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Current velocity and hydrographic measurements were obtained in Mossoró estuary, a tropical semiarid estuary in Northeastern Brazil, to explore the hydrodynamic regime associated with marked seasonal variability in evaporation and precipitation. Measurement campaigns were performed during dry conditions in October 2012 and wet conditions in May 2013. Dry season observations showed along-estuary density gradients of order 0.001 kg/m 4 with salinity increasing upstream in the first 20 km up to a value of 70 g/kg. Salinity then decreased to a value of 48 g/kg at the upstream limit of the section. During this dry season, the residual flow structure changed drastically from spring to neap tides. Neap tide residual flows showed inflow of oceanic water at the surface and outflow of hypersaline water underneath. Spring tide residual flows showed net inflow throughout the water column in the middle of the section and outflow over the flanks, a laterally sheared structure consistent with tidally induced residual flows. In the wet season, along-estuary density gradients were of similar magnitude to the dry season but in the opposite direction. Residual flows in neap tides were as expected for density-driven flows: outflow at surface and inflow underneath. During spring tides, residual flows were dominated by outflows over the flanks and inflow in the middle of the section, once again consistent with tidally driven residuals. Advective accelerations from tides were compared to baroclinic pressure gradients, in the non-dimensional tidal Froude number ( Fr 0 ), to explore the changes from tidally driven to density-driven residual flows. Results indicated that residual flows in this estuary were driven by tidal rectification ( Fr 0 >> 1) in spring tides and by density-gradients ( Fr 0 << 1) in neap tides. Thus, estuarine residual flows switch from density-driven in neaps to tidally driven in springs. In general, it is proposed that the switch can be diagnosed with Fr 0 . [ABSTRACT FROM AUTHOR]

Nine surface water surveys were performed in the Formoso estuary (Brazil) during 2012-2013 mainly in summer and winter periods and during spring tide. Temporal variations of temperature, salinity, phosphate, silicate, total alkalinity, dissolved inorganic carbon, partial pressure of CO2 (pCO2) and water-air CO2 fluxes were analyzed. Low rates of water-air CO2 fluxes (4.7 ± 8.0 mmol C m-2d-1) were estimated despite the different climate conditions. pCO2 values ranged from 190 to 988 µatm. These values are lower than those observed in other tropical estuaries. CO-2 fluxes presented in this study contribute to the characterization of humid tropical estuarine systems, thus filling an important geographical information gap. [ABSTRACT FROM AUTHOR]

This paper aims to study the ontogenetic sexual dimorphism of Genidens genidens in Guanabara Bay, southeastern coast of Brazil. Altogether 378 specimens were anayzed (233 females and 145 males) with total length ranging from 13.3 to 43.5 cm. Specimens were measured for 12 body measurements, sex was identified and maturity stages were recorded and classified. Pearson's linear correlation reveled a significant positive correlation between total length and all other body measures, except for base adipose fin, mouth depth and eye depth for immature females. Analyses nested PERMANOVA desing showed significant differences between maturity stages for each sex, between sexes considering or not maturity stages, indicating a variation in morphometric characteristics driven by sexual dimorphism. Differences among all maturity stages were also found, indicating an ontogenetic morphological difference. But immature individuals didn't differ between sexes indicating that differentiation patterns starts with sexual development. The most important measures differing males and females were related to head characteristics, which appears to be key parameters to evaluate sexual differences. Due to male incubation of fertilized eggs and juvenile individuals <59 mm in their oral cavity, head measures are proposed to be sex dimorphism not related to reproduction, but with post reproductive fase due to ecological and biological needs. [ABSTRACT FROM AUTHOR]

A comparative study of fish assemblages of a marine protected area and an exploited area was carried out in the Sine Saloum estuary (Senegal, West Africa). Data were collected at these two sites between 2008 and 2011. The two areas are morphologically similar, and comparison of the physicochemical parameters (salinity, transparency, temperature and percentage of saturation of dissolved oxygen) showed that the water masses are similar. The bio-ecological indicators and ecological, trophic and size structures were also compared. Given the environmental similarity of the two sites, their differences in bio-ecological characteristics and fish assemblage organization can be explained by the protection status of the MPA. The species richness and fish abundance per sampling unit were higher in the exploited site, but the mean trophic level and the observed maximum size of individuals were higher in the MPA. Although slightly higher for the MPA, the differences observed for biomass and average size between the two sites were not significant. The beta diversity in the MPA was higher than in the exploited site. The fish assemblage was dominated in terms of abundance by two pelagic herbivores Ethmalosa fimbriata (80%) and Sardinella maderensis (12.3%) and in terms of biomass by E. fimbriata (37.4%) and a benthic predator, Arius latiscutatus (23.7%). The assemblage of the MPA had a marine affinity characterized by the presence of piscivorous or generalist predators; large individuals were not uncommon. In the exploited site, the fish assemblage was relatively stable, dominated in abundance by E. fimbriata (33.4%) and S. maderensis (32.8%). In terms of biomass, a species of mullet, Liza dumerili , ranked first (26.2%), followed by E. fimbriata (22.4%) and S. maderensis (14.9%). The assemblage in the exploited site had a more estuarine affinity, dominated by detritivorous or phytophagous herbivores. Individuals observed there were mostly of small or medium size. This study confirms that the establishment of MPA is an effective tool for restoring marine biodiversity and trophic structure of fish assemblages. [ABSTRACT FROM AUTHOR]

This study analyses the spatial and temporal distribution of the dominant Sciaenids in the Caeté estuary on the northern coast of Brazil. Samples were taken by otter trawls in four areas of the Caeté estuary between October 1996 and August 1997 six bimonthly. Stellifer rastrifer, Stellifer naso and Macrododon ancylodon presented the highest biomass out of eleven species of Sciaenidae caught. Minimum and mean length at first maturity were calculated and the main spawning periods determined. Changes in the spatio-temporal distribution of the three species were related to seasonal changes in estuarine salinity and spawning pulses. Larvae and juveniles of S. rastrifer, S. naso and M. ancylodon were found in the inner estuary while larger specimens were more abundant in the outer estuary with higher salinities. M. ancylodon spawned from October to February and rested from April to August whereas S. rastrifer and S. naso spawned throughout the year, though with two peaks, in October-December and June.O presente estudo caracteriza a distribuição espaço-temporal dos peixes com maior abundância dentre a família Sciaenidae no estuário do rio Caeté, litoral norte do Brasil. Estima-se o comprimento de inicio da maturação sexual, o comprimento médio da primeira maturação sexual e os períodos de desova. Para tal, durante os meses de outubro de 1996 a agosto de 1997, foram feitas 6 coletas bimestrais, através de arrastos de fundo. A partir de subamostras das espécies mais abundantes dentro das capturas, construíram-se distribuições de freqüência de comprimento total, que foram analisadas por período e local de coleta. De onze espécies de Sciaenidae coletadas, a maior contribuição em abundância de exemplares foi feita pelas espécies Stellifer rastrifer, Stellifer naso e Macrodon ancylodon. Determinou-se que a distribuição espacial das espécies no sistema, está relacionada com mudanças periódicas na salinidade dentro do estuário e a sua dinâmica de reprodução. Assim, os juvenis de S. rastrifer, S. naso e M. ancylodon distribuíram-se nas áreas mais internas do estuário e os adultos nas águas costeiras, com maiores teores de salinidade. Enquanto que M. ancylodon apresenta desovas periódicas durante outubro a fevereiro, S. rastrifer e S. naso apresentam desovas parceladas com dois picos mais intensos de outubro a dezembro e durante junho.

