Mercury contamination in water has been an issue to the environment and human health. In this article, mercury in marine and oceanic waters has been reviewed. In the aquatic environment, mercury occurs in many forms, which depend on the oxidation-reduction conditions. These forms have been briefly described in this article. Mercury concentrations in marine waters in the different parts of the world have been presented. In the relevant literature, two models describing the fate and behavior of mercury in saltwater reservoirs have been presented, a conceptual model which treats all the oceans as one ocean and the “ocean margin” model, providing that the ocean margins manifested themselves as the convergence of continents and oceans, covering such geological features, such as estuaries, inland seas, and the continental shelf. These two conceptual models have been summarized in the text. The mercury content in benthic sediments usually reflects is level in the water reservoir, particularly in reservoirs situated in contaminated areas (mines, metallurgical plants, chemically protected crops). The concentrations of mercury and its compounds determined in the sediments in surface waters in the different parts of the world have been presented. Due to the fact that the pollution caused by mercury is a serious threat for the marine environment, the short paragraph about mercury bioaccumulation in aquatic organisms has been included. The cited data demonstrated a large scatter of mercury contents both between the fish species and the water areas. Mathematical models, valuable tools which provide information about the possible responses of ecosystems, developed to simulate mercury emissions, both at a small scale, for local water reservoirs, and at a global scale, as well as to model mercury bioaccumulation in the chain web of aquatic systems have been described.

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Mercury in Marine and Oceanic Waters—a Review

Diversity measures in macroinvertebrate and zooplankton communities related to the trophic status of subtropical reservoirs: Contradictory or complementary responses?

The trace metal cadmium (Cd) is a toxic pollutant known to induce oxidative stress and other sublethal to lethal effects on aquatic organisms. We exposed the marine mud shrimp Austinogebia edulis to Cd concentrations of 0, 0.5, and 5 mg/kg for up to 4 days (24, 48, 72, 96 h). We studied the activity of antioxidant enzymes in the hepatopancreas, gill, and muscle of A. edulis. Antioxidant enzymes (SOD, CAT, and GPx) decreased with increasing Cd concentration and extended exposure time in these three organs of the mud shrimp A. edulis. Increasing Cd concentration led to an increase in ROS and resulted ultimately in membrane lipid peroxidation at higher Cd concentrations. Significant damage of the hepatopancreas of A. edulis was noticed at higher concentrations of Cd, showing damages like the disappearance of epithelial cell boundaries, detachment of cells from the basal lamina, cellular swelling, necrosis, and reduction of glycogen. In conclusion, Cd caused oxidative damage by reducing the activities of antioxidant enzymes and by damaging the tissue structure in major organs of the mud shrimp A. edulis.

Effects of cadmium exposure on antioxidant enzymes and histological changes in the mud shrimp Austinogebia edulis (Crustacea: Decapoda)

An exhaustive literature search supplemented by a critical examination of records made it possible to present an annotated checklist of tapeworms (Cestoda) that, as adults or larvae (metacestodes), parasitize freshwater, brackish water and marine fishes, i.e. cartilaginous and bony fishes, in South America. The current knowledge of their species diversity, host associations and geographical distribution is reviewed. Taxonomic problems are discussed based on a critical evaluation of the literature and information on DNA sequences of individual taxa is provided to facilitate future taxonomic and phylogenetic studies. As expected, the current knowledge is quite uneven regarding the number of taxa and host-associations reported from the principal river basins and marine ecoregions. These differences may not only reflect the actual cestode richness but may also be due to the research effort that has been devoted to unravelling the diversity of these endoparasitic helminths in individual countries. A total of 297 valid species, 61 taxa identified to the generic level, in addition to unidentified cestodes, were recorded from 401 species of fish hosts. Among the recognized cestode orders, 13 have been recorded in South America, with the Onchoproteocephalidea displaying the highest species richness, representing c. 50% of all species diversity. The majority of records include teleost fish hosts (79%) that harbour larval and adult stages of cestodes, whereas stingrays (Myliobatiformes) exhibit the highest proportion of records (39%) among the elasmobranch hosts. Fish cestodes are ubiquitous in South America, being mostly recorded from the Warm Temperate Southeastern Pacific (WTSP; 31%) for marine hosts and the Amazon River basin (45%) for freshwater ones. The following problems were detected during the compilation of literary data: (i) unreliability of many records; (ii) poor taxonomic resolution, i.e. identification made only to the genus or even family level; (iii) doubtful host identification; and (iv) the absence of voucher specimens that would enable us to verify identification. It is thus strongly recommended to always deposit representative specimens in any type of studies, including faunal surveys and ecological studies. An analysis of the proportion of three basic types of studies, i.e. surveys, taxonomic and ecological papers, has shown a considerable increase of ecological studies over the last decade.

