Marine Embayment Research Articles

Geology and landforms of Two Peoples Bay Nature Reserve, Western Australia

Context Underlying geology strongly influences landforms, soil composition, and hydrogeology in Two Peoples Bay Nature Reserve, Western Australia, which was mapped by P. E. Playford in 1982. Aims To review the mapping of the Reserve, with the aim to better understand the geological history and landforms of the area. Methods In 2024, I. M. Tyler and K. A. Evans reviewed P. E. Playford’s mapping in the field, viewed aerial photography and geophysical imagery, and reviewed research published since 1984. Key results The oldest rocks are 1290 Ma granitic gneiss and an 1180 Ma granite intrusion. Amalgamation of the Meso- to Neoproterozoic Rodinian Supercontinent put the Albany−Fraser Orogen at the heart of east Gondwana for ~1.0 billion years. At 165 Ma, that plate configuration began to break up, and from 83 Ma, the Eucla Basin opened. Cenozoic landforms and surficial deposits record northward plate movement and collision with south-east Asia at around 23 Ma, causing tectonic uplift, sea-level change, and climate change. The middle to upper Eocene Plantagenet Group was deposited in a shallow marine embayment with Maardjitup Gurlin/Mount Gardner, forming an island. The uplifted Eocene sea floor was lateritized in the Miocene and is presently covered by Holocene eolian sand dunes, peaty swamps and lakes. Maardjitup Gurlin/Mount Gardner was connected to the mainland by Pleistocene eolianite deposits. Conclusions The influence of plate tectonics on the geological evolution of an area is profound, from the origin and composition of the oldest rocks to the present landscape and the youngest surficial deposits. Implications Understanding the geological history of an area is essential to understanding landscape evolution and the natural history of the flora and fauna that inhabit it.

A tale of two end members: Tidal deposits in a semi‐arid, low subsidence, open coastal setting versus a high runoff, high subsidence, restricted environment

AbstractJurassic and Palaeocene tidal deposits of the epeiric Western Interior Sea in Wyoming, USA, differ significantly due to their contrasting climates and tectonic, geographic and depositional settings. Tidally generated, cross‐bedded sandstone bodies contained by incisions are common to both settings and can potentially be uncritically attributed to marine flooding of fluvial systems. Key differences in lithology, ichnology and relationships with surrounding sediment reveal fundamentally different depositional settings, however. The Jurassic system occupied a low accommodation, semi‐arid environment, with geographically open shorelines as relative sea‐level fell, creating an unconformable contact with the underlying, storm wave‐dominated shelf and shoreface deposits. Siliciclastic, intertidal flats formed adjacent to coastal aeolian and fluvial environments during brief turnarounds from the degradational (forced regressive) to aggradational and retrogradational (transgressive) system tract. Basinward of these environments, metre to decimetre‐scale cross‐bedded, bioclastic, subtidal compound dunes and tidal inlet complexes accumulated in areas of minimal clastic flux and within incisions created by submarine tidal currents. By contrast, the Palaeocene tidal systems formed in a high accommodation, subtropical setting, as rising sea levels forced the fluvial to marine transition zone landward and flooded coastal swamps, forming geographically irregular, back‐barrier complexes and tidally influenced fluvial systems. High volumes of siliciclastics, terrigenous organic material and freshwater were delivered by the rivers and created physicochemical stress on the marine embayments. Sandy tidal flat deposits accumulated in lagoons and interdistributary bays, but unlike the Jurassic examples, they do not mark a turnaround from the falling stage to the transgressive system tract. The potential preservation window for tidalites is significantly greater vertically in the aggradational to retrogradational setting than in the degradational system due to greater accommodation. The preservation window is vertically smaller, but areally greater in the Jurassic, forced regressive system because of basinward enhancement of tidal currents driven by complex palaeobathymetry caused by tectonic activity of local pre‐Laramide uplifts.

