Low chironomid counts from Lake Muzzano

I am aware of at least 10 papers authored by Dr Larocque-Tobler where there is good evidence that the chironomid count sum has been misreported (a corrigendum to one of these papers admits that a count sum of 19 was misreported as being at least 50). So naturally, when I read Larocque-Tobler & Pla-Rabès (2015), which reports a chironomid and diatom data from Lake Muzzano, I was interested in the chironomid count sums.

Unfortunately, the paper does not report the chironomid counts sums, but instead states that

Sixty-two samples were analyzed for chironomids, but many had few head capsules and were merged together.

When the count sums are not reported, I think it should be reasonable to assume that they conform to the typical count sizes for the microfossil group. For chironomids, the minimum count sum is typically 50 head capsules, although some authors use a minimum of 30. I think it would be poor practice to have count sums below 30 without reporting it.

Since no data are archived for the Lake Muzzano study, we need to try to infer the count sums from the stratigraphic diagram.

fevo-03-00070-g005

Chironomid stratigraphy (%) from Lake Muzzano.

Let’s take a look at a few of the samples.

The top sample has six equally abundant taxa with just over 10% and a seventh with over 30%. I think this probably represent a count of nine head capsules.

Let’s go down the core into the yellow zone:

  • The first yellow sample has four taxa at 25% giving a probable count of four head capsules.
  • The second sample has two species at 50%, suggesting a count of two.
  • The third has three taxa at 20% and a fourth at 40% suggesting a count of five. This is the sample that appears to have the largest count sum in this zone.

It is of course possible that I have underestimated the count sums and that the two taxa at 50% represent a count of four rather than two, but it is very unlikely that this sample has a count sum of greater than, say, 30. I think at least a third of the samples probably have count sums below 10 and perhaps only one or two of the count sums are greater than 20.

While it is easy to show that the count sums are probably very small, does it matter? I think it does. For example, the discussion of Smittia is probably based on only one head capsule and cannot be expected to be robust (the discussion of Limnophyes is simply wrong).

I think that the count sums in the Lake Muzzano study are so small that their size should have been reported (this is good practice in any case) so that the reviewers and readers can make an informed opinion about the signal and noise in the data. That readers would probably have an unfavourable opinion about such small count sums is no reason to omit this information.

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About richard telford

Ecologist with interests in quantitative methods and palaeoenvironments
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