Patterns of distribution and abundance of the stalked barnacle (Pollicipes pollicipes) in the central and southwest coast of continental Portugal

The stalked barnacle Pollicipes pollicipes is a cirriped crustacean that lives on very exposed rocky shores. This barnacle is the most important economical resource on intertidal rocky shores of continental Portugal. It is highly prized as food and heavily exploited (professional and recreational fishery), but fishery data are scarce and do not estimate the real pressure upon this resource.Despite its socio-economic interest, specific regulations on this fishery are recent and different along the Portuguese coast. Four regions with different regulation can be identified: the marine reserve “Reserva Natural das Berlengas” (RNB) and the marine park “Parque Marinho Prof. Luiz Saldanha” (PMLS) (both in central Portugal); the natural park located in SW Portugal (“Parque Natural do Sudoeste Alentejano e Costa Vicentina”, PNSACV); and the rest of the coast.The main objective of the present study was to study the spatial patterns of percentage cover, biomass, density and size structure of P. pollicipes in areas with different exploitation regimes, including harvested areas and no-take areas. Additionally, variability between mid shore and low shore barnacles was also analysed.Seven areas were sampled with a variable number of sites (a total of 24) randomly sampled in each area during 2011. Photographs and image analysis (percentage cover) and destructive sampling (density, biomass and size) were used.In general, percentage cover, biomass and density were higher in mid shore when compared to low shore, namely in harvested areas. Low shore barnacles had a higher proportion of adults with moderate and high commercial value, while juveniles were relatively more abundant at mid shore.There were no consistent differences in the patterns of distribution and abundance of P. pollicipes among areas subject to different exploitation regimes. The most different area was the harvested area by professional fishers in RNB, where the highest biomass within the study was registered (mid shore, 7.7 kg·m^− 2). Barnacles within this area presented a higher proportion of adults with commercial value, while recruits and juveniles were relatively more abundant in other areas.The hypothesis of a highest percentage cover, density and biomass in the low shore of no-take sites was not supported.     

The Dynamics of an Introduced: Balanus glandula Population in the Southwestern Atlantic Rocky Shores. The Consequences on the Intertidal Community*

Abstract. This paper deals with the population dynamics of the introduced barnacle Balanus glandula in a port shelter and a rocky shore exposed of a southwestern Atlantic area. Replicated areas in both zones were denuded monthly and censused in both the high intertidal and the upper mid intertidal zone. The settlement pattern. recruitment, mortality and growth of B. glandula and a comparative successional pattern in both areas were recorded. Recruitment began in winter, i.e., July in the port and August in the rocky shore. In the port, green algae dominate up to a final community of Balanus glandula all along the intertidal, while in rocky shores the red encrusting alga Hildenbrandia lecanellieri establishes a cover that is replaced by the mytilid Brachidontes rodriguezi in the mid intertidal and by B. glandula in the high intertidal and upper mid intertidal. B. glandula densities were greater in the upper mid intertidal 19 600 and 5050 indiv. · m^-2 in the port and rocky shore, respectively than in the high intertidal 13600 and 1100 indiv.· m^-2, respectively. Mortality was greater in the port up to 62%, but heavy settlement allows a final density 4 times greater than in eulittoral rocky shores and 10 times greater than in the high intertidal. The winter reproduction of Balanus glandula, the absence of predators, the neutral or beneficial effect of algae. with spatial and temporal partitioning of substrate allows it to successfully outcompete mussels and other barnacle species from the intertidal community of both sheltered and exposed areas.     

Spatial variability of intertidal rocky shore assemblages in the northwest coast of Portugal

The spatial variability of rocky shore assemblages of the northwest Portuguese coast was studied in a total of 12 transects, visited twice between March and August 2003. Each transect was positioned from the upper to the lower shore and four replicate samples (50 × 50 cm) were taken at each visually identified assemblage. Multivariate analysis was used to test the null hypothesis of no significant differences among assemblages located on different heights along the transect and among assemblages located at the same height on different transects. The distribution pattern of organisms along the height was not consistent across transects and significant variability could be found in assemblages located at the same height on the shore. Globally, the variability from the lower to the upper shore (vertical axis) was larger than from transect to transect (horizontal axis) but the distribution pattern along height was clearer in sheltered transects than in exposed ones. The heterogeneity in composition between the visually identified assemblages, within the same transect, was, however, the major source of variability in the study area. In the rocky intertidal northwest coast of Portugal, where tidal amplitude is broad and extremely wave-exposed sites are scarce, height above chart datum was the most important factor determining the distribution and species composition of the assemblages. However, variability along the horizontal axis was also significant and should be considered in studies of spatial patterns of distribution of organisms within this area.     

