Estuarine Coastal and Shelf Science

Published by Elsevier
Online ISSN: 1096-0015
Publications
Article
A three-dimensional ocean circulation model is used to investigate the hydrodynamics of a tidal inlet and deltas system in Southeast Florida, and to understand the consequences for suspended and bedload sediment transport patterns. The model reproduces observed tidal currents and provides insight about residual currents caused by spatial asymmetries in the inlet throat and tidal deltas during ebb and flood flows. A particle-tracking approach for suspended and bedload sediment transport is used to simulate deposition patterns for different particle sizes. The simulation results qualitatively correlate with the distribution of sediment characteristics within the tidal inlet and deltas system and demonstrate sensitivity to the choice of advection velocities (e.g., near-bottom versus depth-averaged) and regions of sediment origin. Furthermore, the distinction between suspended and bedload transport as a function of particle size indicates significant differences in deposition patterns and their potential connection to geomorphologic features of the tidal inlet and deltas system.
 
Article
The concentrations of129I and127I were determined in archived time series seaweed samples from Klint in the Kattegat, Bornholm in the Baltic Sea, Roskilde Fjord in Zealand of Denmark, Utsira in the western Norwegian coast and NW Greenland by neutron activation analysis. The results indicate that the129I levels in all locations investigated are one to three orders of magnitude higher than the fall-out background and strongly dominated by the discharges from reprocessing facilities at La Hague and Sellafield. The129I/99Tc ratio is applied to estimate the origin of and transit times of129I. Transit times of129I are estimated to be 1–2 years from La Hague to Klint and Utsira and 9–14 years to NW Greenland. Transfer factors of129I are calculated to be 54 yr m−3from La Hague to Klint, 60 yr m−3to Utsira and 1·2 yr m−3to NW Greenland. Based on the estimated transit times, transfer factors and annual discharge data of radionulides from the reprocessing facilities, the variations of129I concentrations and129I/99Tc and129I/137Cs ratios are modelled. Except129I/137Cs, others are in a good agreement between the modelled and measured values.
 
Article
The spatial variability of δ13C and δD in four individual Ecklonia radiata plants was determined and the range compared to the range of individual values obtained for co-occuring macroalga species. Carbon values varied over a range of 3–4‰ in three of the E. radiata individuals, while values within another plant were found to vary by 7·43‰. Overall the carbon values ranged from −14·01 to −21·44‰, with a mean of . Hydrogen values however, exhibited a far greater range; within individual plants they ranged from 43·01‰ to 89·43‰. The isotopic range exhibited within E. radiata was half that of the range of carbon and one and a half times that of hydrogen values recorded for the co-occurring species analysed. This reduces the value of the techique for tracing the origin of detrital matter from seaweeds. The pattern of isotopic composition observed in E.radiata suggests differential storage of isotopically distinct compounds.
 
Article
In August 1984, 134Cs originating from the British reprocessing plant Sellafield (formerly Windscale) was found in the waters between Canada and Greenland. The transit time from Sellafield to Baffin Bay is approximately eight years. The concentration in the surface waters in the south-eastern part of Baffin Bay of a pollutant coming from the North Sea is approximately 1% of its concentration in the North Sea. The conclusions based upon the observations of 134Cs are supported by determinations of 99Tc in Greenland fucoids. Enhanced discharges of 99Tc apparently began in 1970, i.e. four years earlier than those of radiocesium. The unreported, annual 99Tc discharges in the 1970s prior to 1978 are estimated to be approximately 40 TBq (⋍ 1 kCi).
 
Article
A wide variety of sedimentary subenvironments are found within a 10-km stretch of James River including a flood dominated channel (Rocklanding Channel) and its bank (Rocklanding Shoal), a shoal with a water depth of 1 m separating two channels (Point of Shoals), an ebb-dominated channel (Burwell Bay Channel) and its bank (Burwell Bay Bank) and a tributary (Warwick River). The concentrations of Cs-137, Cu, Pb, Zn and organic carbon in the fine-grained sediments (i.e. < 63 μm) and the amount of fine-grained sediments in eight cores covering these subenvironments were determined. The sedimentation rates, estimated by Cs-137 geochronology, range from 0·4 to > 3 cm year−1. The sedimentation rates in the Burwell Bay region are two or more, times those in the Point of Shoals and in the Rocklanding Channel and Shoal, reflecting the weaker currents in the Burwell Bay region. These sedimentation rates agree well with those obtained independently by measuring changes in the bathymetry of this area between 1873 and 1943. The concentrations of Cs-137, Cu, Pb, Zn and organic carbon in surface sediments vary by a factor of two to three. The concentrations are higher in the Burwell Bay region, probably as a result of the higher rates of accumulation of recently formed sediments in these subenvironments. The inventories of fine-grained sediments and of Cs-137, Cu, Pb, Zn and organic carbon accumulated since 1954 are also up to an order of magnitude higher in the Burwell Bay region. Although the concentrations of fine-grained sediments in three cores obtained in this region are similar, the inventories still vary by a factor of two to three. The inventories of Cs-137, Cu, Pb, Zn, organic carbon and fine-grained sediments correlate well with each other indicating that Cs-137 can be a useful tracer for studying the fate of these metals and organic carbon in estuarine environments. The inhomogeneity of the concentrations and inventories of the different elements along a 10-km segment of a river suggests that a closely-spaced sampling programme is essential for characterizing the sedimentary provinces within an estuary. The concentrations of Cs-137, metals and organic carbon in the coarse-grained sediments (i.e. > 63 μm) are considerably lower than those in fine-grained sediments. Thus, the contribution of coarse-grained sediments to the total inventory of these elements is small.
 
Article
The vertical distribution of the radio-nuclides 7Be, 137Cs and unsupported 210Pb were used to describe the processes of accretion, mixing, mixing depth and focusing, that influence the responses of intertidal bed sediments to contaminant inputs. These processes were studied in the mid and lower Tamar Estuary at six different sites sampled on eight occasions, over a period of 2 years. The maximum depth to which sediment deposits were mixed ranged from 10 cm to greater than 40 cm. Mixing coefficients derived from the 7Be and unsupported 210Pb profiles ranged from 0·56 × 10−7 to 34·2 × 10−7 cm2 s−1. The sediment inventories of 7Be, 137Cs and unsupported 210Pb, the maximum depths of mixing and the mixing coefficients were significantly higher in the bed sediments of the creek site and at two sites situated 12–14 km up the estuary than those observed at sites situated nearer to the seaward end of the estuary. With the exception of the site closest to the mouth of the estuary, the 7Be inventory at all sites was consistently higher during the period October–November than during the period March–September. Using data derived from the 7Be and unsupported 210Pb sediment profiles, the profiles of 137Cs were simulated and compared with the observed data recorded at each site.
 
Article
Ten sediment cores were collected from Ise Bay, Japan, and excess 210Pb and 137Cs were measured gamma-spectrometrically. Using the constant flux of lead-210 (CFL) model, the temporal and spatial variations of sedimentation rates in Ise Bay were determined. A generally increasing trend in sedimentation rate over the last century, especially since the mid-20th century, was found at all of the locations. The increase in sedimentation rate since the mid-20th century is consistent with the rapid economic growth and corresponding intensification of environmental alteration. The spatial distribution of sedimentation rates is time-independent. The high sedimentation rates were found near the Kiso Rivers mouth, indicating the river input is a main source of sediment. The sedimentation rates in the eastern half of the bay are higher than those in the western half, reflecting the transport pathway of suspended matter. The mean sedimentation rates over the last 40 years derived from both 210Pb and 137Cs methods were roughly consistent. The inventories of excess 210Pb and 137Cs in sediment are accounted for by the direct atmospheric fluxes, except one core near the river mouth.
 
Article
In comparing a control vs. a sewage-affected nearshore site off southern California, the natural relative abundances of 13C, 15N and D in Dover sole and Ridgeback prawn muscle were found to be significantly different. This between-site shift in animal isotope abundance is of the type expected if sewage organic materials were an important food source for animals in the latter site. Use of stable isotope natural abundance to trace the incorporation and movement of sewage-derived organics in marine food webs is suggested.
 