Annotated Checklist of Fish Cestodes from South America

While ubiquitous, temporary waters vary greatly in geographic distribution, origin, size, connectivity, hydroperiod, and biological composition. However, all terminate as active habitats, transitioning into either dryness or ice, only to be restored when conditions improve. Hydroperiod in some temporary habitats is cyclical and predictable, while in others it is sporadic. Although the rotifer communities of temporary waters are subjected to unique selective pressures within their habitats, species share many of the same adaptive responses. Here, we review temporary waters and their rotiferan inhabitants, examining community composition, life history, and evolutionary strategies that allow rotifers to flourish in these fluctuating environments.

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Rotifers of temporary waters

The central provinces of Argentina are characterized by the presence of a high number of shallow lakes, located in endorheic basins, many of which have elevated salinities as well as eutrophic or hypereutrophic condition. The zooplankton of four saline shallow lakes of the province of La Pampa was studied on a monthly basis during a 2-year period to determine its temporal and spatial variation.



The surface of these shallow lakes (<2.5 m depth) varied between 56.8 and 215.9 ha, and some have from 8.4 to 20.8 g · l–1. The more saline lakes have “clear” water and the less saline lakes “turbid” water. Fishes, Jenynsiamultidentata , were present in only two lakes during the last two months of the studied period.



The zooplankton was composed of 17 taxa of Rotifera, 5 taxa of Cladocera and 4 taxa of Copepoda. The low diversity and the faunistic composition are characteristic of saline environments. Although the studied lakes share 38% of the species, the faunistic similarity was higher between the two least saline lakes. The lowest diversity was found in the two most saline lakes.



All four shallow lakes were characterized by their very high zooplankton density, especially in the least saline lakes (<80000 ind · l–1). The abundance is significantly correlated with the water transparency but not with salinity.



The zooplankton temporal variation was characterized by the alternation of macro- and microzooplankton, probably regulated by competition and intrazooplanktonic predation. In each lake, the spatial abundance distribution of the macro- and microzooplankton was homogeneous. It was related to the shallow depht of the lakes and their polymictic condition.



The Scheffer model on alternative states in shallow lakes acknowledges that it cannot be applied to saline lakes because Daphnia , the main responsible for the clear water state, is not tolerant to high salinity. Our study shows that the most saline lakes, where the halophylic Daphniamenucoensis is abundant, have also the most clear waters. Another difference that we found with regards to the mentioned model is that, in turbid lakes, it could not have had a top-down control on macrozooplankton exerted by fishes because in these lakes fishes were practically absent. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Zooplankton Seasonal Abundance of South AmericanSaline Shallow Lakes

Fil: Echaniz, Santiago Andres. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; Argentina

Zooplankton richness, abundance and biomass of two hypertrophic shallow lakes with different salinity

The Argentine Valley is a dune formation located in the central part of La Pampa Province, in the semiarid central region of Argentina, which habors a group of shallow lakes fed by rainfalls. These lakes share a high degree of eutrophication but differ in their physical and chemical characteristics, specially in their salinity. In order to integrate information on the composition and variation of their zooplankton assemblages, we analyzed monthly samples of three shallow lakes (“lagunas”) of different trophic degree and salinity, two of them subsaline and a third one hipomesosaline. Both subsaline lakes were turbid, and present cyanobacteria and fishes. Their zooplankton was characterized by a high diversity (32 - 37 species) and abundance, as well as by the dominance of microzooplank ton (mainly rotifers). The macrozooplankton of these lakes was represented by small-sized crustacean species, less vulnerable to the feeding interference caused by filamentous cyanobacteria, and whose low filtration efficiency contributes to keep

