Showing papers in "Estuarine Coastal and Shelf Science in 2005"

Coastal mangrove forests mitigated tsunami

Abstract: A study conducted after the 26th of December 2004 tsunami in 18 coastal hamlets along the south-east coast of India reiterates the importance of coastal mangrove vegetations and location characteristics of human inhabitation to protect lives and wealth from the fury of tsunami. The tsunami caused human death and loss of wealth and these decreased with the area of coastal vegetation, distance and elevation of human inhabitation from the sea. Human inhabitation should be encouraged more than 1 km from the shoreline in elevated places, behind dense mangroves and or other coastal vegetation. Some plant species, suitable to grow in between human inhabitation and the sea for coastal protection, are suggested.

Tidal regime, salinity and salt marsh plant zonation

Abstract: Salt marsh morphology is known to be strongly correlated to vegetation patterns through a complex interplay of biological and physical processes. This paper presents the results of field surveys at several study salt marshes within the Venice Lagoon (Italy), which indicate that salt-marsh macrophyte species may indeed be associated with narrow ranges of soil topographic elevation. Statistical analyses show that several properties of the frequency distributions of halophytes presence are sensitive not only to variations in soil elevation, but also to the specific marsh considered. Through direct in situ sampling and by use of a finite-element hydrodynamic model the role of plant submersion duration and frequency in determining the observed variability of vegetation species is then studied. Measurements of soil salinity have also been performed at selected salt marshes to address its influence on vegetation occurrence. With implications for tidal marshes in general, the distribution of halophytes in the salt marshes considered is found not to be responding to simple rules dictated by the tidal cycle or to salinity, and that such factors, when singularly considered, cannot explain the observed spatial distribution of halophytes. On the basis of observations and modelling results it is thus concluded that a combination of multiple factors, likely dominated by saturated/unsaturated flow in the soil, may be responsible for the observed macrophyte distribution.

A re-examination of fish estuarine dependence: Evidence for connectivity between estuarine and ocean habitats

Abstract: Our understanding of the recruitment of estuarine fishes has been strongly influenced by two views: first, that estuaries are important nurseries and second, that many species are estuarine dependent. Based on an attempt to review the world-wide literature on these topics, it appears that both of these views have merit but could benefit from additional attention and clarification. The term estuarine dependency is used in a variety of ways depending on the author and context and even how one defines estuary. Further, and perhaps most importantly, we often lack the comparative data on habitat use by fishes in the ocean vs. the estuary to make judgments about dependency. To that end we have analyzed the distribution patterns of fish species along the estuarine-coastal ocean ecotone in southern New Jersey, U.S. to evaluate the fish response. As a result, it appears the degree of estuarine use is quite variable among species, as well as at geographic, annual and cohort-specific scales. Thus, further synthesis is necessary and it might focus on: first, more information on fish use in different types of estuaries across a broad geographical range; second, a better understanding of the functional significance of habitats across the habitat landscapes of the estuary–ocean ecotone; third, any further synthesis needs to incorporate of the role of biotic variables (e.g. predation, competition) in order to enhance our understanding of the degree of estuarine dependency; fourth, we need to determine how freshwater flow into estuaries might influence habitat use especially with regard to the potential role of the offshore estuary.

Oil refineries: a review of their ecological impacts on the aquatic environment

Abstract: Pollution of the aquatic environment occurs from many different sources including from oil refineries. Oil refinery effluents contain many different chemicals at different concentrations including ammonia, sulphides, phenol and hydrocarbons. The exact composition cannot however be generalised as it depends on the refinery and which units are in operation at any specific time. It is therefore difficult to predict what effects the effluent may have on the environment. Toxicity tests have shown that most refinery effluents are toxic but to varying extents. Some species are more sensitive and the toxicity may vary throughout the life cycle. Sublethal tests have found that not only can the effluents be lethal but also they can often have sublethal effects on growth and reproduction. Field studies have shown that oil refinery effluents often have an impact on the fauna, which is usually restricted to the area close to the outfall. The extent of the effect is dependent on the effluent composition, the outfall's position and the state of the recipient environment. It is possible to detect two effects that oil refinery effluent has on the environment. Firstly it has a toxic effect close to the outfall, which is seen by the absence of all or most species. Secondly there is an enrichment effect which can be distinguished as a peak in the abundance or biomass. These effects are not limited to just oil refinery effluents, which makes it difficult to distinguish the effects an oil refinery effluent has from other pollution sources. The discharge from oil refineries has reduced in quantity and toxicity over recent decades, allowing many impacted environments in estuaries and coasts to make a substantial recovery.

Coral mortality increases wave energy reaching shores protected by reef flats: Examples from the Seychelles

