Dystrophic Crises Research Articles

Quantification of Major Inorganic Contaminants in a Mediterranean Coastal Lagoon with a Large Dystrophic Crisis.

In August 2021, the Mar Menor, a saltwater lagoon located in the Region of Murcia (Spain), suffered a tragic environmental episode of dystrophic crisis and anoxia. The appearance of numerous dead fish in different areas of the lagoon over the course of days put all the authorities and the population of the area on alert. This paper shows a case study of what happened in the lagoon in terms of the presence of the most common inorganic pollutants. Measurements of the concentration of nitrogen species, phosphates and main heavy metals were carried out at different sampling sites in the Mar Menor from May 2021 to November 2022. Chemical analyses were carried out for each of the species under study. These analyses provide valuable information about the dystrophic crisis caused by a classic eutrophication process that began with the excessive nutrient input into the Mar Menor. Ion chromatography and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) were used as instrumentation for the quantification of these samples. The species whose values were greatly increased after the tragic episode described above were nitrates. The concentration varied significantly at the different sampling sites throughout the study. On the last sampling date, decreased concentrations of all the species were measured at each of the sampling sites, coinciding with the apparent good state of the lagoon.

Shallow waters as critical habitats for fish assemblages under eutrophication-mediated events in a coastal lagoon

Eutrophication is a major driver of the degradation of transitional waters worldwide, especially in environments with a restricted connection to the sea, such as coastal lagoons. In recent decades, intensive agriculture and urban water inputs around the Mar Menor coastal lagoon (Western Mediterranean) have disturbed this originally oligotrophic aquatic system. The nutrient input into the lagoon has triggered its eutrophication, leading to dystrophic crises and mass mortality events for aquatic biota, transforming it into one of the most eutrophication-impacted transitional waters in the Mediterranean basin. In this study, we applied a fish-based indicator to assess the ecological quality of shallow waters under different eutrophication-mediated environmental stress scenarios (from pre-eutrophic reference periods to critical eutrophic periods), as well as to explore the role of confinement (i.e., water renewal time) and shoreline anthropogenic pressure as factors modulating the indicator response. Despite the high magnitude of the eutrophication impact on the lagoon, the ecological quality of the shallow waters decreased only slightly after the mass mortality events. The level of confinement also had slight effects on the ecological quality of the most confined shallow areas in the summer during eutrophic periods. Hence, shallow waters could play a critical role as refuge habitats, both for fish assemblages and other aquatic taxa, by buffering euxinic conditions during eutrophication processes.”. In fact, shallow waters could act as critical habitats, allowing for the recolonisation of aquatic biota from more impacted areas in the lagoon. This attribute further reinforces the need to properly manage and protect the shoreline areas of transitional waters, particularly under eutrophication scenarios.

Nutrient overload promotes the transition from top-down to bottom-up control and triggers dystrophic crises in a Mediterranean coastal lagoon

The excess input of nutrients that triggers eutrophication processes is one of the main destabilizing factors of coastal ecosystems, being coastal lagoons prone to suffer these effects and present dystrophic crises. This process is aggravated by the current trend of rising temperatures and more frequent torrential rains due to climate change. We observed that the Mar Menor lagoon had a great capacity for self-regulation of its trophic web and resistance to the eutrophication process, but after 30 years of nutrient input due to the change in the agricultural regime in its drainage basin in the 1990s, the lagoon ecosystem has suffered several of these events. In this work, we characterize the seasonal dynamic of the pelagic system during the last dystrophic crises. Phosphorus and nitrogen alternate as the limiting nutrient for phytoplankton proliferation. The entrance of phosphorus is mainly related to vacation periods, while nitrogen inputs, both superficial and sub-superficial, are more related to chronic high nitrates concentration in the water table after the agricultural activities carried out in the area changed. Our analysis reveals that the summer season is prone to suffer periodical hypoxia events when the N/P ratio decreases, and the temperature rises. In the Mar Menor, the ecological balance has been maintained in recent decades thanks to, among other mechanisms, the spatial and temporal segregation of top-down control over phytoplankton exerted by three species of jellyfish. However, the deep reduction in the abundance of the summer jellyfish species and the excessive proliferation of phytoplankton has meant the loss of this control. Moreover, we have registered a decline in the abundance of all the other zooplanktonic groups during the dystrophic crises. We suggest that management actions should address the input sources of water and nutrients, and an integrated management of the activities carried out throughout the watershed.

