Outer Lagoon Research Articles

Mangroves buffer marine protected area from impacts of Bovoni Landfill, St. Thomas, United States Virgin Islands

One of the many ecosystem services that mangrove systems provide is their ability to act as buffers between the land and sea, protecting human development from storm surges while also trapping terrestrial pollutants. In St. Thomas, United States Virgin Islands, an ecologically-important mangrove system sits between Bovoni Landfill and a marine protected area, the St. Thomas East End Reserves. To characterize the physical processes driving this mangrove system, groundwater hydraulic head, sediment cores, sediment surface temperatures, and water and sediment chemistry were analyzed. Hydraulic head data from January to November 2014 were used to determine vertical and horizontal groundwater flow directions. Water and sediment samples were tested for heavy metals potentially originating from Bovoni Landfill. Stratigraphic context was provided by the sediment cores and used to infer past environmental conditions. Subsamples were taken from these cores and analyzed for dry bulk density, organic matter content (through loss on ignition), and heavy metals using electron microscopy. Vertical groundwater velocity and sediment porosity were determined by calibrating a one-dimensional finite difference heat transport model to near surface temperature data from depths of 0, 7, 14, and 21 cm. Groundwater was found to flow from the terrestrial upland, through the mangroves, and toward the ocean for the majority of the study. Flow reversal was seen after long periods of little precipitation. In the surface and shallow groundwater samples, trace metal concentrations were measured from 23 to 105 μg/L for Cr, Ni, Sn, and Zn. Sediment samples collected near the landfill contained Bi, Cr, Sn, Ti, and Zn. Very slow flushing of sediment pore water was indicated by the vertical groundwater velocities produced from the heat transport model, which ranged from ±10–7 to ±10–9 m/s. This study revealed that the mangrove system is an important buffer system protecting the outer lagoon of the marine protected area from terrestrial contaminants via sediment trapping and slowing of water fluxes from the upland area into the lagoon. The results presented here can be used as a baseline for future studies and are relevant to local managers and to landfill closure plans.

Measurement of 7Be inventory in the outer Songkhla lagoon, Thailand

The main objective of this study is to estimate the sediment distribution pattern in the outer part of the Songkhla Lagoon, in southern Thailand, by measuring the cosmogenic 7Be in the lake bottom sediment cores. The results indicate that 7Be inventories are larger in the areas where channels collecting water from large subcatchments flow into the lake (mouths of Pak Ro, U-Tapao, Ro-1, and Ro-3 canals). Lower 7Be inventory areas are observed near mouth of channel transporting eroded materials from smaller subcatchments and at the northern tip of Koh Yo island, which is strongly influenced by tidal currents and wind waves which can probably cause sediment re-suspension.

Collaboration between Yamagata University and Kamo Aquarium – Rapid adaptive evolution of jellyfishes inhabiting marine lakes in Palau

The Palau Project Group at the Faculty of Science, Yamagata University, Japan has collaborated with the Tsuruoka City Kamo Aquarium, Yamagata, Japan since 2003. The Palau Islands include approximately 70 marine lakes formed by the rising of ancient coral reefs. In some marine lakes that are completely isolated from outer lagoons, seawater can soak through minute pores in the limestone surrounding the lakes, causing tidal changes to occur. However, marine organisms cannot enter or exit marine lakes. Based on our previous evolutionary genetic analyses, certain fish (in Atherinidae, Apogonidae, and Gobiidae) and mussels (in Mytilidae) exhibit distinct patterns of evolution between marine lake and outer lagoon populations, and also among marine lake populations. Dawson and Jacobs (2001) reported that three distinct species of moon jellyfishes are distributed in Palau; Aurelia sp. 3 and Aurelia sp. 6 inhabit outer lagoons and Aurelia sp. 4 inhabits marine lakes. We surveyed and collected jellyfish and confirmed that the species are highly differentiated both genetically and morphologically. Based on additional comparative observations of Aurelia sp. 4 and Aurelia sp. 3, the former clearly exhibits specific morphological and ethological characters adapted to the environmental conditions that characterize calm marine lakes. Based on geological estimates of marine lake formation, such adaptive evolution in jellyfish occurred rapidly between 5,000 and 15,000 years ago.