Abstract: In the granitic Seychelles, many shores and beaches are fringed by coral reef flats which provide protection to shores from erosion by waves. The surfaces of these reef flats support a complex ecology. About 10 years ago their seaward zones were extensively covered by a rich coral growth, which reached approximately to mean low water level, but in 1998 this was largely killed by seawater warming. The resulting large expanses of dead coral skeletons in these locations are now disintegrating, and much of the subsequent modest recovery by new coral recruitment was set back by further mortalities. A mathematical model of wave energy reaching shorelines protected by coral reef flats has been applied to 14 Seychelles reefs. It is derived from equations which predict: (1) the raised water level, or wave set-up, on reef flats resulting from wave breaking, which depends upon offshore wave height and period, depth of still water over the reef flat and the reef crest profile, and (2) the decay of energy from reef edge to shoreline that is affected by width of reef flat, surface roughness, sea level rise and 'pseudo-sea level rise' created by increased depth resulting from disintegration of coral colonies. The model treats each reef as one entity, but because biota and zonation on reef flats are not homogenous, all reefs are divided into four zones. In each, cover by both living and dead biota was estimated for calculation of parameters, and then averaged to obtain input data for the model. All possible biological factors were taken into account, such as the ability of seagrass beds to grow upwards to match expected sea level rise, reduction in height of the reef flat in relation to sea level as zones of dead corals decay, and the observed 'rounding' of reef crests as erosion removes corals from those areas. Estimates were also made of all these factors for a time approximately a decade ago, representing a time before the mass coral mortality, and for approximately a decade in the future when the observed rapid state of dead coral colony disintegration is assumed to have reached an end point. Results of increased energy over the past decade explain observations of erosion in some sites in the Seychelles. Most importantly, it is estimated that the rise in energy reaching shores protected by fringing reefs will now accelerate more rapidly, such that the increase expected over the next decade will be approximately double than that seen over the past decade. (c) 2005 Elsevier Ltd. All rights reserved.

Rapid sediment accumulation and microbial mineralization in forests of the mangrove Kandelia candel in the Jiulongjiang Estuary, China

Abstract: Rates of sediment accumulation and microbial mineralization were examined at three Kandelia candel forests spanning the intertidal zone along the south coastline of the heavily urbanized Jiulongljiang Estuary, Fujian Province, China. Mass sediment accumulation rates were rapid (range: 10–62 kg m −2 y −1 ) but decreased from the low- to the high-intertidal zone. High levels of radionuclides suggest that these sediments originate from erosion of agricultural soils within the catchment. Mineralization of sediment carbon and nitrogen was correspondingly rapid, with total rate of mineralization ranging from 135 to 191 mol C m −2 y −1 and 9 to 11 mol N m −2 y −1 ; rates were faster in summer than in autumn/winter. Rates of mineralization efficiency (70–93% for C; 69–92% for N) increased, as burial efficiency (7–30% for C; 8–31% for N) decreased, from the low-to the high-intertidal mangroves. Sulphate reduction was the dominant metabolic pathway to a depth of 1 m, with rates (19–281 mmol S m −2 d −1 ) exceeding those measured in other intertidal deposits. There is some evidence that Fe and Mn reduction-oxidation cycles are coupled to the activities of live roots within the 0–40 cm depth horizon. Oxic respiration accounted for 5–12% of total carbon mineralization. Methane flux was slow and highly variable when detectable (range: 5–66 μmol CH 4 m −2 d −1 ). Nitrous oxide flux was also highly variable, but within the range (1.6–106.5 μmol N 2 O m −2 d −1 ) measured in other intertidal sediments. Rates of denitrification were rapid, ranging from 1106 to 3780 μmol N 2 m −2 d −1 , and equating to 11–20% of total sediment nitrogen inputs. Denitrification was supported by rapid NH 4 release within surface deposits (range: 3.6–6.1 mmol m −2 d −1 ). Our results support the notion that mangrove forests are net accumulation sites for sediment and associated elements within estuaries, especially Kandelia candel forests receiving significant inputs as a direct result of intense human activity along the south China coast.

Are invasive species most successful in habitats of low native species richness across European brackish water seas

Abstract: European brackish water seas (Baltic Sea, Black Sea and Sea of Azov, Caspian Sea) are subject to intense invasion of non-indigenous species (NIS). In these seas, salinity is the most important range limiting factor and native species seem to reach a minimum species richness at intermediate salinities. This trend, revealed by Remane in 1934 and later on confirmed by many other scientists, was compared to the salinity range of already established NIS in the European brackish water seas. It turned out that most NIS are well adapted to the salinities holding lowest native species richness, already in their native area, and that NIS richness maximum in brackish water seas occurs in the salinity intervals of native species richness minimum. A predictable pattern in the salinity range of NIS can be used as a tool in initial risk assessment of future invasions in brackish water seas, especially when mapping highly potential donor and recipient areas. A product of empty niches, suitable environmental conditions, and availability of proper vectors might be the most effective predictor for the invasibility of brackish water areas.

Using elemental chemistry of fish otoliths to determine connectivity between estuarine and coastal habitats

Abstract: Connectivity between estuarine and coastal populations is poorly understood but fundamental to the study of population dynamics, as well as the design of effective conservation and management strategies. Naturally occurring elemental signatures (or composition) in the otoliths of fish are an ideal natural tag due to the metabolic inertness of otoliths, continuous growth including daily increments and incorporation of elements that are influenced by environmental variables. In this paper, I review the use of otolith chemistry to determine connectivity between estuarine and coastal habitats focusing on assumptions of using elemental signatures as natural tags, consequences of violating these assumptions and finally providing examples of the application of natural tags to determine connectivity. As a first step to determining connectivity, it is important to determine whether fish residing in different estuaries do in fact have different elemental signatures. Spatial differences must be determined for each species of interest since variability has been found between species collected from the same location. For retrospective determination of origins of fish, it is also necessary to ensure either that there is no temporal variation at both the small (e.g. among months within a year) and large scale (e.g. among years) or to match adults to the appropriate year class of juveniles. In addition, fish should be collected from all possible source groups contributing to the group mixture. The majority of studies that show connectivity between estuarine and open coastal populations using otolith chemistry have determined the contribution of different habitats or estuaries to the adult population, although natal homing has also been examined.

