Volatile organotin compounds (butylmethyltin) in three European estuaries (Gironde, Rhine, Scheldt)

The occurrence of volatile organometallicspecies of tin was evidenced and investigatedin three major European estuaries, such as theGironde (F), the Rhine (NL) and the Scheldt(B/NL), along with the salinity gradient andfor all seasons. The most ubiquitous species,observed in surface water, were found to bemethylated forms of butyl-tin derivatives(Bu_nSnMe_4-n, n = 0–3), withconcentrations significantly higher in theScheldt (ca. 75–2000 fmol l^–1) than in theRhine (ca. 5–125 fmol l^–1) and the Gironde(ca. 5–90 fmol l^–1). Additionally,estuarine anoxic sediments were found tocontain large amount of such volatile tinspecies.The presence of volatile organic tin compoundsis then supposed to result from naturalmethylation processes of both inorganic metaland anthropogenic derivatives accumulated inthe sediments (i.e. tributyltin released fromship antifouling paintings and waste waterdischarges). These results suggest thatmicrobial mediated and/or chemical methylationmechanisms are likely to produce volatileorganotin species in anoxic estuarineenvironments. The production of volatileorganotin species is also mainly dependent onthe direct anthropogenic load of butyltincompounds within the estuary and on theresidence time of such compounds in the system.Estuarine profiles along with the salinitygradient demonstrate that all investigatedestuaries are continuous sources of volatiletin species, although these estuaries presentdifferent anthropogenic organotin discharges.In consequence, significant export of volatiletin species to the adjacent coastal waters werefound. Finally, the evaluation of the seasonalfluxes of volatile tin species to theatmosphere establishes that volatilisation is amajor sink for such compound in estuaries withlong water residence time (i.e. Scheldt, Gironde).     

Methane distribution in European tidal estuaries

Methane concentrations have been measured along salinity profilesin nine tidal estuaries in Europe (Elbe, Ems, Thames, Rhine,Scheldt, Loire, Gironde, Douro and Sado). The Rhine, Scheldt andGironde estuaries have been studied seasonally. A number ofdifferent methodologies have been used and they yieldedconsistent results. Surface water concentrations ranged from0.002 to 3.6 M, corresponding to saturation ratios of 0.7 to1580 with a median of 25. Methane concentrations in thefresh-water end-members varied from 0.01 to 1.4 M. Methaneconcentrations in the marine end-members were close to saturationoffshore and on the order of 0.1 M in estuarine plumes. Methaneversus salinity profiles in river-dominated, stratified estuaries(Rhine and Douro) appeared rather erratic whereas those in thewell mixed, long-residence time estuaries (Elbe, Ems, Thames,Scheldt, Loire, Gironde and Sado) revealed consistent trends. Inthese systems dissolved methane initially decreases withincreasing salinity, then increases to a maximum at intermediateto high salinities before decreasing again going offshore. Tidalflats and creeks were identified as a methane source to estuarinewaters. The global estuarine flux of methane to the atmospherehas been calculated by combining the median water-air methanegradient (68.2 nmol dm^–3) with a global area weighted transfercoefficient and the global area of estuaries. Estuaries emit 1.1to 3.0 Tg CH₄ yr^–1, which is less than 9% of the global marinemethane emission.     

Comparative spring distribution of zooplankton in three macrotidal European estuaries

The zooplankton of three european estuaries (Ems, Gironde and Westerschelde) was investigated during spring 1992 by means of samples taken along the salinity gradient. The three estuaries are comparable in terms of total area, flushing time and salinity gradient but differ by their level of eutrophication (highest in the Westerschelde), suspended matter concentration (highest in the Gironde) and potential phytoplankton production (highest in the Ems). Copepods and meroplankton dominated the zooplankton in the three estuaries. The dominant copepod species were Eurytemora affinis and Acartia bifilosa. The distribution of E. affinis along the salinity gradient differed between the estuaries. Peaks of abundance were observed at 0 PSU in the Gironde, 6 PSU in the Ems and 9 PSU in the Westerschelde. The downstream shift of the population in the Westerschelde was likely due to anoxic conditions occurring in the oligohaline zone. In the Gironde the downstream distribution of E. affinis was limited by the very high suspended matter concentration found in the maximum turbidity zone. Whatever the estuary, the parameters of the population of E. affinis and maximum abundance values were similar. However, the influence of the better quality of the available food was suggested in the Ems where individual dry weights and egg production were higher than in the two other estuaries. The influence of a good quality of food in the Ems was confirmed by the development of a large population of Acartia bifilosa (as abundant as E. affinis) and highest values of adult individual weights.The meroplankton (essentially Polychaete and cirripede larvae) was much more developed in the Ems than in the Westerschelde and Gironde. This was likely due to the large extent of mudflats and hard substrates in the Ems favouring adult settlement and hence the number of larvae locally produced.     

