Showing papers in "Estuarine Coastal and Shelf Science in 2003"

The response of macrofauna communities and shorebirds to macrophyte wrack subsidies on exposed sandy beaches of southern California

Abstract: To investigate the influence of marine macrophyte wrack subsidies on community structure, relationships between community attributes, including species richness, abundance, and biomass of macrofauna and abundance of shorebirds, and a variety of factors, including the standing crop of wrack and beach morphodynamics, were examined on 15 exposed sandy beaches on the southern California coast. The beaches sampled were primarily modally intermediate morphodynamic types, and three were groomed regularly. Species richness, abundance, and biomass of the macrofauna were high compared to values reported for similar beach types in other regions and were not predicted by morphodynamics or other physical factors. Overall species richness and abundance, and the species richness, abundance, and biomass of wrack-associated fauna and selected taxa were significantly correlated with the standing crop of macrophyte wrack. Wrack-associated macrofauna, such as amphipods, isopods, and insects, made up an average of >37% of the species on ungroomed beaches and comprised 25% or more of the total abundance on half of those beaches. The abundance of two shorebird species, plovers that forage using visual cues, was positively correlated with the standing crop of wrack and with the abundance of wrack-associated invertebrates. Significant differences in community structure, including depressed species richness, abundance, and biomass of macrofauna, especially for wrack-associated taxa, were associated with beach grooming and provided strong evidence for the bottom-up effects of wrack subsidies. Grooming also reduced the prey available to vertebrate predators, such as shorebirds. Substantial ecological effects of the large-scale disturbance and removal of organic material, food resources, and habitat are associated with beach grooming. These results suggest that macrophyte wrack subsidies strongly influence macrofaunal community structure, higher trophic levels, and ecological processes on exposed sandy beaches. The supply of macrophyte wrack should be considered as a factor in ecological studies of exposed sandy beaches, particularly where macrophyte production is high.

Sources and distribution of organic matter in a river-dominated estuary (Winyah Bay, SC, USA)

Abstract: The sources and distribution of organic matter (OM) in surface waters and sediments from Winyah Bay (South Carolina, USA) were investigated using a variety of analytical techniques, including elemental, stable isotope and organic biomarker analyses. Several locations along the estuary salinity gradient were sampled during four different periods of contrasting river discharge and tidal range. The dissolved organic carbon (DOC) concentrations of surface waters ranged from 7 mg l−1 in the lower bay stations closest to the ocean to 20 mg l−1 in the river and upper bay samples. There was a general linear relationship between DOC concentrations and salinity in three of the four sampling periods. In contrast, particulate organic carbon (POC) concentrations were significantly lower (0.1–3 mg l−1) and showed no relationship with salinity. The high molecular weight dissolved OM (HMW DOM) isolated from selected water samples collected along the bay displayed atomic carbon:nitrogen ratios ([C/N]a) and stable carbon isotopic compositions of organic carbon (δ13COC) that ranged from 10 to 30 and from −28 to −25‰, respectively. Combined, such compositions indicate that in most HMW DOM samples, the majority of the OM originates from terrigenous sources, with smaller contributions from riverine and estuarine phytoplankton. In contrast, the [C/N]a ratios of particulate OM (POM) samples varied significantly among the collection periods, ranging from low values of ∼5 to high values of >20. Overall, the trends in [C/N]a ratios indicated that algal sources of POM were most important during the early and late summer, whereas terrigenous sources dominated in the winter and early spring. In Winyah Bay bottom sediments, the concentrations of the mineral-associated OM were positively correlated with sediment surface area. The [C/N]a ratios and δ13COC compositions of the bulk sedimentary OM ranged from 5 to 45 and from −28 to −23‰, respectively. These compositions were consistent with predominant contributions of terrigenous sources and lesser (but significant) inputs of freshwater, estuarine and marine phytoplankton. The highest terrigenous contents were found in sediments from the river and upper bay sites, with smaller contributions to the lower parts of the estuary. The yields of lignin-derived CuO oxidation products from Winyah Bay sediments indicated that the terrigenous OM in these samples was composed of variable mixtures of relatively fresh vascular plant detritus and moderately altered soil OM. Based on the lignin phenol compositions, most of this material appeared to be derived from angiosperm and gymnosperm vascular plant sources similar to those found in the upland coastal forests in this region. A few samples displayed lignin compositions that suggested a more significant contribution from marsh C3 grasses. However, there was no evidence of inputs of Spartina alterniflora (a C4 grass) remains from the salt marshes that surround the lower sections of Winyah Bay.

Nutrient conditions in the Yellow Sea and the East China Sea

Abstract: This paper discusses the distributions of micronutrients in the Yellow Sea (YS) and the East China Sea (ECS), based on the data obtained during field observations. It is pointed out that there are abundant nutrients in the area of the east and northeast of the Changjiang River estuary throughout the year. It is believed that the nutrients come from the extension of the Changjiang River diluted water and the transportation of the Subei coastal water. The maximum extension range of the nutrients of the Changjiang River diluted water was observed during the catastrophic flooding period of the Changjiang River in the summer of 1998. Based on the Redfield ratio (Si:N:P = 16:16:1) at which three essential nutrients are utilized by marine phytoplankton, the Si/N/P ratios are calculated and studied for the upper water of the YS and the ECS. The results indicate that the Si/N ratios are very high, which suggests that silicate is not the limiting factor for the growth of phytoplankton in the YS and the ECS. Under the influence of terrestrial runoff, especially the Changjiang River runoff which is rich in combined nitrogen and has very high N/P ratios, high N/P ratios occur in the Changjiang estuary and its adjacent areas such as the south and southwest of the YS, the inshore area of the ECS and the area east of the Changjiang estuary in spring and summer. As a result, in contrast to general open marine systems, the systems in these areas resemble estuarine ones rather than typical marine ones. The primary production in a considerable portion of the YS and the ECS may be limited by phosphate rather than nitrogen.

