Calcareous Dinoflagellate Cysts as Paleo-Environmental Tools
147
mobile. As a consequence, they sink through the
water column towards the bottom of seas and
oceans where they may be fossillized. Several factors such as temperature, day length, irradiance and
nutrient depletion have been studied as possible triggers related to sexuality and resulting encystment
(e.g. Pfiester and Anderson 1987). Among these
factors, nutrient depletion, especially nitrogen (N)
and/or phosphorus (P) deficiency that often occur
at the termination of a dinoflagellate bloom, has been
indicated to be a primary trigger for encystment
(e.g. Anderson et a!. 1984, 1985b; Ishikawa and
Taniguchi 1996). Recently Ishikawa and Taniguchi
(1996) observed that this may also hold for the encystment of the calcareous cysts of Scrippsiella
trochoidea (Stein) Loeblich III in the Onagawa
Bay (Japan). Although they observed that complete
nutrient depletion in the Bay rarely occurred, they
suggest that rapid decreases in nutrient concentrations as well as extended periods with low N and P
concentration gradually decreased cellular nutrient
reserves and enhanced sexual reproduction. It has
been observed both in culture experiments and in
the natural environments that the rate of encystment
of Scrippsiella trochoidea displays an annual pattern of oscillation (Costas and Varela 1989;
Ishikawa and Taniguchi 1996). This suggests that
an endogenous annual encystment rhythm might be
another factor influencing cyst formation.
A common feature for dinoflagellate resting
cysts is the existence of a dormancy period during
which cyst germination apparently cannot occur
(e.g. Dale 1983; Binder and Anderson 1987; Taylor
1987). These dormancy periods may be affected
by storage temperatures with low temperatures
increasing the dormancy period. For the calcareous resting cyst of Scrippsiella trochoideathis dormancy period is observed to last approximately 25
days (Binder and Anderson 1987). For cysts of this
species it has been shown that temperature and
light are primary factors controlling germination
(Dale 1983; Binder and Anderson 1986; Pfiester
and Anderson 1987; Ishikawa and Taniguchi 1996).
Light availability (a pulse as short as one second is
shown to be sufficient) is essential for cyst to germinate whereas temperature probably just controls
the germination rate. Ishikawa and Taniguchi (1996)
suggest that decreased amounts of dissolved oxygen might hamper germination of Scrippsiella
trochoidea in waters of Onagawa Bay (Japan).
They also observed an annual germination rhythm
and assume this, too, to be endogenously controlled.
(Paleo-) Ecology
Although calcareous cysts have frequently been
observed in Late Quaternary to recent sediments,
these occurrences have been mainly restricted to
single observations (Kamptner 1963; Wall and Dale
1968; Muller 1976; Versteegh 1993). These studies generally have a taxonomic character and only
little attention has been given to the (paleo-) ecology of calcareous dinoflagellates. The few studies
presently available on recent distribution patterns
of dinoflagellate cysts, which include their calcareous forms, suggest that they are most abundant in
open oceanic tropical-subtropical environments
(e.g. Kamptner 1967; Wall and Dale 1968; Futterer
1976; Muller 1976; Dale and Dale 1992). As yet,
only one time series of calcareous cysts covering
the last 140.000 years is available from the eastern
Equatorial Atlantic (Core GeoB 1105-4; Holl eta!.
1998). Holl et a!. (1998) compared variations in the
calcareous cyst assemblage from the Late Quaternary eastern Equatorial Atlantic with those in the
ecologically much better known organic-walled
dinoflagellate cysts assemblage. They showed that
calcareous cysts have elevated abundances in
periods of relatively high temperatures and reduced
productivity in the upper water column. Statistical
analyses indicate that, in the studied region, variations in cyst abundance are not related to temperature but rather to changes in productivity. Therefore, it is suggested that calcareous cyst formation
may be enhanced under stratified and relatively
oligotrophic conditions.
Also for the pre-Quaternary period, most studies on calcareous dinoflagellates have a taxonomic
character and only limited information is presented
on.the paleo-ecology of cysts. However, some attempts have been made to relate variations in cyst
associations, diversity and morphological variability of individual species to paleoenvironmental
changes (e.g. Keupp 1981; Keupp and Mutterlose
1984; Zugel 1994; Kohring 1993; Keupp 1991).