Structural complexity and benthic metabolism: resolving the links between carbon cycling and biodiversity in restored seagrass meadows

Abstract. Due to large losses of seagrass meadows worldwide, restoration is proposed as a key strategy for increasing coastal resilience and recovery. The emergence of a seagrass meadow is expected to substantially amplify biodiversity and enhance benthic metabolism by increasing primary productivity and respiration. Nevertheless, open questions remain regarding the metabolic balance of aging seagrass meadows and the roles benthic communities within the seagrass ecosystem play in overall metabolism. To address these questions, we investigated a chronosequence of bare sediments and adjacent Zostera marina meadows of 3 and 7 years since restoration alongside a natural meadow located within a high-temperate marine embayment in Gåsö, Sweden. We combined continuous measurements of O2 fluxes using underwater eddy covariance with dissolved inorganic carbon (DIC) and O2 fluxes from benthic chambers during the productive season (July). Based on the ratio between O2 and DIC, we derived site-specific photosynthetic and respiratory quotients, enabling the conversion of eddy covariance fluxes to DIC. We assessed benthic diversity parameters as potential drivers of metabolic flux variability. We observed high rates of gross primary productivity (GPP) spanning −18 to −82 mmolDICm-2d-1, which increased progressively with meadow age. Community respiration (CR) mirrored the GPP trend, and all meadows were net heterotrophic (GPP < CR), with net community productivity (NCP) ranging from 16 to 28 mmolDICm-2d-1. While autotrophic biomass did not increase with meadow age, macrophyte diversity did, elucidating potential effects of niche complementarity among macrophytes on community metabolism. These findings provide valuable insights into how community composition and meadow development relate to ecosystem functioning, highlighting potential tradeoffs between carbon uptake and biodiversity.

Propagation of ship noise in shallow water over a high shear-speed seabed

Assessing the acoustic impact of shipping close to the coast and within ports and harbours requires an understanding of the propagation of underwater sound in these environments. In the Australian context, this often means propagation over seabeds with shear speeds approaching the in-water sound speed, a situation that results in very different propagation conditions to the low shear speed sediments more commonly encountered in other parts of the world. Acoustic propagation modelling approaches were explored using a dataset of continuous underwater recordings featuring a mix of shipping, industrial, and recreational activities, acquired from 23 Jul to 16 Sep 2022 in Cockburn Sound, off the west coast of Australia. Cockburn Sound is a sheltered marine embayment with a relatively uniform water depth of 17–20 m in the 5 km × 11 km central portion of the basin, with a thin, variable thickness (0.5 m–5 m) layer of silty sediments overlying a calcarenite basement. The results of modelling the calcarenite basement as an equivalent fluid were compared to those obtained by modelling it as an elastic solid, and with measurements. Subsequent implications of the choice of geoacoustic model will be discussed

The southern Wyoming Laramide basin: implications for long-term tectonic control on uplift and subsidence

ABSTRACTAn evolving tectonic setting during the Late Cretaceous and Paleocene drove the dramatic transformation of southern Wyoming from a broad marine shelf setting to a series of lacustrine basins. Early dominant control of depositional patterns by flexural tectonics gave way to control by dynamic topography and Laramide-style deformation. The southern Wyoming region demonstrates how progressive partitioning by Laramide movements exerted increasingly dominant control on regional depositional patterns. It did this by creating a long-lived, Laramide uplift-bounded fluvial catchment and basin largely controlled by Laramide-driven subsidence. The Rock Springs and Rawlins uplifts underpinned the basin and exerted their influence in the subsurface. Episodes of Laramide-driven subsidence produced a series of embayments, including the large Rusty–Allen Ridge embayment and the very large deepwater Lewis embayment. The degree of eustatic control in the region would have been greatest at short time scales in the low coastal–shallow-marine settings, causing shoreline oscillations. Several long transgressive episodes followed relatively punctuated progradational periods of coastal-plain construction when supply was generally high from the thrust belt and surrounding uplifts. Laramide activity in the Paleocene led to enclosure of the fluvial basin and the development of a series of smaller marine embayments that mark the end of influence in the region by open and coastal marine processes.