Assessing connectivity of estuarine fishes based on stable isotope ratio analysis

Abstract: Assessing connectivity is fundamental to understanding the population dynamics of fishes. I propose that isotopic analyses can greatly contribute to studies of connectivity in estuarine fishes due to the high diversity of isotopic signatures found among estuarine habitats and the fact that variations in isotopic composition at the base of a food web are reflected in the tissues of consumers. Isotopic analysis can be used for identifying nursery habitats and estimating their contribution to adult populations. If movement to a new habitat is accompanied by a shift to foods of distinct isotopic composition, recent immigrants and residents can be distinguished based on their isotopic ratios. Movement patterns thus can be reconstructed based on information obtained from individuals. A key consideration is the rate of isotopic turnover, which determines the length of time that an immigrant to a given habitat will be distinguishable from a longtime resident. A literature survey indicated that few studies have measured turnover rates in fishes and that these have focused on larvae and juveniles. These studies reveal that biomass gain is the primary process driving turnover rates, while metabolic turnover is either minimal or undetectable. Using a simple dilution model and biomass-specific growth rates, I estimated that young fishes with fast growth rates will reflect the isotopic composition of a new diet within days or weeks. Older or slower-growing individuals may take years or never fully equilibrate. Future studies should evaluate the factors that influence turnover rates in fishes during various stages of the life cycle and in different tissues, as well as explore the potential for combining stable isotope and otolith microstructure analyses to examine the relationship between demographic parameters, movement and connectivity.

Tropical mangrove species discrimination using hyperspectral data: A laboratory study

Abstract: The aim of this study is to test whether spectra of crown canopy leaves of various tropical mangrove species measured under laboratory conditions contain sufficient spectral information for discriminating mangroves at the species level. This laboratory-level study is one of the most important prerequisites to the future use of airborne and satellite hyperspectral sensors for mangrove studies. First, spectral responses of 16 Thai tropical mangrove species (2151 spectral bands between 350 nm and 2500 nm) were recorded from the leaves, using a spectrometer under laboratory conditions. Next, the mangrove spectra were statistically tested using one-way ANOVA to see whether they significantly differ at every spectral location. Finally, the spectral separability between each pair of mangrove species was quantified using the Jeffries?Matusita (J?M) distance measure. It turned out that the 16 mangrove species under study were statistically different at most spectral locations, with a 95% confidence level (p <0.05). The total number of spectral bands that had p-values less than 0.05 was 1941, of which 477 bands had a 99% confidence level (p <0.01). Moreover, the J?M distance indices calculated for all pairs of the mangrove species illustrated that the mangroves were spectrally separable except the pairs that comprised the members of Rhizophoraceae. Although the difficulties of discriminating the members of Rhizophoraceae are expected, the overall result encourages further investigations into the use of on-board hyperspectral sensors to see whether mangrove species can be separated when the difficulties of the field conditions are taken into account.

Fish assemblage structure of Koycegiz Lagoon–Estuary, Turkey: Spatial and temporal distribution patterns in relation to environmental variation

Abstract: Spatial and temporal variation in fish assemblage structure of Koycegiz LagooneEstuarine System (KLES), located on the northwestern Turkish coast of Mediterranean, was investigated along an estuarine gradient where salinity ranged from 5 in upper reaches to 40 in lower reaches during October 1993eSeptember 1994. Throughout the study, 42 species, consisting of marine (25), marineeestuarine-dependent (12), freshwater (3), catadromous (1), and estuarine resident (1) forms, were collected in trammel nets. Although species richness of marine species was greater than that of other groups, numerical contribution by marine species to the total catch was only 16%. Tilapia spp., the most abundant species mostly during summer and early spring at upper reaches, contributed 17% of the total samples. Among the seven species of Mugilidae, which contributed 42% of the total catch, Mugil cephalus, Liza aurata, and Liza salines contributed 10, 13, and 10% of the total catch, respectively. Consistent with findings from other studies, species richness and abundance were highest during late spring and summer and the lowest during winter and early spring. Samples from sites at or near the sea had more marine species. Samples from upper reaches had more freshwater and marineeestuarine-dependent species. Canonical correspondence analysis (CCA) indicated that salinity and turbidity were the most important environmental parameters affecting fishes. Sites near the sea were associated with high salinity and low turbidity, and sites in upper reaches had low salinity and high turbidity. Thus, the pattern observed in fish assemblage structure appears to be strongly influenced by species’ responses to dominant salinity and turbidity gradients. 2005 Elsevier Ltd. All rights reserved.

Resilience and climate change: lessons from coral reefs and bleaching in the Western Indian Ocean

Abstract: The impact of climate change through thermal stress-related coral bleaching on coral reefs of the Western Indian Ocean has been well documented and is caused by rising sea water temperatures associated with background warming trends and extreme climate events. Recent studies have identified a number of factors that may reduce the impact of coral bleaching and mortality at a reef or subreef level. However, there is little scientific consensus as yet, and it is unclear how well current science supports the immediate needs of management responses to climate change. This paper provides evidence from the Western Indian Ocean in support of recent hypotheses on coral and reef vulnerability to thermal stress that have been loosely termed ‘resistance and resilience to bleaching’. The paper argues for a more explicit definition of terms, and identifies three concepts affecting coral-zooxanthellae holobiont and reef vulnerability to thermal stress previously termed ‘resistance to bleaching’: ‘thermal protection’, where some reefs are protected from the thermal conditions that induce bleaching and/or where local physical conditions reduce bleaching and mortality levels; ‘thermal resistance’, where individual corals bleach to differing degrees to the same thermal stress; and ‘thermal tolerance’, where individual corals suffer differing levels of mortality when exposed to the same thermal stress. ‘Resilience to bleaching’ is a special case of ecological resilience, where recovery following large-scale bleaching mortality varies according to ecological and other processes. These concepts apply across multiple levels of biological organization and temporal and spatial scales. Thermal resistance and tolerance are genetic properties and may interact with environmental protection properties resulting in phenotypic variation in bleaching and mortality of corals. The presence or absence of human threats and varying levels of reef management may alter the influence of the above factors, particularly through their impacts on resilience, offering the opportunity for management interventions to mitigate the impacts of thermal stress and recovery on coral reefs. These concepts are compiled within an overarching framework of spatial resilience theory. This provides a framework for developing linked scientific and management questions relating to the larger scale impacts of climate change on coral reefs, their management needs and prospects for their future. 2005 Elsevier Ltd. All rights reserved.

