Mira Estuary Research Articles

Fine-scale behaviour of the Lusitanian toadfish assessed in situ with the AccelTag

BackgroundThree-axis acceleration sensor acoustic transmitters (AccelTag) programmed to identify specific acceleration patterns associated with particular behaviours (e.g., burrowing, attack) were used to study some aspects of the ecology of the Lusitanian toadfish Halobatrachus didactylus (Bloch & Schneider 1801). The AccelTag combines the features of archival tags (records acceleration in all three directions measuring also roll-independent pitch/tilt angle and roll around the fish’s axis) and acoustic transmitters. Therefore, this tag can autonomously identify and record specific signatures (i.e., behaviour patterns) of different movements transmitting autonomously and periodically the data to an acoustic biotelemetry receiver. Lusitanian toadfish is a subtropical marine teleost confined to estuaries in its northern limit of distribution due to thermal constraints. During 2010 (August and October), 24 toadfish were captured, tagged with the AccelTag and released in the Mira estuary, SW coast of Portugal, where an array of underwater automatic acoustic biotelemetry receivers was deployed.ResultsAround 40% of AccelTag transmissions from tagged fish that stayed in the study area were logged by the acoustic receiver array. The Lusitanian toadfish exhibited low activity during late summer and early autumn (< 3% of time active). The tidal stage and time of day were important factors that influenced the species behaviour and activity. Increased burrowing and re-burrowing movements were registered during spring tides, while attacks prevailed on neap tides and during the night. The tidal cycle only influenced toadfish behaviour and activity in interaction with time of day, with more attacks and higher levels of activity during nocturnal high tides.ConclusionsHigher activity levels and attacks displayed by the Lusitanian toadfish during the night, at high tide periods and during Spring tides are considered to be associated with increased activity and vulnerability of its prey during these periods. The AccelTag proved to be a powerful tool to assess and monitor the activity and fine-scale behaviour of fish in situ. This technology is particularly suited for fish species with biological and ecological features similar to Lusitanian toadfish, i.e., resident species with low activity levels and behaviours with a distinct 3D acceleration signature.

Physico-Chemical Characterization of Two Portuguese Coastal Systems: Ria de Alvor and Mira Estuary

The present study aims to research the physico-chemical processes in two under-researched coastal systems located on the west and south Portuguese coast—Mira Estuary and Ria de Alvor—through the development and exploitation of dedicated coupled physical and water quality models. Both systems are highly dynamic, supporting a wide range of biological diversity; however, they are characterized by distinct environmental and oceanographic conditions, enhancing the importance of a comparative approach. In this context, the Delft3D modeling suite was implemented and successfully calibrated and validated for both systems, accurately reproducing their hydrodynamic, hydrographic, and chemical features. A broad characterization of Mira Estuary and Ria de Alvor was carried out. Results show that the tidal wave interacts differently with the different geomorphology of each estuary. The tidal wave amplitude decreases as it propagates upstream for both estuaries; however, the magnitude for Ria de Alvor is higher. A flood tidal dominance was found for Mira Estuary, allowing the transport of well-oxygenated water into the estuary, contributing to high residence times in the middle estuary and therefore to poor dissolved oxygen (DO) replenishment. Ria de Alvor shifts from ebb dominance at the central area to flood dominance upstream with low residence times, allowing an effective exchange of water properties. Results also reveal that the water temperature is the dominant driver of seasonal dissolved oxygen variations in both estuaries, with the lowest levels occurring during the late summer months when the water temperature is highest. In addition, pH is influenced by biological activity and freshwater inflow.

Baseline Survey on the Accumulation of Microdebris in the Intertidal Sediments of a Reference Estuarine System (Mira Estuary, Portugal)

Microdebris are nowadays a new emerging threat to marine ecosystems. Estuarine systems are considered sinks of contaminants, retaining these in their sediments. Nevertheless, baseline studies are essential, especially in reference estuarine systems such as the Mira Estuary, in order to establish reference conditions for other ecosystem assessment studies. Microdebris were extracted by density separation with saturated NaCl from sediment samples collected at the bare intertidal area of the lower sector of the Mira Estuary. Sediment vertical profiles showed a high abundance of microdebris, dominated by spherical and fibre-like microdebris, but also presenting metallic and uncategorized items. It was possible to observe that microdebris accumulation had its maximum concentration at a depth of 10 cm, indicating a recent increase in its usage and prevalence on this estuarine system. Comparing the item density from this work with previous studies on other aquatic ecosystems, it was found that the sediments analysed here present a very high concentration of microdebris. Although the Mira Estuary has been considered as a reference condition for the classical chemical contaminant descriptors considered in the Water Framework Directive, the data here presented indicate that this concept should be revisited adding microdebris contamination.

