Coastal Embayment Research Articles

Unresolved taxonomy confounds invasive species identification: theLysmata vittataStimpson, 1860 (Decapoda: Caridea: Lysmatidae) species complex and recent introduction ofLysmata vittatasensu stricto in the western Atlantic

AbstractPeppermint shrimp resembling Lysmata vittataStimpson, 1860, a species native to the Indo-West Pacific, were found in the lower Chesapeake Bay and adjacent coastal embayments in 2013, representing the first recorded introduction of this species in the northwestern Atlantic. Conflicting morphological descriptions, inconsistent morphological terminology, and limited molecular data (i.e., unresolved taxonomy), as well as the destruction of the type material of L. vittata, created uncertainty regarding proper identification. We provide the first phylogeny incorporating individuals from across the presumed native and introduced range of L. vittata. Morphological and phylogenetic analyses clearly indicate L. vittata represents a species complex of two widely divergent groups: 1) “Bruce Type” with a uniramous dorsal antennule that agrees with A.J. Bruce’s 1990 redescription of L. vittata, and 2) “Rauli Type” with a one-article accessory branch on the dorsal antennule that agrees most closely with the junior synonym L. rauliLaubenheimer & Rhyne, 2010. Given the taxonomic ambiguity surrounding L. vittata, we designate the individual used by A.J. Bruce to redescribe L. vittata and incorporated in our analyses as a neotype to fix the identity of this species. We therefore identify introduced North American and New Zealand populations as L. vittata sensu stricto and postulate that the native range spans temperate/subtropical East Asia. These data suggest that L. rauli is a valid species, which includes a possible undescribed sister species. We confirm the presence of L. californicaStimpson, 1866 in New Zealand, the first non-native record for this species. We also provide data suggesting L. disparHayashi, 2007 may be more widespread in the Indo-West Pacific than currently known and consider L. lipkeiOkuno & Fiedler, 2010 to be a likely junior synonym.

A distinctive new species of the genus Polyonyx Stimpson, 1858 (Crustacea: Decapoda: Anomura: Porcellanidae) from Okinawa, southwestern Japan.

The new porcellanid crab Polyonyx deezi n. sp. is described on the basis of two specimens from Okinawa Island, Ryukyu Islands, southwestern Japan. The new species belongs to the P. sinensis group and may be closest to P. socialis Werding Hiller, 2019 in the comparatively broad proportions of the carpi of the chelipeds and meri of the ambulatory legs. However, P. deezi n. sp. is immediately distinguished from all other congeners by the median branchial margins of the carapace being bluntly angular and produced laterally and the dorsal surfaces of the carapace and chelipeds with distinct protuberances. The occurrence of P. deezi n. sp. from coral reefs may be unusual in species of the P. sinensis group because many of the known species have been recorded from estuaries or coastal embayments. An identification key to the Indo-West Pacific species of the Polyonyx sinensis group is provided.

Analysis of phytoplankton variations and community structure in Kuwait Bay, Northwestern Arabian Gulf

Environmental vicissitudes cause short-term variability in plankton dynamics. The effect would be more pronounced in shallow, semi-enclosed tidal coastal systems. Here, we analyzed diurnal fluctuations in coastal phytoplankton and environmental factors in relation to seasonal tidal cycles (October 2016, Fall and February–March 2017, Winter) in a sub-tropical coastal embayment (Kuwait Bay) in the northwestern Arabian Gulf. Water-column profiles were obtained for chlorophyll, photosynthetically active radiation (PAR), salinity, temperature, and dissolved oxygen. Winter was characterised by relatively cold, well‑oxygenated, nutrient-rich, and high saline waters than the fall. Nutrient levels were high during low tide and low during high tide. High-performance liquid chromatography (HPLC) analysis of phytoplankton marker pigments revealed the presence of twelve different phytoplankton functional groups. Diatoms and dinoflagellates were the most dominant groups with significant surface-bottom differences during both seasons. The phytoplankton biomass (Chl a) was the highest during the low light hours of the day with apparent day-night differences. The picoplankton community was mainly represented by the autotrophs Synechococcus (in Fall) and picoeukaryotes (in winter) with clear seasonal patterns. Compared to picoautotrophs, picoheterotrophic biomass was relatively high during winter. This study revealed that light availability and tidal mixing are the factors regulating variability in the phytoplankton community composition and biomass (Student’'s t-test, two-tailed; (P ≤ 0.1) in Kuwait Bay. High-resolution monitoring programs are essential to capture the natural variability of phytoplankton and its implication on the biogeochemistry of the shallow tide-dominated coastal systems.