Large-scale spatial patterns in estuaries: estuarine macrobenthic communities in the Schelde estuary, NW Europe

Abstract: Few macrobenthic studies have dealt simultaneously with the two major gradients in estuarine benthic habitats: the salinity gradient along the estuary (longitudinal) and the gradients from high intertidal to deep subtidal sites (vertical gradient). In this broad-scale study, a large data set (3112 samples) of the Schelde estuary allowed a thorough analysis of these gradients, and to relate macrobenthic species distributions and community structure to salinity, depth, current velocities and sediment characteristics. Univariate analyses clearly revealed distinct gradients in diversity, abundance, and biomass along the vertical and longitudinal gradients. In general, highest diversity and biomass were observed in the intertidal, polyhaline zone and decreased with decreasing salinity. Abundance did not show clear trends and varied between spring and autumn. In all regions, very low values for all measures were observed in the subtidal depth strata. Abundance in all regions was dominated by both surface deposit feeders and sub-surface deposit feeders. In contrast, the biomass of the different feeding guilds showed clear gradients in the intertidal zone. Suspension feeders dominated in the polyhaline zone and showed a significant decrease with decreasing salinity. Surface deposit feeders and sub-surface deposit feeders showed significantly higher biomass values in the polyhaline zone as compared with the mesohaline zone. Omnivores showed an opposite trend. Multivariate analyses showed a strong relationship between the macrobenthic assemblages and the predominant environmental gradients in the Schelde estuary. The most important environmental factor was depth, which reflected also the hydrodynamic conditions (current velocities). A second gradient was related to salinity and confirms the observations from the univariate analyses. Additionally, sediment characteristics (mud content) explained a significant part of the macrobenthic community structure not yet explained by the two other main gradients. The different assemblages are further described in terms of indicator species and abiotic characteristics. The results showed that at a large, estuarine scale a considerable fraction of the variation in abundance and biomass of the benthic macrofauna correlated very well with environmental factors (depth, salinity, tidal current velocity, sediment composition).

Fish assemblages across the marine to low salinity transition zone of a temperate estuary

Abstract: This 3-year study provides a large-scale perspective of fish assemblage structure across an ocean–estuarine ecotone, given range of salinity encountered (0.1–32) based on sampling at 12 stations along 40 km from the Mullica River (river), Great Bay (bay), and the adjacent inner continental shelf (ocean) in southern New Jersey. Otter trawl (4.9 m, 6 mm mesh) collections were dominated by young-of-the-year of most of the 49 species encountered. Species richness and abundance appeared greatest in the ocean, decreased (with an increase in inter-station variability) in the bay, and appeared to increase again towards the uppermost river stations. The same areas contained three non-discrete, but identifiable, fish assemblages based on Detrended Correspondence Analysis. Members of the Triglidae and Stromateidae characterized the ocean and bay, whereas representatives of the Percichthyidae and Ictaluridae characterized the river. Several species, including Anchoa mitchilli and Cynoscion regalis, exhibited a ubiquitous distribution across the sampling area. Further analyses with Canonical Correspondence Analysis identified salinity and geographic distance, among the variables examined, as the most important determinants in shaping the assemblages. Other contributors included habitat heterogeneity and water depth. In summary, these observations indicate that large-scale patterns in the structure of this estuarine fish assemblage are primarily a result of individual species' responses to dominate environmental gradients, as well as ontogenetic migrations, whereas smaller-scale patterns appear to be the result of habitat associations that are most likely driven by foraging, competition, and/or predator avoidance.

Differential rates of vertical accretion and elevation change among aerial root types in Micronesian mangrove forests

Abstract: Root systems in mangrove swamps have captured the attention of scientists for decades Among the postulated roles of root structures include a contribution to the geomorphological stability of mangrove soils through sediment trapping and binding In this study, we used feldspar marker horizons and sediment pins to investigate the influence of three different functional root types—prop roots in Rhizophora spp, root knees in Bruguiera gymnorrhiza, and pneumatophores in Sonneratia alba—on vertical accretion and elevation change in three mangrove forests in the Federated States of Micronesia Prop roots facilitated vertical accretion (110 mm year−1) more than pneumatophores or bare soil controls (mean, 83 mm year−1) Sediment elevation, on the other hand, increased at an average rate of only 13 mm year 1 across all root types, with rate differences by root type, ranging from −02 to 34 mm year−1, being detected within river basins This investigation demonstrates that prop roots can assist in the settling of suspended sediments from estuarine waters, yet prop root structures are not as successful as pneumatophores in maintaining sediment elevation over 25 years As root densities increase over time, an increase in turbulence-induced erosion and in shallow subsidence as organic peat layers form is expected in Micronesian mangrove forests

Delta response to decline in sediment supply from the Yangtze River: evidence of the recent four decades and expectations for the next half-century

Abstract: In order to examine the delta response to decline in sediment supply from the Yangtze River during the recent decades, bathymetric maps of the Yangtze subaqueous delta surveyed from 1958 to 1997 were analyzed together with the river sediment dataset of the same period. The net accretion rate over the study area decreased from 38 mm/yr in 1958–1978 to 8 mm/yr in 1978–1997, while the river sediment discharge decreased from 466×106 to 394×10 6 t/yr and the suspended sediment concentration decreased from 0.543 to 0.448 kg/m3 during the same periods, respectively. The outer subaqueous delta is more sensitive to decline in river sediment load in contrast with the inner subaqueous delta. From 1958–1978 to 1978–1997, the net accretion rate decreased from 51 to 2 mm/yr in the outer subaqueous delta and from 25 to 14 mm/yr in the inner subaqueous delta. The accretion rate decreased more rapidly than the river sediment discharge because the amount of sediment transported out of the delta has not decreased. A concept of the critical threshold of river sediment discharge that separates delta progradation from recession is proposed. Although this critical value was found to change temporally and spatially, it was instrumental in predicting the future delta response. Under the impacts of human activities, particularly, the Three Gorges Dam Project, the river sediment load would be reduced below the critical value during the next five decades. This would result in a general delta recession replacing delta progradation; the recession would occur first in the outer subaqueous delta.

