First record of Synidotea laevidorsalis (Miers, 1881) (Crustacea: Isopoda) in Europe (Gironde estuary,France)

This note reports on the presence of a well established population of the isopod Synidotea laevidorsalis (Miers) in the Gironde estuary (southwestern France). This species is new for the European fauna. S. laevidorsalis is a nonendemic cool-temperate to subtropical, shallow-water species which was probably introduced into the study area from Asia. In the salinity range of 1 to 10 g 1^-1 of the Gironde the species constitutes an important component of the brackish-water hyperbenthic community. The population was already present in 1975 when it was misidentified as the native species Idotea emarginata (Fabricius).     

Long-term changes in the population of Eurytemora affinis (Copepoda,Calanoida) in the Gironde estuary (1978–1992)

Long-term changes in the population of Eurytemora affinis were investigated during 15 years (1978–1992) at a fixed station in the Gironde estuary (South West France). Total numbers, sex-ratio, % ovigerous females, proportion of copepodites and clutch-size were taken into account and their long-term distribution was related to temperature, river flow, salinity, suspended matter and chlorophyll a concentrations after the seasonal effect was removed for all variables.There was a great decrease of the river flow during the period of investigation, due to a general deficit in pluviosity. On the contrary, the general trend for salinity was an increase from 1978 to 1992. The same pattern was observed for chlorophyll, indicating an intrusion of marine phytoplankton. Water temperature increased significantly during the study period, following the general increase in air temperature observed in the area. For the suspended particulate matter (SPM), an increase was observed between 1978 and 1981–1982, then a very sharp decrease occurred from 1984 onwards.Numbers of E. affinis were inversely correlated with temperature and salinity, and positively correlated with the river flow. E. affinis was negatively correlated with chlorophyll concentration because of the covariation with salinity. No clear long-term trend was observed for the sex-ratio. A significant correlation was found between females carrying egg-sacs and SPM concentration, probably due to a decrease of the predation pressure in very turbid waters. The percentages of copepodites tended to decrease with time and were inversely correlated with temperature. Clutch-size significantly decreased during the 15-year period. This trend was mainly explained by temperature and salinity.It is concluded that, in the absence of strong human alteration in the Gironde estuary the long-term distribution of zooplankton can be explained by the natural environmental variability. The dominant factors are the river flow which governs the movement of the populations along the estuary and the temperature which influences the reproductive processes. Any change in climate will have consequences on the pelagic community.     

Spatial variations in size, weight and condition factor of the females of Acartia clausi (Copepoda: Calanoida) along a salinity gradient in two contrasting estuaries of the Basque coast (Bay of Biscay)

Variations in prosome length and width, dry weight and condition factor of female Acartia clausi copepods were studied at three salinities (35, 34 and 33 psu) in the euhaline region of two estuaries (Bilbao and Urdaibai) of the Basque coast, with different level of anthropogenic impact. Effect of the environmental variables upon the morphology of A. clausi females on a small geographic scale is discussed. In general, biometric variables showed no significant differences between the two estuaries, but dry weight and condition factor were significantly higher in the estuary of Urdaibai at 35 and 34 psu, whilst at 33 psu they were higher in Bilbao. Body dimensions decreased significantly with decreasing salinity in both estuaries, however, no similar trends were observed for dry weight and condition factor. Temperature appeared the main variable to account size variations, but once eliminated seasonal effect of the temperature body size was related with oxygen concentration in the estuary of Bilbao and with salinity in Urdaibai. This study reveals that morphological characteristics of A. clausi not are only dependent on the temperature, but also, within a limited geographical zone, on local differences in environmental variables, mainly salinity and oxygen concentration.     

