Modelação lagrangeana dos processos de transporte na Ria Formosa

Apresenta-se um modelo de advecção-difusão do tipo Lagrangeano para a simulação da dispersão de massas de água provenientes de fontes pontuais e descreve-se o modelo hidrodinâmico usado na simulação do escoamento. Estes modelos são utilizados para a caracterização hidrodinâmica da Ria Formosa do ponto de vista da qualidade da água. Tentam-se encontrar razões para os problemas associados aos viveiros de bivalves, sugerindo-se formas de melhorar a qualidade da água.

Influência da superfície sedimentar na dinâmica das macroalgas verdes e da sua macroepifauna associada na Ria Formosa

O sistema lagunar, conhecido vulgarmente por Ria Formosa, desenvolve-se na costa meridional Portuguesa, desde o Ancão a ocidente até Cacela a oriente. Com extensão, de aproximadamente 55 km, apresenta a sua maior largura, de 6 km, no sector Norte-Sul entre Faro e o Cabo de Santa Maria. Este sistema é um conjunto de ilhas-barreira que proteje a zona lagunar adjacente à plataforma litoral algarvia, da invasão marinha. A área total do Parque Natural da Ria Formosa é aproximadamente de 163 km2, sendo 48 km2 cobertos por sapal e 32 km2 ocupados por canais, esteiros e baixios (Teixeira & Alvim, 1978). Durante as marés vivas, as áreas intertidais expostas são de aproximadamente 50 km2. Estas áreas são predominantemente cobertas por plantas de sapal (Spartina maritima), angiospérmicas marinhas (Zostera e Cymodocea) e mantos de macroalgas (Entermorpha, Ulva e Fucus). 20 km2 do sistema são ocupados por salinas e aquaculturas (CCRA, 1984).

Hydroinformatics based decision.making integrating modelling, sampling and profiling: the Ria Formosa case

A Waste Water monitoring program aiming to help decision making is presented. The program includes traditional and inboard sensor sampling, hydrodynamic and water quality modeling and a GIS based database to help the decision making of manager authorities. The focus is in the quality of waters receiving discharges from Waste Water Treatment Plants. Data was used to feed model simulations and produce hydrodynamic, effluent dispersion and ecological results. The system was then used to run different scenarios of discharge flow, concentration and location. The results enable to access the current water quality state of the lagoon and are being used as a decision making tool by the waste water managers in the evaluation phase of the treatment plant project to decide the location and the level of treatment of the discharge.

Qualidade da água na Ria Formosa: combinando técnicas de amostragem e de modelação para uma gestão integrada das águas residuais

Aplica-se uma técnica combinada de amostragem clássica, perfilagem in situ com sonda multiparamétrica e modelação matemática para avaliar a qualidade da água da Ria Formosa como meio receptor dos efluentes das ETAR’s. O sistema de modelação desenvolvido baseia-se num modelo hidrodinâmico que resolve as equações de águas pouco profundas pelo método dos volumes finitos acoplado a um modelo de transporte Lagrangiano para a simulação das plumas microbiológicas. Este sistema é usado como ferramenta de gestão para ensaiar diferentes cenários de descarga com variação da localização do ponto de descarga, analisando o impacto das alternativas no meio receptor.

Seasonal variations in gross biochemical composition, percent edibility, and condition index of the clam Ruditapes Decussatus cultivated in the Ria Formosa (South Portugal)

The grooved carpet shell clam, Ruditapes decussatus (L. 1758), is one of the most popular and profitable molluscs exploited in rearing plots in the Mediterranean. However, annual catch has been declining steadily since the early nineties. In order to understand the seasonality of its nutritional value, thus providing an improved basis for economical valuation of the resource, gross biochemical composition, percentage edibility and condition index were investigated during a year with monthly periodicity in a commercially exploited population of the clam Ruditapes decussatus in the Ria Formosa, a temperate mesotidal coastal lagoon located in the south of Portugal. Our results show that total and non-protein nitrogen co-varied during the year, resulting in a protein content that peaked in the warmest months. Although complementary in summer, carbohydrate and lipid contents showed irregular annual trends. The observed seasonality was comparable to that shown by studies elsewhere at similar latitudes, and are underpinned by the reproductive cycle of the species. Our results show the clams to be at their prime nutritional value at the beginning of summer, when protein content peaks.