舟山岩相潮间带动物群落结构的研究

本文应用数理统计方法研究了舟山海区岩岸潮间带中26个测站的春季动物群落结构。根据26个站的位置分为近岸区、近外海区和外海区3个区域。各站均以软体动物和甲壳动物为群落主要组成成分,群落种类组成数从近岸到外海呈增长趋势,且优势种亦从低盐种类向高盐种类演替。近岸区群落主要优势种为短滨螺Littorina brevicula、粗糙滨螺L.scabra、僧帽牡蛎Ostrea cucullata、白脊藤壶Balanus albicostatus等;近外海区为短滨螺、粒结节滨螺Nodilittorinaexigua、僧帽牡蛎、鳞笠藤壶Tetraclita squamosa squamosa、白脊藤壶等;外海区为粒结节滨螺,疣荔枝螺Purpura clavigera、条纹隔贻贝Septifer virgatus、日本笠藤壶T.japonica及藻类等。但群落个体密度和生物量从近岸到外海呈减少趋势。从近岸到外海,群落的Shannon-Wiener多样性指数H和Pielou均匀度J均增加,而McNaughton优势度D减少。群落结构从近岸到外海渐趋复杂。但整体上,舟山海区岩岸春季动物群落结构是比较简单的(绝大多数断面H值小于2.50,J值小于0.5。而D值大于0.6)。近外海区的群落结构比较相似于外海区的群落。根据平均聚类分析,这26个群落可以分为三个生态类型,即隐蔽性岩岸群落,半隐蔽性岩岸群落及开敞性岩岸群落。     

Stock Evaluation of Three Littoral Echinoid Species on the Catalan Coast North-Western Mediterranean

Abstract. We estimated the abundances of the three common littoral echinoid species Paracentrotus lividus, Arbacia lixula and Sphaerechinus granularis in a littoral zone between 0 and 10m depth on the Catalan shores NE Spain. Densities of each species were estimated from a total number of 11 571× 1 m² sampling units deployed at 152 sites along the 13 zones into which the coast was divided. The surface area available in each of these zones was estimated at the scale of the sampling unit 1 m² taking into account the fractal dimension of the shore. The stocks individuals > 2cm test diameter of these species for the whole Catalan shore ≅ 300 km, straight-line distance were estimated to be about 279.1 × 10⁶ individuals for P. lividus , 28.9 × 10⁶ individuals for A. lixula and 10.9 × 10⁶ individuals for S. granularis. These sea-urchins are key species in the regulation of algal communities and some of them P. lividus. S. granularis are of commercial interest. This information will provide a tool for the future monitoring and management of this resource, which now faces diverse pressures of human origin.     

Distribution of Benthic Communities on the Tropical Rocky Subtidal of Armação dos Búzios, Southeastern Brazil

Abstract.  Few studies have described the spatial patterns of rocky sublittoral benthic communities in Brazil, where these habitats are almost exclusively located on the southeast and south coastline. The fauna and flora were analyzed using a quadrat method, and the species abundance and distribution were determined along transects down to the bottom sand plain on 10 rocky shores at Armação dos Búzios, Brazil. The 16 most common species accounted for around 97% of the benthos coverage and included cnidarians, algae, poriferans, and echinoderms. Cnidarians and algae were the most important groups, with abundance ranging from 13–66% and 27–68%, respectively. The species distribution indicated a clear depth zonation pattern. The algal community dominated the shallowest depths in sites more exposed to waves and steeper substrate slope, whereas the cnidarian community, divided into the zoanthidean Palythoa caribaeorum and the coral Siderastrea stellata , was more abundant from intermediate to greater (4 m) depths. Different community patterns were found between sites, demonstrating that different spatially discrete factors may be acting on each rocky shore.     