Middle Miocene final demise of remnants of an eastern Neotethyan seaway, Naga Hills, Indo-Myanmar Range

Miocene planktonic foraminifers occur in shale intercalated with thinly bedded siltstone and sandstone of the Surma Group in the foothills of the Naga Schuppen Belt of the Indo-Myanmar Range. Fourteen species from eleven genera are the first clearly imaged middle Miocene foraminifers recorded from the Surma Group in the Naga Hills. This new M5-M6 assemblage from the upper unit of the Bhuban Formation correlates to the uppermost Burdigalian to Langhian (16–14 Ma). Biostratigraphy, paleoenvironment and paleogeography of the assemblage are all significant. They provide a basis for widespread regional and global correlation constraining the timing of elimination of the final remnants of the Neotethyan seaway between India and eastern Eurasia. Results indicate that, unlike the western and Tibetan Himalayas where similar seaways disappeared before the Miocene, a shallow marine embayment that connected to the Indian Ocean endured in eastern parts of the India-Eurasia collision zone until the Middle Miocene.

Pharmaceuticals in multi-media environment from the Jin River to adjacent marine embayment in Southeast China.

Multi-media environmental distribution of 21 pharmaceuticals in river water, coastal water, groundwater and sediments from the Jin River to adjacent marine embayment, Southeast China, was reported for the first time. All the detected 10 pharmaceuticals were antibiotics. Oxytetracycline (OTC), ciprofloxacin (CFC) and enrofloxacin (EFC) were the most ubiquitous antibiotics and could be detected in all water samples. EFC also showed the highest detection frequency (100%) in both riverine and coastal sediments. The detected antibiotics were more widely distributed in coastal environment of Asia, especially China, rather than Europe, USA and Australia. Sulfamethoxazole (SMX) showed stronger sorption onto sediments compared with other antibiotics due to its higher pseudo-partitioning coefficients (846-10,786 L kg-1). The discharged wastewater and aquaculture were the main sources of antibiotics in the multi-media environment. Risk assessment indicated that CFC and SMX posed high risks to Microcystis aeruginosa and Synechococcus leopolensis in river water, coastal water and groundwater.

Traffic in a nursery: Ship strike risk from commercial vessels to migrating humpback whales (Megaptera novaeangliae) in a rapidly developing Australian urban embayment

The rapid recovery of the Australian humpback whale (Megaptera novaeangliae) population and parallel increase in maritime traffic, has increased the spatial overlap between whales and vessels in Australian waters. Ship strike is a recognized global anthropogenic source of mortality or injury to large whales, and a potentially increasing risk in Australia. However, our understanding and evaluation of this threat to humpback whales around Australia, is hindered by the lack of seasonal whale distribution data in high marine traffic areas. Here, we present five consecutive years (2017–2021) of both north and south migrating humpback whale distribution data to quantify the relative risk of ship strike based on the co-occurrence with commercial ships in Moreton Bay. This marine embayment is home to Australia’s fastest growing container port (The Port of Brisbane) and has recently been identified for its ecological importance to this migrating species. We quantified co-occurrence by multiplying predicted whale and ship densities together to estimate both intra- and inter-annual ship strike risk. Ship strike risk increased during the humpback whale’s southern migration (September-October), coinciding with a substantial habitat shift into the Bay during this time. Groups containing calves were a predominant pod type in Moreton Bay. Given their increased vulnerability to ship strike, this study underscores the need for immediate and effective mitigation actions, such as seasonal vessel speed reductions as well as mariner education and outreach programs.

Effects of lubricant oil and diesel on macrofaunal communities in marine sediments: A five year field experiment in Antarctica

Hydrocarbons pose significant risks to marine ecosystems. A field experiment investigated the effects of four different hydrocarbon products (diesel fuel and three lubricating oils: Unused, Used and Biodegradable) on sediment macrofaunal communities over a five year period, in a shallow Antarctic marine embayment. Sediments were defaunated, treated with a hydrocarbon and deployed in trays (including a control) on the seabed. Diesel fuel had the biggest initial impact on communities, with strong effects at 5 weeks and 1 year, in particular on annelids, but also on amphipods, ostracods and cumaceans. By five years, however, the effect of diesel was less than that of lubrication oils and showed more recovery than oiled treatments and the biggest effect was from the Used oil. There was an effect of hydrocarbons on diversity, especially diesel, at 5 weeks and 1 year, but by 2 and 5 years diversity was not different or greater in hydrocarbon treatments than controls. Total abundance was always lower in hydrocarbon treatments than controls, especially for crustaceans, but annelids were more abundant in oil treatments than controls at 5 years. Oils, and in some cases diesel, enhanced the abundance of some taxa at 2–5 years, including molluscs, some polychaete families (capitellids, cirratulids, dorvilleids), oligochaetes, as well as ostracods, cumaceans and isopods. Amphipods and tanaids were most sensitive to hydrocarbons, and annelids were very sensitive to diesel. The Biodegradable oil had similar magnitude community effects to standard oil at 5 years, but annelids were more affected by Biodegradable oil, particularly at 1 and 2 years, and it did not enhance annelid or mollusc abundance at 5 years like the other oils, except for some polychaete families. Impacts of spilled hydrocarbons in Antarctica will persist well beyond 5 years, but diesel impacts will recover faster than oil.

