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.

A comparative study on mesozooplankton abundance and diversity between a protected and an unprotected coastal area of Andaman Islands.

The study was carried out to understand the variability in phytoplankton production (Chlorophyll a) and mesozooplankton diversity from two different shallow coastal regions of south Andaman viz. Port Blair Bay (PBB), the only real urban area among the islands and Mahatma Gandhi Marine National Park, a Marine Protected Area (MPA) at Wandoor. Seasonal sampling was carried out during the Northeast monsoon (NEM--November 2005), Intermonsoon (IM--April 2006), and Southwest monsoon (SWM--August 2006). Significant (P < 0.05) seasonal variation was observed in the environmental variables at both the regions. Higher average chlorophyll a (Chl. a) and mesozooplankton standing stock were observed at PBB compared to MPA, but the seasonal variation observed was marginal at both the study areas. Chl. a showed a steep increasing gradient from outer to the inner regions of the PBB. The number of zooplankton taxa recorded at both areas was quite similar, but marked differences were noticed in their relative contribution to the total abundance. Eventhough the Copepoda dominated at both the areas, the non-copepod taxa differed significantly between the regions. Dominance of carnivores such as siphonophores and chaetognaths were noticed at PBB, while filter feeders such as appendicularians and decapod larvae were more abundant at MPA. A total of 20 and 21 copepod families was recorded from PBB and MPA, respectively. Eleven species of chaetognaths were observed as common at both areas. Larval decapods were found to be predominant at MPA with 20 families; whereas, at PBB, only 12 families were recorded. In the light of the recent reports on various changes occurring in the coastal waters of the Andaman Islands, it is suspected that the difference in Chl. a as well as the mesozooplankton standing stock and community structure observed between the two study areas may be related to the various anthropogenic events influencing the coastal waters.

Impact of bottom trawling on sediment characteristics--a study along inshore waters off Veraval coast, India.

The present communication is a study on the impact of bottom trawling on the sediment characteristics along Veraval coast, which is the largest trawler port of India. Experimental bottom trawling was conducted from MFV Sagarkripa at five transects of water depths 15-20 m, 21-25 m, 26-30 m, 31-35 m and 36-40 m in commercial trawling grounds. Trawling was conducted for 12 months in a span of 15 months (September 2005-November 2006) excluding the trawl ban period (June to August). The sediment texture was analysed by pipette analysis and organic matter by wet oxidation method. The variations in organic matter and sediment texture were prominent between the stations selected at different depths. The sedimentary organic matter exhibited variations with different water depths and seasons. The organic matter content decreased with depth. Experimental trawling considerably reduced the organic matter content at all depths. Continued and incessant trawling operation can cause even more drastic reductions, where organic matter (OM) content is already very small. The sand proportion showed depth-wise variation; but seasonal and trawling effect was not significant showing highest values at 36-40 m depth. The silt proportion did not exhibit significant depth-wise variation. The seasonal variation of silt was significant whereas trawling effect imparted to silt was not evident. Trawling has no significant effect on clay concentration. But seasonal variation had great influence on the clay distribution and indicated significantly high depth-season interaction. The sediment of the study area was predominant in silt proportion. It was observed that the seasonal/natural variations were more prominent masking the trawling effect on silt.

Effect of water quality parameters on the distribution of Pleuromamma (Copepoda-Calanoida) species in the Indian Ocean: a statistical approach.

