Effects of the Sand Bar Breaching on Typha domingensis (PERS.) in a Tropical Coastal Lagoon

Coastal lagoons are usually subjected to several kinds of human impacts, especially eutrophication. The breaching of the sand bar, which separates the lagoon from the ocean, by human action, is a common process used to decrease the negative effects of eutrophication. The aims of this research were to evaluate the effects of the artificial sand bar breaching on the populations of the aquatic macrophyte Typha domingensis and the subsequent effects on nutrients concentration in a tropical coastal lagoon. Samplings were carried out monthly from February/01 to January/02 in a monospecific stand of T. domingensis at Imboassica lagoon (Rio de Janeiro/Brazil). Two sampling sites, in the middle and in the border of the stand, were marked in three different transects. Water depth was measured and the aerial biomass sampled with a 0.25 m² quadrat. The macrophyte samples were separated into live and dead material and the shoot length, shoot density and number of leaves were analyzed. All plant material was oven dried till constant weight and net primary production, dead stand crop production and the nutrients release through decomposition were estimated at each site. The decrease in water level due to sand bar opening affected negatively T. domingensis populations, but the most intense effects were observed in the middle of the stand. The shoot mortality was highly enhanced after the sand bar breaching and the nutrients were released through decomposition to the water column. It reflected on an input of 11.5 kg C m⁻², 0.22 kg N m⁻² and 0.13 kg P m⁻² into the lagoon, which represent from 22.5 to 44.8 ton P and 35.9 to 71.8 ton N to the lagoon. The decrease of nutrients concentration after the sand bar breaching was not successfully accomplished. The decay of T. domingensis stands due to the sand bar breaching neutralized the exportation of nutrients to the ocean, and contributed to the phosphorous increase in the water column. Thus, to a better management of aquatic ecosystems subjected to human eutrophication, the role of aquatic macrophytes decomposition on internal fertilization of aquatic ecosystems should be accounted.     

Phytoplankton Fluctuations during an Annual Cycle in the Coastal Lagoon of Cullera (Spain)

The seasonal variation and the vertical distribution of the phytoplanktonic population of the lagoon of Cullera, an elongated coastal lagoon with estuarine circulation of water, has been studied in three sampling stations: mouth, centre and source. Seasonal variation is determined by a marine-freshwater interaction. In winter, the sea influence is important, a marine water wedge of anoxic water arrives at the sampling station located at the source and marine and brackish water species dominate the phytoplankton. Also marine species of zooplankton and fish enter the system, which may then be considered as exploited by the sea. In spring the marine wedge retreats from the source but remains in the centre and mouth, salinity diminishes, vertical mixing persists and phytoplankton is dominated by Cyclotella species. From late spring to autumn the freshwater influence prevails and a sharp stratification of the water is produced in the stations at the mouth and the centre, by means of a steep halocline coincident with an oxycline. The phytoplankton in this period follows a typical succession like those described in freshwater eutrophic lakes. Vertical distribution of phytoplankton is determined by the presence of the oxycline, originated by the marine water wedge, whose depth varies seasonally but which is always present in the mouth and centre of the lagoon; only few species of algae can be found below its level.     

Water Quality Trends in a Coastal Lagoon Impacted by Non-point Source Pollution after Implementation of Protective Measures

Water quality data from two different monitoring periods are used to evaluate the trophic state and effectiveness of various protective measures on the restoration of a eutrophic, coastal Mediterranean lagoon. Main protective measures included elimination of municipal/industrial raw wastewater discharges in the rivers outflowing to the lagoon, sediment/erosion control practices in the lagoon’s drainage basin (i.e., construction of sediment/debris dams and grade control structures, reforestation and ban on livestock grazing), and reduction of fertilizer application quantities as a result of changes in crops. Water quality data include, among others, chlorophyll a, dissolved oxygen and nutrient concentrations, various physicochemical parameters, and transparency, measured during two monitoring periods, i.e., before (1983–84) and after (1998–99) implementation of protective measures. Rainfall depth for the two time periods was also available. Empirical equations were developed, from statistical analyses of the data, relating the water quality parameters during the two monitoring periods. These models help identify water quality trends. Based on the analyses, it seems that measures were effective in reducing sediments transported into the lagoon. However, the lagoon remains eutrophic to hypereutrophic, mostly due to phosphorus released in the water column from bottom sediments. Therefore, future restoration efforts should be directed towards the management of bottom sediments.     