Effects of HABs and a dystrophic event on zooplankton community structure in a Mediterranean lagoon (W Greece)

This study reports on the spatiotemporal distributions of zooplankton assemblages during two harmful algal blooms (ΗΑΒs) and a dystrophic crisis in Papas lagoon (W Greece, E Mediterranean), a water body with a long history of eutrophication phenomena. The main focus is placed on the impact of toxic microalgae on the metazooplankton community structure under contrasting environmental conditions including an anoxic event. Towards this aim, we recorded environmental parameters and sampled different size components of plankton communities (microalgae, microzooplankton and mesozooplankton) over the course of a year, in order to assess the metazooplankton assemblages (using nMDS, PERMANOVA and CCA) within a more comprehensive framework, considering lower trophic levels. HABs had a detrimental impact on all key holoplankton and meroplankton taxa regardless of environmental conditions, while their co-occurrence with anoxia resulted in the collapse of zooplankton populations. Recovery of zooplankton abundances after the compounded effects of HABs and anoxia was significantly slower in relation to the sole impact of HABs. Concerning holoplankton, dominance of egg-spawning calanoid copepods (Acartia clausi, Paracartia latisetosa) prior to the compounded extreme events shifted to smaller egg-carrying harpacticoids (Euterpina acutifrons) and cyclopoids (Oithona nana) in the recovered assemblages while in meroplankton, bivalvia larvae were largely replaced by cirripedia nauplii. These results suggested that the cumulative effects of HABs and dystrophic crises may significantly alter the taxonomic composition and size-structure of metazooplankton communities with possible harmful consequences for ecosystem functioning and fish and shellfish recruitment.

Could a freshwater fish be at the root of dystrophic crises in a coastal lagoon?

Eutrophication has a profound impact on ecosystems worldwide. Grass carp Ctenopharyngodon idella, an herbivorous fish, has been introduced to control aquatic plant overgrowth caused by eutrophication, but could have other, potentially detrimental, effects. We used the Po di Volano basin (south of the Po River delta, northern Italy) as a test case to explore whether grass carp effects on canal aquatic vegetation could be at the root of historical changes in N loads exported from the basin to the Goro Lagoon. We modeled the aquatic vegetation production and standing crop, its denitrification potential, and its consumption by introduced grass carp. We then examined whether changes in historical nitrogen loads matched the modeled losses of the drainage network denitrification function or other changes in agricultural practices. Our results indicate that introduced grass carp could completely remove submerged vegetation in the Po di Volano canal network, which could – in turn – lead to substantial loss of the denitrification function of the system, causing in an increase in downstream nitrogen loads. A corresponding increase, matching both timing and magnitude, was detected in historical nitrogen loads to the Goro Lagoon, which were significantly different before and after the time of modeled collapse of the denitrification function. This increase was not clearly linked to watershed use or agricultural practices, which implies that the loss of the denitrification function through grass carp overgrazing could be a likely explanation of the increase in downstream nitrogen loads. Perhaps for the first time, we provide evidence that a freshwater fish introduction could have caused long-lasting changes in nutrient dynamics that are exported downstream to areas where the fish is not present.

Modelling the impact of dredging inlets on the salinity and temperature regimes in coastal lagoons

