parallel series (e.g., Bolivina or Eggerelloides); and coiled
(e.g., Elphidium, Ammonia). Coiling also follows strict
patterns as each chamber is added in a spiral – either
planispiral when chambers are added along a single plane
(e.g., Haynesina, Elphidium) (Figure 1: 2, 5) or trochospiral
when chambers spiral along more than one plane, up into a
spire (e.g., Ammonia, Trochammina) (Figure 1: 6a, b).
The aperture (opening in the shell) can assume a variety
of shapes, positions, and forms and may include additional
structures such as teeth, tubercles, and flaps.
Taxonomically important are also other shell features
such as the shell margin (e.g., keeled or rounded) and surface ornamentation (e.g., bosses, costae, ridges, sutures).
For more detailed descriptions of shell morphology, see
Boltovskoy and Wright (1976) and Haynes (1981).
Biology
Pseudopodia: The foraminiferal shell functions as protection for the soft internal body. Cell interaction with the
external environment occurs via extensions of cytoplasm
called granuloreticulopodia (pseudopodia), which extend
from the test through the aperture. Granuloreticulopodia
branch, creating a network around the test, and carry out
many of the fundamental biological functions in foraminifera. They take part in growth, reproduction, respiration,
metabolism, test construction, locomotion, feeding, and
protection.
Trophic relationships: Benthic foraminifera have various feeding strategies including symbiosis (e.g.,
Alveolinidae), parasitism (e.g., Hyrrokkin sarcophaga),
suspension, and deposit feeding (e.g., Ammotium cassis,
Elphidium spp.) (Pawlowski, 2012). Foraminiferal diets
may include diatoms, dinoflagellates, macroalgae, organic
detritus, and bacteria. Some species are carnivorous and
ingest small copepods, shrimp larvae, and even other foraminifera (cannibalism). For some, the sediment surface
provides a sufficient amount of nourishment, while other
species dig into the sediment to find food. During feeding,
pseudopodia build a feeding cyst surrounding the shell
and provide a safe space for extra- or intracellular digestion (Murray, 1979). Pseudopodia often collect food and
transport it toward the aperture and inside the cell. In addition, some carnivorous species use pseudopodia to catch
prey and/or keep it in the net (e.g., Astrammina rara).
Locomotion: Some benthic foraminifera live attached
to the seabed by extending pseudopodia to anchor themselves to pebbles, macrophytes, mussel shells, or worm
tubes, thereby avoiding displacement by water masses.
Pseudopodia are also used to burrow into the sediments
to avoid predation or destruction and to change location
to find better food sources.
Growth and Reproduction: During growth, pseudopodia build a growing cyst, outlining a new chamber
frame and creating the base for calcification in calcareous
group and for gathering and attaching foreign particles to
in agglutinated group (Haynes, 1981). Benthic species follow a great variety of reproductive models, among which a
life cycle with two (sexual and asexual) generations is well
understood and described (Goldstein, 1999).
Ecology and geographic distribution
Though benthic foraminifera mainly occur in marine habitats, some families (e.g., Allogromidae and Lagenidae)
have been reported in freshwater or even terrestrial environments (Pawlowski, 2012). Benthic foraminifera interact with other components of meio- and macrofauna and
are influenced by a combination of abiotic and biotic factors. Abiotic factors include temperature, salinity, currents, light, dissolved oxygen, nutrients, pH, trace
elements, and substrate. Interaction with other organisms,
e.g., competition for space and food, symbiosis, grazing,
and parasitism, constitutes biotic factors (Murray, 2006).
Some species are more sensitive to ecological factors
and prefer narrow factor ranges, while others have wider
tolerance limits (Murray, 1991).
On the global scale, water depth, temperature, and
salinity are, perhaps, the leading factors determining distribution, diversity, and abundance of benthic foraminifera
(Boltovskoy and Wright, 1976).
The distribution of foraminifera within the water column is controlled by seawater saturation with respect to
CaCO 3 . Occurrence of calcareous assemblages at deepsea settings depends on the carbonate compensation depth
(CCD). The CCD in the central Pacific occurs between
4000–5000 m, while in the Atlantic Ocean, it lies deeper
at around 5000–6000 m (Boltovskoy and Wright, 1976).
Thus, ocean depths located above the CCD are characterized by a highly diverse and rich calcareous benthic fauna.
However, with increasing water depth, calcareous foraminifera decrease in abundance and disappear. Simultaneously, an increase in proportion of agglutinated and
organic-walled taxa takes place. Surface ocean waters
are generally saturated with CaCO 3 ; however, lower temperatures and higher atmospheric CO 2 may cause CaCO 3
dissolution in shallow areas at high latitudes, resulting in
rich agglutinated and organic-walled assemblages. Consequently, sediments from the Antarctic shelf (e.g., Weddell
and Ross Sea) where the CCD lies at 400-500 m water
depth are carbonate impoverished. However, there are a
few calcareous species adapted to such extreme conditions, e.g., Nuttallides umboniferus (Murray, 2006).
Salinity is of great importance to foraminifera in general. While planktonic species are more sensitive to salinity changes, most benthic foraminifera have broad salinity
tolerance ranges. Fully marine conditions (30–40 psu)
favor many benthic species and promote their reproduction, survival, and growth. Therefore, open oceans have
rich and well-preserved benthic foraminiferal assemblages. In environments with salinities <30 psu, foraminiferal reproduction decreases (Bradshaw, 1955;
Bradshaw, 1957) and tests have thinner walls, often loose
ornamentation, and become reduced in size or deformed
(e.g., Almogi-Labin et al., 1992; Stouff et al., 1999;
Polovodova and Schönfeld, 2008).