Location of study area, Pearl River delta and estuary, in East Asia (a) and sample sites (b) within the estuary. Surface sediment and winter/summer POC are from the same sample sites. There is no surface sediment from site PE43, no winter/summer POC from site PE1-40, and no winter POC from site PE76 and 77. 
Map of the Pearl River estuary showing location of cluster groups for the estuarine surface sediment samples and POC samples identi fi ed by winter salinity and sand concentration. Groups G1 e G3 are from freshwater areas; groups G4 e G7 are from brackish areas and G8 e G9 are from marine areas. 
Contour map of contribution of TOM to the surface sediment samples. 
Article
Preservation of organic matter in estuarine and coastal areas is an important process in the global carbon cycle. This paper presents bulk δ13C and C/N of organic matter from source to sink in the Pearl River catchment, delta and estuary, and discusses the applicability of δ13C and C/N as indicators for sources of organic matter in deltaic and estuarine sediments. In addition to the 91 surface sediment samples, other materials collected in this study cover the main sources of organic material to estuarine sediment. These are: terrestrial organic matter (TOM), including plants and soil samples from the catchment; estuarine and marine suspended particulate organic carbon (POC) from both summer and winter. Results show that the average δ13C of estuarine surface sediment increases from −25.0 ± 1.3‰ in the freshwater environment to −21.0 ± 0.2‰ in the marine environment, with C/N decreasing from 15.2 ± 3.3 to 6.8 ± 0.2. In the source areas, C3 plants have lower δ13C than C4 plants (−29.0 ± 1.8‰ and −13.1 ± 0.5‰ respectively). δ13C increases from −28.3 ± 0.8‰ in the forest soil to around −24.1‰ in both riverbank soil and mangrove soil due to increasing proportion of C4 grasses. The δ13CPOC increases from −27.6 ± 0.8‰ in the freshwater areas to −22.4 ± 0.5‰ in the marine-brackish-water areas in winter, and ranges between −24.0‰ in freshwater areas and −25.4‰ in brackish-water areas in summer. Comparison of the δ13C and C/N between the sources and sink indicates a weakening TOM and freshwater POC input in the surface sedimentary organic matter seawards, and a strengthening contribution from the marine organic matter. Thus we suggest that bulk organic δ13C and C/N analysis can be used to indicate sources of sedimentary organic matter in estuarine environments. Organic carbon in surface sediments derived from anthropogenic sources such as human waste and organic pollutants from industrial and agricultural activities accounts for less than 10% of the total organic carbon (TOC). Although results also indicate elevated δ13C of sedimentary organic matter due to some agricultural products such as sugarcane, C3 plants are still the dominant vegetation type in this area, and the bulk organic δ13C and C/N is still an effective indicator for sources of organic matter in estuarine sediments.
 
Article
This study focussed on the determination of the main trophic subsidies for three dominant filter feeding molluscs of the benthic community, namely, Crassostrea gigas (Thunberg), Mytilus edulis (L.) and Crepidula fornicata (L.), cultivated or naturally occurring in the Bay of Mont Michel (France). δ13C and δ15N values revealed that the diet of these filter feeders was primarily based on marine plankton together with a lower contribution of the organic matter derived from salt marsh phanerogames, as estimated through the isotopic mixing equations (Isosource). The microphytobenthos inhabiting the intertidal flat and the salt marshes do not contribute significantly to the diet of cultivated and naturally occurring C. gigas and M. edulis. Hence, in this bay, the major trophic pathways differ from previous results obtained in several coastal systems devoted to shellfish culture. This could result from ecological particularities and/or strong hydrodynamic conditions in the Bay of Mont Michel.
 
Article
From January 2003 to December 2004 microphytobenthic primary production was estimated both from in situ (MPPs) and in the laboratory (MPPp) 14C-incubation of slurries collected in a coastal site of the Gulf of Trieste (northern Adriatic Sea). MPPs values varied from −7.54 ± 3.12 to 34.59 ± 7.66 mg C m−2 h−1 over the whole period. The lowest MPPs were observed in November 2003 and August 2004, while the highest MPPs in July 2003 and May 2004, in correspondence with high PAR at the bottom. Significant correlations between MPPs and the microphytobenthic biomass (BIOM) (r = 0.75, p < 0.001), between MPPs and PAR at the bottom (r = 0.54, p < 0.01) and between MPPs and OXY (r = 0.50, p < 0.05) were revealed. MPPp values were higher than MPPs ones in 15 out of 23 observations, with the highest MPPp recorded in July 2003. At 17 m depth a seasonal pattern of sampling months was revealed by the cluster analysis. The role of abiotic parameters in determining this seasonal pattern was highlighted by the PCA, with the first axis correlated with MPPs and PAR, and the second one with temperature. Applying the fuzzy sets it resulted that spring months showed a higher degree of membership with MPPs, summer months with temperature and autumn–winter months with OXY. The microphytobenthic community did not seem to be photosynthetically active throughout the study period. From August–September to December low or negative MPPs values were recorded. We infer that during these months a shift from the autotrophic to heterotrophic metabolism of the benthic microalgae occurred in correspondence with low PAR and/or high temperature at the bottom. Despite the progressive lowering of the trophy of the study area occurred during the last 20 years, we found higher primary production values than those estimated two decades earlier.
 
Article
The 14C tracer technique for phytoplankton productivity measurements is one of the most precise techniques used widely by phytoplankton ecologists. Most researchers overlook the possible interference of high concentrations of chlorophyll a during liquid scintillation counting, particularly in eutrophic ecosystems. Results from this study revealed that an optimal H2O2 volume of 150 μl, when added prior to scintillation counting, was sufficient to overcome an underestimation in phytoplankton productivity of up to 4.3%.
 
Article
Diatom assemblages of the surface and in core sediment samples from Lake Saroma (Japan) were examined for the purpose of evaluating anthropogenic effect on the coastal environmental changes. Before the first inlet excavation, the lake's water quality and ecology were controlled by water exchange with the Okhotsk Sea as well as lake-level variation. However, large-scale ecological modification occurred, mainly due to artificial excavation and shellfish industrial farms. A distinct record of the succession of the dominant diatom taxa was preserved in core sediments. Low-oxygen water was prevalent in the lake in 1929, before the first inlet excavation. Immediately after the first inlet excavation, the low-oxygen water in the western basin of the lake began to disappear, in a trend that became increasing transparent, which has been attributed to an increasing rate of water exchange. However, the lacustrine environment of bottom sediments resumes deterioration 20 years after since the first artificial excavation: the resultant deposition of river-mouth materials into the deep basin caused eutrophication and environmental disturbance of the lake bottom. At the same time, the eutrophication of surface water became intensified with the onset of intense scallop culturing beginning in 1966. Increasing organic loads deposited onto the bottom layer in the form of excreta from the scallop nursery led to more oxygen deficiency and the elution of nitrogen and phosphorus from the sediment, which again brought about eutrophication of the surface layer. Such environmental change was reflected in a decrease of benthic diatom taxa and an increase of planktonic taxa, trends which have continued until today. Particularly, the numbers of diatom assemblage have been decreasing all over the lake during the last 10 years, which suggests that Lake Saroma's present-day deterioration and eutrophication will continue or become even worse.
 
Article
We monitored inherent optical properties in a turbid, eutrophic estuary to determine the factors affecting the temporal variability in water clarity. Time series of absorption and scattering coefficients were measured at 1-h intervals for nearly 2 years. The seasonal pattern in weekly averaged absorption and scattering coefficients in each year was driven primarily by changes in the particulate matter of both biogenic and mineral origin. Temporal patterns in particulate absorption and scattering resulted from identifiable events that differed in relative magnitude between the 2 years: a spring bloom was followed by a transient “clear-water” phase, followed by increases in non-algal particulate matter to a late-summer maximum, and rapid declines of all parameters in late fall. Interannual variability in the spring bloom was governed by timing and magnitude of nutrient inputs from the watershed, while major patterns in summer variability of both organic and inorganic particulate matter appeared to follow the general cycle of biological activity in the system.
 
