Synechococcus as an indicator of trophic status in the Cochin backwaters,west coast of India

Eutrophication is a major problem in coastal water bodies. Information about the trophic status of water bodies will enable proper management of coastal ecosystems. In this regard, biological organisms which are sensitive to environmental changes can serve as indicators of ecosystem trophic status. In this study, seasonal and spatial variations of picophytoplankton (PP; <3 μm size) community structure was assessed in the Cochin backwaters (CB) with respect to the prevailing environmental conditions during three seasons, post-monsoon (PM-I; October 2011 and PM-II; November 2012), pre-monsoon (PrM; May 2012) and monsoon (MON; August 2012). CB, along the west coast of India, receives continuous load of nutrients throughout the year through anthropogenic wastes. Trophic status index (TRIX) scores showed that CB is highly eutrophic with a high phytoplankton biomass. Synechococcus was the dominant PP observed in the study area. Seasonal and spatial salinity variations influenced the PP distribution, especially Synechococcus where PE-rich Synechococcus (SYN-PE) were dominant in higher saline (>30) and PC-rich Synechococcus (SYN-PC) in lower saline (<30) waters. SYN-PC showed a significant positive relation with chlorophyll a suggesting that this group contributes substantially to the total phytoplankton biomass. TRIX scores and SYN-PC: SYN-PE abundance ratio were negatively correlated with salinity suggesting an influence of the tidal amplitude. SYN-PC correlated positively and SYN-PE negatively with TRIX scores suggesting that these groups occupy contrasting ecological niches. These findings imply that PP distribution pattern can serve as an indicator of the trophic status of coastal water bodies.     

The impact of a salinity barrier on the partitioning of heavy metals in sediments of a tropical backwater system

Abstract

Concentrations of heavy metals (Cd, Co, Cr, Cu and Fe) in surface sediments and their partitioning behaviour between exchangeable, reducible (Fe-Mn oxide bound) and organic/residual phases of the sediments in a typical backwater system of Kerala, viz. the southern upstream part of Cochin Estuarine System (South India), have been studied. Spatial and temporal variations of trace metals are discussed with special reference to pH, dissolved oxygen, salinity, organic carbon and texture of sediment. Metal concentrations in the tide gated part of the estuary were found to be significantly higher when compared to metal concentrations reported from the unrestricted part of the Cochin estuarine system and also those from many of the unpolluted estuaries worldwide. The higher levels of heavy metals in the study area and their characteristic distribution and partitioning behaviour in the surficial sediments were attributed to the presence of a salinity barrier across the backwater system and also by the massive use of pesticides and chemical fertilizers in the vast area of agricultural land near the backwater system.     

Comparative Analysis of Feeding and Schooling Behaviour of the Cyprinidae Alburnus alburnus (L., 1758), Rutilus rutilus (L., 1758), and Scardinius erythrophthalmus (L., 1758) in a Backwater of the Danube near Vienna

Underwater observations of the three common fish species Alburnus alburnus (L., 1758), Rutilus rutilus (L., 1758) and Scardinius erythrophthalmus (L., 1758) in a small part of the Danube flood area near Vienna have been made from June to October 1985 and 1986. Particular emphasis has been laid on the partitioning of feeding resources and habitat. It has been established that these species prefer different water zones. Alburnus a. and Scardinius e. are “obligate” schoolers (BREDER, 1967) whereas Rutilus r. is a facultative schooler. While feeding Rutilus r. and Scardinius e. form “aggregations” (BREDER, 1959) and both adopt equivalent feeding techniques. Furthermore Alburnus a. is a quick moving species living near the surface and chasing mostly in schools. While inter- and intraspecific aggression is rarely observed for Rutilus r. and Scardinius e., Alburnus a. often show interspecific actions.     

Macroinvertebrates as ‘describers’ of morphological and hydrological types of aquatic ecosystems abandoned by the Rhône River

Samples of aquatic macroinvertebrates were taken from abandoned beds of the river Rhône in the Brégnier-Cordon area. This sector of the French Upper Rhône is particularly rich in old beds or lônes which vary in age and morphological type and have more or less direct connections with the river.Samples were collected using a hand net in eight different lônes. The results concerned five groups of fauna: Mollusca, Crustacea, Ephemeroptera, Coleoptera, Trichoptera. The study revealed a wide range of fauna, and the fact that group of taxa can be used to describe types of lônes defined by morphological and hydrological characteristics. This kind of research adds to our understanding of how such aquatic ecosystems evolve, and may be applied in a more general way to other important river systems.     

Mussel responses to flood pulse frequency: the importance of local habitat

1. Understanding mechanisms behind the distribution of organisms along a gradient of hydrological connectivity is crucial for sustainable management of river–floodplain systems. We tested the hypothesis that frequency of flood pulses exerts a direct influence on the distribution of freshwater mussels (Unionoida) by creating a local environment that limits their fitness. 2. Multiscale habitat analyses combined with transplant‐rearing experiments were carried out with a focus on abundance, presence/absence, survival rates and growth rates of mussels. Sixty‐nine floodplain waterbodies (FWBs) were surveyed within a 15‐km lowland segment of the Kiso River in Japan. 3. The abundance of mussels significantly increased with increased frequency of inundation associated with flood pulses at the among‐FWB scale, while the probability of occurrence of mussels was negatively predicted by the amount of benthic organic matter at the within‐FWB scale. 4. Field‐rearing experiments showed that survival rates were low and growth rates nearly zero in infrequently inundated FWBs (these FWBs had no naturally occurring resident mussels). In such FWBs, hypoxia (DO < 2 mg L^?1) was frequently observed near the bottom when temperature was optimal for mussel growth (>15 °C). 5. These findings demonstrated that flood pulse frequency was the most important factor in determining mussel distribution in FWBs because it directly limits mussels’ fitness by mediating local environmental factors, possibly dissolved oxygen (DO) levels. Successful restoration efforts for mussel habitat conservation should focus on processes that lead to improved local conditions.     