Observations on Some Species of Chaetoceros (Bacillariophyceae) with Reduced Number of Setae from a Tropical Coastal Lagoon

Species of Chaetoceros with less than four setae per cell are not common. In this study, five different taxa presenting this characteristic were found in the Sontecomapan lagoon, Mexico, a small tropical coastal lagoon on the Gulf of Mexico:Chaetoceros minimus, C. subtilis var. abnormis f. abnormis, C. subtilis var. abnormis f. simplex, C. throndsenii var. throndsenia, and C. thondsenii var. trisetosa. Using an electron microscope to make observations of C. subtilis var. abnormis f. simplex made evident the absence of rimoportulae suggesting a close relationship to C. minimus. According to our observations, we believe that the reduction in the number of setae in Chaetoceros is related to solitary forms. The five species studied here are associated with quiet brackish-water enclosed environments and can be considered worldwide-distributed organisms.     

Degradation of Macromolecular Organic Compounds in a Tropical Lagoon (Ciénaga Grande,Colombia) and its Ecological Significance

Primary production and decomposition of organic substances were investigated in a tropical lagoon during the rainy season. Production and mineralization were measured using the oxygen method. Total bacteria numbers and biomasses were estimated with epifluorescence microscopy, and the enzymatic degradation capacity of model substrates was determined photometrically. These parameters were measured in the water and sediment of the lagoon itself and also in its effluents and incoming waters. The aim of the study was to determine the sites of highest microbial activity in the lagoon and to compare its activity with other coastal water bodies. Since the shallow water lagoon contains a large amount of particulate matter, it was of special interest to study the degradation of this material and its influence on the microbial population. It was found that up to 14 % of the bacteria colonized the particles and that 62 % of the respiration originated in the particle fraction >8 μm. Highest exoenzymatic activities were measured in the sediment and water of the mangrove belt. It is concluded that decomposition and conditioning of particulate organic matter play dominant roles in the recycling of organic carbon in the lagoon.     

The Relationship between Phytoplankton Diversity and Community Function in a Coastal Lagoon

The decrease of biodiversity related to the phenomena of global climate change is stimulating the scientific community towards a better understanding of the relationships between biodiversity and ecosystem functioning. In ecosystems where marked biodiversity changes occur at seasonal time scales, it is easier to relate them with ecosystem functioning. The objective of this work is to analyse the relationship between phytoplankton diversity and primary production in St. André coastal lagoon – SW Portugal. This lagoon is artificially opened to the sea every year in early spring, exhibiting a shift from a marine dominated to a low salinity ecosystem in winter. Data on salinity, temperature, nutrients, phytoplankton species composition, chlorophyll a (Chl a) concentration and primary production were analysed over a year. Modelling studies based on production-irradiance curves were also conducted. A total of 19 taxa were identified among diatoms, dinoflagellates and euglenophyceans, the less abundant group. Lowest diversities (Shannon–Wiener index) were observed just before the opening to the sea. Results show a negative correlation (p<0.05) between diversity and chlorophyll a (Chl a) concentration (0.2–40.3 mg Chl a m⁻³). Higher Chl a values corresponded to periods when the community was dominated by the dinoflagellate Prorocentrum minimum (>90% of cell abundance) and production was maximal (up to 234.8 mg C m⁻³ h⁻¹). Maximal photosynthetic rates (P_max) (2.0–22.5 mg C mg Chl a⁻¹ h⁻¹) were higher under lower Chl a concentrations. The results of this work suggest that decreases in diversity are associated with increases in biomass and production, whereas increases correspond to opposite trends. It is suggested that these trends, contrary to those observed in terrestrial and in some benthic ecosystems, may be a result of low habitat diversity in the water column and resulting competitive pressure. The occurrence of the highest photosynthetic rates when Chl a is low, under some of the highest diversities, suggests a more efficient use of irradiance under low biomass–high diversity conditions. Results suggest that this increased efficiency is not explained by potential reductions in nutrient limitation and intraspecific competition under lower biomasses and may be a result of niche complementarity.     

Carbon and Nitrogen Stocks and Burial Rates in Intertidal Vegetated Habitats of a Mesotidal Coastal Lagoon

Ecosystems - Coastal vegetated ecosystems such as saltmarshes and seagrasses are important sinks of organic carbon (OC) and total nitrogen (TN), with large global and local variability, driven by...     