Article
Carbon and nitrogen stable isotope signatures were used to assess the response of food webs to sewage effluent discharged into two small intermittently open estuaries in northern New South Wales, Australia. One of these systems, Tallows Creek, has a history of direct sewage inputs, whilst the other, Belongil Creek, receives wastewater via an extensive wetland treatment system. The food webs of both systems were driven by algal sources of carbon, reflecting high autotrophic productivity in response to the nutrients entering the system from sewage effluent. All aquatic biota collected from Tallows Creek had significantly enriched δ15N signatures relative to their conspecifics from Belongil Creek, indicating that sewage nitrogen had been assimilated and transferred throughout the Tallows Creek food web. These δ15N values were higher than those reported from studies in permanently open estuaries receiving sewage effluent. We suggest that these enriched signatures and the transfer of nitrogen throughout the entire food web reflect differences in hydrology and associated nitrogen cycling processes between permanently open and intermittently open estuaries. Although all organisms in Tallows Creek were generally 15N-enriched, isotopically light (less 15N-enriched) individuals of estuary perchlet (Ambassis marianus) and sea mullet (Mugil cephalus) were also collected. These individuals were most likely recent immigrants into Tallows Creek, as this system had only recently been opened to the ocean. This isotopic discrimination between resident (enriched) and immigrant (significantly less enriched) individuals can provide information on fish movement patterns and the role of heavily polluted intermittently open estuaries in supporting commercially and recreationally valuable estuarine species.
 
Article
Mangrove ecosystems may be a source of organic carbon and nutrients to adjacent coastal systems on one hand and provide a sedimentary sink for organic carbon on the other. The balance between these two functions may be sensitive to both natural and anthropogenically induced variability, yet these effects have not been thoroughly evaluated in mangrove ecosystems. We determine organic matter sources and carbon burial rates over the past 160 years in three lagoons on the Yucatan Peninsula, Mexico. Carbon isotopes and C/N elemental ratios are utilized to trace the three sources contributing to sedimentary organic matter, mangroves, seagrasses and phytoplankton, while nitrogen isotopes are used to elucidate potential post-depositional biogeochemical transformations in mangrove lagoon sediments. All three organic matter sources contribute to organic carbon burial. Phytoplankton and mangroves are the dominant sources of organic matter in lagoon bank sediments and seagrasses are a significant source to central lagoon sediments. Organic carbon burial rates are higher at the lagoon fringes, where mangrove vegetation dominates, than in seagrass-dominated mid-lagoon areas. A reduction in mangrove contribution to the sedimentary organic matter pool concurrent with reduced total organic carbon burial rates is observed in the recent past at all three lagoons studied. Natural cycles in sediment organic matter source over the past 160 years are observed in a high-resolution core. These fluctuations correspond to climatic variability in this region, as recorded in deep-sea foraminiferal assemblages. Additional work is required in order to differentiate between recent anthropogenic perturbations and natural variability in organic carbon sources and burial rates within these ecosystems.
 
Article
Bacterial communities in eight 16S rDNA clone libraries from calcareous sediments were investigated to provide an assessment of the bacterial diversity on sediments of the Great Barrier Reef (GBR) and to investigate differences due to decreased water quality. Sample effort was spread across two locations on each of four coral reefs, with two reefs located nearshore and two reefs on the outer shelf to allow robust statistical comparison of nearshore reefs (subjected to enhanced runoff) and outer shelf reefs (pristine conditions). Out of 221 non-chimeric sequences, 189 (85.5%) were unique and only one sequence occurred in more than one library. Rarefaction analyses and coverage calculations indicated that only a small fraction of the diversity was sampled. Cluster analyses and comparison to published sequences indicated that sequences retrieved belonged to the α, γ and δ subdivision of the Proteobacteria (6.8, 29.4 and 13.6% of the total, respectively), Cytophaga-Flavobacteria-Bacteroidetes (CFB) group (20.4%), Cyanobacteria (5.4%), Planctomycetaceae (7.7%), Verrucomicrobiaceae (6.8%), Acidobacteriaceae (2.7%). Analysis of Similarity (ANOSIM, based on grouping all retrieved sequences into 9 phylogenetic groups) indicated that subtle differences do exist in the community composition between nearshore and outer shelf reefs. Similarity percentage analysis (SIMPER) indicated that Acidobacteriaceae and Cyanobacteriaceae were the main contributors to the dissimilarity. A significant difference between bacteria on nearshore and outer shelf reefs also existed on the molecular level (FST = 0.008, p = 0.007 for all samples, 0.006, p = 0.022 when repeated sequences within libraries were removed). Thus, bacterial communities on carbonate sediments investigated were highly diverse and differences in community composition may provide important leads for the search for indicator species or communities for water quality differences.
 
Article
Bacteria, as the most abundant sediment organism, play a major role in the fate of pollutants. Therefore, many pollutant-related bacteria have been studied in harbor sediments, yet the entire bacterial profiles have not been reported. The bacterial diversity and community structures from sediments in Victoria Harbor (Hong Kong), including two polluted (VH and VHW) and two adjacent (open oceanic, TLC; estuary discharge affected, PC) sites, were characterized by analyses of four 16S rDNA clone libraries. Upon comparisons of RFLP patterns from 254 clones in the libraries, 178 unique phylotypes were retrieved. LIBSHUFF and Rarefaction analyses indicated that the sediment bacterial communities at the four sites showed high 16S rDNA richness and were significantly different from each other. Phylogenetic analysis of full-length 16S rDNA revealed 19 bacterial phyla in Victoria Harbor sediments. γ- and δ-proteobacteria, holophaga/acidobacteria, and planctomycetales were recorded in all the libraries. In addition, γ- and δ-proteobacteria were dominant at all sites (33.33–11.67%). Besides these two phyla, ε-proteobacteria, firmicutes, aminobacterium, holophaga/acidobacteria and bacteroidetes were judged to be major components of a given library since they constituted 10% or more of the total OTUs of the given library. The cyanobacteria, verrucomicrobia, β-proteobacteria, aminobacterium, chlorofiexi, and candidate division OP1, OP8 were detected in minor proportions in various libraries. A portion of the clones were only distantly related to sequences in the GenBank, suggesting bacteria in Victoria Harbor sediments were unique and diversified.
 
Article
A study of the diurnal and seasonal variation in the physico-chemical conditions within intertidal rock pools on the West coast of Scotland was undertaken to provide data on the environmental conditions experienced by animals inhabiting these pools. The temperature, pH, partial pressure of oxygen (PO2) and salinity were measured every hour for 24 h and the total alkalinity, partial pressure of carbon dioxide (PCO2) and carbon dioxide content (CCO2) calculated. This sampling regime was carried out once a month for 12 months to determine the extent of seasonal variation in conditions within temperate pools.Large diurnal variations were recorded in nearly all the physico-chemical parameters measured. The greatest variation was recorded in the temperature and PO2 of the water but significant changes in pH and PCO2 were also recorded. Total alkalinity varied little during any 24 h period but carbonate alkalinity, which was always lower than total alkalinity, showed slightly greater variation. There was also considerable variation in the magnitude of these diurnal changes between pools at different heights on the shore.Diurnal variation in the physico-chemical conditions within the pools were observed throughout the year although the magnitude of these changes varied seasonally. Detailed studies on individual pools demonstrated that appreciable local variation existed in the physico-chemical conditions within each pool.
 
