Emma Orive

Causes, historical development, effects and future challenges of a common environmental problem : eutrophication

The impact of the presence of us humans as well as our activities to nature has led to over-exploitation of natural resources and to dramatic changes in land-use including the use of artificial fertilizers contributes to the deterioration of the natural environment. The population density, industrial processes and the use of fertilizers are the main causes for the eutrophication of river systems, estuaries and seas. There are several ways to determine the actual nutrient levels back to the 1950s, back to 1900 or even back to 1800. Available data indicate that the natural background concentrations of nutrients (pristine conditions or the period prior to the widespread use of artificial fertilizers and detergents) were dramatically lower than today. Available time series on chemical and biological data collected from different parts of the world show the (sometimes tremendous) increase in nutrient levels and the related productivity. The same time series, however, also show the decreases in values when measures were taken to reduce the nutrient emissions. Investigations of different systems all over the world show that nearly every system responses differently to eutrophication. Especially physical boundary conditions play an important role in the manifestation of the ultimate effect of local eutrophication. Apart from the physical boundary conditions also the transformation and retention of nutrients in estuarine and coastal systems contribute to system specific responses. Depending on all these different conditions, site specific responses with even site specific problems may occur. The challenge of this millennium is to really reach a balance between nature and mankind including its population size. A beneficial step in this discussion is assessing criteria to reduce eutrophication back to a level acceptable to both humans and nature.

Morphological and genetic characterization of benthic dinoflagellates of the genera Coolia, Ostreopsis and Prorocentrum from the south-eastern Bay of Biscay

Benthic dinoflagellates of the genera Coolia, Ostreopsis and Prorocentrum isolated from coastal waters of the south-eastern Bay of Biscay were identified morphologically by means of light microscopy (LM) including epifluorescence microscopy, and scanning electron microscopy (SEM). To identify the strains to species level, molecular phylogenetic analyses using the nuclear large subunit rDNA (LSU) were performed for 16 strains of the three genera. These morphological and phylogenetic analyses revealed the presence of the following species: Coolia canariensis S. Fraga, Coolia monotis Meunier, Ostreopsis cf. siamensis Schmidt, Prorocentrum emarginatun Fukuyo, P. lima (Ehrenberg) Dodge, P. rhathymum Loeblich III, Sherley & Schmidt, and two as yet unidentified species, which in the phylogenetic tree were grouped with different strains of Prorocentrum emarginatun and P. fukuyoi Murray et Nagahama from GenBank. A strain from Minorca (Balearic Islands, western Mediterranean Sea) analysed in this study for comparative purposes and fitting morphologically into the P. emarginatum/P. fukuyoi group also appeared in this cluster, which seems to include morphologically cryptic or semicryptic species. The most common taxa were Coolia monotis, Ostreopsis cf. siamensis and Prorocentrum lima, which appeared at most sampling sites. Only the strains corresponding to Ostreopsis cf. siamensis and Prorocentrum lima were toxic to Artemia franciscana.

Primary plankton production, respiration and nitrification in a shallow temperate estuary during summer

Abstract Patterns of longitudinal and temporal variation in rates of primary production, respiration and nitrification were investigated in the Urdaibai estuary during August 1994. Rates of primary production, as measured with the 14C technique, varied between 0.002 and 2.828 mg C l−1 d−1. 14C and oxygen based rates of primary production showed a good correlation, but photosynthetic quotients (mean PQ of 2.2) were higher than expected from considerations of the N source used by the algae. Chlorophyll a biomass showed an inverse correlation with salinity and tidal flushing is hypothesized to be a major controlling factor of its spatial variability. Temporal variations in chlorophyll a concentration were associated primarily to changes in the lunar cycle and following rain events. Rates of community respiration varied between 0.154 and 6.857 mg O2 l−1 d−1 and were significantly and positively correlated with both bacterial abundance and chlorophyll a concentration. The relationship between respiration and primary production suggested that respiration rates based on substrates not associated with the autochthonous pelagic primary production increased greatly from the outer to the inner estuary and that the consumption of autotrophic production by heterotrophs in the water column was higher in the less productive outer estuary than in highly productive intermediate and inner areas. Except at the innermost station, temporal variations in respiration rates followed variations in temperature. The ratio of gross primary production to respiration ( GP R ) showed marked spatial and temporal variations, ranging from 0.24 to 17.94. Rates of nitrification, measured as allylthiourea sensitive rates of CO2 fixation, varied from undetectable levels to 9.3 μg C l−1 d−1.In general, highest rates of nitrification were observed at the inner estuary under conditions of elevated ammonia concentration, high bacterial abundance and high turbidity. Rates of nitrification were frequently associated with the > 3 μm size fraction. Oxygen consumed in nitrification was estimated to account on average for 4.7 ± 8.3% of total oxygen consumption.