Typhoon Disturbance and Stand-level Damage Patterns at a Subtropical Forest in Taiwan1

We examined the typhoon wind disturbance regime of the Fu-Shan Experimental Forest in northeastern Taiwan. Mean number of typhoons passing within 200 kilometers of Taipei (40 kilometers from the site) was 1.4 per year. Category 4 and 5 typhoons, which are intense enough to uproot large numbers of trees, occurred every 8.3 and 12.5 years respectively, although it is likely that some category 4 and 5 typhoons did not produce extensive blowdowns at Fu-Shan because the area of maximum winds missed the study site. Uprooting was more common than snapped boles; the most common damage to trees, however, was probably defoliation, although this damage was not quantified in the current study. Thirty-five percent of wind-damaged trees were associated with a gap. Six percent of the land area was in gaps. Canopy turnover time was calculated at 175 years when all gaps ≤ 9 years old were included in the calculation, but the time decreased when older gaps were excluded from the calculation. Turnover time was somewhat higher than calculated for other tropical forests. Because turnover time increases as the percent of land in gaps decreases, the short life span of gaps at Fu-Shan probably contributed to our higher calculated time. Probability of being damaged was not related to tree species identity, and only a few species of trees were found regenerating in gaps. Principal Components Analysis indicated that damaged trees varied largely in treefall orientation and aspect; gaps varied primarily in aspect and in gap size.     

Seasonal Variation of the Macrozoobenthic Community Structure at Low Salinities in a Mediterranean Lagoon (Monolimni Lagoon,Northern Aegean)

The macrozoobenthic community structure and dynamics at low salinities (0.3–6 psu) in a Mediterranean lagoon (Monolimni lagoon) were investigated. Samples were collected monthly from February 1998 to February 1999 at two sampling stations. Community structure was analyzed by means of uni‐ and multivariate methods. 21 taxa were collected; the amphipod Corophium orientale and the gastropod Ventrosia maritima dominated the assemblages. Total abundance peaked (50,000–60,000 individuals m^–2) in mid or late autumn. Community structure showed an almost even seasonal periodicity; seasonal changes were mainly derived from the intense variation in abundance of most species and the non–occurrence of a few ones (e.g. Corophium insidiosum, Polydora ciliata) in spring and summer. Non– occurrence, which led to a depression of the most diversity indices, was possibly the only direct impact of the extremely low salinities (~0.3 psu) on community structure. The main structuring factors of the community in the deeper outer part of the lagoon were water temperature and depth, and in the innermost part, where a Ruppia maritima meadow occurred, were water temperature and predation pressure by crabs (Carcinus aestuarii) and gobies (Knipowitchia caucasica). A temporary decline in total abundance in summer followed an increase in abundance of these predators. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spatiotemporal Variation in Shallow-Water Freshwater Fish Distribution and Abundance in a Large Subtropical Coastal Lagoon

Patos Lagoon is located off the southern Brazilian coast and represents one of the largest coastal lagoons in the world. We estimated hydrological and physicochemical conditions associated with spatial variation in the abundance and diversity of freshwater fishes along the lagoon, and inter-annual variability in abundances of freshwater fishes occurring in its estuarine zone. During our study, the region experienced two periods of average rainfall and two periods with above-average rainfall. The characids Astyanax eigenmaniorum and Oligosarcus jenynsii and the siluriform Parapimelodus nigribarbis were the most abundant freshwater fishes in the estuary during wet periods when water levels were higher and salinity was lower. Increases in abundance of these species in the estuarine area, all of which members of primary-division freshwater families, apparently were associated with pulses of reproduction and passive transport from freshwater habitats located near middle and upper lagoon reaches. Abundance of species from secondary freshwater families, such as poeciliids and cichlids, were less correlated with hydrological conditions, and their patterns of occurrence in the estuary suggest active migration from nearby freshwater habitats draining into this area. Findings indicate that freshwater discharge in the basin and expansion/retraction of freshwaters in the middle-upper lagoon determined patterns of freshwater fish abundance and species richness in the estuarine zone.     

Intra‐annual variation of the spatiotemporal distribution and abundance of Talitridae and Oniscidea (Crustacea,Peracarida) at Bizerte Lagoon (northern Tunisia)

During 1 year from spring 2007 to winter 2008, we conducted four seasonal samplings along a transect in the supralittoral zone of Bizerte Lagoon at Menzel Jmil (Tunisia) to study the intra‐annual variation of Peracarida diversity, Talitridae and Oniscidea. For each season, one transect was studied and quadrates were placed successively from the shoreline to the road backing the shore. Talitridae and Oniscidea were the most abundant taxa in our samples reaching highest densities in summer, when fourteen species were found. The minimum and maximum values of species richness of Talitridae were observed in winter (four species) and summer (eight species), respectively, while for Oniscidea, species richness ranged from one species in winter and five species in spring. Both Talitridae and Oniscidea exhibited intra‐annual variation in their spatial distribution; in that, they moved away from the shoreline in winter and were found near the waterline in the other seasons. ANOVA test shows a high significant correlation between both Talitridae with Suaeda maritima and Oniscidea with the plants S. maritima,Salicornia arabica and Obione portulacoides.     