Article
Life-history parameters and diet of spurdog (Squalus acanthias) sampled from the SE Black Sea were studied. Spurdog from age classes I to XIV were identified, with a dominance of age class VIII for both sexes. The length–weight relationship was W=0·0040*L2·95and the mean annual growth rates in length and weight were 7·2 cm and 540·1 g, respectively. The estimated von Bertalanffy growth parameters were: W∞=12021 (g), L∞=157 (cm), K=0·12 (year−1) and t0=−1·30 (year). The size at first maturity was 82 cm for males and 88 cm for females. Mean biennial fecundity was also found to be 8 pups/female. The relationships between fecundity–length, fecundity–weight and fecundity–age were found to be: F=−17·0842+0·2369*L (R=0·93), F=0·3780+0·0018*W (R=0·89) andF =−0·7859+1·1609*A (R=0·94) respectively. The spurdog can be considered an opportunistic feeder. Their natural diet was composed mainly of teleost fishes, followed by Crustaceans, Nematodes and Actinarians (=sea anemones). Whiting (Merlangius merlangus euxinus) was the predominant prey item among their fish prey. Demersal teleosts formed the majority of the diet, and there was no difference (P>0·05) among the food items of immature, maturing and mature individuals of both sexes.
 
Article
The feeding ecology, growth and spatial–temporal abundance and distribution of Pomatoschistus microps (Krøyer, 1838) and Pomatoschistus minutus (Pallas, 1770) were studied between June 2003 and June 2004, based on beam trawl surveys and macrobenthic samples conducted in the Mondego estuary, Portugal. Polychaetes, molluscs and amphipods were the most important items in the diet of P. microps, while for P. minutus the dominant preys were polychaetes, mysids and decapods. Pomatoschistus microps' recruitment lasted for six months and was composed of three new cohorts per year. Pomatoschistus minutus had an uncommon long reproductive season, from April to November, and population segregation was found, corresponding to the two reproductive peaks. Populations of both species were composed mainly of 0-group individuals with sand gobies presenting a more extended life span. In the Mondego estuary, inter- and intra-specific spatial segregation occurred between the two species and between the 0+ and 1+ age groups of P. microps.
 
Article
A survey was carried out from April 1998 to June 2000 to study the structure of the population and the secondary production of Hediste diversicolor (Copenhagen 32 (1776) 274) in the Loire estuary, Atlantic coast of France. Each month, samples were collected in the intertidal zone of the Mindin harbour. In 1999, the mean annual density was 900±594 individuals (ind.) m−2 with a minimum of 304 ind. m−2 in February and a maximum of 2560 ind. m−2 in April. The mean annual biomass (dry weight) was g m−2 with a minimum of 1.2 g m−2 in January and a maximum of 26.0 g m−2 in July 1999. The density and the biomass of the population of H. diversicolor decreased during winter and increased during spring/summer. Size frequency histograms allowed the analysis of cohorts and gave the growth curves. Two recruitment periods were detected each year, in June/July and October. The secondary production was estimated by the method of Crisp (Methods for the study of marine benthos, Blackwell, Oxford, 1971). From June 1998 to May 1999, with and the ratio and from June 1999 to May 2000, with and . The annual secondary production in 1999 was with and . The differences observed between the 1986–1988 and 1998–2000 populations of H. diversicolor in the Loire estuary are discussed and could be explained by environmental changes, as competition or by migration of individuals.
 
Article
The age, growth and reproduction of an Atlantic population of Atherina boyeri is discussed on the basis of an examination of 2510 specimens from the Guadalquivir river (37°N, 6°25′W). The life-span was short with a winter age structure of 80·4% in 0+ group, 13·2% in 1 + group and 6·4% in 2+ group. Growth was continuous throughout the year except at the peak of the spawning period (March–April). The formation of annuli extended from April to July. The condition cycles (before and after removing gonad weight) were similar for both sexes, with a minimum in May and a maximum in July. The maximum average Gonadosomatic Index (GSI) in females (8%) was twice as high as in males (4%). One-year-old males and females achieved maturity during the spawning season of the following year at an average of 40 mm FL (fork length). A. boyeri successively spawned from March to June with a maximum in April. Longer specimens spawned earlier (January). The fecundity (Fec) of this stock, before the beginning of reproduction, was represented by the formula Fec=0·865 FL (cm)2·486. The overall gender ratio did not differ significantly from 1:1. In this unstable and productive environment A. boyeri displayed the same life-history tactics as Aphanius iberus, Gambusia affinis and Fundulus heteroclitus, three small fish species found in the same area and characterized by fast growth rates, early maturity, frequent spawning over a long breeding season and reduced longevity.
 
Article
Caging and a mark–recapture design were used to estimate the growth rate of the brittle, infaunal bivalve Soletellina alba in the Hopkins River estuary. The growth of both caged and uncaged individuals was monitored at three sites near the mouth of the estuary over 180 days. Growth rates did not differ for caged and uncaged bivalves, or for bivalves subject to different amounts of handling, or between sites. Growth did differ between consecutive time intervals, which was attributable to negligible growth occurring during the colder months of autumn/winter. Comparisons of the condition (as indicated by total mass for length3) of S. alba were inconsistent between sites for caged and uncaged bivalves and for those subject to different amounts of handling. Soletellina alba is a rapidly growing bivalve with mean growth rates for the three time intervals being in summer, in autumn and from summer to winter. Using existing literature, it was shown that a significant relationship exists between maximum shell length and onset of sexual maturity in bivalve molluscs. This relationship predicts that S. alba should reach the onset of sexual maturity at 15.8 mm length. Therefore, it appears that it may be possible for juvenile S. alba (<1 mm) to grow, reach sexual maturity and reproduce in between annual mass-mortality events caused by winter flooding.
 
Article
Red emperor, Lutjanus sebae, were examined from commercial catches in the Northern Demersal Scalefish Fishery (NDSF) of north-western Australia from 1997 to 1999. Specimens ranged from 183 to 728 mm fork length (FL); males had a mean FL of 509 mm, and were significantly larger than females that had a mean FL of 451 mm. Ages were estimated from thin sections of sagittal otoliths. Marginal increment analysis of sagittal otoliths showed a single annual minimum during September and October and indicated that one annulus is formed each year. Male L. sebae (n=977; 211–728 mm FL) ranged from age 2 to 30 years and females (n=1384; 183–584 mm FL) ranged from age 1 to 34 years. Sagittal otolith weight and height were significantly correlated with age for each sex. There was significant differential growth between sexes. The relationship of observed fork length at age was described by the von Bertalanffy growth equation for males, Lt=627·8 {1−exp [−0·151 (t+0·595)]} and females, Lt=482·6 {1−exp [−0·271 (t−0·065)]}. The slow growth, long life span and large size and age at maturity of L. sebae indicate that this species has a low production potential and hence spatial area closures are vulnerable to over-exploitation. The instantaneous rate of natural mortality (M) ranged from 0·104 to 0·122. The optimum rate of fishing mortality was estimated to be 0·052–0·061. The instantaneous rate of total mortality (Z) estimated from catch at age data for fully recruited ages, was 0·374 in 1997/98 and 0·242 in 1998/99. Hence, the NDSF population of L. sebae is exploited above optimum levels. Given their low production potential, populations of L. sebae in north-western Australia and elsewhere in the Indo-Pacific region require prudent management. Furthermore, fishery managers need to consider as part of any harvest strategy for these fish to preserve significant levels of the spawning stock.
 