Assessing land–ocean connectivity via submarine groundwater discharge (SGD) in the Ria Formosa Lagoon (Portugal): combining radon measurements and stable isotope hydrology

Natural radioactive tracer-based assessments of basin-scale submarine groundwater discharge (SGD) are well developed. However, SGD takes place in different modes and the flow and discharge mechanisms involved occur over a wide range of spatial and temporal scales. Quantifying SGD while discriminating its source functions therefore remains a major challenge. However, correctly identifying both the fluid source and composition is critical. When multiple sources of the tracer of interest are present, failure to adequately discriminate between them leads to inaccurate attribution and the resulting uncertainties will affect the reliability of SGD solute loading estimates. This lack of reliability then extends to the closure of local biogeochemical budgets, confusing measures aiming to mitigate pollution. Here, we report a multi-tracer study to identify the sources of SGD, distinguish its component parts and elucidate the mechanisms of their dispersion throughout the Ria Formosa – a seasonally hypersaline lagoon in Portugal. We combine radon budgets that determine the total SGD (meteoric + recirculated seawater) in the system with stable isotopes in water (δ2H, δ18O), to specifically identify SGD source functions and characterize active hydrological pathways in the catchment. Using this approach, SGD in the Ria Formosa could be separated into two modes, a net meteoric water input and another involving no net water transfer, i.e., originating in lagoon water re-circulated through permeable sediments. The former SGD mode is present occasionally on a multi-annual timescale, while the latter is a dominant feature of the system. In the absence of meteoric SGD inputs, seawater recirculation through beach sediments occurs at a rate of  ∼  1.4  ×  106 m3 day−1. This implies that the entire tidal-averaged volume of the lagoon is filtered through local sandy sediments within 100 days ( ∼  3.5 times a year), driving an estimated nitrogen (N) load of  ∼  350 Ton N yr−1 into the system as NO3−. Land-borne SGD could add a further  ∼  61 Ton N yr−1 to the lagoon. The former source is autochthonous, continuous and responsible for a large fraction (59 %) of the estimated total N inputs into the system via non-point sources, while the latter is an occasional allochthonous source capable of driving new production in the system.

Spatial distribution patterns and movements of Holothuria arguinensis in the Ria Formosa (Portugal)

Holothurian populations are under pressure worldwide because of increasing demand for beche-de-mer, mainly for Asian consumption. Importations to this area from new temperate fishing grounds provide economic opportunities but also raise concerns regarding future over-exploitation. Studies on the habitat preferences and movements of sea cucumbers are important for the management of sea cucumber stocks and sizing of no-take zones, but information on the ecology and behavior of temperate sea cucumbers is scarce. This study describes the small-scale distribution and movement patterns of Holothuria arguinensis in the intertidal zone of the Ria Formosa national park (Portugal).Mark/recapture studieswere performed to record theirmovements over time on different habitats (sand and seagrass). H. arguinensis preferred seagrass habitats and did not show a size or life stage-related spatial segregation. Its density was 563 ind. ha−1 and mean movement speed was 10 m per day. Movement speed did not differ between habitats and the direction of movement was offshore during the day and shoreward during the night. Median home range size was 35 m2 and overlap among home ranges was 84%. H. arguinensis' high abundance, close association with seagrass and easy catchability in the intertidal zone, indicate the importance of including intertidal lagoons in future studies on temperate sea cucumber ecology since those systems might require different management strategies than fully submerged habitats.

Population genetics of Cerastoderma edule in Ria Formosa (southern Portugal): the challenge of understanding an intraspecific hotspot of genetic diversity

Coastal lagoons are highly variable environments that may act as hotspots of genetic diversity as a consequence of their ecological role as nursery habitats of marine species with both ecological and fisheries importance. The edible cockle (Cerastoderma edule) is a commercially important shellfish resource inhabiting coastal lagoons in Europe and their fisheries management urgently needs genetic studies to design appropriate strategies to promote the recovery of exploited populations. The aim of this study was to assess the C. edule genetic diversity and population structure at a small geographic scale, inside Ria Formosa coastal lagoon (southern Portugal) using mitochondrial cytochrome oxidase I sequences in six locations. Outcomes pointed to a common pattern of high haplotype diversity and non-significant genetic structuring inside the Ria Formosa lagoon. A high level of gene flow was detected between all localities and the presence of a single stock from a genetic point of view may be considered for fisheries management purposes. The existence of a high number of haplotypes and high values of haplotype diversity of C. edule in Ria Formosa lagoon could be consistent with the hypothesis that higher genetic diversity is expected in populations occurring in coastal lagoons, suggesting that lagoons could increase standing genetic variation and an adaptive potential of lagoon populations as an ecological response to a highly variable environment.

Feeding habits of the gilthead seabream (Sparus aurata) from the Ria Formosa (southern Portugal) as compared to the black seabream (Spondyliosoma cantharus) and the annular seabream (Diplodus annularis)

The feeding habits of Sparus aurata L., Diplodus annularis L. and Spondyliosoma cantharus L. in the Ria Formosa (southern Portugal) lagoon system were studied using three simple methods (frequency of occurrence, numeric percentage and percentage weight) and a composite index [index of relative importance (IRI)]. The Ivlev index was used to evaluate diet selectivity, while the Schoener overlap index was used to compare diets, and diet diversity was characterized by the Simpson index. The diets of the three species consist of a wide variety of food organisms, nevertheless S. aurata seems to be the most specialized. No significant dietary overlap was found, with S. aurata preferentially selecting gastropods and bivalves. while S. cantharus preferentially selected a wide variety of crustaceans and D. sargus a wider array, including crustaceans, gastropods and bivalves.