Coastal lagoons support intense human activity. Dredging or closing the inlets to regulate water exchanges in order to manage fisheries or improve navigation, prevent floods, reduce pollution or prevent dystrophic crises are among the most frequent management actions.Increased social concerns about the Mar Menor have arisen during the last decades due to the speed and magnitude of changes in its water conditions, including eutrophication and the siltation of some of the channels connecting it to the Mediterranean. In response, the idea of opening the inlets in order to increase water exchange and renovation in the lagoon has gradually convinced managers and the public as being a potential solution.However, changing the morphology of the inlets does not only involve reducing or diluting nutrients or pollutants or facilitate fish movements, but may also affect the physical-chemical parameters governing the ecosystem, as temperature, that regulates metabolic activity and physiological performance of individuals and hence the biogeographical limits in the distribution of species, or salinity that is considered the key factor that determines species composition in brackish waters.In this framework, using a 3D model, we analyse the effect of different scenarios of dredging (up to 1.5 m more than the present depth of the two shallower inlets) on the spatio-temporal patterns in salinity and temperature in the Mar Menor coastal lagoon. We also check the ability of a geomorphological index (the openness parameter) to predict the observed changes.The magnitude and spatial extent of the impacts are proportional to the magnitude of the dredging activities, but they also depend on the season of the year and on the location of the dredged channels in relation to the main circulatory paths. On average, the salinity ratio can decrease by up to 3.45% with respect to the undisturbed scenario in the most extensive dredging simulation and the yearly average temperature can increase by up to 8.24% in the case of simple maintenance activities. All scenarios show a trend towards a smoothing out of extreme values in environmental conditions and the loss of spatio-temporal heterogeneity at basin scale. Even the most moderate actions can be of biological relevance at a local scale, and may have consequences for the whole lagoon affecting the possibilities of colonization or reproduction by some species and the ecosystem homeostatic regulation capacity. The openness parameter is seen to act as a good indicator of potential impacts of geomorphological alterations of the channels on lagoon salinity and temperature. Coastal lagoons are complex biological systems, and this kind of measure has to be suitably assessed in terms of the induced gain or loss for the functioning of the entire ecosystem.

Long-Term Dynamic in Nutrients, Chlorophyll a, and Water Quality Parameters in a Coastal Lagoon During a Process of Eutrophication for Decades, a Sudden Break and a Relatively Rapid Recovery

Coastal lagoons are considered among the marine habitats with the highest biological productivity, and support a great variety of human activities and pressures that make them especially vulnerable to trophic imbalances. While dystrophic crises are common in many lagoons, others like the Mar Menor show homeostatic mechanisms, high resilience, and clear waters. This paper analyses the water column descriptors dynamic during the last 22 years in this coastal lagoon, in the context of a eutrophication process produced by an increase in nutrient inputs, mainly derived from agriculture. Despite water column nitrate concentration increased by one order of magnitude, the lagoon maintained homeostatic regulation for two decades, keeping the water transparency and relatively low levels of nutrients and chlorophyll a (Prebreak phase), followed by a sudden change of state in 2016 with an abrupt increase in average nutrients and chlorophyll a concentration and loss of water transparency (Break phase), and a relatively rapid recovery after the reduction of nutrient discharges (Recovery phase). The activation of the regulation mechanisms seems to manifest through an ammonium production in the water column, as a consequence of the activity in the trophic web. The low correlation between chlorophyll a and nutrients concentration, mainly at small spatio-temporal scales, is in disagreement with eutrophication traditional models, and suggests a rapid response of primary producers to nutrient inputs and a zooplankton control in the short-term, which in turn is controlled by the rest of the trophic web components. Homeostatic properties that in the Mar Menor lagoon have provided resistance to eutrophication are based on several mechanisms: channeling its production toward the benthic system (maintaining high biomasses of primary producers, filter feeders, and detritivores), a top-down control of the pelagic trophic web exerted by ichthyoplankton and jellyfish, and exporting surplus production outside the system. Resilience of the system would be based on the high turnover in the species composition related to the restricted connectivity to the sea, the spatio-temporal variability of the environmental conditions, and the multiplicity of spatial–temporal scales involved in lagoon processes. TRIX index was sensitive to the trophic and water quality changes. However, in our study, its current score does not allow to anticipate or alert the eutrophication risk and the trophic breakpoint of the system.