Stratigraphy, facies analysis and sequence stratigraphy of the Eocene succession in the Shabrawet area (north Eastern Desert, Egypt): an example for a tectonically influenced inner ramp carbonate platform

The Eocene rocks in the Shabrawet area (north Eastern Desert, Egypt) have been subdivided into three formations that are from base to top: the Minia Formation (Late Ypresian), the Sannor Formation (Bartonian) and the Maadi Formation (Priabonian). These three formations are disconformable with each other. In addition, the whole Eocene succession is disconformably overlain by the Oligocene rocks and is underlain by the Cretaceous rocks with an angular unconformity surface. The Sannor Formation has been subdivided into three informal units: lower, middle and upper units. The overall sedimentary nature of the Eocene rocks in the study area is dominated by carbonate-siliciclastic rocks. Detailed microfacies analysis has enabled discrimination of 22 sedimentary microfacies types, which are grouped into six facies associations, equivalent to six depositional environments sited on an inner ramp setting. These depositional environments are floodplain-dominated fluvial, lacustrine/palustrine, tidal flat, restricted inner lagoon, shoal bar and outer lagoon with open circulation. A suitable depositional model of the Eocene rocks is given. In addition, four discrete benthonic foraminiferal biozones were reported in the Eocene succession, arranged from base to top: (1) Alveolina frumentiformis biozone (Late Ypresian), (2) Orthoplecta clavata biozone (Bartonian), (3) Dictyoconus aegyptiensis biozone (Bartonian) and (4) Discorbis vesicularis biozone (Priabonian). In terms of sequence stratigraphy, the studied Eocene succession exhibits three superimposed depositional sequences, each of which shows retrogradational (transgressive systems tract) and aggradational (highstand systems tract) to progradational (lowstand systems tract) packages of facies. The retrogradational package displays a predominance of outer lagoon and restricted inner lagoon facies. The aggradational package shows an increase of shoal bar and tidal flat facies, whereas the progradational package marks the occurrence of continental facies (floodplain-dominated fluvial and lacustrine deposits). In this study, it is noticed that there are lateral and vertical changes in the depositional environments of the Eocene rocks, between shallow marine and continental environments. Also, many unconformities have been recorded in between and within these rock units. Such remarks indicate that the Eocene rocks were deposited within a highly tectonically active area that was consequently influenced by the transgression and regression of the Neo-Tethys. Such tectonic activity could be related to the Syrian Arc System that was renewed and enlarged several times during the Late Cretaceous up to the Neogene in the eastern and southeastern Mediterranean domain.

Foraminiferal biotopes and their distribution control in Ria de Aveiro (Portugal): a multiproxy approach.

Ria de Aveiro, which is located in the centre of Portugal (40° 38' N, 8° 45' W), is a well-mixed and complex coastal lagoon that is separated from the sea by a sandy barrier and connects with the Atlantic through an artificial inlet. Tidal currents are the main factor controlling the lagoon's hydrodynamics and, to a great extent, the sedimentary dynamic. The inner lagoonal zones receive input from several rivers and experience the pressure caused by the accumulation of organic matter and pollutants (namely, trace metals) from diverse anthropic activities. This paper is the first piece of work aiming to recognize, characterize and explain the main benthic foraminiferal biotopes in Ria de Aveiro. To provide a broad overview of this kind of setting, our results are compared to those of previous published studies conducted in similar transitional environments. The research is based on an investigation of 225 sites spread throughout this ecosystem. Utilizing a statistical approach, this study analyses the details of dead benthic foraminiferal assemblages composed of 260 taxa, the texture and composition (mineralogical and geochemical) of the sediment and physicochemical data. On the basis of the results of R-mode and Q-mode cluster analyses, several different biotopes can be defined as marsh biotope/near-marsh biotope; marginal urban/marginal urban mixing biotope; inner-outer lagoon biotope or enclosed lagoon; outer lagoon biotope, mixed sub-biotope; and outer lagoon, marine sub-biotope. These biotopes are related to foraminifera assemblages and substrate type and are influenced by local currents, water depth, chemical and physicochemical conditions, river or oceanic proximity, and anthropogenic impact, as evidenced by the mapping of the six factor loadings of the principal component analysis conducted herein. Based on a similar methodology of analysis as that applied in previous studies in the Lagoon of Venice, comparable biotypes were identified in Lagoon of Aveiro.