Seasonal Patterns of Flowering and Fruiting in a Dry Tropical Forest in Jamaica1

Tropical dry forests occupy more area and are more endangered than rainforests, yet their regeneration ecology has received less study and is consequently poorly understood. We recorded the flowering and fruiting phenology of a tropical dry forest in Jamaica over a period of 26 mo within ten 15 × 15‐m plots. Community‐wide recruitment reached a maximum in the wet season, whereas no recruitment occurred during the dry season. We observed a unimodal peak in rainfall and fruit production, and the periodicity and intensity of seed production were significantly correlated with rainfall seasonality (the optimal time for germination). Flowering at the community and system levels lagged behind a significant increase and subsequent decrease in rainfall by 7 and 3 mo, respectively, indicating that the dominant factor controlling flowering periodicity is the passage of the major (4‐mo long) rainy season and changes in soil moisture conditions. Fruiting lagged behind flowering by 2 mo and a significant increase in fruiting occurred 2 mo prior to a significant increase in rainfall. At the population level, a correspondence analysis identified a major dichotomy in the patterns of flowering and fruiting between species and indicated two broad species groups based on their time of peak fruiting and the number of times they were in fruit. These were either individuals which were usually in peak fruit 1–2 mo prior to the start of the major rainy season or those that were in fruit more or less continuously throughout the year with no peak fruiting time. This study supports the view that seasonal variation in rainfall and hence soil water availability constitutes both the proximate and the ultimate cause of flowering periodicity in tropical dry forests.     

Habitats and Distribution Patterns of Marine Luminous Bacteria in the Western Baltic Sea

Numbers of luminous bacteria were counted at three stations of the brackish water ecosystem of the western Baltic Sea from July 1985 to July 1986. Additional samples were taken during three cruises from stations at the North Atlantic Ocean, the Norwegian Sea and adjacent marine areas. — In Kiel Bight (western Baltic) values varied between 0 and 68,000 luminous cfu 1⁻¹. With exception of the coastal station a distinct seasonal distribution pattern was shown in a water depth of 20 m: high numbers found in summer were opposed to low numbers in winter, the peaks being rather high in comparison to those of other areas. Statistical analysis showed that the results of 20 m were significantly different from those of 0 and 10 m depth; however, there was no correlation with temperature and salinity. Taxonomic studies revealed that the population consisted primarily of the genus Photobacterium. — The optimum of salinity was not a brackish but a marine one and was about 30% for the majority of the strains tested. A smaller number of strains grew best at a salinity between 10 and 15%. Optima of temperature ranged from 15 to 20 °C for most of the test strains. — Taxonomic analysis was also performed with luminous strains from marine areas adjacent to the western Baltic Sea, Photobacterium being the dominant genus here, too. Luminous bacteria were also enriched from the external surface and the gut contents of whitings (Merlangius merlangus) and cods (Gadus morhua). A model is proposed which explains the distribution pattern found. According to this, the gut-dwelling luminous bacteria are transported by their hosts from the North Sea into the western Baltic Sea. Here they are released into the environment, thus inhabiting another niche.     

Influence of Environmental Gradients on the Abundance and Distribution of Mycobacterium spp. in a Coastal Lagoon Estuary