Diversity and abundance of sulfate-reducing microorganisms in a Mediterranean lagoonal complex (Amvrakikos Gulf, Ionian Sea) derived from dsrB gene

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 79:209-219 (2017) - DOI: https://doi.org/10.3354/ame01829 Diversity and abundance of sulfate-reducing microorganisms in a Mediterranean lagoonal complex (Amvrakikos Gulf, Ionian Sea) derived from dsrB gene Christina Pavloudi1,2,3,*, Anastasis Oulas1, Katerina Vasileiadou1, Georgios Kotoulas1, Marleen De Troch3, Michael W. Friedrich2, Christos Arvanitidis1 1Institute of Marine Biology, Biotechnology and Aquaculture, Hellenic Centre for Marine Research, PO Box 2214, 71003 Heraklion, Greece 2Microbial Ecophysiology Group, Faculty of Biology/Chemistry and MARUM, University of Bremen, 28359 Bremen, Germany 3Marine Biology Research Group, Department of Biology, Faculty of Sciences, University of Ghent, 9000 Ghent, Belgium *Corresponding author: cpavloud@hcmr.gr ABSTRACT: Sulfate-reducing microorganisms (SRMs) are a phylogenetically and physiologically diverse group of microorganisms, responsible for the dissimilatory reduction of sulfate. SRMs thrive under anaerobic conditions with high availability of organic matter. Such conditions characterize lagoonal ecosystems which experience regular dystrophic crises. The aim of the present study was to explore the biodiversity patterns of SRMs and to examine the extent to which these patterns are associated with biogeographic and environmental factors. Sediment samples were collected from 5 lagoons in the Amvrakikos Gulf (Ionian Sea, western Greece). DNA was extracted from the sediment and was further processed through pyrosequencing of a region of the dissimilatory sulfite reductase β-subunit (dsrB). The results of this exploratory study show that the majority of the observed operational taxonomic units (OTUs) belong to the Deltaproteobacteria supercluster and more specifically, to the Desulfobacteraceae family. Salinity and ammonium ions are the environmental factors that best correlated with the SRM community pattern. Furthermore, the SRM community of the brackish lagoons is differentiated from that of the brackish-marine lagoons and the studied lagoons have distinct SRM communities. KEY WORDS: dsrB gene · Amvrakikos Gulf · Lagoon · Pyrosequencing · Sediment · Sulfate-reducing microorganisms Full text in pdf format Supplement 1 Supplement 2 Supplement 3 PreviousNextCite this article as: Pavloudi C, Oulas A, Vasileiadou K, Kotoulas G, De Troch M, Friedrich MW, Arvanitidis C (2017) Diversity and abundance of sulfate-reducing microorganisms in a Mediterranean lagoonal complex (Amvrakikos Gulf, Ionian Sea) derived from dsrB gene. Aquat Microb Ecol 79:209-219. https://doi.org/10.3354/ame01829 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 79, No. 3. Online publication date: June 12, 2017 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2017 Inter-Research.

Spatiotemporal dynamics of submerged macrophyte status and watershed exploitation in a Mediterranean coastal lagoon: Understanding critical factors in ecosystem degradation and restoration

Increases in the intensity of disturbances in coastal lagoons can lead to shifts in vegetation from aquatic angiosperms to macroalgal or phytoplankton communities. Such abrupt and discontinuous responses are facilitated by instability in the equilibrium controlling the trajectory of the community response. We hypothesized that the shift in macrophyte populations is reversible, and that this reversibility is dependent on changes in the pressures exerted on the watershed and lagoon functioning. Biguglia lagoon (Mediterranean Sea, Corsica) is an interesting case study for the evaluation of long-term coastal lagoon ecosystem functioning and the trajectory of submerged macrophyte responses to disturbances, to facilitate the appropriate restoration of ecosystems. We used historical data for a two hundred-year period to assess changes in human activities on the watershed of the Biguglia lagoon. Macrophyte mapping (from 1970) and monitoring data for dynamics (from 1999) were used to investigate the trajectory of the community response. The changes observed in this watershed included a large number of hydrological developments affecting salinity and resulting in changes in macrophyte distribution. Nutrient inputs over the last 40 years have led to a shift in the aquatic vegetation from predominantly aquatic angiosperm community to macroalgae and phytoplankton in 2007 (dystrophic crisis). Changes in hydrological management and improvements in sewage treatment after 2007 led to a significant increase of aquatic angiosperms over a relatively short period of time (4–5 years), particularly for Ruppia cirrhosa and Stuckenia pectinata. There has been a significant resurgence of Najas marina, due to changes in salinity. The observed community shift suggests that Biguglia lagoon is resilient and that the transition may be reversible. The restored communities closely resemble those present before disturbance. These findings demonstrate the need to understand watershed exploitation and ecosystem variability in lagoon restoration.