Article
Analysis of a series of historical bathymetric surveys has revealed large changes in morphology and sedimentation from 1856 to 1983 in San Pablo Bay, California. In 1856, the morphology of the bay was complex, with a broad main channel, a major side channel connecting to the Petaluma River, and an ebb-tidal delta crossing shallow parts of the bay. In 1983, its morphology was simpler because all channels except the main channel had filled with sediment and erosion had planed the shallows creating a uniform gently sloping surface. The timing and patterns of geomorphic change and deposition and erosion of sediment were influenced by human activities that altered sediment delivery from rivers. From 1856 to 1887, high sediment delivery (14.1 × 106 m3/yr) to San Francisco Bay during the hydraulic gold-mining period in the Sierra Nevada resulted in net deposition of 259 ± 14 × 106 m3 in San Pablo Bay. This rapid deposition filled channels and increased intertidal mudflat area by 60% (37.4 ± 3.4 to 60.6 ± 6.2 km2). From 1951 to 1983, 23 ± 3 × 106 m3 of sediment was eroded from San Pablo Bay as sediment delivery from the Sacramento and San Joaquin Rivers decreased to 2.8 × 106 m3/yr because of damming of rivers, riverbank protection, and altered land use. Intertidal mudflat area in 1983 was 31.8 ± 3.9 km2, similar to that in 1856. Intertidal mudflat distribution in 1983, however, was fairly uniform whereas most of the intertidal mudflats were in the western part of San Pablo Bay in 1856. Sediment delivery, through its affect on shallow parts of the bay, was determined to be a primary control on intertidal mudflat area. San Pablo Bay has been greatly affected by human activities and will likely continue to erode in the near term in response to a diminished sediment delivery from rivers.
 
The distribution of Salilota australis as determined by observer and research vessel data.
Monthly changes in the frequency occurrence of various maturity stages of the gonad of Salilota australis (a) females and (b) males.
Changes in rip egg size in female Salilota australis with L T .
Changes in the fecundity of Salilota australis with L T (a) and M T (b).
Changes in batch fecundity of Salilota australis as a function of L T (a) and M T (b).
Article
The reproductive biology of a shelf morid, red cod (Salilota australis) was investigated in the Falkland Islands, in order to expand our knowledge of the reproductive strategy of this relatively unstudied family of fishes. Red cod spawn to the south and south-west of West Falkland between August and October. Length frequency and sex ratio data suggest that females arrive at the spawning grounds first. The greatest spawning activity occurred in early evening and this timing may be an adaptation to reduce predation on eggs. Ripe egg size varied from 0.95 to 1.26 mm and was not dependant on female size. There was no regulative atresia during maturation and the formation of fecundity and fecundity increased with increasing fish total length (LT) from 300,000 (42–45 cm LT) to 4.5–9.0 million eggs (75–83 cm LT). The fecundity of most of the population was between 2 and 5 million eggs. Red cod releases small batches of eggs over the spawning period. Batch size ranged from 30,000–90,000 (39–42 cm LT) in smaller animals to 400,000–800,000 (>75 cm LT) in larger animals and the batch size of first spawners was significantly higher than for advanced spawners. The study allows us to discuss the evolutionary relationships between the Gadiformes.Highlights► The reproductive biology of red cod was examined. ► Red cod spawn to the south of West Falkland between August and October. ► The greatest spawning activity occurred in early evening. ► Fecundity increased with increasing fish length. ► Red cod releases small batches of eggs over the spawning period.
 
Article
The southernmost stable population of Armases (=Metasesarma) rubripes (Brachyura, Grapsoidea, Sesarmidae) is found in Montevideo, Uruguay, in the northeastern coast of the Rio de la Plata estuary. Isolated individuals have seldom been collected in the southwestern coast of this huge estuary. Since pelagic larvae are primarily responsible for the dispersion of A. rubripes, and crab larvae are generally less tolerant than adults to extreme environmental conditions, we tested the survival and intermolt period of zoeae in different combinations of salinity (10, 20, and 30 psu) and temperature (16 and 20 °C). These salinity and temperature conditions are usually found in the estuary and adjacent waters during spring and summer. We found that the survival rate of the larvae increased and they developed faster at 30 psu and 20 °C. It is unlikely that larvae from the Montevideo population of A. rubripes could be transported south and westward due to the hydrographic conditions of the region. The Rio de la Plata seems to function as a biogeographic barrier to A. rubripes, and probably to other crab species as well. However, this barrier is not absolute: it hinders, but does not entirely prevent, the dispersal of larvae.
 
Article
The chemical forms and distribution of dissolved arsenic species in the estuary of the River Beaulieu (Hampshire, U.K.) are reported. ‘Inorganic arsenic (V)’ in both the marine and riverine estuary inputs are in true solution, passing through ultrafiltration membranes having a nominal molecular weight cut-off of 500 daltons. Extensive removal of dissolved ‘inorganic arsenic (V)’ is apparent from the distribution of arsenic in the estuary, with laboratory mixing experiments indicating that removal is favoured in the low salinity region. ‘Inorganic arsenic (III)’ and methylated arsenic species account for up to 41% and 70% of the dissolved arsenic, respectively, but are only found during the warmer months when water temperatures exceed ca. 12°C.
 
Article
Trends of dissolved oxygen content of the surface and bottom layers of the northern Adriatic Sea are analysed for the period 1911–1984. An increase in the surface layer and a decrease in the bottom layer are observed in all seasons except winter. Although the oxygen content of the water column as a whole has not changed significantly, it is inferred, from the increasing difference between the surface and the bottom layer, that the primary productivity of the northern Adriatic Sea is increasing. As the average midsummer oxygen content of the bottom layer decreases, the frequency of mass mortality in the benthic fauna is expected to increase, especially in the northern and western subareas.
 
Mean number (þS.D.) of isopods in four quadrants of containers in the absence of both vegetation and fish. The same letter above each bar indicates no significant differences between quadrants.  
(A and B) Diatoms (Nitzschia spp.), bacteria and fungal threads on the stem of Ruppia maritima. (C) Bacteria and fungal fibres. (D) Bacteria. Key: Ni ¼ Nitzschia spp.; Ba ¼ bacterium; and FT ¼ fungal threads. (Scale bar in A ¼ 10 mm; in B ¼ 500 mm; in C and D ¼ 100 mm.) Specimens processed using standard techniques and viewed on a Tescan Vega SEM at an accelerating voltage of 10.0 kV (A þ B), 20 kV (C þ D).  
PCA ordination of qualitative data (% TFA) on producers (Rupp ¼ Ruppia maritima, Spar ¼ Spartina maritima, Sporo ¼ Sporobolus virginicus, Hinc ¼ Hincksia sordida) as well as sediments (Sed) and the isopod consumer (E. hylo ¼ Exosphaeroma hylocoetes) collected in the Kasouga Estuary. Arrows running parallel to each axis indicate the influence of the specified fatty acids having loading values >AE0.2.  
Article
The role of submerged macrophytes as refugia from fish predation and as possible food sources for the estuarine isopod Exosphaeroma hylocoetes (Barnard, K.H., 1940) was investigated. Laboratory experiments tested the effectiveness of artificial vegetation, replicating submerged vegetation, in enabling isopods to elude selected fish predators Rhabdosargus holubi, Glossogobius callidus, Monodactylus falciformis and Clinus cottoides. Isopods preferentially hid in the vegetation (>90%), even in absence of fish. The predatory fish had varying success in finding isopods within the vegetation. Isopod mortality ranged from 2% (R. holubi) to a maximum of 87% (C. cottoides) within vegetation, depending on the fish predator present. Stable isotope and fatty acid analyses ruled out the submerged macrophyte Ruppia maritima and inundated fringing grasses as direct food sources, but highlighted the epiphytic biota (mainly diatoms) found on the submerged vegetation and sediments as more likely food sources. These findings are consistent with gut content analyses. The results suggest that the close association of E. hylocoetes with R. maritima is the result of the vegetation providing the isopod with a refuge against fish predation as well as areas of increased food availability.
 
