Larval stages of Carcinus maenas (L.) were intensively sampled in the Canal de Mira ( h a de Aveiro, Portugal) during 2 lunar months: February 12 to March l 1 and May 9 to June 7, 1990. Each sampling period included fifteen 25 h fixed-station sampling cycles beginning at intervals of 4 tide cycles. Within each 25 h sampling cycle, plankton samples were collected hourly at several depths using a pump. Analysis of the data from these sampLing periods indicated tidal and die1 cycles of abundance of first stage C. maenas larvae. A semilunar component was also identified. These patterns were expressed as peaks of abundance during ebb tides, with highest peaks during nocturnal neap ebb tides around the first and last quarters of the moon. Peaks of nocturnal abundance could occur at any time during the night but consistently followed high water. In contrast, megalopae were present in the samples primarily during nocturnal flood tides. Intermediate zoeal stages of C. maenas were not collected. As indicated by an analysis of variance, the main effects of phases of the tide and day on the abundance of first zoeae and megalopae were significant (p < 0.05). These results provide evidence that a component with sermlunar periodicity is associated with the release of C. maenas larvae. That the release activity occurs well after sunset is also an additional interesting feature of these observations, inasmuch as larval release in decapods is usually concentrated within the first few hours after dusk. These observations support earlier observations that it is the time during the day-night cycle of high tide, as opposed to tidal amplitude, which is the important factor promoting synchrony with the lunar cycle.

Four seasonal sampling surveys were carried out between December 1985 and September 1986 in Canal de Mira (Ria de Aveiro, Portugal). A total of 40 sampling stations, distributed over 13 transects, was used. Salinity, temperature, dissolved oxygen and pH of the water mass were measured. Sediment temperature, and salinity and pH of interstitial water were determined. Sediment variables also included granulometric composition and organic matter contents. Bottom macrofauna samples were collected at each station.Ordination (PCA and MDS) and classification of the sampling stations were performed, using the physicochemical and the biological data sets separately. Average linkage cluster analysis using the unweighted paired-group method, arithmetic averages, was used for both sets of data.With a salinity range from 35.1%o to 0.0%0, Canal de Mira behaves like a tidally and seasonally poikilohaline estuary. Water temperature (8.5 -24.7~ decreased along the channel towards its inner part during the cold season; an inverse and more pronounced trend was observed during the hot season. Dissolved oxygen contents was generally high during the day (50% to 240% saturation). Oversaturation was observed throughout the growing season, with peaks in areas with large amounts of rooted vegetation.The pH values, largely correlated with dissolved oxygen, ranged from 6.8 to 8.9. Four types of sediment were present in Canal de Mira, medium and muddy sands being dominant.Two major gradients were identified: (i) a typical longitudinal estuarine gradient, associated with distance from the mouth, representing physicochemical variables such as tidal amplitude, salinity and temperature; this gradient was accompanied by an upstream increase in dominance; the community composition changes were mainly related to salinity; (ii) a lateral gradient, related to current velocity, depth and sediment composition; the subtidal community had a comparatively low species richness and abundance. Groups of stations could be recognized along the environmental gradients. Benthic community changes, however, appeared to be gradual rather than marked by abrupt transitions.

Spatial and seasonal changes of brackish peracaridan assemblages and their relation to some environmental variables in two tidal channels of the Ria de Aveiro (NW Portugal)'~e p a r t a m e n t o de Biologia, Universidade de Aveiro, 3810 Aveiro. Portugal '~aboratoire dVOceanographie Biologique, UMR 5805 (CNRS-UBl). 2 rue Jolyet, 33120 Arcachon. France ABSTRACT: The shallow-water fauna of 2 rnain channels in the Ria de Aveiro (Canal de Ovar and Canal de Mira) was sarnpled between June 1995 and June 1996 using a suprabenthic sled. Sarnples were collected monthly at 5 stations and every third month at 11 other stations, covering both channels from the lower to the upper reaches. The channels differ in their hydrodynamics. in the distribution of the sediment environments and in the salinity gradient, thus providing an invaluable exarnple for field studies. The results presented herein concern peracaridan crustaceans. Multivariate analysis (MDS, ANOSIiM and UPGMA) of the faunal data showed significant differences between the 2 channels. Spatial and seasonal variations within the channels were also significant. The distinctive structural features were the higher number of species and overall dorninance of mysids in the Canal de Mira as opposed to the dorninance of arnphipods and higher densities in the Canal de Ovar. In both channels there was a spatial pattern of high densities in areas with a rich sediment environrnent (fine sediments. high organic content, more diversified and stable food sources). Specific life cycle features, unfavourable ternperature and salinity conditions, and probably also increased predation pressure induced a general impoverishment of the peracaridan assemblage during winter. Amphipods (rnainly epibenthic and tube dwellers) and mysids (characteristic suprabenthic) showed defined spatial and seasonal patterns. Amphipods dominated the areas with rnore stable food sources, while the highly rnotile mysids succeeded in colonising and dominated in rnore dynarnic and unpredictable environrnents. Density fluctuations of amphipods and rnysids occurred seasonauy in non-coincident cycles. On the whole, rnysids were dominant during winter and spring and arnphipods dunng surnmer and auturnn.