Composition and functionality of bacterioplankton communities in marine coastal zones adjacent to finfish aquaculture

Finfish aquaculture is a fast-growing primary industry and is increasingly common in coastal ecosystems. Bacterioplankton is ubiquitous in marine environment and respond rapidly to environmental changes. Changes in bacterioplankton community are not well understood in semi-enclosed stratified embayments. This study aims to examine aquaculture effects in the composition and functional profiles of the bacterioplankton community using amplicon sequencing along a distance gradient from two finfish leases in a marine embayment. Results revealed natural stratification in bacterioplankton associated to NOx, conductivity, salinity, temperature and PO4. Among the differentially abundant bacteria in leases, we found members associated with nutrient enrichment and aquaculture activities. Abundant predicted functions near leases were assigned to organic matter degradation, fermentation, and antibiotic resistance. This study provides a first effort to describe changes in the bacterioplankton community composition and function due to finfish aquaculture in a semi-enclosed and highly stratified embayment with a significant freshwater input.

Sea level rise may contribute to the greening of Arctic coastal freshwaters – Implications from the ontogeny of Greiner Lake, Nunavut, Canada

Global sea level rise and increased storm activity triggered by climate change pose a serious threat to low-lying Arctic coastal landscapes, which commonly host numerous freshwater lakes. Marine inundation of these ecosystems would result in significant ecological changes. We elucidated effects of changing levels of marine influence to lake ecosystems by exploring the ontogeny of coastal Greiner Lake in Arctic Canada. Using paleolimnological methods on a sediment core, we explored functional assemblage compositions of aquatic biota (diatoms and chironomids), biomarkers (pigments and fatty acids) and geochemistry (stable isotopes and organic matter) throughout the isolation history of the lake. The biological and geological data collectively indicated a paleoenvironmental shift from marine embayment to brackish lagoon in the Late-Holocene and to a freshwater lake ca. 500 BP. We observed that the lake was most productive during a phase of mixed freshwater and marine influence, based on higher chlorophyll-a and β,β-carotene concentrations, omega-3 fatty acids (ω-3) as well as sediment organic content. We suggest that, in addition to reorganization of aquatic communities and altered ecosystem services provided by coastal lakes, coastal freshwaters may become more productive under increasing marine influence caused by climate change. Global sea level rise may thus trigger a new pathway to increasingly greener Arctic.

Aureococcus anophagefferens (Pelagophyceae) genomes improve evaluation of nutrient acquisition strategies involved in brown tide dynamics.

The pelagophyte Aureococcus anophagefferens causes harmful brown tide blooms in marine embayments on three continents. Aureococcus anophagefferens was the first harmful algal bloom species to have its genome sequenced, an advance that evidenced genes important for adaptation to environmental conditions that prevail during brown tides. To expand the genomic tools available for this species, genomes for four strains were assembled, including three newly sequenced strains and one assembled from publicly available data. These genomes ranged from 57.11 to 73.62 Mb, encoding 13,191-17,404 potential proteins. All strains shared ~90% of their encoded proteins as determined by homology searches and shared most functional orthologs as determined by KEGG, although each strain also possessed coding sequences with unique functions. Like the original reference genome, the genomes assembled in this study possessed genes hypothesized to be important in bloom proliferation, including genes involved in organic compound metabolism and growth at low light. Cross-strain informatics and culture experiments suggest that the utilization of purines is a potentially important source of organic nitrogen for brown tides. Analyses of metatranscriptomes from a brown tide event demonstrated that use of a single genome yielded a lower read mapping percentage (~30% of library reads) as compared to a database generated from all available genomes (~43%), suggesting novel information about bloom ecology can be gained from expanding genomic space. This work demonstrates the continued need to sequence ecologically relevant algae to understand the genomic potential and their ecology in the environment.

