New Hydrographic Apparatus

✍ Scribed by Kaare Münster Ström

• Publisher: John Wiley and Sons
• Year: 1931
• Tongue: English
• Weight: 335 KB
• Volume: 25
• Category: Article
• ISSN: 1434-2944
• DOI: 10.1002/iroh.19310250308

✦ Synopsis

With 3 figures.

1. Plankton Catcher. Though the disadvantages of nets for quantitative catches of planktic metazoa have long been agreed upon, they are still the only implements in general use. In freshwater and coastal waters the pump method is sometimes resorted to, but the inherent disadvantage of this method is that it cannot be employed a t great depths, besides requiring very clumsy apparatus ; a disadvantage specially manifest in lake work where all apparatuses have to be transported from lake to lake and re-installed on different boats.

As physical and chemical dates are obtained a t definite depths, and all analyses of phytoplankton are referred to definite volumes caught by water-samplers, it becomes a paramount need in quantitative work on zooplankton to be able also to refer analyses to definite volumes from definite depths, and leave the net method with its innumerable sources of error. At the best, results obtained by nets must be referred to vertical columns of water of considerable height, or if obtained by horizontal closing nets can hardly be regarded as quantitative a t all.

It is thus surprising that no more advance has been made towards the construction of suitable plankton catchers capable of obtaining plankton from 20-100 litres of water. Kofoid (1905) gives a detailed description of a "water-bucket,' capable of taking 20 litres of water. The net weight is 25 kgms. The bucket is a modification of the Kriimmel and Pettersson-Nansen water-bottles, thus a weak point is that the opening of the cylinder *