Water flux management and phytoplankton communities in a Mediterranean coastal lagoon. Part I: How to promote dinoflagellate dominance?

The Biguglia lagoon is a shallow Mediterranean coastal ecosystem where eutrophication is increasing for years. A channel supplying freshwater was cleared in 2009 to enhance lagoon water circulation and alleviate dystrophic crises. Monthly monitoring was started in 2010 to document the impacts of this action on abiotic characteristics and phytoplankton communities. Three stations were surveyed (by microscopy and HPLC). Evidence suggests that this operation had an unexpected outcome. Salinity footprints indicated the succession of three main hydrological sequences that depended on rainfall and circulation pattern. Diatoms and dinoflagellates dominated the first sequence, characterized by heavy rainfall, while Prorocentrum minimum became progressively the dominant species in the second period (increasing salinities) with extensive bloom over the whole lagoon (5.93×10-5cells·L−1) during the third period. These phytoplankton successions and community structures underline the risk of pernicious effects arising from remediation efforts, in the present case based on increasing freshwater inputs.

Dystrophic crisis event in Papas Lagoon, Araxos Cape, Western Greece in the summer 2012

A dystrophic crisis occurred in late June 2012 in the Lagoon of Papas, Araxos region, Western Greece (Ionian Sea) resulting in massive mortalities of aquatic organisms. The whole event was monitored through the basic aquatic physicochemical parameters (temperature, salinity, dissolved oxygen and pH) recorded before, during and after its occurrence. Although the phenomenon was manifested locally, it resulted in complete anoxia at the largest part of the lagoon which lasted ten days. Water quality of the entire lagoon was greatly affected by the dystrophic event and first signs of recovery were observed four months later.

Tracking Mid- to Late Holocene depositional environments by applying sedimentological, palaeontological and geochemical proxies, Amvrakikos coastal lagoon sediments, Western Greece, Mediterranean Sea

This study presents sedimentological, palaeontological, geochemical, mineralogical, and organic petrography data from a 30 m deep core representing a Mid- to Late Holocene lagoonal depositional environment, of a coastal area of Amvrakikos Gulf, Western Greece. Three horizons were dated using 14C. The sedimentological, palaeontological and geochemical interpretations of the lagoonal sediments reveal three major lithological units deposited between around 5200 and 1600 BP. The upper lithological unit extended to a depth of 11.20 m, the middle from 11.20 to 21.30 m, and the lower one from 21.30 to 30.00 m. A mean rate of sedimentation of 5.7 mm/y and a maximum rate of 12.6 mm/y were estimated. The mineralogical analysis and the magnetic susceptibility of the core points to a constant sediment – source supply. The Mid- to Late Holocene depositional environment mainly reflects inundation by the braid plain of the Arachthos and secondarily by the Louros River. The reconstruction of the depositional environments corresponds to a shallow marine and deltaic brackish lagoon and specifically to an environment proximal to river supply. The high rates of sedimentation, as well as the interpretation of depositional environments, indicate that the coastal sedimentological processes during the Mid- to Late Holocene were mainly controlled by the progradation of river deltas. Moreover, the geochemical proxies, the recovered molluscs and the microfauna, as well as the organic petrography analyses indicate periods of dysoxic and hypoxic conditions. These Holocene dysoxic and hypoxic events indicate that the recent dystrophic crises in the Amvrakikos Gulf are not only the result of human activities but also the contribution of natural processes.