Biosedimentary record of postglacial coastal dynamics: high‐resolution sequence stratigraphy from the northern Tuscan coast (Italy)

Integrating analysis of the benthic palaeoecological record with multivariate ordination techniques represents a powerful synergy able to provide an improved characterization of coastal depositional facies in a sequence stratigraphical perspective. Through quantitative analysis of benthic foraminifer, ostracod and mollusc associations from the postglacial succession of Core M3 (Arno coastal plain, Tuscany, Italy), and application of detrended correspondence analysis (DCA) to the mollusc sub‐data set, we offer a refined picture of stratigraphical variations in faunal content from a paralic depositional setting, and reconstruct the palaeoenvironmental gradients that account for such variations. Despite distinct ecological behaviours, and taphonomic and sedimentological constraints, a strong ecological control on meio‐ and macrofaunal biofacies and taxa turnover is documented across the study succession. Amongst all possible mechanisms that may play a role in ‘shaping’ fossil distribution, the ecological signal driven by salinity represents the most prominent factor controlling the composition of fossil associations in the cored succession. Molluscs can even provide outstanding quantitative estimates of palaeosalinity along the sampled core. When plotted stratigraphically, the three fossil sub‐data sets show consistent patterns of vertical evolution that enable prompt identification of the key surfaces for sequence stratigraphical interpretation in otherwise lithologically indistinguishable deposits. The concomitant maximum richness of species with strong marine affinity, paralleled by the highest DCA salinity estimates, allows recognition of the maximum flooding zone, dated to ∼7.7 cal. ka BP, within a homogeneous succession of outer lagoon clays. These clays are sandwiched between early transgressive, swamp to inner lagoon deposits and overlying prograding coastal−alluvial plain facies.

Mesozooplankton Distribution in Kavaratti Atoll, Lakshadweep Archipelago, South West Coast of India with Special Reference to Calanoid Copepods

Lakshadweep archipelago is a group of coral Islands on the West coast of the Arabian Sea. It is one among the unique coral atolls in India that are well known for several species of fishes and other biotic resources. Seasonal variation in mesozooplankton, particularly of copepod abundance and distribution in the inner and outer lagoon of Kavaratti atoll were studied during April 2013 (premonsoon), September 2013 (monsoon) and January 2014 (postmonsoon). Copepods were the most dominant taxa in all the stations and seasons, that accounted 44.15 to 85.97% of the total mesozooplankton abundance. Ostracoda (premonsoon), crustacean larvae (monsoon) and chaetognaths (postmonsoon) formed the abundant groups in the respective seasons. Mesozooplankton community in the study area exhibits temporal variation corresponding to the variation in abiotic parameters therefore can be used as potential indicators of water quality. Calanoid copepods formed the dominant taxa during monsoon and postmonsoon, while cyclopoid copepods dominated during premonsoon. Among the copepods, species of the family Candacidae, Calanidae, Pontellidae, Temoridae, Psuedodiaptomidae, Centropagidae and Oithonidae were predominant. The ten species of calanoids

Ecology of the ciguatera causing dinoflagellates from the Northern Great Barrier Reef: Changes in community distribution and coastal eutrophication

