Aquatic Vegetation Biomass Research Articles

Dynamic distribution monitoring and biomass estimation of aquatic vegetation in Jupiá Hydropower Station, Brazil

Study RegionJupiá Hydropower Station, the junction of São Paulo and Mato Grosso, Brazil. Study FocusDuring the flood season, a large amount of aquatic vegetation is brought to the front of the dam, which not only threatens the safety of the project but also causes internal pollution in the reservoir. This study combined the field data with the remote sensing technology to analyze the temporal and spatial succession of aquatic vegetation in the Jupiá Reservoir. The biomass inversion models were established to estimate the biomass of aquatic vegetation in the whole reservoir area. New hydrological insights(1) The area of aquatic vegetation in rainy season could reach twice that in dry season. From 2018–2022, the total area of aquatic vegetation in the reservoir area showed an overall trend of increase. (2) The total biomass of floating vegetation and submerged vegetation in the reservoir area fluctuated little from 2018 to 2022, with an annual average of 32.14 × 104 t, of which the average biomass of floating vegetation only accounts for 23.5% of the total biomass. Submerged vegetation was an important object of aquatic vegetation management in this reservoir.

Numerical study on regime shifts in an urban subtropical shallow lake: Xinglong Lake, China

Aquatic ecosystem degradation is a considerable challenge of global interest. Although substantial efforts have been accomplished to restore phytoplankton-dominated shallow lakes to a clear state with high coverage of submerged macrophytes, the phenomenon, driving mechanism, and threshold range of such nonlinear regime shifts remain unclear. Here, we constructed an aquatic ecological model based on PCLake, simulated and predicted the aquatic ecological changes before and after treatments of Xinglong Lake, a subtropical artificial shallow lake that had been completed ecological restoration in Chengdu, China. The model included the future prediction of TN, TP, Chl-a, and aquatic vegetation biomass, as well as the threshold of regime shifts using bifurcation analysis. We also quantified the impact of some common management measures (point and non-point source pollution control, water level regulation) on the stability of the lake's aquatic ecosystem. The results showed that the thresholds of Xinglong Lake from a clear state to a turbid state were 1.405 mg/m2/day and vice versa 0.68 mg/m2/day, indicating its initial turbidity and transitional state after treatment. After treatment, phosphorus loads still exceeded the threshold for a clear-water state, while the non-point source pollution of Xinglong Lake accounted for more than 80%. To prevent the aquatic ecosystem from collapsing in the future, it is necessary to combine upstream water quality improvement, runoff and air pollution control to reduce total pollution by 60%. Reasonable water level regulation, such as adjusting the water level downwards by 0.5 m in spring, is beneficial in maintaining the health and stability of aquatic ecosystems. The present study can be used to evaluate the effectiveness of the management measures of Xinglong Lake as well as to provide scientific support for the management of shallow lakes.

Analysis of Resource Potential of Emergent Aquatic Vegetation in the Curonian Lagoon of the Baltic Sea

This paper presents results of an aquatic vegetation resource potential assessment. The study is aimed at assessing the perspective of biotechnological approaches to reducing the biogenic pollution of water bodies by the removal of aquatic vegetation. The article analyzes the dominant species of aquatic vegetation in the Curonian Lagoon, and their productivity and resource potential. It was established that the concentrations of protein and fat in the biomass of four dominant plants are extremely low, making it impossible to speak of their values in terms of biomass processing. Based on elemental composition, we can conclude that the biomass of Phragmites australis should have a high calorie content because it has a high carbon and hydrogen content (49.6% and 7.1%, respectively), resulting in a high energy value. Synchronous thermal analysis revealed that the maximum energy values of biomasses of Phragmites australis and Scirpus lacustris have a net calorific value of 12.62 and 12.55 MJ/kg, respectively. At the same time, the biomass of these plants has a low ash content (around 6.6–7.6%) and a low sulfur content (less than 0.41%). An analysis of the composition of aquatic vegetation biomass samples allowed us to establish that, given the permissible collection time (no earlier than September), the search for directions in the utilization of aquatic vegetation should focus on processing cellulose with the production of crystalline cellulose, biochar, or biofuel via anaerobic digestion. The removal of the excess biomass of aquatic vegetation (Phragmites australis) will allow the reduction of the nitrogen and phosphorus load in the water body by 140 kg/ha and 14 kg/ha, respectively.