The composition of the mesozooplanktonic community was studied in the Punta Morales estuary, Gulf of Nicoya,Pacific coast of Costa Rica,during 1997.Oblique plankton hauls were performed during high and low tide using a 280 µm mesh screen net equipped with a flowmeter.The community was characterized by holoplanktonic and meroplanktonic organisms.For the holoplanktonic community,the main groups were copepods (80%)and chaetognaths (16%).The most abundant species were the copepods Acartia lilljeborgii and Paracalanus parvus.A.lilljeborgii is a typical estuarine species that maintains high populations in estuarine systems.Meroplankton was represented mainly by crustacean larvae (66%),and icthyoplankton (18%).The dominance of crustacean larvae and icthyoplankton is an evidence of the ecological importance of the Punta Morales zone.Rev.Biol.Trop.52(4):897-902.Epub 2005 Jun 24.Se estudió la composición de la comunidad mezoplanctónica en Punta Morales,Golfo de Nicoya, Pacífico de Costa Rica,en 1997,arrastrando oblicuamente una red de plancton (280 µm,con flujómetro)durante marea alta y baja.La comunidad estuvo caracterizada por la presencia de organismos holo y meroplanctónicos.Los principales grupos holoplanctónicos fueron copépodos (80%)y quetognatos (16%).Las especies más abundantes fueron los copépodos Acartia lilljeborgii y Paracalanus parvus;A. lilljeborgii es una especie estuarina típica que mantiene altas poblaciones en sistemas estuarinos.El meroplancton estuvo representado principalmente por larvas de crustáceos (66%),e ictioplancton (18%).La dominancia de larvas de crustáceos e ictioplancton evidencian la importancia ecológica de la zona de Punta Morales.

The lack of knowledge about highly anthropised tropical ecosystems poses a problem for their conservation. Using carbon and nitrogen stable isotopes, we studied the food web structure of the estuarine ecotone of the Santa Cruz Channel (SCC), which constitutes a critical habitat for many socio-economically important species in northeast Brazil. Therefore, we assessed the spatial (estuary/coast) and seasonal (dry/rainy) isotopic variation of basal food sources, invertebrates and fishes. We also used Bayesian mixing models to trace the origin (estuary vs coast) of the organic matter sources supporting SCC fishes food webs according to their feeding habits. We found a wide range of δ13C and δ15N values for basal sources, invertebrates, and fish in coastal and estuarine environments, but isotopic compositions showed greater variability in the estuary. This illustrated the heterogeneity of primary producers and sources in estuaries, intensified by SCC morphology, as both accesses to the sea provide strong mixing between riverine and marine inputs. Additionally, we found differences between fish isotope compositions according to their guilds. Coastal basal sources significantly support zoobenthivorous, piscivorous and zooplanktivorous fish estuarine food webs. Conversely, detritivores are supported by enriched sources of organic matter, especially during the dry season, which may be derived from terrestrial inputs. As contaminated land-based inputs can affect food webs and coastal fisheries, developing a management plan that includes all interconnected habitats is necessary. • Coastal basal sources support estuarine fish food webs in the study area. • Carbon sources supporting fish communities varied according to their trophic guild. • Estuarine geomorphology may influence food web structure. [ABSTRACT FROM AUTHOR]

In the Matang Mangrove Forest Reserve (MMFR), the role of microzooplankton (20–200 μm) grazing on phytoplankton as a channel for carbon transfer to higher trophic levels was investigated. Our results showed that primary production was higher during the southwest monsoon (SWM) (1905 ± 1478 μgCl−1d−1) than in the northeast monsoon (NEM) (708 ± 474 μgCl−1d−1). Microzooplankton grazing was tightly coupled to primary production in both SWM and NEM, accounting for 97% and 68% of primary production, respectively. Both primary production (activation energy: 1.29 ± 0.54 eV) and microzooplankton grazing (2.05 ± 0.63 eV) showed temperature dependency, and revealed a shift towards heterotrophy with seawater warming, specifically at temperatures above 32 °C. As a conclusion, the microbial food web in MMFR is characterised by high primary production that was efficiently grazed by microzooplankton. • Relative to other tropical mangrove forests, primary production in the mangrove estuary of Matang was high. • Microzooplankton grazing was tightly coupled to primary production. • There were monsoonal differences in the classical food chain but not in the microbial loop. [ABSTRACT FROM AUTHOR]

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Total mercury concentrations were determined by atomic absorption spectrometry in muscle tissue of two commercially important species of carnivorous fishes croaker ( Micropogonias furnieri) and cutlassfish ( Trichiurus lepturus) caught in Itaipu estuary, Rio de Janeiro. In this study, whitemouth croaker presented more mercury than Atlantic cutlassfish. Bioaccumulation differences can be explained by the biological behavior of juveniles whitemouth croaker, that remain in the estuary up to maturity, which makes them good indicators of local environmental impacts (0.110 mg Kg HgT). It also can be explained by differences in nutritional requirements between the different life stages of two species. The analysis showed the presence of low levels of the metal. However, our results suggest a possible risk to human health, depending on the level of fish consumption. [ABSTRACT FROM AUTHOR]