Ciguatera fish poisoning (CFP) is known to be caused by the ciguatoxins from the dinoflagellate genus Gambierdiscus, however, there is the potential for other toxins such as okadaic acid and dinophysistoxins from the genus Prorocentrum, and palytoxin from the genus Ostreopsis, to contaminate seafood. These genera may also be indicators of ecosystem health and potentially impact on coral reef ecosystems and the role they may play in the succession of coral to macroalgae dominated reefs has not been researched. Sixteen GBR field sites spanning inshore, mid-lagoon and outer lagoon (offshore) regions were studied. Samples were collected from September 2006 to December 2007 and abundance of benthic dinoflagellates on different host macroalgae and concentration of nutrients present in the water column were determined. The maximum abundance of Prorocentrum, Ostreopsis and Gambierdiscus found was 112, 793 and 50 cells per gram wet weight of host macroalgae, respectively. The average level of Dissolved Inorganic Nitrogen (DIN) in the water column across all sites (0.03mg/L) was found to be more than double the threshold critical value (0.013mg/L) for healthy coral reefs. Compared to a previous study 1984, there is evidence of a major shift in the distribution and abundance of these dinoflagellates. Inshore reefs have either of Prorocentrum (as at Green Island) or Ostreopsis (as at Magnetic Island) dominating the macroalgal surface niche which was once dominated by Gambierdiscus, whilst at offshore regions Gambierdiscus is still dominant. This succession may be linked to the ongoing eutrophication of the GBR lagoon and have consequences for the sources of toxins for ongoing cases of ciguatera.

Facies associations and controls on the evolution from a coastal bay to a lagoon system, Santa Catarina Coast, Brazil

The diverse Holocene morphological features along the south coast of the state of Santa Catarina include lagoons and residual lakes, a barrier, a delta (constructed by the Tubarão River), and pre-existing incised valleys that have flooded and filled. This scenario contains the sedimentary record of the transition from a bay to a lagoon system, which occurred during the rise and subsequent semi-stabilisation of the relative sea-level during the Holocene. The geomorphological evolution of this area was investigated using a combination of morphology, stratigraphic analysis of rotary push cores, vibracores and trenches with radiocarbon dating, taxonomic determination and taphonomic characterisation of Holocene fossil molluscs. Palaeogeographic maps were constructed to illustrate how the bay evolved over the last 8000years. The relative sea-level rise and local sedimentary processes were the prime forcing factors determining the depositional history and palaeogeographic changes. The Holocene sedimentary succession began between 8000 and 5700cal BP with the deposits of transgressive sandsheets. These deposits correspond to the initial marine flooding surface that was formed while the relative sea-level rose at a higher rate than the input of sediments, prior to the formation of the coastal barrier. The change from a bay to a lagoon system occurred around 5700 and 2500cal BP during the mid-Holocene highstand with the formation of the barrier and with the achievement of a balance between sea-level rise and sedimentary supply. Until 2500cal BP, the presence of this barrier, the following gentle decline in sea level and the initial emergence of back-barrier features restricted the hydro-dynamic circulation inside the bay and favoured an increase in the Tubarão River delta progradation rate. The final stage, during the last 2500years, was marked by the increasing back-barrier width, with the establishment of salt marshes, the arrival of the delta in the back-barrier, and the advance of aeolian dunes along the outer lagoon margins. This study shed light on the mechanisms of coastal bay evolution in a setting existed prior to the beginning of barrier–lagoon sedimentation.

Benthic foraminifera from two coastal lakes of southern Latium (Italy). Preliminary evaluation of environmental quality

Benthic foraminifera and sediment texture were studied on a total of 37 samples, collected from two brackish-water coastal basins: Fogliano Lake and Lungo Lake (central Italy). The research was performed as a preliminary low-cost survey to highlight the degree of the environmental stress and to recognize a possible anthropogenic disturbance. The sedimentological and foraminiferal data were processed by bivariate and multivariate statistical analysis. Three distinct assemblages, referable to different environments were recognized for the Fogliano Lake: inner, intermediate and outer lagoon. Only the outer lagoon assemblage was found in the Lungo Lake. The distribution of foraminifera in the Fogliano Lake suggests a natural environmental stress probably due to the ecological instability typical of marginal environments, while the absence of the inner and intermediate lagoon assemblages in the Lungo Lake suggests an environmental disturbance possibly related to human activities. An interdisciplinary survey including geochemical analyses is recommended in order to deduce the nature and degree of pollution in the Lungo Lake.

