Maria José Costa

Differential Use of Nursery Areas Within the Tagus Estuary by Sympatric Soles, Solea solea and Solea senegalensis

The spatio-temporal pattern of estuarine use by both Solea solea and Solea senegalensis was investigated between April 1995 and November 1996 by beam trawl surveys. Spatial and seasonal distribution and abundance were different for each species. The highest densities of S. solea were recorded in deeper, warmer, low salinity areas and where the sediment consisted of a high proportion of fine sand and presented a high abundance of amphipods. The 0-group individuals of this species first occurred on the nursery ground in April. Numbers peaked in June and July, and from October to April abundance was low. S. senegalensis had a wider distribution and its abundance was related to food availability. The 0-group individuals of this species occurred in the nursery areas later than S. solea, from June to August.

Seasonal and spatial patterns of distribution of subtidal benthic invertebrate communities in the Mondego River, Portugal : a poikilohaline estuary

The use of benthic assemblages to assess ecological quality of estuarine environments is a major tool for the implementation of the Water Framework Directive (2000/60/CE) for European aquatic ecosystems. Benthic communities show spatially heterogeneous distributions and experience seasonal variations due to both natural and anthropogenic stresses. The major goal of this study was to quantify the relationships between environmental gradients and the spatial and temporal patterns of the benthic communities along a Portuguese estuary. Seasonal and spatial variations relating macrobenthic communities and measures of water and sediment quality along the northern branch of the Mondego River estuary were examined at seven sampling stations from July 2000 to June 2001. Cluster analysis of biological data indicated three major groups of communities based on spatial distribution patterns: (1) a lower sector with stronger marine influence and dominated by Streblospio shrubsolii and Cerastoderma glaucum; (2) a middle sector with dominance of S. shrubsolii and Corophium multisetosum; (3) and an upper sector where C. multisetosum dominates a community characterized by a lower number of species. Canonical correspondence analyses of biological and environmental data determined a major salinity gradient influencing benthic communities. Seasonal changes of benthic communities were mainly determined by freshwater input and salinity changes that imposed a strong decrease in densities and number of species during winter, followed by a recovery during spring. Benthic ecological structure and contaminant levels indicated that the Mondego northern branch is moderately disturbed, although opportunistic species dominated the benthic community, suggesting that natural and anthopogenic sources of stress may be acting together. The Mondego River estuary, a poikilohaline-type estuary, characterized by strong seasonal changes in water flow and salinity, cannot be consistently stratified into salinity regions based upon the Venice classi- fication system. Biotic communities, exemplified here by the benthic communities, are seasonally displaced, compared to a homiohaline-type estuary where the Venice system can be applied without modification. Future identification of reference conditions and design of monitoring programs cannot be accomplished without understanding how interactions between biotic and physico-chemical dynamics differ between homiohaline and poikilohaline estuaries. Results obtained in this study could be used to assist future assessments in other Portuguese estuaries.

River flow influence on the fish community of the Tagus estuary (Portugal)

The influence of river flow on the fish community was assessed for the Tagus estuary (Portugal), based on sampling surveys carried out between 1979 and 2002. Four estuarine areas were sampled using similar fishing gear and effort in all the years considered in this study (1978–1980; 1995–1997; and 2001–2002). According to river freshwater flow values, sampling years were classified as wet (mean value of 714 m3 s−1, sd = 110 m3 s−1) or dry (mean value of 164 m3 s−1, sd = 19m3 s−1). Species richness varied between 22 and 39 according to the year, but no significant differences were related to river flow. The number of species per ecological guild was also similar in wet and dry years. Fish assemblage was dominated by marine occasional, estuarine resident and marine-estuarine opportunist species that represented near 90% of all fish species. The highest densities were represented by estuarine resident species. Fish density in dry and wet years differed significantly (mean density of 10.51 individuals 1,000 m−2 and 3.62 individuals 1,000 m−2, respectively), and the major differences were registered for estuarine resident, marine-estuarine opportunist and catadromous species. These differences probably reflected the estuarine habitat availability and also differences in fish densities in some estuarine areas under different flow conditions. The multivariate ordination analyses performed outlined both seasonal and spatial variation trends in fish distribution and abundance. The estuarine longitudinal gradient and its relationship with species distribution were less evident in dry years. Relationships between species abundance and river flow were different according to species, which is probably due to different needs in the timing and magnitude of river flow.