Morphological Differentiation Between Geographically Separated Populations of <Emphasis Type="Italic">Neomysis integer</Emphasis> and <Emphasis Type="Italic">Mesopodopsis slabberi</Emphasis> (Crustacea,Mysida)

Morphological variation was examined in Neomysis integer and Mesopodopsis slabberi, two abundant, low dispersal mysid species (Crustacea, Mysida) along the European coasts. Both species dominate the hyperbenthic communities in the northeast Atlantic, and M. slabberi is also widely distributed in the Mediterranean and Black Sea. Three populations of these species were sampled throughout their distribution range; samples of N. integer were collected in the northeast Atlantic Eems-Dollard, Gironde and Guadalquivir estuaries; in the case of M. slabberi, mysids were sampled in two northeast Atlantic estuaries (Eems-Dollard and Guadalquivir) and one Mediterranean site (Ebro Delta). A total of 12 morphometric and 2 meristic characters were measured from 30–64 mysids per sample. Multivariate analysis showed clear morphometric differences between populations of both species. The morphological differentiation within M. slabberi was highly concordant with the available genetic data from mitochondrial loci, pointing to a large divergence between the Atlantic and Mediterranean populations. However, due to some overlap of individuals between the different populations, the present morphometric analysis does not suffice to assign the different populations to a separate (sub)species status. In the case of N. integer, the morphometric patterns showed a divergence of the Gironde population. Differentiation of populations within this mysid, as in M. slabberi, were mainly related to eye and telson morphology. Potential interactions of the mysid morphology and environmental conditions are discussed.     

Dietary compositions of the sparid <Emphasis Type="Italic">Acanthopagrus</Emphasis><Emphasis Type="Italic"> butcheri</Emphasis> in three normally closed and variably hypersaline estuaries differ markedly

We have compared the species composition and diversity of the diets of black bream, Acanthopagrus butcheri, in three normally closed estuaries on the central south coast of Western Australia, which vary markedly in the extents to which they become hypersaline during dry periods. Although black bream was caught seasonally in Stokes Inlet during this 3-year study, it was obtained from the Hamersley and Culham inlets only during the earlier seasons because salinities in those two estuaries subsequently rose to levels that caused massive mortalities of this sparid. Although a wide range of taxa, including macrophytes, polychaetes, molluscs, crustaceans, insects and teleosts, were ingested by A. butcheri in each estuary, the frequencies of ingestion and volumetric dietary contributions of these taxa varied greatly among the fish in these three estuaries. Thus, for example, in comparison with other estuaries, relatively greater contributions were made to the diet by polychaetes and crustaceans in Stokes Inlet, by macrophytes in Hamersley Inlet, and by insects (mainly chironomid larvae) in Culham Inlet. The relatively greater contribution of teleosts to the diets of black bream in the Hamersley and Culham inlets than in Stokes Inlet, and also differences in the main teleost species ingested in the first two estuaries, are consistent with differences in the densities of fish overall and of the main fish species in those estuaries. The diversity of the diet was far greater in Stokes Inlet than in the other two far more variably saline estuaries, presumably reflecting a greater diversity of food. The dietary compositions of black bream in upstream pools in the tributary of Culham Inlet, which offer refuge when salinities increase markedly in the main body of the estuary, differ from those in those downstream regions, further emphasising the opportunistic nature of the feeding behaviour of black bream. The dietary compositions of black bream underwent size-related changes, but the taxa contributing most to those changes varied greatly among estuaries. Size-related changes would be particularly beneficial in reducing intraspecific competition for food in the two estuaries that vary greatly in salinity and would thus be likely to contain a less diverse range of prey.     

Comparative study of the hyperbenthos of three European estuaries

The hyperbenthic fauna of the subtidal channels of the Eems (N. Netherlands), Westerschelde (S.W. Netherlands), and Gironde (S.W. France) estuaries was sampled within a 15-day period in summer 1991. In each estuary, quantitative samples were taken at regularly spaced stations covering the entire salinity gradient from marine conditions at the mouth to nearly freshwater conditions upstream. The diversity of the samples and the distribution of the species along the main estuarine gradients were assessed. Hyperbenthic communities were identified using different multivariate statistical techniques. The species composition and the density and biomass of the dominant species of each community were compared among communities.     