Ontogenetic patterns of concentration indicate lagoon nurseries are essential to common grunts stocks in a Puerto Rican bay

Estimates of abundance and size of three commercially exploited grunt species indicate ontogenetic changes in habitat utilization concentrate their juveniles within the lagoon of the Bay of La Parguera, Puerto Rico. Eleven biotopes, defined by four benthic structures (reef, mangrove, vegetation beds and unconsolidated sediments) and three geographic zones (inner lagoon, outer lagoon and bank shelf) were sampled randomly by visual surveys. French, bluestriped and white grunt ( Haemulon flavolineatum, Haemulon sciurus and Haemulon plumeri) were common in the bay and appeared to exhibit similar life history patterns of cross-shelf migration and habitat selection. Recently settled grunts were dispersed over vegetated and unconsolidated soft-bottom sediments of the bay. The juvenile stage occurred in highest densities in shallow lagoon biotopes among the submerged prop-roots of mangrove stands and on inshore reefs. Length data indicates that grunts migrate offshore to adult habitat via increasingly deep reefs. Indices of biotope nursery function based on standing stock estimates of juveniles identified three biotopes, all within the inner lagoon as essential habitat for juveniles of 5–10 cm length interval. This concentration of juveniles within biotopes of the lagoon could represent a bottleneck to recruitment for grunt stocks. Evidence that quantity and quality of lagoon nurseries may limit recruitment indicates that these areas represent a key component of a marine protected area designed to restore fisheries within the bay.

Late Quaternary history of the Nouméa lagoon (New Caledonia, South West Pacific) as depicted by seismic stratigraphy and multibeam bathymetry: A modern model of tropical rimmed shelf

The barrier reef tract of New Caledonia is the second largest in the world enclosing lagoons of variable width. The Late Quaternary evolution of these barrier reefs and lagoons is poorly known. A recent high resolution seismic and multibeam bathymetry survey was carried out in the south-western lagoon from shoreline to open ocean across the barrier reef pass systems to perform sequence stratigraphy and to better understand the Quaternary evolution of the lagoon. Two depositional sequences bounded by type-1 erosional surfaces can be identified. The bounding surfaces delineate the bottom of two generations of incised valleys. System tracts comprising a complete succession of regressive, lowstand, transgressive and highstand tracts were observed only in the upper sequence. Chronostratigraphic and sedimentological interpretations of the seismic data are based on correlations with the chronology defined in the nearby cores drilled through the reefs and in the gravity cores previously recovered in the inner lagoon. Interpretation of seismic data is also carried out on the basis of correlation with multibeam bathymetric data. Our results indicate that the history of the New Caledonian lagoon probably does not exceed 200ka marked by two or three brief episodes each of immersion of about ten thousand years. The bathymetric data reveal that during successive low sea level stands, the lagoon was dependent upon erosional fluvial networks. The deep fluvial valleys were connected to the continental slope through the passes. Seismic records reveal that upstream palaeo-channels are not connected to the modern coastal rivers. In contrast, many aggrading deposits, including numerous stacking channels, and extending across the proximal part of the outer lagoon, can be identified. Examination of drainage network morphology suggests a progressive tilt of the outer lagoon. Such evolution reveals that the Nouméa lagoon which is one of the widest in the world is an exceptional modern example of a rimmed shelf providing data to analyze the past counterparts.