Structural and functional composition of fish communities associated to Zostera noltii meadows as a response to natural habitat recovery

Abstract During 2008, the Zostera noltii meadows located in the lower Mira estuary (SW Portugal) disappeared completely. However, during 2009, symptoms of natural recovery were observed, and in 2015 totally mature patches were detected. This allowed to investigate the temporal and spatial distribution patterns of the composition and structure of ichthyofaunal communities under two distinct habitat ecological conditions: before the collapse of mature vegetation of seagrass beds, in the 1980s (historical data), and after the natural habitat recovery process (new data). Significant differences were detected in the fish communities i) before and after the recovery process; and ii) in the seagrass beds and adjacent bare areas before the collapse, but no differences were observed after the natural recovery between seagrass fish communities and bare adjacent areas. Fish communities of seagrass beds in the 1980s were, in general, characterized by higher values of species richness, diversity and abundance. Apparently, the collapse of seagrass beds led to the disappearing of some fish species and to a decrease in abundance of others. Generally, such fish species have not returned to the system or recovered the population status during this early recovery process. This study addressed significant shifts that occurred in the lower Mira estuary fish communities in the last 30 years. Climate change may have influenced those alterations, although the event of the seagrass beds collapse seems to be the main driver of the community shifts.

Nematode biomass and morphometric attributes as descriptors during a major Zostera noltii collapse

Benthic nematodes are recognized as suitable organisms to provide valuable information on the potential ecological effects of natural and anthropogenic disturbances in aquatic ecosystems. The biomass and morphometric attributes of nematodes (body length, width, and length/width) collected in the Mira estuary (SW Portugal) were analysed before the collapse and during the natural recovery process of the Zostera noltii bed. In addition, their relationship with community characteristics and environmental variables was studied. Moreover, biomass and morphometric attributes were investigated for their potential use as a complementary tool to the classical descriptor “density” (from which several other descriptors are derived) when studying nematodes as biological indicators. Nematode biomass and morphometric attributes proved to be valuable as correlate with the environmental changes associated with the Z. noltii collapse. High values of nematode biomass, length, width, and length/width ratio were observed during the early recovery process of Z. noltii, contrasting with nematode densities, which showed consistently higher values before the collapse. These findings suggest that biomass and morphometric attributes indicate a functional adaptation of nematode communities to the new environmental conditions in the early recovery process of Z. noltii. Therefore, these traits may be used to provide complementary information to standing stocks of nematode assemblages so as to assess ecological changes over spatial and temporal scales in marine ecosystems, particularly within seagrass bed habitats.

An Update on the Invasion of Weakfish Cynoscion regalis (Bloch &amp; Schneider, 1801) (Actinopterygii: Sciaenidae) into Europe

New information on weakfish introduction vectors, its invasive status, distribution, and use as a fishing resource arose after the publication of “The transatlantic introduction of weakfish Cynoscion regalis (Bloch &amp; Schneider, 1801) (Sciaenidae, Pisces) into Europe” by Morais and Teodósio (2016). Currently, the first known report of weakfish in Europe dates back to September 2009, with a specimen captured in the Schelde estuary (Belgium/The Netherlands). This fact suggests that weakfish could have been introduced into Europe via multiple and independent ballast water introduction events, and not through a point-source introduction event with subsequent dispersion as previously hypothesized. It is also unlikely that Schelde weakfish migrated southwards to colonize Iberian aquatic ecosystems. Weakfish have established a population in the Gulf of Cádiz region and have already reached an invasive status in the Sado estuary (Portugal). Weakfish were also captured in several other locations along the Portuguese coast, including the Tagus and Mira estuaries at least since 2013 or 2014, and the Ria Formosa lagoon in 2017. Tagus anglers caught weakfish specimens of ~1 kg and ~40 cm in November 2016, which corresponds to fish of 3+ years of age in the native range. The presence of weakfish in the Tagus estuary is still fairly unknown to local anglers. Sado weakfish has already been sold in local fish markets in southern Portugal for 3 to 10 € kg−1. However, we consider that the weakfish sale price is underrated in comparison with other wild species (e.g., meagre, seabass, gilthead seabream). Increasing sale price will convince fishers to use weakfish as a new fishing resource; however, it is necessary to promote the species among consumers and evaluate consumers’ preference in respect to other species. A putative biological threat might turn into a new valuable fishing resource by implementing adequate management solutions.