Historical ecology of semi-enclosed coastal embayments: tools and techniques for discovering ecological events of the recent past

The sheltered environments of coastal embayments have played a vital role for humans for millennia and their resources have underpinned modern industrial development globally. Their effective management and restoration remains an enormous challenge, owing, in part, to lack of recognition of the threshold changes that occurred in many bays prior to scientific study (i.e. >50 years ago). Advances in marine extraction technologies and increased clearing of catchments for agriculture and urbanisation in recent history (∼400 years) have resulted in profound physical, chemical and biological changes to these ecosystems. More recently, the integration of ecology, history, archaeology, economics and fisheries science have contributed to the emerging field of ‘marine historical ecology’ (MHE). The synthesis of information from these different disciplines can markedly improve knowledge of past ecosystem condition, thereby assisting managers to set realistic goals for environmental restoration to improve biodiversity and ecosystem function. This paper reviews historical knowledge of long-term environmental degradation processes in coastal embayments, summarising the wide range of methods and techniques used as evidence and providing examples from around the world, thereby illustrating the need for longer time-frames of reference for contemporary restoration ecology.

Constraining nitrogen sources to a seagrass-dominated coastal embayment by using an isotope mass balance approach

Nitrogen (N) is often the key nutrient limiting primary production in coastal waters. Quantifying sources and sinks of N is therefore critical to understanding the factors that underpin the productivity of coastal ecosystems. Constraining nitrogen inputs can be difficult for some terms such as N fixation and marine exchange as a consequence of uncertainties associated with scaling and stochasticity. To help overcome these issues, we undertook a N budget incorporating an isotope and mass balance to constrain N sources in a large oligotrophic coastal embayment (Western Port, Australia). The total N input to Western Port was calculated to be 1400 Mg N year−1, which is remarkably consistent with previous estimates of sedimentation rates within the system. Catchment inputs, N fixation, marine sources and atmospheric deposition comprised 44, 28, 28 and 13% of N inputs respectively. Retention of marine-derived N equated to ~3 and ~10% of total N and NOx flushed through the system from the marine end-member. The relatively high contribution of N fixation compared with previous studies was most likely to be due to the high proportion of nutrient-limited intertidal sediments where N is mediated by seagrasses and sediment cyanobacteria.

REGIONAL COASTLINE CHANGES AND FUTURE PREDICTED SCENARIO ON SOUTHERN BRAZIL

The Rio Grande do Sul (RS) coastline consists of a 615 km long sandy barrier, with a NE-SW orientation. It is characterized by alternating slightly concave and convex segments extending from the rocky headlands at Torres up to the Chuí stream, at the Uruguayan border. In general, the genesis of this geographical area is related to changes in sea level in the Quaternary, when a complex Lagoon-barrier system was created. This study presents a compilation of decades of studies about short-term monitoring and long-term projections conducted by the two local main research centers on the subject. In this study, trends in shoreline behavior between 2002 to 2013 were analyzed. Results indicated that 43,5% of the coastline was stable, 41% was under moderate erosion, 9% in moderate progradation, 3% under pronounced progradation, and 3,5% under severe erosion. The specific causes of these variations are not yet fully understood. However, some factors are likely to be responsible for coastline behavior in the long and short term: geological inheritance which influenced coastline orientation, regional sediment budget, as well as shoreface gradient and bathymetry. The main erosive hotspots found along the RS coastline are influenced by wave energy focus due to refraction caused by the local bathymetric features and coastline orientation. The Cassino Beach sector, however, has a pronounced progradation which in the long term can be mainly related to its coastline orientation, and more recently due to jetties built at the Patos Lagoon inlet, which provided more sediment retention of the prevailing net longshore drift to the northeast. This study also offers a review about shoreline changes along the four existing inlets. Coastal vulnerability to sea-level rise (SLR) analyzed through coastline recession distances in long-term scenarios (2030 and 2100) indicated that the most vulnerable sectors are those located along coastal embayments, which coincide with low gradient shorefaces.

