Adjacent Bay Research Articles

Occurrence, distribution, and associated pollutants of plastic pellets (nurdles) in coastal areas of South Texas

Nurdles, also known as plastic resin pellets, are now a major source of plastic pollution on beaches globally, thus it is important to elucidate their weathering patterns and environmental fates as well as the associated pollutants. In this study we collected nurdles from 24 sites in the coastal bend region of south Texas, covering areas from the near shore railway stations to the adjacent bays and barrier islands. The morphologies of nurdles and associated pollutants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and mercury, were investigated. The results showed that the nurdles varied greatly in color, shape, polymer composition, and oxidation degree. More than 80 % of the nurdles were made with polyethylene, and the rest with polypropylene, polyester, polystyrene, polyethylene-vinyl acetate, and polyvinyl chloride based on Fourier Transform Infrared Spectroscopy (FTIR) analysis. PCBs were not detected on nurdles. PAHs and mercury on nurdles were detected at 12 % and 20 % of the sampling sites. The total concentrations of detectable PAHs ranged from 92.59 to 1787.23 ng/g-nurdle, and the detectable mercury concentrations ranged from 1.23 to 22.25 ng/g-nurdle. Although the concentrations of these pollutants were not at the acute toxic effect level, the presence of PAHs and mercury suggested the potential risk of pollutant exposure to marine organisms in ecosystems, given the fact that nurdles are persistent in the environment.

Divergence in life-history traits among three adjoining populations of the sea snake Emydocephalus annulatus (Hydrophiinae, Elapidae)

Life-history traits such as rates of growth, survival and reproduction can vary though time within a single population, or through space among populations, due to abiotically-driven changes in resource availability. In terrestrial reptiles, parameters such as temperature and rainfall generate variation in life-histories—but other parameters likely are more important in marine systems. We studied three populations of sea snakes (Emydocephalus annulatus) in adjacent bays in the IndoPacific archipelago of New Caledonia. The extreme philopatry of individual snakes allows us to unambiguously allocate each animal to one of the three populations. Although water temperatures and rainfall do not differ over this small scale, one site experiences more intense winds, restricting opportunities for foraging. Our 18-year mark-recapture dataset (> 1,200 snakes, > 2,400 captures) reveals significant divergence among populations in life-history traits. Survival rates and population densities were similar among sites, but snakes at the most wind-exposed site (Anse Vata) exhibited lower body condition, slower growth, less frequent production of litters, and smaller litters. Weather-driven variation in feeding rates thus may affect life-history traits of marine snakes as well as their terrestrial counterparts, but driven by different parameters (e.g., wind exposure rather than variation in temperatures or rainfall).

Changes in water column oxygen, estimates of productivity and the development of anoxia in a major embayment of the southern Benguela eastern boundary upwelling system

The metabolic balance of autotrophy and heterotrophy in St Helena Bay was investigated through estimates of net community production (NCP) and respiration (R), as determined by changes in water column oxygen. Compared to adjacent coastal waters St Helena Bay was shown to be an area of low-enrichment and high-retention. Productivity during the upwelling season was found to be nutrient limited in the upper few metres (0–3 m) and light limited through self-shading below these surface waters. During the upwelling season the maintenance of thermal stratification in the bay leads to consistently low nutrients (nitrate x¯ = 1.41 mmol m−3) in the surface waters (0–3 m). High biomass maintained through mechanisms of cyclonic retention and entrainment from the Namaqua shelf underlies the rapid attenuation of light through the water column and the consequent limitation of subsurface productivity. As a result productivity maxima were located in surface waters (0 or 3 m) irrespective of the low nutrient concentrations in these waters and the presence of subsurface biomass maxima. Estimates of gross community production (GCP) normalised to Chl a therefore declined sharply below 3 m depth. The mean community compensation depth (Zcc), where R = GCP, was determined to be 9.16 m and was shallower than the 1% light depth for PAR (Z1%PAR) at 15.42 m. The role of light in limiting productivity was clearly evident in that 48% of water column biomass was located below the Zcc. The importance of the light environment in controlling the seasonality of productivity was further evident in that daily rates of productivity in surface waters normalised to Chl a were clearly linked to day length. Phytoplankton community composition and successional status were also shown to influence productivity with the contribution of R to GCP increasing with the succession of phytoplankton communities. Estimates of mean water column Chl a (8.60 mg m−3 as determined from discrete water samples and 8.40 mg m−3 as estimated from profiles of fluorescence) and mean integrated water column productivity (5.38 g C m−2 d−1 as determined by the light-and-dark bottle oxygen method) were ~ 1.5 fold higher than past measurements most of which were made during the late 1970s and 80s. Oxygen depletion within St Helena Bay is locally enhanced as a result of the entrainment and retention of biomass in St Helena Bay and causes it to function as an area of higher carbon sequestration.