Assessing artisanal fishing effort and catches in remote tropical coastal areas is a continuous challenge for fisheries data collection. This is the first spatio-temporal analysis of the large tidal weir (LTW) fishery operating on intertidal sand banks along the world's longest mangrove coast, north Brazil. Airborne synthetic-aperture radar (SAR) images and aerial photos were integrated with field sampling to investigate catch and discard compositions of seven LTW during the main fishing season. LTW measurements on the SAR images were used to generate estimates on daily catch,wood extraction, and sand accumulation. In a coastal stretch of 67 km, 793 LTW were identified on SAR images from 2004, including 573 active LTW. The number of active LTW in Taperaçú Bay and Caeté Bay had increased from 87 in 1998 to 132 in 2004 (52% increase), and from 92 to 202 (106% increase), respectively. Sixty-five fish species from 24 families were captured in the LTW. Ariidae, Sciaenidae, Haemulidae, and Carangidae accounted for 45, 20, 10, and 7% of the total sampled catch weight of 3441 kg, respectively. The mean daily catch per LTW was 110 kg+9 SE. Total discards in outer estuarine LTW were .3 times higher than in inner estuarine LTW. All Aspredinidae, Belonidae, Tetraodontidae, and Trichiuridae, and >75% of Auchenipteridae, Clupeidae, Engraulidae, Ephippidae, Loricariidae, Scombridae, and Soleidae were discarded. The LTW fishery apparently practices balanced harvesting; however, the massive LTW increase suggests fishing effort reduction to moderate levels. Mangrove wood extraction for LTW construction (22 835 m³ or 855 390 trees) and sand accumulation (144 802 m³) likely have only local scale effects, negligible for the overall ecosystem dynamics. The study highlights the potential of SAR images for use in fisheries data collection and management of tropical coasts, emphasizing the need for integration with ground-truthing field studies. [ABSTRACT FROM AUTHOR]

Accurate determination of abundance and richness of fish early stages in estuarine zones is critical to support management and protection plans; it is therefore necessary to consider all influential factors. Habitat diversity, seasonality, moon phase and diel variations, and their interactions are factors that can affect richness and abundance estimations. Appropriate spatial and temporal scales in sampling design are important to understand the assemblage dynamics of fish early stages. The objective of this research is to test how temporal and spatial scales influence the determination of abundance and richness of fish early stages based on a hierarchical sampling design considering season (dry and rainy), moon phase (new, crescent, full, and waning), day period (sunrise, midday, sunset, and night), habitat (coastal, riverine, mangrove, and Vallisneria americana beds), and their interactions. Samples were collected using a conical zooplankton net and towed horizontally for 5 min at a depth of 50 cm. A variance component analyses model showed that day period, season, and their interactions were the main factors determining variations in fish early stage abundances and richness (26.68, 10.78, and 12.82 %, respectively). The highest abundance and richness occurred at night, with significant seasonal variations related to the runoff from the Grijalva-Usumacinta basin. Abundance and richness were higher in the dry season, which were related to higher dissolved oxygen and water transparency. Presented findings can be generalized to tropical and subtropical estuaries with shallow waters. [ABSTRACT FROM AUTHOR]

While there is already a comprehensive understanding of the effects of environmental variables, such as dissolved oxygen, temperature and salinity, on the structure, biomass and metabolism of aquatic biota in estuarine habitats, the effect of sedimentation, a harmful underlying factor, remains unclear. The aim of this study was to assess the differences in fish assemblages along the freshwater to salt water gradient of a large tropical estuary, and to evaluate the effects on them of habitat disturbance associated with shallow water sedimentation in the intertidal areas. Fish and environmental variables were recorded in the upper, middle and lower salinity zones of the estuary at ebb tide in both the dry and wet seasons. Sediment samples associated with different levels of habitat disturbance were analysed using granulometry, and their organic content and dissolved oxygen levels were quantified. Water temperature, salinity, pH and dissolved oxygen levels were also measured. Habitat disturbance was found to be correlated with the density, biomass and richness of fish assemblages. A total of 77 species were recorded, forming two distinct fish assemblages, with the Eleotridae family dominating in the upper zone, and Gerreidae, Gobiidae and Tetraodontidae the most common in the middle and lower estuary. Changes in the structure of fish assemblages, including reductions in density, biomass and richness, were associated with disturbance to natural features, where muddy sediment was replaced by sandy sediment and the quantity of organic matter fell. Atherinella brasiliensis was the species which showed a preference for the disturbed areas in the middle and lower zones, while Dormitator maculatus showed a preference for them in the upper estuary. They may be taken as indicators of habitat disturbance due to shallow sedimentation. [ABSTRACT FROM AUTHOR]

Background: Recent studies suggest that increasing ocean acidification (OA) should have strong direct and indirect influences on marine invertebrates. While most theory and application for OA is based on relatively physically-stable oceanic ecological systems, less is known about the effects of acidification on nearshore and estuarine systems. Here, we investigated the structuring of a benthic infaunal community in a tropical estuarine system, along a steep salinity and pH gradient, arising largely from acid-sulphate groundwater inflows (Sungai Brunei Estuary, Borneo, July 2011-June 2012). Results: Preliminary data indicate that sediment pore-water salinity (range: 8.07 - 29.6 psu) declined towards the mainland in correspondence with the above-sediment estuarine water salinity (range: 3.58 - 31.2 psu), whereas the pore-water pH (range: 6.47-7.72) was generally lower and less variable than the estuarine water pH (range: 5.78-8.3), along the estuary. Of the thirty six species (taxa) recorded, the polychaetes Neanthes sp., Onuphis conchylega, Nereididae sp. and the amphipod Corophiidae sp., were numerically dominant. Calcified microcrustaceans (e.g., Cyclopoida sp. and Corophiidae sp.) were abundant at all stations and there was no clear distinction in distribution pattern along the estuarine between calcified and non-calcified groups. Species richness increased seawards, though abundance (density) showed no distinct directional trend. Diversity indices were generally positively correlated (Spearman's rank correlation) with salinity and pH (p <0.05) and negatively with clay and organic matter, except for evenness values (p >0.05). Three faunistic assemblages were distinguished: (1) nereid-cyclopoid-sabellid, (2) corophiid-capitellid and (3) onuphid-nereid-capitellid. These respectively associated with lower salinity/pH and a muddy bottom, low salinity/pH and a sandy bottom, and high salinity/pH and a sandy bottom. However, CCA suggested that species distribution and community structuring is more strongly influenced by sediment particle characteristics than by the chemical properties of the water (pH and salinity). Conclusions: Infaunal estuarine communities, which are typically adapted to survive relatively acidic conditions, may be less exposed, less sensitive, and less vulnerable than epibenthic or pelagic communities to further acidification of above-sediment waters. These data question the extent to which all marine infaunal communities, including oceanic communities, are likely to be affected by future global CO2-driven acidification. [ABSTRACT FROM AUTHOR]