Palaeoshoreline reconstruction and underwater archaeological potential of Liman Tepe: A long-occupied coastal prehistoric settlement in western Anatolia, Turkey

Rising post-glacial sea levels had a major influence on the prehistoric settlement of the Aegean coastal zone. At Liman Tepe, an important Chalcolithic-Bronze Age coastal settlement on the south coast of the Bay of Izmir, archaeological evidence suggests a Neolithic (ca. 9600-5500 BCE) presence, but no settlement has been discovered on land. Sea levels during the Neolithic period were between 6 and >20 m below present and there is high potential for discovery of submerged prehistoric sites. Marine sediment coring and geophysical investigations (bathymetry, sub-bottom seismic profiling; >600 line-km) were conducted over a 4-km2 inshore area to assess the underwater archaeological potential. Multi-proxy sediment analysis (sedimentary facies, micropalaeontology, micro-XRF geochemistry) was conducted on 20 cores to reconstruct the relative sea level (RSL) history and coastal palaeogeography. Palaeoshoreline positions were estimated by back-stripping of the decompacted sediment thickness from a digital bathymetric model (DBM).The DBM reveals a drowned middle Holocene coastal plain with well-preserved relict river channels, palaeoshorelines and coastal headlands. The inshore stratigraphy consists of shoreface, foreshore and lagoonal deposits overlying terrestrial clay and palaeosols, defining a marine transgressive surface (MTS). The MTS records the inundation of the coastal plain prior to ca. 4000 BCE (transgressive systems tract; TST) and is marked in cores by an increasing abundance of foraminifera and a rise in Ca/Ti. During the Early Neolithic (ca. 6700 BCE), the shoreline was >500 m seaward (RSL ∼ −14 to −16 m) and Karantina Island was a broad coastal headland with a sheltered western embayment. By the Middle Chalcolithic (ca. 4800 BCE), the coastline had transgressed ∼800 m inland of the present shoreline and the Liman Tepe headland was separated from the mainland by a shallow coastal wetland. The maximum transgression (∼1 km inland at ca. 4000 BCE) was followed by a shift to a high-stand systems tract (HST) and rapid coastline progradation by barrier accretion and lagoon development. Palaeogeographic maps identify areas with high underwater archaeological potential: 1) palaeoriver channels and lowland riverine habitats formed during the TST, prior to 4000 BCE, 2) submerged palaeoshorelines and coastal promontories (water depths 10–14 mbsl) with high potential for Neolithic sites, and 3) protected coastal embayments and lagoons representing possible prehistoric anchorage sites.

Connections and clustering of Paralytic Shellfish Toxin events among coastal embayments in an archipelago partly mediated by advection

The potential for advection to influence harmful algal bloom (HAB) spread in adjacent embayments and islands has not been investigated in the Philippines as previous studies have focused on HAB dynamics within specific embayments. Advection of HABs may be relevant in the Samar-Leyte region where adjacent sites are subject to recurrent blooms of Pyrodinium bahamense. We used different analyses to extract the potential role of advection in blooms in the region. First, we used Bayesian and information theoretic approaches applied to historical data on shellfish bans to quantify spatial dependencies in HAB occurrences between sites. Then, to determine whether such dependencies are related to circulation patterns in the region, we analyzed connectivity using a hydrodynamic model coupled with a conservative tracer-based HAB model. The Bayesian network showed that in 7 out of 11 sites, the probability of a shellfish ban depended on the state of an adjacent site. Site pairs with direct dependence relations also shared relatively high similarity in HAB occurrences over time. In the modelled network, bans tend to occur sequentially, spreading from a few sites with relatively high probabilities for ban events. A subset of sites (sources) were found to be informative of future HAB event probabilities in other sites (destinations) over time lags that are generally longer the farther the destination. Modelled surface advection showed high connectivity strengths between sources and destinations associated with circulation features, e.g., an anticyclonic current in Leyte, wind-driven coastal current in western Samar, and tidally-driven flow in the shallow embayments in southwest Samar. High connectivities were correlated with direct dependence relations in the Bayesian network. Connectivity explained up to about 1/3 of the variance in statistical dependencies between ban signals. Our results show that Paralytic Shellfish Toxin events within this region can be due to advection of blooms originating from nearby areas rather than localized cyst dynamics within an embayment. Particular sites were also identified as potential indicator sites within spatial clusters for monitoring since they are typically where blooms originate and spread from.

