorded that correlations of
Mg/Ca with the salinity at which organisms calcified were more highly significant
than those with calcification temperatures.
5 Discussion
In general, both Foraminifera and ostracods are highly adaptable and efficient
colonisers of new aquatic habitats. A key to success for the Foraminifera has been
that they are not highly specialised. Leven (2010) claims that the reason why some
species of Fusulinida (e.g. Pseudostaffella) became extinct in the Middle Carboniferous, was because they attained too high a degree of specialisation. In general,
Foraminifera as simple, unicellular organisms maintained high plasticity and the
ability to adapt to changing environmental conditions. Ostracods are more specialised but they have flexible genetic systems which allow species to readily adapt
to the local environment (Carbonel et al. 1988).
Calcification in Foraminifera probably appeared during the Early Cambrian
radiation, when miliolid and agglutinated Foraminifera separated from each other
(Pawlowski et al. 2003). Building the test was one of the key adaptations for the
initial diversification of Foraminifera. The test provided some protection against
106
A. Iglikowska and J. Pawłowska
observed that precipitation occurs at the mineralisation site, which is isolated from the
outside medium, however, the medium supplies the extraneous ions for precipitation.
The biomineralisation reservoir is similar but not necessarily identical to sea water in
composition. Sea water provides chemicals for calcification and controls the diffusion
gradient, and thus influences the test composition. Organisms probably extract calcium from vacuoles with sea water into the storage organelles (Elderfield et al. 1996).
According to Hottinger 2000) new chamber formation in Foraminifera includes
two processes: rhizopodial extrusion and biomineralisation. It seems that the rhizopodia play a key role in a test formation. A new chamber is built on a rhizopodial
skeleton formed by microtubules. In the next stage rhizopodial skeleton is saturated
with skeleton elements in a biomineralisation process (Hottinger 2000). Most
probably in a low mineralisation environment they cannot complete the precipitation of new test, but the naked rhizopodial skeleton is not hard enough to protect
them against predators and other unfavourable environmental conditions.
The following parameters seem to be involved in the control of foraminiferal
Mg/Ca and Sr/Ca ratios: water temperature, salinity, calcite saturation, carbonate
ions concentration, water pressure, ontogeny and growth rate (Elderfield et al. 1996;
Lea 2003; Dueñas-Bohórquez et al. 2009, 2011). An impact of salinity on foraminiferal calcification has been observed in several studies (e.g. van Raden et al.
2011). According to Dueñas-Bohórquez et al. (2009) the average Mg/Ca values of
planktonic Foraminifera Globigerinoides sacculifer increase in higher salinities
despite the relatively large inter-individual variability. Ferguson et al. (2008) suggested that salinity is the most likely environmental factor to explain unusually high
Mg/Ca ratios of Mediterranean Foraminifera. They recorded that correlations of
Mg/Ca with the salinity at which organisms calcified were more highly significant
than those with calcification temperatures.
5 Discussion
In general, both Foraminifera and ostracods are highly adaptable and efficient
colonisers of new aquatic habitats. A key to success for the Foraminifera has been
that they are not highly specialised. Leven (2010) claims that the reason why some
species of Fusulinida (e.g. Pseudostaffella) became extinct in the Middle Carboniferous, was because they attained too high a degree of specialisation. In general,
Foraminifera as simple, unicellular organisms maintained high plasticity and the
ability to adapt to changing environmental conditions. Ostracods are more specialised but they have flexible genetic systems which allow species to readily adapt
to the local environment (Carbonel et al. 1988).
Calcification in Foraminifera probably appeared during the Early Cambrian
radiation, when miliolid and agglutinated Foraminifera separated from each other
(Pawlowski et al. 2003). Building the test was one of the key adaptations for the
initial diversification of Foraminifera. The test provided some protection against
106
A. Iglikowska and J. Pawłowska