Resistance and resilience of ecosystem descriptors and properties to dystrophic events: a study case in a Mediterranean lagoon

Mediterranean lagoons are naturally exposed, during the dry season, to dystrophic and hypoxic events determining dis-equilibrium conditions along temporal and spatial scales, which are linked to metabolism and life cycle of the biotic components. 2 - In summer 2008, Lesina lagoon (SE Italian coastline) was interested by a geographically localized dystrophic crisis which affected up to 8% of the total lagoon surface. 3 - Temporal dynamics of principal descriptors of abiotic (water, sediment) and biotic (phytoplankton, benthic macroinvertebrate) compartments have been followed during the 2008 by collecting data inside stressed and control lagoon areas before a dystrophic event and in the six months after the dystrophic event. 4 - The aim of the study was to analyse the pathways of ecosystem responses to dystrophic stress, searching for the characteristic scales of ecosystem compartment resistance and resilience. 5 - The characteristic time-scale of abiotic and biotic component time responses varied from days, for the selected markers of the water column, to year, for the benthic ones. Short-term biotic and abiotic responses in the water column were strongly coupled while biotic and abiotic responses at the sediment level were remarkably un-coupled. Dynamics and recovery time of water column and benthic components do not match in Lesina following the dystrophic crisis, highlighting an intrinsic individualistic behavior within the lagoon community driving ecosystem processes and ecosystem level responses. 6 - Taxonomic and non-taxonomic descriptors of both phytoplankton and benthic macroinvertebrates showed different response patterns as early warning signals and overall resilience. The emphasized differences in the stability components, i.e., resistance and resilience, of water column and sediment abiotic and biotic characteristics as well as of taxonomic and non-taxonomic descriptors has key implication in planning monitoring strategies and programs for transitional waters in the Mediterranean and Black Sea EcoRegions.

The importance of habitat-type for defining the reference conditions and the ecological quality status based on benthic invertebrates: The Ria Formosa coastal lagoon (Southern Portugal) case study

Coastal lagoons are complex systems, with considerable habitat heterogeneity and often subject to high temporal dynamics, which constitutes a great challenge for ecological assessment programs. For defining reference conditions for benthic invertebrates, under the EU Water Framework Directive objectives, historical data from the Ria Formosa leaky lagoon (wet surface area of about 105km2) located in Southern Portugal was used. The influence of habitat features, such as channel depth, sediment type and seagrass cover, on the expression of these biological communities, was inferred by analyzing subtidal data collected at stations with different environmental characteristics. Such heterogeneity effect was analyzed at the community compositional and structural levels, and also for three indices in the multimetric Benthic Assessment Tool (BAT). This tool for the assessment of ecological status includes the Margalef index, Shannon–Wiener diversity index, and AZTI's Marine Biotic Index (AMBI). Significant variations associated with environmental features were reflected on specific reference conditions at four habitats in the lagoon. After habitat calibration, the Benthic Assessment Tool (BAT) revealed that, in general and for the period of time covered by this historical data set, the status of the lagoon corresponded to a good ecological condition, which is mainly due to its high water renewal rate. Such classification is in accordance with the majority of studies at the lagoon. However, at punctual sites with human induced high water residence times, significantly lower BAT values were registered. Such community degradation can be associated with physical stress due to salinity increase and to a degradation of water quality, with occurrence of occasional dystrophic crisis, triggered by low water renewal. Habitat differentiation was a crucial step for a correct evaluation of the ecological condition of invertebrate communities across the lagoonal system.

Trophic status of earthen ponds used for semi-intensive shrimp ( Litopenaeus stylirostris, Stimpson, 1874) farming in New Caledonia (Pacific Ocean)

We have investigated temporal variability in the quantity and biochemical composition of sediment organic matter along with variables proxies of water eutrophication (e.g., inorganic nutrient and chlorophyll-a) at two shrimp farms located in the Southern coast of New Caledonia and characterised by clear differences in shrimp feeding practices and levels of initial trophic conditions. The results of our study reveal that the trophic status of the water column increased during the rearing cycle at both sites, determining a general, though moderated, eutrophication. However, the water column trophic descriptors did not allow to discriminate differences in the trophic status among the investigated sites or between sites in the same farming plant, even if they were subjected to different feeding practices and largely different initial characteristics of the sediment. Temporal variations in biopolymeric C and phytopigment sedimentary contents (used as proxies of benthic eutrophication) varied inconsistently among sites. The multivariate analyses did not identify significant temporal patterns in the benthic trophic status, but allowed discriminating the four investigated sites. The semi-intensive shrimp farming significantly contributed to changing the water column and sediments trophic status of the earthen ponds, but the extent of those changes was not consistently observed in all ponds. In any of the investigated ponds the trophic status exceeded concerning thresholds over which hypoxia or anoxia could occur. We conclude that the established semi-intensive practices adopted so far for shrimp farming activities in the earthen ponds of New Caledonia are able to maintain the status of the ponds below the eutrophication levels over which dystrophic crises could sharply abate most of the reared biomass.