Long-term changes of the zooplankton variability in a turbid environment: The Gironde estuary (France)

Abstract: Zooplanktonic variability at the maximum turbidity zone was investigated for the Gironde estuary for 18 years. This ecosystem is characterized by a high concentration of suspended matter and five dominant zooplankton species: the copepods Eurytemora affinis, Acartia bifilosa, A. tonsa and the mysids Neomysis integer and Mesopodopsis slabberi. Four major sources of variation in density were analyzed: (a) spatial variation (vertical and longitudinal variability) and (b) temporal variation (seasonal and annual variability) in the oligo-mesohaline area of the estuary. Temporal variability was related to environmental parameters: temperature, salinity, suspended matter concentration and active chlorophyll in the water column. Seasonal and annual variability were identified as significant sources of variation which explains the fluctuations of all zooplankton densities. No long-term trend was observed for zooplankton densities except for A. tonsa, a species recently introduced into the oligo-mesohaline area of the estuary. Temperature and salinity were important factors explaining the interannual variability of E. affinis as well as of both mysids. Suspended matter concentration controlled the long-term trends of E. affinis and A. tonsa. Annual variability of A. bifilosa and both mysid species was also explained by the proportion of active chlorophyll. Seasonal variability, calculated as the between-month variation, represented the dominant type of variability for all species. Seasonal variations of copepods were essentially explained by salinity. N. integer was significantly correlated with temperature and copepod densities, whereas M. slabberi was correlated with temperature and salinity. Zooplankton also showed significant spatial variation. Mysids demonstrated significant differences between surface and bottom densities whereas vertical variability of copepod densities did not represent a significant source of variation. In terms of longitudinal variability, density of E. affinis was similar along the salinity gradient, whereas Acartia spp. and mysids occurred at significantly greater densities at the downstream station. The high turbidity, which characterizes the Gironde estuary, seems to be a determining factor that acts directly on copepod temporal variability and indirectly on mysid long-term fluctuations by limiting the nutritional quality of the environment.

Coastal oceanographic regimes of the Northern Argentine Continental Shelf (34–43°S)

Abstract: The oceanographic regimes of the Northern Argentine Continental Shelf (NACS, 34 � e43 � S) are derived from advected waters of subantarctic origin, local sources of continental run-off, and a locally generated salinity maximum. Based on 3690 CTD profiles, monthly mean wind fields at coastal stations, and river discharge data, we define the oceanographic regimes over the shelf by analyzing salinity characteristics and spatial distribution: (1) a maximum in salinity (33.7e34.2) originating from the Gulf of San Matias; (2) a relative salinity minimum (30.0e33.3) of the El Rincon estuarine system; (3) a salinity minimum (0e33.0) originating in the Rio de la Plata; and (4) waters of the continental shelf (33.5 and 33.7). Temperature over the shelf is controlled by seaeair heat exchange coupled with bathymetry. An analysis of the Simpson parameter of stability (f) provided an objective definition of a vertically homogenous coastal zone separated from seasonally stratified shelf waters south of 37 � S. Bottom temperature gradients and synoptic sections in the winter and spring indicate the presence of a shallow sea front at the 40e50-m isobaths south of 37 � S, persistent throughout the year. We define two seasonal periods, autumnewinter and springesummer, based on seasonality in monthly mean winds fields, continental run-off, fresh water balance and the spatial distribution of salinity signals. Maximum seasonal variation in the extent and location of the oceanographic regimes occurs within the coastal zone. In the autumnewinter period, we observe a northward extension of the Rio de la Plata and Gulf of San Matias waters, as well as a reduction of the El Rincon and Continental Shelf waters near the coast. The springesummer period is characterized by Rio de la Plata waters flowing to the south and east, a reduction of Gulf of San Matias waters and an invasion of El Rincon and Continental Shelf waters into the coastal areas. In a general sense, waters across the NACS undergo a seasonal oscillation in distribution and extension that implies a springesummer reversal of the characteristic shelf-wide northenortheastward direction of flow within the coastal zone. 2005 Elsevier Ltd. All rights reserved.

Nutrients, light and phytoplankton succession in a temperate estuary (the Guadiana, south-western Iberia)

Abstract: Seasonal changes in freshwater flow, leading to alteration of the nutritional environment and hence affecting phytoplankton composition, will probably be enhanced in the Guadiana estuary (SW Iberia) by the recently built Alqueva dam. The main goal of this study is to assess the relationship between dissolved inorganic macronutrient concentrations and ratios, light availability and phytoplankton succession in the upper estuary of the Guadiana River prior to the completion of the dam. From April to October 2001 three locations along the upper estuary were sampled fortnightly. Several physical and chemical parameters were analysed and phytoplankton composition, abundance and biomass were determined through inverted and epifluorescence microscopy. Phytoplankton showed a uni-modal cycle with a biomass maximum during spring. A relationship between phytoplankton succession and nutrient ratios seemed to exist. In early spring, N:P was high, Si was abundant and a diatom bloom occurred. This bloom collapsed and an increase in green algae abundance was observed later in spring, with low Si and high N:P. In the summer, N:P and Si were low, and a cyanobacteria bloom developed. This bloom included the potentially toxic Microcystis. Light was probably limiting throughout the sampling period, particularly to non-motile cells. Enhancement of cyanobacteria blooms can be expected, and as the river water is used by local human populations, continued monitoring of the Guadiana estuary will be necessary to evaluate the effects of the Alqueva dam construction on phytoplankton dynamics. 2005 Elsevier Ltd. All rights reserved.