Estuarine systems undergo different physical processes that simultaneously control their stratification and mixing dynamics. This energy balance determines both, the estuarine hydrodynamics and the dynamics of water. This article presents a quantitative and comparative analyses between the forces maintaining stratification (surface heating; rainfall precipitation; and differential advection of the longitudinal density gradient due to the vertical velocity field) and those responsible for the vertical mixing (mechanical stirring of bottom tidal stress; mechanical stirring ofsurface wind stress; and surface evaporation) in the lower estuary ofthe Jaboatão River (JE), Pemambuco, NE-Brazil. The energy available to mix the water column at the' lower Jaboatão was 2.2 and 2.0-fold greater than that available to promote stratification, during the dry and rainy seasons, respectively. The bottom shear turbulence caused by the tides was the major source of energy for the vertical mixing. A theoretical analyses revealed that the turbulence decay time-scale io both seasons was much greater (dry=29min; rainy=25 min) than the stratification time-scale (dry=8 mio; rainy=7 min) and than the slack water time-scale (15 min). Thus the estuary was vertically well-mixed even during slack water periods during both, dry and rainy seasons. Theoretical results were confirmed by field data and are in agreement with earlier numerical simulations.Sistemas estuarinos estão sujeitos à influência simultânea de processos fisicos que controlam tanto sua dinâmica de estratificação quanto de mistura. Este balanço energético determina seu comportamento hidrodinâmico e a dinâmica das propriedades da água. O presente artigo apresenta uma análise quantitativa e comparativa das forças de manutenção da estratificação (aquecimento superficial; precipitação pluviométrica e advecção diferencial do gradiente longitudinal da densidade devida ao campo vertical da velocidade), e daquelas responsáveis pela mistura vertical (turbulência de fimdo devido às marés; turbulência de superficie devida à ação dos ventos e evaporação superficial) no baixo estuário do Rio Jaboatão (JE), Pemambuco, NE-Brasil. A quantidade de energia disponível para misturar a coluna d'água foi 2,2 e 2 vezes maior que aquela disponível para manter a estratificação durante as estações seca e chuvosa, respectivamente. O atrito turbulento de fimdo pelas marés foi a principal fonte de energia do sistema para a mistura da coluna d'água. Uma análise teórica revelou que a escala de tempo para o decaimento turbulento nas duas estações sazonais foi superior (seca=29 min; chuvosa=25min) que a escala de tempo para estratificação (seca=8min; chuvosa=7 min) e que a escala de tempo dos estofos de maré (15 min). Assim, o estuário apresentou-se verticalmente bem misturado mesmo durante os estofos de preamar e baixa-mar tanto na estação seca quanto chuvosa. Os resultados teóricos foram confirmados pelos dados de campo e estão em concordância com aqueles obtidos em estudos prévios de simulação numériCa.

Microplastics (MPs) are widely distributed in marine ecosystems, and their ubiquitous presence is raising concern, particularly about possible impacts on fisheries resources. In tropical regions, shellfish fisheries represent an essential source of income and subsistence for traditional communities, and adverse effects on these resources may have severe consequences on human health. In the present study, bivalve molluscs of the species Anomalocardia flexuosa , captured in the region of the Itapessoca estuary in Pernambuco, Brazil, were analysed. A total of 90% of the individuals presented MP particles in their tissue. We observed an average of 5.15 ± 3.80 MP particles per individual, and for each gram of soft tissue, 3.66 ± 2.59 MP particles were found. Our results showed that MPs are present in clams captured on the Pernambuco coast and that the species studied proved to be suitable for monitoring the levels of microplastic pollution. • This is the first record of microplastic in Anomalocardia flexuosa in South America. • Microplastics were present in 90% of the specimens analysed. • For each gram of A. flexuosa soft tissue, 3.66 ± 2.59 microplastic particles were found. • Anomalocardia flexuosa can be used to monitor the levels of MP contamination. [ABSTRACT FROM AUTHOR]

Four sediment cores representing adjacent mudflat and mangrove sub-environments of middle estuary (Shastri) were analyzed for sand, silt, clay, and organic carbon. Total metal concentration of iron (Fe), manganese (Mn), nickel (Ni), zinc (Zn), chromium (Cr), copper (Cu), cobalt (Co), and lead (Pb) and chemical speciation of Fe, Mn, and Co on selected samples was also carried out on mudflat cores. The sediments in the upper middle estuary were found to be deposited under highly varying hydrodynamic energy conditions; whereas lower middle estuary experienced relatively stable hydrodynamic energy conditions with time. The tributary joining the river near the upper middle estuary is found to be responsible for the addition of enhanced organic carbon and metal concentrations. Speciation study indicated Fe and Co are from natural lithogenic origin while Mn is derived from anthropogenic sources. Higher Mn and Co than apparent effects threshold can pose a high risk of toxicity to organisms associated with these sediments. [ABSTRACT FROM AUTHOR]

A twelve-month investigation was undertaken on how copepod community structure varied in relation to environmental factors in the Coleroon estuary, south-east India. Sampling was monthly, from Station 1 in the sea to Station 4 in the Vettar backwaters. Canonical correspondence analysis (CCA) was applied to elucidate the environmental factors affecting the copepod community. A total of 104 copepod species in 38 genera and 26 families were recorded, with the Calanoids, Acartia erythraea and Oithona brevicornis being the most dominant. At all four stations, both these species loaded near the intercept of CCA axes 1 and 2, perhaps reflecting that they were autochthonous. Most species occurred in distinct seasonal patterns. Abundances ranged from 13 × 103 to 215 × 103 (ind. m−3). Coleroon waters showed high diversity (bits/ind.), from 5.29 at Station 3 to 4.97 at Station 4. Abundance correlated positively with temperature and salinity and negatively with rainfall, dissolved oxygen concentration (DO) and pH. Species diversity correlated strongly with abundance (P < 0.01). Abundance and diversity were highest during the summer, and both correlated positively with salinity. Temperatures (air and water), salinity, pH and DO varied in the ranges 26–36°C, 25–34.2°C, 9–38, 7.0–8.7 and 3.0–6.8 ml l-1, respectively. Nitrate, nitrite, phosphate and silicate (µM) varied in the ranges: 4.7–64.5, 0.4–14.1, 0.2–12.9 and 9.3–148, respectively. [ABSTRACT FROM PUBLISHER]

