Biomass depletion in the big picture

Debbie MacKenzie debimack at
Fri May 25 16:01:52 EDT 2001

Hi Coral-list,

The discussion on the causes of mass coral bleaching has been very
interesting, thanks, but I've still not gotten answers to two of my main
questions: Do you see a physical difference between what happens in mass
bleaching events and what you would expect to see in food starvation? - and
- Do you have any time-series data on the abundance of tropical ocean
zooplankton? A strong case can be made that fishing has made a large
contribution to the rise in atmospheric CO2.

Debbie MacKenzie


An increase in atmospheric CO2 is an expected consequence of removal of the
marine biota. It is demonstrated that the progressive fishing-induced
biomass depletion of the world’s ocean is a more plausible explanation for
what has triggered the rising CO2 in the atmosphere, than is our more
recent history of burning fossil fuels. Proof for the long-term trend in
biomass depletion is found by examining the contrasting pictures of
abundant marine species pre-fishing and the life-depleted status of the
world’s ocean today. The realization that biomass depletion has “bottom-up”
effects as well as “top-down” ones leads to the inevitable conclusion that
marine primary productivity is functioning at a significantly lower level
now than it did in the past, when the ocean-atmosphere maintained a steady
carbon balance. 

Humans cannot remember the great abundance of sea life that existed even
500 years ago...but the ocean can. Deep water circulation patterns today
bring carbon to the surface in ocean upwelling areas, in the same manner
and quantity as they always have. This carbon is “exhaled” to the
atmosphere in a process known as “outgassing.” What comes out of the sea is
“very old” carbon, the memory of marine primary production that took place
centuries ago. The deep water contains a vast pool of carbon, and it
circulates only very slowly; the average turnover time may be about 1000
years. For many thousands of years the ocean and atmosphere maintained a
carbon balance, and atmospheric levels were steady, but no longer. “New”
carbon cycled into the deep water annually balanced the amount that was
cycled out...but a rather long lag time exists between the two. Due to the
drop in marine primary productivity, todays carbon input to the deep water
falls significantly short of what is required to balance the amount that
the ocean sends out via “outgassing.” Due to the 1000 year lag time between
the input and output ends of the cycle, readjustment will take a while. The
ocean and atmosphere are seeking a new state of carbon balance. The amount
of CO2 exhaled annually by the ocean today represents the average amount of
carbon put into the deep pool on a yearly basis over the last 1000 years.
Due to the fishing-induced imbalance, CO2 levels in the atmosphere are
rising. For the past two centuries the sea has “exhaled” larger amounts of
CO2 than it has “inhaled.” This is an unrecognized consequence of human
fishing, and continued fishing will only exacerbate the situation. 

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