Short Time Scale Changes in Underwater Irradiance in a Wind-exposed Lagoon (Vaccarès Lagoon,France): Efficiency of Infrequent Field Measurements of Water Turbidity or Weather Data to Predict Irradiance in the Water Column

High frequency water sampling in the wind-exposed Vaccarès lagoon revealed frequent and rapid changes in suspended solid (SS) concentrations in the water column. SS concentrations, sometimes higher than 800 mg l⁻¹, were significantly correlated with antecedent wind conditions. Mean wind velocity during the 5–33 h before water sampling or maximal wind velocity during the previous 8.5–22 h were good predictors of SS concentrations in the water column. Underwater irradiance at canopy level was modeled (r² = 0.66, n = 7584) using the SS calculated from the relationship between SS and antecedent mean wind velocity and the surface irradiance data measured at the weather station close to the study site. On the other hand, we have shown that in this wind-exposed lagoon, mean underwater irradiance can not be effectively estimated using infrequent measurements of the optical properties of water.     

Comparison of bacterial populations and chemical composition of dairy wastewater held in circulated and stagnant lagoons

AIMS: This study compared the chemical, physical and bacterial composition of circulated and stagnant dairy wastewaters. METHODS AND RESULTS: Samples taken from circulated and stagnant wastewater lagoons, over a 1-year period, were analysed for 10 chemical (total N, NH3, NO3, NO2, Na, Ca, HCO3, Fe, P and K) and six physical (biological oxygen demand, chemical oxygen demand, dissolved solids, electrical conductivity, pH and sodium absorption ratio) parameters and were found to be similar. The 16S rDNA genes from the samples were amplified, cloned and BLAST analysed. In total, 996 stagnant and 1052 circulated wastewater derived sequences were obtained, comprising 294 and 362 operational taxonomic units (OTUs) from the circulated and stagnant wastewaters respectively. Coverage estimates of the OTUs identified were 72.1% for the stagnant, and 63.6% for the circulated wastewater libraries. The greatest difference between the two wastewaters was a c. sixfold greater number of sequences representative of the family Chromatiaceae in the circulated wastewater derived library and a c. fivefold greater number of sequences representative of the phylum Chloroflexi in the stagnant wastewater derived library. CONCLUSIONS: Circulation of dairy wastewater does not affect any of the chemical or physical parameters tested; however, circulation does alter the bacterial community structure. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides evidence that circulation of dairy wastewater promotes the growth of bacteria within the family Chromatiaceae and that stagnant systems promote the growth of the phylum Chloroflexi.     

Spatial structure of fish assemblages in a tropical estuarine lagoon: combining multivariate and geostatistical techniques

The spatial structure and seasonal changes of estuarine fish assemblages in the Ciénaga Grande de Santa Marta (CGSM) were analysed based on four seasonal comprehensive surveys conducted in 1993-1994 and 1997. Geostatistical and multivariate techniques were used to: (a) determine seasonal changes in spatial distribution of the species richness, and (b) identify assemblages of estuarine fish and their relation to abiotic factors. Potential biotic interactions affecting the assemblage structure were also explored. A total of 11075 individuals representing 39 species were collected, with Eugerres plumieri, Diapterus rhombeus, Micropogonias furnieri, Mugil incilis, Cathorops spixii, Elops saurus and Anchovia clupeoides as dominant species between seasons. Spatial distribution of fish richness differed between rainy and dry seasons in each year, whereas species mapping showed spatial patchiness in 1993-1994 and gradients during 1997. Strong evidence of species saturation was found in all seasons, suggesting biotic interactions limiting species richness at a threshold density of ca. 50 ind./5000 m². Marine, marine-estuarine and freshwater species were classified in each season according to their capability to cope with salinity fluctuations. Associations defined by functional feeding guilds were also identified. Empirical and statistic evidence showed that fish assemblages differed between seasons within each year, and each assemblage was always dominated by a small number of species, notably E. plumieri in both years 1993-1994 and 1997. Between-season differences in fish assemblage structure in the CGSM seem to be driven by abiotic factors; however, evidence of species saturation could suggest the existence of density-dependent factors operating together.     

pH and Eh on Aldabra atoll 1. comparison of marine and reshwater environments

An account is given of the range of pH and Eh in marine and freshwater aquatic sites on one atoll (Aldabra, Indian Ocean). There is a very wide range in values of pH and Eh for both marine and freshwater environments, the range for pH in general being wider in freshwater ones and Eh in marine ones. Photosynthetic microbial communities on lagoon sediments may be arranged in an approximate order of their association with sediments of particular Eh values. These are, from high to low: Scytonema sp., pennate diatoms, Schizothrix sp., Microcoleus chthonoplastes, Hyella balani, purple phototrophic bacteria.     