Nonlinear supersonic post-flutter response of two-bay composite laminate curved panels

Aeronautical external structures are typically composed of multiple curved panels connected by reinforcement elements that allow structural interaction between the bays. In this context, the present study performs a numerical investigation on the nonlinear aeroelastic behavior of multibay composite laminate curved panels exposed to cross-stream supersonic flow. The post-flutter behavior of thin cylindrical shallow shells with H/h=1 and H/h=2 curvature ratios is examined for symmetric and asymmetric cross-ply laminates. Different from the majority of the studies, the nonlinear panel flutter assessment was not exclusively based on oscillation amplitudes but also energy quantification. Results have shown that the interaction between adjacent bays leads the system to a more complex behavior with higher energetic LCO compared to the widely used single panel approach. Additionally, the mechanical energy discretization concerning the fluttering two-bay panel arrangement exhibited how each bay operates with remarkably distinctive amounts of mechanical energy, which may be used as a direction in the design of active and passive control techniques for flutter suppression.

Integrated Ecological Assessment of Heavily Polluted Sedimentary Basin within the Broader Industrialized Area of Thriassion Plain (Western Attica, Greece)

The Thriassion Plain, the Saronikos Gulf and Eleusis Bay, Western Attica in Greece, receive pressures from the enormous industrial activity, as well as the Athens metropolitan area and the Piraeus port. Therefore, it is considered as brownfield in the Eastern Mediterranean Sea. The multi-component industrial activity has impacted the soil, the groundwater of Thriassion Plain and the coastal marine sediments of the adjacent Eleusis Bay, part of Saronikos Gulf as well as a brackish lagoon, Koumoundourou Lake. The industrial activity is expressed by high contents of metals, and oil products. This study presents the pollution record of selected published papers that indicate the temporal evolution of legislated polluting compounds, supporting researchers to provide solutions and policy makers to focus on the whole spectrum of potential policy alternatives.

The Holocene evolution of Lake St Lucia, Africa's largest estuary: Geological implications for contemporary management

The Holocene evolution of one of Africa's largest estuaries, Lake St Lucia on the east coast of South Africa, is examined and juxtaposed with previous and contemporary management practices aimed at fixing the estuary state at a single point along the system's overall evolutionary pathway. The estuary has been heavily altered over the course of the last century, mostly through mouth management activities aimed at maintaining a direct connection with the ocean. Based on a high-resolution seismic reflection dataset, LiDAR and bathymetry data of the lake system, together with palaeontological (foraminifera and diatoms) and sulfur isotope geochemical data from three long (14–16 m) piston cores, we investigate the system-wide and coeval evolution of the three different sub-basins (False Bay, North Lake and South Lake) that comprise the current estuarine lake system. The northern and southern sections of the system evolved independently of each other since the Last Glacial Maximum, with each area responding differently to early sea-level forcings. In North Lake, the lagoon evolved from fully estuarine (8300 cal. BP) to a restricted lagoon with occasional marine incursions, steadily decreasing tidal prism and the development of marginal spits by wind-driven lagoonal waves. The tidal inlet closed approximately 6200 cal. BP and fluvial conditions became more dominant as main back-barrier conditions became attuned to fluvial supply. Similar conditions prevailed in the adjacent False Bay basin, albeit with an earlier onset due to sheltering by prominent bedrock peninsulas. In contrast, South Lake evolved from a fully estuarine system (9500 cal. BP) with a persistent ocean connection, to a segmented system with a diminished tidal connection by 5500 cal. BP. The inlet sealed at this point and an isolated back barrier system developed. This prompted the system-wide impoundment of waters causing back-barrier flooding and in situ drowning of bayhead deltas and segmenting spits. By 2000 cal. BP, these areas had flooded sufficiently to connect over a bedrock high that had diverted the initial palaeo-valleys to the north and south. A new, single lagoon, representative of the modern-day system formed, with a new marine connection to the modern day Mfolozi River and contemporary estuary. Periodic desiccation of the lake sub-basins since this point has been apparent. Given the complex management plans implemented to stop excess sedimentation, hypersaline events, and the continuation of “normal” lake levels, this is at odds with the natural system's evolution to a pan or wetland-type state. This geological background should be key to informing management plans that work within the natural evolutionary trajectory of the system, as opposed to attempting to maintain an unattainable status quo.