Hydrobiology of the Cochin backwater system – a review

On the south west coast of India, there is an extensiveestuarine system of backwaters, of which Vembanad Lake is the largest. The backwaters of Kerala support as much biological productivity and diversity as tropical rain forests. They are responsible for the rich fisheries potential of Kerala. Cochin backwaters situated at the tip of the northern Vembanad lake is a tropical positive estuarine system extending between 9° 40 and 10° 12N and 76° 10' and 76° 30 E with its northern boundary at Azheekode and southern boundary at Thannirmukham bund. The lake has a length of 80 km and the width varies between 500 and 4000 m. A channel, about 450 m wide at Cochin gut and another at Azheekode, make permanent connections with the Arabian Sea. The depth of the estuary varies considerably. While the shipping channels are maintained at a depth of 10–13 m, the major portion of the estuary has a depth range of 2–7 m. Water from two major rivers viz., Periyar and Muvattupuzha drain into this estuary. During south west monsoon, the estuary is virtually converted into a freshwater basin even in areas around barmouth where salt water penetration occurs below 5 m depth only. The major hydrological variable in the Cochin backwaters is salinity, similar to the situations encountered in estuaries with a gradual declension of salinity from 30 at the entrance of the estuary to 0.2 at the point of entry of the rivers. Salinity gradient in the Cochin backwaters supports diverse species of flora and fauna depending on their capacity to tolerate oligohaline, mesohaline or marine conditions. Low lying swamps and tidal creeks, dominated by sparse patches of mangroves with their nutrient rich physical environment, support larvae and juveniles of many economically important species. Backwaters also act as nursery grounds of commercially important prawns and fishes. The fields around the backwater are suitable for aquaculture. These areas support traditional, seasonal and perennial prawn fishery. The changes in the hydrology controlled by the seasons play an important role in regulating the migrant fauna of the estuary. The Cochin backwater supports a well established endemic fauna. The nutrients and pollutants introduced into the estuary control to a great extent the distribution and abundance of less tolerant species in ecologically sensitive areas in the backwaters. Cochin backwaters, widely regarded as one of the polluted estuaries in India, receive contaminated freshwater inputs and discharges of effluents and partially treated sewage from many points throughout its tidally mixed zone. Recently, changes brought about in the estuary like reclamation and consequent shrinkage of the backwaters and the discharge of pollutants have made an adverse impact on the potential of aquatic ecosystems that used to support high levels of bioproductivity and biodiversity. The construction of Thannirmukham bund and Thottapally spillway to prevent salt water penetration into the paddy fields during pre-monsoon has led to serious ecological problems by interrupting the natural ebb and flow of tides. The hydrography, floral and faunal composition – its spatial and temporal variation plus assessments of the impact of the anthropogenic activities are presented in this review. An attempt to critically evaluate the status of the estuary from the biological and pollutional stand point is also done.     

The Processing of Leaves of Trees and Aquatic Macrophytes in the Network of the River Rhone

Breakdown rate of terrestrial and aquatic leaves was found to depend on leaf species and on the biotope considered. As the leaves started decaying at different dates and had different breakdown rates, consumable allochthonous or autochthonous organic matter was fed to the aquatic system throughout the year, from one summer to the next. A comparison with former results on the main channel confirms the existence of a transversal gradient in the fluvial network: under the influence of fungal and invertebrate colonization, breakdown was fastest in the channel of the river, slower in an open side-arm, and slower still in a more lateral and closed side arm, in which organic matter accumulated in hypoxic conditions.     

Young fish distribution in backwaters and main-channel borders of the Kanawha River, West Virginia

Fish in the Kanawha River were collected with a 0^.5-m plankton net in main-channel borders and in open areas of backwaters and with a 1-m² enclosed dropbox in shallow backwater habitats. Larval emerald shiners, Notropis atherinoides , were twice as dense, and gizzard shad, Dorosoma cepedianum , 2^.5 times as dense in main-channel borders as in backwaters; larval Lepomis spp. were 20 times as dense in backwaters as in main-channel borders. Smaller Lepomis larvae used open-water backwater areas primarily; larger larvae migrated to vegetated backwater habitats later in the summer. Backwaters appear crucial for the maintenance of nest-building fish species in temperate rivers, just as floodplains are necessary for the maintenance of high species diversity in tropical rivers.     

Seasonal dynamics of rotifers in relation to physical and chemical conditions of the river Yamuna (Delhi), India

We examined the seasonal succession of the rotifer assemblages in the backwaters of the Delhi segment of the river Yamuna in relation to 18 physical–chemical variables across one year. These shallow, weedy, and perennial aquatic biotopes support a diverse and abundant zooplankton. A total of 89 rotifer species belonging to 34 genera and 18 families were recorded. Their seasonal dynamics were characterized by (i) maxima and minima in total densities during spring–early summer and winter, respectively; (ii) individual species reaching maximum and minimum densities during different seasons; and (iii) an absence of seasonal variation in species diversity. The relative importance of various physical and chemical factors in determining rotifer community structure and seasonal succession is evaluated and Pearson-product moment correlations between physical–chemical variates and rotifer densities are analyzed and discussed.