Uptake and distribution of metals in two dominant salt marsh macrophytes, Spartina alterniflora (cordgrass) and Phragmites australis (common reed)

Abstract: We examined patterns of biomass accumulation and tissue concentrations of five metals—mercury, copper, zinc, chromium, lead—and two elements—carbon and nitrogen—to determine differences in net metal accumulation and distribution between Phragmites australis (common reed) and Spartina alterniflora (cord grass) which were growing intermingled in a contaminated low marsh. Data were collected at 2-month intervals across a growing season (April–October, 1999). Although they comprise only 5–15% of whole plant biomass for both species, roots consistently contained 70–100% of the whole plant metal burdens for both S. alterniflora and P. australis (shoot:root ratio <0.42). Stems and rhizomes had low and similar concentrations between plant species throughout the summer. Leaves of S. alterniflora, however, had consistently greater concentrations of Hg and Cr than those of P. australis. In contrast, the micronutrients Cu and Zn were enriched in P. australis leaf tissue in October, compared to S. alterniflora. Pools of metal in aboveground biomass were similar between plant species, but throughout the season S. alterniflora allocated more of this burden to leaf tissue than P. australis, which allocated more of the aboveground burden to stem tissue, a recalcitrant tissue with lower concentrations but greater biomass. The consistently higher concentrations and total pools of Hg and Cr in S. alterniflora leaf tissue and higher Zn and Cu in P. australis may result from differences in leaf phenology, root-influenced metal availability, or transport of dissolved metals. Because S. alterniflora shifts more of its Hg and Cr load into highly decomposable leaf tissues (as opposed to recalcitrant stems, roots, and rhizomes) this pathway of metal bioavailability would be reduced when S. alterniflora is replaced by P. australis.

Behaviour of the optical properties of coloured dissolved organic matter under conservative mixing

Abstract: The optical properties of coloured dissolved organic matter (CDOM) can be used, in some environments, to trace water masses and provide information about the dynamics of the dissolved organic fraction in natural waters. This work presents the results from a modelling exercise, laboratory experiment and field data, which describe the variations in the optical properties of CDOM during mixing. The exponential slope coefficient (S) is frequently used to characterise different CDOM pools; however, its behaviour during conservative mixing of two different CDOM types is often misunderstood. Identification of a theoretical conservative mixing line allows the rapid identification of non-conservative processes (e.g. in situ production, flocculation and degradation) acting on the pool during mixing. The results suggest that some of the patterns reported in the literature could purely be a result of conservative mixing rather than a product of non-conservative processes.

High-resolution trace element profiles in shells of the mangrove bivalve Isognomon ephippium : a record of environmental spatio-temporal variations?

Abstract: The shell chemistry of Isognomon ephippium from three Kenyan sites (Tudor, Gazi and Mida) has been investigated to determine whether these bivalves record environmental parameters. The Mg, Sr, Ba and Mn distributions in the calcite shell layer were determined by using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). In addition, whole-shell analyses were made to evaluate inter-site differences. While some variability is observed for mean Mg concentrations, the mean Sr concentrations were similar for the three sites. The decreasing mean Ba and Mn concentrations, following the order Tudor > Gazi > Mida, are related to distinct regimes of freshwater and nutrient supply. The Mg profiles, determined by LA-ICP-MS, displayed a close to regular sinusoidal pattern, depending on specimen and sample site. For the Tudor shells, an arbitrary fitting of the Mg profiles to sea-surface temperature (SST) variations emphasised the good relationship between these two parameters and allowed for the calculation of mean annual growth rates. In most of the shells, Sr partly co-varied with Mg and Ba, highlighting the complexity of Sr incorporation. The Ba and Mn profiles of the Tudor shells displayed several sharp maxima. With a time scale deduced from the Mg–SST relationship, the Ba and Mn maxima of the Tudor shells closely followed periods of maximal rainfall associated with the southeast monsoon. These Ba and Mn maxima were tentatively associated with algal bloom events known to succeed these periods of high rainfall. The less clearly marked seasonality of the Ba and Mn maxima for the Gazi and Mida specimens is thought to result from weaker seasonal variations in nutrient supply and reduced nutrients inputs. This study highlights the potential of I. ephippium as a recorder of spatio-temporal environmental variations in tropical coastal ecosystems.

Impact of Mississippi River freshwater reintroduction on enhancing marsh accretionary processes in a Louisiana estuary

Abstract: To counteract extensive wetland loss a series of diversion projects have been implemented to introduce freshwater and sediment from the Mississippi River into Louisiana coastal wetlands. To keep pace with increases in water level due to subsidence Louisiana coastal marshes must vertically accrete through the accumulation of both organic matter and mineral sediment. The impact of Mississippi River freshwater diversion on enhancing vertical marsh accretion (mineral and organic matter accumulation) was examined in Breton Sound estuary, a coastal wetland experiencing marsh deterioration as result of subsidence and salt water intrusion. Using 137 Cs dating and artificial marker horizons, increases in the rate of vertical marsh accretion were measured at marsh sites along a spatial gradient which has been receiving diverted water from the Mississippi River (Caernarvon diversion) since 1991. Vertical accretion and accumulation of mineral sediment organic matter and nutrients in the marsh soil profile, increased at marsh sites receiving freshwater and sediment input. Iron and manganese content of the marsh surface sediment were shown to be an excellent signature of riverine sediment deposition. Soil extractable phosphorus was higher and extractable sodium was lower at sites nearest freshwater and sediment input. Results demonstrated that freshwater diversion through sediment input and lowering of salinity will enhance marsh accretion and stability, slowing or reversing the rate of wetland loss.