Seasonal dynamics of ciliated protozoa and their potential food in an eutrophic estuary (Bay of Biscay)

Ciliate assemblages, together with phytoplankton and heterotrophic nanoflagellates (HNF) as their potential food, have been surveyed monthly along the salinity gradient of the Nervion River estuary from March 2000 to March 2002. A total of 135 taxa of ciliate have been identified corresponding to 20 orders. Scuticociliates, naked choreotrichs and oligotrichs were the most abundant groups, distributed throughout a broad range of salinity. In addition to these groups, which were the dominant taxa in the middle estuary, tintinnids were characteristic of the ciliate assemblages of the outer estuary whereas in the innermost part naked choreotrichs and oligotrichs decreased in number, being substituted by sessilids, hymenostomatids, peniculids and cyrtophorids. Total ciliate concentrations were among the highest reported in the literature for other estuaries and coastal waters, frequently reaching 10 5 cells l � 1 . Meanwhile, tintinnid concentrations were comparable with those of other estuarine and coastal waters. Based on a principal component analysis (PCA) three main groups were delineated, with ciliates and their potential food sources as variables. One was that constituted by freshwater ciliate such as sessilids, hymenostomatids, cyrtophorids and pleurostomatids, which appear in low numbers in the innermost part, mainly in winter. Another group contained diatoms, chlorophytes, flagellates, euplotids and scuticociliates, all of them broadly distributed along the estuary and reaching their maximum density in late spring- summer. The third group was made up of taxa mainly appearing at the seaward end such as dinoflagellates, cyanobacteria, haptorids, tintinnids, naked choreotrichs and oligotrichs, which reached the highest densities in summer and early autumn. Ciliates do not seem to be food limited in the Nervion River estuary or much controlled by metazoan grazing. 2003 Elsevier Ltd. All rights reserved.

Seasonal variations of diatoms and dinoflagellates in a shallow, temperate estuary, with emphasis on neritic assemblages

Seasonal changes in the diatom and dinoflagellate assemblages were examined in the neritic zone of the Urdaibai estuary (north Spain) with regard to some major physical and chemical variables during an annual cycle. A total of 81 diatoms and 38 dinoflagellates were identified and quantified during the study period. Both groups displayed a distinctive pattern of seasonal succession. The seasonal distribution of the Shannon index showed a trend of increasing values from the upper estuary to the lower neritic segment. The diatom diversity maxima were observed in February, April and September, and dinoflagellate maxima in April–May, July and October. Diatoms dominated the assemblages, reaching 1×106 cells l−1 from April to September. A shift from large diatoms and dinoflagellates to small bloom-forming taxa was observed during winter–early spring. A spring diatom bloom composed of Rhizosolenia spp. was observed in April, while small chain-forming taxa (chiefly Chaetoceros spp.) dominated from June to September. Cell maxima for both groups in late summer were produced by the diatoms Chaetoceros salsugineum and Skeletonema costatum, and by the dinoflagellates Heterocapsa pygmaea and Peridinium quinquecorne. Silicate availability by river supply and strong tidal-mixing of the water column seem to determine the year-round dominance of diatoms over dinoflagellates.

Phytoplankton assemblages and their dominant pigments in the Nervion River estuary

In the Nervion River estuary surface samples were taken from March to September 2003 at six sites covering most of the salinity range with the aim to know the biomass and taxonomic composition of phytoplankton assemblages in the different segments. Nine groups of algae including cyanobacteria, diatoms, dinoflagellates, chlorophytes, prasinophytes, euglenophytes, chrysophytes, haptophytes, raphidophytes and cryptophytes were identified by means of a combination of pigment analysis by high-performance liquid chromatography (HPLC) and microscopic observations of live and preserved cells. Diatoms, chlorophytes and cryptophytes were the most abundant algae in terms of cells number, whereas fucoxanthin, peridinin, chlorophyll b (Chl b) and alloxanthin were the most abundant auxiliary pigments. Based on multiple regression analysis, in the outer estuary (stations 0, 1, 2 and 3) about 93% of the chlorophyll a (Chl a) could be explained by algae containing fucoxanthin and by algae containing Chl b, whereas in the rest of the estuary most of the Chl a (about 98%) was accounted for by fucoxanthin, Chl b and alloxanthin containing algae. The study period coincided with that of most active phytoplankton growth in the estuary and fucoxanthin was by far the dominant among those signature pigments. Several diatoms, chrysophytes, haptophytes and raphydophytes were responsible for fucoxanthin among identified species. Besides, dinoflagellates with a pigment pattern corresponding to chrysophytes and type 4 haptophytes were identified among fucoxanthin-bearing algae. Cryptophytes were the most abundant species among those containing alloxanthin. The maximum of Chl b registered at the seaward end in April coincided with a bloom of the prasinophytes Cymbomonas tetramitiformis, whereas the Chl b maxima in late spring and summer were accounted for by prasinophytes in the middle and outer estuary and by several species of chlorophytes in the middle and inner estuary. Other Chl b containing algae were euglenophytes and the dinoflagellate Peridinium chlorophorum. Dinoflagellates constituted generally a minor component of the phytoplankton.