First description of heavy skeletal deformations in Palaemon shrimp populations of European estuaries: the case of the Gironde (France)

This study aims at analyzing morphological deformities in Palaemon population in the Gironde estuary. The most frequent abnormalities affected cephalothorax and rostrum, and to a lesser extent scaphocerites and uropods (with spectacular dissymmetry), whilst only few cases of antenna and telson deformities were observed. References on morphological abnormalities of crustaceans can be found in the literature, but dealing with only isolated individuals and not for Palaemonids species, whilst in the Gironde estuary up to 40% of adult individuals are affected. Deformities likely depend on water pollutants, among others heavy metals and PCBs. This hypothesis should be tested considering other European estuaries with similar features. Handling editor: P. Viaroli     

Do different degrees of human activity affect the diet of Brazilian silverside Atherinella brasiliensis?

The aim of the present study was to test whether different degrees of human activity affect the diet of the Brazilian silverside Atherinella brasiliensis in two tropical estuaries. Fish were collected along the salinity gradient of two Brazilian estuaries, the heavily impacted Paraiba Estuary and the less impacted Mamanguape Estuary, in the dry and wet seasons. The findings confirm that A. brasiliensis has generalist feeding habits and is able to change its diet under different environmental conditions. The results indicate clear spatial (i.e. along the estuarine gradient) changes in diet composition in both estuaries, but diet was also influenced by the degree of anthropogenic disturbance. During the wet season in the nutrient enriched Paraiba Estuary, when human activity was higher, the diet of A. brasiliensis was poorer and dominated by few dietary items, reflecting the potential impoverishment of prey items in this heavily disturbed system. The specimens collected in the most affected estuary also had a greater frequency of micro‐plastics and parasites in their stomachs, reflecting the greater degree of human disturbance in the estuary. The present findings suggest that the diet of A. brasiliensis could be a useful indicator of changes in the ecological quality of these and other tropical estuaries of the western Atlantic Ocean.     

Numerical modelling of suspended sediment transport in tidal estuaries: A comparison between the Tagus (Portugal) and the Scheldt (Belgium-the Netherlands)

A numerical model to simulate the transport of suspended sediment in tidal estuaries is presented. The model is applied to the two large European estuaries the Tagus (Portugal) and the Scheldt (Belgium-The Netherlands). Calculated suspended sediment concentrations compare favourably with observations in the Tagus (r=0.84) and in the Scheldt (r=0.73). The parametrization scheme indicates that the bottom content of fine sediment is correlated with depth in the Tagus; but a different relationship is used in the Scheldt. Because of tidal range differences, average suspended sediment concentrations are lower in the Tagus (80 mg l⁻¹) than in the Scheldt (130 mg l⁻¹), but a larger relative variation between spring and neap tide concentrations may occur in the Tagus.     

Meiobenthic distribution and nematode community structure in five European estuaries

Meiofauna from the intertidal zone of five European estuaries (Ems, Westerschelde, Somme, Gironde, Tagus) was investigated. Samples represented a cross section of various benthic habitats from near-freshwater to marine, from pure silts to fine-sandy bottoms. The meiobenthic community comprised everywhere a fauna strongly dominated by nematodes, with meiobenthic density increasing with increasing salinity. The Ems differed from the other estuaries due to the presence of a well developed community of Copepods, Gastrotrichs, large Ciliates and/or soft-shelled Foraminiferans in some sites. The Westerschelde stood out due to the near-absence of harpacticoid copepods and, as in the Tagus, the lower meiobenthic densities in the marine part of the estuary. For nematode community analysis, we also included data from the Tamar which were obtained from the literature (Warwick &; Gee, 1984). This resulted in the enumeration of 220 species, belonging to 102 genera, each with a characteristic distribution along the salinity, sedimentary and latitudinal gradients. Using the multivariate technique CANOCO, a zonation along these different physicochemical determinants was observed as well although salinity and sediment characteristic (scale of hundreds of meters to kilometers) proved to be more important in explaining community structure than latitudinal differences (scale of hundreds of kilometers). Nematode diversity was nearly entirely determined on the genus level and was positively related to salinity. Deviations from this general trend in the Gironde and the Tamar were attributed to sedimentary characteristics or to low macrobenthic predation. The presence of a typical opportunistic colonizing nematode species Pareurodiplogaster pararmatus in the low-salinity region of the Gironde could indicate (organic?) pollution or disturbance of the intertidal mud-flats.     