Locomotor activity patterns of two sympatric species Orchestia montagui and Orchestia gammarellus (Crustacea,Amphipoda)

Freshly adult individuals of two sympatric species, Orchestia gammarellus and Orchestia montagui, collected in spring from the supralittoral zone of Bizerte lagoon (Northern of Tunisia) at Menzel Jemil, were housed in a controlled environment cabinet. Locomotor activity rhythm was recorded in isolated individuals and groups by infrared actograph every 20 min by a data-logger, at a constant temperature of 18 ± 0.5 °C under constant darkness. According to double-plotted actograms and waveform curves, results showed the presence of two different locomotor patterns; in fact, individuals of O. gammarellus concentrated their activity during the hours of subjective night, whereas O. montagui were active during the subjective night and beyond the subjective dawn. Furthermore, whatever the species studied, periodogram analysis indicated a distinct circadian pattern of activity. Moreover, whatever the experiment condition is, the most clearly defined rhythms were found in O. gammarellus. In contrary to O. gammarellus, the group effect on the locomotor rhythm parameters seems to be less marked in O. montagui. On the other hand, a highly inter-individual variability was observed in the activity time for these two species and especially for O. montagui groups.     

Seasonal distribution of phytoplankton in the Aby lagoon system,Ivory Coast,West Africa

Seasonal variability of phytoplankton species composition, abundance and physical and chemical factors influencing phytoplankton dynamics were investigated in the Aby lagoon system, south-eastern Ivory Coast, covering the main climatic seasons in 2006–2007. Seasonal and spatial variability of nutrient concentrations in the system were influenced by freshwater inflow from the Bia and Tanoé rivers. The decrease in the salinity gradient in Aby Lagoon, which is permanently stratified during the long dry season, increased the bottom inputs of soluble reactive phosphate and soluble reactive silicate which, in combination with good light penetration during the long dry season, enhanced phytoplankton production in the system. During the rainy seasons, water discharges into the system washed phytoplankton biomass out, preventing the development of blooms. Overall, 192 taxa from eight phyla were recorded: Bacillariophyta (32%), Chlorophyta (31%), Cyanobacteria (23%), Euglenophyta (12%), Dinophyta (0.5%), Xanthophyta (0.5%), Chrysophyta (0.5%) and Rhodophyta (0.5%). During the long dry season, Cyanobacteria cells comprised >50% of the phytoplankton abundance. The main phytoplankton taxa responsible for this high abundance were Microcystis aeruginosa, Oscillatoria princeps, Pseudanabaena limnetica, Aphanizomenon sp. 2 and Anabaena planctonica.     

Spatial and seasonal biomarker responses in the clam Ruditapes decussatus

The clam Ruditapes decussatus is an important resource to preserve in coastal lagoon systems around the Mediterranean including the South Portugal. To assess spatial and temporal biomarker responses to contamination in the species, a multibiomarker approach was conducted using antioxidant enzymes, MFO system phase I and II; acetylcholinesterase, metallothionein (MT), δ-aminolevulinic acid dehydratase and lipid peroxidation (LPO). The condition index (CI), metals and polycyclic aromatic hydrocarbons (PAHs) were also determined. The levels of contaminants were not particularly high and the antioxidant enzymes, acetylcholinesterase (AChE), MT in the digestive gland, and δ-aminolevulinic acid dehydratase (ALAD) do not provide a suitable seasonal and spatial discrimination reversely to that regarding CYP450, glutathione-S-transferase (GST), MT in the gills, and LPO in both tissues. However, even those could vary with natural variables that may act as confounding factors. Thus, seasonal variability and natural range of biomarker responses must be carefully and accurately taken into account in ecotoxicological approaches of environmental quality assessment programmes.     