Combining quadrat, rake, and echosounding to estimate submerged aquatic vegetation biomass at the ecosystem scale

AbstractMeasuring freshwater submerged aquatic vegetation (SAV) biomass at large spatial scales is challenging, and no single technique can cost effectively accomplish this while maintaining accuracy. We propose to combine and intercalibrate accurate quadrat‐scuba diver technique, fast rake sampling, and large‐scale echosounding. We found that the overall relationship between quadrat and rake biomass is moderately strong (pseudo R2 = 0.61) and varies with substrate type and SAV growth form. Rake biomass was also successfully estimated from biovolume (pseudo R2 = 0.57), a biomass proxy derived from echosounding. In addition, the relationship was affected, in decreasing relevance, by SAV growth form, flow velocity, acoustic data quality, depth, and wind conditions. Sequential application of calibrations yielded predictions in agreement with quadrat observations, but echosounding predictions underestimated biomass in shallow areas (< 1 m) while outperforming point estimation in deep areas (> 3 m). Whole‐system quadrat‐equivalent biomass from echosounding differed by a factor of two from point survey estimates, suggesting echosounding is more accurate at larger scales owing to the increased sample size and better representation of spatial heterogeneity. To decide when an individual or a combination of techniques is profitable, we developed a step‐by‐step guideline. Given the risks of quadrat‐scuba diver technique, we recommend developing a one‐time quadrat–rake calibration, followed by the use of rake and echosounding when sampling at larger spatial and temporal scales. In this case, rake sampling becomes a valid ground truthing method for echosounding, also providing valuable species information and estimates in shallow waters where echosounding is inappropriate.

In situ remediation mechanism of internal nitrogen and phosphorus regeneration and release in shallow eutrophic lakes by combining multiple remediation techniques

Large anthropogenic inputs of N and P alter the nutrient cycle and exacerbate global eutrophication problems in aquatic ecosystems. This study in Lake Datong, China, investigates the remediation mechanism of multiple remediation technique combinations (dredging, adsorbent amendment, and planting aquatic vegetation) on sediment N and P loads based on two high-resolution sampling techniques (HR-Peeper and DGT) and P sequential extraction procedures. The results showed that high temperature and low dissolved oxygen considerably enhanced pore water dissolved reactive P (DRP) and NH4+ concentrations attributable to abundant Fe-P and organic matter content in the sediment. Fe reduction is critical for regulating pore water DRP release and promoting N removal. Overall, for Lake Datong, combining multiple remediation techniques is more effective in controlling sediment P loads (pore water DRP, P fluxes, forms of P, and labile P), from a long-term perspective, than a single remediation. Lanthanum-modified bentonite (LMB) inactivation treatment can transfer mobile P in the surface sediment into more refractory forms over time, thereby reducing the risk of sediment labile P release. However, it is difficult to effectively remediate internal P loads owing to inappropriate dredging depths and low biomass of aquatic vegetation. Future lake restoration practices should optimize the selection of different remediation technique combinations based on internal N and P pollution characteristics, while reducing external wastewater input. These results are important for understanding the remediation mechanisms of internal N and P and provide suggestions for sediment management of shallow eutrophic lakes.

Interactions between aquatic vegetation, hydraulics and fine sediment: A case study in the Halswell River, New Zealand

AbstractThis paper contributes a field study of suspended sediment transport through aquatic vegetation. The study was run over a 3 month period which was selected to coincide with scheduled weed cutting activities. This provided the opportunity to obtain data points with no vegetation cover, as well as to investigate the effects of weed cutting on Suspended Sediment Concentrations (SSC), particle size distributions and river hydraulics. Aquatic vegetation cover was quantified through remote sensing with Unmanned Aerial Vehicles and biomass estimated from ground truth sampling. SSC was highly dependent on aquatic vegetation abundance, and the distance upstream that had been cleared of aquatic vegetation. The data indicates that fine sediment was being trapped and stored by aquatic vegetation, then likely remobilised after vegetation removal. Investigation of suspended sediment spatial dynamics illustrated changes in particle size distribution due to preferential settling of coarse particles within aquatic vegetation, for example D50 decreased from 36.08 μm to 15.64 μm after suspended sediment travelled 304.2 m downstream and passed ~3700 kg of aquatic vegetation biomass. Hydraulic resistance in the study reach (parameterized by Manning's n) dropped by over 70% following vegetation cutting. Prior to cutting hydraulic resistance was discharge dependent (likely due to vegetation pronating at higher flows), while post cutting hydraulic resistance was approximately invariant of discharge. Aerial surveying captured interesting changes in aquatic vegetation cover prior to vegetation cutting, where some very dense regions of aquatic vegetation were naturally removed (without any high flow events) leaving behind unvegetated riverbed and fine sediment. The weed cutting boat had a lower impact on SSC than was originally expected, which indicates that it may offer a less damaging solution to aquatic vegetation removal in rivers than some other approaches such as mechanical excavation. This paper contributes valuable field data (which are generally scarce) on the research topic of flow‐vegetation‐sediment interactions, to supplement laboratory and numerical studies.