Long-term changes in North Adriatic soft-bottom polychaete assemblages following a dystrophic crisis

In the Northern Adriatic Sea, the combination of natural and anthropogenic processes causes periodic hypoxia and anoxia, which can cause mass mortality of benthic organisms. Here, we report the results of a 20-year monitoring programme carried out after an anoxic event in 1989 that caused benthic mass mortality over an area of about 1200 km2. The recovery dynamics of the polychaete fauna was followed at three stations (including one sampled a year before the anoxic event). Samples (0.1 m2 Van Veen grab, 2-mm sieve) were collected from 1989 to 1994 and from 2003 to 2008. A total of 6519 specimens belonging to 186 species were identified. The analyses of univariate biodiversity indexes highlighted higher temporal variation of assemblage diversity in the period following the dystrophic crisis, followed by higher stability in the next decade. PERMANOVA suggested that the highest component of assemblage variation belonged to the factor year. However, differences across years varied in magnitude, depending on stations and were portrayed by non-metric multidimensional scaling plots of each year's centroids for each of the three stations. SIMPER analysis identified the species most characterizing the assemblages in each year for each of the three stations. Our results highlight the importance of analysing long-term data sets in order to understand assemblage dynamics following strong disturbance events. Assuming the 1989 anoxia as the event determining the biodiversity change, and considering our outcomes, which suggest that the assemblages still show a pattern of non-random changes through years, our data indicate that the polychaete fauna is still recovering without having reached a pattern of among-years stability. Focusing on the biology of the species characterizing the different periods might help in understanding the ecological processes that have determined the observed pattern.

Macrobenthic community structure in a Brazilian chocked lagoon system under environmental stress

Saquarema-Jaconé lagoonal system (SJLS) comprises a sequence of five interconnected shallow brackish lagoons with access to the sea by a single permanent tidal channel. It is a eutrophic system, receiving constant input of organic load from its urbanized catchments. The relationship between several environmental variables and the spatial-temporal distribution of the benthic macrofauna was assessed during four seasonal samplings (dry and wet periods of 2007-2009). Sediment replicates were sampled at seven sites for biological identification and analyzes of organic matter, carbonates, phytopigments, grain size and heavy metals. Salinity, dissolved oxygen and redox potential were measured in situ. SJLS was characterized by sandy bottoms with very reducing conditions. Redox potential significantly discriminated between the dry and wet periods and anoxic conditions were observed in the latter. No significant seasonal differences were observed in the macrofauna. A total of 37 taxa were identified, of which Capitella sp, oligochaetes and Laeonereis culveri (Webster, 1880) were the dominant, representing the early stage of community recovery following dystrophic crises. The faunistic pattern seems to be determined by complex combinations of silt+clay with salinity, organic matter and redox potential. On the other hand, the low concentrations of heavy metals found did not seem to influence the structure and distribution of the biota. SJLS is undergoing persistent environmental stress, dominated by first-order opportunistic species linked to organically enriched sediments.

Seasonal steady-state budgets of nutrients and stoichiometric calculations in an Eastern Mediterranean lagoon (Papas Lagoon-Greece)

