Input-export fluxes of heavy metals in the Cochin estuary, southwest coast of India.

Cochin estuary (CE) is one of the largest tropical estuaries along the southwest coast of India, sustaining rich bio-resources. Several studies enlighten the environmental changes in the CE caused by anthropogenic activities. In the present study, an attempt has been made to quantify the heavy metal (dissolved and particulate) fluxes brought by the six rivers into the CE with their exchange into the coastal ocean through the major inlet at Cochin during a steady flow period (October-November 2015). The water flux across the inlet was quantified using an acoustic doppler current profiler. The measured daily input of dissolved metals from the rivers was 2.43 × 103 kg Fe, 334 kg Zn, 259 kg Ni, and 83 kg Cr, while that of particulate metals were 85.30 × 103 kg Fe, 8. 6 × 103 kg Mn, 236.9 kg Cr, and 111.9 kg Zn. The net export of metals through the Cochin inlet (per tidal cycle) was 3.3 × 103 kg Fe, 515 kg Cr, 150 kg Zn, and 5 kg Ni in dissolved form and 3.32 × 105 kg Fe, 1747 kg Mn, 1636 kg Cr, 1397 kg Zn, and 586 kg Ni in particulate form. The high concentrations of metals during ebb tides are clear indications of their contribution from the industrial conglomerates (industrial units of metallurgy, catalyst, fertilizer, and pesticides) located in the Periyar River. The significance of this study is that the export fluxes may increase further during the summer monsoon (June to September), which may impact the abundant fishery emanating in the coastal environment during the period due to intense upwelling.

Viral-Induced Mortality of Prokaryotes in a Tropical Monsoonal Estuary.

Viruses are recognized as the most abundant and dynamic biological entities in the marine and estuarine environment. However, studies on the dynamics and activity of viruses in transient estuarine systems are limited. This study examines temporal and spatial variations in viral abundance (VA) and viral activity across the salinity gradient in a monsoon-driven tropical estuarine system (Cochin estuary, CE) along the southwest coast of India. Water samples were collected from five stations (with different hydrological settings) every 3 h for 24 h period during two distinct seasons, namely pre-monsoon (PRM, dry season) and monsoon (MON, wet season). Time series measurements were made for a spring and neap tidal cycle for each season at all the stations. The results showed marked spatial and seasonal variability with relatively low diel and tidal variations in VA and lytic activity. Viral activity was found to be distinct in five stations studied with the maximum activity in the mesohaline regions (salinity <20) of the estuary. This region was characterized by high VA, lytic infection and viral production, accompanied by low (BGE) and high bacterial respiration. Based on viral lytic production, lytic viruses were found to be responsible for the release of ca. 72.9 ± 58.5 µg C L-1d-1 of bacterial carbon. The contribution of the viral shunt to the dissolved organic carbon (DOC) pool was higher during the dry season (PRM) than MON. Statistical analysis confirmed a significant association of viruses with the host availability and salinity. This work demonstrates the spatiotemporal distribution of viruses in a tropical estuarine ecosystem and highlights their role in microbial mortality across different salinity gradients. This study forms the first report on viral processes from a monsoon-driven tropical estuarine ecosystem.

Diurnal variations in bacterial and viral production in Cochin estuary, India.

Microbes play a central role in the decomposition and remineralization of organic matter and recycling of nutrients in aquatic environments. In this study, we examined the influence of physical, chemical, and biological parameters on the rate of bacterial production (BP) and viral production (VP) with respect to primary production over a diurnal period in Cochin estuary. Time series measurements were made every 2 h for 12 h (6 a.m.-6 p.m.) during periods of low and high salinities. The light intensity as photosynthetically active radiation, temperature, salinity, nutrients like NO3-N, SiO4-Si, and PO4-P, and chlorophyll a (Chl a) were measured along with BP, VP, and net primary production (NPP). NPP showed a strong positive correlation with light and Chl a (r (2) = 0.56 and 0.47, respectively), while VP showed a strong positive correlation with light, salinity, and Chl a (r (2) = 0.37, 0.58, and 0.37, respectively) and a negative correlation with BP (r (2) = -0.39) at P ≤ 0.05. We observed a diurnal pattern in BP but did not have any significant correlation with light. Similar diurnal pattern was seen in VP, the peak of which was in succession with BP, suggesting that virus-mediated lysis plays an important role in loss processes of bacteria in Cochin estuary. The results of our study highlight the light-dependent and physicochemical-dependent diurnal variation in virioplankton production in a tropical estuarine ecosystem.

Impact of eutrophication on the occurrence of Trichodesmium in the Cochin backwaters, the largest estuary along the west coast of India.