Fish assemblages of shallow intertidal habitats of the Ria Formosa lagoon (South Portugal): influence of habitat and season

Fish assemblages in seagrass and unvegetated habitats located in shallow intertidal creeks within the saltmarsh area of the Ria Formosa coastal lagoon were sampled with a Riley push net at 3 sites on a monthly basis over a 1 yr period. The objective was to test if both habitats support similar fish assemblages in terms of abundance, diversity, assemblage structure, and size distribution, and to investigate how site and season affect the assemblages. Fish assemblages associated with these habitats were significantly different in terms of diversity, abundance, and assemblage structure. Seagrass supported a larger number of species and greater diversity, while unvegetated habitat supported greater fish numbers but only of a few species. The habitats were dominated by different groups of resident species that were responsible for major differences in fish assemblage structure between habitats. Pomatoschistus microps and young-of-the-year (YOY) Atherina presbyter dominated the unvegetated habitat, while seagrass was dominated by a diverse group of species, in particular syngnathids and small labrids, revealing different habitat preferences. Site and season were determinant factors conditioning the role of habitat in structuring fish assemblages. Distance between habitats, site elevation, and the amount of marsh drained affected fish assemblages in both habitats. Seasonal fluctuations in the presence and abundance of YOY from marine migrant and resident species were responsible for comparable changes in fish assemblage structure in both habitats. Both habitats provide a distinctive nursery area for different species, while common species reveal ontogenic distributional changes between habitats, where smaller fish appear first in unvegetated creeks.

Length-weight relationships of six syngnathid species from Ria Formosa, SW Iberian coast

In this study, the length-weight (LWR) parameters were estimated for six syngnathid species, including 2 seahorses and 4 pipefishes, from Ria Formosa, a temperate lagoon from the south coast of Portugal. A total of 5070 fishes were used to determine the LWR. The estimated b value ranged from 2.95 (Nerophis ophidion) to 3.36 (Syngnathus abaster). To the authors' best knowledge, LWR parameters were estimated for the first time for Nerophis ophidion and Syngnathus typhle for the Atlantic waters. Data here present are essential for management and conservation of these flagship species.

Long-term changes in fish communities of the Ria Formosa coastal lagoon (southern Portugal) based on two studies made 20 years apart

Fish communities of the Ria Formosa coastal lagoon (south Portugal) were sampled on a monthly basis with a beach seine at 4 sites, during two different time periods: 1980-1986 and 2001-2002. Community indices, species ranking and multivariate analysis were used in order to identify changes in the fish community between the two time periods. A total of 153,511 fish representing 57 taxa were recorded. Although species composition was very similar for both sampling periods, multivariate analysis performed on annual species abundance in number and weight revealed differences in fish community structure between the two periods. Structural changes in fish community were related mostly to a sharp decrease in the abundance of Mugilidae from 1980-1986 to 2001-2002. These changes were probably associated to a decrease in organic matter contents and nutrients concentrations due to improvements in sewage treatment and better water circulation inside the lagoon. The changes in fish community structure are more evident in the inner areas of the lagoon than near the inlet. The association between changes in sewage patterns and changes in the ichthyofaunal community structure reinforces the importance of fish communities as a biological indicator of human induced changes in marine systems. (c) 2007 Elsevier Ltd. All rights reserved.

Seasonal, tidal and diurnal changes in fish assemblages in the Ria Formosa lagoon (Portugal)

Fish fauna were collected in two different subtidal shallow sites, seagrass and sand, using a small beam trawl in the Ria Formosa lagoon (South Portugal). Samples were taken at low and high tides, during day and night, and in each season. Fish assemblages associated with each site were significantly different, with seagrass site supporting greater fish abundance and higher number of species than sand. These site-related differences in fish assemblages were stronger than any other factor studied. Both sites showed seasonal variations in their fish assemblages, mainly because of recruitment of marine juvenile migrants during spring and summer. No significant tidal or diel changes were observed in the fish assemblages of either site, but there was a significant site-tide interaction, with higher fish abundance in seagrass at low tide. In sand, tide effect was evident only for certain species, with resident species more abundant at high tide and marine species more abundant at low tide. Within the Ria Formosa coastal lagoon, ichthyofaunal composition and structure is mainly influenced by site followed by season. (c) 2005 Elsevier Ltd. All rights reserved.

Site fidelity and movements of gilthead sea bream (Sparus aurata) in a coastal lagoon (Ria Formosa, Portugal)

Short-time site fidelity and movements of gilthead sea bream (Sparus aurata) in a coastal lagoon were determined using passive acoustic telemetry. Nine fish, ranging from 20.1 to 32.5 cm total length, were surgically implanted with acoustic transmitters and monitored for up to 179 days. Minimum convex polygon areas ranged from 18,698.6 m(2) to 352,711.9 m(2). Home range sizes were small, with individuals using core areas on a daily basis. However, these core areas shifted within the study site over time towards the opening to the sea. Two different diel behaviors were recorded, with some individuals more active at night and others during day time. Some individuals also demonstrated homing abilities, returning to the capture site after being released more than 4 km away. (C) 2008 Elsevier Ltd. All rights reserved.