A major developmental defect observed in several Biscayne Bay,Florida, fish species

Synopsis Stunted or missing dorsal spines or rays, sometimes accompanied by a depression in the dorsal profile, were found in 10 fish species in six families from North Biscayne Bay. The same morphological abnormality occurred inHaemulon sciurus, H. parrai, H. plumieri, Lagodon rhomboides, Archosargus rhomboidalis, Diplodus argenteus, Lutjanus griseus, Kyphosus sectatrix, Sphoeroides testudineus, andLactrophyrys quadricornis. Another morphological abnormality, scale disorientation, was found in six species:H. parrai, L. rhomboides, A. rhomboidalis, L. griseus, andAbudefduf saxatilis. Pugheadedness, jaw deformities, and other abnormalities also were observed. The occurrence of similar deformities across such a spectrum of fishes from the same location suggests the deformity was induced by something in the environment common to all these species. Although there could be other explanations for the unusual cluster of abnormalities, it is suspected that the same environmental contaminant or group of contaminants is adversely affecting a common developmental pathway of these fishes. Biscayne Bay is an urban estuary that receives agricultural, industrial, and residential run off.     

Some reflections on the structure of the mandibleplate ofEurytemora affinis (Copepoda,Calanoida)

The mandibleplates of several specimen of the copepodEurytemora affinis collected from the Westerschelde and the Gironde estuary were studied. Using the Edge index (ITOH, 1970) this species could be classified as an omnivore. Pictures obtained by light and scanning electron microscopy reveal that the mandible teeth ofE. affinis have a molar-like structure, which likely changes in functional morphology with developmental stage, sex and age of the adults. Based on these observations, the desirability to consider the three dimensional structure of copepod mandibles for feeding mode classification is discussed.Communication no. 540 of the Delta Institute for Hydrobiological Research, Vierstraat 28, 4401 EA Yerseke, The Netherlands.     

Feeding rates and productivity of the copepod Acartia bifilosa in a highly turbid estuary; the Gironde (SW France)

Acartia spp. are the dominant copepod species in the Gironde estuary, seaward of the turbidity maximum area. Acartia bifilosa develop a large population in spring and early summer whereas Acartia tonsa appear in late summer. High values and high variability of chlorophyll a/suspended particulate matter ratio are found seaward of the turbidity maximum area. Feeding rates of A. bifilosa were measured by fluorometry. Phytoplankton ingestion was found to be highly variable, between 8 to 80% of copepod carbon body weight. Except for adult females, copepods were heavier in summer than in winter. PB ratios, estimated by the instantaneous growth rate method, varied from 0.03 d^–1 to 0.14 d^–1. The gut contents and P/B ratios of Acartia bifilosa were related to chl a/SPM ratio. From those data, and a few obtained for A. tonsa, it is concluded that only in summer months phytoplankton ingestion is enough to maintain secondary production.     

Variation in the breeding system of two sympatricDombeya species on La Réunion island

The high frequency of dioecy on oceanic islands has attracted a great deal of attention in plant evolution. In this study we quantify variation in the breeding system of two sympatricDombeya species on La Réunion island. BothDombeya species are cryptically dioecious, each sex retaining non-functional morphological structures of the other sex. One species is strictly dioecious, whilst the other shows leaky dioecy, with 8/13 males producing fruit during two years of study. Males that set fruit did so following outcrossing but not after self-pollination despite the growth of self-pollen tubes in the style. This suggests the occurrence of a late-acting self-incompatibility system. Several morphologically intermediate individuals are recognized and suggested to be a result of interspecific hybridization. These purported hybrids are hermaphrodite and self-compatible, consistent with a complementary breakdown in dioecy and self-compatibility.     

Is the copepod egg production in a highly turbid estuary (the Gironde, France) a function of the biochemical composition of seston?

The influence of the biochemical composition of particles originating from surface waters of the Gironde estuary on egg production rates of Eurytemora affinis zooplanktonic population was studied. In the high turbidity zone, suspended particulate matter had a low nutritional quality because the easily available organic fraction represented less than 15% of the overall particulate organic matter. In waters located seaward of the high turbidity zone, a slight increase in nutritional quality was observed. As a result, the sum of easily extractable organic macromolecules represented 15 to 33% of the overall particulate organic matter. The present study suggests that the low egg-production rate of Eurytemora affinis, occurring in the high turbidity zone, results from combined effects of temperature and bad feeding conditions in the area. Low copepod production can be explained by little phytoplankton growth due to light limitation and, therefore, restricted food availability, as well as difficulties in food selection, non-living particle may being dominant.     