Distribution and dynamics of epibiota on hard structures for coastal protection

Abstract: Hard structures for protection against erosion of shores are some of the most common human-made constructions in coastal areas. Nevertheless, little is known as to how marine organisms respond to their presence. The composition and distribution of intertidal epibiota at different positions around different types of defence structures (groynes and breakwaters) at three stations along the Emilia Romagna coast (Italy) were analysed. Sampling covered a range of scales: meters (distance among replicate plots), hundreds of meters (distance among replicate areas) and tens of kilometres (distance among stations). The colonisation and dynamics of conspicuous species over 1 year, following maintenance works on two structures, were also quantified. Assemblages on defence structures were characterised by a notably low richness of species, by strong spatial dominance of mussels and green ephemeral algae, and by high rates of colonisation. Abundance of mussels, Enteromorpha intestinalis and filamentous algae differed significantly among nearby areas within stations. Mussels were significantly less abundant along the landward side of breakwaters compared with all other positions on both groynes and breakwaters. Overall, however, fewer differences, than expected, were observed in the distribution of species at different positions around groynes and breakwaters, probably as a consequence of the low complexity of the colonising assemblages. Possible factors explaining the patterns of distribution observed are discussed, including the roles of harvesting of mussels and frequent maintenance works on the structures. The implications of the low richness of species observed in terms of management of defence structures and other human-made constructions are discussed.

The diatom Paralia sulcata as an environmental indicator species in coastal sediments

Abstract: Paralia sulcata is a diatom commonly found in both the plankton and benthos of coastal environments. This species is heavily silicified and thus preserves well in sedimentary records, making it a potentially useful paleoindicator species. However, its tychopelagic nature and association with a wide range of environmental conditions have made detailed paleoecological interpretations complicated. The abundance and size of P. sulcata vary in sediments along the Swedish west coast. While most cells have diameters from 12 to 18 μm, cells greater than 20 μm can constitute over 50% of the population. High-resolution stratigraphies in sediment cores from two Swedish fjords reveal changes in the abundance and valve diameter of P. sulcata over a 200 year time span. P. sulcata is abundant in non-laminated sediment sequences. Cells with large diameters (>20 μm) are, however, more common in laminated sections. The connections between environmental parameters and P. sulcata abundance and size were further investigated in the surface sediments along the Swedish west coast. Multivariate analyses highlight the importance of surface water properties and water column stability in the abundance, and size distribution of P. sulcata along the coast. Water columns that are vertically mixed have more upwelling of nutrient-rich, high salinity water to the surface; and these conditions result in large populations of small-sized P. sulcata . In contrast, stratified water columns with low surface water salinity and low phosphorus concentrations show reduced quantities of P. sulcata , but a higher percentage of cells greater than 20 μm. These results help clarify the potential of P. sulcata as a paleoindicator species in coastal environments.

Temperature and salinity regimes in a shallow, mesotidal lagoon, the Ria Formosa, Portugal

Abstract: In a recent study of the mesotidal Ria Formosa, a coastal lagoon in southern Portugal, water temperature in the channels ranged from 12 °C in winter to 27 °C in summer and salinity from 13 to 36.5, although much higher values were observed in saltpans. Conditions in the Ria Formosa were not homogeneous despite a large tidal exchange of water; the inner channels of the Ria Formosa were brackish in winter but hypersaline in summer. Water in inner areas of lagoon had significantly different temperature and salinity characteristics compared to the inflowing coastal water, both in winter and in summer. Areas with these differences in temperature and salinity were detectable both at low water and at high water neaps. Deterioration of water quality is therefore more probable in these areas. The waters went through a complex heating and cooling cycle in summer with diurnal difference of ∼6 °C and 2 in temperature and salinity, respectively. The lack of freshwater input and high insolation meant the outflowing water of the lagoon was more saline that the inflowing coastal waters. In summer, the temperature controlled density with the least dense waters also being the most saline, whereas in winter salinity was the major density controlling parameter. The effects of these freshwater inputs were localised to the vicinity of the Gilao River. No evidence was found of persistent or widespread temperature or salinity stratification in the Ria Formosa and so this shallow lagoon appears to be vertically well mixed. Vertical mixing does not allow a dense, stagnant, bottom layer of water to form that would aggravate a deterioration of water quality. The net effect of these processes is a parcel of water that moves through the lagoon with minimal dilution and potentially receiving waste discharges.

Diet shifts of Caribbean grunts (Haemulidae) and snappers (Lutjanidae) and the relation with nursery-to-coral reef migrations

Abstract: The spatial size distribution of grunts and snappers have previously indicated the separation of juveniles in nursery habitats from the adults on the coral reef. This implies life cycle migrations from nursery habitats (such as seagrass beds and mangroves) to the coral reef. If diet shifts are related to such migrations, then the diets of these fish must change before or around the fish size at which such migrations take place. A wide size range of juveniles of two grunt species ( Haemulon sciurus and Haemulon flavolineatum ) and of two snapper species ( Lutjanus apodus and Ocyurus chrysurus ) were caught in seagrass beds and mangroves, and their gut contents identified and quantified. Regression analysis between fish size and dietary importance of small crustaceans showed a negative relationship in all four species. Positive relations were found for H. sciurus , L. apodus and O. chrysurus between fish length and the dietary importance of decapods, and for L. apodus and O. chrysurus between fish length and prey fish importance. Critical changes in the fish diets with fish size were examined by application of a Canonical Correspondence Analysis (CCA). The CCA yielded three clusters of size-classes of fishes with similar diets, and application of a Mantel test showed that each of these clusters had significantly different diets, and that each cluster diet was significantly specialised. The size at which a fish species ‘switched’ from one cluster to another was compared with size-at-maturity data and with the typical size at which these species migrate from the nursery habitats to the coral reef. H. sciurus and H. flavolineatum may be prompted to migrate from the nursery habitats to coral reef habitats because of dietary changes, or because of the development of the gonads. For L. apodus and O. chrysurus , a dietary changeover forms a more likely explanation for nursery-to-reef migrations than does sexual maturation because these species reach maturity at sizes much larger than the maximum size of individuals found in nursery habitats. Although other factors may theoretically initiate or promote the migration patterns, the results of this study indicate that ontogenetic dietary changes may crucially influence the nursery-to-coral reef migrations of these reef fish species.