Macrobenthic Mollusca of the Prince Gustav Channel, Eastern Antarctic Peninsula: An Area Undergoing Colonisation

In 2018 RRSJames Clark Rossinvestigated the marine benthic biodiversity of the Prince Gustav Channel area which separates the eastern coast of the Antarctic Peninsula from James Ross Island. The southern end of this channel had been covered by the Prince Gustav Ice Shelf until its collapse in 1995. Benthic samples were collected by an epibenthic sledge at six stations (200–1,200 m depth) in the channel and adjacent Duse Bay. In total 20,307 live collected mollusc specimens belonging to 50 species and 4 classes (Solenogastres, Bivalvia, Gastropoda, and Scaphopoda) were identified. The area may be characterised by it’s low species richness (ranging from 7 to 39 species per station) but high abundances (specifically of the Scaphopods with 11,331 specimens). The functional traits of the community were dominated by motile development and mobility type. Assemblage analyses of the molluscan species abundances within the Prince Gustav Channel stations sit distinct, with no pattern by depth or location. However, when bivalve assemblages were analysed with reference to the wider Weddell Gyre region (15 stations from 300 to 2,000 m depth), the Prince Gustav Channel sits distinct from the other Weddell Gyre stations with a higher dissimilarity between the deeper or more geographically distant areas. The Prince Gustav Channel is undergoing colonisation following the recent ice shelf collapse. With many Antarctic ice shelves threatened under climate warming, this area, with future monitoring, may serve as a case study of benthic faunal succession.

Study on Collapse Resistance of RC Frame under the Corner Column Removal Scenario.

The progressive collapse of buildings induces a variety of catastrophic consequences, such as casualties and property loss over the past few decades. The corner column is more prone to abnormal load events compared to the inner column and outer column; thus, it is easier to trigger progressive collapse. By considering the effects of floor slabs and adjacent bays on progressive collapse behavior, the pseudo-static loading method was used to study the progressive collapse test of a 1/3 scaled, one story, 2 × 2-bay cast-in-place reinforced concrete frame substructure under the removal condition of a corner column. The test results show that the flexural deformation principally concentrates upon the components of a directly affected part (DAP), and compressive arch actions are observed in members of the indirectly affected part (IAP). Moreover, the slab adjacent to the removed column and periphery elements contributes great resistance to a progressive collapse.

Outwelling of total alkalinity and dissolved inorganic carbon from the Hooghly River to the adjacent coastal Bay of Bengal.

The seasonal variability of the lateral flux of total alkalinity (TAlk) and dissolved inorganic carbon (DIC) of the tropical Hooghly estuary is analyzed in this work. In situ observations of water temperature, salinity, dissolved oxygen, TAlk, and pH were measured in four different stations of the Hooghly estuary. It was measured once every month during 2015-2016, and subsequently, DIC was estimated. A carbon budget was constructed to quantify carbon flows through the freshwater-marine continuum of the Hooghly estuary, and plausible impacts on the adjacent coastal ocean, the northern Bay of Bengal, were examined. The biogeochemical mass balance box model was used to compute the seasonal flow of carbon flux, and subsequently, the annual budgeting of lateral fluxes of TAlk and DIC to the adjacent coastal ocean was carried out. The net annual TAlk and DIC flux from the Hooghly estuary to the adjacent coastal ocean were 4.45 ± 1.90 × 1011mol and 4.59 ± 1.70 × 1011mol, respectively. The net annual DIC flux of the Hooghly estuary is about 30 to 60 times higher than surface area integrated air-water CO2 flux, which is an indication of promoting acidification in the adjacent coastal ocean. The present study indicates that the lateral DIC flux has increased substantially in the Hooghly estuary during the last two decades. The increase in inorganic carbon load in the Hooghly estuary due to the enhanced discharge of inorganic and organic matter load in the upper reaches of the estuary led to this increase in lateral DIC flux. The results strongly establish the need of having such regional studies for better understanding the estuarine carbon dynamics, and its role in controlling the adjacent coastal ocean dynamics.