Brazilian mangroves have ecological and economic importance, with molluscs, crustaceans and polychaetes being diverse and common faunal groups. The present study characterizes the macrofauna associated with logs from two mangrove forests in Pará State, northern Brazil, sampled in September, January and April, between 2008 and 2010, at three different distances from a tidal channel (2, 10, 20 m). In each forest, five logs (diameter/length: 10/40 cm) were randomly selected at each distance, totalling 15 logs per sampling date. The macrofauna was removed, counted and identified. Three-way analysis of variance was used to compare mean numbers of individuals, numbers of taxa and Berger–Parker dominance per log, between forests and among sampling dates and distances from the tidal channel. Non-metric multidimensional scaling and permutational multivariate analyses of variance were used to investigate macrofaunal structure in relation to the three factors. A total of 5437 individuals from both estuarine and terrestrial faunas was found in both forests, with 85 taxa distributed among Mollusca, Annelida, Arthropoda and Nemertea. Abundance increased from September through January to April in both mangrove forests. The most dominant species was Neoteredo reynei, representing 48% of total abundance. No significant difference in any variable was found among the two forests and between the three distances. Logs may represent a stable microhabitat for the macrofauna, with little variation in humidity, salinity or temperature, despite different distances from the tidal channel. However, macrofaunal structure varied significantly between forests and among sampling dates, probably due to seasonal differences in precipitation and salinity between both locations. [ABSTRACT FROM PUBLISHER]

The article discusses research investigating fish community structure and its relationship to the environment in Sabancuy Estuary in Campeche State, Mexico during a dry season and a rainy season. The authors' objective was to determine fish distribution and abundance using several environmental parameters to improve resource management practices. The most abundant families recorded were Gerridae, Sciaenidae, Sparidae, Lutjanidae, and Ciprinodontidae.

Abstract: The 3-day diurnal dynamics of carbonate system and related parameters on Luhuitou fringing reef of Sanya Bay-adjacent to the South China Sea (SCS) were observed in December of 2009 (early winter), April (spring), July (summer) and November (late-autumn) of 2010. The Luhuitou fringing reef ecosystem was generally dominated by macro and planktonic algae throughout the year except by coralline algae in winter. The system parameters showed distinct diurnal trends in the four seasons. Averaged ranges of diurnal variation for dissolved oxygen and partial pressure of CO2 (pCO2) were higher in the autumn, 4.67mgL−1 and 218.2μatm, respectively than other seasons. Averaged ranges of diurnal variation for normalized total alkalinity (NTA) was higher in the winter (61.3μmolkg−1), and lower in the spring (16.0μmolkg−1). The diurnal variations are mainly controlled by biological activities, especially by the processes of photosynthesis and respiration in the reef ecosystem. In winter, however, calcification and dissolution contributed more to the diurnal variations, compared with the other three seasons. Total alkalinity was largely related to seasonal changes in river inflow rates. Dissolved oxygen, pH, total CO2 and aragonite saturation also showed seasonal variations. These variations were mainly controlled by the seasonal changes of photosynthesis and respiration, which were mainly affected by changes in benthic community structure, temperature and river inflow rates. The oversaturated pCO2 in the reef ecosystem with respect to the atmosphere in the winter and summer resulted in CO2 discharge from the reef ecosystem to the SCS. The whole system served as net source of CO2 to the atmosphere and the adjacent South China Sea on an annual time scale. [Copyright &y& Elsevier]

Macrofaunal community structure is determined by a number of environmental variables. The riverine run-off during the monsoon brings about drastic changes in the physico-chemical parameters of a tropical estuary. The aim of the present study was to investigate the influence of rainfall in structuring the benthic macrofaunal community of a tropical estuary. The temporal dynamics of the macrobenthic community in the monsoon dominated Mandovi estuary (central west coast of India) was studied fortnightly from June 2007 to June 2009. A fixed location, downstream of the Madovi river, was sampled for benthic and water parameters. Ten replicates were collected during each sampling date using a Van Veen grab (0.04 m2). The macrofaunal abundance showed temporal fluctuation. The multivariate analysis showed the clustering of the samples linked to the environmental parameters (CCA and LINKTREE). The temporal variation observed in the macrofaunal abundance was basically due to changes in abundance of the dominant species. The variation in macrofaunal abundance was brought about by the recruitment and settling of re-suspended adults. It can be concluded that the macrofaunal structuring is influenced by temporal changes in the environment associated with the annual monsoon rainfall. Hence climate induced changes in the monsoonal pattern may affect the macrobenthic assemblages of tropical estuaries. [ABSTRACT FROM PUBLISHER]

Seasonal studies were carried out from 21 stations, comprising of three zones, of Cochin Estuary, to assess the organic matter quality and trophic status. The hydographical parameters showed significant seasonal variations and nutrients and chlorophylls were generally higher during the monsoon season. However, chemical contamination along with the seasonal limitations of light and nitrogen imposed restrictions on the primary production and as a result, mesotrophic conditions generally prevailed in the water column. The nutrient stoichometries and δC values of surficial sediments indicated significant allochthonous contribution of organic matter. Irrespective of the higher content of total organic matter, the labile organic matter was very low. Dominance of carbohydrates over lipids and proteins indicated the lower nutritive aspect of the organic matter, and their aged and refractory nature. This, along with higher amount of phytodetritus and the low algal contribution to the biopolymeric carbon corroborated the dominance of allochthonous organic matter and the heterotrophic nature. The spatial and seasonal variations of labile organic components could effectively substantiate the observed shift in the productivity pattern. An alternative ratio, lipids to tannins and lignins, was proposed to ascertain the relative contribution of allochthonous organic matter in the estuary. This study confirmed the efficiency of an integrated biogeochemical approach to establish zones with distinct benthic trophic status associated with different degrees of natural and anthropogenic input. Nevertheless, our results also suggest that the biochemical composition alone could lead to erroneous conclusions in the case of regions that receive enormous amounts of anthropogenic inputs. [ABSTRACT FROM AUTHOR]

