Generation studies on benthic amphipod-Quadrivisio bengalensis, Stebbing (Gammaridae) from the Kochin Estuary, Southwest coast of India.

Quadrivisio bengalensis (Stebbing Records of Indian Museum, 1, 159-161, 1907), a eurythermal (26.5-32.2 °C) and euryhaline (0.10-26.2 psu) tropical species, makes a profound contribution as a fodder organism to the benthic biomass of tropical backwaters. Studies on life span, variations in broods, fecundity, sex ratio, brooding behaviour, brood stock assessment, growth rate, antennal segments as an index of growth, moulting frequency, mortality and starvation resistance of Q. bengalensis were made for the first time under controlled laboratory conditions of 12-h photo period for 252 days on 8 pairs of specimens (male and female) collected from the field and their successive broods. The life span of females was found to be higher (maximum 220 days) than males (maximum 175 days). Number of broods varied between 5 and 15, depending on the "status of the brood" (early or late). The maximum number of juveniles in a single brood was 24 and that by a single female over the entire life span was 211. The incubation time varied between 6 and 9 days and the duration of moults (8-18 days) was found to increase with the age of the animals. Maximum growth is usually attained by the offspring arising from the 5th to 7th broods. The 4th to 7th broods were the optimal broods for the maximum number of females attaining maturity. For broods 3 to 7 of the parental set, probability of extinction (ξ) calculated on applying stochastic branching process to generation studies for the first time showed an increasing trend with number of broods while a decreasing trend for ξ for 8th and 9th broods, with least ξ for broods 5 to 7 of the 5th, 6th and 7th generations, suggesting life span and fecundity rates as functions of the "brood status" (early or late). Whether it is true with higher crustaceans remains to be explored.

Mesoscale process-induced variation of the West India Coastal Current during the winter monsoon.

This manuscript presents the analysis of current meter records at Kollam and Kannur along the 20-m isobaths during November-December 2005. Currents in the coastal waters are strongly influenced by winds (both local and remote forcing), tides, propagation of coastal Kelvin and Rossby waves, etc. We hypothesize that the mesoscale (spatial scales of 10-500 km and temporal scale of 10-100 days) features in ocean are also competent to alter the characteristics of coastal currents to a large extent. Analysis of sea level anomaly from the merged altimeter data reveals the existence of a large anticyclonic eddy in the southeastern Arabian Sea during the winter monsoon. The eddy moves westward with an average speed of ∼15 km day(-1) corresponding to an increase in sea level amplitude up to 28 cm. Off southwest India, the poleward flow is along the western flank of this anticyclonic eddy and the geostrophic current completes the circulation around the eddy. The eastward component of the geostrophic current at the northern edge of the eddy is bifurcated at ∼9° N: one flowing towards north and the other towards south. Current meter records at station Kollam revealed a dominant southward current due to the bifurcated southward component. The bifurcated northward component coalesced with the poleward flow along the western flank of the anticyclonic eddy. At Kannur, a poleward flow along the coast is responsible for a predominant northward trend in the observed current pattern during the initial phase of observation. A reversal in the current direction is caused by the southward-flowing geostrophic current along the eastern flank of the subsequent anticyclonic eddy centered at 73.5° E and 13° N. The stations were located at the eastern periphery of these anticyclonic eddies, where the mesoscale features overwhelm the seasonal characteristics of the West India Coastal Current (WICC).

Transport of dissolved nutrients and chlorophyll a in a tropical estuary, southwest coast of India.

Intra-tidal variability in the transport of materials through the Cochin estuary was studied over successive spring and neap tides to estimate the export fluxes of nutrients and chlorophyll a into the adjoining coastal zone. The results showed that there was a substantial increase in the freshwater flow into the estuary following heavy rains (~126 mm) prior to the spring tide observations. The estuary responded accordingly with a relatively larger export through the Cochin inlet during spring tide over neap tide. Despite an increased freshwater discharge during spring tide, the export fluxes of phosphate and ammonia were high during neap tide due to their input into the estuary through anthropogenic activities. The significance of this study is that the export fluxes from the Cochin estuary could be a major factor sustaining the spectacular monsoon fishery along the southwest coast of India.