The Useful Results from 150 Years of Marine Biogeography
25
A further obvious difference between patterns of distribution of benthic and pelagic
organisms is the degree to which benthic distribution patterns are locked to physical
features of the coastal regions: both the pattern of the distribution of sediment types on
the continental shelf, and the association of the circulation pattern of water masses over
the shelf with coastal features such as gulfs, bays, capes and river mouths. However, some
of the major discontinuities in the distribution of benthic communities match those that
form the basis of pelagic biogeography. We shall return to this in detail later, but it is
striking to what extent the boundaries between the benthic faunistic subregions of Ekman
(1953) and Briggs (1974) match those that have been proposed by several authors for
the major faunistic subdivisions of the pelagos. These locations tend to be where major
frontal regions between oceanic gyres, or coastal boundary currents, intersect with the
coastline.
Biogeographic Regions of the Pelagos
The boundaries between physical oceanographic regimes are coincident with the primary
discontinuities in pelagic biogeography. So, in thinking about partitions in ecological
geography, we should perhaps first consider how far taxonomic biogeographers agree
on how to partition the oceans to reflect discontinuities in their data. Agreement, we
shall find, is quite good between individual suggestions, and most of them support the
thesis to be reviewed in the next chapter that links oceanic frontal regions to partitions
in ecological geography.
Not surprisingly, oceanic phytogeography, essentially based on the distributions of
diatoms (e.g., Semina, 1997), does not yield a partition as specific as marine zoogeography.
The generalized series of phytoplankton ranges suggested by Margalef in 1961 can be
sustained in more recent data, except that we now know that few species are entirely
excluded from one or other ocean basin: cosmopolitan distributions within climatic
zones appears to be the dominant pattern. The resultant partitions are not mutually
exclusive, presumably because of the extensive passive drift of cells, and do not form a
useful categorization of the surface ocean. Even less useful for our present purpose is
the recognition of “range bases” in the five subtropical gyres, and “expatriation areas”
elsewhere, by Semina. We have a much more comprehensive phytogeography of the
North Atlantic than for anywhere else, thanks to the many years of deployment of towed
Continuous Plankton Recorders from the Plymouth laboratory. In the Atlas of those data,
repetitive pattern is clear: arctic, Atlantic, and subtropical oceanic species of diatoms and
dinoflagellates are distinct, as are shelf species. Expatriation is also evident from these
areas. Had we equivalent observations for the whole ocean, the required partition would
perhaps become clear. But we do not have such observations, and consequently I shall
not expect to evoke a global partition of phytoplankton as for other organisms.
Reviews of historical progress in oceanic zoogeography generally start with the map
of Steuer (1933), based on copepod distributions. He recognized circumpolar arctic and
antarctic regions and then divided each ocean basin (where appropriate) into subpolar,
subtropical (north and south), and tropical regions. This is not very different from Sven
Ekman’s proposal at approximately the same time for a “pelagic warm-water fauna,
northern and southern cold-water plankton, and a neritic plankton.” In those early years,
the emphasis was on sea surface temperature as the primary determinant of pelagic
species distributions, so summer and winter boundaries between biogeographic zones
were often defined. Progressively, interest came to be given rather to features in the global
circulation rather than to temperature itself. Whatever the basis of the classification, all
authors were agreed on one thing: that the pelagic realm should be divided into zonal
features stretching across each ocean at approximately the same latitude. These zones
25
A further obvious difference between patterns of distribution of benthic and pelagic
organisms is the degree to which benthic distribution patterns are locked to physical
features of the coastal regions: both the pattern of the distribution of sediment types on
the continental shelf, and the association of the circulation pattern of water masses over
the shelf with coastal features such as gulfs, bays, capes and river mouths. However, some
of the major discontinuities in the distribution of benthic communities match those that
form the basis of pelagic biogeography. We shall return to this in detail later, but it is
striking to what extent the boundaries between the benthic faunistic subregions of Ekman
(1953) and Briggs (1974) match those that have been proposed by several authors for
the major faunistic subdivisions of the pelagos. These locations tend to be where major
frontal regions between oceanic gyres, or coastal boundary currents, intersect with the
coastline.
Biogeographic Regions of the Pelagos
The boundaries between physical oceanographic regimes are coincident with the primary
discontinuities in pelagic biogeography. So, in thinking about partitions in ecological
geography, we should perhaps first consider how far taxonomic biogeographers agree
on how to partition the oceans to reflect discontinuities in their data. Agreement, we
shall find, is quite good between individual suggestions, and most of them support the
thesis to be reviewed in the next chapter that links oceanic frontal regions to partitions
in ecological geography.
Not surprisingly, oceanic phytogeography, essentially based on the distributions of
diatoms (e.g., Semina, 1997), does not yield a partition as specific as marine zoogeography.
The generalized series of phytoplankton ranges suggested by Margalef in 1961 can be
sustained in more recent data, except that we now know that few species are entirely
excluded from one or other ocean basin: cosmopolitan distributions within climatic
zones appears to be the dominant pattern. The resultant partitions are not mutually
exclusive, presumably because of the extensive passive drift of cells, and do not form a
useful categorization of the surface ocean. Even less useful for our present purpose is
the recognition of “range bases” in the five subtropical gyres, and “expatriation areas”
elsewhere, by Semina. We have a much more comprehensive phytogeography of the
North Atlantic than for anywhere else, thanks to the many years of deployment of towed
Continuous Plankton Recorders from the Plymouth laboratory. In the Atlas of those data,
repetitive pattern is clear: arctic, Atlantic, and subtropical oceanic species of diatoms and
dinoflagellates are distinct, as are shelf species. Expatriation is also evident from these
areas. Had we equivalent observations for the whole ocean, the required partition would
perhaps become clear. But we do not have such observations, and consequently I shall
not expect to evoke a global partition of phytoplankton as for other organisms.
Reviews of historical progress in oceanic zoogeography generally start with the map
of Steuer (1933), based on copepod distributions. He recognized circumpolar arctic and
antarctic regions and then divided each ocean basin (where appropriate) into subpolar,
subtropical (north and south), and tropical regions. This is not very different from Sven
Ekman’s proposal at approximately the same time for a “pelagic warm-water fauna,
northern and southern cold-water plankton, and a neritic plankton.” In those early years,
the emphasis was on sea surface temperature as the primary determinant of pelagic
species distributions, so summer and winter boundaries between biogeographic zones
were often defined. Progressively, interest came to be given rather to features in the global
circulation rather than to temperature itself. Whatever the basis of the classification, all
authors were agreed on one thing: that the pelagic realm should be divided into zonal
features stretching across each ocean at approximately the same latitude. These zones