Leite, N.R., Magalhães, A., Palma, M.B., Flores Montes, M., Pereira, L.C.C. and Costa, R.M. da, 2013. Diel variation in the zooplankton of a highly dynamic Amazonian estuary. In: Conley, D.C., Masselink, G., Russell, P.E. and O'Hare, T.J. (eds.), Proceedings 12th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1146-1151, ISSN 0749-0208.--> The short-term dynamics (circadian and tidal cycles) of the zooplankton community were investigated in the Taperaçu estuary in northern Brazil. The plankton samples were collected in April (rainy season) at a fixed station, located in the middle sector of this estuary, through horizontal tows (plankton net with 200 μm mesh), every 3 hours over a 24-hour period, during the spring tide. Altogether, 51 zooplankton taxa were identified, of which the copepods Paracalanus quasimodo (34.6 to 13,852.8 ind.m−3; mean: 2,320.8±3,842.2 ind.m−3), Labidocera fluviatilis (2.0 to 3,209.2 ind.m−3; mean: 484.5±804.4 ind.m−3), Pseudodiaptomus marshi (9.7 to 1,599.6 ind.m−3; mean: 453.9±580.5 ind.m−3), and Acartia tonsa (27.6 to 3,953.6 ind.m−3; mean: 694.4±1,269.4 ind.m−3) were the dominant species. While no significant short-term variation was observed in hydrological or biological parameters, fluctuations related to tidal height were recorded in abiotic parameters and the density of the principal zooplankton taxa. The temporal variation in copepod populations tended to reflect that of total zooplankton abundance. Mean zooplankton density varied from 509.1 ind.m−3 (ebb tide, at 16:30 h) to 25,514.3 ind.m−3 (flood tide, at 10:30 h), with an overall mean of 5,872.1±8,286.4 ind.m−3. Oscillations in the density of P. quasimodo, L. fluviatilis, and P. marshi were influenced by the morphological and morphodynamic characteristics of the Taperaçu estuary, associated with the recruitment of individuals from the adjacent Caeté estuary, which constitutes an important factor determining the structure of the zooplankton community recorded in the present study. [ABSTRACT FROM AUTHOR]

Melo, K.R., Tagliaro, C.H. and, Beasley, C.R., 2013.Seasonal changes in the subtidal benthic macrofauna of a mangrove coast Mangrove coasts in northern Brazil are subject to seasonal discharges of freshwater input from rivers and terrestrial runoff. However, little is known about the effects of freshwater discharge on the subtidal benthos in the region. Thus, three sites, each representing a different level of seasonal discharge, Canela island (low), Ajuruteua beach (medium), and the Caeté Bay (high) were sampled in the dry (October) and wet (April/May) seasons of 2007 and 2008, respectively. Sampling was carried out using a Petersen grab and a bottom dredge (total n=74). Additional replicas (n=12) were obtained by grab for sediment analyses. Salinity and turbidity of the bottom waters, and percentage of silt/clay in the sediment were also measured. Benthic macrofauna and environmental data were analyzed using uni- and multivariate techniques. A total of 661 individuals were distributed among 47 taxa of which polychaetes and crustaceans dominated at all three sites. No significant differences in macrofaunal abundance were found among sites and dates. At all sites, in the wet season, the number of taxa was low and dominance was high, especially in the Caeté Bay. The polychaete Nephtys fluviatilis only occurred in the Caeté Bay in the wet season, and yet was the dominant taxon (22.7% of total abundance). The Ajuruteua beach and Canela island samples were composed of typically marine taxa. The polychaete Armandia sp., the gastropod Olivella minuta, mysiid and phoxocephalid crustaceans and the echinoderm family Mellitidae were most abundant in the dry season at Canela island. Salinity was the most important environmental factor associated with high numbers of taxa in the dry season. Silt and turbidity were associated with low numbers of taxa in the wet season. In conclusion, the subtidal benthic macrofauna at Canela island, Ajuruteua beach and the Caeté Bay is mainly composed of polychaetes and crustaceans. The higher freshwater discharge in the wet season, resulting in lower salinity, higher percentage silt and greater turbidity, is associated with lower abundance, fewer taxa and a different faunal composition at Canela and Ajuruteua, and strong dominance of an oligohaline polychaete in the Caeté Bay [ABSTRACT FROM AUTHOR]

The contribution of the estuarine channel of Recife harbour to the eutrophication of the Recife coastal area was evaluated by quantifying the instantaneous transport of salt, dissolved inorganic nutrients (Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed., SiOH[sub 4], Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed., Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. and, Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed.), material in suspension, Chlorophyll-a, pico-nanoplankton and microplankton during the rainy (June 2007) and dry (November 2007) seasons. The results showed that all of the dissolved nitrogenated nutrients, the silicate and the material in suspension had higher concentrations during the rainy season, whereas the phosphate and Chlorophyll-a (both the total and the pico-nanoplankton and microplankton fractions) showed greater concentrations during the dry season. All of the materials considered were exported to the sea except for Chlorophyll-a (pico-nanoplankton and microplankton fractions) during the dry season, when these materials were imported into the area. The total liquid transport in the rainy season was three times higher than that found for the dry season. Silicate represented nearly 85% of the total exported material during the rainy period, whereas during the dry season, phosphate and silicate represented 79% of the total exported material. The stratification and circulation processes indicated a well mixed environment. The water-renewal rate was low, as demonstrated by the input of phytoplankton biomass during November. The area was characterised as eutrophic during the months investigated. This work is a first effort to assess the transport of salt and nutrients in a tropical estuarine system in Brazil. The objective of this study was to characterise the transport of these properties and phytoplankton biomass in an estuarine channel. The total liquid transport in the rainy season was three times higher than that found for the dry season and the stratification and circulation processes indicated a well mixed environment. [ABSTRACT FROM AUTHOR]

Abstract: The Hooghly River estuary provides a unique experimental site to understand the effect of monsoonal river discharge on freshwater and seawater mixing. Water samples collected bi-weekly for a duration of 17months were analyzed for salinity, δ18O, δ13CDIC, as well as δD to investigate the differential mixing of freshwater and seawater. The differences in salinity and δ18O of samples collected during low and high tides on the same day are strongly correlated suggesting a well mixed water column at our sampling site. Low salinity and depleted δ18O during monsoon is consistent with increased river discharge as well as high rainfall. We identified different slopes in a δ18O versus salinity plot for the estuary water samples collected during monsoon and non-monsoon seasons. This is driven by composition of the freshwater source which is dominated by rainwater during monsoon and rivers during non-monsoon months. Selected δD analyses of samples indicate that groundwater contributes significantly to the Hooghly Estuary during low rainfall times of the year. δ13CDIC measured in the water recorded low values towards the end of monsoon indicating low productivity (i.e. increased organic respiration) while progressively increasing δ13CDIC values from October till January as well as during some of the pre-monsoon months can be explained by increasing productivity. Very low δ13CDIC (~−20‰) suggests involvement of carbon derived from anaerobic oxidation of organics and/or methane with potential contribution from increased anthropogenic water supply. An estimate of seawater incursion into the Hooghly Estuary at different times of the year is obtained by using salinity data in a two-component mixing model. Presence of seawater was found maximum (31–37%) during February till July and lowest (less than or equal to 6%) from September till November. We notice a temporal offset between Ganges River discharge farther upstream at Farakka and salinity variation at the Hooghly Estuary. We believe that this time lag is a result of the physical distance between Farakka and Kakdweep (our sampling location) and put constraints on the travel time of river water during early monsoon. [Copyright &y& Elsevier]

