The copepod Eurytemora in estuaries

a letter on Eurytemora,
a brackish water plankton copepod

Dear friend,

somebody found your paper "Distribution of Eurytemora americana in the Duwamish River estuary" in internet and sent an outprint to me.

I find your paper very interesting, although I do not do any marine or estuarine studies since many years, I am retired, and my main subject is to look after psychic and spiritual diseases that lead man to exploit and destroy nature. But my former pet was Eurytemora affinis, and I also studied a few other estuarine copepod species.

Enclosed are two papers of my friend Ali and myself, one of which you mentioned but confused it with another paper of ours in the reference list (see our lists). The other you may not yet have seen, it is a kind of final conclusion at the termination of all our Eurytemora work. I am not able to send you any other of my/our papers since they are out of stock.

Your paper is - apart from the RESULTS - mainly based on suggestions of the rank of hypotheses, which is not yet enough for giving a description of, and final conclusion on natural phenomena. This shows that a lot more of this kind of work will have to be done in order to understand fully what is going on in estuaries. And it is worth doing so since still estuarine nature is not well understood. Studying the Eurytemora distribution and transport or retention, respectively, may be promising to understand more about the transport mechanisms in estuaries in general. This will have bearings on pollution studies, especially with regard to changes of the pollutants´ quality during passage through the estuary. Copepods are easily detectable - in comparison to suspended particles (seston) or chemicals.

From our paper in Bull. Plankton Soc. Japan, you can see that many parameters must be measured together with copepod counting etc (1), to obtain evidence (see Karl POPPER's work on scientific methods) for certain relationships as they might have been hypothesized beforehand.

(1) "etc" means that qualitative indicators for
different sub-populations or "herds" are usefull
such as the extent of infestment with ciliata.

By statistical means correlations between copepod density and parameters can be expressed and compared.

If any hypothesis test includes very low salinity (vls) as a parameter or a certain range of salinity within this stretch, a very sensitive method must be used - titration is not enough in this case, electrical conductivity (ec) may be better - although at low salinity, ec is no direct and linear indicator for salinity. Here, ec must not be converted into salinity because this will greatly distort accuracy. But it gives a relative impression and it is a rather exact number for further calculations, may be the exactest available. It does not represent the exact relationship between the copepod and salinity but between the copepod and its position within the estuarine hydrographical system. In this vls region or stretch, if any parameter is correlated against salinity as calculated from ec, a few more parameters may unintentionally be included (that influence ec besides of salinity) and blur the view.

In many published papers a clear conclusion of the relationship between copepod abundance and salinity could not been drawn by the authors - only hypotheses (2) or speculations (3) were given. May be the reasons for this are that salinity was given instead of ec, or that the research was not done far enough upstream so that the upstream slope of abundance was not seen, or the ec or salinity data were not widely enough spread on the abscissa (for example as log log data) so that details were darkened.

(2) often hypotheses were not made according
to the rules of science cognition
theory (see Karl POPPER and others)
and were put francly into the rank of
a theory for which no sufficient
evidence is given. Often such "hypotheses"
are not more than mere speculations.
Scientifically seen and in respect to
practical use of published results,
this is useless and at times even dangerous.

(3) speculations may, however, have good grounds,
they may come from collection of observations
that are not scientific but happen in daily
life accidentally and are stored in the brain
in a diffuse way, not systematically.
Almost unconsciously the brain collects
data from such observations and forms
ideas, experiences of life, pictures of existence etc.
All this is then used to formulate speculations,
they have got only little food from exact observations.
Much biological science works resemble this and

they are, thus, not really exact science.
And speculations are the ground to formulate hypotheses.
These have then to be tested to find the
truth - yes or no must be the answer of such tests.

With regard to migration it is difficult to believe that these tiny animals together with their offspring can migrate actively in an estuary like the Weser - with all its current speed (up to 2 m/sec) and turbulence, the same may be said with regard to vertical migration (as it was seen in crab megalopas that are, however, much bigger and live in low current regimes). May be BAROSS & CRUMP (see AVENT`s paper) have never seen them living or have not kept in mind the enormous mechanical energy prevalent in some tidal estuaries. And even if the copepods would ride on the tidal wave, they would not be retained in their habitat because the net water transport is downstream. But these remarks of mine are as speculative as the remarks of many authors are.

There is no other possibility for Eurytemora affinis in the Weser than to feed on suspended particles, there is nothing else (or on dissolved matter which is not believable - look at the mouth parts). And these particles are not part of the turbidity maximum because this is farther downstream. These particles are riverborne and contain much claiy substances and much organic matter - partly derived from the catchment area of the river (i.e. from erosion), perhaps more from sewage, but hardly from the sea (this seems to be different in mechanically undisturbed estuaries like the Amazone where marine diatoms have been found hundreds of kms upstream). It does not seem that the copepods actively search for a region where such food is densily supplied and rally round there, because where they are amassed there is no special amassment of suspended particles. I can, however, not say anything about the horizontal distribution of quality parameters of these particles in correlation with copepod distribution (except content of organic carbon, but I forgot the results).

Where in the Weser the copepod abundance maximum occurs there is no water stratification - due to high turbulence which is due to canalisation (except a stratification of current speed and turbulence, being lower near the bottom and the shore). And there are practically no prey animals either in this area nor in other places upstream of the salt wedge area due to impoverishment of natural life (due to pollution, current speed etc).

So Eurytemora affinis seems to be almost the only planktonic animal species in the Weser Estuary that can stand man's impact, somehow it seems to play a similar role as rats on land, feeding on man's refuse. But apart from this remark it is a specialized estuarine species which does not occur elsewhere in fresh or marine habitats in considerable numbers.

We have collected quantitative plankton samples by a 1 or 2 l sampler, Ruttner or van Doorn or the like, and poured through a net. This gives a mean value over a much greater mass of water than sampling 1o l in one collection. In addition in situ measurements of ec, oxygen, temperature, light transparency in red over 1 to 1o cm light path, pH, currents and pressure (or wire angle) for depth of the equipment were done from on board and read there. The meters were fixed in a heavy iron frame which was lowered from a crane from the anchored ship. In case of drifting with the current, the assembly need not be so heavy, it can be much simpler.

By Aryaman Stefan Wellershaus
28th November 1997

A few water colour paintings from 1978 in the Weser: a female and a male. The background colour represents rougly the colour of the estuarine water.

The female, pregnant with nine eggs. On the back an empty structure of ciliata (epi-zoons). The smaller red picture shows the eye enlarged. A long bag with spermatozoons is fixed to the abdomen.

The male. The extraordinary structure at the end of the row of swimming-legs is the pair of fifth legs used to fix the bag of spermatozoons to the abdomen of the female - copulation.