Sediment deposition and production in SE-Asia seagrass meadows

Abstract: Seagrass meadows play an important role in the trapping and binding of particles in coastal sediments. Yet seagrass may also contribute to sediment production directly, through the deposition of detritus and also the deposition of the associated mineral particles. This study aims at estimating the contribution of different seagrass species growing across an extensive range of deposition to inorganic (carbonate and non-carbonate) and organic sediment production. Total daily deposition measured with sediment traps varied from 18.8 (±2.0) g DW m −2 d −1 in Silaqui (Philippines) to 681.1 (±102) g DW m −2 d −1 in Bay Tien (Vietnam). These measurements correspond to a single sampling event and represent sedimentation conditions during the dry season in SE-Asia coastal areas. Enhalus acoroides was the most common species in the seagrass meadows visited and, together with Thalassia hemprichii , was present at sites from low to very high deposition. Halodule uninervis and Cymodocea species were present in sites from low to medium deposition. The mineral load in seagrass leaves increased with age, and was high in E. acoroides because it had the largest and long-lived leaves (up to 417 mg calcium carbonate per leaf and 507 mg non-carbonate minerals per leaf) and low in H. uninervis with short-lived leaves (4 mg calcium carbonate per leaf and 2 mg non-carbonate minerals per leaf). In SE-Asia seagrass meadows non-carbonate minerals accumulate at slower rates than the production of calcium carbonate by the epiphytic community, consequently the final loads supported by fully grown leaves were, as average, lower than calcium carbonate loads. Our results show that organic and inorganic production of the seagrasses in SE-Asia represents a small contribution (maximum of 15%) of the materials sedimented on a daily base by the water column during the sampling period. The contribution of the carbonate fraction can be locally significant (i.e. 34% in Silaqui) in areas where the depositional flux is low, but is minor (

The composition of sedimentary organic matter in relation to the dynamic features of a mangrove-fringed coast in French Guiana

Abstract: The sedimentary organic matter content of a series of 2-m-deep cores was examined in relation to the evolution of mangrove forest, on the basis of geochemical analyses and optical observations. Avicennia-dominated forest deposits, developing along the highly dynamic coastline of French Guiana, were collected in five stations based on stage of forest evolution. The sedimentary organic matter in the upper sediment of the youngest mangrove swamp is mainly derived from algal mats with low carbon:nitrogen ratios (C:N ratio, from 6 to 8) and typical greyish amorphous organic flakes as observed in optical studies. Indeed, rare young Avicennia trees are present, and effectively, geochemical parameters do not give evidence of a litter made up of higher plant debris, these rare debris being probably exported by the tides. A slight increase with depth in the first decimetres of both total organic carbon (TOC) content and C:N ratio results from the development of the radial cable root-system of the pioneer Avicennia germinans. Early diagenetic conditions of this young forest are rather controlled by dominant suboxic processes, as suggested by high Eh values (range, 200–400 mV) and local anoxic processes (occurrence of pyrite) in micro-environments: this is mainly due to the oxygen available by roots and crab bioturbation. The organic content of the senescent mangrove sediment is mainly derived from higher plant debris in the uppermost 30 cm, as indicated by relatively high C:N ratios and the predominance of ligno-cellulosic debris. The strong decrease in hydrogen index values results from the degradation of the higher plant debris, losing hydrogen bounds through decay processes. Moderately acidic pH values, low Ehs and the presence of pyrite framboids point towards the reducing decay processes in surficial layers of the senescent mangrove mediated by sulphate-reducing bacteria. Whatever the stage of evolution of the forest, the geochemical characteristics of the sediment below 30 cm are those of the shoreface one, with opaque refractory debris derived from the Amazon river detritus discharge. The sediment collected from dead mangrove forests, subsequently recolonized by pioneer mangroves, contains organic markers, which predate recolonization, recording previous phases of erosion and accretion.

What limits the distribution of subtidal macrobenthos in permanently open and temporarily open/closed South African estuaries? Salinity vs. sediment particle size

Abstract: Thirteen estuaries in the Eastern Cape Province, South Africa, were assigned to one of four types of estuaries (river-dominated permanently open, marine-dominated permanently open, medium-sized temporarily open/closed and small temporarily open/closed), and macrobenthic zonation patterns were compared using multivariate statistics. Three major habitat zones were identified: two relating to substrate (a sand zone and a mud zone), and a third zone characterised by water of low salinity (≤2.2). These zones are inhabited by four major groups of macrobenthos. The distribution of two of these (estuarine endemic sand fauna and estuarine endemic mud fauna) is limited by the nature of the substratum, whereas the distribution of the other two (fauna originating from the marine habitat and oligohaline fauna) is limited by salinity. Estuarine endemics were present in all four types of estuaries. Marine fauna was numerically important only in permanently open systems, while oligohaline fauna was abundant only in the upper reaches of river dominated open systems. Medium-sized temporarily open/closed estuaries lacked both marine and oligohaline forms, but these were present to a limited extent in small temporarily open/closed estuaries. Hence, salinity is not the primary environmental variable determining zonation patterns in Eastern Cape estuaries, and particularly in temporarily open/closed estuaries, it is of minor importance.

