43 
uncertainty as to the food of these animals in spite of the older and more recent 
investigations, for example Dakin's. I shall not endeavour to discuss this matter 
in detail here, but merely refer to the Kiel investigations (Hensen, Brandt, 
Lohmann), which show that tbe mass of the plankton animals, at least at several 
places and at different times, is much greater than the mass of the plankton 
plants, so that it is difficult to understand, where the animals get their food from; 
even if we include the commonest organisms ( Vollplankton), Lohmann is still of the 
opinion, that at certain times at least, in the winter, we must look round for other 
sources of food than the plants and he refers to the dust-fine detritus. We should not 
believe, therefore, that the plankton at such times has anything left over for the food 
of the bottom animals, or that it has for them any importance on the whole, except 
perhaps as detritus-formation, especially in the form of dead animals and excrement. 
In his famous work of 1887 Hensen endeavours, naturally quite pro- 
visionally and as a sort of estimate, to give an idea of the annual production of 
plankton per m.? in the Western Baltic, where the water is ca. 20 meters deep, 
and he came to the result, that of the really organic dry-matter, not silicate, 
ca. 150 gm. are produced annually, but ca. 134 gm. of this was based on a few 
experiments with the feeding of Copepods in closed hbottles; for the other animals 
there should thus remain only ca. 16 gm. per m.?”, presumably not only for the 
bottom-animals but also for the plankton animals. The whole production of 150 
gm. per m.? is not small in comparison with the production of hay on the land, 
it is almost the same; but the amount remaining for the benthos fauna is 
obviously too little. The amount of dry matter in these is often 23—35 gm. per 
m.? in the Limfjord, and in this fjord with its shallow water the quantity of the 
plankton according to my investigations is not in any way so great as in the 
Kattegat or in the Belts. Further, the existing bottom-fauna must as a matter of 
fact eat its own weight severaJ times in the course of a year if it is to live and 
grow, so that far too little material is obviously left over from the plankton for 
its nourishment. We cannot attach any very great accuracy to the results of these 
preliminary reports, nor does Hensen do so; I have only mentioned them in 
order to show, that their results are not in opposition to what has been displayed 
above, namely, the importance of the detritus and plankton in the Limfjord. 
Whilst very fine detritus is clearly of advantage for the growth of many 
animal species, I must nevertheless agree with Lohmann (1909 p, 227) when he 
says, that the great quantities of detritus in the coastal waters is »låstig« for 
several plankton organisms. He has touched upon an important problem here — 
the absence of certain plankton organisms from the neighbourhood of the coasts, 
in spite of high salinity and suitable temperature etc. Is it not likely to be the 
dust-fine detritus, which is directly harmful to many clean-water organisms? I 
have often seen quantities of the pelagic forms of the North Sea, such as e. g. 
Pleurobrachaa, floating in with the current into the Limfjord, but rapidly perish 
and go to the bottom covered with a thick gray layer of the detritus which is so 
plentiful in the western parts; on the other hand, other plankton organisms are 
able to bear this detritus. 
In this connection I may mention, that Brandt has shown in the Kiel 
Canal, that there is there but a very sparse plankton in spite of a rich bottom 
