The Four Primary Biomes of the Upper Ocean
91
networks) changes regionally, because this is clearly an attribute likely to take characteristic
values for individual ecosystems (or biomes): unfortunately, for very few water bodies
is there a complete enumeration of the species present, let alone any comprehensive
measure of characteristic ecosystem diversity. A good illustration of this problem is
provided by one of the most complete and recent enumerations of pelagic biota, that of
Margalef (1994), which compares species lists of phytoplankton from small flagellates to
very large dinoflagellates and diatoms taken at two stations, one each in the Caribbean
and in the western Mediterranean. These yielded lists of 353 and 257 named species,
respectively, with about 50 more unidentified taxa at each. To complete an inventory
of autotrophic cells, to these counts would have to be added the flagellate flora of the
nano- and ultraplankton and the cells of the photosynthetic picoplankton (cyanobacteria
and prochlorophytes). It is very unusual to be able to locate even single samples of
the heterotrophs (micronekton, meso- and micro-metazoans, and the protists) that have
been analyzed taxonomically as well as Margalef ’s phytoplankton.
To obtain regional fields of diversity within which we might hope to discern discontinuities, we would need observations such as those described by Margalef (but completed
by inclusion of all taxonomic groups) on a suitable grid across the ocean, repeated seasonally. Obviously, as was discussed in Chapter 2, such information exists for no group
of organisms, and probably for no location in all the oceans is there a complete listing
of the kind required.
Another way of proceeding would be to seek information on the global distribution of
biota at higher taxonomic levels than species, hoping to aggregate these into ecologically
meaningful groups. It is reasonable to hope that such data might be accessible in a
more uniform format than the almost hopelessly diverse descriptions of species lists
at individual stations that can be found in the biogeographic literature. Fortunately,
the Smithsonian Institution has for many years used a standardized first-order sorting
technique for the plankton samples it archives, and these protocols have been adopted
uniformly by other sorting centers. An archive of these sheets from several plankton
sorting centers thus enables a first-order analysis of the composition of zooplankton
globally; in one case, this was done with data from 4166 stations from all oceans where
sampling nets had been worked between the surface and 250 m (Longhurst, 1985b).
The counts were allocated to six functional groups (gelatinous predators, raptorial
predators, micro- and macroparticle herbivores, omnivores, and detritivores) and also
among taxonomic groups (medusae, siphonophores, chaetognaths, polychaetes, ostracods, copepods, mysids, euphausiids, and pteropods). These counts were then stratified
regionally and seasonally to represent first-order differences between oceans and continental shelf faunas of the polar, temperate, and tropical zones. The general results are
shown in Table 6.1, which enables the quantification of some latitudinal trends and
seasonal changes in plankton composition that were well known for only a few study
sites, although also suspected to occur more generally.
To illustrate the possibilities offered by such data, note how they quantify the change
in dominance of copepods from 67% of zooplankton biomass in polar seas to 33% in the
tropics, and how predators (both gelatinous and raptorial) increase from 22% in high
latitudes to 47% at low latitudes. A striking aspect of these zonal differences is the increasing contribution of gelatinous predators equatorward: from 0.9% of total zooplankton
biomass in polar latitudes to 14.3% in the tropics. The more equal distribution of relative
biomass among both the taxonomic and trophic groups in the tropical, compared with
the polar, seas is also clearly recorded.
Other data can also be consulted for confirmation of regional boundaries established
otherwise: consider the case of calanoid diversity in the samples from the Continuous
Plankton Recorder (CPR) survey of the North Atlantic. Long-term taxonomic richness of
calanoid copepods in several thousand transects (Beaugrand et al., 2000a) shows a zonal
91
networks) changes regionally, because this is clearly an attribute likely to take characteristic
values for individual ecosystems (or biomes): unfortunately, for very few water bodies
is there a complete enumeration of the species present, let alone any comprehensive
measure of characteristic ecosystem diversity. A good illustration of this problem is
provided by one of the most complete and recent enumerations of pelagic biota, that of
Margalef (1994), which compares species lists of phytoplankton from small flagellates to
very large dinoflagellates and diatoms taken at two stations, one each in the Caribbean
and in the western Mediterranean. These yielded lists of 353 and 257 named species,
respectively, with about 50 more unidentified taxa at each. To complete an inventory
of autotrophic cells, to these counts would have to be added the flagellate flora of the
nano- and ultraplankton and the cells of the photosynthetic picoplankton (cyanobacteria
and prochlorophytes). It is very unusual to be able to locate even single samples of
the heterotrophs (micronekton, meso- and micro-metazoans, and the protists) that have
been analyzed taxonomically as well as Margalef ’s phytoplankton.
To obtain regional fields of diversity within which we might hope to discern discontinuities, we would need observations such as those described by Margalef (but completed
by inclusion of all taxonomic groups) on a suitable grid across the ocean, repeated seasonally. Obviously, as was discussed in Chapter 2, such information exists for no group
of organisms, and probably for no location in all the oceans is there a complete listing
of the kind required.
Another way of proceeding would be to seek information on the global distribution of
biota at higher taxonomic levels than species, hoping to aggregate these into ecologically
meaningful groups. It is reasonable to hope that such data might be accessible in a
more uniform format than the almost hopelessly diverse descriptions of species lists
at individual stations that can be found in the biogeographic literature. Fortunately,
the Smithsonian Institution has for many years used a standardized first-order sorting
technique for the plankton samples it archives, and these protocols have been adopted
uniformly by other sorting centers. An archive of these sheets from several plankton
sorting centers thus enables a first-order analysis of the composition of zooplankton
globally; in one case, this was done with data from 4166 stations from all oceans where
sampling nets had been worked between the surface and 250 m (Longhurst, 1985b).
The counts were allocated to six functional groups (gelatinous predators, raptorial
predators, micro- and macroparticle herbivores, omnivores, and detritivores) and also
among taxonomic groups (medusae, siphonophores, chaetognaths, polychaetes, ostracods, copepods, mysids, euphausiids, and pteropods). These counts were then stratified
regionally and seasonally to represent first-order differences between oceans and continental shelf faunas of the polar, temperate, and tropical zones. The general results are
shown in Table 6.1, which enables the quantification of some latitudinal trends and
seasonal changes in plankton composition that were well known for only a few study
sites, although also suspected to occur more generally.
To illustrate the possibilities offered by such data, note how they quantify the change
in dominance of copepods from 67% of zooplankton biomass in polar seas to 33% in the
tropics, and how predators (both gelatinous and raptorial) increase from 22% in high
latitudes to 47% at low latitudes. A striking aspect of these zonal differences is the increasing contribution of gelatinous predators equatorward: from 0.9% of total zooplankton
biomass in polar latitudes to 14.3% in the tropics. The more equal distribution of relative
biomass among both the taxonomic and trophic groups in the tropical, compared with
the polar, seas is also clearly recorded.
Other data can also be consulted for confirmation of regional boundaries established
otherwise: consider the case of calanoid diversity in the samples from the Continuous
Plankton Recorder (CPR) survey of the North Atlantic. Long-term taxonomic richness of
calanoid copepods in several thousand transects (Beaugrand et al., 2000a) shows a zonal