Diversity of terrestrial isopods in the supralittoral zone of Ghar El Melh lagoon (Tunisia)

In Tunisia, while wetlands are considered as remarkable habitats for their faunal and floral diversity, few studies on the species diversity of terrestrial isopods were performed. To fill this gap, the spatio‐temporal distribution of Oniscidea at Ghar El Melh lagoon (north‐east of Tunisia) was analysed. Sampling was carried out with 50 × 50 cm quadrats along a perpendicular transect to the shoreline. Nine species of terrestrial isopods belonging to seven genera were identified. Chaetophiloscia elongata Dollfus, 1884 was the most abundant species in all seasons except for summer; its relative abundance ranged from 38.9% to 77% in summer and autumn, respectively. Hill diversity indices ranged from 0.86 to 0.94 and equitability indices from 0.33 and 0.68. The statistical analysis showed a significant difference of isopod species and plant associations among seasons.     

Topographic effects of coastal seas on the composition of the culturable bacterial communities in marine sediments

Five published indirect methods to estimate benthic secondary production of intertidal mudflats and a new proposed formulation based on quarter-power allometric scaling and the “Universal Temperature Dependence” of biological processes (UTD) were compared. For this purpose, a dataset consisting of an annual series of samples, taken from the Lagoon of Venice from March 1996 to March 1997, at sites characterised by different seagrass coverage was used. All methods resulted in that biomass and secondary production decreased progressively when moving from the seagrass meadow toward areas of unvegetated substrate, suggesting an influence of the available marine phanerogams on the neighbouring sites. The equation proposed in this paper gives results comparable with those obtained using empirical regression models from literature. The main conclusion from this study is that general equations proposed by the “metabolic theory of ecology” can be applied for indirect estimations of secondary production of benthic communities.     

Evaluation of ammonium and phosphate release from intertidal and subtidal sediments of a shallow coastal lagoon (Ria Formosa – Portugal): a modelling approach

During an annual cycle, overlying water and sediment cores were collected simultaneously at three sites (Tavira, Culatra and Ramalhete) of Ria Formosa’s intertidal muddy and subtidal sandy sediments to determine ammonium, nitrates plus nitrites and phosphate. Organic carbon, nitrogen and phosphorus were also determined in superficial sediments. Ammonium and phosphate dissolved in porewater were positively correlated with temperature (P < 0.01) in muddy and sandy sediments, while the nitrogen-oxidized forms had a negative correlation (P < 0.02) in muddy sediments probably because mineralization and nitrification/denitrification processes vary seasonally. Porewater ammonium profiles evidenced a peak in the top-most muddy sediment (380 μM) suggesting higher mineralization rate when oxygen is more available, while maximum phosphate concentration (113 μM) occurred in the sub-oxic layer probably due to phosphorus desorption under reduced conditions. In organically poor subtidal sandy sediments, nutrient porewater concentrations were always lower than in intertidal muddy sediments, ranging annually from 20 μM to 100 μM for ammonium and from 0.05 μM to 16 μM for phosphate. Nutrient diffusive fluxes predicted by a mathematical model were higher during summer, in both muddy (104 nmol cm⁻² d⁻¹––NH₄⁺; 8 nmol cm⁻² d⁻¹––HPO₄⁻²) and sandy sediments (26 nmol cm⁻² d⁻¹––NH₄⁺; 1 nmol cm⁻² d⁻¹––HPO₄⁻²), while during lower temperature periods these fluxes were 3–4 times lower. Based on simulated nutrient effluxes, the estimated annual amount of ammonium and phosphate exported from intertidal areas was three times higher than that released from subtidal areas (22 ton year⁻¹––NH₄⁺; 2 ton year⁻¹––HPO₄⁻²), emphasizing the importance of tidal flats to maintain the high productivity of the lagoon. Global warming scenarios simulated with the model, revealed that an increase in lagoon water temperature only produces significant variations (P < 0.05) for NH₄⁺ in porewater and consequent diffusive fluxes, what will probably affect the system productivity due to a N/P ratio unbalance.