Stable isotope analysis of some representative fish and invertebrates of the Newfoundland and Labrador continental shelf food web

Abstract: We examined stable carbon and nitrogen isotopic signatures of 17 fish and 16 invertebrate taxa common to the Newfoundland and Labrador (NL) continental shelf food web. Particular sampling emphasis was placed on Atlantic cod (Gadus morhua) and related prey species (e.g. shrimp, Pandalus borealis, and capelin, Mallotus villosus). We found highly significant (p

A general formula for non-cohesive bed load sediment transport

Abstract: A bed load transport formula for non-cohesive sediment, based on the bed-shear concept of Meyer-Peter and Muller, was developed and validated for steady flows, oscillatory flows, and combined steady and oscillatory flows. The bed load formula introduced in this study was examined using data from experimental and field measurements for a wide range of flows and sediment conditions, as occurring in river, coastal, and marine environments. More than 1000 steady and 500 oscillatory flow cases were used in the study. The relationship between the bed load transport and the total Shields parameter to the power 1.5 was first confirmed for the steady flows. An exponential factor to take into account the effect of the critical Shields parameter was introduced. The proposed formula for the steady current was expanded and generalized to take into account the effects of oscillatory flows as well as oscillatory flows with a superimposed current at an arbitrary angle. The time-dependent bed load transport was treated in a ''quasi- steady'' manner using the quadratic value of the instantaneous Shields parameter for the two half-periods of the wave (when the total instantaneous velocity u is in the direction of the wave, u O 0, or in the opposite direction, u ! 0). A good correlation was found between the bed load formula and the measurements for colinear oscillatory and steady flows when no phase-lag occurred in the experiments. However, a marked scatter was observed since the Shields parameter had to be estimated and not derived directly from measured data. Finally, the validity and limitations of the obtained bed load transport formula are discussed. 2004 Elsevier Ltd. All rights reserved.

Seasonality of Coastal Phytoplankton in the Baltic Sea: Influence of Salinity and Eutrophication

Abstract: In this study long-term (1984–2001) phytoplankton and physico-chemical monitoring data representing different salinity regimes of the Baltic Sea were compiled from HELCOM, national and regional databases. The aim was to define seasonal succession patterns of phytoplankton in seven different areas of the Baltic sea, characterised by different salinity, climate, and trophic conditions and to delineate a set of phytoplankton community indicators that are independent of season and salinity, but indicative of trophic status of different coastal areas. The cluster analysis of the combined data set resulted in eight phytoplankton community types, common for all locations, and characterised by different taxonomic composition representing different stages of seasonal succession. A hierarchy of explanatory variables that best predicted the communities, dominated by either diatoms, cyanophytes, cryptophytes or dinoflagellates, was revealed through a redundancy analysis (RDA). Nutrients were not found to be significant factors shaping the common phytoplankton community types for all locations. RDA analysis at the location level, covering all seasonal succession stages, confirmed phytoplankton community composition to be sensitive to nutrient concentrations. Even with the limitations of utilizing databases from different sources we identified community types that were indicative of climatic conditions (particularly temperature), salinity and eutrophication. The dominance of cyanobacteria as such, would not be an appropriate indicator of trophic conditions in the Baltic Sea, in the areas where cyanobacteria blooms occur naturally. The structure of both diatom- and cyanophyte-dominated communities is governed by salinity, and thus the abundances of these groups cannot be directly used as an indicator across the whole Baltic Sea.

Habitat triage for exploited fishes: Can we identify essential “Essential Fish Habitat?”

Abstract: There is little doubt that estuarine habitat is important for some exploited fish species, at some times, and in some places. However, it is also clear that we do not have enough resources to conserve or restore all estuarine habitat. Consequently, a simple, quantitative and transparent approach to prioritizing estuarine habitat management is required. Here, we present a general framework for identifying critical habitats of exploited fishes. Our approach requires three basic steps: (1) develop stage-structured models and identify sensitive life history stages; (2) determine what habitats, if any, are important to these stages; and (3) identify sites in which high densities of critical life stages occur in important habitat. We will illustrate the utility of this approach using red drum, Sciaenops ocellatus. Results of a simulation-based sensitivity analysis of a stage-structured matrix model show that most of the variability in population growth rate (l) of red drum is explained by larval and juvenile survival rates. Thus, this approach indicates that larval/juvenile red drum habitat should be given higher priority for conservation and/or restoration than habitats used by other life history stages. To illustrate the potential importance of juvenile habitat to red drum, we modeled the growth of a hypothetical red drum population using different population matrices as manifestations of varying habitat conditions. These numerical experiments revealed that restoration of both marsh and seagrass habitats would yield a ca. 24% increase in post-settlement survival and would result in a ca. 2% increase in ldan increase sufficient to stem a long-term population decline. Our results illustrate that protection of fish habitat depends not only on protecting sites where fish occur but also on protecting the ecological processes that allow populations to expand. Quantitative and synthetic analyses of ecological data are a first step in this direction. 2005 Elsevier Ltd. All rights reserved.