The Papas Lagoon is an enclosed, small shallow water body in western Greece. The lagoon is naturally affected by eutrophication phenomena, but occasionally during the summer season, dystrophic crises occur, related to the decomposition of large beds of macroalgae. Physicochemical data collected monthly, from June 1998 to September 1999, were compiled and coupled with historical meteorological data, in order to construct seasonal water, salt and nutrients budgets using a single box single layer LOICZ model. Nutrients and other hydrochemical parameters exhibit great spatial and temporal variations. The non-conservative dissolved inorganic phosphorus flux (ΔDIP) is always positive, thus indicating that the system acts as a net source of DIP for the adjacent coastal waters. Higher values were estimated uring summer and autumn, probably due to organic matter mineralisation and release of DIP from surficial sediments in the reduced environment. In contrast to the ΔDIP, the non-conservative balance of dissolved inorganic nitrogen (ΔDIN) is negative for most of the year, except for the summer, indicating the dominance of DIN removal processes in the Papas Lagoon. The Ulva growth and decomposition processes seem likely to be of essential importance for the evaluation of the non-conservative DIN fluxes. During the investigated period the amount of organic carbon respired and mineralized is greater than that produced by gross photosynthesis and the Papas Lagoon is a net heterotrophic system. Losses of DIN via denitrification appear to dominate over its inputs through nitrogen fixation throughout the year.

Renewal time in a population of Abra segmentum (Mollusca, Bivalvia): a case of marked r strategy

Abra segmentum is a common and frequently abundant species in the Mediterranean coastal lagoons, playing a dominant role, both in numbers and biomass, in the infauna of these habitats and is an important food for a variety of species. The main objective of this work is to describe the renewal time of Abra segmentum in Lesina lagoon. The insurgence of hydrogen sulphide which exterminated the benthic macrofauna in an area of Lesina lagoon during July 2008 allowed us to accurately observe the re-colonization time of this bivalve. In order to achieve this aim, the population structure and spatial distribution of A. segmentum before and after the dystrophic crisis were investigated in the entire Lesina lagoon and, in detail, in the area affected by the crisis. 51 sampling units were collected in Lesina lagoon in May and October 2008, allowing to compare the situation before and after the dystrophic crisis. The length-frequency distribution showed the existence of two size groups in both May and October 2008. The individuals were counted, their individual length measured and their total wet biomass weighed. The total number of individuals decreased after the crisis in the entire lagoon, but this drop was strongly observed in the perturbed area. The length-frequency distribution showed the existence of two size groups in both May and October 2008. After dystrophic crisis, the two size groups were clearly separated and juveniles group (2-5 mm) was located in the area interested by dystrophic event. The results obtained in this study highlight the rapidity of re-colonisation of A. segmentum after the strong disturbance caused by the insurgence of dystrophic crisis. The dynamics of the population was particularly clear when considering the area affected by the dystrophic crisis. In May the population was structured as in the rest of the lagoon, but in October there was a marked difference. The insurgence of a dystrophic crisis in Lesina lagoon allowed to clearly observe the resilience of A. segmentum to environmental stress, confirming it as an r strategy species.

Spatial and temporal description of the dystrophic crisis in Lesina lagoon during summer 2008

Lagoons are vulnerable ecosystems often exposed to eutrophication due to anthropogenic activities. They are characterized by high vulnerability to climatic factors and biogeochemical impairment that, in some cases, can lead to dystrophic crisis. Here we analyze the short term temporal pattern of climatic, physical and chemical parameters during a dystrophic crisis occurred in Lesina lagoon in Summer 2008, focusing on the interactive effect of their variations. To this aim, we integrated meteorological data, satellite image analysis and local physical and chemical measurements in order to have a more detailed sight of processes that can give raise to a dystrophic crisis and to describe how the crisis evolves. Results show that an unusual change in main wind direction, sun radiation, and other meteorological parameters with respect to the previous years together with a temporal closing of tidal channel that assure the seawater inflow led to an hydrologic isolation of the western basin of Lesina lagoon occurred in summer 2008. The consequent unbalance in biogeochemical cycles produced a dystrophic crisis and a shift, in this area, from a macrophytes based system toward a phytoplankton based system. Since changes in climatic factors or in hydrologic regimes into the eutrophic lagoon probably already happened previously in different moments without giving rise to dystrophic event, the crisis was likely triggered by the co-occurrence of both factor variations. It is essential to understand the mechanistic linkages in space and time between man-made alterations of hydrologic and nutrient load regimes (that can be managed or controlled) and unpredictable climatic factors in the context of the individual ecosystem for managing transitional water ecosystems incurring in nutrient enrichment.