Shallow Estuarine Areas Research Articles

Effect of short-term meteorological disturbances on the submerged aquatic vegetation and associated fauna in the Patos Lagoon estuary, southern Brazil

Occluded fronts are naturally cyclogenic areas that have been intensified by global warming. Studies evaluating the effects of occluded fronts in the submerged aquatic vegetation (SAV) and its associated fauna in shallow estuarine areas may provide insights on the impacts of climate change-induced extreme weather events on coastal ecosystems functioning. The present dataset describes data on benthic fauna and flora in the Patos Lagoon Estuary (PLE), in southern Brazil, seasonally obtained during intense occluded fronts. Using a hierarchical sample design, based on Beyond BACI protocols (Before/After and Control/Impact), fauna and flora were sampled before and after four occluded fronts passage throughout 2019.Three habitats were sampled: SAV Meadow, SAV Edge and adjacent Sandflat. A total of 432 macrozoobenthic samples (216 samples for stratum); 216 samples for bellow and aboveground biomass, vegetation coverage, canopy height and marine macrophytes morphology; 144 samples by sedimentology and organic matter; 72 water column depth measurements; and 8 temperature and salinity measurements were collected during the study period. The data is available at the Global Biodiversity Information Facility (GBIF), in Darwin Core standard format (DwC), organized according to the OBIS-ENV-DATA model, with CC-BY-NC-4-0 license for use. The present dataset adds to the comprehension of the temporal variability of estuarine benthic communities in subtropical systems, and how short-term meteorological process can affect zoo and fitobenthic communities in the context of climate changes.

Spatial and temporal variations of sediments in a subtropical microtidal estuary

Sediment dynamics are determined by the synergy between the hydrodynamic condition and sediment properties. This study analyzed, between the years 2015-2017, the spatial and temporal changes in sediment texture of a shallow embayment in the Patos Lagoon estuary (Southern Brazil), and the influence of environmental parameters in these variations. Two areas were selected: an area more exposed to the estuary main channel dynamics and NE winds, and the other protected from them by islands. Each area was divided in shallow (mean depth <2m) and deeper zones (mean depth ≥2 m). The organic matter content presented a spatial and temporal variation, with maximum values higher than previously reported. Due to elevated rainfall rates during the winter and spring of 2015, higher values of fine sediments and organic matter were recorded, mainly at deeper zones. The protected area presented small grain sizes and their variability was correlated with wind speed and direction. While in the exposed area the water depth has a higher influence in the granulometric variations, decreasing grain sizes with depth increases. The greater seasonality in the granulometric variation was observed in the deeper zones, which presented the smaller grain sizes and lower values of asymmetry, decreasing these values in winter and spring. In conclusion, few centimeters in water depth may cause large changes in bottom types (or in the relative amount of sand, silt and clay) of shallow estuarine areas. From the environmental variables measured, wind, rainfall and bathymetry were the most influential in the temporal variation of the sediments, while hydrodynamic exposure on the spatial differences.

Microgobius meeki as a potential bio-indicator of habitat disturbance in shallow estuarine areas: a useful tool for the assessment of estuarine quality.

The relationships between changes in habitat quality (disturbed and undisturbed sites) and the population parameters (density, size distribution, reproductive activity and diet) of a goby Microgobius meeki were investigated in a tropical estuary to assess its value as an indicator of anthropogenic changes, predominantly the effects of sedimentation and mangrove removal in shallow estuarine areas. Fish sampling surveys were conducted bimonthly between June 2009 and May 2010 over the entire estuarine gradient of the Paraguaçu River estuary, located on the central Brazilian coast. A predictive model was developed to assess the population changes of this species in 10 other tropical estuaries with different dimensions, basin features and distinct levels of anthropogenic disturbance. General linear models were used to relate the population structure of M. meeki to sediment type, habitat type resulting from mangrove conservation status, anthropogenic pressure and environmental characteristics such as salinity, dissolved oxygen concentrations and temperature. Sediment type and the presence of mangrove forests were the most effective predictors of local variability in the population structure of M. meeki. Individuals with mature gonads and high rates of feeding activity were associated predominantly with undisturbed habitats. Estuaries and estuarine sectors with high levels of sedimentation in shallow marginal areas, anthropogenic pressure from domestic and industrial effluents, and evidence of mangrove deforestation yielded the lowest capture rates of both juvenile and adult M. meeki. Based on these findings, M. meeki is identified as a potential indicator of the consequences of anthropogenic disturbance in transitional waters. A simple, but efficient collection protocol, in which overt signs of distress can be promptly observed is proposed. Testing the generality of this approach across different systems might prove useful in a broader conservation biology context.