Management of a shallow temperate estuary to control eutrophication: The effect of hydrodynamics on the system’s nutrient loading

Abstract: The Mondego estuary, a shallow warm-temperate intertidal system located on the west coast of Portugal, has for some decades been under severe ecological stress, mainly caused by eutrophication. Water circulation in this system was, until 1998, mainly dependent on tides and on the freshwater input of a small tributary artificially controlled by a sluice. After 1998, the sluice opening was effectively minimised to reduce the nutrient loading, and the system hydrodynamics improved due to engineering work in the upstream areas. The objective of the present study was to evaluate the effect of the mitigation measures implemented in 1998. Changes to the hydrodynamics of the system were assessed using precipitation and salinity data in relation to the concentrations of dissolved inorganic nutrients, as well as the linkage between dissolved N:P ratios and the biological parameters (phytoplankton chlorophyll a concentrations, green macroalgal biomass and seagrass biomass). Two distinctive periods were compared, over a ten year period: from January 1993 to January 1997 and from January 1999 until January 2003. The effective reduction in the dissolved N:P atomic ratio from 37.7 to 13.2 after 1998 is a result of lowered ammonia, but not the oxidised forms of nitrogen (nitrate plus nitrite), or increased concentrations of dissolved inorganic phosphorus. Results suggest that the phytoplankton is not nutrient limited, yet maximum and mean biomass of green macroalgae was reduced by one order of magnitude after the mitigation measures. This suggests that besides lowering the water residence time of the system, macroalgal growth became nitrogen limited. In parallel to these changes the seagrass-covered area and biomass of Zostera noltii showed signs of recovery.

Mapping mangrove leaf area index at the species level using IKONOS and LAI-2000 sensors for the Agua Brava Lagoon, Mexican Pacific

Abstract: Using both IKONOS and in situ LAI-2000 sensor data, a map of estimated LAI, based on NDVI, was created for the Agua Brava Lagoon, Mexican Pacific. The LAI values were then aggregated according to four classes; red mangrove (Rhizophora mangle), healthy white mangrove (Laguncularia racemosa), poor condition white mangrove and dead mangrove. Of the live mangrove, calculated at approximately 85% of the forest, mean LAI values of 2.49, 1.74 and 0.85 were determined for the red, healthy white and poor condition white mangrove, respectively. Excluding the dead areas, an overall estimated mangrove LAI value of 1.81 was ascertained for the 71 km2 of mapped mangrove forest. Although the results do suggest the technique as a very rapid and effective method for monitoring the condition of mangroves at the species level, potential limitations are also discussed.

Heavy metal accumulation in a flow restricted, tropical estuary

Abstract: Levels of heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn), organic carbon content and textural characteristics in the surficial sediments of Cochin estuary (SW coast of India) and adjacent coast are presented. Anthropogenic inputs from industries have given rise to a gradient in concentration of metals in estuarine sediments. Metal accumulation initiated by precipitation of iron complexes is probably responsible for the enrichment of Cd, Cu, Pb and Zn in the estuary, whereas the coastal sediments did not accumulate them to the same degree. Statistical analyses of the coastal and estuarine geochemical data indicated a different association of elements in the two provinces. The present enrichment factors for Zn (×25) and Cd (×10) place the region among the impacted estuaries in the world. Accumulation of metals in this estuarine system is aggravated by the weak flushing. These pressures are deemed inevitable with growth initiated in the harbour and associated with mega city development in the offing.

Patterns of Chinook salmon migration and residency in the Salmon River estuary (Oregon)

Abstract: We examined variations in the juvenile life history of fall-spawning Chinook salmon, Oncorhynchus tshawytscha, for evidence of change in estuarine residency and migration patterns following the removal of dikes from 145 ha of former salt-marsh habitat in the Salmon River estuary (Oregon). Mark-recapture studies and abundance patterns in the estuary during 2000e2002 describe the following life-history types among Chinook salmon: (1) fry disperse throughout the estuary, and many move into restored tidalmarsh habitats in the early spring soon after emergence; (2) juveniles reside in freshwater for several months, enter the estuary in June or July, and remain for (a) a few weeks or (b) several months before entering the ocean; and (3) juveniles enter the ocean later in the fall after an extended period of rearing upriver and/or in the estuary. The absence of fry migrants in the estuary during spring and early summer in 1975e1977 d a period that precedes restoration of any of the diked marshes d and the extensive use of marsh habitats by fry and fingerlings AprileJuly, 2000e2002 indicate that wetland restoration has increased estuarine rearing opportunities for juvenile Chinook salmon. Year-to-year patterns of estuarine rearing and abundance by juvenile salmon may be influenced by flood and drought conditions that affected adult spawner distribution and over-winter survival of salmon eggs. However, persistent changes in spawner distribution since 1975e1977, including the concentration of hatchery strays in the lower river, may account for the large proportion of fry that now disperse into the estuary soon after emergence in the spring. Although few of these earliest migrants survived to the river mouth, many fry and fingerlings from mid- and upper-basin spawning areas distributed throughout a greater portion of the estuary during the spring and summer and migrated to the ocean over a broader range of sizes and time periods than thirty years ago. The results suggest that wetland recovery has expanded life history variation in the Salmon River population by allowing greater expression of estuarine-resident behaviors. 2005 Elsevier Ltd. All rights reserved.