Effects of transparent exopolymer particles and muddy terrigenous sediments on the survival of hard coral recruits

Abstract: Sedimentation is a major cause of mortality in scleractinian coral recruits.In this study, we compared the effects of muddy coastal sediments, withand without enrichment by "marine snow" on the survivorship of recruits ofthe hard coral Acropora willisae. Transparent exopolymer particles (TEP)were measured as characteristic components of marine snow using astaining method (Passow&Alldredge 1995). Four-week old recruits wereexposed to (i) muddy coastal sediments, (ii) TEP, (iii) TEP-enriched muddycoastal sediments, and (iv) unfiltered sea water, for 43 h in aerated flowchambers. Thirty-three percent (± 5 SE) of coral recruits died after 43-hexposure to TEP-enriched muddy coastal sediments (~14 mg cm-2sediments enriched with 3.8 ± 0.2 mg cm-2 gum xanthan equivalents [GX]TEP). In contrast, no or minimal mortality was observed in the other threetreatments. Mortality increased to >80% when the amount of deposited TEPwas almost tripled (10.9 ± 1.3 mg cm-2 GX) and sediment increased by50%. Thus, coral recruits survived short-term exposure to low levels of TEPand low levels of muddy sediments, but sediments enriched with TEP atconcentrations recorded at some of the inshore stations proved to bedetrimental. Concentrations of TEP were measured around and away fromreefs in inshore and shelf regions ???of the central Great Barrier Reef(latitude 16 ? 18° S) in summer, the season of coral spawning andrecruitment. Within 40 km off thecoast. Our study suggests that both sediment composition and short-term(43 h) sediment deposition affect survivalof coral juveniles, which has implications for the capacity of inshore reefs to be recolonised by corals to recover from large-scale disturbance events.

Phytoliths of common grasses in the coastal environments of southeastern USA

Abstract: Thirty-four grass species were collected for phytolith analysis from a variety of coastal environments in the southeastern USA (Georgia, Florida, and Louisiana), including salt marshes, freshwater/brackish marshes, pine/oak forests, maritime hardwood forests, and sand dunes. Phytoliths produced by these modern grasses include a large diversity of shapes and types. We propose a preliminary relationship between modern coastal plant communities and their predominant phytolith contents. The dominant grasses of coastal sand dunes, such as Uniola paniculata, produce primarily flat tower and two-horned tower phytoliths. Rondel/ saddle ellipsoid phytoliths are mainly produced by Spartina alterniflora, the most common plant in coastal salt marshes. Rondel and spool/horned tower phytoliths are common in brackish marsh grasses. Plants from interdune meadow produce primarily dumbbell phytoliths, as well as small cross and Cyperaceae-type phytoliths. These results provide a basis for the interpretation of fossil phytolith assemblages and the reconstruction of coastal environmental changes. 2003 Elsevier Ltd. All rights reserved.

Feeding habits and trophic organization of the fish community in shallow waters of an impacted tropical habitat.

Abstract: The feeding ecology and trophic organization of 32 fish species found in an highly impacted waters from four sites of the eastern Johor Strait, Singapore has been studied. Among the wide variety of prey consumed, calanoid copepod (46.9% domination) was the most important dietary component of fishes in this ecosystem. In general, fishes show a narrow range in adaptive radiation of feeding habits, with only three main guilds identified. Spatially, a more complex guild was recorded for the habitat with more complex structure, although the number of guilds was consistent at three to four guilds. Seasonally, a change of guild organization was observed. Many fish species placed in one guild might be classified in another guild during a different season. This information facilitates the examination of complex associations of fishes and identifies groups of species that use similar resources within a specific community and can serve as a reference for feeding ecology of fishes in highly impacted tropical habitats.

Effects of organic matter input from a fish farming facility on a Posidonia oceanica meadow

Abstract: In the Mediterranean, the development of aquaculture along the coasts appears as a source of disturbance to the littoral ecosystems, and in particular to Posidonia oceanica seagrass meadows. Although the impact of fish farms in Northern Europe has been studied over the last few years, the data are more scarce in the Mediterranean. Thus, a number of physico-chemical and biological parameters have been examined here in order to evaluate the impact of a fish farm in a littoral bay of Corsica. The following values that were recorded in the vicinity of the fish farm are much higher than those at the reference station: organic content of the sediment (24–21 versus 2%), nitrogen concentrations (ammonium: 19.5–8.4 versus 1.8lM) and phosphorous levels in the pore water (orthophosphates: 5.2–1.3 versus 1.7lM). The seagrass meadow vitality also seems to be affected in the vicinity of cages, with densities that drop from 466 (reference station) to 108 shoots m � 2 (20 m from cages). Total primary production also varies from 1070.6 to 87.9 g m � 2 year � 1 . The main impact factors seem to be the input of organic matter originating from the cages and the high epiphyte biomass caused by the nutrient enrichment. The high level of organic matter and the presence of mud seem to alter the physico-chemical characteristics of the bottom sediment; moreover, the plant/epiphyte competition seems to lead to a leaf fragility and, more importantly, to a decrease in available light. 2003 Elsevier Science B.V. All rights reserved.

Controls on suspended aggregate size in partially mixed estuaries

Abstract: Knowledge of aggregate size in estuaries is important to determining the fate and transport of suspended sediment and particle adherent contaminants. We have used a suite of in situ instruments to determine the controls of aggregate size distributions in three muddy, partially mixed estuaries in the mid-Atlantic USA. A novel method is presented to estimate turbulent kinetic energy (TKE) production and the resulting Kolmogorov microscale (λK) using a profiling acoustic Doppler velocimeter that has been contaminated by boat motion. The physical processes that control particle size distribution differ in the three estuaries due to the different hydrodynamics and benthic characteristics. Controls within each estuary also vary with different depth regimes. Surface particle size dynamics in all the studied estuaries are affected by irregular advection events. In the hydrodynamically energetic York River, mid-depth regions are controlled tidally by the combined processes of small λK decreasing particle size at high TKE and differential settling increasing particle size during lower TKE, more stratified conditions. Mid-depth regions in the lower energy Elizabeth River are controlled by irregular resuspension and trapping at the pycnocline of large low density particles. Bottom regions in all estuaries are most strongly influenced by resuspension, tidally in the energetic estuaries and irregularly in the low energy estuary. Near-bed particle size distributions are controlled by both λK and the distribution of particles in the bed in the higher energy estuaries. Just above the bed, large porous particles survive resuspension in the lower energy Elizabeth River, particles become smaller with decreased λK in the more energetic York River, and biological aggregation causes large dense particles to resist turbulent breakup in the Chesapeake Bay, which has a more active benthic community. The net result just above the bed is that particle size and settling velocity are positively correlated to TKE production and sediment concentration in the estuary with higher currents and a biologically active bed, negatively correlated in the estuary with higher currents and a bed reworked by rapid erosion and deposition, and poorly correlated in the estuary with lower currents and a disturbed and contaminated bed.

