Caete Estuary Research Articles

Influence of a Drought Event on Hydrological Characteristics of a Small Estuary on the Amazon Mangrove Coast

The effects of atypical climatic conditions, such as those of a drought event, are remarkably accentuated in minor estuaries filled with sediments and with reduced or sporadic freshwater input, where the salinity intrusion is pronounced. To understand these effects, hydrological and hydrodynamic parameters were evaluated during a drought period in a small estuary located on the eastern Amazon coast in northern Brazil. Five campaigns were conducted between June 2012 and June 2013. Samples were collected from the surface and bottom layer every 3 h over a 25-h period at three stations of the Taperacu Estuary. To compare drought and post-drought periods, in terms of salinity and chlorophyll-a, data was recorded until June 2015. Taperacu is a relatively shallow estuary of the Amazon coastal zone, which is characterized by the absence of any direct fluvial discharge, although it does receive freshwater input from adjacent wetlands, as well as less saline waters from the Caete Estuary through the Taici Creek. Hydrological variables were controlled by rainfall levels and the tidal range, and the water became more saline and more oxygenated, with reduced dissolved nutrient and chlorophyll-a concentrations when precipitation decreased. A significant variation was found between the months of June 2012 (most intense drought) and 2013 (less intense drought). The connection to the neighboring Caete Estuary and adjacent mangroves and wetlands contributed to the influx of nutrient-enriched waters. Overall, then, it is hoped that the results of this study can contribute to the understanding of the effects of drought events in other minor estuaries on the highly indented Amazon coast, as well as in other areas of the equatorial zone with similar environmental characteristics.

Observation of an Estuarine Turbidity Maximum in the Highly Impacted Capibaribe Estuary, Brazil

Estuarine turbidity maxima (ETM) are features present in some estuaries where the concentration of suspended particulate matter (SPM) is higher than elsewhere along the fresh-marine water transition in the estuarine domain (POSTMA, 1967; SCHUBEL, 1968; GEYER, 1993; DYER, 1995). The presence of ETM has important ecological implications: since they occur at places where there is an accumulation of organic matter: bacterioplancton and zooplankton dynamics in estuaries is affected by ETM behavior (CRUMP; BAROSS, 1996; MORGAN et al., 1997). ETM are also important in the pollutants dynamics of an estuary, mainly for those that occur adsorbed to fine clayey sediments (BRUNK et al., 1996). ETM are formed and maintained as the result of complex interactions between river discharge, tidal dynamics and gravitational circulation (DYER, 1988). The concentration of SPM in the ETM varies over time on tidal, sinodical and seasonal time scales (GRABEMANN et al., 1997). ETM have been studied in many estuaries abroad (ALLEN et al., 1980; GELFENBAUM, 1983; UNCLES et al., 1994; WOLANSKI et al., 1995). In some estuaries they are of an ephemeral nature (KISTNER; PETTIGREW, 2001), while in other cases they do not occur at all (SCHETTINI; TOLDO JUNIOR, 2006; SCHETTINI et al., 2006). The physics underlying the formation of the ETM has been studied using both analytical and numerical models (GEYER, 1993; JAY; MUSIAK, 1994; BURCHARD; BAUMERT, 1998; YU et al., 2014) in which the effect of gravitational circulation and tidal pumping is of primary importance, with a high degree of interaction between the flow and the bed. Most ETM have been reported in meso or macro-tidal estuaries. As regards the Brazilian coast, it is not expected to find ETM in the Southeastern and Southern Regions basically because the tidal regime is microtidal. Some papers have reported ETM processes in Paranagua Bay (PR) (e.g., RIBEIRO et al., 2011), although the higher turbidity zone in that estuary is linked rather to re-suspension due to tidal currents (MANTOVANELLI et al., 2004) than to the occurrence of a true ETM. Other studies on SPM in southern Brazilian estuaries have not reported the presence of ETM (SCHETTINI; TOLDO JUNIOR, 2006; D´AQUINO et al., 2010). On the other hand, meso and macro tides occur on the shores of the Northeastern and Northern Regions, where there would be a greater likelihood of observing ETM. Nevertheless, there are not many studies of the fine sediment dynamics of this area, and the few that are available do not report the presence of ETM. The fine sediment dynamics of the Caravelas estuary, Bahia has been assessed (SCHETTINI; MIRANDA, 2010; SCHETTINI et al., 2013), despite the fact that this estuary presents a very small freshwater inflow, and the major source of sediments is the inner shelf. Such conditions are unfavorable to the formation of ETM. The eastern shores of Para seem to present favorable conditions for the formation of ETM, and a single survey carried out in the Caete estuary has shown a feature in the longitudinal distribution of SPM which fits in with what is expected of an ETM (ASP et al., 2012), even though it has not yet been assessed.A series of surveys has been carried out in the Capibaribe estuary since 2012 to investigate its circulation, fine sediment transport, deposition patterns and recent environmental evolution. The main appeal of and reason for these assessments was the fact that the Capibaribe estuary is a relatively small system (~ 10 km