Plankton responses to hydrological changes induced by freshets in a shallow mesotidal estuary

Daily variations in the plankton community of the Gernika estuary (Bay of Biscay) were studied over three week-long periods in order to evaluate the effects of large increases in river runoff due to intense rain pulses. Both tidal and river inflow changes determined the hydrological zonation within the estuary during the study periods. Chlorophyll a appeared to be related to riverine inputs and resuspension processes rather than to phytoplankton growth dynamics. The spatio-temporal distributions of plankton assemblages were related to hydrological conditions. Thus, a successional progression involving short-term interactions among plankton populations was severely affected by increased river discharge. Freshets removed neritic populations and returned the plankton community to an initial state. As hydrological conditions became more marine, the progression towards a community with metazoan predominance was paralleled with a rise in neritic plankton abundance further up the estuary. The development of estuarine populations, which can reach high densities under stable conditions, seemed to be limited by frequent river runoff disturbances occurring in this estuarine system.

The genus Pseudo-nitzschia (Bacillariophyceae) in a temperate estuary with description of two new species: Pseudo-nitzschia plurisecta sp. nov. and Pseudo-nitzschia abrensis sp. nov.

The genus Pseudo‐nitzschia contains potentially toxic species of problematic taxonomy, making it one of the most intensively studied diatom genera. The study of 35 clonal strains isolated from the Bilbao estuary, an area that experiences recurrent blooms of Pseudo‐nitzschia, revealed the presence of two new species, P. abrensis and P. plurisecta, differing from their congeners in both morphology and gene sequence. The morphological features were analyzed by LM and EM, whereas molecular analyses were based on the internal transcribed spacer (ITS) and large subunit (LSU) regions of the rDNA. P. plurisecta appears closely related to P. cuspidata/P. pseudodelicatissima in the phylogenetic tree, whereas P. abrensis forms a moderately supported clade with P. heimii/P. subpacifica and P. caciantha/P. circumpora. Comparison of the secondary structure of ITS2 regions reveals marked differences in the most highly conserved regions among related taxa. Morphologically, the new species differ from their closest congeners in the arrangement of the poroid sectors and the density of valve striae and fibulae. The two species share similar pigment composition, and belong to the group of Pseudo‐nitzschia species containing only chlorophyll c2 and c3.

Assessing river water quality by means of multifactorial methods using macroinvertebrates. A comparative study of main water courses of Biscay.

Abstract Ninety two taxa of benthic macroinvertebrate were used to ordinate 175 sites from main water courses of Biscay (Basque Country) by means of correspondence analysis (CA). On the plane of the first two axes from CA, changes in macroinvertebrate community structure were observed between rivers due to differences in natural eutrophication and also as a result of the combined effect of industrial and urban sewage. The groups of taxa observed could be interpreted in ecological terms and were representative of headwater reaches, moderately eutrophic waters and polluted waters, respectively. This method of ordination provides more information on differences in water quality among the non-polluted sites than does a biotic index (BMWP score).

Day-to-day variability in the plankton community of a coastal shallow embayment in response to changes in river runoff and water turbulence

Abstract The day-to-day variations over a 17-day period in the plankton community of a shallow embayment located in the Basque Country (Bay of Biscay) were studied and related to changing environmental conditions. Fluctuations in river runoff due to several rain pulses determined most of the changes in the chemical properties of the embayment. Other physical forcing functions like wave originated high turbulence in the water column, regulating the quantity and quality of seston and chlorophyll a. As a response to the combined effects of these processes, different patterns of variation were observed in phyto- and zooplankton populations. Skeletonema costatum developed after nutrient inputs into the system and resulted in enhanced primary production levels. Population growth was also controlled by turbulence, while the disappearance of this pulse could be associated with the depletion of silicate. Zooplankton abundance fluctuations can be explained mainly by their motility to avoid the environmental stress imposed by water turbulence and sediment resuspension.