Residence times in a hypersaline lagoon: Using salinity as a tracer

Generally the waters of the Ria Formosa Lagoon, Portugal have a short residence time, in the order of 0.5 days (Tett, P., Gilpin, L., Svendsen, H., Erlandsson, C.P., Larsson, U., Kratzer, S., Fouilland, E., Janzen, C., Lee, J., Grenz, C., Newton, A., Ferreira, J.G., Fernandes, T., Scory, S., 2003. Eutrophication and some European waters of restricted exchange. Continental Shelf Research 23, 1635–1671). This estimation is based on the measurements of currents and the modelling of water exchange at the outlets to the ocean. However, observations of the temperature and salinity in the inner channels imply that residence time is greater in these regions of the lagoon. To resolve this apparent contradiction, spatial measurements of the temperature and salinity were made with a meter for conductivity, temperature and depth along the principal channels of the western portion of the lagoon, with a sampling frequency of two per second. Evaporation rates of 5.4 mm day −1 were measured in a salt extraction pond adjacent to the lagoon and used to determine the residence time through salinity differences with the incoming seawater. In June 2004, the water flooding in from the ocean had an average salinity of 36.07 which contrasted with a maximum of 37.82 at mid ebb on a spring tide, corresponding to a residence time of >7 days; the mean residence time was 2.4 days. As the tide flooded into the channels, the existing water was advected back into the lagoon. Although there was a small amount of mixing with water from another inlet, the water body from the inner lagoon essentially remained distinct with respect to temperature and salinity characteristics. The residence time of the water was further prolonged at the junction between the main channels, where distinct boundaries were observed between the different water masses. As the water ebbed out, the shallow Western Channel was essentially isolated from the rest of the outer lagoon, and the water from this channel was forced down the Ramalhete Channel, from where it was unable to exit the lagoon in one tidal cycle due to the extensive path length of ∼14 km to the sea. Although the overall exchange rate of water is short in the outer lagoon, this study emphasizes that management models should take into account additional complexities that might arise from the much longer exchange rates of the inner lagoon. For example, the principal sewage discharge for the urban area of Faro is into the section of the Ramalhete Channel where efficient flushing is impeded by the relatively high residence times of the water body in this channel. The implementation of the techniques used for this study are a quick and relatively cost effective approach to testing assumptions about water quality and exchange in shallow coastal systems.

Horizontal mixing of Great Barrier Reef waters: Offshore diffusivity determined from radium isotope distribution

The Great Barrier Reef (GBR), northern Australia, is the largest coral reef system in the world and provides habitat for highly diverse tropical marine ecosystems. Mixing in the coastal waters of the GBR is an important parameter influencing the health of these ecosystems. We have used the distribution of the four naturally occurring radium isotopes to determine the rate of mixing of nearshore waters of the central part of the GBR lagoon with water from the Coral Sea. The observed radium distribution is modeled using a one‐dimensional diffusion model. The model improves on previous radium offshore mixing models by incorporating the benthic flux of radium diffusing across the sediment‐water interface and offshore changes in water column depth. We find that the inner lagoon diffusivity (<20 km offshore) is best estimated using the short‐lived isotopes 224Ra and 223Ra. The concordance of Kx estimated using the two different isotopes and the apparent consistency between measured riverine inflows to the lagoon and inflows inferred from the modeled salinity distribution provide confidence in the results. The mean value of Kx for the inner lagoon region of the southern central zone between latitudes 15.8°S and 19.0°S (265 ± 36 m2 s−1) is more than twice that in the northern central zone (14.3°S to 15.8°S). This difference likely reflects the different reef matrix density in the two zones. The distribution of the longer‐lived isotope 228Ra indicates more rapid mixing in the middle and outer lagoon. These results indicate that central GBR water within 20 km of coast is flushed with outer lagoon water on a timescale of 18–45 days, with the flushing time increasing northward.

Bathymetric and Environmentally Influenced Patterns of Carbonate Sediment Accumulation in Three Contrasting Reef Settings, Danjugan Island, Philippines

Abstract This study assesses patterns of biogenic carbonate sediment production associated with three different reef and reef-related settings at Danjugan Island in the Philippines. Sediments were collected along transects on windward and leeward sides of the island (1–28-m depth) and from a semirestricted lagoon (1.5–2.5-m depth). Sediment assemblages from all sites are dominated (in decreasing order of abundance) by coral (29.1%), Halimeda (28.8%), mollusks (13.5%), and benthic foraminifera (10.2%). Sediments from windward sites are dominated by fragments of corals (15.0–42.5%), Halimeda (14.0–32.1%), mollusks (8.5–21.6%), and benthic foraminifera (7.8–32.9%). Bryozoans represent a significant secondary component (2.77–14.6%). Leeward sediments primarily comprise coral, Halimeda, and molluscan grains, although are characterized by a higher abundance of Halimeda (29.7–49.2%) than the windward transect. Lagoon sediments comprise primarily coral (1.3–42.7%) and Halimeda (13.8–37.2%) in the outer lagoon, bu...