Temporal interactions with flamingo (Phoenicopterus roseus) foraging plasticity: basal resources, assemblage structure and benthic heterogeneity

Shorebird foraging plasticity and consequences for community structure, heterogeneity and ecosystem functioning are poorly understood in marine sediments, but temporal interactions with plasticity is an additional knowledge gap. Here we report on time-dependant effects of foraging plasticity by Greater Flamingos on intertidal sedimentary assemblages in Langebaan Lagoon - a marine embayment on the west coast of South Africa. In situ comparisons of foraging structures of different sizes (products of plastic foraging) with adjacent un-foraged sediments indicated greater concentrations of sediment organic matter in small structures following feeding relative to large ones. Results also indicate greater abundances of the grazing gastropod Assiminea globulus in smaller structures, particularly a week following foraging. These findings highlight the differential time-dependent impacts flamingo foraging plasticity can generate on basal trophic resources and higher consumers. Results also indicate that, feeding structures generally became enriched with microalgae following foraging, with this effect also occurring in un-foraged control sediments, though the strength of channel- and control enrichment was site -specific. This finding suggests that flamingo foraging may be responsible for creating sediment patches enriched with microalgae over time. This may oppose negative effects of bioturbation on microalgae by burrowing sandprawns, which are dominant ecosystem engineers in the study area. Overall, our findings highlight the relevance of Greater Flamingos in influencing basal trophic resource levels, community structure and spatio-temporal heterogeneity and (2) the need for time-dependent effects of foraging plasticity to be included in research on predation in marine sediments.

Temperature drives spatial and temporal variation in the reproductive biology of the blue swimmer crab Portunus armatus A. Milne-Edwards, 1861 (Decapoda: Brachyura: Portunidae)

Abstract Sound fisheries management requires knowledge of how the reproductive biology of targeted species varies over space and time and responds to external drivers. We determined the size at maturity and fecundity of the blue swimmer crab Portunus armatus (A. Milne-Edwards, 1861) (Brachyura: Portunidae) along the west coast of Australia at monthly, annual and interdecadal (1990s versus 2010s) time scales. The size at maturity of females determined by abdominal morphology (carapace width (CW) at 50% maturity (CW50)) was highest in sub-tropical Shark Bay at 26°S (104 mm), and declined latitudinally to temperate Geographe Bay at 34°S (93 mm). A notable exception was in a marine embayment at 32°S (Cockburn Sound), where CW50 was significantly lower than all other locations (83 mm). In contrast, batch fecundity was lower in sub-tropical (830,000 eggs at 127 mm CW) than temperate waters (950,000–990,000 eggs). Temporally, CW50 was significantly higher during January-June (typical growth period, encompassing the warmest months of the year) than during July-December (breeding period), and also differed between months, years, and decades. Positive correlations between water temperature, monthly and annual estimates of CW50, and functional maturity (size at first ovigery), were detected in most locations. Annual CW50 also increased with population density, particularly in locations where abundances and biomass were lowest. Results highlight plasticity in the reproductive biology of this portunid in response to environmental drivers such as temperature. Regular review of such parameters is important for ensuring robust fisheries management and stock assessments.

The Santo André lagoon at the Atlantic coast of Portugal – Holocene evolution and event history

