A comparison of the marine and estuarine benthic fauna of the nearshore regions of the Arabian Sea.

Abstract

The distribution and abundance of the benthic fauna of the Arabian sea were studied in the nearshore region at a depth of 10 fathoms, about 7 miles off Cochin. The results showed that the macrofauna was more abundant than the meiofauna. The foraminiferans and the nematodes formed the dominant groups of the meiofauna. The larger foraminifera such as Rotalia beccarii occurred in fair numbers in the macrofauna as well. The macrofauna was mostly represented by gastropods, bivalves and a few small bottom-dwelling fishes. A comparison of the benthic fauna of this area with that of the backwater revealed that although the main groups of the fauna were the same in both the areas, the species composition was different. The benthic biomass in the nearshore area was higher than those regions of the backwater which had similar substrata. The values obtained were 6.37 gm/m2 in the nearshore region as compared to 2.44 gm/m2 and 3.36 gm/m2 in the estuarine region. However, the benthic biomass at the mouth of the backwater as has been reported earlier was considerably higher than that of the nearshore region. In the backwaters the variations in the salinity and the nature of substrata were thought to be the main factors controlling the distribution and abundance of the benthic fauna; but in the nearshore region, since salinity is less variable, it seems that the nature of the substratum is the primary factor governing the abundance of the bottom fauna. The substratum in the nearshore region was predominantly clayeysilty and this may account for the absence of larger macrofauna