24
Chapter 2: Biogeographic Partition of the Ocean
to the seed banks of forests. Here, many taxa of algae and heterotrophs exist, each taking
small numbers, but each available to populate a bloom under appropriate and different
conditions.
With all this, one cannot but agree but unfortunately it is difficult to know what is
in the minds of those who use the term biodiversity: is it political rectitude, a marketing
ploy, or an interesting analysis of the processes of microevolution? Unfortunately for
Margalef’s useful suggestion, I believe that the word has now lost the possibility of having
any special meaning. It will be better to leave it where it is now most useful, as a label
for well-meaning efforts to stem the loss of species from the biosphere. Further, we shall
then not need to consider such odd notions as the “levels of diversity that are useful for
Nature and for Society” (van der Spoel, 1994).
As Steele (1991) demonstrated, the most significant diversity in marine ecosystems
is functional diversity, or the variety of responses that any marine ecosystem can make
to environmental change. This concept has led to that of the regime shift in marine
ecosystems that we shall meet frequently in the following chapters. These shifts may
be caused either by a change in top-down forcing of ecosystem structure induced by the
removal of a large organism, as in the “trophic cascade” theory of lake ecosystems, or
in bottom-up forcing, induced by changes in the oceanographic regime. In neither case
can we advance our understanding as rapidly by simply concentrating our attention on
“biodiversity” or genetic richness, as we can by analysis of the structural diversity of the
ecosystems under question. Temporal shifts in ecosystem structure, contingent on shifts
in climatic regime, have been investigated principally in the eastern Pacific and to a lesser
extent on the European continental shelf, but the process certainly occurs everywhere.
In the chapters that follow, I shall want on many occasions to discuss the various and
complex manner in which the diversity of marine ecosystems varies in space, time and
function, but I shall not expect to use the term biodiversity again.
The Useful Results from 150 Years of Marine
Biogeography
It will be useful to remind ourselves at this juncture exactly what we are looking for from
the accumulated biogeographic literature, to know what will be useful to our purpose.
If we want to find a partition of the ecology of the oceans into biotopes comparable with
characteristic vegetation types ashore (forest, steppe, tundra, desert, and so on) we need
to know if changes in the distribution of the characteristic marine species assemblages
are spatially continuous, or are discontinuous? And if there are discontinuities between
them, how are they forced and are they predictable in space and time? All this shall be
discussed in the following chapter, but it will be useful to examine how the concept of
discontinuity emerged progressively in biogeographic studies.
Even a superficial examination of the subject reveals some simple principles. Perhaps
the most important is the consequence of the different motility of adult benthic and
pelagic organisms, even if both usually resort to planktonic larvae. Pelagic and planktonic
organisms are highly cosmopolitan and many species occur in all three nonpolar oceans,
while bipolarity is rather common. Benthic organisms of the continental shelves are, on
the other hand, rarely cosmopolitan so that very few species, although many genera, occur
in both Indo-Pacific and Atlantic faunas. Bipolarity in benthos is unusual—demersal
fish, for example, of boreal and austral polar seas have a very high degree of endemism.
Ekman suggests that 90% of species and 65% of genera of demersal fish of the austral
polar shelf are endemic.
Chapter 2: Biogeographic Partition of the Ocean
to the seed banks of forests. Here, many taxa of algae and heterotrophs exist, each taking
small numbers, but each available to populate a bloom under appropriate and different
conditions.
With all this, one cannot but agree but unfortunately it is difficult to know what is
in the minds of those who use the term biodiversity: is it political rectitude, a marketing
ploy, or an interesting analysis of the processes of microevolution? Unfortunately for
Margalef’s useful suggestion, I believe that the word has now lost the possibility of having
any special meaning. It will be better to leave it where it is now most useful, as a label
for well-meaning efforts to stem the loss of species from the biosphere. Further, we shall
then not need to consider such odd notions as the “levels of diversity that are useful for
Nature and for Society” (van der Spoel, 1994).
As Steele (1991) demonstrated, the most significant diversity in marine ecosystems
is functional diversity, or the variety of responses that any marine ecosystem can make
to environmental change. This concept has led to that of the regime shift in marine
ecosystems that we shall meet frequently in the following chapters. These shifts may
be caused either by a change in top-down forcing of ecosystem structure induced by the
removal of a large organism, as in the “trophic cascade” theory of lake ecosystems, or
in bottom-up forcing, induced by changes in the oceanographic regime. In neither case
can we advance our understanding as rapidly by simply concentrating our attention on
“biodiversity” or genetic richness, as we can by analysis of the structural diversity of the
ecosystems under question. Temporal shifts in ecosystem structure, contingent on shifts
in climatic regime, have been investigated principally in the eastern Pacific and to a lesser
extent on the European continental shelf, but the process certainly occurs everywhere.
In the chapters that follow, I shall want on many occasions to discuss the various and
complex manner in which the diversity of marine ecosystems varies in space, time and
function, but I shall not expect to use the term biodiversity again.
The Useful Results from 150 Years of Marine
Biogeography
It will be useful to remind ourselves at this juncture exactly what we are looking for from
the accumulated biogeographic literature, to know what will be useful to our purpose.
If we want to find a partition of the ecology of the oceans into biotopes comparable with
characteristic vegetation types ashore (forest, steppe, tundra, desert, and so on) we need
to know if changes in the distribution of the characteristic marine species assemblages
are spatially continuous, or are discontinuous? And if there are discontinuities between
them, how are they forced and are they predictable in space and time? All this shall be
discussed in the following chapter, but it will be useful to examine how the concept of
discontinuity emerged progressively in biogeographic studies.
Even a superficial examination of the subject reveals some simple principles. Perhaps
the most important is the consequence of the different motility of adult benthic and
pelagic organisms, even if both usually resort to planktonic larvae. Pelagic and planktonic
organisms are highly cosmopolitan and many species occur in all three nonpolar oceans,
while bipolarity is rather common. Benthic organisms of the continental shelves are, on
the other hand, rarely cosmopolitan so that very few species, although many genera, occur
in both Indo-Pacific and Atlantic faunas. Bipolarity in benthos is unusual—demersal
fish, for example, of boreal and austral polar seas have a very high degree of endemism.
Ekman suggests that 90% of species and 65% of genera of demersal fish of the austral
polar shelf are endemic.