Ecological aspects and potential impacts of the non-native hydromedusa Blackfordia virginica in a temperate estuary

The hydrozoan Blackfordia virginica has been reported over a wide geographical area, although it is mainly restricted to scattered records within estuarine areas of temperate and tropical regions. The aim of this study was to understand the spatial and temporal variability of an established population of this non-indigenous species on a temperate estuarine ecosystem, and its impacts over the plankton community. Sampling was conducted from 2011 to 2013 in the Mira estuary (Portugal) and higher densities were observed during the summer of 2013, with a maximum of 1689.3 medusae.m−3. Spatially, higher abundances of medusae were associated with sites of higher abundance of oyster shells and higher percentage of hard substrate in the river bed. Smaller jellyfish were sampled in the vicinity of these hard substrate locations, suggesting these might be habitats for polyp fixation. A higher potential predation impact on the copepod population along the estuary was estimated for the summer of 2013, with a median half life of 6.1 days.

Natural recovery of Zostera noltii seagrass beds and benthic nematode assemblage responses to physical disturbance caused by traditional harvesting activities

In the intertidal seagrass beds of Zostera noltii of Mira estuary (SW, Portugal) the harvesting practices are frequent. The traditional bivalve harvesting not only affects the target species as the remaining biological assemblages. The main aim of this study was to assess the disturbance caused by sediment digging in the recovery of the seagrass beds habitat, through an experimental fieldwork. The responses of the seagrass plant condition, the sediment microbial activity and the nematode assemblages were investigated after the digging activity in seagrass beds. A total of four experimental plots were randomly demarcated in situ, two plots were subjected to the disturbance - “Digging” - while other two were “Control”; the sampling occurred in five occasions, from May to October: T0–before digging; T1–14days after digging; T2–45days; T3–75days; and T4–175days. The environmental variables measured in the sediment and the photosynthetic efficiency (α) of the Z. noltii plants in each plot and sampling occasion registered similar values, throughout the experiment. The extracellular enzymatic activity (EEA) clearly presented a temporal pattern, although no significant differences were obtained between digging and control plots. Nematode assemblages registered high densities, revealing the absence of the digging effect: control plots maintained similar density and diversity throughout the experiment, while the density and diversity between digging plots was significantly different at T0 and T4; the trophic composition was similar for both control and digging plots, characterized mainly by non-selective deposit feeders (1B) and epigrowth feeders (2A).Organic matter, nitrate and mean grain size explain a significant amount of the variation in the nematode genera composition. This study demonstrated the capacity of the seagrass habitat to recover under low intensity physical disturbance associated to harvesting.

DNA Barcoding and Morphological Identification of Benthic Nematodes Assemblages of Estuarine Intertidal Sediments: Advances in Molecular Tools for Biodiversity Assessment

Concerns regarding the status of marine ecosystems have increased in part due to traditional and emerging human activities in marine waters, driving a demand for approaches with high sample throughput capability to improve ecosystem monitoring. Nematodes are already used as indicator species in biodiversity assessments and biomonitoring of terrestrial and marine systems, with molecular approaches offering the opportunity to utilize these organisms further in large scale ecological surveys and environmental assessments. Based on an available nematode dataset for estuarine sediments of the Mira estuary (SW coast, Portugal), we evaluated the diversity of the nematode community of this system, using the molecular markers 18S rRNA and COI genes. These approaches were compared to voucher specimens from a morphological characterization of the same samples allowing validation and comparison between nematode communities. The spatial and temporal variability of the density and diversity of the nematode assemblages was analyzed based on morphological characterization to allow the validation and efficiency of the genetic characterization. A PCO ordination plot showed a distinct separation of the assemblages between sampling occasions confirmed by PERMANOVA analysis, which showed significant differences, although no significant differences were detected between sampling sites. The morphological characterization identified 50 genera of which only 26 and 25 distinct 18S rRNA and COI DNA barcodes, respectively, were obtained. 90.2% of the morphologically identified specimens representing eleven different genera, successfully generated DNA barcodes for both 18S rRNA and COI genes. This study confirmed that the success of the 18S rRNA gene PCR amplification is higher than of COI gene with 43 species amplified against 34. The study highlights a limitation of available sequences for both targets in databases when compared to the known diversity of marine nematodes. The gene sequences of this study enriched the databases, contributing gene sequences from 7 and 16 new genera for the 18S rRNA and COI genes, respectively. A robust database of gene sequences is a prerequisite for the development of robust high sample throughput techniques to be applied in marine assessing and monitoring programs.