Article
According to coastal measurements, global mean sea-level has risen at a rate of 1.8 mm yr−1 between 1950 and 2000, with large spatial variability at regional scales. Within the Bay of Biscay, trends computed from coastal tide gauges records have revealed that sea-level rise is accelerating over this period of time; this is in agreement with rates obtained from satellite imagery in the open ocean since 1993. The objectives of the present study are: (1) to assess the evidence of the relative sea-level rise on coastal morphology and habitats in the Gipuzkoan littoral zone (Basque coast, northern Spain) for the period 1954–2004, and (2) to evaluate the relative contribution of local anthropogenic versus sea-level rise impacts for explaining inter-supratidal habitat changes. A high-resolution airborne laser altimetry data (LIDAR) has been used to derive a Digital Terrain Model (DTM) of 15-cm vertical resolution. Coastal habitats were mapped for two periods, using historic airborne photography (1954) and high-resolution imagery (2004). Analysis of tide gauge records from Santander (northern Spain) has revealed that relative mean sea-level has been rising at a rate of 2.08 ± 0.33 mm yr−1 from 1943 to 2004; this is consistent with sea-level trends from other measurements within the area (St. Jean de Luz and Bilbao), obtained over shorter periods of time, and with previous results obtained in the Bay of Biscay. Based upon this sea-level trend and by means of a LIDAR-based DTM, the results have indicated that the predicted change along the Gipuzkoan coast due to sea-level rise was of 11.1 ha within the 50-yr period. In contrast, comparison of historical and recent orthophotography has detected only 2.95 ha of change, originated possibly from sea-level rise, and 98 ha transformed by anthropogenic impacts. Hence, coastal changes due to sea-level rise might be overwhelmed by excessive human impacts, at the spatial and temporal scales of the analysis. This work highlights that local anthropogenic impact is the major threat to Basque coastal and estuarine habitats, compared with natural erosive processes and global climate change driving forces over recent times.
 
Article
Changes in seagrass cover on Success and Parmelia Banks, Western Australia between 1965 and 1995 were mapped from aerial photography using changes in the distribution and size of phototonal categories. Aerial photography from 1965, 1972, 1982 and 1995 was used to determine the temporal and spatial changes in seagrass distribution. Aerial photography was rectified using photogrammetric techniques, and manually interpreted at a scale of 1:10 000 to determine the extent of seagrasses and unvegetated sands. The 1995 data were also ground-truthed to determine the seagrass species assemblages. The mapping of seagrass cover using phototones is only feasible for species of seagrasses with a dense leaf canopy. The species that fit this criteria, and that have high cover on Success and Parmelia Banks, are Amphibolis antarctica, Amphibolis griffithii, Posidonia australis, Posidonia sinuosa and Posidonia coriacea.The results of this analysis indicates that the percentage of seagrass cover on Success Bank has increased from 21% (507 ha) in 1965 to 43% (1036 ha) in 1995, whereas on Parmelia Bank the percentage of seagrass cover has remained relatively constant with 46% cover in 1965 (735 ha) and 44% in 1995 (699 ha). The east, central and western regions of Success Bank have all shown an increase in seagrass cover from 1965 to 1995. On Parmelia Bank the seagrass cover on the western region has increased. Whereas, the seagrass cover on the eastern region has decreased. On both Success and Parmelia Banks it appears that the majority of seagrass growth between 1975 and 1995 has been in assemblages that are predominantly single species or mixed species meadows of A. griffithii and P. coriacea. These taxa have previously been considered to be relatively static, not known to colonize over large areas, but this study shows that on Success and Parmelia Banks they are actively colonizing at rates that can be mapped at a scale of 1:10 000.
 
Article
Winter thermohaline properties of the northern Adriatic are analysed here with the aim of getting a better insight into dense water formation on the shelf. The hydrographic parameters collected in February in the 1967–2000 interval at two stations, the first located close to the eastern shore (station 1), and the second positioned near the Po river mouth (station 2), are compared. Two types of winter hydrographic conditions are distinguished: type A when bottom salinity and density are higher at station 1 than at station 2 and type B when these parameters are higher at station 2 than at station 1. Type A is more likely to occur in warmer and type B in colder winters. Both A and B distribution types can occur in periods when the Adriatic is under the influence of very saline waters of Mediterranean origin. Interannual changes in density are, at both stations, more dependant on haline than on thermal variations. At both stations temperature was somewhat higher in the early seventies than during the eighties and nineties, while salinity and density were lower in the early seventies and early nineties than in other years of the analysed period. By comparing the 1967–2000 changes in hydrographic conditions in February to monthly values of northern Adriatic surface fluxes and Po river discharge rates, it is shown that winter thermohaline characteristics in the region depend on processes which occur much earlier, i.e. during the previous autumn and late in spring of the preceding year, and even during the previous winter, 12 months before.
 
Article
Eutrophication has been a major environmental change affecting the water quality both in the coastal and open sea areas of the Baltic Sea since the 1960s. Although the total nutrient loading to open sea and also to the Finnish coastal waters is rather well known, the relative importance of various loading sources in different areas is still obscure. We found in the Archipelago Sea, SW Finland, that the great majority of nutrients come as non-point-source loading with the river discharges in the innermost archipelago zone. Fish farming in the middle archipelago zone exerts a remarkable influence on water quality there. The outer archipelago facing the Gulf of Finland and the Baltic proper is influenced by both depending on the season. In a time series study after the initial general rise since the 1970s the increase of nutrient concentrations culminated and levelled off or even turned to a decline in most of the locations studied. It is difficult to single out the cause of this culmination. A reasonable explanation is the general economical decline in Finland. However, same kind of culmination has been found in some other coastal areas of the Baltic Sea, too. The development of the N:P-ratio indicates that during the last two decades nitrogen has developed towards the limiting nutrient in the area studied. The general conclusion is that environmental care should be directed at different targets depending on the archipelago area in question.
 
Article
The ecological model BIOGEN, describing the carbon, nitrogen, phosphorus and silicon cycling throughout aggregated chemical and biological compartments of the planktonic and benthic marine systems, has been implemented in the north-western Black Sea to assess the response of this coastal ecosystem to eutrophication by the Danube River. The trophic resolution of BIOGEN was chosen to simulate the major ecological changes reported in this coastal area since the 1960s. Particular attention was paid to establishing the link between quantitative and qualitative changes in nutrients, phytoplankton composition and food-web structures. The BIOGEN numerical code structure includes 34 state variables assembled in five interactive modules describing the dynamics of (1) phytoplankton composed of three distinct groups, each with a different trophic fate (diatoms, nanophytoflagellates, non-silicified opportunistic species); (2) meso- and microzooplankton; (3) trophic dead-end gelatinous organisms composed of three distinct groups (the omnivorous Noctiluca and the carnivores Aurelia and the alienMnemiopsis ), and organic matter degradation and associated nutrient regeneration processes by (4) planktonic and (5) benthic bacteria. The capability of the BIOGEN model to simulate the recent ecosystem changes reported for the Black Sea was demonstrated by running the model for the period 1985–1995. The BIOGEN code was implemented in an aggregated and simplified representation of the north-western Black Sea hydrodynamics. The numerical frame consisted of coupling a 0-D BIOGEN box model subjected to the Danube with a 1-D BIOGEN representing the open-sea boundary conditions. Model results clearly showed that the eutrophication-related problems of the north-western Black Sea were not only driven by the quantity of nutrients discharged by the Danube, but that the balance between them was also important. BIOGEN simulations clearly demonstrated that phosphate, rather than silicate, was the limiting nutrient driving the structure of the phytoplankton community and the planktonic food-web. In particular, it showed that a well-balanced N:P:Si nutrient enrichment, such as that observed in 1991, had a positive effect on the linear, diatom–copepod food-chain, while the regenerated-based microbial food-chain remained at its background level. When present, the gelatinous carnivores also benefited from this enrichment throughout their feeding on copepods. A synergetic effect of fishing pressure and cultural eutrophication was further indirectly suggested by modifying the mortality coefficient of copepods. However, BIOGEN scenarios with unbalanced nutrient inputs, such as nitrogen or phosphate deficiency recorded in 1985 and 1995, predicted the dominance of an active microbial food-web in which bacteria and microzooplankton played a key role; the former as nutrient regenerator, the latter as a trophic path to the copepods and hence to the carnivorous. In such conditions, however, a significant biomass reduction of all gelatinous organisms was simulated, in perfect agreement with recent observations. From these model scenarios it is suggested that the observed positive signs of Black Sea ecosystem recovery might well be related to the reduction of nutrient loads in particular phosphate, by the Danube.
 