The Resuspension and Deposition of Biomediated Sediments in Upper South Cove, Nova Scotia, Canada

Sutherland, T.F.; Amos, C.L., and Grant, J., 2022. The resuspension and deposition of biomediated sediments in Upper South Cove, Nova Scotia, Canada. Journal of Coastal Research, 38(1), 19–34. Coconut Creek (Florida), ISSN 0749-0208. Coastal seabed sediment stability is mediated by microalgal and bacterial biofilms. The resuspension of organic suspended particulate matter (SPM) in biomediated sediments increases nutrient fluxes to the water column and supplements particulate food supplies for suspension feeders. Thus, quantifying benthic-pelagic exchange pathways of biogeochemical parameters is essential to provide an accurate assessment of carrying capacities of coastal embayments supporting both natural and cultured bivalve populations. Benthic-pelagic transport coefficients such as erosion threshold (U*CRIT-SPM-EROSION), net erosion rate (NERSPM), peak erosion rate (PERSPM), depositional threshold (U*CRIT-SPM-DEPOSITION), and deposition rate (DRSPM) were determined using an in situ benthic flume (Sea Carousel) in the protected inner termination of Upper South Cove (USC). The layered gel-like muddy seabed consisted of a thin biofilm or flocculated material overlying highly reduced black sediments. Eroded material was analyzed for concentrations of SPM, chlorophyll-a (CHL), phaeopigment (PHA), and organic/inorganic content. All stations exhibited a consistent pattern of staggered erosion thresholds of seabed constituents, where U*CRIT-SPM > U*CRIT-PHA > U*CRIT-CHL. Erosion thresholds of these sediment constituents were inversely related to NERSPM, NERCHL, and NERPHA fluxes as part of a principal component analysis. U*CRIT-SPM-EROSION was generally higher than U*CRIT-SPM-DEPOSITION across the individual USC stations, suggesting that SPM deposition largely occurs before erosion. A tight coupling was observed between both the mean NERSPM (1.37×10–3 kg m–2 s–1) and DRSPM (1.23×10–3 kg m–2 s–1) and the occurrence frequency between erosion (44.2%) and deposition (52.5%) phases derived from a 4-day U* time-series profile. Although these results highlight a tight benthic-pelagic coupling system in USC, some overlap appears to occur between the deposition and erosion phases, which can be attributed to the presence of diverse SPM size classes that alter during erosion (shearing) and velocity deceleration (floc-forming) processes. Benthic-pelagic coupling supports the sustained near-bottom turbidity conditions observed in USC.

Biochemical Composition of Seston Reflecting the Physiological Status and Community Composition of Phytoplankton in a Temperate Coastal Embayment of Korea

The biochemical composition of seston along a salinity gradient were examined in the low-turbidity, temperate, estuarine embayment, Gwangyang Bay in Korea. Seasonal variations in sestonic protein (PRT), carbohydrate (CHO), and lipid (LIP) concentrations were analyzed to assess the effects of physiological status and taxonomic composition of phytoplankton. The concentrations of biochemical compounds displayed a close relationship with chlorophyll a (Chla). PRT:CHO ratios were high (>1.0) in the estuarine channel in warmer months and in whole bay in February, indicating a N-replete condition for phytoplankton growth. High CHO:LIP ratios (>2.5) in the saline deep-bay area during the warmer months (>2.0) emphasized the importance of temperature and photoperiod over nutritional conditions. The low POC:Chla (<200), molar C:N (~7) ratios, and biopolymeric carbon concentrations coupled with high primary productivity indicated a low detrital contribution to the particulate organic matter pool. Diatom dominance throughout the year contributed to consistently high carbohydrate concentrations. Furthermore, generalized additive models highlighted that phytoplankton community (i.e., size) structure may serve as an important descriptor of sestonic biochemical composition. Collectively, our results suggest that physiological and taxonomic features of phytoplankton play prominent roles in determining the biochemical composition of seston, supporting the fact that the ecosystem processes in Gwangyang Bay are largely based on phytoplankton dynamics.

