20
Chapter 2: Biogeographic Partition of the Ocean
were being recruited at some major oceanographic institutions. But despite all the effort
expended, even now—150 years after the Challenger voyage—the total number of species
in each major group of pelagic organisms is not even approximately agreed upon and we
have descriptions of the seasonal distribution of no more than a very small proportion
of them. Although a quantitative comparison cannot be made, the number of stations at
which marine plankton have been collected, identified, and enumerated must be many
orders of magnitude smaller than it is for the terrestrial invertebrates, although the area
of the oceans is more than twice that of the continents.
Sven Ekman (1953) remarked that biogeography should not confine itself simply to
describing the occurrence of living forms and arranging them regionally. It must also
proceed historically, and an important objective of biogeographers has long been to
understand the progressive dissemination of species or higher taxonomic groups during
the evolution of the ocean basins and seas. For this reason, a criterion very often used in
even relatively recent global biogeographic systems for marine biota (e.g., Briggs, 1974)
is the degree of endemism of the fauna of each region. Although ecologists must be
alert to the consequences of the opening and closing of connections between oceans
during geological time, this will not be a serious concern to them: ecologists will be more
concerned with the functional differences between the warm-water benthic fauna of the
western coasts of Atlantic and Pacific Oceans than with the wonderful occurrence on
each coast of a remnant of the Jurassic fauna, the horseshoe crabs Limulus polyphemus
and L. moluccensis.
Taxonomic Diversity: The Shifting Baseline
of Biogeography
The basis of biogeography is said to be the distribution of individual species, but this
simple adage is questionable today when the term species remains imprecise. Integration
of accumulated biogeographic data is hampered by the continual evolution of taxonomy,
so that biogeographers must work with a shifting taxonomic baseline.
Indeed, one of the more enduring discussions in biology has been about the nature of
“species.” Many biologists and the general public have become convinced in the couple
of centuries since Carolus Linnaeus that the diversity of animals and plants is necessarily
partitioned into this fundamental unit, although it has long been recognized that the
Linnaean binomial does not, in practice, represent a single level of biological organization.
During 50 years or more of modern discussion, biogeographers have settled down to
use the concept of the biological species, following the magisterial examination of the
“species problem” by Huxley (1942) that bears rereading today. We should remember
his admonition that taxonomy exists for human convenience and not in the interest of
“some Platonic eidos stored up in Heaven,” as he put it. He concluded that for everyday
biological purposes the binomial species, even if broadly interpreted, must remain the
central entity, although the trinomial geographic race or subspecies may also be required.
Since, in this view, the basic unit of taxonomy is loosely defined, closure of the global or
regional listing of species must remain an elusive objective.
The taxonomy of marine biota is almost entirely based on biological species and, to
classify the geographically separated populations of individual species, we have come to
use the very satisfactory trinomial nomenclature associated with this concept. Taxonomic
compilations, such as FishBase, are conformable with this arrangement and are useful
in some activities—as, for example, the management of marine fisheries. But, as I shall
discuss later, the new on-line taxonomic data archives may not be as useful as hoped,
both because they risk being undermined by a new “phylogenetic” taxonomy and also
Chapter 2: Biogeographic Partition of the Ocean
were being recruited at some major oceanographic institutions. But despite all the effort
expended, even now—150 years after the Challenger voyage—the total number of species
in each major group of pelagic organisms is not even approximately agreed upon and we
have descriptions of the seasonal distribution of no more than a very small proportion
of them. Although a quantitative comparison cannot be made, the number of stations at
which marine plankton have been collected, identified, and enumerated must be many
orders of magnitude smaller than it is for the terrestrial invertebrates, although the area
of the oceans is more than twice that of the continents.
Sven Ekman (1953) remarked that biogeography should not confine itself simply to
describing the occurrence of living forms and arranging them regionally. It must also
proceed historically, and an important objective of biogeographers has long been to
understand the progressive dissemination of species or higher taxonomic groups during
the evolution of the ocean basins and seas. For this reason, a criterion very often used in
even relatively recent global biogeographic systems for marine biota (e.g., Briggs, 1974)
is the degree of endemism of the fauna of each region. Although ecologists must be
alert to the consequences of the opening and closing of connections between oceans
during geological time, this will not be a serious concern to them: ecologists will be more
concerned with the functional differences between the warm-water benthic fauna of the
western coasts of Atlantic and Pacific Oceans than with the wonderful occurrence on
each coast of a remnant of the Jurassic fauna, the horseshoe crabs Limulus polyphemus
and L. moluccensis.
Taxonomic Diversity: The Shifting Baseline
of Biogeography
The basis of biogeography is said to be the distribution of individual species, but this
simple adage is questionable today when the term species remains imprecise. Integration
of accumulated biogeographic data is hampered by the continual evolution of taxonomy,
so that biogeographers must work with a shifting taxonomic baseline.
Indeed, one of the more enduring discussions in biology has been about the nature of
“species.” Many biologists and the general public have become convinced in the couple
of centuries since Carolus Linnaeus that the diversity of animals and plants is necessarily
partitioned into this fundamental unit, although it has long been recognized that the
Linnaean binomial does not, in practice, represent a single level of biological organization.
During 50 years or more of modern discussion, biogeographers have settled down to
use the concept of the biological species, following the magisterial examination of the
“species problem” by Huxley (1942) that bears rereading today. We should remember
his admonition that taxonomy exists for human convenience and not in the interest of
“some Platonic eidos stored up in Heaven,” as he put it. He concluded that for everyday
biological purposes the binomial species, even if broadly interpreted, must remain the
central entity, although the trinomial geographic race or subspecies may also be required.
Since, in this view, the basic unit of taxonomy is loosely defined, closure of the global or
regional listing of species must remain an elusive objective.
The taxonomy of marine biota is almost entirely based on biological species and, to
classify the geographically separated populations of individual species, we have come to
use the very satisfactory trinomial nomenclature associated with this concept. Taxonomic
compilations, such as FishBase, are conformable with this arrangement and are useful
in some activities—as, for example, the management of marine fisheries. But, as I shall
discuss later, the new on-line taxonomic data archives may not be as useful as hoped,
both because they risk being undermined by a new “phylogenetic” taxonomy and also