Article
Mangrove forests in many parts of the world are declining at an alarming rate—possibly even more rapidly than inland tropical forests. The rate and causes of such changes are not known. The forests themselves are dynamic in nature and are undergoing constant changes due to both natural and anthropogenic forces. Our research objective was to monitor deforestation and degradation arising from both natural and anthropogenic forces. We analyzed multi-temporal satellite data from 1970s, 1990s, and 2000s using supervised classification approach. Our spatio-temporal analysis shows that despite having the highest population density in the world in its periphery, areal extent of the mangrove forest of the Sundarbans has not changed significantly (approximately 1.2%) in the last ∼25 years. The forest is however constantly changing due to erosion, aggradation, deforestation and mangrove rehabilitation programs. The net forest area increased by 1.4% from the 1970s to 1990 and decreased by 2.5% from 1990 to 2000. The change is insignificant in the context of classification errors and the dynamic nature of mangrove forests. This is an excellent example of the co-existence of humans with terrestrial and aquatic plant and animal life. The strong commitment of governments under various protection measures such as forest reserves, wildlife sanctuaries, national parks, and international designations, is believed to be responsible for keeping this forest relatively intact (at least in terms of area). While the measured net loss of mangrove forest is not that high, the change matrix shows that turnover due to erosion, aggradation, reforestation and deforestation was much greater than net change. The forest is under threat from natural and anthropogenic forces leading to forest degradation, primarily due to top-dying disease and over-exploitation of forest resources.
 
Article
Surveys of the distribution, abundance and size of the ctenophore Mnemiopsis leidyi were carried out in Narragansett Bay, R.I. over a 5-year period, 1975–1979. Yearly variations were observed in time of initiation of the ctenophore increase and maximum abundance. Biomass maxima ranged from 0·2 to 3 g dry weight m−3 at Station 2 in lower Narragansett Bay while maximum abundance varied from 20 to 100 animals m−3. Ctenophores less than 1 cm in length generally composed up to 50% of the biomass and 95% of the numerical abundance during the peak of the M. leidyi pulse. During the 1978 maxima and the declining stages of the pulse each year, 100% of the population was composed of small animals. M. leidyi populations increased earlier, reached greater maximum abundances, and were more highly dominated by small animals in the upper bay than toward the mouth of the bay. The averageclearance rate of M. leidyi larvae feeding on A. tonsa at 22°C was 0·36 l mg−1 dry weight day−1, with apparent selection for nauplii relative to copepodites. Predation and excretion rates applied to ctenophore biomass estimated for Narragansett Bay indicated that M. leidyi excretion is minor but predation removed a bay-wide mean of 20% of the zooplankton standing stock daily during August of 1975 and 1976. Variation in M. leidyi predation at Station 2 was inversely related to mean zooplankton biomass during August and September, which increased 4-fold during the 5-year period.
 
Article
Distributions of physical, chemical and biological characteristics observed in the frontal region of the western Irish Sea during July 1977 are presented. High chlorophyll concentrations and phytoplankton cell numbers were associated with the lateral thermal discontinuity. The characteristics of the stratified and mixed waters varied along the length of the front, such that the changes recorded across each frontal transect were unique. The qualitative composition of the diatom population on either side of the front, however, was distinctive. Observations, concentrated on one transect, showed that the diatom population at the front was a mixture of the populations on either side, and that the high phytoplankton standing crop there was predominantly stimulated by nutrient complementation.
 
Article
The results of a phytoplankton survey conducted in coastal waters off western Ireland in 1980/1981 are reported. Surface values of temperature, salinity, NO3N, PO4P, Si, total N, total P and chlorophyll a (Chla) collected at 6 stations during 14 cruises are presented along with the species composition of the net phytoplankton.The spring bloom occurred in late April and was dominated by diatoms. Between April and July further diatom blooms occurred. In July and August dinoflagellates were dominant. This change was associated with the stratification of offshore water and low concentrations of Chla and nutrients. In Autumn large blooms of Ceratium tripos were found; it is suggested that the cause was heavy freshwater runoff. In autumn and winter some warm water oceanic species (e.g. Oxytoxum scolopax) occurred.
 
Article
The scyphomedusae of the surface waters off Oregon and southern Washington were collected with commercial purse seines from May–August 1981. Twelve east-west transects, located from north of the Columbia River to south of Coos Bay were sampled from the 37 m isobath to distances up to 48 km from shore. Chrysaora fuscescens was the dominant species collected in each month. Maximum sampled abundances reached 18001 of medusae per 105 m3. Using an estimated carbon content of 0·280% of wet weight, this medusa density was calculated to contain approximately 50 mg Cm−3. Seven of the 263 samples contained so many medusae that they exceeded the capacity of the sampling gear. In all months but May, when medusa densities were relatively low, the density of C. fuscescens was greatest closest to shore and decreased rapidly offshore. Mean umbrella diameter increased from 8·6 cm in May to 18·5 cm in August, while the largest specimens increased from 19 cm in May to 37 cm in August. Aurelia aurtia, Cyanea capillata and Phacellophora camtschatica were also collected, but were much less abundant than C. fuscescens. The relative abundance of C. fuscescens was compared with the maximum abundance of copepods off the Oregon coast, and the hydrographic features influencing medusa distribution patterns are discussed.
 
Article
The importance of El Niño-Southern Oscillation (ENSO) on regional-scale climate variability is well recognized, although the communication of this atmospheric signal onto the watershed and ultimately estuarine salinity structure at the bay system level is less understood. The Texas coast, situated in a climatic gradient, is an ideal location to study ENSO influences on estuaries. The seven major estuaries found on the coast share similar physical properties, yet each one is maintained by a hydrologically isolated watershed. Inflow differences maintain estuaries spanning the range from positive, to neutral, to negative. Three monthly measures of ENSO indices (Niño 3.4 sea surface temperature anomaly, atmospheric Southern Oscillation sea level pressure anomaly, and Pacific Decadal Oscillation sea surface temperature anomaly) were related to estuarine-wide average salinities during the period 1982–2004. Empirical Orthogonal Function analysis revealed that most of the variation in salinity is related primarily to five fundamental frequencies (1.02, 1.94, 3.55, 5.33, and 10.67 years), and these periodicities closely correspond with frequencies related to the ENSO measures. Cross-correlation analysis showed the ENSO signals are communicated to the salinity structure of Texas estuaries within a 4- to 6-month timeframe. Despite having very different underlying salinity regimes, the seven estuaries of the Texas coast appear to be operating in near unison to the low frequency forcing signals of ENSO. Current water management in Texas focuses much attention on maintaining estuarine salinity conditions at a monthly, bi-monthly, or seasonal scale. At this temporal resolution, water resource management efforts may not adequately address the important ENSO-driven periodicities governing coastal estuarine salinity patterns.
 
Article
The repeated occurrence of a monospecific bloom of the plankton diatom Rhizosolenia delicatula at Roscoff (western English Channel) was made the subject of an interdisciplinary research programme. Samples were taken at daily intervals from April to July and at longer intervals during the remaining part of the year 1985. Routine physical parameters, light transmission, nutrients, dissolved oxygen, particle load, particulate N and P, chlorophyll content, phytoplankton counting, and zooplankton biomass were measured as a basis for more specific studies (to follow as subsequent papers in this series).The area is characterized by: high tidal range, permanent mixing throughout the year, low attenuation coefficients, moderate nutrient supply, and the dominance of benthic algae over phytoplankton. The spring bloom is significantly delayed with respect to the usual model for the temperate seas. Tidal cycles are expected to exert the main influence on bloom dynamics at the time scale of phytoplankton growth.
 