Zonation of intertidal macrobenthos in the estuaries of Schelde and Ems

Based on data, collected in 1980–1990, the intertidal benthic macrofauna of the Schelde and Ems estuaries was compared. The spatial occurrence of the benthic macrofauna along the salinity gradient, including the freshwater tidal area was emphasized. Both estuaries appeared to have a very similar species composition, especially at genus level. The higher number of species observed in the Schelde estuary was probably due to a greater habitat diversity. In both estuaries species diversity decreased with distance upstream. The total density did not vary along the estuarine gradient, whereas biomass is highest in the polyhaline zone.In both estuaries distinct intertidal benthic communities were observed along the salinity gradient: a marine community in the polyhaline zone, a brackish community in the mesohaline zone, and a third community in the oligohaline and freshwater tidal zones of the estuary. These three communities were very similar between both estuaries. Their main characteristics were discussed together with the occurrence and distribution of the dominant species.For the Schelde estuary and to a lesser extent also for the Ems estuary, there was evidence that anthropogenic stress had a negative effect on the intertidal macrobenthic communities of the oligohaline/freshwater tidal zone. Only Oligochaeta were dominating, whereas the very euryhaline and/or true limnetic species were missing. In the mesohaline zone, the Schelde estuary was dominated by large numbers of short-living, opportunistic species, whereas in the Ems estuary relatively more stable macrobenthic communities were observed. A comparison with some other European estuaries showed in general similar trends as those observed for the Schelde and Ems estuaries.     

The significance of spatial and temporal patterns of algal mat deposition in structuring salt marsh vegetation

Question: Are there hot spots of algal mat deposition in space and time at the marsh scale and, if so, how does this affect the coexistence of a dominant (Spartina anglica) and gap dependent (Salicornia europaea) species? Location: The Rattekaai salt marsh in the Scheldt estuary in the southwestern Netherlands (NW Europe). Methods: Mat cover and the abundance of the gap dependent species Salicornia europaea were monitored at the scale of a marsh. The effects of mat cover on the vegetation structure were studied by applying three mat removal treatments over three growing seasons. Results: The low marsh border was found to be a hot spot of algal mat deposition during the growing season, which had a correlated spatial pattern between two successive years at a 20 m X 20 m scale. The combination of duration, timing and repetition of mat cover determined growth inhibition of the competitive dominant Spartina anglica, and thereby the abundance of subordinates such as Salicornia europaea. Mat cover reduced the storage of carbon reserves in Spartina and our results imply that repetition of non‐lethal mat cover can lead to ‘gap creation’. Gaps gave only temporary habitat to less dominant species since Spartina quickly re‐invaded them. The gap dependent annual Salicornia was most abundant at intermediate levels of disturbance measured as a function of both space and time. Conclusions In addition to disturbance level, the spatial and temporal distribution of disturbance are important in creating and maintaining habitat for gap dependent species. Relatively small disturbances will have a large effect on diversity if the spatial and temporal distribution of the disturbances leads to ‘disturbance hot spots’.     

Seasonal and spatial shifts in copepod diets within tropical estuaries measured by fatty acid profiles

Fatty acids are the main components of lipids and are necessary for the production and permeability of cell membranes, playing an essential role in the physiological responses of organisms. The biochemical composition of zooplankton might be used as bio-indicators of the trophic status of aquatic ecosystems. Aiming to fill the gap of knowledge in tropical estuaries, the main aim of this study was to test if the fatty acid profiles can reveal spatial and temporal shifts in the diet of copepods and therefore can be used as indicators of the trophic status of estuarine systems. We investigated the fatty acids composition of copepod species and their possible food sources along the salinity gradient of two tropical estuaries (Paraíba do Norte and Mamanguape estuaries, northeastern Brazil), during the rainy and dry seasons. We found clear seasonal differences regarding fatty acids composition and concentration in copepods, with maximal concentrations and diversity of total fatty acids during the rainy season. The copepods species were mainly carnivorous in the dry season and omnivorous in the rainy season and, in both estuaries, the diet of most copepods was dependent on food availability. The fatty acid profiles suggest that, in general, feeding patterns of zooplankton change spatially and temporally, reflecting the shifts in their food sources abundance (i.e., dominance among diatoms and flagellates, terrestrial detritus and small animals). We observed a residual proportion of terrestrial detritus and green algae in the diets and these items were only present in the dry season. Furthermore, the food sources in the Paraiba do Norte estuary, a system with high levels of anthropogenic disturbance, showed lower feeding quality, with lower essential fatty acids concentrations. Our study showed that fatty acid profiles can be used as ecological indicator to assess seasonal and spatial shifts in the trophic ecology of copepods in tropical estuaries and to distinguish systems with different levels of human impact in a fast and accurate way.     