Phytoplankton studies in early 1970s have shown the annual dominance of diatoms and a seasonal abundance of Trichodesmium in the lower reaches of the Cochin backwaters (CBW) and adjacent coastal Arabian Sea during the pre-summer monsoon period (February to May). Surprisingly, more recent literature shows a complete absence of Trichodesmium in the CBW after 1975 even though their seasonal occurrence in the adjacent coastal Arabian Sea continued without much change. In order to understand this important ecological feature, we analyzed the long-term water quality data (1965-2005) from the lower reaches of the CBW. The analyses have shown that salinity did not undergo any major change in the lower reaches over the years and values remained >30 throughout the period. In contrast, a tremendous increase was well marked in levels of nitrate (NO(3)) and phosphate (PO(4)) in the CBW after 1975 (av. 15 and 3.5 µM, respectively) compared with the period before (av. 2 and 0.9 µM, respectively). Monthly time series data collected in 2004-2005 period from the lower reaches of the CBW and coastal Arabian Sea have clearly shown that the physical characteristics like salinity, temperature, water column stability, and transparency in both regions are very similar during the pre-summer monsoon period. In contrast, the nutrient level in the CBW is several folds higher (NO(3), 8(;) PO(4), 4; SiO(4), 10; and NH(4), 19 µM) than the adjacent coastal Arabian Sea (NO(3), 0.7; PO(4), 0.5; SiO(4), 0.9; and NH(4), 0.6 µM). The historic and fresh time series data evidences a close coupling between enriched levels of nutrients and the absence of Trichodesmium in the Cochin backwaters.

Short-term variability of water quality and its implications on phytoplankton production in a tropical estuary (Cochin backwaters-India).

Changes in the phytoplankton biomass (chlorophyll a), production rate, and species composition were studied over two seasons using the time series measurements in the northern limb of the Cochin estuary in relation to the prevailing hydrological conditions. The present study showed the significant seasonal variation in water temperature (F=69.4, P<0.01), salinity (F=341.93, P<0.01), dissolved inorganic phosphorous (F=17.71, P<0.01), and silica (F=898.1, P<0.01) compared to nitrogen (F=1.646, P>0.05). The uneven input of ammonia (3.4-224.8 µM) from upstream (Periyar River) leads to the inconsistency in the N/P ratio (range 6.8-262). A distinct seasonality was observed in Si/N (F=382.9, P<0.01) and Si/P (F=290.3, P<0.01) ratios compared to the N/P ratio (F=1.646, P>0.05). The substantial increase in chlorophyll a (average, 34.8±10 mg m(-3)) and primary production (average, 1,304±694 mg C m(-3) day(-1)) indicated the mesotrophic condition of the study area during the premonsoon (PRM) and it was attributed to the large increase in the population of nanoplankton (size<20 µ) such as Skeletonema costatum, Thalassiosira subtilis, Nitzschia closterium, and Navicula directa. In contrast, during the post monsoon (PM), low chlorophyll a concentration (average, 9.3±9.2 mg m(-3)) and primary production (average, 124±219 mg C m(-3) day(-1)) showed heterotrophic condition. It can be stated that favorable environmental conditions (optimum nutrients and light intensity) prevailing during the PRM have enhanced the abundance of the nanoplankton community in the estuary, whereas during the PM, the light limitation due to high turbidity can reduce the nanoplankton growth and abundance, even though high nutrient level exists.

Trace metal dynamics in fishes from the southwest coast of India.

The concentration of Fe, Co, Ni, Cu, Zn, Cd, and Pb in the muscle tissue of marine fishes like Lates calcarifer, Nemipterus japonicus, Caranx melampygus, Rastrelliger kanagurta, and Cyanoglossus macrostomus was estimated from samples collected in the continental shelf waters off Kochi and Mangalore on southwest coast of India. Species-specific and spatially heterogeneous patterns of tissue metals loads were apparent within the pelagic and demersal fish species for the two regions. The concentration ranges of Fe (541.60 to 649.60 ppm), Ni (12.12 to 13.92 ppm), and Cu (3.09 to 3.62 ppm) were higher in the demersal species C. melampygus, whereas Co (9.10 to 11.80 ppm) and Zn (79.30 to 84.30 ppm) were higher in the pelagic species L. calcarifer and Cd (4.35 to 6.38 ppm) were higher in the demersal species N. japonicus, possibly due to enhanced bioavailability of these metals from ecological processes associated with upwelling during the summer monsoon. The fish species showed a great capacity to accumulate metals, with highest bioaccumulation for the essential element iron and lowest bioaccumulation for the non-essential element lead. Among the demersal species, C. melampygus and N. japonicus had high concentration factors for the metals Fe (280,268 to 322,808), Ni (88,252 to 96,891), Cu (2,351 to 2,600), and Cd (29,637 to 32,404). In contrast, the pelagic species L. calcarifer and R. kanagurta had high concentration factors for the metals Zn (40,812 to 46,892), Co (280,285 to 423,037), and Pb (854 to 1,404).

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.