The region between 10 degrees N and 10 degrees S latitude was known to be congenial for distribution of Pleuromamma species. Diel and ontogenetic migrations were observed for Pleuromamma xiphias. Multivariate analyses such as factor analysis on species' abundance and predictive step-up multiple regression models of water quality parameters: temperature, salinity, dissolved oxygen and their first order interaction effects on Pleuromamma species' abundance, were carried out in the regions, off 10 degrees N, 10 degrees N to 10 degrees S, 10 degrees S to 30 degrees S, along the Somali Coast (38 degrees S-40 degrees S) and a fifth region along the western boundary of the above four regions. Relation between Pleuromamma species' abundance and the water quality parameters showed a decreasing trend in the variability explained (VE) from region 1 (VE = 55.19%) to region 4 (VE = 31.15%) in the models, indicating that the influence of other ecological factors was of higher significance in the south than in the north, with a north south gradient. Indices of diversity (Shannon-Weaver) and evenness (Heips) were calculated and lognormal distributions fitted for these indices were found to be a good fit (p < 0.05). The five regions were compared, based on critical ratio of the diversity index. Shannon-Weaver diversity showed higher values during night collections than day collections, justifying the tendency for diurnal variations. Diversity and dominance were highly (r = 0.95) correlated. A multilinkage cluster analysis by group averaging method for the species, based on the standardised values of log(10) (X + 1) transformed species' abundance, showed that Pleuromamma indica, Pleuromamma gracilis and Pleuromamma abdominalis were not segregated in any of the five regions. Bray and Curtis (1957) coefficient of similarity for the species in the five regions combined together, showed 50% similarity for the cluster containing circum-global species, Pleuromamma piseki, P. gracilis, P. abdominalis and P. borealis. The species, P. indica and P. xiphias entered this cluster at 22% similarity level. Multivariate factor analysis by row normalisation (for species) and column normalisation (for stations), using varimax rotation to simple structure for unique grouping of species as well as stations, carried out in the five regions, showed that the maximum number of species' clusters were obtained in region 2, indicating a higher variability in the ecological conditions in this region than in the other four regions. The significance of the factor model and the differential factor groups of species were also determined in the studied regions. On a broader scale, based on the ecological aspect, the first four regions could be reduced to two regions, viz, region 1 including the north off 10 degrees N, Central Indian Ocean and the area of subtropical convergence, and region 2 consisting exclusively of the equatorial region between 10 degrees N and 10 degrees S based on distribution of Pleuromamma species. The plot of the species abundance with respect to latitude also showed such a demarcation.

Step-up multiple regression model to compute chlorophyll a in the coastal waters off Cochin, southwest coast of India.

The interaction effects of abiotic processes in the production of phytoplankton in a coastal marine region off Cochin are evaluated using multiple regression models. The study shows that chlorophyll production is not limited by nutrients, but their physiological regulations (responses to nutrients, pH, temperature and salinity) are mainly responsible for the increased biological production. The model explaining 77% of variability for chlorophyll a production is indicative of preconditioning of the coastal waters. The phytoplankton production is found to be sensitive to the environment, which varies seasonally. Further, the study suggests that supply of organic matter and grazing of zooplankton (not included) would improve the model efficiency. Despite this, the good agreement in the computed and measured chlorophyll a values shows that step-up multiple regression model is a useful tool to understand the influence of environmental variables on the production of phytoplankton in these coastal waters.

Effects of eyestalk ablation on moulting and growth of penaeid prawn Metapenaeus dobsoni (de Man).

Penaeid prawns M. dobsoni of two different size ranges were ablated both unilaterally (UEA) and bilaterally (BEA) and subjected to individual study. The UEA prawns consumed almost the same amount of food as the control prawns in the size group, 35-40mm, but consumed about 57.8% more food than the control prawns in the larger size group, 48-53mm. Growth was estimated as length and weight changes and significant variation was observed. The moult rate and dry moult weight showed marked differences. Average intermoult period increases with second ablation. Dry weight of moult in every succeeding moult was found to decrease irrespective of the level of ablation. Unilateral eyestalk ablation resulted in increase in dry weight whereas bilateral eyestalk ablation reduced the dry weight of moult and this decrease in the rate increased after each subsequent moult. In the larger size group, values of protein efficiency ratio (PER) were almost same as that of the lower size group. The UEA prawns exhibited highest conversion efficiency. The production rate of UEA prawns was 84% more than that of the control whereas BEA prawns indicated negative production. The same trend followed for net growth efficiency also. The results suggest that unilateral eyestalk ablation can be resorted to accelerate growth and conversion efficiency. Eyestalk ablation has been frequently resorted in matured forms for inducing maturation of gonads. For the first time attempts have been made to compare between the effects of removing one eyestalk versus two and changes taking place in juvenile forms especially in their physiology related to growth.