An ensemble of Bayesian SPARROW models for the Precambrian Shield in the eastern Georgian Bay drainage basin, Ontario, Canada

The present study applied an ensemble of Bayesian SPARROW models in the eastern Georgian Bay drainage basin informed by multi-agency tributary water quality monitoring data collected in the area. Consistent with our current understanding of the role of wetlands in the Precambrian Shield, our analysis showed that they could be responsible for nearly 30% of the total phosphorus (TP) loading from forested areas and 23% of the delivered TP from the eastern Georgian Bay drainage basin. Agricultural areas contribute over 40% of the TP loading associated with anthropogenic activities, which was two times higher than the predicted nutrient losses per unit area in southern Georgian Bay. This finding raises concerns regarding the likelihood of elevated eutrophication risks from future expansion of agriculture in central and northern Ontario. Considering the uncertainty pertaining to their broader influence, cottage septic fields were estimated to be the second anthropogenic P source after agriculture, accounting for 9% of the delivered TP loading to the downstream outlets into Georgian Bay. Research on eutrophication of coastal embayments in Georgian Bay has historically focused on factors, such as basin morphometry, internal P loading, and dreissenid-mediated nearshore shunt. In this context, our SPARROW model offered an additional perspective by estimating that a significant fraction (≈90%) of the TP loading delivered to the Georgian Bay embayments could be originating from upstream sites, even though our predictions suggested that nearly half (49%) of P loading reaching the stream network deposits on the sediments of inland lakes in central Ontario.

Anthropogenic nitrogen loading and risk of eutrophication in the coastal zone of Atlantic Canada

Nutrient pollution derived from human land-use activities remains a major cause of the eutrophication of coastal ecosystems around the world. In this study, we conduct a nutrient loading analysis for the coastal watersheds bordering the Bay of Fundy and Scotian Shelf of Atlantic Canada, a cold temperate region of the Northwest Atlantic that exhibits strong gradients in oceanographic conditions and human uses of the coastal zone, and where coastal development is expected to increase in the coming decades. Our objective was to apply the Nitrogen Loading Model (NLM) framework to determine the regional distribution and intensity of nitrogen inputs from land-based sources (wastewater, atmospheric deposition, land use, fertilizer applications, and regional industries) to coastal marine environments, and subsequently identify coastal embayments at risk of developing symptoms of eutrophication. Across all 109 watersheds examined, the estimated mean total nitrogen load varied by three orders of magnitude. The largest loads occurred in the most heavily urbanized and densely populated watersheds, where wastewater inputs contributed the most (>80%) to loading rates. Where the footprint of human activity was small, atmospheric deposition of nitrogen was an important contributor to the total load; however, localized point sources (i.e. seafood processing, fur farming) were significant contributors to the total load in smaller sized watersheds. Coastal embayments with small surface areas and low tidal exchange volumes were most likely to have estuarine loading rates that exceeded previously established thresholds for the loss of submerged aquatic vegetation (e.g., eelgrass). In contrast, none of the embayments were deemed likely to develop anoxia. This analysis enables a novel comparison of nitrogen loading from watersheds across a range of land cover types, watershed characteristics, and human land-use activities, while providing a baseline for the detection of future environmental change in the region. Overall, we emphasize the importance of including human activities that occur on the landscape in future marine coastal planning.

Phytoplankton Fuel Fish Food Webs in a Low-Turbidity Temperate Coastal Embayment: A Stable Isotope Approach