Variations in crab claw morphology and diet across contrasting inter‐tidal habitats

Crabs are important predators of inter‐tidal ecosystems, controlling the abundance and distribution of their prey populations. Often the same crab species occupies several habitats and, although their effects on prey have been quantified across habitats, crabs’ dietary and morphological responses to differing environmental influences have been overlooked. Here, we used the crabs Eriphia verrucosa and Pachygrapsus marmoratus as model species to examine differences in claw morphometry – size and wear – and diet between rocky shore and heterogeneous sand flat habitats. We predicted that, intra‐specifically, crabs from rocky shores would consume more hard‐shelled prey owing to their high availability and consequently, would display chelipeds with the following claw characteristics: a higher degree of claw damage, stronger musculature (higher propel height) and increased mechanical advantage (defined as the ratio of input lever length to output lever length) than crabs in the heterogeneous sand flat habitats. Sampling was performed in heterogeneous sand flat habitats and rocky shores of the Central Portuguese coast. For each crab species, carapace width, diet composition and several claw morphometric measures were recorded, revealing significant intra‐specific differences (using multivariate analysis) between shore types. We found that E. verrucosa and P. marmoratus consumed more hard prey on rocky shore than on sand flat habitats, which resulted in rocky shore crabs having more accentuated dentition wear and larger musculature than their sand flat habitat counterparts. We suggest that the strong response of crab claw morphometry to environmentally induced diet variations is an important mechanism in the successful adaptation of crab species to inhabit differing habitats. A major implication is that the impact of the same species on prey may vary largely with habitat type as a result of predation efficiency varying with claw condition.     

Ocean wave characteristics around New Zealand

Nearly 17 years wave records from deep water and shore‐based stations are used to describe the ocean wave characteristics around New Zealand. The wave environment is dominated by west and southwest swell and storm waves generated in the temperate latitude belt of westerly winds. As a result, the west and south coasts are exposed, high energy shores, the east coast is a high energy lee shore, and the northern coast from North Cape to East Cape is a low energy lee shore sheltered from these winds and waves. South of New Zealand, wave energies are extremely high; the prevailing deep water wave is 3.5–4.5 m high and has a 10–12 s period, with a slight increase in wave heights in winter.

The west coast wave environment is mixed, and consists of locally generated westerly and southerly storm waves, and swell waves generated to the south. The prevailing wave is t.0–3.0 m and 6–8 s period. There are no strong seasonal rhythms, only shorter period cycles of wave height (5 day) associated with similar quasi‐rhythmic cycles in the weather.

The east coast also has a mixed wave climate with southerly swells, originating in the westerlies south of New Zealand, and locally generated southerly and northerly storm waves. The prevailing wave is 0.5–2.0 m and 7–11 s period. A short period rhythmic cycle, similar to that on the west coast, is superimposed on a weak seasonal cycle. The seasonal, cycle results from an increase in the frequency of local northerly waves in summer.

The prevailing wave on the north coast is a northeasterly, 0.5–1.5 m high and 5–7 s period. Subtropical disturbances and southward‐moving depressions generate a mixed wave environment and a possible seasonally reflecting a winter increase in. storminess.     

A STUDY OF THE DISTRIBUTION OF RECENT OSTRACOD FAUNAS FROM COASTAL AREAS OF THE EAST CHINA AND YELLOW SEAS

A total of 91 species belonging to 57 genera were recovered from the coastal areas of the north East China Sea ana the south Yellow Sea, of which, 42 species of 30 genera were collected alive. The biocoenoses of estuaries, supralittoral and eulittoral zones are dominated by orackish and euryhaline species, of which Albileberis sheyangensis, A. sinensis, Leptocythere ventriclivosa, Loxoconcha ocellata, Sinocytheridea latiotata and S. longa are ubiquitous; Propontocypris euryhalina, Spinileberis furuyaensis and S. pulchra are restricted to the supralittoral zone; Neomonoceratina crispata and Pontocythere lit-toralis are only present in the eulittoral zone. The community structure of these biocoenoses is generally marked by low snecies diversity (H(S) and 5) and high incidence and dominance. Among the environmental factors investigated, it was found that salinity was the most important in controlling the distribution of living ostracods, and high-energy hydrodynamic condition was the main cause of the grea     

Population variations in the grazing turbinid Lunella smaragda (Mollusca: Gastropoda)

The grazing turbinid gastropod Lunella smaragda was sampled regularly over 3.5 y from precise sites of different microtopography and height on the platform shore at Goat Island Beach near Leigh, Northland, New Zealand. Growth is linear for over 3 y, and the year‐classes distinct. The position of the different size‐classes is related to both the shelter afforded by the microtopography, and to the height on the shore. The populations in the mid‐eulittoral turf flats, low eulittoral bare rock areas, and the sublittoral fringe are distinct, and there is a general movement down the shore with age and size. Wave action apparently dislodges the animals from higher areas when they grow to a critical size and transports them to sites lower on the shore, where wave disturbance is less. Field experiments with marked animals and laboratory studies with a wave tank confirm that the wave‐effected distribution is size related. However measurements showed that the ratio of foot attachment area to the shell area presented to the wave does not vary with animal size. The possible benefits of wave dislodgment and wave‐effected distribution are considered.     