Bromine soil/sediment enrichment in tidal salt marshes as a potential indicator of climate changes driven by solar activity: New insights from W coast Portuguese estuaries.

This paper aims at providing insight about bromine (Br) cycle in four Portuguese estuaries: Minho, Lima (in the NW coast) and Sado, Mira (in the SW coast). The focus is on their tidal marsh environments, quite distinct with regard to key biophysicochemical attributes. Regardless of the primary bromide (Br-) common natural source, i.e., seawater, the NW marshes present relatively higher surface soil/sediment Br concentrations than the ones from SW coast. This happens in close connection with organic matter (OM) content, and is controlled by their main climatic contexts. Yet, the anthropogenic impact on Br concentrations cannot be discarded. Regarding [Br] spatial patterns across the marshes, the results show a general increase from tidal flat toward high marsh. Maxima [Br] occur in the upper driftline zone, at transition from highest low marsh to high marsh, recognized as a privileged setting for OM accumulation. Based on the discovery of OM ubiquitous bromination in marine and transitional environments, it is assumed that this Br occurs mainly as organobromine. Analysis of two dated sediment cores indicates that, despite having the same age (AD ~1300), the Caminha salt marsh (Minho estuary) evidences higher Br enrichment than the Casa Branca salt marsh (Mira estuary). This is related to a greater Br storage ability, which is linked to OM build-up and rate dynamics under different climate scenarios. Both cores evidence a fairly similar temporal Br enrichment pattern, and may be interpreted in light of the sun-climate coupling. Thereby, most of the well-known Grand Solar Minima during the Little Ice Age appear to have left an imprint on these marshes, supported by higher [Br] in soils/sediments. Besides climate changes driven by solar activity and impacting marsh Br biogeodynamics, those Br enrichment peaks might also reflect inputs of enhanced volcanic activity covarying with Grand Solar Minima.

Structural and Functional Composition of Benthic Nematode Assemblages During a Natural Recovery Process of Zostera noltii Seagrass Beds

In 2008, the stable seagrass beds of the Mira estuary (SW Portugal) disappeared completely; however, during 2009, they have begun to present early symptoms of natural recovery, characterised by a strongly heterogeneous distribution. This study was designed to investigate the spatial and temporal variability patterns of species composition, densities and trophic composition of the benthic nematode assemblages in this early recovery process, at two sampling sites with three stations each and at five sampling occasions. Because of the erratic and highly patchy seagrass recovery and the high environmental similarity of the two sampling sites, we expected within-site variability in nematode assemblages to exceed between-site variability. However, contrary to that expectation, whilst nematode genus composition was broadly similar between sites, nematode densities differed significantly between sites, and this between-site variability exceeded within-site variability. This may be linked to differences in the Zostera recovery patterns between both sites. In addition, no clear temporal patterns of nematode density, trophic composition and diversity were evident. Nematode assemblages generally resembled those of other estuarine muddy intertidal areas, which have a high tolerance of stress conditions.

Abundance, seasonal patterns and diet of the non-native jellyfish Blackfordia virginica in a Portuguese estuary

Blackfordia virginica, a non-indigenous hydrozoan introduced in many systems around the world, has been observed in the Mira estuary, southwest of Portugal, since 1984. Monthly sampling (January 2013–January 2014) at a fixed location with high abundance of the medusae confirmed the occurrence of a seasonal cycle associated with temperature and photoperiod. The beginning of the medusa cycle occurred in May immediately after the spring zooplankton bloom during April. Examination of the gut contents of B. virginica medusae revealed that copepods, the most abundant group in the zooplankton community, were highly predated. Barnacle nauplii, decapod crustacean larvae and anchovy eggs were also identified in the guts. The medusae showed positive selection for copepods, and negative selection for barnacle nauplii, decapod crustacean larvae and anchovy eggs. The mortality rate of copepods (used as a model prey group) induced by medusae predation was estimated and showed the potential impact of this species in the ecosystem, ranging between 2.34 d−1 and 0.02 d−1, with a minimum copepod half-life of 0.30 days.