Effects of Sewage on Natural Environments of the Amazon Region (Pará-Brazil)

ABSTRACT Sousa, N.S.S.; Monteiro. M.C.; Gorayeb, A.; Costa, R.M., and Pereira, L.C.C., 2016. Effects of sewage on natural environments of the Amazon region (Para-Brazil). In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 158–162. Coconut Creek (Florida), ISSN 0749-0208. The negative effects of sewage discharge were analyzed in two Amazonian environments (the Caete Estuary and the Cereja River) subject to different levels of anthropogenic impact. For this, samples of surface water were collected for the analysis of physical, chemical, and microbiological parameters during dry and wet season. In the Caete Estuary, the results indicated high levels of total nitrogen and fecal coliforms in the upper sector. Eutrophic conditions were recorded in the wet and dry season. Natural and anthropogenic sources may contribute to the input of dissolved nutrients, ...

Tidal Modulation of Moderate Wave Energy on a Sandy Tidal Flat on the Macrotidal Amazon Littoral

ABSTRACT Trindade, W.; Pereira, L.C.C., and Vila-Concejo, A., 2016. Tidal modulation of moderate wave energy on a sandy tidal flat on the macrotidal Amazon littoral. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 487–491. Coconut Creek (Florida), ISSN 0749-0208. The present study focusses on the Vila dos Pescadores, a tidal flat located at the mouth of the Caete estuary in the northeast of the Brazilian state of Para. The aim was to establish the interactions amongst climatological and hydrodynamic processes, as well as fluvial dischages under different conditions. Eight campaigns were undertaken between June 2012 and April 2014. Results show that during the dry season, winds were moderate to strong and blew mainly from the northeast, coinciding with migration of the Intertropical Convergence Zone (ITCZ) to the northern hemisphere. During the rai...

The Trophic Status of an Amazonian Estuary Under Anthropogenic Pressure (Brazil)

ABSTRACT Monteiro, M.C.; Pereira, L.C.C., and Jimenez, J.A., 2016. The trophic status of an Amazon estuary under anthropic pressure (Brazil). In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. XX-XX. Coconut Creek (Florida), ISSN 0749-0208. The effects of the anthropogenic process on the trophic status of the Caete estuary (located 150 km southwest of the Amazon delta) were undertaken under different climate conditions. To do this, oceanographic data were carried out, covering the dry season of 2010 (August–December: rainfall 363 mm), and the wet (January–July, rainfall 2483 mm) and dry seasons of 2011 (August–October, rainfall 135 mm). During the dry season (2010 and 2011) the mean discharge of the Caete River was less than 20.0 m3 s−1, while, during the wet season, the mean discharge increased to 73.6 m3 s−1. Tidal ranges oscillated between 2.2 and...