Adaptive neural network based on segmented particle swarm optimization for remote-sensing estimations of vegetation biomass

In this study, the segmented particle swarm optimization (SPSO) algorithm and the concepts of the gradient boosting decision tree algorithm (GBDT) were combined to propose the SPSO adaptive neural network (SANN) method. The purpose of this method is to address the inadequacies of the traditional basis function (BP) and radial basis function (RBF) neural networks when solving problems that involve local optima and overfitting. Experimental results indicated that, overall, the SANN method is accurate in remote-sensing estimations of aquatic vegetation biomass. However, accuracies of estimations were unsatisfactory for certain indicators and sessions when data was taken. The estimations were analyzed using three sets of indicators: (i) root mean square error, average relative error, and total relative error; (ii) correlation coefficient and coefficient of determination, and their scatter plots; and (iii) relative error values and their distributions. The results clearly showed that the SANN method was superior to the BP neural network as well as the stepwise multiple linear regression analysis (SR). However, when the relative errors in biomass estimations by the other two methods were low, the advantages of the SANN method were less pronounced. This was particularly true when the relative errors were <30%, in which case SANN was only marginally better than the other two methods.

Combined Hydrothermal Conversion of Biomass (Algae and Aquatic Vegetation) from Lake Baikal Littoral Zone and Heavy-Oil Resids to Produce Biofuel

The prodigious growth of filamentous algae that has been occurring since 2011 in the littoral zone of Lake Baikal poses an acute ecological problem. Samples of algal biomass and aqueous vegetation were collected from the littoral zone of Lake Baikal and converted by hydrothermal treatment into biofuel in the presence of ammonium heptamolybdate. It was demonstrated that algal biomass from the Baikal littoral zone could be a potential source of feedstock for producing biofuel by thermocatalytic treatment. The addition of heavy-oil resids to algal and aquatic vegetation biomass increased the motor-fuel yield and modified its composition.

Long‐term zooplankton community records (1996–2017) for Lake Suwa (Japan)

AbstractThe impact of eutrophication on aquatic ecosystems remains an important topic in aquatic ecology; however, recent successes in water quality restoration in highly eutrophicated water bodies present new research potential regarding re‐oligotrophication. Successfully reducing nutrient loading from sewage treatment through restoration activities, induces large changes in phytoplankton composition and biomass, particularly replacement of cyanobacterial dominance. In Lake Suwa, a shallow eutrophic lake in central Japan, recovery has occurred due to water quality restoration efforts since the 1970s. The improvement of lake trophic state from hypertrophic to mesotrophic is accompanied by various changes, such as rapid decreases in biomass of phytoplankton, benthic invertebrates and planktivorous pond smelt, and increases in biomass of aquatic vegetation, mainly floating leaved plants. During re‐oligotrophication, zooplankton are important because they are major secondary producers in lake ecosystems. In Lake Suwa, the Research and Education Center for Inland Water Environment, Shinshu University has collected bi‐weekly zooplankton samples and analyzed species composition since 1996, when the lake was in a hypertrophic state with serious Microcystis blooms. Lake Suwa is one representative lake for re‐oligotrophication in a shallow eutrophic system, and our zooplankton dataset can be used to understand the changes in ecosystem structure and function.