Composition, temporal changes and ecological guild classification of the ichthyofaunas of large European estuaries – a comparison between the Tagus (Portugal) and the Elbe (Germany)

Fish species densities from 1025 hauls obtained with beam trawl and stow net catches from the southern Tagus and northern Elbe estuaries were analysed for two different periods of time between 1978 and 1997. The data were related with environmental factors to compare species composition and densities, contributions of different ecological guilds, structuring environmental key factors, intra‐annual cyclicity and interperiodical stability of ichthyofaunas in large European estuaries at different latitudes. Although the total number of species in both the Tagus and Elbe estuaries (Tagus: 57 species, Elbe: 58 species) was very similar, significant differences were estimated in species compositions, species densities and number of species, and individuals of the different ecological guilds between both estuaries. A total of 15 species occurred in both estuaries but only two of these species, the catadromous Anguilla anguilla and the marine estuarine opportunist Pleuronectes flesus, contributed substantially to the total abundance. Marine species together contributed more than 5% of the total number of species in the Tagus and Elbe estuaries, whereas their contribution in number of individuals amounted to 22% in the Tagus and only 9% in the Elbe. In terms of number of individuals, the ichthyofauna of the Tagus estuary was dominated by estuarine species (especially Pomatoschistus spp.) contributing 68% of the total abundance. In contrast, the fish fauna of the Elbe estuary was dominated by high numbers of anadromous species (88%) individuals, especially Osmerus eperlanus. Canonical corresponding analyses (CCA) indicated that, besides intra‐annual variables, salinity and mouth distance were two of the most important environmental factors structuring the fish communities in both estuaries. Moreover, water depth was found to be an important environmental factor in the Tagus estuary, whereas the water temperature substantially affected the ichthyofaunal composition in the Elbe estuary. In both estuaries, contributions by number of species and number of individuals of the different ecological guilds were not statistically different between the two periods considered, 1978–80 and 1995–97 for the Tagus, and 1981–86 and 1989–95 for the Elbe. Nevertheless, from 1981–86 until 1989–95 a remarkable increase of about 4.5 times in the densities of O. eperlanus was observed in the Elbe estuary, probably related to improved water quality, especially of oxygen conditions in the nurseries since 1990. This was also supported by the results of CCA, suggesting important influences of the years 1989 and 1990 on the Elbe estuary fish assemblage. Climate change as a result of global warming may be evident for the observed changes of the densities of P. flesus which decreased in the southern Tagus estuary and, in contrast, increased in the northern Elbe estuary during comparable periods of time. It is recommended to use the ecological guild classification scheme which was applied for the Tagus and Elbe estuaries for further studies of European estuarine fish assemblages.     

Bicephality,a seldom occurring developmental deformity in Tegenaria atrica caused by alternating temperatures

The experiment was aimed at demonstrating the relationship between deformities of the front part of the prosoma accompanied by changes in the brain structure in bicephalous Tegenaria atrica and exposure of their embryos to temperature fluctuations. By exposing spider embryos to alternating temperatures of 14 and 32 °C for the first 10 days of embryonic development, we obtained eight two-headed individuals, subsequently divided into three groups according to morphological differences. We described in detail morphological abnormalities of the prosoma identified in members of each group. Histological examination confirmed a close relationship between morphological deformities and the brain structure of teratogenically changed spiders. The fusion of appendages (pedipalps and chalicerae) was accompanied by the fusion of corresponding ganglia. The absence of appendages (pedipalps) was accompanied by the absence of corresponding ganglia. This correlation may have resulted from previously impaired neuromere development which led to changes in the morphological structure of the prosoma. Since no deformities were identified in control animals, it can be concluded that bicephaly was caused by exposing embryos to alternating temperatures.     