Endogenous Activity Rhythms of Larval Fish Assemblages in a Mangrovefringed Estuary in North Brazil

In Caete Estuary, the decrease of larval abundance downstream was attributed to reduced retention, since ebb tide densities prevailed mainly in the middle and lower estuary during the rainy season due to increased freshwater out- flow. Anchovia clupeoides, Stellifer microps and Guavina guavina were most abundant in the late dry season on flood tides in the upper estuary, whereas ebb tide densities of these species prevailed in other regions. Environmental fluctua- tions associated with lunar periodicity, such as tidal amplitude, may account for weekly variability of recruitment and re- production of some fish species. A. clupeoides showed increased spawning activity during first quarter moon, whereas new moon phases seemed to be reproduction periods of Cynoscion acoupa. Vertical migration was not employed by the most abundant species to enable river retention, since larval densities of these species were not significantly higher at the bottom on ebb tides, except for C. acoupa and Stellifer rastrifer. This result may be related to system turbulence or to the dominance of younger stages unable to migrate vertically at the time of sampling. Lateral movement to the river bank is proposed as a possible retention mechanism. Diel effects on larval abundance related to trophic activity and gear avoid- ance.

Biomass flow structure and resource potential of two mangrove estuaries: insights from comparative modelling in Costa Rica and Brazil

Trophic models were compared for mangrove fringed estuaries in Costa Rica (Gulf of Nicoya, at the Pacific shore) and Brazil (Caete estuary, NE of Belem) in order to evaluate biomass and energy flow distributions, productivity and fisheries potential, and to obtain guidelines for conservation and management of these systems. As the same network modelling approach (ECOPATH II) and a similar number of system compartments were used, a comparison based on the network models seemed attractive. Differences in biotic structure, energy flow and resource productivity’s between both systems and their causes were assessed. They proved to be substantial and largely due to differences in topography, tidal regime and mangrove cover between both systems. While the Gulf of Nicoya is exposed to semidiurnal tides and an efficient daily water exchange between the mangrove stands and the gulf and thus to a strong mangrove matter export to the gulf water, the mangrove forest of the Caete estuary is flushed each fortnight only and the largest part of the mangrove production thus remains within the forest. This is reflected in great differences in food web structure and the amount and type of resources produced in both systems. In the Gulf of Nicoya, detritus matter exported from the mangroves to the estuary feeds an aquatic food web with shrimps and other aquatic detritivores in the centre of the web, while in the Caete estuary, most energy remains in the benthic domain of the mangrove forest where it is transferred to an enormous biomass of leaf consuming mangrove crabs, the principal resource of this system. Findings imply that generalizations among mangrove systems need to be tempered with caution and differences in trophic relationships among systems must be considered. Rev. Biol. Trop. 54 (Suppl. 1): 69-86. Epub 2006 Sept. 30.

Population structure, catch composition and CPUE of the artisanally harvested mangrove crabUcides cordatus(Ocypodidae) in the Caeté estuary, North Brazil: Indications for overfishing?

To evaluate the population structure of Ucides cordatus in the Caete estuary, crabs were sampled bimonthly over 13 months in three Rhizophora mangle forest stands that differed in their accessibility and fishing history. Additionally, sex- and size composition of the commercial catch and catch per unit of effort (CPUE – the number of crabs captured per fisherman per day) were monitored between 1997 and 2003. Average and maximum crab sizes (carapace width, CW) from all three sampling sites combined were 6.1 cm and 8.8 cm in males, respectively, and 5.5 and 7.3 cm in females. Crabs were largest at the site that had been reportedly less exploited in the past. The overall sex ratio was skewed towards males (53−62%). Egg carrying females were only encountered during the rainy season. Mean crab abundance and biomass was 1.7 specimens m−2 and 142 g m−2 fresh mass. Only large males were commercially harvested (98% ≥ 6.5 cm CW). Their biomass was 53 g m−2 and the Caete estuary yields an annual production of 1200 t of these large specimens. This is approximately the quantity that is currently being harvested. CPUE was similar in 1997 and 1998, then decreased by 15% until 2000 and stabilized for the rest of the study period. Mean capture size (cm CW) ranged between 7.2 ± 0.5 and 7.5 ± 0.2 and was above the size of 50% (and even 100%) male maturity and the legal minimum capture size. There is no evidence that the Caete crab population is overfished, despite over 30 years of de facto open access exploitation. Apparently, the selectivity of fishermen and consumers for large male crabs as well as the local artisanal capture techniques are key factors in preventing an overfishing of the Caete crab population until today. Our results suggest that the economic and social sustainability of this fishery will be affected well before the biological one, which should be considered in the recently proposed coastal co-management plan for the region.

