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Greetings fellow fishheads (and Lisa),
In reponse to:
> FURTHERMORE...since fishing has been dragging down the whole system for
> centuries, plankton levels have also been in decline for that length of
> time. This includes phytoplankton...and the result of the gradual drop
John Gibey wrote:
I still do not
understand why phytoplankton numbers should fall if you remove the fish,
surely the opposite would be the case?
Playing devil's advocate for a moment--this can easily be explained by a
trophic cascade argument--i.e. fewer fish allow zooplankton to flourish, and
the newly abundant zooplankton will draw down phytoplankton stocks (see
Carpenter et al. 1985).
Does this actually happen? Most of the examinations of the existence of
trophic cascades have been in limnetic systems, so its tough to say for
marine systems. The evidence from lake and mesocosm experiments seems to
indicate an 'uncoupling' at the zooplankton-phytoplankton link--i.e. changes
in zooplankton population size don't seem to effect phytoplankton
populations (see McQueen et al. 1988). This may be due to the very
different temporal (and spatial?) scales of fish, zooplankton, and
phytoplankton population control...
Debbie's ideas are not completely new, of course. Talk of 'fertilizing' the
ocean to increase fishery productivity has been going on for years. I
recall one of the plenary speakers at the 1999 ASLO convention discussing
how a certain company (sorry can't recall the name..) has bought up the
rights to all fishing in the EEZ around Fiji, and plans to dump nitrogen in
the water on a massive scale and then sit back and reap the increased
harvest (theoretically). They even patented the idea! (actually, I guess
that's a good thing--will keep other crackpots from doing it...). I
shudder to think what would actually happen to marine ecosystems if this
were actually allowed to happen.
Suffice it to say we aren't planning on stopping our nutrient reduction
efforts here in the Chesapeake Bay.
Cheers,
Bill
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Bill Mowitt
MD Dept. of Nat. Res. Fisheries Division
Tawes State Office Bldg. C-2
Annapolis, MD 21401
410-260-8263
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