The Food of the Bottom Fauna of the Plymouth Fishing Grounds

Abstract

1. The food of the bottom fauna of the Plymouth fishing-grounds, at an average depth of 27 fathoms, lias been investigated. This has been done by the examination of the stomach contents of animals, both fresh and preserved, and supplemented by observation of living animals in aquaria.2. The sources of food have been discussed. Attention is drawn to the importance in these regions, not so much of organic detritus, which is considered by Petersen and Blegvad to be the only important ultimate supply in Danish waters, but of the contributions from the plankton itself and from the considerable microflora and microfauna inhabiting the bottom deposits.3. Petersen and Boysen Jensen have stated that the detritus present in Danish waters can be traced almost entirely to the annual decay of the Zostera beds. The area occupied by Zostera in Plymouth waters is very smalLin.comparison with that in the Danish fjords and the detritus found here, though considerable in quantity, and in appearance much as described by Petersen, must originate largely from other sources. The possible1 sources of origin apart from land-sources are the coastal Algse and the plankton. A consideration of the annual production of each of these' suggests that the plankton is the more important factor.4. Blegvad has classified marine animals according to their food into Herbivores, Carnivores, and Detritus-eaters, but this classification does not fit the conditions in the area here studied and is not therefore of general application. Herbivores are absent from these grounds, and few of the animals could be described strictly as detritus-eaters. The animals fall into the following natural groups, according to their food and the mode and location of their feeding:—A.Carnivores—Animals which feed mainly upon other animals, either living or as carrion.B.Suspension-feeders—Animals which feed by selecting from the surrounding water the suspended micro-organisms and detritus.C.Deposit-feeders—Animals which feed upon the detritus deposited on the bottom, together with its associated micro-organisms.5. Following the preceding classification the food of the common animals of the Plymouth fishing-grounds has been described briefly.