A comparative analysis of benthic nematode assemblages from Zostera noltii beds before and after a major vegetation collapse

Benthic nematodes are widely regarded as very suitable organisms to monitor potential ecological effects of natural and anthropogenic disturbances in aquatic ecosystems. During 2008, the seagrass beds of Zostera noltii located in the Mira estuary (SW Portugal) disappeared completely. However, during 2009, slight symptoms of natural recovery were observed, a process which has since evolved intermittently. This study aims to investigate changes in patterns of nematode density, diversity, and trophic composition between two distinct habitat conditions: “before” the collapse of seagrass beds, and during the early recovery “after” the seagrass habitat loss, through the analysis of: i) temporal and spatial distribution patterns of nematode communities, and ii) the most important environmental variables influencing the nematode assemblages. The following hypotheses were tested: i) there would be differences in nematode assemblage density, biodiversity and trophic composition during both ecological conditions, “before” and “after”; and ii) there would be differences in nematode assemblage density, biodiversity and trophic composition at different sampling occasions during both ecological conditions. Nematode density and diversity were significantly different between the two ecological situations. A higher density was recorded before, but a higher diversity was evident after the collapse of Z. noltii. In spite of the disturbance caused by the seagrass habitat loss in the Mira estuary, the nematode trophic composition did not significantly differ between the before and after seagrass collapse situations. Despite the significant differences found among sampling occasions, a consistent temporal pattern was not evident. The response of nematode communities following this extreme event exhibited considerable resistance and resilience to the new environmental conditions.

Sequence variation in ostreid herpesvirus 1 microvar isolates detected in dying and asymptomatic Crassostrea angulata adults in the Iberian Peninsula: Insights into viral origin and spread

The Portuguese oyster Crassostrea angulata was the main oyster species produced in Europe until the 1970s when mass mortalities almost led to its disappearance. At that time, mortality events were associated with detection of irido-like viruses and no record of herpes-like virus exists. Nowadays, C. angulata is only present in relatively few locations in the Iberian Peninsula, unlike in Asia where production is widespread. In 2011 and 2013, we observed mortality outbreaks of C. angulata adults collected in the Ria Formosa (Portugal) with a cumulative mortality of 47 and 59%, respectively, a few days after the oysters were transferred to indoor conditions. Ostreid herpesvirus 1 (OsHV-1) DNA was detected by PCR in all dying oysters analyzed and a high viral load was observed by real time PCR. Sequence analysis of ORFs 4, 42, 43 and 88 as well as a non-coding region near ORF4 revealed that the OsHV-1 genotype was the microvar (μvar) variant. No nucleotide sequence variation was observed in the regions analyzed in any of the 18 isolates. However, polymorphism was observed in a non-coding region (NC1/NC2 region) located between ORFs 49 and 50. Two genotypes in the NC1/NC2 region differing by several nucleotides were identified during the 2 mortality outbreaks and each genotype was unique to each mortality event. In addition, a third genotype in the NC1/NC2 region of OsHV-1 μvar was observed in asymptomatic adults of C. angulata collected in Carrera River (Spain). OsHV-1 DNA was not detected by PCR in any of the oysters collected in Sado and Mira estuaries. The results obtained in the present study suggest that the NC1/NC2 region may be a highly polymorphic region and hence of particular interest for molecular epidemiological studies. In light of the results of the present and previous studies on the genetic diversity and detection of OsHV-1 in C. angulata, we hypothesize that the virus was introduced recently in Europe from Asia, possibly with the introduction of C. gigas in the 1970s or soon after.

Testing a 3-axis accelerometer acoustic transmitter (AccelTag) on the Lusitanian toadfish

A consortium composed of Thelma Biotel and Center of Oceanography developed and tested an acoustic 3-axis accelerometer transmitter. The first testing phase took place in experimental tanks and consisted of externally attaching prototype data logging tags in Lusitanian toadfish (Halobatrachus didactylus Bloch & Schneider, 1801) and comparing raw logged data with observed behaviours to obtain characteristic accelerometer data patterns that could be assigned to those typical movements. Four behavioural “signatures” were considered, two different burrowing movements, attack towards a prey and general activity. The second phase was the development of a prototype with integrated software capable of identifying those accelerometer typical patterns, process the information and transmit relevant data acoustically. Burrowing movements and activity were detected and transmitted with 100% accuracy while attacks were detected with a 61% successful rate. The third phase took place in the Mira estuary (SW Portugal) with 2 groups (five and six individuals each) of free living toadfish to test the codified acoustic signal transfer from the AccelTag to the acoustic receiver array. The novelty of the AccelTag is that is has the measuring capabilities of an accelerometer archival tag but without the necessity of recapture the tagged fish, since it has the ability of analysing the logged data, extract very detailed species dependent information and transmit the relevant processed data.