Grazing impact of micro- and mesozooplankton during a spring situation in coastal waters off the Gironde estuary

The aim of this study was to characterize the grazing link betweenphytoplankton and zooplankton. Quantifying rates of phytoplanktonutilization by micro- and mesozooplankton is an attempt to understandthe control of phytoplankton populations in marine ecosystemsand the export flux of organic matter to the depths. Sampleswere taken in the plume of dilution of the Gironde estuary duringspring (May 1995). The mesozooplankton community was dominatedby the heterotrophic dinoflagellate Noctiluca scintillans andby copepods. Our estimates showed that on average, 26% of thetotal primary production was grazed daily by mesozooplankton.However, the pressure exerted by microzooplankton on the primaryproduction was estimated to be approximately four times higher.As a consequence, during this spring situation in the plumeof dilution of the Gironde estuary when small cells dominated,microzooplankton represented the most important grazing communityand could potentially control the growth of phytoplankton.     

Biomonitoring of trace metal contamination in mangrove-lined Brazilian coastal systems using the oyster Crassostrea rhizophorae: comparative study of regions affected by oil, salt pond and shrimp farming activities

The oyster Crassostrea rhizophorae has been used as a biomonitor of trace metal contamination in two Brazilian coastal systems. C. rhizophorae were collected in January 1998 from 15 stations (from 4 coastal inlets (including 1 estuary) and 1 coastal beach) near Macau, Rio Grande do Norte (RN), Brazil, a region affected by the activities of the oil industry and salt manufacture in coastal salt ponds; oysters were also collected in September 1999 from 8 stations in the Curimatau estuary (RN), an estuary becoming increasingly affected by shrimp farming activities. C. rhizophorae is a net accumulator of trace metals and can be used as a biomonitor, the accumulated soft tissue concentrations representing integrated records of bioavailable metal over the life of the oyster. At Macau, significant differences in oyster accumulated concentrations (and hence bioavailabilities to the oyster) of Fe, Zn, Cu, and Mn were found between stations; raised zinc availabilities at the coastal site are in close proximity to oil industry activities but the very high availabilities of Fe, Cu and Mn in the Rio dos Cavalos estuary originate from an unknown source. In the Curimatau estuary, bioavailabilities of Mn, Pb and Cd, but particularly of Cu and Zn, to the oysters are raised at the two most downstream sites, the only sites below the effluent of a large shrimp farming enterprise. The oysters also act as a local food source, and concentrations of Zn, Cu and Pb of some of the oysters are above typical public health recommended limits.     

Hybridization and genetic variation in Danish populations of European crab apple (Malus sylvestris)

The aim of the present study was to investigate the genetic variation in Danish populations of the endangered European crab apple (Malus sylvestris). Special emphasis was given to hybridization between the wild species and its cultivated relative Malus ×domestica. A total of 178 wild individuals from four Danish populations were studied along with a reference sample of 29 old cultivars. The genetic variation within and among samples was studied at ten microsatellite marker loci. Additionally, a morphological analysis was carried out to identify hybrids and test for correspondence between phenotypic and genotypic indices of hybridization. From application of ordination and a model-based cluster analysis to the molecular data, two clusters were identified consisting of wild and cultivated individuals, respectively. This indicates that pronounced admixture between the two species is not present. At the population level, a high correspondence was found between geographic isolation from M. ×domestica and genotypic and morphological indices of hybridization. As expected, isolated populations appeared less affected by hybridization than poorly isolated populations. Isolated “pure” M. sylvestris populations could thus be identified. However, morphological and molecular evidences of hybridization were found to be divergent at the individual level. This is suggestive of some historical introgression into the M. sylvestris gene pool and indicates that relying exclusively on either morphological or molecular characters as diagnostic markers in studies of hybridization between M. ×domestica and M. sylvestris might lead to fallible results. Combined application of genetic and morphological markers is therefore recommended.     

Recruitment and year-to-year variability in a population of Macoma balthica (L.)