Trophic contributions of diverse OM sources to estuarine and coastal food webs differ substantially across systems around the world, particularly for nekton (fish, cephalopods, and crustaceans), which utilize basal resources from multiple sources over space and time because of their mobility and feeding behaviors at multiple trophic levels. We investigated the contributions of putative OM sources to fish food webs and assessed the spatiotemporal patterns, structures, and trophic connectivity in fish food webs across four seasons from three closely spaced (10–15 km) sites: an estuarine channel (EC), a deep bay (DB), and an offshore (OS) region in Gwangyang Bay, a high-productivity, low-turbidity estuarine embayment off the Republic of Korea. While nearly all previous studies have focused on few representative species, we examined δ13C and δ15N values of whole nekton communities along with dominant benthic macro-invertebrates, zooplankton, and their putative primary food sources. The δ13C and δ15N values coupled with MixSIAR, a Bayesian mixing model, revealed that these communities utilized multiple primary producers, but phytoplankton comprised the primary trophic contributor (46.6–69.1%). Microphytobenthos (15.8–20.4%) and the seagrass Zostera marina (8.6–19.8%) made substantial contributions, but the role of river-borne terrestrial organic matter was negligible. Spatially different species composition and stable isotope values, but higher utilization of coastal phytoplankton by estuarine fish, indicated disparate food webs structures between the EC and DB/OS coastal areas, with considerable trophic connectivity. Greater overlaps in fish and cephalopod isotopic niches than among other consumers and a higher estimated carbon trophic enrichment factor for EC nekton confirmed feeding migration-mediated biological transport of coastal OM sources to the estuary. Further, the seasonally consistent structures and resource utilization patterns indicate that fish food webs are resilient to changes at lower trophic levels. Our results contrast with those for other highly turbid coastal systems depending highly on diversified basal sources, including exported terrestrial and wetland detritus alongside autochthonous phytoplankton. Finally, this study provides a novel perspective on the role of OM sources in such low turbidity and highly productive coastal embayments and enhances our understanding of marine ecosystems.

Dispersal of yellowtail kingfish (Seriola lalandi) from a coastal embayment following a recreational fisheries enhancement stocking program: attempts to integrate aquaculture and habitat-based initiatives

Fisheries enhancement initiatives including marine stocking and artificial reef deployments are becoming increasingly common in many parts of the world. Combining the two by releasing hatchery reared fish onto artificial reefs is used in sea-ranching operations but is an approach rarely adopted for recreational fisheries. Yellowtail kingfish (Seriola lalandi) form a valuable recreational fishery in Australia and in 2018 a pilot stocking program was initiated to enhance this fishery. Fish were released onto estuarine artificial reefs in Botany Bay to evaluate if estuarine artificial reefs are suitable release habitat for juvenile yellowtail kingfish and to monitor their dispersal patterns using acoustic telemetry and a tag-recapture program. Both approaches showed similar patterns, indicating juvenile yellowtail kingfish rapidly dispersed from the release location and can travel at least 60 km during their first weeks in the wild. Twenty percent of the acoustically tagged fish entered nearby estuaries to the north and south and dart tagged fish were also recaptured in these estuaries, indicating that the estuaries provide habitat for juveniles. There was little interaction between stocked fish and two large coastal artificial reefs positioned near Botany Bay. Stocked yellowtail kingfish will likely disperse rapidly from release locations which is consistent with their pelagic life history. While this may present challenges to fisheries managers, increasing release numbers to maintain stocking densities over a broader area may provide a solution. Future releases of fish on coastal natural and artificial reefs are an important next step in refining stocking practices for this species and will help further identify key juvenile habitats.

An assessment of residence and influence times in Xiamen Bay, China

Water transport time scales are important indicators to assess the renewal of substance inside coastal embayments. Estimates of water renewal efficiency represented by residence and influence times in Xiamen Bay were made via a series of numerical experiments, using the instantaneous tracer injection method. It was found that the average e-folding threshold residence time in the bay is approximately 16.5 days, and that the residence time increases near the entrances to land because water exchange between the bay and the Taiwan Strait is the dominant water-renewal process. The seawater influence time has a similar spatial distribution to the residence time. The freshwater influence time is much shorter in the western region of the bay than in the eastern region, which shows that the influence of Jiulong River freshwater is largely restricted to the western region. The changes in the residence and influence times reveal that increased river discharge mainly accelerates water renewal in the western region of the bay, whereas increased tides mainly accelerate water renewal in the eastern region and the northern part of the western region. The drivers of water renewal were examined using effective transport velocities that were defined based on the decomposition of tracer flux, and showed that tidal residual flow determines the extent of water renewal in Xiamen Bay. The estimation of residence time is sensitive to the operation of instantaneous method. The release of tracer at spring tide results in a shorter residence time and the use of a small threshold can improve the consistency of estimated threshold residence times.