Heavy metal distribution and early-diagenesis in salt marsh sediments from the Medway Estuary, Kent, UK

Abstract: Salt marsh cores are increasingly being used to study metal pollution chronologies. Salt marshes in macro-tidal estuaries, however, tend to retain a time-integrated or ‘smoothed’ signal rather than a record of discrete pollutant inputs, due to extensive sediment reworking. More generally, an accurate chronology of metal input to salt marsh sediments can be difficult to assess because of the potential early-diagenetic mobility of both the radionuclides used for dating and the contaminants of interest. A dated salt marsh core from the macro-tidal Medway Estuary, southeast England, was assessed using both total sediment metal data and partitioning data. These data indicate that both Mn and Fe have been significantly remobilised and that these diagenetic processes have slightly modified the vertical distributions of Cu, Pb and Zn. Zinc is the most diagenetically reactive followed by Cu and then Pb. However, general trends in pollutant loading can still be identified with maximum inputs occurring between ca. 1900 and 1950, decreasing towards the present day.

Spatio-temporal and interspecific variation in otolith trace-elemental fingerprints in a temperate estuarine fish assemblage

Abstract: We tested whether estuarine fishes have site-specific differences in the concentrations of trace elements in their otoliths that can be used as ‘fingerprints’ to identify them to their estuary of origin. To evaluate the robustness of this approach, we tested whether elemental fingerprints were consistent among individuals of five species that were collected in 1996 from three temperate estuaries in southern California. We also tested whether elemental fingerprints were consistent between spring and autumn 1996 for three species in one of the sites, Carpinteria Marsh. The species evaluated comprised a mid-water-dwelling smelt ( Atherinops affinis ), two benthic gobies ( Clevelandia ios and Ilypnus gilberti ), and two flatfish ( Paralichthys californicus and Hypsopsetta guttulata ). The concentrations of six elements (Mn, Cu, Zn, Sr, Ba, and Pb) were determined in the otoliths using inductively coupled plasma-mass spectrometry (ICP-MS). Within estuaries, the five species exhibited strong variation in elemental concentration, indicating substantial interspecific differences in otolith environmental history. When the five fish species were considered separately, multivariate (MANOVA) and univariate (ANOVA) analyses of variance indicated that the elemental composition of otoliths differed significantly among the estuaries in four of the five species. Based on linear discriminant function analyses (DFA), differences were strong enough that trace element composition could be used to accurately assign fish to their site of origin [mean (range): 93.5% (74–100%)]. However, elemental signatures within Carpinteria Marsh were not consistent between spring and autumn 1996, and this was reflected in a substantial reduction in the accuracy of assigning fish to their true site of origin. When we compared site differences between fish species (site×species interactions), the elemental fingerprints were most similar between closely related species (e.g. the two gobies and the two flatfish) and most dissimilar between distantly related species, both phylogenetically and ecologically. Among the six elements analyzed, Sr and Ba exhibited the most inconsistent pattern among species, with significant differences in 80 and 70% of the pairwise species comparisons, respectively. The remaining four elements showed ≥70% consistency in the pattern of variation among sites for the different species. Thus, while otolith elemental fingerprinting can be a useful tool for inferring estuarine residency, such fingerprints may be temporally variable and species specific.

Numerical modelling of shoal pattern formation in well-mixed elongated estuaries

Abstract: The formation of channel and shoal patterns in a schematic estuary is investigated using a 2-D depth-averaged numerical model based on a description of elementary flow and sediment transport processes. The schematisations apply to elongated inland estuaries, sandy, well-mixed and tide-dominated. The model results show how, due to non-linear interactions, a simple and regular pattern of initially grown perturbations merges to complex larger-scale channel/shoal patterns. The emerging patterns are validated with field observations. The overall pattern agrees qualitatively with patterns observed in the Westerschelde, The Netherlands, and in the Patuxent River estuary, Virginia. Quantitative comparison of the number of channels and meander length scales with observations and with an analytical model gives reasonable accordance. Complementary to other research approaches, this model provides a tool to study the morphodynamic behaviour of channels and shoals in estuaries.

Pattern of distribution and diversity of demersal assemblages in the central Mediterranean Sea

Abstract: A highly diversified mix of fish species, cephalopods and crustaceans, together with several macro-epibenthic organisms, compose trawl catches in the Mediterranean Sea. Management of Mediterranean trawling needs a multispecies approach that considers the community and not the single species as the basic unit of the analysis. While many studies have correlated several environmental factors to the spatial organizations of demersal organisms, few have focused on the role of macro-epibenthic communities in structuring demersal assemblages. In this paper, the following hypotheses were tested: (1) there are discrete demersal assemblages in the central Mediterranean Sea; (2) the distribution and diversity of demersal communities does not change on small temporal scales (1 year); (3) the demersal assemblages were segregated across both different epibenthic assemblages and depth gradients. Shallow stations were separated into coastal and middle-deep shelf assemblages while stations on the slope formed three main assemblages: slope edge, upper slope and middle slope assemblages. The demersal community did not show a substantial change at the small temporal scale. Sandy, sand-muddy and detritic epibenthic communities characterized coastal shelf assemblages, while epibenthic assemblage on muddy bottoms were dominant in the deeper areas of the shelf. A well-defined difference in macro-epibenthic faunal associations among stations on the slope (depth >200 m) was not found. Depth appeared to affect diversity of the main taxa of demersal organisms in different ways. Teleostean diversity did not show any trend with depth, the number of cephalopod species increased on the shelf and decreased on the slope while crustacean and elasmobranch species richness increased significantly from the shelf to the middle slope. The strong correlation shown in this study between epifaunal benthic communities and demersal fish assemblages requires the formulation of an ecosystem-based management for the Mediterranean Sea trawl fisheries. The existence of such biological diversity certainly contributes to the Mediterranean ecosystem health and its conservation should become one of the main objective of demersal resources management in the future.