Controls on Nutrient Cycling in Estuarine Mangrove Lake Sediments

We estimated the net exchange of nitrogen and phosphorus species using core incubations under light and dark conditions in estuarine lakes that are the aquatic interface between the freshwater Everglades and marine Florida Bay. These lakes and adjacent shallow water Florida Bay environments are sites where the restoration of hydrological flows will likely have the largest impact on salinity. Sediment respiration, measured by oxygen uptake, averaged (±S.D.) −2400 ± 1300, −300 ± 1000, and 1900 ± 1400 μmol m−2 h−1 for dark incubations, light incubations, and gross photosynthesis estimates, respectively, with dark incubations consistent with oxygen uptake measured by microelectrode profiles. Although most fluxes of soluble reactive phosphorus, nitrate, and N2–N were low under both light and dark incubation conditions, we observed a number of very high efflux events of NH4+ during dark incubations. A significant decrease in NH4+flux was observed in the light. The largest differences between light and dark effluxes of NH4+ occurred in lakes during periods of low coverage of the aquatic macrophyte Chara hornemannii Wallman, with NH4+ effluxes > 200 μmol m−2 h−1. Increasing freshwater flow from the Everglades is expected to expand lower salinity environments suitable for Chara, and therefore, diminish the sediment NH4+ effluxes that may fuel algal blooms.

COVID-19: dental aerosol contamination in open plan dental clinics and future implications.

Study design An experimental study design was used to investigate the spread of splatter/aerosol during simulated dental procedures on a mannequin in open plan clinic and dental clinical teaching laboratory settings. All experiments were based on crown preparation of an artificial maxillary central incisor using a high-speed air turbine over a ten-minute period. Fluorescein dye was introduced into the irrigation system of the handpiece (model 1) and the mannequin's mouth was used to simulate salivary flow (model 2) under varying experimental conditions (suction flow rate, cross ventilation and exposure time). Six experiments were conducted in the open plan clinic while three experiments were undertaken in the clinical laboratory. Customised rigs with collection platforms consisting of filter papers were placed in open plan bays and adjacent walkways. Samples were also collected from a 400 cm2 area in each of the eight adjacent bays. Time course experiments repeated the same procedures on three occasions in a clinical laboratory and utilised a rig with eight four-metre rods supporting collection platforms around a dental mannequin. The distribution of fluorescein dye was analysed by fluoroscopy and spectrofluorometry.Results Contamination levels showed variations under different experimental conditions. In the absence of suction and cross ventilation, contamination was observed at large distances. Use of suction reduced contamination in the operating bay by 53% and 81.83%, while cross ventilation reduced contamination in adjacent and distant areas by 80-89%. Minimal contamination was detected at a distance of >5 m from the operating bay, with the use of medium-volume suction demonstrating that 1.5-metre-high partitions with open fronts limit 99.99% of splatter from aerosol generating procedures (AGPs) to the operating bay. Minimal additional aerosol contamination was detected ten minutes after the procedure.Conclusions Contamination from dental AGPS has the potential to contaminate distant sites in open plan clinics. Risk of cross infection is small if the bays are >5 m apart and contamination can be minimised with the use of suction and cross ventilation.

Unravelling tidal effect on zooplankton community structure in a tropical estuary.