The Santo André lagoon is located on the southern west coast of Portugal, about 80 km south of Lisbon. Although the beach barrier separating the lagoon from the open sea was occasionally breached in the past and has artificially been opened on an annual basis for the last decades, the lagoon still represents an appropriate geo-bio-archive for reconstructing the Holocene palaeoenvironmental evolution. For this purpose, a 10-m-long sediment core was taken from the centre of the lagoon by using a floating platform. Sedimentological, geochemical and micropalaeontological analyses were performed in order to unravel past sedimentological, environmental and climatic conditions. Due to the lagoon's exposure to storms from the Atlantic and possible tsunamis triggered by earthquakes along the Eurasian-African plate boundary south of Portugal, it is of high interest to identify short-term high energy events that might have crossed or breached the shielding barrier, leaving their footprint in the sedimentary record of the lagoon.The sediment core archived the palaeoenvironmental evolution of the Santo André lagoon for at least the last eight millennia. The sandy deposits of the core's lowermost part most likely represent a former coastal flood plain that developed when the postglacial marine transgression had reached the area. The continued sea-level rise deposited alternating layers which indicate varying environmental conditions, characterized by peat growth, stagnant-water areas, as well as disconnections from and reconnections with the open sea. Since approximately 5000 BP, the longshore transport had formed a beach barrier, separating the marine embayment from the open sea and creating a lagoon. In addition, four sudden significant marine inundations between ~8500 and 6000 BP are indicated by the sedimentary and microfaunal analyses. Two of these layers can be correlated to extreme wave events (unit B-II), while for the other two layers an ingression caused by sea-level rise or extreme wave events remains debatable.

Crab Diets Differ Between Adjacent Estuaries and Habitats Within a Sheltered Marine Embayment

Portunid crabs contribute to significant commercial and recreational fisheries globally and are commonly fished in estuaries and/or marine embayments, which are amongst the most degraded of all aquatic ecosystems. Portunus armatus were collected seasonally between April and February from five locations across three systems in temperate south-western Australia. The dietary composition of crabs was quantified and compared between two estuaries (Peel-Harvey and Swan-Canning) and a sheltered marine embayment (Cockburn Sound) containing three distinct habitats: shallow seagrass, shallow sand and deep sand. Overall, crabs ingested large volumes of bivalves (both live organisms and dead shell), polychaetes, crustaceans (e.g., amphipods, small decapods), and smaller volumes of teleosts, echinoderms and plant material (seagrass, algae). Analysis of Similarities showed that dietary composition varied significantly among the five locations (two estuaries and three habitats within Cockburn Sound) and seasons, with greater location than seasonal differences in the two estuaries. Diets were most distinct in the Cockburn Sound seagrass due to greater volumes of decapods and teleosts and smaller volumes of bivalve shell consumed in this habitat. Crabs from both estuaries consumed greater quantities of bivalves than those from Cockburn Sound. Seasonal differences in both estuaries were greatest between summer and winter, with a more diverse range of prey and large quantities of bivalves ingested in summer, whereas small bivalves and bivalve shell in the Peel-Harvey and polychaetes and other crustaceans in the Swan-Canning, were consumed in greater quantities in winter. The summer diet in the Peel-Harvey Estuary in the current study was compared to that 20 years previous and with documented change in the benthic macroinvertebrate fauna. Currently, crabs consume smaller volumes of high-calorie prey, i.e., polychaetes, small bivalves and teleosts, and instead ingest greater proportions of calcareous material than previously. This marked shift in dietary composition parallels changes in benthic macroinvertebrates in the Peel-Harvey Estuary. Overall, prey availability appears to be the major factor influencing the spatial and temporal differences in P. armatus diets in these three coastal systems.

Mid‐ to late Holocene environmental changes and human‐environment interactions in the surroundings of La Silla del Papa, SW Spain

AbstractIn southern Iberia, the surroundings of the Strait of Gibraltar are known as a crossroad for population movements, cultural exchanges, and trade from Late Prehistory to modern times. However, questions remain about the impact of this historical development on the environment. The settlement of La Silla del Papa, an important hillfort in southern Andalusia (Cádiz), was occupied during the entire Iron Age, replaced by the coastal town Baelo Claudia during Roman times, and re‐occupied during Early Medieval times. As such, La Silla del Papa and its territory represent an ideal location for long‐term studies on human‐environment interactions. Within the framework of the interdisciplinary project “Archeostraits,” geoarchaeological investigations in the surroundings of La Silla del Papa aimed at constraining ecological conditions and human‐environment interactions during the mid‐ and late Holocene and during major human occupation phases. Our results document an early mid‐Holocene marine embayment in the lower floodplain of the Río del Cachón, rapidly turning into a coastal lagoon and later into freshwater‐dominated wetlands. After approximately 2100 BP (c. 150 BC), fluvial and alluvial deposition i600ing a high anthropogenic impact on the local landscape during Roman or post‐Roman times. Palynological results reveal fluctuating agricultural and pastoral activities and distinct periods of landscape opening during the Neolithic and Iron Age.