Sources and cycling of nitrogen revealed by stable isotopes in a highly populated large temperate coastal embayment

The identification of nitrogen sources and cycling processes is critical to the management of nitrogen pollution. Here, we used both stable (δ15N-NO3−, δ18O-NO3−, δ15N-NH4+) and radiogenic (222Rn) isotopes together with nitrogen concentrations to evaluate the relative importance of point (i.e. sewage) and diffuse sources (i.e. agricultural-derived NO3− from groundwater, drains and creeks) in driving nitrogen dynamic in a shallow coastal embayment, Port Phillip Bay (PPB) in Victoria, Australia. This study is an exemplar of nitrogen-limited coastal systems around the world where nitrogen contamination is prevalent and where constraining it may be challenging. In addition to surrounding land use, we found that the distributions of NO3− and NH4+ in the bay were closely linked to the presence of drift algae. Highest NO3− and NH4+ concentrations were 315 μmol L−1 and 2140 μmol L−1, respectively. Based on the isotopic signatures of NO3− (δ15N: 0.17 to 21‰; δ18O: 3 to 26‰) and NH4+ (δ15N: 30 to 39‰) in PPB, the high nitrogen concentrations were attributed to three major sources which varied between winter and summer; (1) nitrified sewage effluent and drift algae derived NH4+ mainly during winter, (2) NO3− mixture from atmospheric deposition, drains and creeks predominantly observed during summer and (3) groundwater and sewage derived NO3− during both surveys. The isotopic composition of NO3− also suggested the removal of agriculture-derived NO3− through denitrification was prevalent during transport. This study highlights the role of terrestrial-coastal interactions on nitrogen dynamics and illustrates the importance of submarine groundwater discharge as a prominent pathway of diffuse NO3− inputs. Quantifying the relative contributions of multiple NO3− input pathways, however, require more extensive efforts and is an important avenue for future research.

Sedimentological evidence for seiching in a swell-dominated headland-bay system: Table Bay, Western Cape, South Africa

Table Bay, South Africa, is a typical headland-bay system with a shoreline that can be described by a logarithmic spiral. A peculiarity and unique feature of Table Bay is the juxtaposition of Robben Island opposite its headland. As a consequence, the bathymetry defines an ellipsoidal basin which was postulated to potentially resonate in the form of long-period standing waves (seiches). One aim of this study, therefore, was to investigate whether any evidence for such resonant oscillations could be detected in the geomorphology and sediment distribution patterns. Indeed, the ellipsoidal shape of the basin can be framed by two converging log-spirals with their centres located opposite each other, one off Robben Island and the other on the Cape Town side of the bay. The so-called apex line, which divides the two spirals into equal parts is aligned SW–NE, i.e. more or less parallel to the direction of ocean wave propagation. The distribution patterns of all sedimentary parameters were found to be characterised by a strikingly similar trend to either side of the apex line. This supports the hypothesis that the basin of Table Bay appears to resonate in the form of a mode 1 standing wave, with the node positioned above the apex line in the centre of the bay. The maximum period of such a standing wave was calculated to be around 37 min. The study demonstrates that large-scale sediment distribution patterns can reveal the existence of specific hydrodynamic processes in coastal embayments. It is recommended that this phenomenon be investigated in greater detail aimed at verifying the existence of resonant oscillations in Table Bay and, in the event, at establishing its precise nature and trigger mechanism.

Life at the continental–marine interface: palaeoenvironments and biota of the Alcobaça Formation (Late Jurassic, Central Portugal), with a formal definition of the unit appended

The Kimmeridgian Alcobaça Formation of the Lusitanian Basin forms a mixed carbonate–siliciclastic unit between basinal deposits of the Abadia Formation, and fluvial–terrestrial strata of the Lourinhã Formation. This study presents >2.5 km of detailed logs of nine outcrop sections of the Alcobaça Formation in its type region. Eight of these sections encircle the Caldas da Rainha Diapir, which was a prominent, emergent, passive salt diapir during the time of deposition. Palaeoenvironments of the unit form a complex mosaic of low- to high-energy, carbonate- or siliciclastic-dominated shallow shelf settings; coastal embayments and lagoons; and coastal plains with rivers, lakes and playas. In the strata, abundant microfauna is often joined by a rich macrofauna, usually dominated by bivalves. Locally, corals, calcareous sponges or oysters form meadows or patch reefs. These autochthonous to parautochthonous remnants of former communities are assigned to 35 benthic macrofaunal associations. The integration of palaeoecological analysis of these associations with microfaunal and sedimentological data provides constraint on their salinity ranges, which range from slightly hypersaline to freshwater. Frequent temporal and spatial salinity fluctuations are attributed to variations in relative sea-level, salt tectonics or climate. The NNE-trending Caldas da Rainha Diapir induced pronounced facies differentiation. Predominantly, non-marine siliciclastic facies in the northwest and carbonate to siliciclastic, marine to brackish facies in the southwest are contrasted by shallow-marine carbonate facies east of the diapir. Comprehensive exposure and well-preserved fossils make the Alcobaça Formation an excellent showcase to demonstrate how biofacies analysis can help to disentangle the interplay of climate changes, sea-level fluctuations and salt tectonics. Based on the improved characterisation of the unit, the Alcobaça Formation is formally defined, and seven members are established.