Because of methodological problems, macrobenthic studies usually neglect the juvenile stages of invertebrate communities, due to the fact that appearance of recruits in samples is only detected some weeks or even months after their true recruitment. During this period, the temporary meiobenthos undergoes high rates of mortality. From year to year, juvenile survival rate is thus responsible for temporal patterns observed in adult population densities.The results presented here relate to the population dynamics of the tellinid bivalve Macoma balthica (L.). A study of temporary meiobenthos was conducted over two consecutive years in an intertidal Macoma-community located at the mouth of the Gironde Estuary in southwest France. Sampling of juvenile stages required short intervals (2 weeks) between successive samplings and a fine sieving mesh size (63 µm). Other population parameters, such as temporal patterns in density, reproductive cycle, and individual growth, were recorded.Recruitment processes showed a year-to-year variability, with regard to settlement density, settlement period, and survival rate. In 1983, recruitment was moderate and protracted over several months. Only one main recruitment period was detected in 1984, resulting in a high juvenile density. In a previous study (1977), by contrast, recruitment was almost non-existent.This variability is discussed as a function of climatic and sedimentological conditions which prevailed in the estuary throughout the study period. However, none of these physical factors appeared to underlie the recruitment fluctuation in Macoma balthica. It is suggested that biological interactions are of prime importance in regulating population densities in this community.     

From horticultural plantings into wild populations: movement of pollen and genes in <Emphasis Type="Italic">Lobelia cardinalis</Emphasis>

The Southern Grassland biome in Brazil has long been neglected by the government and by the scientific community as well. Lack of studies about the effects of disturbance (mostly fire and grazing) on plant community and populations are the main hindrances for the future management plans, which complicates the conservation of this rich and unique biome. In this study, the population biology of a rosette species, Eryngium horridum (Apiaceae), has been investigated, in order to compare the effects of fire, grazing and abandonment. E. horridum is a very common species and many farmers consider it a nuisance. Two different areas were chosen for the study purposes: Morro Santana and the Research Center Pró-Mata. Areas under different types (fire and grazing) and disturbance histories were compared. Populations were analysed in plots of 25 m², divided in age-state classes (seedlings, young, adult and reproductive individuals). Both morphological and phenological traits have been investigated. Fire influenced populations in a direct way, whilst grazing showed an indirect effect. Seedlings were found only in areas excluded from disturbance for 3 years on Morro Santana. Due to this, seedling establishment might be more related to environmental conditions than to disturbance regimes. Young individuals were mainly found in recently burned areas, while adult individuals were dominant in areas excluded from disturbance. Additionally, individuals from E. horridum showed a great capacity of resprouting after plant damage. Reproductive individuals also showed the capacity of producing new rosettes after the death of the inflorescence axis. This strategy is probably of great importance for the survival of populations in areas excluded from disturbance. Therefore, vegetative reproduction seemed to be the most important strategy for the maintenance and survival of its populations, allowing longer population persistence over time, even in the absence of disturbance.     

Comparative spring distribution of zooplankton in three macrotidal European estuaries

The zooplankton of three european estuaries (Ems, Gironde and Westerschelde) was investigated during spring 1992 by means of samples taken along the salinity gradient. The three estuaries are comparable in terms of total area, flushing time and salinity gradient but differ by their level of eutrophication (highest in the Westerschelde), suspended matter concentration (highest in the Gironde) and potential phytoplankton production (highest in the Ems). Copepods and meroplankton dominated the zooplankton in the three estuaries. The dominant copepod species were Eurytemora affinis and Acartia bifilosa. The distribution of E. affinis along the salinity gradient differed between the estuaries. Peaks of abundance were observed at 0 PSU in the Gironde, 6 PSU in the Ems and 9 PSU in the Westerschelde. The downstream shift of the population in the Westerschelde was likely due to anoxic conditions occurring in the oligohaline zone. In the Gironde the downstream distribution of E. affinis was limited by the very high suspended matter concentration found in the maximum turbidity zone. Whatever the estuary, the parameters of the population of E. affinis and maximum abundance values were similar. However, the influence of the better quality of the available food was suggested in the Ems where individual dry weights and egg production were higher than in the two other estuaries. The influence of a good quality of food in the Ems was confirmed by the development of a large population of Acartia bifilosa (as abundant as E. affinis) and highest values of adult individual weights.The meroplankton (essentially Polychaete and cirripede larvae) was much more developed in the Ems than in the Westerschelde and Gironde. This was likely due to the large extent of mudflats and hard substrates in the Ems favouring adult settlement and hence the number of larvae locally produced.     