Samples of Nassarius reticulatus (L.) were obtained from May to July 2000 on the W Portuguese coast. N. reticulatus imposex (superimposition of male characters onto female prosobranchs) increased with the proximity of harbours. The percentage of imposex-affected females (%I) varied between 0 and 100%. The penis length index (PLI) and the relative penis length index (RPLI) were between 0 and 10.7 mm and 0.0 and 92.1%, respectively. The vas deferens sequence index (VDSI) ranged from 0 to 5. The average oviduct stage (AOS) varied between 0.0 and 1.3. Sterile females (22 specimens) were found at 8 of the 40 sampling stations with frequencies between 5 and 50% of the total females sampled at each site. Sterility occurred only in females highly affected with imposex. Tributyltin (TBT) and triphenyltin (TPT) female body burden varied from < 20 to 1368 and from <10 to 256 ng Sn g -1 dry weight (dry wt), respectively. The TPT residue was, on average, 18% of the TBT residue, and there was a highly significant correlation between TBT and lnTPT (r = 0.88, p < 0.001). Dibutyltin (DBT) and monobutyltin (MBT) female body burden varied from < 34 to 721 and from < 24 to 703 ng Sn g -1 dry wt, respectively. TBT represented the major fraction (34 to 60%) of the total butyltins, followed by DBT (24 to 40%) and MBT (10 to 31%). Highly significant correlations (p < 0.001) were established between the lnTBT female residue and the indices RPLI (r = 0.88), VDSI (5) (r = 0.81) and AOS (r = 0.72), as well as between TBT and percentage female sterility (%STER) (r = 0.61).KEY WORDS: Nassarius reticulatus · Imposex · Portugal · Tributyltin · Triphenyltin · SterilityResale or republication not permitted without written consent of the publisher

The population of Corophium multisetosum Stock, 1952 in AreaÄ o displayed a semiannual, iteroparous life history. Mean longevity was 6 mo, with the estimated life span longer for overwintering individuals born in autumn than for individuals born in spring. Length-frequency data indicated that the length increment per moult is probably higher in males than females; however females moulted more frequently and achieved a larger body size. Preliminary growth rates were 100 lm d )1 for juveniles and 19 to 29 lm d )1 for mature females, with the lower values occurring during the winter. It was estimated that under favourable conditions females may attain reproductive size and mature within 1 mo. Although incubating females were present all year round, recruitment occurred in spring, almost ceased during the summer, peaked in autumn, and decreased again during the winter. Extreme temperatures and very low salinities during winter and summer may have deterred breeding, while moderate temperatures (15 to 20°C) and salinities >1 psu in spring and autumn were apparently favourable for reproduction. The unfavourable summer conditions constrained breeding and synchronised the timing of reproduction. In late-autumn and during the winter, as temperature decreased and brooding time increased, synchrony was progressively lost. Brood size varied as a function of embryonic developmental stage, size of incubating females, and season. The life-history pattern and reproductive features of C. multisetosum in AreaÄ o are closely related to temperature and salinity; other environmental conditions such as oxygen content of the water and food availability may also be relevant.

The prosobranchs Nucella lapillus, Nassarius reticulatus, Hydrobia ulvae and Littorina littorea were sampled from May to July 1998 at 45 stations in the Ria de Aveiro (NW Portugal) and the adjacent coastal zone. The distribution patterns of these populations were related to the salinity gradients. The tributyltin (TBT) concentration in the water was determined for 17 stations spread over the study area during a neap tide in July 1998 and varied from 9 to 42 ng Sn l

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The reproductive cycle of Nassarius (Hinia) reticulatus was investigated in the Ria de Aveiro on the north-west Portuguese coast during 1992 and 1993. A clear seasonal pattern was observed with the beginning of gametogenesis in August followed by ripening of the gonads in January and February and spawning from February to July. The increase of water temperature above 11°C in February 1993 was associated presumably with the release of gametes. Recruitment inside the Ria of juveniles with 6·5 mm mean shell height was detected in February 1993 and these individuals were spawned in the previous year. Males of N. reticulatus exhibited a considerable variation in length of the penis throughout the reproductive cycle. The accuracy of the use of relative penis length (RPL) index for intersite comparisons of imposex is discussed and the magnitude of the error that might be involved when comparisons are made using populations in different phases of the reproductive cycle is evaluated.