Estimating the biomass of unevenly distributed aquatic vegetation in a lake using the normalized water-adjusted vegetation index and scale transformation method

Satellite remote sensing is advantageous for the mapping and monitoring of aquatic vegetation biomass at large spatial scales. We proposed a scale transformation (CT) method of converting the field sampling-site biomass from the quadrat to pixel scale and a new normalized water-adjusted vegetation index (NWAVI) based on remotely sensed imagery for the biomass estimation of aquatic vegetation (excluding emergent vegetation). We used a modeling approach based on the proposed CT method and NWAVI as well as statistical analyses including linear, quadratic, logarithmic, cubic, exponential, inverse and power regression to estimate the aquatic vegetation biomass, and we evaluated the performance of the biomass estimation. We mapped the spatial distribution and temporal change of the aquatic vegetation biomass using a geographic information system in a test lake in different months.The exponential regression models based on CT and the NWAVI had optimal adjusted R2, F and Sig. values in both May and August 2013. The scatter plots of the observed versus the predicted biomass showed that most of the validated field sites were near the 1:1 line. The RMSE, ARE and RE values were small. The spatial distribution and change of the aquatic vegetation biomass in the study area showed clear variability.Among the NWAVI-based and other vegetation index-based models, the CT and NWAVI-based models had the largest adjusted R2, F and the smallest ARE values in both tests. The proposed modeling scheme is effective for the biomass estimation of aquatic vegetation in lakes. It indicated that the proposed method can provide a most accurate spatial distribution map of aquatic vegetation biomass for lake ecological management. More accurate biomass maps of aquatic vegetation are essential for implementing conservation policy and for reducing uncertainties in our understanding of the lake carbon cycle.

Composition and Biomass of Aquatic Vegetation in the Poyang Lake, China.

The distribution of aquatic vegetation and associated community diversity and biomass in the Poyang Lake were investigated. The results showed that (1) 43 species of aquatic vascular plants were found in the Poyang Lake watershed which belonged to 22 families; (2) the vegetation of the Poyang Lake scattered in different areas which could be divided into 31 major plant communities and 5 plant zones including amphibian, emergent, floating-leaved, submerged, and floating input; (3) there were 67 aquatic plants in the lake area, and the standing stock (fresh weight) was 1519.41 t. The number of amphibians was the dominant plant species in the Poyang Lake, and the quantity and percentage of amphibians were predominant, which was far more than the other three life forms.

Analysis of nutrient transport and ecological response in Honghu Lake, China by using a mathematical model

A two-dimensional (2D) water quality model was established to determine the response of water quality variables and submerged aquatic vegetation biomass to load reduction from watershed inflows and enclosure aquaculture in Honghu Lake in China. Results showed that the total nitrogen (TN) and total phosphorus (TP) loads from upstream discharge were the major external loads in the lake, accounting for 70% and 63% of the total loads, respectively. Scenario simulation results indicated that 93.2% of the lake area in summer (August) and 89.5% in autumn (November) could reach the protective targets (TN<1.0mg/L) under 50% reduction of inflow TN loads. Meanwhile, 58.7% of the lake area in summer and 63.1% in autumn could reach the protective targets (TP<0.05mg/L) under 50% reduction of aquaculture areas. The mass budget results of TN and TP showed that TP immobilisation was larger than TN immobilisation. The immobilisations for TN and TP from July to September were higher than those of other months under the combined impacts of increasing runoff during the wet period, phytoplankton bloom and water residence time. The 2D water quality model provided a relevant example for assessing the effects of runoff and aquaculture activities and served as scientific support for lake management to improve water quality in large shallow macrophytic lakes.

Macrophytobenthos of the Caspian Sea: Diversity, distribution, and productivity

In the Russian sector of the northern and middle Caspian Sea, 36 species of macroalgae have been identified. The green and red algae from the mesosaprobic group are dominant. An increase in the number of green algae species is revealed. The distribution of macroalgae is inhomogeneous. It is confined to the solid substrate and epiphyton. The biomass of seaweeds reaches 1.5 kg/m2. Climate change has little influence on the appearance of new species in the northern Caspian Sea, but new invaders can appear in the Middle and Southern Caspian. The distribution of aquatic and coastal hygrophytic vegetation shows considerable spatial dynamics due to fluctuations in the level and salinity of the Caspian Sea. The biomass of aquatic vegetation varies in a wide range from 0.5 to 10.0 kg/m2. Spatially detailed mathematical models adequately reflect the changes in key species of aquatic plants in space and time. It is shown that expansion of the zone of the seagrass Zostera noltii to shallow water areas is occurring at present, as well as shrinkage of the range of the dominant littoral aquatic plant Phragmites australis.