The variability in zooplankton density and species composition in response to tidal oscillations were investigated in the lesser saline upper reaches (E1) and higher saline lower reaches (E2) of the Mahanadi Estuary, located at the mouth of the third largest river in Indian Peninsula. This is the first of its kind high frequency observation over the tidal cycle ranging from highest high tide to lowest low tide in this estuary revealing dynamic variability of zooplankton assemblages. Zooplankton abundance was higher during high tide in comparison to low tide, irrespective of salinity regimes. On the diurnal scale, it was higher at night in comparison to the day at both E1 and E2. The higher abundance of zooplankton groups such as Copepoda, Cladocera, and planktonic larvae during the night at E1 as well as E2 indicating an upward migration. Many of the zooplankton taxa (e.g., Pseudodiaptomus serricaudatus, Pseudodiaptomus sp., Acartia danae, Acrocalanus longicornis, Oithona sp., Corycaeus andrewsi) migrated towards E1 due to tidal effect during high tide and maintained their position even during low tide. In contrast, the prevalence of limnetic taxa (e.g., Brachionus rubens, Polyarthra vulgaris, Bosminopsis deitersi, Moina micrura, Heliodiaptomus sp.) at E2 during low tide indicated a predominant riverine source. The tidal variability of Brachyura (zoea and megalopa) revealed different emergence times that indicated dispersal of zoeas to the adjacent Bay of Bengal and the return of magalopa to the Mahanadi Estuary. Species diversity index was higher during high tide, and prominent at E2. At E1, marine, fresh, marine-brackish, and marine-brackish-fresh zooplankton species dominated during high tide, while brackish-fresh taxa dominated during low tide. Differently, E2 was enriched with marine, marine-brackish, and marine-brackish-fresh taxa during high tide, whereas fresh, brackish-fresh, and marine-fresh dominated during low tide. Salinity and suspended matter influenced the dominant zooplankton taxa at E2 and E1, respectively. Zooplankton assemblages exhibited a pattern of prominent diurnal-spatial variation in comparison to the tidal scale in the Mahanadi Estuary. Overall, this study documented a very high zooplankton diversity (92 taxa belonging to 13 groups) and significant variations in species abundance which highlighted the importance of carrying out sampling over the tidal cycle at contrasting salinity regimes.

A Comprehensive Assessment of Sediment Dynamics in the Barataria Basin (LA, USA) Distinguishes Riverine Advection from Wave Resuspension and Identifies the Gulf Intracoastal Waterway as a Major Sediment Source

Barataria (LA, USA) is an interdistributary deltaic basin that has experienced extensive marsh loss. The fate of these marshes is strongly controlled by the concentration of total suspended sediments (TSS) in the adjacent open bay water. This parameter, however, is poorly constrained, thus limiting the ability to predict the future marsh evolution. Here we investigate the open bay water sediment dynamics using three complementary approaches: monthly field surveys at 37 locations along the bay axis over 22 years, remote sensing over 20 years, and turbidity time series at 5 locations over 4 years. Monthly field sampling and remote sensing reveal that the TSS is highly seasonal and spatially variable. In particular, the sediment delivered through the Gulf Intracoastal Waterway (GIWW) during the flood season (January–April) dominates the TSS signal in mid-Barataria. This sediment originates mainly from the Atchafalaya River and is advected for more than 100 km before reaching Barataria. Because of a hysteresis in sediment transport, the TSS in the river water, and hence in the GIWW, is not uniquely related to the river discharge. As such, late flood season discharges do not contribute much sediment to Barataria. We estimate that the GIWW delivers on average 0.21 Tg of sediment per year to mid-Barataria. A different sediment input is instead present in lower Barataria, where river-borne sediment exiting the “birdfoot” of the Mississippi Delta is advected by easterly winds, especially during spring. At all five stations within Barataria, turbidity time series reveal that the daily sediment dynamics is mainly associated with local wind wave resuspension. River inputs and wave resuspension contribute nearly equally to the yearly averaged TSS, of about 80 mg/l on average. The GIWW, built in the 1920s, is an important but overlooked source of sediments for Barataria that can serve as a present-day analogue for the proposed Mississippi River sediment diversions.

Submarine groundwater discharge and associated nutrient fluxes in the Greater Bay Area, China revealed by radium and stable isotopes

