Ed Caryl likes to research, and a short time ago wrote an essay about phytoplankton, see here. Some readers pointed out a flaw, and so Ed has insisted on posting a correction – as is appropriate in science. Happens to the best of us. (We’re not Penn State or CRU here).
The Phytoplankton are not Starving
By Ed Caryl
In a comment to the original article, The Phytoplankton are Starving, R. de Hann made the following comment:
So I have big trouble accepting the loss of plankton for fact.
In regard to the claim of over-fishing and fishing methods (by other reports), which is a serious problem in several places, we see the gap of lost volume filled up with other species very quickly.
We know for example that tuna eat jellyfish and in those waters where the tuna numbers have been reduced the numbers of jellyfish have exploded, compensating for the “loss of mass”.
So one species is quickly replaced by another.
Willis Eschenbach made this comment:
Humans catch and remove about 70 million tonnes of mostly big fish from the ocean annually. But the amount of mass at each trophic level reduces by about 90%. Tuna are four trophic levels up from phytoplankton. This means that for every kilo (pound) of fish that we eat, there are about 10,000 kilos (pounds) of phytoplankton that are supporting that fish.
That means that we are removing something on the order of one ten-thousandth (0.01%) of the nutrients that the phytoplankton that fed those tuna depend on …
However, that’s not all. Much of the phytoplankton goes to feed things that are generally not eaten by humans. As a result, the reduction in phytoplankton nutrients is even smaller than 0.01%. Much of it is never seen by humans in any form.
As a result, your hypothesis (reduction in plankton results from human usage of the required nutrients) fails by a number of orders of magnitude. We simply don’t remove enough nutrients to make a difference.
These comments forced me to re-think my position. I went back to the literature.
The total autotrophic biomass production in the oceans is about 48 billion tons carbon per year. We are currently harvesting about 80 million tons of fish and shellfish per year. The harvest has averaged over 70 million tons per year for the last 30 years, and over 40 million tons per year for the 30 years before that. Over the last 60 years we have harvested about 3.5 billion tons. The total biomass production in the ocean is circulating production. The fish we pull out removes that mass from circulation. So the reduction in phytoplankton nutrients is in fact small. Willis is correct; this doesn’t explain the 40% reduction in phytoplankton. As Willis correctly states, the food web in the oceans has several trophic levels, each about 10% of the level below it.
So thanks to R. de Hann and Willis Eschenbach for their comments.