Investigations Exploring the Use of an Unstructured-Grid, Finite-Volume Modelling Approach to Simulate Coastal Circulation in Remote Island Settings—Case Study Region, Vanuatu/New Caledonia

Understanding coastal circulation and how it may alter in the future is important in island settings, especially in the South West Pacific, where communities rely heavily upon marine resources, and where sea level rise (SLR) is higher than the global average. In this study we explore the use of an unstructured-mesh finite-volume modelling approach to assist in filling the knowledge gaps with respect to coastal circulation in remote island locations—selecting the Vanuatu and New Caledonia archipelagos as our example study site. Past limited observations and modelling studies are leveraged to construct and verify a regional/coastal ocean model based on the Finite-Volume Community Ocean Model (FVCOM). Following verification with respect to tidal behaviour, we investigate how changes in wind speed and direction, and SLR, alter coastal water levels and coastal currents. Results showed tidal residual circulation was typically associated with flow separation at headlands and islands. Trade winds had negligible effect on water levels at the coast, however, wind-residual circulation was sensitive to both wind speed and direction. Wind-residual currents were typically strongest close to coastlines. Wind residual circulation patterns were strongly influenced by Ekman flow, while island blocking, topographic steering and geostrophic currents also appear to influence current patterns. Tidal amplitudes and phases were unchanged due to SLR of up to 2 m, while maximum current speeds altered by as much as 20 cm/s within some coastal embayments. Non-linear relationships between SLR and maximum current speeds were seen at some coastal reef platform sites. Under higher sea levels, tidal residual currents altered by less than ±2 cm/s which is relatively significant given maximum tidal residual current speeds are typically below 10 cm/s. Our findings indicate that under higher sea levels, coastal processes governing sediment transport, pollutant dispersal and larval transport are likely to alter, which may have implications for coastal environments and ecosystems. Given winds influence coastal circulation and subsequent coastal processes, changes in trade winds due to climate change may act to further alter coastal processes. It is felt that the current modelling approach can be applied to other regions to help fill critical knowledge gaps.

Morphological evolution of river mouth spits: Wave effects and self-organization patterns

Sand spits as a type of common landform features, associated with wave-dominated deltas, may be influenced by self-organization processes due to shoreline instability at the downdrift flank of the delta, which forms an asymmetric plan morphology for the delta. Here, we examine the spatial-temporal variations and their controlling processes of the sand spit system at the Changhua River mouth, northwest of the South China Sea, by combining 34-year (1986–2019) satellite-derived shoreline data with an ERA5 wave hindcast dataset. The spit system is characterized by extension towards the sea, as well as recurvature towards the land, in response to dominating N-NE waves, whilst, for the sheltered coastal embayment behind the spit, echelon reverse spits have developed due to the dominating S-SW waves. The wave action is governed by a combination of the short period local marine climate of the area (monsoonal regime) and large-scale weather cycles (i.e., El Niño and La Niña), resulting in inter-seasonal and inter-annual variations of the spit neck morphology. Furthermore, the river mouth spit shows self-organization patterns at different temporal-spatial scales, as indicated by the cyclical behavior of the updrift coast, together with the stepwise formation of the echelon reverse spits. Such behavior influences the spit morphology and its rate of change. The geomorphological self-organization patterns contain the information on local dynamic processes, as well as on large scale air-sea interactions as exemplified by the ENSO events. Thus, the analysis presented in this study is valid to describe and estimate the morphological evolution of highly dynamic barrier-spit systems elsewhere, based on wave energy flux estimated by available wave parameters.