SeaWiFS retrievals of chlorophyll in Chesapeake Bay and the mid-Atlantic bight

Abstract: This paper presents three years (1998–2000) of chlorophyll a (chl a) data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) for Case 2 waters of Chesapeake Bay and the middle Atlantic bight (MAB) to describe phytoplankton dynamics on seasonal to interannual time scales. We used extensive data on inherent and apparent optical properties in conjunction with satellite retrievals to: (1) characterize the bio-optical properties of the study area relevant to processing and interpreting SeaWiFS data; (2) test the applicability of the SeaWiFS bio-optical algorithm (OC4v.4) for the estuarine and coastal waters; (3) evaluate the accuracy of the SeaWiFS remote sensing reflectance (RRS) and chl a products on regional and seasonal bases using in situ observations. The characteristically strong absorption by chromophoric dissolved organic matter (acdom) and non-pigmented particulate matter (ad) in estuarine and coastal waters contributed to overestimates of chl a using OC4v.4 applied to in situ radiances for the Bay (mean ratio 1.42±1.20) and the MAB (2.60±1.36). Values of RRS from SeaWiFS in the blue region of the spectrum were low compared to in situ RRS, suggesting that uncertainties remain in atmospheric correction. Direct comparisons of SeaWiFS retrievals of chl a with in situ chl a for the Bay showed larger biases and uncertainties (mean ratio 1.97±1.85) than for chl a estimated from OC4v.4 applied to in situ RRS. The larger biases were attributed to errors in SeaWiFS radiances and the larger uncertainties to time-space “aliasing” of satellite observations and in situ measurements. To reduce the time differences between SeaWiFS and in situ data, we compared chl a obtained from continuous underway fluorometric measurements on selected ship tracks to SeaWiFS chl a and showed that SeaWiFS captured phytoplankton dynamics in much of the Bay. The agreement of SeaWiFS chl a with in situ chl a was strongest in the mid- (regions 3, 4) to lower Bay (regions 1, 2), and deteriorated toward the upper Bay (regions 5, 6), in part due to a reduction of sensitivity and an increase of noise for SeaWiFS products in the highly absorbing, low RRS waters of the upper Bay. A three-year time-series of SeaWiFS and in situ data showed that SeaWiFS accurately and reliably captured seasonal and interannual variability of chl a associated with variations of freshwater flow. Significant short-term variability of chl a in summer that was unresolved with shipboard data was detected in the SeaWiFS time-series and the implications are discussed. The overall performance of SeaWiFS in the mid- to lower Bay and the MAB, combined with high spatial (∼1 km2) and temporal (∼100 clear scenes per year) resolution, indicate current SeaWiFS products are valuable for quantifying seasonal to interannual variability of chl a in estuarine and coastal waters.

Lagoon-sea exchanges, nutrient dynamics and water quality management of the Ria Formosa (Portugal)

Abstract: Historical data from the Ria Formosa lagoon are classified according to the EEA 2001 guidelines to provide a frame of reference to evaluate the effect of management during the implementation of the environmental legislative Directives. Water samples from the Ria Formosa lagoon were significantly enriched in nitrogen (NH4+ NO2− and NO3−) with respect to the adjacent coastal waters indicating that inputs from sewage, agricultural runoff and benthic fluxes were not fully assimilated within the lagoon. Tidal flushing was insufficient in the inner areas of the lagoon to remove or effectively dilute these inputs. Enrichment was most severe close to the urban centres of Faro and Olhao, as well as in the Gilao Estuary and the shallow extremities. Dissolved oxygen undersaturation (mean 75% during daylight hours) was associated with the area close to the sewage outlets of Faro. In the shallow west end of the lagoon during summer, dissolved oxygen supersaturation reached 140% during the day but fell to 50% at night. Classification using the EEA (2001) guidelines suggests the system is “poor” or “bad” with respect to phosphate concentrations for the majority of the year and “poor” in nitrogen contamination during the autumn rainy period. Due to the high overall nitrogen load in the lagoon, there is a net export to the coastal waters, especially during November and December, and phosphate only becomes limiting briefly during the spring bloom (April). Therefore, substantial phytoplankton populations may be supported year-round in the lagoon. The consequences of water quality deterioration in the Ria Formosa would negatively affect the lagoon as a regional resource, important for its ecological, economic and recreational value. The industries most affected would be tourism, fisheries and aquaculture. Management options include Urban Waste Water Treatment, dredging, artificial inlets, limits on urban development and changes in agricultural practices.

Biological impacts of oil pollution and cleaning in the intertidal zone of exposed sandy beaches: Preliminary study of the “Prestige” oil spill

Abstract: On 13th September 2002, the oil tanker ‘‘Prestige’’ sunk off the Galician coast, causing one of the most important oil spills in history, which affected the entire coastline, particularly the exposed rocky shores and sandy beaches. Seventeen exposed sandy beaches were analysed along the Galician coast, in May 2003, and results were compared with previous data for September 1995 and 1996. The intertidal areas of the beaches were sampled in four tidal zones along the beach profile: swash, resurgence, retention and dry sand. Six cores of 0.05 m 2 were taken at each level and washed through a 1 mm mesh. Sediment samples were collected at each level for sediment analysis. The species were grouped into six main taxonomic groups: polychaetes, molluscs, marine crustaceans, semi-terrestrial crustaceans, insects and others. The total number of species was calculated in each group before and after the oil spill. The disturbance effect on each tidal level was determined. A decrease in the species richness was generally observed in all the studied beaches, although this decrease was not homogeneous in all the taxonomic groups. Polychaetes, insects, semi-terrestrial crustaceans and others lost species in all cases, while marine crustaceans did not show this tendency, losing species in some cases and gaining in others. The most affected beaches lost up to 66.7% of the total species richness after the oil spill. The most disturbed levels were swash, losing most of the polychaetes, and dry sand, with decrease in insects and semi-terrestrial crustaceans in many cases. Dry sand level received a high amount of oil and was more affected by grooming and cleaning activities where fuel and polluted material were removed, including algal wrack that is used by the supratidal macrofauna as food and shelter. 2005 Published by Elsevier Ltd.