Fishers' resource mapping and goliath grouper Epinephelus itajara (Serranidae) conservation in Brazil

Goliath grouper (Epinephelus itajara) aggregations and relative abundances were described and mapped through the use of fishermen's local ecological knowledge in Babitonga Bay in southern Brazil. Six well-experienced informants were asked to individually provide information about goliath grouper abundance and distribution, drawn over a satellite image of the study area, which was later overlaid and gathered into a final map. According to our informants, the goliath grouper occurs along a broad salinity and depth range, from shallow estuarine areas (less than 5 m deep) with high freshwater input (smaller individuals, up to 150 kg) to coastal marine-dominated environments (at least 35 m deep); (larger individuals more common, frequently reaching more than 300 kg). Fishermen referred to goliath groupers inhabiting hard substrates such as rocky reefs around islands and continental shores, submerged rocky outcrops and shipwrecks (juveniles and adults). At least two aggregation sites mapped (ranging from 2 to 60 individuals) could be concluded as spawning aggregation sites through evidence of high abundance and spawning activity. Priority research and conservation targets were identified and discussed for Babitonga Bay (e.g., design of a tagging experimental program and establishment of a marine protected area). Fishers' resource mapping provided a means of exchanging information among various disciplines while maintaining methodological rigor in a clear and straightforward way of presenting fishers' knowledge. The use of fishers' sketch maps is a promising tool for marine conservation in Brazil, with special regard to adaptive co-management regimes, where frequent environmental re-evaluations are needed.

A Stochastic Dynamic Methodology (SDM) to the modelling of trophic interactions, with a focus on estuarine eutrophication scenarios

Abstract In the face of global change, declines in environmental quality are of increasing concern, especially in shallow coastal areas, densely populated and commonly affected by nutrient enrichment. The warm temperate Mondego estuary (Western Portugal), in common with many other shallow estuarine areas, is exhibiting increased macroalgal growth due to nutrient enrichment. The increase of macroalgal biomass and possible shift of other primary producers resulting from eutrophication, may have profound effects on estuarine trophic chain. The present paper examined the performance of a holistic Stochastic Dynamic Methodology (SDM) in predicting the tendencies of three representative trophic levels as a response to the increase of nutrient concentrations. Therefore, the proposed methodology has been developed by focusing on the interactions between conceptually isolated key-components, such as primary producers (macroalgae and seagrass), some relevant benthic macroinvertebrates, wading birds and changes in local physicochemical conditions. The dynamic model developed was preceded by a conventional multivariate statistical procedure (stepwise multiple regression analysis) performed to discriminate the significant relationships between prevailing biological and environmental variables. Since this statistical analysis is static, the dataset recorded from the field included true gradients of habitat changes. The data used in the model construction was sampled between January 1993 and September 1995 in three areas of the estuary mudflats for benthic macroinvertebrates, macroalgae, environmental and physicochemical factors and from October 1993 to October 1994 for wading birds. The model validation was based on independent data collected in two different periods, from January 1996 to January 1997 and from February 1999 to April 2000 for all the variables selected. Overall, the simulation results are encouraging since they seem to demonstrate the model reliability in capturing the trophic dynamics of the studied estuary by predicting the behavioural pattern for the most part of the components selected under a very complex and variable environmental scenario.

Composition and abundance of invertebrate benthic fauna in Farfantepenaeus paulensis culture pens (Patos Lagoon estuary, Southern Brazil)

Annual Farfantepenaeus paulensis landings in Patos Lagoon are highly variable, and pen culture in shallow estuarine areas has been developed as an alternative for artisanal fishermen. However, there is a concern about the impact of this system in the natural environment. This study was conducted to evaluate macrobenthos occurrence and variation in relation to rearing cycle and production characteristics of pen culture in Patos Lagoon estuary. Macrobenthic invertebrates, organic matter and mud content were sampled inside and outside pens (control). Six major groups (Polychaeta, Tanaidacea, Isopoda, Gastropoda, Amphipoda and Bivalvia) were observed and 11 species were identified. After 21 days of culture, benthos abundance inside pens dropped by around 86%, but no differences between the stocking densities were detected. Benthic species showed different responses to the shrimp culture, and the impact (predation and/or disturbance) on abundance of the macrobenthic invertebrate community was noted. Mud and organic matter content did not differ across sampled areas during culture period. Shrimp attained higher average weight in lowest stocking density. Although the impact of the pen culture is apparently limited to the fenced area and restricted to a short period (3–4 months), the expansion of this method of culture in the shallow waters areas of the Patos Lagoon must be monitored to ensure that greater than expected impacts do not occur.