Primary production dynamics in a pristine groundwater influenced coastal lagoon of the Yucatan Peninsula

Dzilam lagoon is a shallow (0.6 m mean depth) ecosystem with 9.4 km 2 surface area, located in the north coast of the Yucatan Peninsula, and connected to the Gulf of Mexico through a permanent inlet. Freshwater input is possible through numerous sinkholes distributed throughout the lagoon, which also represent a continuous source of nitrate and silicate. The low anthropogenic influence has maintained a pristine condition in Dzilam lagoon, manifested in a spatial heterogeneity of water quality and primary production strongly related to the environmental fluctuations. To determine the annual variability of primary production and identify the factors controlling it, 12 monthly samplings were undertaken at six stations, from September 1998 to August 1999. Thus, physical–chemical parameters, inorganic nutrients concentrations, chlorophyll- a, phytoplankton production and seagrass biomass were measured. The water residence time in Dzilam lagoon is higher during dry season due to the significant evaporation rate, and shorter in rainy season because of increase in precipitation and volume of groundwater discharge. The multivariate analysis results suggest that the salinity gradient, changes in aquatic vegetation biomass, and the remineralized nutrients in sediments constitute key processes depicting the water quality and net primary production in Dzilam lagoon. Furthermore, the biogeochemical benthic processes, combined with a longer stay of phytoplankton cells within the lagoon, enhanced primary production in the water column during dry season, as opposite as rainy period, when the inferior water residence time yielded lower production values. The seagrasses ( Halodule wrightii and Ruppia maritima) showed the highest biomass (110.5 g dw/m 2/d) in dry season, while the lowest recordings were observed during cold fronts, with a salient belowground contribution (rhizomes and roots). Seagrasses and phytoplankton participation to the total primary production in Dzilam lagoon were seasonally alternated, yielding a high primary productivity along the annual cycle. Despite of this complementary arrangement, the submerged aquatic vegetation displayed an overall higher contribution during the year (65%) relate to phytoplankton.

Estimate of net primary productivity of aquatic vegetation of the Amazon floodplain using Radarsat and JERS‐1

Synthetic aperture radar images, combined with field measurements, were used to estimate net primary productivity (NPP) of aquatic vegetation in the lower Amazon. Input data for a NPP model are (i) the total biomass of aquatic vegetation, determined by radar imagery and field measurements and (ii) the area occupied by aquatic vegetation, determined from radar imagery. After correction for monthly biomass losses, the NPP of one growth cycle of aquatic vegetation was calculated in the image domain. The total net primary productivity of Hymenachne amplexicaules, the dominant aquatic vegetation in the area, was on average 19×1011 g C yr−1 for the entire area. Spatially, lower values of produced organic carbon (<900 g C m−2 yr−1) are confined to regions where the plants developed only in the beginning of the rising phase of the hydrological cycle. In general, values are higher (>5000 g C m−2 yr−1) in areas closer to the Amazon River where the availability and influence of nutrient‐rich water is greater.

Growth and mortality of transient shrimp populations (Farfantepenaeus spp.) in a coastal lagoon of Mexico: role of the environment and density-dependence

Abstract The influence of environmental (temperature, salinity, aquatic vegetation) and density-dependent (abundance of recruits) factors on growth and mortality of four Farfantepenaeus species were evaluated during their period of estuarine residence, through a 2-year field study at Celestun lagoon, Mexico. Growth rates of the three most abundant species (F. brasiliensis, F. duorarum, F. notialis) were positively related with temperature and aquatic vegetation biomass, whereas some significant relationships between environmental factors and mortality rates were also demonstrated. Our results suggest that density-dependent processes regulate growth and mortality in these shrimp populations. Density-dependent mortality was also suggested by a strong compensatory relationship between recruits and juveniles. We conclude that population dynamics of Farfantepenaeus shrimps during their estuarine phase seem to be driven by the combined forces of density-dependent and environmental factors operating together.

Aquatic plant communities and predictors of diversity in a sub-tropical river floodplain: the upper Rio Paraná, Brazil