Correlation between percentage of lower esophageal sphincter relaxation and response of technetium esophageal transit time to isordil in idiopathic achalasia

Generally the waters of the Ria Formosa Lagoon, Portugal have a short residence time, in the order of 0.5 days (Tett, P., Gilpin, L., Svendsen, H., Erlandsson, C.P., Larsson, U., Kratzer, S., Fouilland, E., Janzen, C., Lee, J., Grenz, C., Newton, A., Ferreira, J.G., Fernandes, T., Scory, S., 2003. Eutrophication and some European waters of restricted exchange. Continental Shelf Research 23, 1635–1671). This estimation is based on the measurements of currents and the modelling of water exchange at the outlets to the ocean. However, observations of the temperature and salinity in the inner channels imply that residence time is greater in these regions of the lagoon. To resolve this apparent contradiction, spatial measurements of the temperature and salinity were made with a meter for conductivity, temperature and depth along the principal channels of the western portion of the lagoon, with a sampling frequency of two per second. Evaporation rates of 5.4 mm day−1 were measured in a salt extraction pond adjacent to the lagoon and used to determine the residence time through salinity differences with the incoming seawater. In June 2004, the water flooding in from the ocean had an average salinity of 36.07 which contrasted with a maximum of 37.82 at mid ebb on a spring tide, corresponding to a residence time of >7 days; the mean residence time was 2.4 days. As the tide flooded into the channels, the existing water was advected back into the lagoon. Although there was a small amount of mixing with water from another inlet, the water body from the inner lagoon essentially remained distinct with respect to temperature and salinity characteristics. The residence time of the water was further prolonged at the junction between the main channels, where distinct boundaries were observed between the different water masses. As the water ebbed out, the shallow Western Channel was essentially isolated from the rest of the outer lagoon, and the water from this channel was forced down the Ramalhete Channel, from where it was unable to exit the lagoon in one tidal cycle due to the extensive path length of ∼14 km to the sea.Although the overall exchange rate of water is short in the outer lagoon, this study emphasizes that management models should take into account additional complexities that might arise from the much longer exchange rates of the inner lagoon. For example, the principal sewage discharge for the urban area of Faro is into the section of the Ramalhete Channel where efficient flushing is impeded by the relatively high residence times of the water body in this channel.The implementation of the techniques used for this study are a quick and relatively cost effective approach to testing assumptions about water quality and exchange in shallow coastal systems.

Cross-Shelf Habitat Utilization Patterns of Reef Fishes in Southwestern Puerto Rico

In June 2000, the National Ocean Service and University of Puerto Rico initiated a long-term reef-fish-monitoring program in La Parguera, Puerto Rico. Objectives of this ongoing work are to: 1) develop spatially-explicit estimates of reef fish habitat utilization patterns to aid in defining essential habitats, and 2) provide a quantitative and ecologically sound foundation to delineate marine reserve boundaries. Central to this effort are recently completed digital and georeferenced benthic habitat maps for the near-shore waters of Puerto Rico. The GIS-based map served as a framework for development of a spatially stratified reef-fish-monitoring program across the shelf. Simultaneous collections of fish size and abundance data, and micro-scale habitat distribution and quality data were taken along a 25 x 4 m transect for each monitoring station. Sampling included coral reef, mangrove, and seagrass habitats within three cross-shelf zones unique to the insular shelf of La Parguera (inner lagoon, outer lagoon, and bank-shelf). A total of 106 stations were surveyed during the first year of sampling. Over 50,000 fishes, representing 123 species and 36 families were counted. Analyses showed clear patterns of habitat utilization across the seascape, and ontogenetic shifts in habitat selection within some species. Results also indicated that habitat type was more important than cross-shelf location in determining spatial patterns among reef fishes in the study area. Mesoscale spatially-explicit logistic models were developed to estimate distribution and expected density of some species among habitats.