Using stable isotope analysis to study the diet of Gilchristella aestuaria larvae: preliminary insights into the foodwebs of six South African estuaries

South African estuarine systems are becoming increasingly altered by anthropogenic and environmental factors, but the consequences of such changes for these systems are still not fully understood. The most common approach for evaluating the ecological status of aquatic systems is studying their associated foodwebs. Due to their high abundance and important ecological role, the larvae of estuarine round herring Gilchristella aestuaria (Gilchrist, 1913) are key candidates for examining the foodweb structure and function of southern African estuaries. The foodwebs and trophic interactions of G. aestuaria larvae in six estuaries in South Africa were compared using larvae sampled in November 2013 and analysed using δ¹³C and δ¹⁵N and Bayesian isotopic mixing models. The main prey type for G. aestuaria larvae in all estuaries was zooplankton. We found a high similarity among the Kariega, Gamtoos, Great Fish and Sundays estuaries in terms of consumers and potential sources for both δ¹³C and δ¹⁵N signatures. Significant differences were found in δ¹³C values among marine-dominated estuaries, such as the Kromme Estuary, and the more freshwater-dominated systems. In addition, in the Kromme Estuary particulate organic matter was very important in the diet of G. aestuaria larvae. Our results suggest that both food availability and physical environmental parameters strongly affect the diet and condition of G. aestuaria and, consequently, the entire foodweb in the system.     

Effects of recent increases in salinity and nutrient concentrations on the microbialite community of Lake Clifton (Western Australia): are the thrombolites at risk?

There has been a strong research focus on optical properties in temperate estuaries but very much less in tropical estuaries. These properties comprise light and beam attenuation dominated by suspended particulate matter, Chl a, and CDOM. Spatially and temporally distributed data on optical properties in a tropical wet and dry estuary are compared and discussed in relation to those of temperate estuaries. Sampling in the Nha Phu estuary, Vietnam, consisted of five stations on a transect from head to mouth that was sampled four times during dry conditions and three times during wet conditions between May 2006 and April 2008. Methods comprised CTD, optical measurements, and water sampling for suspended matter, Chl a, and CDOM. Results showed high light attenuation—K _d(PAR)—in wet conditions and low in dry. K _d(PAR) was highest at the estuary head and lower in the outer part. Spatial and temporal variations in K _d(PAR) were in general dominated by variations in suspended particulate matter concentrations in both wet and dry conditions. Chl a concentrations were low and showed no strong variations between wet and dry conditions. CDOM absorption coefficients were higher in wet conditions with high values at the head and lower in the central part of the estuary. The depth of the photic zone was reduced by up to 50% during wet conditions. A residence time in the estuary of 5–6 days was derived from the rate of change of K _d(PAR) after a period of heavy rain and discharge of freshwater into the estuary. This complied with a residence time of four and a half days derived from a basic physical relation. Optical properties were in general comparable to temperate estuaries in dry conditions although Chl a concentrations were lower in Nha Phu. A second distinctive point, as compared to temperate estuaries, was the episodic character with days of strong rainfall followed by longer periods of dry weather. All sampling, both wet and dry, was carried out in the dry season which implies a less definitive perception of wet and dry seasons.     

High levels of sediment contamination have little influence on estuarine beach fish communities

While contaminants are predicted to have measurable impacts on fish assemblages, studies have rarely assessed this potential in the context of natural variability in physico-chemical conditions within and between estuaries. We investigated links between the distribution of sediment contamination (metals and PAHs), physico-chemical variables (pH, salinity, temperature, turbidity) and beach fish assemblages in estuarine environments. Fish communities were sampled using a beach seine within the inner and outer zones of six estuaries that were either heavily modified or relatively unmodified by urbanization and industrial activity. All sampling was replicated over two years with two periods sampled each year. Shannon diversity, biomass and abundance were all significantly higher in the inner zone of estuaries while fish were larger on average in the outer zone. Strong differences in community composition were also detected between the inner and outer zones. Few differences were detected between fish assemblages in heavily modified versus relatively unmodified estuaries despite high concentrations of sediment contaminants in the inner zones of modified estuaries that exceeded recognized sediment quality guidelines. Trends in species distributions, community composition, abundance, Shannon diversity, and average fish weight were strongly correlated to physico-chemical variables and showed a weaker relationship to sediment metal contamination. Sediment PAH concentrations were not significantly related to the fish assemblage. These findings suggest that variation in some physico-chemical factors (salinity, temperature, pH) or variables that co-vary with these factors (e.g., wave activity or grain size) have a much greater influence on this fish assemblage than anthropogenic stressors such as contamination.     