Abundance, feeding ecology and growth of 0-group sea bass, Dicentrarchus labrax, within the nursery areas of the tagus estuary

The spatio–temporal abundance pattern of 0-group sea bass, Dicentrarchus labrax , was investigated between April 1995 and November 1996 by beam trawl surveys. The highest densities of D. labrax were recorded in shallow areas. Dicentrarchus labrax density was also significantly related to water temperature and salinity, but the variation pattern was not linear. The 0-group individuals of this species first occurred on the nursery ground in May and the highest densities were recorded in June. Diet of 0-group D. labrax was mainly composed of crustaceans, the most important food items being Decapoda, Mysidacea and Isopoda. Feeding activity increased during summer. Short-term variations were related to the period of the day and tidal cycle. The growth rate determined for 0-group D. labrax was higher than those reported for the UK and northern France, and was similar to those obtained in eastern Mediterranean.

The demersal fish assemblage of the coastal area adjacent to the Tagus estuary (Portugal): relationships with environmental conditions

The subtidal fish assemblage of Tagus estuary coastal area was sampled in order to infer about its relationship to environmental conditions and its possible nursery function for marine species. Fish sampling took place between May 2001 and February 2002 with an otter trawl. In addition to fish sampling, a physical, chemical and biological characterization of the water column and bottom sediment was performed. Density and biomass were determined and ecological and feeding guilds assigned to each fish species. Correspondence analysis (CA) was used to determine the spatio-temporal structure of the assemblage and its correlation to environmental variables. A total of 36 fish species were identified. The fish assemblage was dominated by few species, both in terms of density and biomass. The main fish species were Callionymus lyra, Arnoglossus laterna, Diplodus bellotti, Echiichthys vipera and Raja undulata. Seasonally Trachurus trachurus, Sardina pilchardus and Engraulis encrasicolus were also abundant. Over 50% of the fish caught were juvenile stages. Benthic carnivorous species feeding on invertebrates dominated the assemblage. CA results indicated that distinct fish species occur in the northern and southern areas, although they distance only a few kilometres from each other. Depth and sediment type were the main structuring factors of the fish assemblage. Temperature and salinity showed reduced importance on overall assemblage structure although that may result from the particular climatic regime of the sampling year. The environmental preferences of the most important species are briefly discussed and the importance of integrating various spatial scales in multispecific studies of coastal fish assemblages emphasized. The presence of high densities of marine species juveniles indicates that this area may function as a spring–summer nursery for several species.

Do eel grass beds and salt marsh borders act as preferential nurseries and spawning grounds for fish? An example of the Mira estuary in Portugal☆

Abstract The fish communities of the Mira estuary (Portugal) have been studied as a whole since 1986. It was possible to identify two different types of habitat that act as nursery areas and spawning grounds for a large number of fish species — the eel grass beds and the salt-marsh-bordered zone. The importance of these habitats is due, not only to the number of species present, but also to their abundance. However, as the eel grass beds only extend over a small surface in the Mira estuary, the salt marshes become of vital importance for the marine fish, especially those with economical value. As several major modifications are planned for the Mira estuarine bed and valley in the near future, suggestions are given in order to preserve the estuarine ecosystem equilibrium.

Structure and dynamics of a benthic invertebrate community in an intertidal area of the Tagus estuary, western Portugal: a six year data series

The intertidal benthic invertebrate community adjacent to “Parque das Nac o es”, Tagus estuary, western Portugal, was studied at seven sites between October of 1996 and 2002. Grain size analysis revealed that the area was essentially muddy with total organic matter ranging from 5.4 to 11.4%. Annelida represented more than 85% of the total abundance. The dominant taxa were Oligochaeta, Streblospio shrubsolii, Scrobicularia plana, Hediste diversicolor, Hydrobia ulvae and Cirratulidae. Analysis of abundance revealed high seasonal and interannual heterogeneity, although clear aggregations between winter/spring and summer/autumn sampling periods were detected by multivariate techniques. Paragnathia formica and Dolichopodidae were closely related to winter/spring cluster while S. shrubsolii, Cossura sp., S. plana and Corbula gibba were associated to the summer/autumn aggregation. Although other taxa were abundant in several seasons, constancy in their numbers throughout the year could be observed. Temperature, rainfall and daylight hours were the environmental variables best related to the biological data. Temperature and daylight hours were important for the establishment of the two seasonal aggregations. Rainfall has also shown to be an essential factor on the structuring of this intertidal community, closely related to the abundance increase of Cirratulidade and decrease of Polydora sp., Nephtys spp., Cerastoderma glaucum, Corophium spp. and other Gammaridea. Sediment composition seems to play an important role in changing the community characteristics during the year since some species abundance appear to be favoured by coarser particles and many by fine sediments.