Sources of organic matter in Ria Formosa revealed by stable isotope analysis

The aim of this study is to assess the major sources of organic matter for macroconsumers in the Ria Formosa tidal lagoon. The C, S and N isotopic natural abundances of abundant primary producers of particulate organic matter (POM) and Mytilus galloprovincialis muscle and digestive gland were analysed. The chlorophyll a (Chl a), the suspended particulate matter (SPM) and the POM were measured along the Faro-Olhao channel. The range of variation of stable isotope values among primary producers in Ria Formosa was low suggesting difficulties in the assessment of their relative contribution to higher levels of the food web. Chl a values decreased from outer station to inner station, while SPM and POM values increased. The multiple isotope approach illustrates that POM values along the Faro-Olhao channel, may result from a mixture of upland plants, benthic plants and phytoplankton. Mussel values indicate a selective diet of benthic macrophytes and phytoplankton, with the relative proportions of each determined by the location in the channel. During winters, the upland plants may be an important source of organic matter in the inner lagoon while phytoplankton was an important source of organic matter in the outer lagoon.

Reservoir-Scale Heterogeneity in Depositional Packages and Diagenetic Patterns on a Reef-Rimmed Platform, Upper Miocene, Mallorca, Spain

Predictive models for interwell-scale variations in heterogeneous carbonate rock are best made from outcrop studies of well-exposed limestone and dolomite, such as the upper Miocene reef complex that crops out in the sea cliffs of Mallorca, Spain. The sea-cliff sections reveal highly complex lithofacies stacking patterns that could lead to ambiguous lateral correlations of coeval units. The stratigraphic complexity and distribution of primary and secondary porosity are the result of a sea-level-driven hierarchical stacking of different magnitudes of accretional units. Thickest sections of porous and permeable rocks are in the aggradational portions of the reef, upper slope, and outer lagoon units. The relative volume of the various accretional units and heterogeneity in the lithofacies architecture were dependent on the amount of carbonate production, which was related to (1) accommodation changes controlled by sea-level fluctuations and (2) depositional profile. Moldic porosity, mostly from the dissolution of aragonitic constituents, is the predominant porosity type, and its heterogeneous distribution is related to the lateral and vertical distribution of lithofacies. The secondary porosity in much of this reef complex was produced mainly during early dolomitization. Dolomite patterns are complicated, apparently mainly related to shallow flooding of the platform during third- or fourth-order sea level highs and to geographic location of permeable pathways for brine reflux, probably primarily through fourth-order aggradational reef units. Many of these stratigraphic complexities and diagenetic patterns are below the resolution of seismic and well analyses; thus models based on outcrop data such as this can enhance reservoir development in certain shallow-water carbonate rocks.

Distribution of pollen in surface sediments of a barrier-lagoon system, Virginia, USA

Fine-grained surface sediments of the U.S. middle Atlantic coast contain pollen that are characteristic of the local vegetation. The pollen concentrations and pollen associations in lagoonal sediment appeared to be affected by physical characteristics of the landscape and the dynamic characteristics of the atmosphere and water. Arboreal pollen from the elevated mainland had a greater influence on uniform distribution of pollen in lagoons than arboreal pollen from the low profile barrier islands. The concentration of airborne pollen from the mainland decreased in a seaward direction across the lagoon. The maximum dispersion distance from the mainland was 7–10 km. Non-arboreal plants on the low profile barrier islands of the Virginia coast primarily provided pollen grains to the outer part of the coastal lagoon. The changes in pollen concentration and the relationship between arboreal and non-arboreal pollen documented in this study clearly differentiate into inner, middle and outer lagoon pollen spectra.