Distribution of phytoplankton pigments in nine European estuaries and implications for an estuarine typology

Phytoplankton pigments were studied by LiquidChromatography (HPLC) in nine West Europeanestuaries. Three estuaries, i.e. the Rhine,Scheldt and the Gironde were sampled four timesto cover the different seasons, whereas theother six estuaries were sampled once. Pigmentdistributions in estuaries reflect bothriverine inputs as well as autochthonousblooms. Fucoxanthin was the most commonaccessory photosynthetic pigment showing thatDiatoms were the most common group in thestudied estuaries and were particularlydominant during autumn and winter. In the veryturbid Gironde estuary, degradation processeswere predominant between salinities 1 and 20,while Diatoms, Dinoflagellates and Cryptophytesbloomed above 20 salinity during spring andsummer. This contrasted with the highlyeutrophic but less turbid Scheldt, wherephytoplanktonic blooms occurred at lowsalinities close to the city of Antwerp. In theScheldt, we observed both a tenfold fluctuationof phytoplankton biomass and a fluctuatingpigment diversity index. In contrast,chlorophyll a was always low in theGironde, but we observed large variations ofpigment diversity among samplings duringdifferent seasons. Distribution of pheopigmentsshowed that the maximum turbidity zone (MTZ)was a highly reactive region for heterotrophicphytoplankton degradation. The Scheldt and theThames were the most anthropogenic influencedestuaries contrasting with the Gironde estuarythat has a less urbanised watershed. Anestuarine typology is proposed based on threeclusters emerging from a correspondenceanalysis of pigment variables and variablescharacterising the anthropogenic impact andphysical forcing.     

Use of metallothionein in gills from oysters (Crassostrea gigas) as a biomarker: seasonal and intersite fluctuations

The use of oyster gills for the analytical determination of metallothionein (MT) concentration as a biomarker of metal exposure was investigated. Temporal variations in MT and metal concentrations (which can interfere with inter-site differences) were examined over a 7 month period (from spring to autumn) in Japanese oysters from a clean site (Bay of Bourgneuf, France) and a metal-rich site (Gironde estuary, France) as well as in individuals translocated from the clean to the contaminated area. The ratio between the annual average of MT concentrations in specimens from the clean and the metal-rich sites was 1.3. During the last 3 months of the experiment, significant differences were no longer registered between transplants and residents from the Gironde estuary. Metals concentrations in oyster gills differed consistently between the clean and the metal-rich sites (annual average ratios of 1.5, 2.7 and 9.8, respectively, for zinc, copper and cadmium) and a fast increase in metal concentrations (over a few months) was observed in transplants, mainly for cadmium. MT and soluble metal concentrations were found to be positively and significantly correlated over the period of the study. This relationship is a positive argument for a possible use of gill MT concentration as a biomarker of metal pollution in contrast to previous findings on the digestive gland, there being a smaller amount of seasonal variability in the weight of oyster gills.     

Occurrence of vertebral deformities in Gobiidae (Pisces) from the Tagus estuary

In four species of gobiid fish caught in Tagus estuary during 1996, the incidence of skeletal deformities ranged from 2 to 5%. Differences between sampling stations or between the two most abundant species Pomatoschistus minutus and Gobius niger were statistically not significant (p > 0.05). The type of deformity depended upon species. P. minutus and P. microps showed bone nodules at the inferior side of the abdominal vertebrae, whilst G. niger and G. paganellus had shortened caudal vertebrae (achondroplasia) and deformed ural plates. The possible role of pollution or other conditions in the Tagus estuary is discussed.