Environmental mycobacteria are of increasing concern in terms of the diseases they cause in both humans and animals. Although they are considered to be ubiquitous in aquatic environments, few studies have examined their ecology, and no ecological studies of coastal marine systems have been conducted. This study uses indirect gradient analysis to illustrate the strong relationships that exists between coastal water quality and the abundance of Mycobacterium spp. within a U.S. mid-Atlantic embayment. Mycobacterium species abundance and water quality conditions (based on 16 physical and chemical variables) were examined simultaneously in monthly samples obtained at 18 Maryland and Virginia coastal bay stations from August 2005 to November 2006 (n = 212). A quantitative molecular assay for Mycobacterium spp. was evaluated and applied, allowing for rapid, direct enumeration. By using indirect gradient analysis (environmental principal-components analysis), a strong linkage between eutrophic conditions, characterized by low dissolved-oxygen levels and elevated nutrient concentrations, and mycobacteria was determined. More specifically, a strong nutrient response was noted, with all nitrogen components and turbidity measurements correlating positively with abundance (r values of >0.30; P values of <0.001), while dissolved oxygen showed a strong negative relationship (r = −0.38; P = 0.01). Logistic regression models developed using salinity, dissolved oxygen, and total nitrogen showed a high degree of concordance (83%). These results suggest that coastal restoration and management strategies designed to reduce eutrophication may also reduce total mycobacteria in coastal waters.Environmental mycobacteria, or nontuberculous mycobacteria (NTM), include all species of mycobacteria other than those in the Mycobacterium tuberculosis complex and M. leprae. In general, NTM are aerobic, acid-fast, gram-positive, non-spore-forming, nonmotile organisms found as free-living saprophytes in soil and water (12, 14, 20, 21, 35). However, several members of this group can cause serious disease in humans, including pulmonary infections, cervical lymphadenitis, ulcerative necrosis, skin infections, and disseminated infections associated primarily with autoimmune disorders (12, 29). For example, disseminated infection with the Mycobacterium avium complex can occur in up to 40% of late-stage AIDS patients in developed countries (43). NTM can also have costly and problematic effects on wild and domesticated animals (17, 23). Thus, understanding the sources and reservoirs of these bacteria has become a priority in recent years (12, 34).While the mode of infection has been poorly established for many cases involving NTM, water is commonly implicated as either a source or a vector (12, 43). NTM are considered to be ubiquitous in the environment and have been cultured globally from samples obtained from freshwaters and marine natural waters (12), swimming pools and hot tubs (11, 25), and drinking water supplies (12, 13), among others. However, only a limited number of attempts have been made to examine the association of their distribution and abundance with environmental parameters (1, 21, 24). The abundance of the M. avium complex was found to correlate positively with water temperature and levels of zinc and humic and fulvic acids and negatively with the dissolved-oxygen content and pH in brown-water swamps in the southeastern United States (24). In a study of Finnish brook waters, acidic conditions, along with the presence of peatlands, chemical oxygen demand, increased precipitation, water color, and concentrations of several metals, were found to favor total NTM (20, 21). However, recent efforts with samples from the Rio Grande River in the United States found positive correlations with the presence of coliforms and Escherichia coli counts and negative correlations with chemical toxicity and water temperature in this alkaline, oligotrophic system (1). Although system-specific differences may be apparent, no attempts to examine mycobacterial ecology in marine and estuarine systems have been reported to date.Historically, researchers have relied on culture-based techniques for detection and enumeration of mycobacteria from environmental samples (1, 20, 21, 43). Because of the slow growth of many mycobacteria, culture from environmental samples requires decontamination, which can severely impact both the quantity and diversity of species recovered (18, 19). Recently, quantitative PCR (qPCR) has gained favor as a means of rapidly enumerating organisms or genes in environmental samples (5, 15, 38, 40). This method allows for the continuous monitoring of the reaction through the use of fluorescent reporter molecules or DNA stains. Because of this strategy, the reaction can be evaluated at the peak of the exponential phase, reducing errors of reagent depletion and assay efficiency associated with end point reads. Quantification is based on the principle that the amount of the starting template is directly proportional to the number of cycles required to reach the peak of the exponential phase, and is evaluated through the preparation of standards.Like many coastal lagoon estuaries, the shallow embayments bordering the Maryland and Virginia seaboard are highly susceptible to anthropogenic influence, as they are visited by millions of people annually for vacation and water-related recreation (44). While eutrophication and degraded environmental conditions have been generally linked to factors or organisms which can ultimately influence human health, little attention has been given to the response of bacteria (16, 45). In this paper, we describe our efforts to examine environmental influences on the abundance and distribution of NTM in a dynamic estuarine system.     