Influences of river hydrodynamic behaviours on hydrochemistry (salinity, pH, dissolved oxygen saturations and dissolved phosphorus) were evaluated through high spatial and temporal resolution study of a sandbar-regulated coastal river. River hydrodynamic during sandbar-closed event was characterized by minor dependency on tidal fluctuations, very gradual increase of water level and continual low flow velocity. These hydrodynamic behaviours established a hydrochemistry equilibrium, in which water properties generally were characterized by virtual absence of horizontal gradients while vertical stratifications were significant. In addition, the river was in high trophic status as algae blooms were visible. Conversely, river hydrodynamic in sandbar-opened event was tidal-controlled and showed higher flow velocity. Horizontal gradients of water properties became significant while vertically more homogenised and with lower trophic status. In essence, this study reveals that estuarine sandbar directly regulates river hydrodynamic behaviours which in turn influences river hydrochemistry. [ABSTRACT FROM AUTHOR]

Abstract: In this work, two field campaigns were performed in July 2008 (wet season) and March 2009 (dry season) to produce original data on the concentration, partition and distribution of mercury and butyltin compounds along the tropical Bach Dang Estuary located in North Vietnam (Haiphong, Red River Delta). The results demonstrate that mercury and butyltin speciation in the surface waters of this type of tropical estuary is greatly affected by the drastic changes in the seasonal conditions. During high river discharge in the wet season, there was a large estuarine input of total Hg and tributyltin, while the longer residence time of the waters during the dry season promotes increasing MMHg formation and TBT degradation. Although most of the Hg and TBT is transported into the estuary from upstream sources, tidal cycle measurements demonstrate that this estuary is a significant source of TBT and MMHg during the wet (∼3kgTBT/day) and dry (∼3gMMHg/day) seasons. [Copyright &y& Elsevier]

Abstract: Breakdown of mangrove litter, adjacent to Hooghly-Matla estuarine ecosystem, plays a major role in regulating the fish population of the estuary. For last several decades, there has been a gradual decline in fish population due to over exploitation of resource but the exact cause of this decrease in production is still not known. To know this cause, an eleven compartment holistic model of nutrient source to estuary and grazing food chain is constructed. Model results depict the role of mangroves in regulating fish population dynamics of the estuary and predation rate of carnivorous fish on detritivorous fish is sensitive parameter in maintaining the balance between grazing food chain and detritus food chain. [Copyright &y& Elsevier]

Abstract: This paper reports for the first time upon the effects of increasing CO2 concentrations on a natural phytoplankton assemblage in a tropical estuary (the Godavari River Estuary in India). Two short-term (5-day) bottle experiments were conducted (with and without nutrient addition) during the pre-monsoon season when the partial pressure of CO2 in the surface water is quite low. The results reveal that the concentrations of total chlorophyll, the phytoplankton growth rate, the concentrations of particulate organic matter, the photosynthetic oxygen evolution rates, and the total bacterial count were higher under elevated CO2 treatments, as compared to ambient conditions (control). δ13C of particulate organic matter (POM) varied inversely with respect to CO2, indicating a clear signature of higher CO2 influx under the elevated CO2 levels. Whereas, δ13CPOM in the controls indicated the existence of an active bicarbonate transport system under limited CO2 supply. A considerable change in phytoplankton community structure was noticed, with marker pigment analysis by HPLC revealing that cyanobacteria were dominant over diatoms as CO2 concentrations increased. A mass balance calculation indicated that insufficient nutrients (N, P and Si) might have inhibited diatom growth compared to cyanobacteria, regardless of increased CO2 supply. The present study suggests that CO2 concentration and nutrient supply could have significant effects on phytoplankton physiology and community composition for natural phytoplankton communities in this region. However, this work was conducted during a non-discharge period (nutrient-limited conditions) and the responses of phytoplankton to increasing CO2 might not necessarily be the same during other seasons with high physicochemical variability. Further investigation is therefore needed. [Copyright &y& Elsevier]

Abstract: Rare earth elements (REEs) in the suspended particulate matter (SPM) of the Mandovi estuary indicated that the mean total-REEs (∑REE) and light REE to heavy REE ratios are lower than that of the average suspended sediment in World Rivers and Post-Archean average Australian shale. High ∑REE were associated with high SPM/low salinity and also with high SPM/high salinity. Although the ∑REE broadly agree with SPM levels at each station, their seasonal distributions along transect are different. SPM increased seaward in the estuary both during the monsoon and pre-monsoon, but consistently low at all stations during the post-monsoon. The mean ∑REE decreased marginally seaward and was <25% at sea-end station than at river-end station. Spatial variations in ∑REE are maximum (64%) during the pre-monsoon. Strong to moderate correlation of ∑REE with Al, Fe and Mn in all seasons indicates adsorption and co-precipitation of REEs with aluminosilicate phases and Fe, Mn-oxyhydroxides. The ratio of mean ∑REE in sediment/SPM is low during the monsoon (1.27), followed by pre-monsoon (1.5) and post-monsoon (1.62). The middle REE- and heavy REE-enriched patterns with positive Ce and Eu anomalies are characteristic at every station and season, both in SPM and sediment. They also exhibit tetrad effect with distinct third and fourth tetrads. Fe-Mn ore dust is the most dominant source for REEs. However, the seasonal changes in the supply of detrital silicates, Fe-Mn ore dust and particulates resuspended from bottom sediments diluted the overall effect of salinity on fractionation and distribution of REEs in the estuary. [Copyright &y& Elsevier]

Abstract: West African tropical estuaries play an important role in the growth and survival of many commercially exploited fish species and enable the sustainability of considerable artisanal fishery yields. However, their trophic functioning remains poorly understood. In the Sine Saloum estuary (Senegal), a marine protected area (MPAs) was designated in 2003 to manage fisheries resources. The present study aimed to determine the structure, trophic functioning and seasonal patterns of the fish assemblages in this MPA. Throughout the study, 28 fish species were collected, with higher values of biomass (3826kgkm−2) recorded during the wet season and lower values during the dry season (1228kgkm−2). Fish assemblages in both seasons were dominated by species with marine affinity, which accounted for 87% of the total biomass in the wet season and 70% in the dry season, with their abundance varying from 83% to 57%, respectively. Based on stable isotopic composition (δ13C and δ15N), species were combined into trophic groups. Primary consumers were partitioned into suspensivores (pelagic copepods, oysters and mussels), which fed mainly on particulate organic matter, and intermediate consumers, feeding on freshly deposited organic matter and benthic microalgae (Sarotherodon melanotheron and Arca senilis). Secondary consumers were divided into three groups. The first group included mullet, which fed by grazing on benthic microalgae (benthic affinity feeders). The second group, pelagic affinity feeders, was the most heterogeneous and fed mainly on pelagic components. The last secondary consumer group termed the intermediate group, included piscivores and benthic and pelagic invertebrate feeders, which dominated the top of the food web. The food chain in October was lengthened due to the occurrence of tertiary consumers. Food webs were dominated by secondary consumers, which constituted 89% of total biomass in the dry season and 71% in the wet season. The fish food web varied largely with season in faunal composition and food chain length. This study highlighted the need to take into account the seasonal dynamic of the food web both in terms of composition and structure to assess carbon fluxes in tropical estuaries. [Copyright &y& Elsevier]