El zooplancton de tres lagos someros de diferente salinidad y estado trofico en la region semiarida pampeana (argentina) zooplankton of three shallow lakes of different salinity and trophic state in the semiarid pampean region (argentina)

Many aspects of the ecology of temporary wetlands are known in other countries, but not in Argentina. Although many conclusions about the functioning of temporary ecosystems can be adapted to those of Argentina, the presence in them of many neotropical endemic taxa makes their application may be limited. The aims of this work were to analyze the variation in the environmental variables and zooplankton of a temporary lake of the central region of Argentina and to test the hypothesis that specific richness and abundance decrease whereas biomass increases due to increased salinity accompanying drying. Water and zooplankton samples were taken from December 2005 (salinity = 10.4 g.L -1 ) until -1 ), before it became dry. The lake was hypereutrophic and had reduced transparency. We recorded 16 taxa and verified the decrease in taxonomic richness and replacement, with the appearance of halophilic crustaceans towards the end of the study. Contrary to our expectations, the density increased towards the end. Rotifers predominated, accounting for 96% of total density and contributing over 47% of total biomass. This makes the lake studied more similar to other shallow lakes of La Pampa but with lower salinity, permanent, with fishes and very low proportion of inorganic suspended solids.

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Changes in the zooplankton and limnological variables of a temporary hypo-mesosaline wetland of the central region of Argentina during its drying

Temporary wetlands alternate dry phases with hydroperiods of varying duration. When their salinity is high it becomes one of the abiotic factors more influencing on wetland ecology. Due to the temporary nature of the ecosystem, the physico-chemical and biological parameters exhibit relatively large variation in short time periods; therefore studies limited to short periods cannot record long-term dynamics. Temporary aquatic ecosystems in other latitudes have been well studied; however those in Argentina have received little attention, despite their high frequency; particularly in the semi-arid central-west belt. Given that in La Pampa province (central region of Argentina) data previously collected from different hydroperiods of several temporary saline lakes are available, the aim of this study was to compare and establish relationships between physico-chemical parameters, and zooplankton taxonomic composition, diversity and biomass, recorded in two consecutive annual cycles in a saline lake in the northern of the province. Seasonal water and zooplankton samples were obtained during 2006 and 2007. Salinity differed, and increased from a mean of 23.98 g.L-1 (2006) to 36.71 g.L-1 (2007). Transparency, total phosphorus, chlorophyll-a, and total suspended solid concentrations did not differed. Total species richness was reduced (six and three species in 2006 and 2007, respectively), and was negatively correlated with salinity. Halophilic species, including Boeckella poopoensis, Brachionus plicatilis, and Moina eugeniae were registered during both years. Total zooplankton density and biomass were not significantly distinct, neither those of copepods and rotifers; however cladocerans were negatively affected by salinity, resulting in decreased density and biomass in 2007. The zooplankton species inhabiting this saline lake are halophilic, which can explain the few differences observed in biological parameters between the two annual cycles.

https://www.journal-aquaticscience.com/article_73515_ca61aabc8c3b018535911b63be27e240.pdf

Do temporary lakes vary from year to year? A comparison of limnological parameters and zooplankton from two consecutive annual cycles in an Argentine temporary saline lake

Santiago Andrés Echaniz

Papers

Zooplankton Seasonal Abundance of South AmericanSaline Shallow Lakes

Zooplankton richness, abundance and biomass of two hypertrophic shallow lakes with different salinity

El zooplancton de tres lagos someros de diferente salinidad y estado trofico en la region semiarida pampeana (argentina) zooplankton of three shallow lakes of different salinity and trophic state in the semiarid pampean region (argentina)

Changes in the zooplankton and limnological variables of a temporary hypo-mesosaline wetland of the central region of Argentina during its drying

Do temporary lakes vary from year to year? A comparison of limnological parameters and zooplankton from two consecutive annual cycles in an Argentine temporary saline lake