From Pristine to Modified Ecosystems
31
An exception that proves Thorson’s rule has been provided recently by Gallardo and
Pencheszardeh (2001) in their study of the response of hatching mode to latitude in South
American littoral gastropods. On the Pacific coast, the rule is observed impeccably, the
proportion of prosobranch species having pelagic larvae decreasing poleward. But along
the Atlantic coast, benthic development predominates even into subtropical latitudes.
This difference, they say, is attributable to the different composition of the gastropod
faunas on the two coasts: the scarcity of pelagic development on the Atlantic shelf reflects
the near-continuous soft-bottom habitat there, whereas on the Pacific coast the benthic
habitat at all latitudes is more diverse. Thus, an exception to Thorson’s rule may be stated:
that, other things being equal, very soft muddy habitats favor the in situ development of
gastropod larvae at the expense of pelagic development.
From Pristine to Modified Ecosystems
I have suggested elsewhere, not entirely facetiously, that perhaps Intelligence is a deadly
pathogen that infects all habitable planets. Observations here on Earth show how rapidly
it learns to obtain energy by reversing the geochemical fluxes that hitherto maintained
the surface conditions of the planet hospitable to life. Intelligence appears to be capable
of sufficiently modifying the surface environment of a planet as to put its own survival
in doubt.
Indeed, the consequences of “intelligent” exploitation and management of marine
resources over the last century are such that they cannot now be ignored in any discussion
of the regional characteristics of marine ecosystems, even if this is not done in the spirit of
seeking solutions. I should state my position at the outset, so that you should not expect
any helpful suggestions in this section: these problems are without scientific solution.
Studies of the modification of the natural world have been a growth industry for
some decades even as the process continues, very little abated by the acquisition of an
understanding of what is happening. For the marine environment, I suppose that most
attention has been given to the problems of chemical contamination and its effects both
insidious and spectacular. Rather than adding to the torrent of material about marine
pollution, I propose instead to discuss—very briefly—two other aspects of our unintentional modification of marine ecosystems: first, the insidious corruption of biogeography
by the careless transport of organisms from one region to another and, second, the much
more spectacular modification of the structure of marine ecosystems by industrial fishing.
The unintentional transport of living organisms has increased significantly in recent
decades, principally because of recent change in the design of ships and shipping patterns.
Commercial ships are much larger and somewhat faster than they were 50 years ago,
and on every voyage may carry unintended passengers, either attached to their hulls or
in ballast water to be discharged when the ship takes on cargo. Examples of what has
been called the “globalization of marine ecosystems” abound in any appropriate text and
although we cannot know the rate at which nonindigenous species are transported, it
has been suggested that the rate at which we are discovering them in the Mediterranean
is very high: during the last 5 years, a new exotic species there has been recorded each
month in the scientific literature!
Most of these travelers are coastal biota, and we might think that this problem is
unlikely to occur—or that should it occur, it would have little significance—in the open
ocean. But this is not the case, and we must be prepared for significant changes to occur
in the entire pelagic ecosystem structure, as has occurred recently in the Black Sea (q.v.).
Diatoms, all older textbooks tell us, lie near the base of the open-ocean ecosystem.
Although, as we shall see in the next section, this is no longer seen to be a correct model,
31
An exception that proves Thorson’s rule has been provided recently by Gallardo and
Pencheszardeh (2001) in their study of the response of hatching mode to latitude in South
American littoral gastropods. On the Pacific coast, the rule is observed impeccably, the
proportion of prosobranch species having pelagic larvae decreasing poleward. But along
the Atlantic coast, benthic development predominates even into subtropical latitudes.
This difference, they say, is attributable to the different composition of the gastropod
faunas on the two coasts: the scarcity of pelagic development on the Atlantic shelf reflects
the near-continuous soft-bottom habitat there, whereas on the Pacific coast the benthic
habitat at all latitudes is more diverse. Thus, an exception to Thorson’s rule may be stated:
that, other things being equal, very soft muddy habitats favor the in situ development of
gastropod larvae at the expense of pelagic development.
From Pristine to Modified Ecosystems
I have suggested elsewhere, not entirely facetiously, that perhaps Intelligence is a deadly
pathogen that infects all habitable planets. Observations here on Earth show how rapidly
it learns to obtain energy by reversing the geochemical fluxes that hitherto maintained
the surface conditions of the planet hospitable to life. Intelligence appears to be capable
of sufficiently modifying the surface environment of a planet as to put its own survival
in doubt.
Indeed, the consequences of “intelligent” exploitation and management of marine
resources over the last century are such that they cannot now be ignored in any discussion
of the regional characteristics of marine ecosystems, even if this is not done in the spirit of
seeking solutions. I should state my position at the outset, so that you should not expect
any helpful suggestions in this section: these problems are without scientific solution.
Studies of the modification of the natural world have been a growth industry for
some decades even as the process continues, very little abated by the acquisition of an
understanding of what is happening. For the marine environment, I suppose that most
attention has been given to the problems of chemical contamination and its effects both
insidious and spectacular. Rather than adding to the torrent of material about marine
pollution, I propose instead to discuss—very briefly—two other aspects of our unintentional modification of marine ecosystems: first, the insidious corruption of biogeography
by the careless transport of organisms from one region to another and, second, the much
more spectacular modification of the structure of marine ecosystems by industrial fishing.
The unintentional transport of living organisms has increased significantly in recent
decades, principally because of recent change in the design of ships and shipping patterns.
Commercial ships are much larger and somewhat faster than they were 50 years ago,
and on every voyage may carry unintended passengers, either attached to their hulls or
in ballast water to be discharged when the ship takes on cargo. Examples of what has
been called the “globalization of marine ecosystems” abound in any appropriate text and
although we cannot know the rate at which nonindigenous species are transported, it
has been suggested that the rate at which we are discovering them in the Mediterranean
is very high: during the last 5 years, a new exotic species there has been recorded each
month in the scientific literature!
Most of these travelers are coastal biota, and we might think that this problem is
unlikely to occur—or that should it occur, it would have little significance—in the open
ocean. But this is not the case, and we must be prepared for significant changes to occur
in the entire pelagic ecosystem structure, as has occurred recently in the Black Sea (q.v.).
Diatoms, all older textbooks tell us, lie near the base of the open-ocean ecosystem.
Although, as we shall see in the next section, this is no longer seen to be a correct model,