Reconstructing recent sea-level change in the Mira estuary, SW Portugal, using salt-marsh sediments

Reconstructing recent sea-level change in the Mira estuary, SW Portugal, using salt-marsh sediments

Environmental evolution of the Mira estuary (SW Portuguese coast) in the Late Quaternary

Environmental evolution of the Mira estuary (SW Portuguese coast) in the Late Quaternary

Vulnerability of Portuguese estuarine habitats to human impacts and relationship with structural and functional properties of the fish community

Estuaries are extremely productive ecosystems, providing habitat for numerous species and considered essential nurseries for many marine species. However, environmental changes caused by anthropogenic threats affect the quantity and quality of estuarine habitats. Habitat loss and degradation, conspicuous in estuaries worldwide, is considered a major threat to the function of estuaries. Information on threatening processes leading to habitat loss and degradation and on relative vulnerability of different habitats is imperative for conservation planning. The vulnerability of estuarine habitats (saltmarsh, mudflat and subtidal) from five Portuguese estuaries (Ria de Aveiro, Tejo, Sado, Mira and Guadiana) to the major anthropogenic threats affecting them was assessed through a threat ranking approach developed with basis on expert's judgment. Simultaneously, fish communities in these habitats (in two sites per estuary) were sampled seasonally in 2009, in order to relate habitat vulnerability and habitat use by fish communities. Experts ranked threats such as nutrient input, changes in river flow and land reclamation as having stronger impacts on estuarine habitats, making them more vulnerable to destruction or degradation. Averaging all threats, vulnerability scores were higher in mudflats, followed by subtidal and saltmarsh habitats. Overall, habitats in the Tejo and Sado estuaries were ranked as the most vulnerable and in the Mira estuary as the least vulnerable. Relationships between vulnerability values and fish community indicators in sampled habitat types and areas evidenced similarities between intertidal habitats (saltmarsh and intertidal mudflats), highlighting their priority in conservation and management contexts. The presented approach provides a useful tool as it allows prioritizing threat mitigation and identifies the most vulnerable habitats to potential degradation and destruction.

Benthic condition in low salinity areas of the Mira estuary (Portugal): Lessons learnt from freshwater and marine assessment tools

The assessment of the ecological integrity of aquatic ecosystems based on benthic macroinvertebrate communities has progressed in recent years, due to the implementation of water quality regulations worldwide, including the European Water Framework Directive (WFD). Several biotic indices have been developed in order to evaluate the ecological status of freshwater and marine ecosystems but the assessment of estuarine condition is much less developed because of its transitional characteristics. Some adaptations of marine indices have been proposed for estuarine areas, but very few include specific thresholds to be used in low salinity areas, where freshwater species can also be found. This study focused on the tidal freshwater and brackishwater sections of the Mira estuary, where salinities lower than 0.5 were registered at least during a certain period. Since no reference conditions are defined for benthic macroinvertebrate communities of Portuguese transitional waters, physicochemical variables recognized as indicative of human stress (organic and nutrient enrichment and oxygen levels) were used to classify the study area. Metrics commonly used to assess benthic condition in marine and freshwater systems were calculated and a modification of the AMBI and IBMWP indices was proposed. Two different ecotopes based on salinity were defined across the tidal freshwater–estuarine interface of the Mira estuary, a tidal freshwater and a brackish water ecotope. Only AMBI, IBMWP and the proposed modified versions of those indices responded predictably to human pressure indicative variables, but the ecological quality status classifications indicated that ecotope specific reference conditions need to be defined in order to improve the performance of those indices.

Modelling the effects of extreme events on the dynamics of the amphipod Corophium orientale

The brackish water amphipod Corophium orientale is the dominant macroinvertebrate species in the upper Mira estuary, a small mesotidal system located in the southwest coast of Portugal. As climate changes will increase the frequency and intensity of extreme events such as floods and droughts, these will have a negative effect on benthic estuarine invertebrates, namely C. orientale. In order to understand the effects of these events on C. orientale, a dynamic model, based on published information and calibrated with field data, was developed and different scenarios were tested. For model construction, the annual development of three cohorts of C. orientale, their growth rates, and the establishment of the timing of each cohort rise and extinction are introduced. This structure can be repeated indefinitely, for years, and few parameters are required. The model simulations highlight the need for refuge areas that enable a fast recovery of the amphipod population after an extreme event and the recolozination of the affected areas.