Phosphorus fractionation was employed to find the bioavailability of phosphorus and its seasonal variations in the Panangad region of Cochin estuary, the largest estuarine system in the southwest coast of India. Sequential extraction of the surficial sediments using chelating agents was taken as a tool for this. Phosphate in the water column showed seasonal variations, with high values during the monsoon months, suggesting external runoff. Sediment texture was found to be the main factor influencing the spatial distribution of the geochemical parameters in the study region. Similarly, total phosphorus also showed granulometric dependence and it ranged between 319.54 and 2,938.83 μg/g. Calcium-bound fraction was the main phosphorus pool in the estuary. Significant spatial variations were observed for all bioavailable fractions; iron-bound inorganic phosphorus (5.04-474.24 μg/g), calcium-bound inorganic phosphorus (11.16-826.09 μg/g), and acid-soluble organic phosphorus (22.22-365.86 μg/g). Among the non-bioavailable phosphorus, alkali-soluble organic fraction was the major one (51.92-1,002.45 μg/g). Residual organic phosphorus was comparatively smaller fraction (3.25-14.64% of total). The sandy and muddy stations showed distinct fractional composition and the speciation study could endorse the overall geochemical character. There could be buffering of phosphorus, suggested by the increase in the percentage of bioavailable fractions during the lean pre-monsoon period, counteracting the decreases in the external loads. Principal component analysis was employed to find the possible processes influencing the speciation of phosphorus in the study region. [ABSTRACT FROM AUTHOR]

Natural disturbances along with human interference make the tropical estuaries amongst the most disturbed areas globally. In spite of this, information on the seasonal variability of macrofauna from tropical estuaries is few. Temporal variability of macrofaunal community from Mormugao Bay, Zuari estuary, on the west coast of India was examined from 2003 to 2004 at seven stations. Environmental variability was assessed through physicochemical parameters of water and sediment. The changes in macrobenthic community were assessed using abundance, biomass and species diversity indices. The environmental parameters showed a significant seasonal variation influenced by monsoonal changes. The changes in the environmental conditions brought about variation in the macrobenthic community. Macrofaunal abundance, biomass and species diversity were the highest during post-monsoon influenced by recruitment. In monsoon, the macrobenthic community was dominated by polychaetes (92.17%), whereas bivalves dominated during the post-monsoon (57.7%). The macrofauna showed drastic decline during the stable pre-monsoon season, a period when the highest abundance of fauna is observed in the tropical estuary. Therefore, the macrobenthic community in the area did not follow the seasonal trend generally observed in a tropical estuary. Further, the community during pre-monsoon season was dominated by the opportunistic polychaete species indicating a possible influence of harbour activities in structuring the benthic community of the area. [ABSTRACT FROM AUTHOR]

Methane is one of the important greenhouse gases that contribute to a rise in global mean surface temperature. Aquatic environments are postulated to contribute > 50% of the total global methane (CH4) flux to the atmosphere (de angelis and Lilley, 1987). Dissolved methane concentration in surface waters was measured from January to December 2008 at two selected sites upper reaches (ONGC Bridge) and lower reaches (Dumas) of Tapi estuary, Gulf of Cambay, Gujarat, India. Besides, the important hydrochemical parameters like total organic carbon (TOC), dissolved oxygen (DO), salinity and nutrients (phosphate, nitrate and sulphate) were also analyzed. The mean dissolved CH4 concentration for all water samples at upper reaches was 1369.00 nmol/L and at lower reaches was 1082.04 nmol/L. The positive correlation was found between dissolved methane content and total organic carbon. On the contrary, the negative correlation was observed between methane concentration and nutrients like dissolved oxygen, salinity, phosphate, nitrate and sulphate. The probable causes for varying dissolved methane concentration and saturation at different reaches with hydrochemical parameters are discussed. [ABSTRACT FROM AUTHOR]

The effects of water flow, fish feed and cage position on net biofouling was examined in a floating cage fish farm. Fouling of 16 mm mesh net panels suspended inside and outside net cages and exposed to different treatments were monitored weekly until net apertures were completely occluded by the fouling organisms (8 weeks). Results indicate a dramatic reduction in water flow velocity throughout the fish farm due to the cage units themselves and net biofouling. The reduced water flow (<10 cm s−1) inside net cages promoted rapid net biofouling, while rapid water flow outside the net cages (>25 cm s−1) kept the net fouling organisms at bay. Although fish rearing in net cages with inputs of commercial pellet feed increased sessile biofouling (222% higher than outside the net cages) and non-sessile biofouling (570% higher), the type of fish feed used did not significantly affect biofouling development. The study recommends that the geometry of serially arranged net cages, as commonly deployed in tropical tidal estuaries, be reconfigured to improve flow through in order to minimize the impact of fouling. [ABSTRACT FROM AUTHOR]

Abstract: A model was developed to estimate the relative impacts of different functional groups of piscivores on the shallow-water estuarine nursery assemblage of tropical north-eastern Australia. Data on variability in the occurrence, number and type of fish in the diet of different piscivores was combined with estimates of the abundance of each group. The model predicts that previously overlooked small and occasional or ‘minor’ piscivores, such as sillaginids, ambassids, sparids and small juvenile carangids, inflict mortality on new recruits to shallow-water nursery habitats that is orders of magnitude greater than that imparted by more conspicuous larger piscivores. Because of their high abundance, a shift in the diet of minor piscivores to prey on new recruits results in a massive increase in the consumption of fish prey by the piscivore assemblage as a whole. Even if the evidence that minor piscivores switch to target new recruits was rejected, the model shows that the highly abundant minor piscivores must still exert a significant proportion of predation mortality experienced by recruiting fishes. As a broad functional group, minor piscivores occur in most aquatic systems around the globe and are likely to play an important but largely overlooked role as predators that shape communities through predation on critical early life stages of other fishes. [Copyright &y& Elsevier]