Asymmetric outcomes: assessing central aspects of the biological, economic and social sustainability of a mangrove crab fishery, Ucides cordatus (Ocypodidae), in North Brazil

Central aspects of the sustainability of a mangrove crab fishery in the Caeté estuary, Pará, North Brazil, are assessed according to biological, economic and social criteria and based on a 5-year data series. Ucides cordatus is probably a keystone species in this mangrove ecosystem. Over half of rural coastal households depend on the crab for at least part of their income. The fishery shows seasonal and annual differences in terms of labour input, capture volumes and productivity. During the rainy season, more crab collectors work than during the dry season, although labour productivity is generally lower. A reason for this seemingly irrational producer behaviour is the lack of alternative income sources during this time of year. Labour productivity over the monitoring period decreased by 16%. Present crab fishery does not seem to endanger the U. cordatus population as a whole. Mostly mature old crabs, which have reproduced several times already, are captured. Females are not targeted due to lack of market demand. Nonetheless, males are slightly more abundant than females suggesting that the reproductive output of the crab stock is maintained at a sufficient level. Central for the economic and social sustainability of the fishery is crab collectors' purchasing power, which, between 1998 and 2001, fell by 20%. In 2001, the economic sustainability threshold was reached as crab collectors' incomes net of operational and investment costs fell to about the level of the official Brazilian minimum wage. This means that crab collection is now being undertaken at an income level which only just covers the regeneration of crab collectors' labour. At the same time, an ongoing erosion of social sustainability is reflected in territorial conflicts between crab collectors and in the incidence of alcoholism and reliance on child labour in crab collector households. Thus, the current fragility of economic sustainability and the undermining of social sustainability are accompanied by apparently undisturbed biological sustainability conditions. This highly asymmetric outcome is a challenge for transdisciplinary efforts to establish relevant fishery management priorities with the active participation of the centrally affected stakeholders.

Seasonal changes in density, biomass, and diversity of estuarine fishes in tidal mangrove creeks of the lower Caeté Estuary (northern Brazilian coast, east Amazon)

The present study investigated the assemblage of fish species in an intertidal mangrove forest during high tide in a macrotide region. We describe the seasonal changes in the fish assemblage composition in relation to biomass, density, and species number in tidal creeks of the Furo do Meio, Caete Estuary, Brazil. A total of 29 107 individuals of 49 species in 26 families were caught using a block net. Their total weight was 526 kg (total density 0.11 ind. m -2 and total biomass 2.1 g m -2 ). Analysis of the catch data showed that the number of species varied significantly between creeks, and that total fish biomass differed significantly between seasons. The densities and biomass of the 2 most important species, Cathorops pleurops and Colomesus psittacus, were significantly different between seasons. The densities and biomass of C. pleurops, Pterengraulis atherinoides, Pseudauchnipterus nodosus, and Stellifer naso showed significant temporal differences. Significant differences between creeks were observed in the density and biomass of Anchovia clupeoides and Rhinosardinia amazonica. The abundance-biomass comparison (ABC) plots for the fish fauna in the creeks of the Furo do Meio showed that the dominant species increased in number and weight at the beginning of the rainy season. As a result of increased rainfall in March and April, salinity declined to values between 6 and 8 psu. At that time, the dominant species made up more than 60% of the total biomass and density and Hill's index of diversity (N1) declined, whereas the number of species (NO) and evenness (E2) did not change. After April, rainfall decreased, and density and biomass returned to levels similar to those before the rainy season. The number of species and the density and biomass in the mangrove tidal creeks are compared with published data for other tropical and subtropical estuaries. Migration trends were inferred from the results of the seasonal fluctuations of density and biomass of the most important species in the Furo do Meio, and are compared with data from other studies in the main channel of the Caete Estuary.