Environmental influences shaping microbial communities in a low oxygen, highly stratified marine embayment

Microbial communities in the marine environment drive biogeochemical and nutrient cycles. However, microbial composition and therefore their role in ecosystems is likely to be strongly influenced by the environment. Here, we examined Macquarie Harbour, a highly stratified system on the west coast of Tasmania, Australia, to determine environmental factors driving microbial diversity. Water was sampled along spatial and environmental gradients to examine the structure and composition of the microbial communities, using high-throughput sequencing. The spatial distribution of the communities was found to be homogenous throughout the harbour’s surface, although it differed from riverine and oceanic samples. In contrast, the distribution and composition of microbial communities varied with depth-related changes in salinity and oxygen. Prokaryotes associated with riverine and brackish waters dominated the oxic surface waters. Phytoplankton metabolite-related bacteria and nitrite oxidizers were abundant at the halocline, whereas microbes linked to the consumption of organic matter, nitrogen and sulphur metabolization inhabited the hypoxic bottom waters and may be acting as major players in oxygen consumption throughout the harbour’s water column. This study provides valuable insights into microbial community ecology in a semi-enclosed and highly stratified environment and will improve our knowledge on how bacterial and archaeal distribution may be influenced by a changing environment.

The morphosedimentary record of glacial to postglacial environmental changes in fjord-lake Mékinac and adjacent areas (southeastern Canadian Shield)

Fjords can transition from marine embayments to lacustrine waterbodies under glacio-isostatic change following their deglaciation. However, little is known on how a transition from fjord to lake is influenced by glacial dynamics and how it influences sedimentation in and around the basin. Here, we analyse swath bathymetry imagery and subbottom profiles pri in Lake Mékinac (southern Québec) as well as glacial landforms from LiDAR imagery around the lake to document the evolution of a fjord basin into a lacustrine body during the transition from the Late Pleistocene to the Holocene. These analyses helped refine local glacial history and show that the study area was probably under the up-ice reach of the St. Lawrence Ice Stream during full glacial conditions. The mapping of moraines in and around Lake Mékinac shows that deglaciation of the study area was marked by stabilization of the ice-margin during the Mars-Batiscan Event, which is traditionally correlated to the climate deterioration at the end of the Younger Dryas. The architecture of acoustic facies in the lake indicates a transition from glacial conditions (U1), to proglacial-paraglacial (U2) and to postglacial conditions (U3). The bottom of Lake Mékinac also contains multiple mass movement deposits related to progradation of the Du-Milieu River delta and probably to late-Holocene earthquakes. The acoustic architecture of sediments within the lake indicates that the sedimentation regime was most dependant on the sediment input regime and that the transition from fjord to lake did not significantly influence sedimentation during deglaciation of the watershed. Further work on dating the mass movement deposits that characterise the sediment architecture should provide a better assessment of natural hazard associated with seismological events.

Temporal changes in the growth of a crustacean species, Portunus armatus, in a temperate marine embayment: evidence of density dependence

AbstractGrowth is a key attribute influencing population dynamics and fishery production, and understanding factors that affect the growth of individuals in a population is essential in fisheries science and management. This study analyses 18 years of fishery-independent trawl data to determine the relationships among temperature, density, primary productivity and growth of the blue swimmer crab, Portunus armatus, in a temperate marine embayment. Growth was modelled using mixture distribution analyses and cohort-specific seasonal growth curves to estimate the size of crabs at the age of 0.5 and 1.5 years. Growth was highly seasonal, with size-at-age increasing during the austral summer periods and slowing/ceasing during the cooler winter months. The results from the mixture models were used to estimate the mean size of the 0.5- and 1.5-year-old crabs in each year. Linear models showed that the mean size of adult P. armatus at 1.5 years was negatively related to the density of juvenile (0.5 year) crabs in the previous year (i.e. the same cohort) and chlorophyll a concentrations in this year. Increased chlorophyll a levels may increase the survival of larval and megalopal P. armatus, leading to density-dependent effects such as increased competition among juveniles for food and spatial resources, and ultimately, reduced growth.