Spatial shifts in food sources for macrozoobenthos in an estuarine ecosystem: Carbon and nitrogen stable isotope analyses

Abstract: Carbon and nitrogen stable isotope (d 13 C and d 15 N, respectively) analyses were made on estuarine macrozoobenthos in order to examine the relationships between their feeding habits (feeding mode and food selectivity) and the spatial shifts in food sources from upstream to downstream in an estuary. The d 13 C values of two ocypodid crabs were similar to those of benthic diatoms, indicating that they use their specialized mouth parts to selectively feed on benthic diatoms. The d 13 C values of a gastropod and another ocypodid crab at the site furthest downstream were higher than values at an upstream site, suggesting that these unselective deposit feeders shift from feeding mainly on benthic diatoms downstream to feeding on sediment organic matter (SOM) upstream. The d 13 C values of deposit feeding polychaetes were not significantly different among sampling sites, indicating that they feed mainly on SOM at all sites. These results show that species- and site-specific feeding habits must be considered when evaluating the roles of macrozoobenthos in regulating estuarine material flows. 2005 Elsevier Ltd. All rights reserved.

Differences in macrofaunal and seagrass assemblages in seagrass beds with and without seaweed farms

Abstract: Since it was introduced to Zanzibar (Tanzania), seaweed farming has significantly contributed to local, socio-economic development. However, several investigations have shown impacts on the coastal environment near where the farms are located. As many seaweed farms are located on seagrass beds, there is a risk that seaweed farming could affect seagrass beds, and thereby disturb important ecosystem functions and the flow of ecological goods and services. This study compares characteristics of macrophytes (focusing on seagrasses), benthic macrofauna and sediment in seagrass beds, with and without seaweed farms, and a sand bank without vegetation in Chwaka Bay, Zanzibar. The results showed that seagrass beds underneath seaweed farms generally had less seagrass and macroalgae, finer sediment, lower sediment organic matter content and a reduced abundance and biomass of macrofauna, than seagrass beds without seaweed farms. Further, the macrofaunal community structure in seaweed farms showed more similarities to that on the sand bank than in the unfarmed seagrass beds. Most of the dissimilarity was attributable to Lucinidae (suspension-feeding bivalves), which were almost absent in the seaweed farms, resulting in the large difference in biomass between the seaweed farms and the unfarmed seagrass beds. When interpreted together with information from farmers, the observed pattern is believed to be caused by the seaweed farming activities. This indicates that more research is needed to establish the effects of seaweed farming on seagrass beds, and that more attention should be given to the location of farms and the choice of farming methods.

Fine sediment budget on an inner-shelf coral-fringed island, Great Barrier Reef of Australia

Abstract: A field study was undertaken to determine the deposition and removal budget of fine sediments on the windward and leeward sides of an inner-shelf coral-fringed island of the central Great Barrier Reef. Total sedimentation rates were about 2000 mg cm−2 yr−1 at all depths, with 30–60% imported from the reef-surrounding waters during calm periods, and the remaining material locally resuspended during storms. Storms resuspended fine sediment at depths less than ∼5.5 m on the leeward reef side and ∼12 m on the windward side. In these shallow waters there appeared to be a net annual sediment balance between import and export by resuspension events. Below these depths, there was no resuspension during storms; further there was a tenfold increase of the sedimentation rate during storms and most of this additional mud originated from resuspended material from shallower waters on the island slopes. The mud had accumulated on these deeper coral reefs to levels of about 9000 mg DW cm−2, equivalent to ∼4 years of sediment deposition that is presumably flushed out only during tropical cyclones. The data show that increased rates of advection of fine suspended sediments from soil erosion on land can result in increased sediment accumulation on inshore coral reefs below the depth of storm resuspension, with negative effects on the coral communities.

Macroalgae response to a mercury contamination gradient in a temperate coastal lagoon (Ria de Aveiro, Portugal)

Abstract: Primary producers represent an important pathway for mercury incorporation in aquatic food webs. With eutrophication processes occurring worldwide, macroalgae may represent a substantial pool of mercury, as a result of its high growth rate and capacity to bind trace metals. The main aim of this work was to evaluate the response of the macroalgae to a human-induced environmental mercury gradient in a temperate coastal lagoon, by assessing the total and organic mercury contamination levels of the dominant species (Enteromorpha, Fucus and Gracilaria). Total mercury in the plant tissues ranged from 0.02 to 2.1 μg g−1 dwt. Fucus was the most contaminated algae, followed by Gracilaria and Enteromorpha. As a whole, organic mercury never exceeded 15% of total mercury content, but tended to increase with distance to metal source on all macroalgae indicating complex physiological responses from these primary producers in areas of high and low mercury concentrations. Sessile macroalgae may be important mercury immobilisation agents, while free-floating algae (Enteromorpha) play an important role in mercury transport from contaminated areas (±10 g ha−1) to other areas of the lagoon and even to coastal waters. Based on the present results the use of macroalgal biomass from contaminated areas for direct or indirect human use (e.g. agricultural, industrial and food purposes) may result in health risks, due to the high bioaccumulation capacity (as high as 104 the dissolved mercury concentrations).