Groundwater mixing, nutrient diagenesis, and discharges across a sandy beachface, Cape Henlopen, Delaware (USA)

Abstract: Groundwater and associated nutrients discharge from the beachface to the Delaware Estuary at Cape Henlopen, Delaware, and appear to contribute significantly to the ecological structure of the adjacent intertidal and subtidal benthic communities. The cross-sectional distributions of salinity and nutrient concentrations at one seepage site indicate that there are two distinct groundwater masses that mix with seawater in the sandy beachface during discharge. The dissolved nutrient concentrations in the beachface at this site are substantially higher than those found in the adjacent estuarine surface water. Nutrient concentrations and distribution in the beachface water reflect: (1) the discharge of nutrient-rich upland water; (2) mixing between nutrient-rich groundwater and estuarine water; and (3) diagenetic recycling of estuarine organic material in the beachface mixing zone. Simple mixing and hydrological models are used to determine the relative magnitude of upland and diagenetic contributions and to estimate absolute nutrient discharges across the beachface. Nutrient fluxes during the summer at this site are sufficient to support carbon fixation rates of 4–17 mol C/m/year along the beachface. These nutrient fluxes are substantially higher than can be supported by the upland discharge alone. This suggests that beachfaces serve as traps and reservoirs of estuarine particulate matter and associated nutrient elements. During the summer, when samples were collected at the Cape Henlopen site, nutrient concentrations in the estuary are low and the remineralization of particles in the beachface may contribute significantly to the productivity of the dense plant and animal communities found adjacent to the beachface.

The relationship of environmental factors to the structure and distribution of subtidal seaweed vegetation of the western Basque coast (N Spain)

Abstract: Subtidal vegetation distribution patterns in relation to environmental conditions (pollution, wave exposure, sedimentation, substratum slope and depth) were studied along the western Basque coast, northern Spain, by applying canonical correspondence analysis and log–linear regressions. A total of 90 species of macrophytes were recorded by systematic sampling along 21 transects. Mesophyllum lichenoides and Cystoseira baccata were the most abundant (accounting for 47% of the overall algal cover). Gelidium sesquipedale, Pterosiphonia complanata, Zanardinia prototypus, Codium decorticatum and Asparagopsis armata (Falkenbergia phase) were other macrophytes with significant cover. Ordination analysis indicates that the five environmental variables explored account between them for 52% of the species data variance. Pollution, sedimentation and wave exposure were the principal factors explaining differences in flora composition and abundance (24, 14 and 12% of the explained variance, respectively). Log–linear regressions and canonical correspondence analyses reveal that C. baccata and G. sesquipedale exhibit a negative relationship with pollution, while sediment loading negatively affects G. sesquipedale, and C. baccata cannot stand high wave exposure levels. In contrast, P. complanata and C. decorticatum show a positive relationship with pollution and can bear high levels of sedimentation and wave exposure. M. lichenoides and Z. prototypus present a wide tolerance range for all these factors. Macroalgal cover, species richness and diversity remain practically constant from unpolluted to slightly polluted sites, but they decrease sharply under moderately polluted conditions. In the same way, algal cover decreases as sediment loading increases, but diversity and species richness show the highest values at intermediate levels of sedimentation. In relation to wave exposure, maximum algal cover was achieved at very exposed habitats whereas diversity and species richness were higher under semi-exposed conditions. � 2003 Elsevier Science B.V. All rights reserved.

The importance of fine-scale, vertical profiles in characterising nematode community structure

Abstract: The spatial heterogeneity of the nematode community on an intertidal flat (the Molenplaat) in the Westerschelde estuary (SW Netherlands) has been investigated. The extent to which macroscale (km) variability was more important than microscale (m) variability was tested. In addition, the importance of vertical distribution profile in the sediment in explaining the horizontal macroscale variability was evaluated. Differences in the structure of the community were analysed at a kilometre scale at three sites that differed in chemico-physical features. The differences in geochemical and physical conditions on a horizontal scale were reflected in species composition and trophic structure of the nematode communities, and to a much lesser extent in their total abundance and species diversity. Detailed investigation of vertical depth profiles showed more pronounced differences between environmentally divergent sites. Sediment granulometry appears to be important in controlling the fauna in the upper sediment layers. At depth, similar faunal assemblages were found irrespective of sediment granulometry, suggesting that other environmental features are more dominant. Vertically, nematode species showed depth distributions that were indicative of sediment characteristics related to the site-specific hydrodynamic regime. Pronounced vertical segregation of nematode species was observed within sandy sediment under strong hydrodynamic and food-stressed conditions. A surface-dwelling nematode community of large predatory enoplids was separated from a deposit feeding xyalid-microlaimid community in deeper sediment layers (beneath 2 cm). Causal factors for this segregation are thought to be species interactions, feeding strategies and/or physical disturbance. In the finest sediments, with high silt content, almost all nematode species were confined to the upper sediment layers (1.5 cm). A sharp decline in density and diversity with depth was observed. Key factors for this distribution pattern are possibly related to the limited oxygen penetration in surface layers and the occurrence of sulphide in deeper sediment layers. At intermediate hydrodynamic and granulometric conditions, a gradual shifting of nematode community was observed with depth, with dominant nematode species maxima present at specific depth layers.