中国沿海主要岛屿植物区系的性质及其相互关系与分布格局

通过植物区系谱、多样性指数、主坐标排序及聚类分析等方法,研究了中国沿海主要岛屿(从渤海、黄海、东海及南海海域,选取不同纬度所在地的岛屿)的植物区系性质、相互关系及分布格局,为沿海岛屿的生态保护和生物多样性保育提供依据。结果表明:(1)中国沿海主要岛屿植物区系地理成分表现出纬向分异性,温带成分比例随着纬度降低呈递减趋势,而各种热带成分比例呈递增的分布格局,这与不同海岛所处位置气候的纬向地带性基本一致;(2)不同沿海岛屿植物区系的Shannon指数(1.887~2.197)和Simpson指数(0.780~0.865)均无显著差异,而区系间Pearson相关系数(0.199~0.997)则有明显的差异;(3)通过聚类分析和主坐标排序生成的树状图和最小生成树,可将22个岛屿划分为5个集合,揭示了沿海岛屿植物区系属的类似性和南北纬度分布格局。     

Seasonal and areal features of the lagoonal environment in Lake Nakanoumi,a shallow coastal lagoon in Japan

Lake Nakanoumi is a shallow coastal lagoon connected with the Japan Sea by a narrow channel. Over the past decade, land reclamation resulted in a 33% reduction of the lagoon's surface area. The remaining water basin of Lake Nakanoumi is scheduled to be artificially freshened to supply irrigation water for the newly reclaimed lands. This paper deals with the seasonal and areal features of the lagoonal environment prior to the beginning of the artificial desalinization.     

Temporal Trends in Macrobenthos Community Structure and Redundancy in a Shallow Coastal Lagoon (Valli di Comacchio,Northern Adriatic Sea)

Temporal trends in macrobenthic communities of the Valli di Comacchio, the largest lagoonal ecosystem in the Po River deltaic area, were examined at four sampling sites located along a putative stress gradient and characterized by different levels of disturbance. Trends of parameters characterizing macrobenthic community structure were analyzed using data collected quarterly from 1996 to 2002. The positive slopes in trends of proportion of abundance of opportunistic species observed at all the four study sites indicated the persistence of stressful conditions. Conversely, temporal trends of species richness and diversity showed a positive slope at three out of four sites, thus indicating an increase of community structural complexity. It is suggested that the increase in abundance of detritivorous opportunistic species, as well as the increase in diversity and species richness, is probably driven by the frequency of physical disturbance that resets the ‘successional clock’ of the benthic communities of the Valli. Redundancy was assessed through multivariate analyses and a ‘forward selection backward elimination’ algorithm. At the ecosystem level (i.e., merging counts from the four sites), two response units (a response unit is the smallest subset of species for which the Spearman rank correlation with sample similarities for the full species set exceeds a predetermined value) were obtained. Each of the response units encompassed quite a large taxonomic and functional spread, since all guilds were well represented. Conversely, at the local level, only one response unit was obtained. Species number and function is essential to long-term maintenance of community and ecosystem processes over a complete cycle of common disturbance events. Since redundancy reflects the resistance to change of community functioning, we hypothesize that the macrobenthic communities of the Valli di Comacchio are quite resistant to environmental changes, despite disturbances that generate fluctuations in species abundance and complement at the local level.     

Effects of sand bar openings on some limnological variables in a hypertrophic tropical coastal lagoon of Brazil

This study describes the spatial and temporal dynamics of several physical, chemical and biological variables in the Grussai lagoon, and their relationship to ephemeral sand bar openings and to a constant in natura waste water input. The spatial variation in pH, dissolved oxygen, electrical conductivity, total alkalinity and nutrients (e.g. soluble reactive silicate, soluble reactive phosphate and ammonium) was associated to the anoxic and nutrient rich groundwater discharge, the development of aquatic macrophytes, the biological activities of phytoplanktonic community and the marine influence. During the period when the sand bar was closed (isolated), the lagoon water was supersaturated with dissolved oxygen and exhibited high values of pH (8–10), total alkalinity (3.000–5.000 μeq l^-1), and chlorophyll a contents (60-300 μg l^-1), and had low values of dissolved nutrients (nearly undetectable). These suggest a biological processes dominance. When the sand bar was opened, there was an enrichment with dissolved inorganic nutrients (e.g. ammonium and soluble reactive phosphorus up to 120 and 5 μM, respectively) and a decrease in pH (below 8), total alkalinity (below 3.000 μeq l^-1) and dissolved oxygen during the initial second to eight days. Subsequently there was a period when the physical and chemical characteristics of seawater prevailed. The lagoon returned chemical to the pre-opening water conditions in a few days (∼ 10–20). This quick return implies highly efficient biological mechanisms. The high levels of chlorophyll a, total nitrogen and phosphorus in the water column indicate a high eutrophication stage in the Grussai lagoon during the sand bar closed periods. This revised version was published online in July 2006 with corrections to the Cover Date.