Microphytobenthic primary production within the flocculent layer, its fractions and aggregates, studied in two shallow Baltic estuaries of different eutrophic status

Investigations concerning the primary production of the microphytobenthos were carried out in two shallow estuarine areas different in their trophic status at the southern Baltic Sea. On top of the sediment surface, a flocculent layer was present at both sites, mainly consisting of bioseston, detritus and mineral particles. Separation of this fluffy layer from the sediment below showed a clear dominance of photoautotrophic versus heterotrophic processes within the layer. In the bare sediment, formerly buried algae were exposed to light again, and immediately, significant photosynthetic activity could be measured. Both findings are of important ecological meaning in the shallow Bodden, where even low wind velocities will lead to a resuspension of the fluffy layer and lateral transport might occur. During deposition, the particles of the flocculent layer will be fractionated due to their different sinking velocity, and therefore might contribute differently to pelagic production. Experimentally gained fractions of the flocculent layer all showed positive oxygen net production already under low light intensities (20–50 μE m −2 s −1), but the finest fraction contained the highest pigment concentrations and metabolic activities. The photoautotrophic character was also confirmed for the single aggregates of the flocculent layer. Investigations of the light climate and the oxygen penetration within aggregates by microelectrodes showed that, even under dark conditions, no anoxic zones could be detected. The dominance of photoautotrophic processes in the flocculent layer and its particles was indicated at both study sites. However, taken into account the different morphometry and hydrography of the study sites, it became clear that the high trophic status of study site A had a negative impact on the benthic primary production rates and changed species composition.

Nursery use of shallow habitats by epibenthic fishes in Maine nearshore waters

Species richness and abundance of epibenthic fishes were quantified with daytime beam trawl tows in shallow water habitats during April–November 2000 of three mid-coast Maine estuaries: Casco Bay, Muscongus Bay and the Weskeag River. Five shallow (<10 m) habitats were sampled, Zostera marina, Laminaria longicruris, Phyllophora sp., Microciona prolifera and unvegetated sandy areas. Thirty-two species of fishes were collected. Species richness per tow was greater in Casco Bay followed by the Weskeag River and Muscongus Bay. Catch per unit effort (CPUE) of fishes was greater in Casco Bay than in the Weskeag River or Muscongus Bay. Species richness and faunal abundances were positively associated with vegetation, particularly Zostera, at all sampling locations. CPUEs of fishes were higher in Zostera primarily due to the abundance of Gasterosteus aculeatus, Apeltes quadracus, Pungitius pungitius, Myoxocephalus aenaeus, and Cylcopterus lumpus. The fish community of mid-coast estuaries was dominated by young-of-the-year (YOY) and juvenile fishes and all of the habitat types function as nursery areas. Twelve species (38%) of commercial and recreational importance were collected in the three estuaries, but the percentage was higher in Casco Bay (44%) and the Weskeag River (46%). These species included Anguilla rostrata, Clupea harengus, Gadus morhua, Microgadus tomcod, Pollachius virens, Urophycis chuss, Urophycis regia, Urophycis tenuis, Osmerus mordax, Macrozoarces americanus, Tautogolabrus adspersus, and Pleuronectes americanus. Four species, G. morhua, M. tomcod, P. virens, and U. tenuis were more common in spring than summer or autumn. P. americanus was most abundant in summer followed by spring and autumn. This study documents the importance of shallow estuarine areas in Maine as nurseries for these species.

Do Shallow-water Habitats Function as Refugia for Juvenile Fishes?

The role of shallow salt marsh creeks as refuges for juvenile fish is unclear and recent investigations have produced conflicting results. Using gill nets, this study examined the distribution of large piscivorous fish in a range of shallow and deep water environments in a temperate southern African estuary. Results indicated that intertidal creeks, along with adjacent shallow water habitats, were not utilized by a number of piscivorous fish species which were common in the deeper estuarine channel environment. This study provides support for the hypothesis that shallow estuarine areas may provide refugia for fishes vulnerable to predation.

Estimating Densities of Small Fishes and Decapod Crustaceans in Shallow Estuarine Habitats: A Review of Sampling Design with Focus on Gear Selection

Shallow estuarine habitats often support large populations of small nekton (fishes and decapod crustaceans), but unique characteristics of these habitats make sampling these nekton populations difficult. We discuss development of sampling designs and evaluate some commonly used devices for quantitatively sampling nekton populations. Important considerations of the sampling design include the size and number of samples, their distribution in time and space, and control of tide level. High, stable catch efficiency should be the most important grear characteristic considered when selecting a sampling device to quantify nekton densities. However, the most commonly used gears in studies of estuarine habitats (trawls and seines) have low, variable catch efficiency. Problems with consistently low catch efficiency can be corrected, but large unpredictable variations in this gear characteristic pose a much more difficult challenge. Study results may be bised if the varibility in catch efficiency is related to the treatments or habitat characteristics being measured in the sampling design. Enclosure devices, such as throw traps and drop samplers, have fewer variables influencing catch efficiency than do towed nets (i.e., trawls and seines); and the catch efficiency of these enclosure samplers does not appear to vary substantially with habitat characteristics typical of shallow estuarine areas (e.g., presence of vegetation). The area enclosed by these samplers is often small, but increasing the sample number can generally compensate for this limitation. We recommend using enclosure samplers for estimating densities of small nekton in shallow estuarine habitats because these samplers provide the most reliable quantitative data, and the results of studies using these samplers should be comparable. Many kinds of enclosure samplers are now available, and specific requirements of a project will distate which gear should be selected.