埃塞俄比亚Alatish国家公园大型哺乳动物多样性、分布及其与栖息地的联系

于2004年8月-2005年3月间研究了Alatish国家公园在雨季和旱季期间大型哺乳动物的多样性和分布.基于地形图、卫片和预调查结果,在4种生境类型中识别出37个100 km2或者更小的斑块.在4个植被类型中随机选择了11个斑块,沿随机选择的样线进行了调查,样线10 km 长,0.2 km宽,覆盖了该区域面积的20%.使用Shannon-Wiener多样性指数、DISTANCE 5.0 软件以及 Simpson相似性指数分析了大型哺乳动物的多样性以及分布的相似性.记录了20种体型较大的哺乳动物;河边林地在雨季和旱季都有最高的多样性,林地的多样性最低;旱季中4种类型的栖息地具有相似的分布型;由于栖息地退化不能确定物种的分布格局.联合距离取样分析揭示出,旱季和雨季大型哺乳动物的密度较低,分别为4.067只/km2和6.263只/km2.所观察的哺乳动物可分为草食动物(15%)、游牧动物(30%)、杂食动物(25%)与食肉动物(30%).     

Seasonal and spatial patterns in cellular energy allocation in the estuarine mysid Neomysis integer (Crustacea: Mysidacea) of the Scheldt estuary (The Netherlands)

The seasonal and spatial patterns in cellular energy allocation of the estuarine mysid Neomysis integer (Leach, 1814) were investigated in the Scheldt estuary over a 2-year period. Using the recently developed cellular energy allocation (CEA) assay, energy reserves (protein, lipid and sugar) and energy consumption (as derived from the cellular respiration rate) were integrated into a general indicator of physiological stress. Total energy reserves were relatively unaffected by sampling season or location, whereas the individual energy reserve fractions of N. integer were differentially influenced by sampling location and season. Seasonal effects were apparent for mysid weight and were related to the population biology, whereas spatial effects on the weight of N. integer may depend on pollution-induced effects on cellular energy allocation in the two most upstream sites (Bath and Doel). These upstream sites coincide with the most polluted part of the sampled area and were characterized by a significant increase in energy consumption, resulting in a significantly lower CEA. Due to the recent amelioration in the oxygen concentration at these sites, it can be expected that N. integer will migrate further upstream, similar to what is observed in other European estuaries. It will, therefore, be important to assess the physiological consequences and potential population effects on mysids from these polluted areas in the Scheldt estuary. This study provides evidence that the CEA assay has potential under field conditions as an in situ biomarker of pollutant effects.     

Movement patterns of catfishes (Ariidae) in a tropical semi‐arid estuary

From December 2005 to November 2006, 216 samples were taken from the main channel of the Goiana Estuary, representing a total sampled area of 23 ha. Ariidae species were the most abundant in density (1600 individuals ha^?1, 53%) and biomass (18 813 g ha^?1, 63%). Cathorops spixii was the most abundant in density (1340 individuals ha^?1) and biomass (14 203 g ha^?1). The variables: number of species, total density and biomass, showed significant interactions between the factors of areas and seasons (P < 0·01). The highest total density (7394 individuals ha^?1) and biomass (70 292 g ha^?1) occurred in the middle and upper estuaries, respectively, during the early‐rainy season. The density of C. spixii differed significantly between areas and seasons (P < 0·01), while Cathorops agassizii differed significantly only between seasons (P < 0·01). The biomass differed significantly for the species C. spixii, C. agassizii and Sciades herzbergii between seasons, and C. spixii and C. agassizii between areas. Also, the density and biomass of C. spixii and C. agassizii showed interaction between areas and seasons. Only the biomass of S. herzbergii showed interaction between areas and seasons (P < 0·01). This indicates that seasonal variations influenced the distribution of Ariidae species in the different areas of the Goiana Estuary. Moreover, canonical correspondence analysis highlighted a strongly significant correlation (P < 0·01) between the seasonal variations of the environmental gradients (salinity and water temperature) and distribution of catfishes. The management and conservation of estuaries should take into account the life cycle of these species in different estuarine areas and hydrological seasons.