271
carbonate carbon and 25.6 % to organic carbon. If these figures are combined to yield typical
pteropod values, the resulting C/N ratio for the whole animal is 7.2, i.e. an increase by about
11 % with respect to the value in the organic matter. Omori (1969) tabulated weight
measurements and elemental analyses for a number of zooplankton species in the North
Pacific, including four pteropods; the highest C/N value, for Limacina infiata, is 12.9, a 95%
increase over the Redfield ratio. Whether or not the pteropod specimens were decalcified prior
to analysis is not explicitly stated, but indirect clues suggest that they were not, and that it is
reasonable to assume that the reported discrepancy with respect to the Redfield ratio is largely
due to carbonate carbon. The same is true for Beers (1966) data from the Sargasso Sea, where
the C/N ratio for pteropods ranges from 6.4 to 9.7, with a mean value of 8.2, i.e. a 24%
increase over the Redfield ratio.
At least part of the thecosomatous pteropods occupy a specialized niche in the pelagic trophic
webs. Together with gelatinous organisms (e.g. salps and appendicularians), they are among
a number of forms that use ciliary-mucous mechanisms to collect their food; these mechanisms
are part of a filtration system in the gelatinous plankters and take the form of an external net
in the pteropods. As a result, these organisms are most often able to feed on very small
particles, down to bacterial size in the case of appendicularians (King et al., 1980). The
ability to feed on protozoan-sized plankton is well-documented in the pteropod genus Limacina
(e.g. Longhurst and Williams, 1979), although the larger species, such as L. helkina also use
their net to capture metazoans such as small copepods (Gilmer and Harbison, 1990). Large
populations of small pteropods tend to develop by feeding on protozoans preying upon
bacteria, in situations where the latter are recycling accumulated particulate organic matter
(see Le Fevre and Frontier, 1988). In northern temperate seas, pteropods can accordingly be
expected to dominate in autumn, when significant recycling of the biomass built up in the
productive season takes place. Indeed, in the Norwegian Current region, Peinert et al. (1989)
report that Limacina are quite abundant at the time when the copepod populations significantly
decrease and that Limacina shells are a major component of the material recovered in
sediment traps (at a depth of 1000 m) from September to November (and at that time of the
year only). In European waters, high abundance of Limacina has also been reported earlier
in the annual cycle, in situations where large phytoplankton stocks were apparently being
decomposed by bacteria rather than being grazed upon by herbivores (Le Fevre, 1986). More
carbonate carbon and 25.6 % to organic carbon. If these figures are combined to yield typical
pteropod values, the resulting C/N ratio for the whole animal is 7.2, i.e. an increase by about
11 % with respect to the value in the organic matter. Omori (1969) tabulated weight
measurements and elemental analyses for a number of zooplankton species in the North
Pacific, including four pteropods; the highest C/N value, for Limacina infiata, is 12.9, a 95%
increase over the Redfield ratio. Whether or not the pteropod specimens were decalcified prior
to analysis is not explicitly stated, but indirect clues suggest that they were not, and that it is
reasonable to assume that the reported discrepancy with respect to the Redfield ratio is largely
due to carbonate carbon. The same is true for Beers (1966) data from the Sargasso Sea, where
the C/N ratio for pteropods ranges from 6.4 to 9.7, with a mean value of 8.2, i.e. a 24%
increase over the Redfield ratio.
At least part of the thecosomatous pteropods occupy a specialized niche in the pelagic trophic
webs. Together with gelatinous organisms (e.g. salps and appendicularians), they are among
a number of forms that use ciliary-mucous mechanisms to collect their food; these mechanisms
are part of a filtration system in the gelatinous plankters and take the form of an external net
in the pteropods. As a result, these organisms are most often able to feed on very small
particles, down to bacterial size in the case of appendicularians (King et al., 1980). The
ability to feed on protozoan-sized plankton is well-documented in the pteropod genus Limacina
(e.g. Longhurst and Williams, 1979), although the larger species, such as L. helkina also use
their net to capture metazoans such as small copepods (Gilmer and Harbison, 1990). Large
populations of small pteropods tend to develop by feeding on protozoans preying upon
bacteria, in situations where the latter are recycling accumulated particulate organic matter
(see Le Fevre and Frontier, 1988). In northern temperate seas, pteropods can accordingly be
expected to dominate in autumn, when significant recycling of the biomass built up in the
productive season takes place. Indeed, in the Norwegian Current region, Peinert et al. (1989)
report that Limacina are quite abundant at the time when the copepod populations significantly
decrease and that Limacina shells are a major component of the material recovered in
sediment traps (at a depth of 1000 m) from September to November (and at that time of the
year only). In European waters, high abundance of Limacina has also been reported earlier
in the annual cycle, in situations where large phytoplankton stocks were apparently being
decomposed by bacteria rather than being grazed upon by herbivores (Le Fevre, 1986). More