147
mobile. As a consequence, they sink through the
water column towards the bottom of seas and
oceans where they may be fossillized. Several factors such as temperature, day length, irradiance and
nutrient depletion have been studied as possible triggers related to sexuality and resulting encystment
(e.g. Pfiester and Anderson 1987). Among these
factors, nutrient depletion, especially nitrogen (N)
and/or phosphorus (P) deficiency that often occur
at the termination of a dinoflagellate bloom, has been
indicated to be a primary trigger for encystment
(e.g. Anderson et a!. 1984, 1985b; Ishikawa and
Taniguchi 1996). Recently Ishikawa and Taniguchi
(1996) observed that this may also hold for the encystment of the calcareous cysts of Scrippsiella
trochoidea (Stein) Loeblich III in the Onagawa
Bay (Japan). Although they observed that complete
nutrient depletion in the Bay rarely occurred, they
suggest that rapid decreases in nutrient concentrations as well as extended periods with low N and P
concentration gradually decreased cellular nutrient
reserves and enhanced sexual reproduction. It has
been observed both in culture experiments and in
the natural environments that the rate of encystment
of Scrippsiella trochoidea displays an annual pattern of oscillation (Costas and Varela 1989;
Ishikawa and Taniguchi 1996). This suggests that
an endogenous annual encystment rhythm might be
another factor influencing cyst formation.
A common feature for dinoflagellate resting
cysts is the existence of a dormancy period during
which cyst germination apparently cannot occur
(e.g. Dale 1983; Binder and Anderson 1987; Taylor
1987). These dormancy periods may be affected
by storage temperatures with low temperatures
increasing the dormancy period. For the calcareous resting cyst of Scrippsiella trochoideathis dormancy period is observed to last approximately 25
days (Binder and Anderson 1987). For cysts of this
species it has been shown that temperature and
light are primary factors controlling germination
(Dale 1983; Binder and Anderson 1986; Pfiester
and Anderson 1987; Ishikawa and Taniguchi 1996).
Light availability (a pulse as short as one second is
shown to be sufficient) is essential for cyst to germinate whereas temperature probably just controls
the germination rate. Ishikawa and Taniguchi (1996)
suggest that decreased amounts of dissolved oxygen might hamper germination of Scrippsiella
trochoidea in waters of Onagawa Bay (Japan).
They also observed an annual germination rhythm
and assume this, too, to be endogenously controlled.
(Paleo-) Ecology
Although calcareous cysts have frequently been
observed in Late Quaternary to recent sediments,
these occurrences have been mainly restricted to
single observations (Kamptner 1963; Wall and Dale
1968; Muller 1976; Versteegh 1993). These studies generally have a taxonomic character and only
little attention has been given to the (paleo-) ecology of calcareous dinoflagellates. The few studies
presently available on recent distribution patterns
of dinoflagellate cysts, which include their calcareous forms, suggest that they are most abundant in
open oceanic tropical-subtropical environments
(e.g. Kamptner 1967; Wall and Dale 1968; Futterer
1976; Muller 1976; Dale and Dale 1992). As yet,
only one time series of calcareous cysts covering
the last 140.000 years is available from the eastern
Equatorial Atlantic (Core GeoB 1105-4; Holl eta!.
1998). Holl et a!. (1998) compared variations in the
calcareous cyst assemblage from the Late Quaternary eastern Equatorial Atlantic with those in the
ecologically much better known organic-walled
dinoflagellate cysts assemblage. They showed that
calcareous cysts have elevated abundances in
periods of relatively high temperatures and reduced
productivity in the upper water column. Statistical
analyses indicate that, in the studied region, variations in cyst abundance are not related to temperature but rather to changes in productivity. Therefore, it is suggested that calcareous cyst formation
may be enhanced under stratified and relatively
oligotrophic conditions.
Also for the pre-Quaternary period, most studies on calcareous dinoflagellates have a taxonomic
character and only limited information is presented
on.the paleo-ecology of cysts. However, some attempts have been made to relate variations in cyst
associations, diversity and morphological variability of individual species to paleoenvironmental
changes (e.g. Keupp 1981; Keupp and Mutterlose
1984; Zugel 1994; Kohring 1993; Keupp 1991).