The estuary-bay system is a common and complex coastal environment. However, quantifying submarine groundwater discharge (SGD) and associated nutrient fluxes in the complex coastal environment is challenging due to more dynamic and complicated riverine discharge, ocean processes and human activities. In this study, SGD and SFGD (submarine fresh groundwater discharge) fluxes were evaluated by combining stable and radium isotopes in the Guangdong-Hong Kong-Macau Greater Bay Area (GBA), a typical estuary-bay system. We first built a spatially distributed radium mass balance model to quantify SGD fluxes in coastal areas of GBA integrating the Pearl River Estuary (PRE), bays and shelf. We then used the stable water isotope (δ2H and δ18O) end-member mixing model to distinguish submarine fresh groundwater discharge (SFGD) from SGD. Based on the 228Ra mass balance, the estimated SGD fluxes in the PRE, adjacent bay, and shelf areas were (6.14 ± 2.74) × 108 m3 d-1, (3.00 ± 1.11) × 107 m3 d-1, and (5.00 ± 5.64) × 108 m3 d-1, respectively. Results showed that the largest area-averaged SGD was in the PRE, followed by that in the adjacent shelf and the bay. These differences may be mainly influenced by ocean forces, urbanization and benthic topographies controlling the variability of groundwater pathways. Further, the three end-member mixing model of 228Ra and salinity was developed to confirm the validity of the estimated SGD using the Ra mass balance model. In the two models, groundwater end-member and water apparent age estimation were the main sources of uncertainty in SGD. The estimated SFGD flux was (1.39 ± 0.76) × 108 m3 d-1, which accounted for approximately 12% of the total SGD. Combining stable and radium isotopes was a useful method to estimate groundwater discharge. Moreover, the estimated SGD associated dissolved inorganic nitrogen (DIN) flux was one order of magnitude higher than other DIN sources. SGD was considered to be a significant contributor to the DIN loading to the GBA. The findings of this study are expected to provide valuable information on coastal groundwater management and environmental protection of the GBA and similar coastal areas elsewhere.

Nonlinear supersonic flutter of multibay cross-stream shallow shells

This work investigates the interaction between adjacent bays and the effect of the curvature ratio in the nonlinear response of cross-stream curved panels. The study presents a numerical investigation of shallow shells’ linear and nonlinear dynamic behavior exposed to supersonic flutter. The finite element model embedding the aerodynamic piston theory and the Newmark method for direct time-domain integration of the nonlinear aeroelastic equations are used. Results show that the downwind bay of a two-bay cross-stream curved panel oscillates with much higher amplitudes than the equivalent single panel approach for all curvature ratios under consideration. Jump discontinuities in the LCO amplitudes were observed for a range of post-flutter dynamic pressure. The mutual existence of LCO branches in the amplitude envelope was checked through the sensitivity to initial conditions. No sudden jump in the LCO amplitudes was found for the higher curvatures, whereas a more complex behavior is encountered, especially for the downwind bay. Amplitude envelopes show that the nonlinear coupling between adjacent bays severely influences the dynamic behavior of curved panels subjected to cross-stream supersonic flow. Consequently, relying on single panel modeling may be unsafe for structural design and fatigue-life prediction for supersonic panel flutter suppression.

Stage-specific overcompensation, the hydra effect, and the failure to eradicate an invasive predator

As biological invasions continue to increase globally, eradication programs have been undertaken at significant cost, often without consideration of relevant ecological theory. Theoretical fisheries models have shown that harvest can actually increase the equilibrium size of a population, and uncontrolled studies and anecdotal reports have documented population increases in response to invasive species removal (akin to fisheries harvest). Both findings may be driven by high levels of juvenile survival associated with low adult abundance, often referred to as overcompensation. Here we show that in a coastal marine ecosystem, an eradication program resulted in stage-specific overcompensation and a 30-fold, single-year increase in the population of an introduced predator. Data collected concurrently from four adjacent regional bays without eradication efforts showed no similar population increase, indicating a local and not a regional increase. Specifically, the eradication program had inadvertently reduced the control of recruitment by adults via cannibalism, thereby facilitating the population explosion. Mesocosm experiments confirmed that adult cannibalism of recruits was size-dependent and could control recruitment. Genomic data show substantial isolation of this population and implicate internal population dynamics for the increase, rather than recruitment from other locations. More broadly, this controlled experimental demonstration of stage-specific overcompensation in an aquatic system provides an important cautionary message for eradication efforts of species with limited connectivity and similar life histories.

Connectivity of Avicennia marina populations within a proposed marine transboundary conservation area between Kenya and Tanzania