Article
During the summers of 1987 and 1988, the New York Bight once again experienced a series of incidents in which waterborne, floatable, waste materials and debris were stranded on area beaches. Medically-related wastes were of particular concern. The sources of floatable wastes are identified and local climatological data are used to explain the process by which floatable material was transported.The climatology of the summers of 1987 and 1988 are compared with that of 1976, when similar strandings of floatable wastes occurred on the south shore of Long Island. The summer wind records of these years are also compared with the historical wind record, 1959–1988. The basis of these comparisons are measures of wind persistence and relative energy. These analyses indicate the unusual nature of the conditions that prevailed in 1976, 1987 and 1988 and how they differed from each other. During unusually persistent winds, floatable debris in near surface waters can be transported in excess of 100 km in a direction opposed to the general flow over the continental shelf. While major washups of floatable wastes are unusual, we now know under what conditions they are likely to occur. Emphasis must be placed on alleviating the problem at the sources.a
 
Article
Over a one-year cycle, several shifts occur in the phytoplankton community of the Bay of Banyuls-sur-Mer, a French northwestern Mediterranean shallow bay. In order to determine what drives these shifts, seasonal changes in littoral phytoplankton are considered together with environmental parameters. Our methodology combined a survey of the physical structure and nutrient contents of the water column with the complete characterization of the phytoplankton community structure at 3-m and 24-m depths. The sampling did provide a detailed record of the seasonal changes and successions that occur in northwestern Mediterranean littoral waters. Intrusions of low salinity water clearly had a significant impact on phytoplankton community structure. Such water freshening events both freshened the surface water and introduced substantial amounts of nutrient. The ratio between nitrogen and phosphorus changed on these occasions and proved to be a reliable clue for the characterization of phytoplankton community structure. Picophytoplankton predominated when the N:P ratio was below 10:1 under summer warm oligotrophic situations (Synechococcus and Prochlorococcus) and at the start of water nutrient enrichment (picoeukaryotes). As the N:P ratio increased in late winter–early spring period, eukaryotic phytoplankton was promoted at the expense of Synechococcus and Prochlorococcus. Successions in pico-, nano- and microphytoplankton communities appeared mainly to be driven by differences in the ability to acquire nutrients and by differences in species-specific growth rates. Further characterization of picophytoplankton from samples collected during summer when the N:P ratio reached 5:1 suggested the existence of two cyanobacteria sub-populations. This study clearly shows that northwestern littoral Mediterranean waters are not always well mixed and that nutrient availability in the Bay of Banyuls-sur-Mer depends primarily on low salinity water intrusions.
 
Article
As part of a study of the reasons for declining commercial banana prawn catches in the Weipa area of the Gulf of Carpentaria, and in order to assess whether changes in predator numbers may be a factor influencing prawn numbers, the species composition, numbers and biomasses of fishes in the Embley estuary were re-examined in February 2005 for comparison with the results of a study between 1986 and 1990. The new study duplicated previous methods and used the same sampling sites and the same gear employed during February sampling periods from 1986 to 1990. Overall, the species diversity and catch rates, as well as the numbers of penaeid prawn predators had changed little over 20 years. The overall catch rate for 2005 was 37.4 g m−1 h−1, not significantly different from the overall catch rate of 32.8 g m−1 h−1 (SE 6.6) for the period from 1987 to 1989. The results are discussed in relation to environmental factors and climate change, as well as the substantial declines in prawn catches, which had fallen from over 800 tonnes per annum prior to 1998, to about 70 tonnes per annum.
 
Article
The seasonal occurrence and reproductive strategy of the nemertean Tetrastemma fozensis, which inhabits the mantle cavity of the bivalve Scrobicularia plana, was studied through the analysis of the temporal diversity of a T. fozensis population. Bimonthly sampling was carried out from February 2001 to January 2002 at mudflats of Villaviciosa estuary (Asturias, Northern Spain). Nemerteans were found throughout the study period, but variations in their abundance were detected, with a maximum during winter months and a minimum during summer months. Moreover, variations in mean size of nemerteans were found, with maximal sizes at the end of the spring and the beginning of the summer and minimum size at early autumn. The annual variations in population parameters (decrease in abundance and complete disappearance of large individuals in summer) suggest that T. fozensis has a distinct reproductive season and a semelparous reproductive strategy.
 
Article
The coastal water in the Eastern English Channel, named ‘ fleuve côtier ’ (FC) between the River Seine and the Cape Gris-Nez, is a low-salinity water mass because of the integrated continental runoffs. This coastal water is often limited seaward by coastal front(s) and is characterized as a transfer pathway from the English Channel to the North Sea. The results of this study show that the phytoplankton production start is located off the Seine and Somme Estuaries, and the phytoplanktonic production is lower in the deep and turbulent waters off the Pays-de-Caux, in spite of their nutrient richness. The dispersion of the nearshore produced biomass is often seaward-limited by the coastal front. Nevertheless, the system is complex and the overall biomass distribution is not always limited by the front because production exists offshore of the front. The production seems limited by the depth (20–25 m) independently of the FC structure. In fact, the FC itself appears neither sufficient nor indispensable to develop the phytoplanktonic production in the Eastern English Channel. The broad Picardy Bay, including a part of FC and offshore water, is revealed as an isolated phytoplanktonic system.
 
Article
Quantitative variability of the copepod assemblages in the northern Adriatic Sea was investigated at two stations, during 43 cruises, from January 1993 to October 1997. Samples were taken at 0.5, 10, and 20 m, as well as near the bottom, using 5-l Niskin bottles. For inter-annual variation in the density of copepod assemblages data were presented as total number of nauplii and copepodites with adult copepods of the following groups: Calanoida, Cyclopoida-oithonids, Cyclopoida-oncaeids and Harpacticoida. Moreover, hydrographic conditions, both fractions of phytoplankton, non-loricate ciliates and tintinnids were taken into consideration. Nauplii are the most numerous fraction at both stations with an average over 74% in the total number of all copepod groups. Their numbers were significantly higher at the western eutrophic station, while at the eastern oligotrophic station, an absolute maximum of 693 ind. l−1 was noted. The maximum values of calanoids and oithonids occur generally during summer and these copepods are always more numerous at the western station: 33–50% and 50–63%, respectively. The most abundant taxa identified were the calanoid Paracalanus parvus and the cyclopoid Oithona nana. Oncaeid species Oncaea waldemari and Monothula subtilis dominated during late autumn and winter. An atypical increase in the abundance of oncaeids during the summer of 1997 could be related to an invasion and mass occurrence of the calycophoran siphonophore Muggiaea atlantica. It can be concluded that these dominant copepods are responsible for the stabilization of very complex processes. Atypical appearances of major copepod groups and disturbances in the copepod population structure itself can significantly influence changes in the ecosystem of this very sensitive region.
 
Article
Dissolved organic nitrogen (DON) dynamics in the North Sea was explored by means of long-term time series of nitrogen parameters from the Dutch national monitoring program. Generally, the data quality was good with little missing data points. Different imputation methods were used to verify the robustness of the patterns against these missing data. No long-term trends in DON concentrations were found over the sampling period (1995–2005). Inter-annual variability in the different time series showed both common and station-specific behavior. The stations could be divided into two regions, based on absolute concentrations and the dominant times scales of variability. Average DON concentrations were 11 μmol l−1 in the coastal region and 5 μmol l−1 in the open sea. Organic fractions of total dissolved nitrogen (TDN) averaged 38 and 71% in the coastal zone and open sea, respectively, but increased over time due to decreasing dissolved inorganic nitrogen (DIN) concentrations. In both regions intra-annual variability dominated over inter-annual variability, but DON variation in the open sea was markedly shifted towards shorter time scales relative to coastal stations. In the coastal zone a consistent seasonal DON cycle existed with high values in spring–summer and low values in autumn–winter. In the open sea seasonality was weak. A marked shift in the seasonality was found at the Dogger Bank, with DON accumulation towards summer and low values in winter prior to 1999, and accumulation in spring and decline throughout summer after 1999. This study clearly shows that DON is a dynamic actor in the North Sea and should be monitored systematically to enable us to understand fully the functioning of this ecosystem.
 
Top-cited authors
Angel Borja
Erik Kristensen
  • University of Southern Denmark
Ibon Galparsoro Iza
Henrique Cabral
Angel Perez-Ruzafa
  • University of Murcia