FORAMINIFERS (BENTHIC)
253
(e.g., Elphidium, Ammonia). Coiling also follows strict
patterns as each chamber is added in a spiral – either
planispiral when chambers are added along a single plane
(e.g., Haynesina, Elphidium) (Figure 1: 2, 5) or trochospiral
when chambers spiral along more than one plane, up into a
spire (e.g., Ammonia, Trochammina) (Figure 1: 6a, b).
The aperture (opening in the shell) can assume a variety
of shapes, positions, and forms and may include additional
structures such as teeth, tubercles, and flaps.
Taxonomically important are also other shell features
such as the shell margin (e.g., keeled or rounded) and surface ornamentation (e.g., bosses, costae, ridges, sutures).
For more detailed descriptions of shell morphology, see
Boltovskoy and Wright (1976) and Haynes (1981).
Biology
Pseudopodia: The foraminiferal shell functions as protection for the soft internal body. Cell interaction with the
external environment occurs via extensions of cytoplasm
called granuloreticulopodia (pseudopodia), which extend
from the test through the aperture. Granuloreticulopodia
branch, creating a network around the test, and carry out
many of the fundamental biological functions in foraminifera. They take part in growth, reproduction, respiration,
metabolism, test construction, locomotion, feeding, and
protection.
Trophic relationships: Benthic foraminifera have various feeding strategies including symbiosis (e.g.,
Alveolinidae), parasitism (e.g., Hyrrokkin sarcophaga),
suspension, and deposit feeding (e.g., Ammotium cassis,
Elphidium spp.) (Pawlowski, 2012). Foraminiferal diets
may include diatoms, dinoflagellates, macroalgae, organic
detritus, and bacteria. Some species are carnivorous and
ingest small copepods, shrimp larvae, and even other foraminifera (cannibalism). For some, the sediment surface
provides a sufficient amount of nourishment, while other
species dig into the sediment to find food. During feeding,
pseudopodia build a feeding cyst surrounding the shell
and provide a safe space for extra- or intracellular digestion (Murray, 1979). Pseudopodia often collect food and
transport it toward the aperture and inside the cell. In addition, some carnivorous species use pseudopodia to catch
prey and/or keep it in the net (e.g., Astrammina rara).
Locomotion: Some benthic foraminifera live attached
to the seabed by extending pseudopodia to anchor themselves to pebbles, macrophytes, mussel shells, or worm
tubes, thereby avoiding displacement by water masses.
Pseudopodia are also used to burrow into the sediments
to avoid predation or destruction and to change location
to find better food sources.
Growth and Reproduction: During growth, pseudopodia build a growing cyst, outlining a new chamber
frame and creating the base for calcification in calcareous
group and for gathering and attaching foreign particles to
in agglutinated group (Haynes, 1981). Benthic species follow a great variety of reproductive models, among which a
life cycle with two (sexual and asexual) generations is well
understood and described (Goldstein, 1999).
Ecology and geographic distribution
Though benthic foraminifera mainly occur in marine habitats, some families (e.g., Allogromidae and Lagenidae)
have been reported in freshwater or even terrestrial environments (Pawlowski, 2012). Benthic foraminifera interact with other components of meio- and macrofauna and
are influenced by a combination of abiotic and biotic factors. Abiotic factors include temperature, salinity, currents, light, dissolved oxygen, nutrients, pH, trace
elements, and substrate. Interaction with other organisms,
e.g., competition for space and food, symbiosis, grazing,
and parasitism, constitutes biotic factors (Murray, 2006).
Some species are more sensitive to ecological factors
and prefer narrow factor ranges, while others have wider
tolerance limits (Murray, 1991).
On the global scale, water depth, temperature, and
salinity are, perhaps, the leading factors determining distribution, diversity, and abundance of benthic foraminifera
(Boltovskoy and Wright, 1976).
The distribution of foraminifera within the water column is controlled by seawater saturation with respect to
CaCO 3 . Occurrence of calcareous assemblages at deepsea settings depends on the carbonate compensation depth
(CCD). The CCD in the central Pacific occurs between
4000–5000 m, while in the Atlantic Ocean, it lies deeper
at around 5000–6000 m (Boltovskoy and Wright, 1976).
Thus, ocean depths located above the CCD are characterized by a highly diverse and rich calcareous benthic fauna.
However, with increasing water depth, calcareous foraminifera decrease in abundance and disappear. Simultaneously, an increase in proportion of agglutinated and
organic-walled taxa takes place. Surface ocean waters
are generally saturated with CaCO 3 ; however, lower temperatures and higher atmospheric CO 2 may cause CaCO 3
dissolution in shallow areas at high latitudes, resulting in
rich agglutinated and organic-walled assemblages. Consequently, sediments from the Antarctic shelf (e.g., Weddell
and Ross Sea) where the CCD lies at 400-500 m water
depth are carbonate impoverished. However, there are a
few calcareous species adapted to such extreme conditions, e.g., Nuttallides umboniferus (Murray, 2006).
Salinity is of great importance to foraminifera in general. While planktonic species are more sensitive to salinity changes, most benthic foraminifera have broad salinity
tolerance ranges. Fully marine conditions (30–40 psu)
favor many benthic species and promote their reproduction, survival, and growth. Therefore, open oceans have
rich and well-preserved benthic foraminiferal assemblages. In environments with salinities <30 psu, foraminiferal reproduction decreases (Bradshaw, 1955;
Bradshaw, 1957) and tests have thinner walls, often loose
ornamentation, and become reduced in size or deformed
(e.g., Almogi-Labin et al., 1992; Stouff et al., 1999;
Polovodova and Schönfeld, 2008).
FORAMINIFERS (BENTHIC)
253