Threatened ecosystems such as intertidal mangrove forests often span political boundaries and require cross-border conservation planning initiatives. Population connectivity is key to establish transboundary collaborative actions. In this study, we assessed genetic diversity and connectivity of mangrove populations in a proposed transboundary conservation area (TBCA) between Kenya and Tanzania, where human demography exerts increasing pressure on biodiversity and ecosystem services. East African mangrove ecosystems comprise a complex pattern of estuaries and coastal bays, with Avicennia marina as a major mangrove component. Our main objective was to test a hypothesis of overall migration directionality reflecting regional ocean surface current flows. Fourteen microsatellite markers in 670 A. marina trees revealed no overall significant difference in allele or gene diversity levels between populations but showed an overall effect of geographic distance with a gradient of admixed gene pools. Migration tests and Approximate Bayesian computations supported a customized stepping-stone model of overall south to north migration with bidirectional gene flow and admixture between adjacent bays near the Kenya-Tanzania border. Observed patterns of gene flow suggest an important effect of large rivers and connections via creeks. Our results indicate that relevance for conservation and management of mangroves areas may remain largely within a hydrological connectivity context of each bay, despite prevailing genetic estimates reflecting historically well-connected mangroves between bays. For sustainable management, populations must be considered complementary and not redundant. Hence, transboundary regions must primarily adhere to local contemporary conservation and management, and not solely rely on the assumption of strong regional connectivity built historically.

Measuring mutual movements, mixing, and mingling among multiple mangrove bays by an important estuarine sea bream (Archosargus rhomboidalis)

Quantifying the spatial and temporal aspects of fish residency is needed to understand energy transfer, habitat function, contaminant exposure, and effective design of MPAs in estuarine systems. The spatial and temporal movements of 19 sea bream (Archosargus rhomboidalis), an ecologically important species in mangrove estuaries of the western Atlantic, were investigated in multiple bays on a Caribbean Island over two years using surgically implanted acoustic transmitters. Fish were almost continuously monitored (residency index 96–100%) by an array of hydrophones during the 11–13 month battery-life of their transmitters. Individual fish utilized small core areas (mean = 9.8 ha during daytime and 11.0 ha at night), displayed daily site fidelity (mean = 57% overlap in day night core area), showed no evidence of an ontogenetic increase in core habitat size, and many exhibited a change in the bays utilized during winter months which is coincident with suspected spawning. Fish captured from the same bay generally occupied the same spaces within the study area, and in similar proportions, compared to fish captured in adjacent bays. Fish from different bays did not mix and wander throughout the ecosystem even though it is all suitable habitat and is used by different groups of localized individuals. This similarity of occupancy patterns is limited to the spatial scale of bays and temporal scales of weeks or months. When considered at the resolution of individual receivers and hourly time steps, most fish are not in close proximity to one another for the vast majority of the time. Although some pairs of fish had as many as 84% of their hourly detections on the same receivers in the month after tagging, they gradually spent less time near each other, even though their overall pattern of movements was consistent at the scale of whole bays. This highlights the importance of examining movements of fish on multiple spatial scales and time-intervals to understand their interactions.

The effect of curvature in nonlinear supersonic flutter of panels with adjacent bays

Structural skins of aerospace vehicles are typically made of large, internally reinforced curved panels. The presence of stiffening components subdivides the panel into several bays that interact structurally. In this context, the present study investigates the effects of adjacent bays interaction in curved panels under supersonic flutter. The analyses reveal severe jumps in the post-flutter LCO amplitudes and sub-critical bifurcation with the coexistence of different LCO branches for a specific range of dynamic pressure. These discontinuities consist of abrupt changes in the LCO amplitudes, directly related to the nonlinear coupling between adjacent bays under supersonic flutter with strong sensitivity to initial conditions.

Redirecting sediment and rearranging social justice

Efforts to manage the Mississippi River have produced hydrologic, geomorphic, and social change. Sediments have been the focus of contentious litigation; and engineers in the mid-nineteenth century argued for returning sediment to the city to raise land. Levees, built of sediment, protected the city and also guarded the powerful planter class. By forcing the sediment-bearing discharges into the Gulf of Mexico, the levee system denied sediment to most of the floodplain which allowed the delta to subside at a pace that was faster than land building caused by crevasses, and also permitted the intrusion of salt water into the valuable fisheries in the adjacent bays and estuaries. Further manipulations in the form of massive spillways followed the 1927 flood. This hydrologic re-plumbing disrupted the ecology and economy of floodplain and coastal areas. Current plans to restore the disappearing delta using sediment diversions will further disrupt the re-established economies. Upstream, reservoirs now capture much of the river-borne sediment which limits the viability of restoration efforts. The redirection of sediment has produced both geomorphic and social change in the lower delta and efforts to restore coastal wetlands, as previous alterations, will impose disruptions on the state’s marginalized residents.