Habitat use of inter‐tidal chitons – role of colour polymorphism

This study presents a new approach to examining European chiton habitat use according to morphological characteristics. Time‐search transects were conducted on four Portuguese rocky shores at two shore levels. The chiton species, abundance and individual morphometric features were recorded and related to the substratum dominant epiphytes and surface roughness. The chiton Lepidochitona cinerea (Linnaeus 1767) was the dominant species (77%), followed by Leptochiton algesirensis (Capellini 1859) (15%) and Acanthochitona crinita (Pennant 1777) (8%). Species abundance did not vary significantly with shore level or amongst shores. Six colour morphs were considered for Lepidochitona cinerea, four for A. crinita and one for Lepidochiton algesirensis. Substratum characteristics significantly explained the variation in species and colour morph distribution. There was a high correlation between the presence/absence and type of epiphytic algae and the substratum surface roughness level. We hypothesize that three mechanisms operating either independently or in interaction may explain the non‐random distribution of colour polymorphisms according to their habitat characteristics: (i) presence of algae that are part of their diet; (ii) use of rock as shelter – for instance, crevices and cover resulting from algae fronds and; (iii) morph–rock colour matching as a camouflage mechanism to reduce predation pressure.     

中国近海江珧科的初步报告

江珧科至今在世界上发现的种类虽不算多,但因其经济价值教高,某些种产量大而分布较广,故长期以来一直为人们所重视。江珧科的种类全部是海产,分布在温带和热带海区,尤以印度洋和太平洋的种类为最多,主要生活在浅海,一般自潮间带的中、下区直到100多米的深度皆有发现,自低潮线附近至50米深度之间的浅水区最为繁盛。 从我们所搜集的资料中,可以看出江珧的形态变异极大,不仅幼体与成体的形态变化大,而且不同个体之间及地区间的差异也较大,所以在鉴定种类时常遇到较大的困难。Reeve虽早已注意到这一点,但他仍将许多同一种中的形态变异的个体订为不同的种,以至后来为许多学者所合并。 本文的资料,大部为中国科学院海洋研究所历年在中国沿海潮间带所采集的标本,小部分系全国海洋普查底栖生物拖网所获。经初步鉴定共有3亚属9种,其中除栉江珧在我国各海区都有分布、细长裂江珧及羽状江珧在东海及南海均有分布外,其余各种仅分布在南海。我们根据较多的标本对以往记载的种,特别是形态变异比较大的种,做了详细的观察比较,澄清了一些种名混乱的现象。     

Localized versus regional adaptation in limpet shell morphology across the Iberian Peninsula

The climate‐envelope approach to predicting climate‐induced species range shift is limited. There are many possible reasons for this, but one novel explanation is that species adapt to changes in temperature at the expense of adaptation to other stressors. Here we test this hypothesis using the limpet Patella depressa (Mollusca, Patellidae), over a large geographical area covering most of the Atlantic coast of the Iberian Peninsula, known to consist of a genetically inter‐connected population. We examine limpet shell morphology on four shores in each of three regions, from Northern Spain to Southern Portugal. Within each region, shell morphology (measured as maximum shell profile to length ratio) varied between shore types differing in their insolation, wave action, microhabitat availability and biological factors. However, this ratio, which is known to be an adaptive response to heat stress, was found to be consistently higher in more southern latitudes despite differences between shore types being found in all regions. This implies that localized adaptation to shore type (most likely through phenotypic plasticity) is compromised by factors that change over latitudinal or regional scales, or which could occur in response to climate change. Although such climate‐induced changes may initially be localized, compromised adaptation (through phenotypic or genetic plasticity) may result in altered community interactions and potentially large shifts in community structure.     