Analysis of field survey data collected during 1999, from waterbodies (river channel, secondary channels and backwaters, temporary lagoons, permanent lagoons) within the riverine floodplain wetlands of the Upper Rio Paraná in southern Brazil showed: (i) strong dominance by five aquatic macrophyte species (most important being Eichhornia azurea), out of 28 species recorded at the survey stations; (ii) based on TWINSPAN clustering, the existence of three major aquatic vegetation types. These comprised an E. azurea– Limnobium laevigatum sub-community (at 20% of stations sampled); an E. azurea– Salvinia sub-community (commonest, at 67% of stations); plus a Nymphaea amazonum– Myriophyllum aquaticum community (rarest, at 13%) which occurred in habitats showing significant between-type differences in environmental conditions for water (depth, underwater light regime, conductivity, pH, alkalinity, phosphate) and sediments (redox potential, calcium, total Kjeldahl nitrogen, phosphate, iron); (iii) predictable patterns of variation in plant size and shape, among populations of the dominant plant species present: E. azurea, Cyperus diffusus, Polygonum ferrugineum, Salvinia spp., Eichhornia crassipes, N. amazonum, along gradients of water and sediment physico-chemistry; (iv) significant variation in both macrophyte community abundance and species diversity between the three vegetation types, with the highest species richness occurring in the E. azurea– L. laevigatum sub-community, but highest community biomass in the E. azurea– Salvinia sub-community. Minimal linear models are presented which use a combination of environmental and vegetation attribute data as predictor variables to predict species richness and biomass of aquatic vegetation for the floodplain waterbodies. Such models can be used to assess vegetation response to likely scenarios of future change in river conditions in sub-tropical areas, for example modification of flow regime by dam construction.

Influence of estuarine zonation on exploited shrimp populations in a Mexican biosphere reserve: a feature for management and conservation

The influence of estuarine zonation in a coastal lagoon on the population variability of exploited penaeid shrimps Farfantepenaeus aztecus, F. brasiliensis, F. duorarum and F. notialis (Crustacea: Decapoda) at the ‘Ría Celestún’ Biosphere Reserve, Mexico, was evaluated. Monthly samples of shrimp and environmental factors were taken throughout 1997 and 1998 in three zones (seaward, middle, inner) of Celestún lagoon. Salinity and aquatic vegetation biomass exhibited a clear spatial heterogeneity of habitat. A total of 20,757 shrimps were collected mainly at the seaward zone, which registered the highest salinity and aquatic vegetation biomass. This revealed the critical contribution of the seaward zone as the most suitable habitat for shrimp populations, mainly for recruits. Results support the implementation of spatially-explicit management strategies, such as the closure of the seaward zone for fishing activities. The significant relationship between the recruits and the subsequent abundance of shrimp in the lagoon also support this operational measure.

Nutrient and Solids Controls in Virginia’s Chesapeake Bay Tributaries

A model package including a watershed model, an atmospheric loading model, a hydrodynamic model, and a eutrophication model are used to evaluate the benefit of nutrient and solids load controls on the Virginia tributaries to the Chesapeake Bay. Quantities examined include nutrients, solids, chlorophyll, anoxic volume, mesozooplankton, benthos, light attenuation, and submerged aquatic vegetation. Nutrient load controls are beneficial in reducing chlorophyll concentration and anoxic volume but produce no major benefits for zooplankton and benthos. Load controls benefit aquatic vegetation biomass, but more extensive solids controls are required to restore widespread SAV distribution.

Population Variability of Four Sympatric Penaeid Shrimps (Farfantepenaeus spp.) in a Tropical Coastal Lagoon of Mexico

Spatial and temporal variations in the relative abundance of the species and population components ofFarfantepenaeus shrimps were investigated in Celestun Lagoon, Mexico. The influence of salinity, water temperature and aquatic vegetation biomass on the distribution and abundance of shrimps was evaluated. The paper documents for the first time an annual analysis of the population variability of Farfantepenaeus notialis in its new range extension for the north-western Atlantic Ocean. A total of 11335 shrimps belonging to four Farfantepenaeus species (F. aztecus, F. brasiliensis, F. duorarum and F. notialis) were collected monthly during 1997 at three hydrological zones (seaward, middle, inner). The species represented 9·3, 25·1, 31·5 and 22·4% respectively of the total collection, the remaining 11·7% corresponding to small unidentified shrimps classified as recruits. The four penaeid species occurred throughout the year. Recruits, juveniles and subadults had a clear bimodal pattern, with a gap of 1–4 months between peaks of each population component, indicating a strong linkage between life stages. Two major peaks of recruits occurred during December–February and May–June: the first might be related to F. duorarum and F. notialis, while the second one could be attributed to F. brasiliensis and F. aztecus, suggesting differential recruitment timing. An ontogenetic spatial partitioning is also suggested to explain the observed patterns. The climatic seasons generated strong differences in temperature, salinity and aquatic vegetation biomass, which in turn affected the spatial patterns of shrimp density. The significant preference of all species, recruits and juveniles for the seaward zone highlights its strong nursery role for Farfantepenaeus species.