The fauna of brackish fauna of Port Canning, Lower Bengal

Nelson Annandale ; Indian Museum

Table of Contents (ToC)

  1. Introduction
  2. Fauna of the ponds

Introduction

The settlement of Port Canning is situated on the Matla river one of the numerous creeks which run up into the delta of the Ganges, about sixty miles from the open sea. Partly at any rate in connection with the Port Canning Improvernent Scheme, which was believed some forty years ago to be about to transform the place into a port rivalling that of Calcutta, a high embankment has been built up along the bank of the estuary, protecting the low-lying land in the neighbourhood from all but exceptional floods. The earth out of which this embankment was formed was apparently dug from a series of pits situated at a short distance, varying up to about a quarter of a mile, from the present edge. These pits are further supplemented by a nurnber of smaller ones immediately behind the embankment, which is repaired with earth dug from the latter when it is injured by an unusually high flood. The original pits vary in size, but all have an area of something approaching half an ??aere. They are now filled with water and are the ponds dealt with in this paper. Judging from maps in the office of the Port Commissioners, Calcutta, they did not exist in 1855. It is evident from Stoliezka's account??, however, that at any rate some of them existed thirty-nine years ago, and he does not say that they had then been dug recently.

The account referred to deals in particular with an Actinian and a Polyzoon taken in the ponds; but it is by no rneans clear in which pond Stoliezka found his Sagartia schillertana, as there are several ponds «close to the railway station.» This point is of importance, beeause he was only able to find the Actinian in one pond, the position of which he deseribes in the manner indicated. One factor in the environrnent of forty years ago, however, has certainly changed; for lie gives as olie reason why the Actinian was not to be found in the other ponds that the one close to the station alone contained logs of wood to which the animal could attach itself, and now these logs are no longer to be found, either in the pond which is nearest to the railway station or in any other in the neighbourhood - they have evidently been removed by human agency or else have rotted away. The bottom of all the ponds now consists of soft mud, which is devoid of any hard substances except an occasional twig, small tree-stump, or brick, and as there are very few trees in the vicinity, twigs are rare and tree-stumps still more so. The bricks are also scarce, being derived from ruined drains and wells, and there are no stones in this part of Bengal. The ponds are all shallow (probably at no point more than ten feet deep when full) but the depth of the mud at their bottom is considerable. It is black beneath the surface, contains a large amount of organie matter and smells foul when disturbed.

The flora of the ponds consists chiefly of filamentous and unicellular algae but in some cases two or three species of Phanerogams occur, notably at least two of Naias , a duckweed and a true water-lily, the last being rare, the first abundant in some of the ponds.

An important factor in the environment is the nature of the water. I have deseribed the ponds as brackish, but at some time of the year the water may contain the same proportion of soluble salts as the sea, at others it may even be more strongly saline, and again at others it is much more nearly fresh. As a rule the ponds are completely isolated both from one another and from the estuary. During the cold weather they are exposed to evaporation, which becomes intensified during the hot weather. During the rainy season, on the other hand, they become filled up with fresh water and probably often coalesce. They are also liable to be placed in temporary communication with the estuary occasionally, owing to a flood bursting the emibankment, but this does not occur by any means every year. When it does happen, it happens owing to the estuary being swollen with fresh water, which is flowing down from up-country; so that the ponds, even under these conditions, are practically cut off from the sea. .

Stoliczka, apparently in 1868 or 1869, had the water of the ponds analysed ; but he does not say at what time of year his samples were obtained. He found that the proportion of soluble solids was 12-87 per thousand, sea-water containing from 32 to 39 per thousand. Mr. D. Hooper, Curator of the Industrial Section of the Indian Museum, has kindly examined saniples taken by myself in December and March last. Two samples came from a pond in which the Hydrozoon Irene ceylonensis , as well as the Aetinian, was reproducing its species, and in which the plant Naias was abundant. A sample taken from this pond at the beginning of December, a few weeks after the end of the rainy season, was found to contain 12-13 per thousand of soluble salts, while another taken on March 17th contained 20-22 per thousand. At the latter date water from the edge of the MIatla at Port Canning contained 25-46 per thousand, and that from a second pond near the first 23-16. This second pond had a fauna almost identical with that of the first except in the absence of the Hydrozoon - but its flora was entirely cryptogamic.

I am indebted to Capt. J. A. Black-, I.M.S., Chemical Examiner to the Government of India, for a more detailed analysis of a sample from the second pond taken on january 6th. It is as follows
Chloride of Sodium 13-8 parts per thousand
Chloride of Magnesium 0-6 parts per thousand
Sulphate of Magnesium 0-7 parts per thousand
Sulphate of Calcium 2-1 parts per thousand
Nitrates, etc. 0-3 parts per thousand
Total 17-5 parts per thousand

Stoliczka's analysis was, in detail, as follows
Chloride of Sodium (including Potassium) 9-81 parts per thousand
Chloride of Calcium 0-46 parts per thousand
Chloride of Magnesium 0-93 parts per thousand
Sulphate of Magnesium 1-17 parts per thousand
Carbonic acid, etc. 0-50 parts per thousand
the soluble substances being also caIculated in parts per 1000.

Stoliczka noted that the water in the ponds was almost fresh during the rains, and in the tank from which my first sample was taken the water-level had sunk only a short distance below the top of the bank, the dry weather having been of no more than a few weeks duration. All that can be said, therefore, as regards the salinity of the water in the ponds, is that it varies considerably at different times of the year. The range in variation which the members of the fauna are able to survive, is perhaps more remarkable than what may be regarded in different instances either as the deficiency or the excess of salt in the medium in which they live.

ToC

Fauna of the ponds

[ ... ] Fish . - Specimens of the following Fish were taken in the ponds

[ ... ] Ophiocephalus punctatus [ ... ]

Some of the species (e.g., O. punctatus ) extend inland even as far as mountain tarns in the Himalayas.

[ ... ]

ToC

Acknowledgement and Source(s)

This text was originally published under the above title in: Records of the Indian Museum . 1907, vol. 1, no. 1, pp. 35-42. The copyright owner Zoological Survey of India has granted snakeheads.org the right to publish it on the org's site. The copyright of the text is still with the owner in full amount.

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