Calcification depth and spatial distribution of Thoracosphaera heimii cysts: Implications for palaeoceanographic reconstructions

For the optimal use in palaeoceanographic studies of the stable oxygen isotopic signal and elemental composition of the calcareous photosynthetic dinoflagellate Thoracosphaera heimii, it is essential to gain detailed information about its calcification depth and spatial distribution. We therefore studied the vertical and horizontal distribution patterns of T. heimii in the upper water column (0–200 m) along three transects: an inshore–offshore gradient off Cape Blanc (CB), a south–north transect from CB to the Portuguese coast and a north–south transect off Tanzania. We compared concentrations of living cysts (cells with cell content) with chlorophyll-a, salinity and temperature measurements at the sampling depth. In order to explore the seasonal variability in cyst production, three transect off CB were sampled at three different times of the year.Living T. heimii cysts were found in the upper 160 m of the water column with highest concentrations in the photic zone indicating that the calcification of T. heimii occurs in the upper part of the water column. Maximal abundances of living cysts were found relatively often in or just above the deep chlorophyll maximum (DCM), the depth of which varies regionally from about 20–40 m off CB to about 80 m off Tanzania and along the transect from CB to the Portuguese Coast. However, there was no significant correlation at the 95% confidence level between the cyst concentrations and temperature, salinity and chlorophyll-a concentrations at the sampling depths observed.In both the Atlantic and Indian Oceans, the highest abundances of T. heimii were observed in regions where the upper water masses contained relatively low nutrient concentrations that are influenced only sporadically, or not at all, by enhanced photic zone mixing related to the presence of upwelling cells or river outflow plumes at or close to the sampling sites. The seasonal production of cysts by T. heimii appears to be negatively related to the presence of upwelling filaments across the sampling sites. Our study suggests that turbulence of the upper water masses is a major environmental factor influencing T. heimii production.     

Deposits of the 1983 and 1993 tsunamis on the coast of Primorye

Deposits of the two strongest tsunamis of the 20th century have been found on the eastern coast of Primorye. The tsunamis had epicenters in the Sea of Japan west of the coast of Hokkaido. The distribution and preservation of deposits in bays of different geomorphological structure have been analyzed. The best defined sedimentary covers occur in the upper part of sections in low-lying areas of bay shores, where the wave runup was more than 3 m. The best preserved deposits have been observed in bays attributed to loworder streams. Variations of the structural composition of tsunami deposits formed by traction processes associated with the tsunamis have been analyzed depending on distance from the shoreline; the sources of material have been identified. Tsunami waves transported sand not only from beaches, ancient storm ridges, and terraces, but also from the underwater coastal slope; waves also grabbed material from estuarine lagoons and lakes located in the shore inundation zone. Deposits include marine diatoms with dominant sublittoral planktonic and benthic species, which suggests that the material was transported from a depth no more than 15 m. Deep-sea species of diatoms and their fragments have been encountered. Among freshwater diatoms are species with different ecological identities, indicating erosion and redeposition of material transported from various sources.     

Inter- and intra-estuarine fish assemblage variability patterns along the Portuguese coast

Estuaries along the Portuguese coast differ considerably in terms of their structure, geomorphologic and hydrologic characteristics. They play an important ecological role for different fish species, namely acting as important nursery areas. The fish assemblages of nine estuaries of the Portuguese coast were investigated in order to evaluate their main inter- and intra-estuarine variability patterns. Fish sampling surveys were conducted in May and July 2006, covering the full estuarine gradient. The different saline areas in each estuary were mapped using a Geographic Information System and fish assemblages’ were described and compared using a functional guilds approach. Generalized linear models were used to relate fish species richness to geomorphologic, hydrologic and environmental characteristics of the estuaries considered and correspondence analyses were performed to evaluate similarities in fish assemblages’ structure. At a large scale, river flow was the most important factor explaining the variability in species richness in estuaries along the Portuguese coast. At a regional scale, different abiotic factors explained the occurrence and abundance of fish species in the estuaries. Nonetheless, the overall role of the estuary was strongly related with the dominant saline zone within each estuary.     