Assessing food web dynamics and relative importance of organic matter sources for fish species in two Portuguese estuaries: a stable isotope approach.

Stable carbon and nitrogen isotopes (δ¹³C, δ¹⁵N) were used to analyse food web dynamics of two of the main estuaries of the Portuguese coast: Tejo and Mira. The ultimate sources of organic matter supporting production of some of the most abundant and commercially important fish species were determined; and seasonal, inter- and intra- estuarine differences in the trophic relations among producers and consumers were identified. Stable isotope analysis was performed in different producers, primary consumers (main prey items for fish) and fish species (Solea solea, Solea senegalensis, Pomatoschistus microps, Dicentrarchus labrax, Liza ramada, Diplodus vulgaris and Atherina presbyter) of two areas in each estuary, in July and October 2009. Model calculations showed that the main prey for the fish species in the Tejo estuary used mostly salt marsh-derived organic matter as nutritional sources, with no marked differences between the sampled months. Trophic levels of fish species from the same estuary differed at multiple scales: inter-species, seasonally and spatially (both between and within estuaries). Significant differences in isotopic composition of fish species were more pronounced spatially (between the two sampled areas in the estuary) than seasonally (between sampled months). Trophic relationships in both estuaries demonstrated that organic matter is transferred to higher trophic positions mainly through benthic pathways. This shows the flexibility of these species to share resources and to exploit temporary peaks in prey populations. The present results showed that extensive disturbance in intertidal habitats from both estuaries may potentially change the balance of organic matter in the base of these complex food webs.

Development of a fish-based multimetric index to assess the ecological quality of marine habitats: the Marine Fish Community Index

In this paper the Marine Fish Community Index (MFCI) for the assessment of ecological status of marine environment is proposed. The MFCI was divided into 4 typologies: Rocky subtidal; shallow, intermediate and deep soft-bottoms. Based on the typical community associated to each typology and the DPSIR analysis performed, a set of metrics were selected and tested through a multiple correlation matrix (Pearsons coefficient) and the core ones included in the index. The MFCI was applied in all typologies and the scores obtained with each metric were analyzed. In order to test the robustness of the MFCI the final ecological value of each zone was recalculated by removing successively one metric at a time. The MFCI showed a sensitive and robust response in the ecological status assessment. Since it incorporates both functional and structural community information, the MFCI can be useful in the context of the Marine Strategy Framework Directive as well as in other contexts of conservation and sustainable management of the marine environment.

Discards of the beach seine fishery in the central coast of Portugal

Abstract The beach seine fishery is performed regularly along the Portuguese coast in shallow water sandy areas. The catches and discards of this fishery were studied from March until November 1999, on the coast south of Lisbon. Fishing operations were monitored weekly and estimates of the weight of catches and discards per species were determined for each haul. A total of 60 fish species was identified in the catches but Scomber japonicus, Trachurus trachurus and Diplodus bellottii represented approximately 90% of the catches. For most of the species the percentage of discarded fish was extremely high (ca. 100%). The species for which the estimates of discards were lower than 25% of the catches were Sardina pilchardus, Merluccius merluccius, Dicentrarchus labrax, Dicentrarchus punctatus, T. trachurus, several Sparidae species, Spicara maena, S. japonicus, Solea senegalensis, and Solea solea. Most of the species exhibited a marked seasonal abundance pattern that varied according to the species. Discards also varied considerably within and between seasons. The relationships between discards and total catch, species catch, mean length of fish and percentage of fish above minimum legal size were different according to species. For S. japonicus and S. pilchardus discards were negatively correlated with their catch, mean length of fish and percentage of fish above minimum legal size, while for T. trachurus significant correlations were obtained only for the last two variables.