Factors influencing the distribution of coastal lichens Hydropunctaria maura and Wahlenbergiella mucosa

Responses to abiotic and biotic stresses that potentially drive the vertical zonation of the intertidal lichens Hydropunctaria maura, an upper littoral lichen, and Wahlenbergiella mucosa, a lower littoral lichen, were investigated in field and laboratory experiments. When transplanted, both lichens exhibited an inability to survive outside their normal vertical distribution range. W. mucosa appeared to be unable to tolerate prolonged periods of desiccation following translocation from lower to upper littoral regions, whereas H. maura was unable to survive in lower littoral zones possibly owing to increased grazing pressure. The effect of desiccation in both lichens was compared using pulse amplitude modulated chlorophyll fluorescence and infra‐red gas analysis; results indicated a more hydration‐dependent nature of W. mucosa. Photosynthetic (algal) pigments and phenolic compounds were determined in both lichen thalli, and a range of additional coastal lichens occupying a natural gradient from upper to lower shore levels. Pigment composition and concentration in both lichen thalli were similar whereas levels of phenolic compounds were up to three times higher in W. mucosa than H. maura. Pigment and phenolic concentration and composition exhibited some seasonality across 13 different lichens originating from different shore levels. Phenolic concentration increased towards the lower shore, suggesting a potential anti‐herbivory function. This marks the first study of pigments and phenolics in coastal lichen communities, and prompts further investigations on the particular physiological features of marine and maritime lichens that enable them to thrive in this extreme environment.     

舟山潮间带生态学研究：Ⅱ.数量及其分布

舟山潮间带生物种类数量的平面分布与盐度和海岸开敞性有关,垂直分布与潮汐有关;群落数量的水平分布与底质和海岸开敞性有关,垂直分布与潮汐有关。舟山潮间带生物有明显的分带现象,隐蔽的岩岸区分为:滨螺带和藤壶-牡蛎带两个带;开敞性岩岸区分为:滨螺带,藤壶-(虫戚)-藻类带及藻类带3个带。沙滩区分为:沙蟹带和浅蛤-斧蛤带两个带;泥沙滩区分为:盐碱植物-滨螺带和招潮蟹-大眼蟹带;泥滩区分为:蟹守螺-囊螺带和蟹守螺-织纹螺带。     

Using thermoterrace dimensions to calculate the coastal erosion rate

Thermoterraces in syngenetic ice complexes are widespread along the erosion dominated Yakutia Arctic coast. Thermoterraces progressively record quantitative information about their existence, which may be used to determine the mean shore retreat rate during the time they are present. Initial measurements of four thermoterraces on the south coast of the Dmitry Laptev Strait were carried out by the authors in 2002 and shore retreat rates were calculated. Comparison of erosion rates obtained using thermoterrace dimensions and geodetic survey results with those determined using aerial photographs showed that erosion rate values obtained in these two ways are approximately of the same order.     

Relative importance of estuarine flatfish nurseries along the Portuguese coast

The relative importance of nursery areas and their relationships with several environmental variables were evaluated in nine estuarine systems along the Portuguese coast based on trawl surveys. Historical data were used to outline changes and trends in the nursery function of some of these estuaries over the past decades. The dominant flatfish species in Portuguese estuaries were Platichthys flesus (Linnaeus, 1758), Solea solea (Linnaeus, 1758), Solea senegalensis Kaup, 1858 and Monochirus hispidus Rafinesque, 1814, but their occurrence differed among the estuaries. P. flesus only occurred in estuaries north of the Tejo estuary (39°N), S. solea was quite rare along the southern Portuguese coast (south of 37°30′N), S. senegalensis occurred in estuaries throughout the coast, but its abundance varied considerably, and the occurrence of M. hispidus was limited to the Sado estuary and Ria Formosa. A Correspondence Analysis was performed to evaluate the relationships between flatfish species abundance and geomorphologic and hydrologic characteristics of estuaries (latitude, freshwater flow, estuarine area, intertidal area, mean depth and residence time). Abiotic characteristics (depth, temperature, salinity, sediment type) of nursery grounds of each flatfish species were also evaluated. Results showed that some estuaries along the Portuguese coast have nursery grounds used by several flatfish species (e.g. Ria de Aveiro, Sado estuary), while in other systems a segregation was noticed, with juveniles of different species occurring in distinct estuarine areas (e.g. Minho and Mondego estuaries). This emphasizes the relevance of niche overlap, but the potential for competition may be considerably minimized by differences in resource use patterns and by an extremely high abundance of resources. Peak densities of flatfishes recorded in nurseries areas along the Portuguese coast were within the range of values reported for other geographical areas. Inter-annual abundance variability of all the species in the Tejo and Sado estuaries was extremely high, with a drastic decrease in P. flesus in the Tejo estuary, probably related to higher water temperature in recent years due to global climate change.