Intertidal Environments Research Articles

The genome of the intracellular bacterium of the coastal bivalve, Solemya velum: a blueprint for thriving in and out of symbiosis.

BackgroundSymbioses between chemoautotrophic bacteria and marine invertebrates are rare examples of living systems that are virtually independent of photosynthetic primary production. These associations have evolved multiple times in marine habitats, such as deep-sea hydrothermal vents and reducing sediments, characterized by steep gradients of oxygen and reduced chemicals. Due to difficulties associated with maintaining these symbioses in the laboratory and culturing the symbiotic bacteria, studies of chemosynthetic symbioses rely heavily on culture independent methods. The symbiosis between the coastal bivalve, Solemya velum, and its intracellular symbiont is a model for chemosynthetic symbioses given its accessibility in intertidal environments and the ability to maintain it under laboratory conditions. To better understand this symbiosis, the genome of the S. velum endosymbiont was sequenced.ResultsRelative to the genomes of obligate symbiotic bacteria, which commonly undergo erosion and reduction, the S. velum symbiont genome was large (2.7 Mb), GC-rich (51%), and contained a large number (78) of mobile genetic elements. Comparative genomics identified sets of genes specific to the chemosynthetic lifestyle and necessary to sustain the symbiosis. In addition, a number of inferred metabolic pathways and cellular processes, including heterotrophy, branched electron transport, and motility, suggested that besides the ability to function as an endosymbiont, the bacterium may have the capacity to live outside the host.ConclusionsThe physiological dexterity indicated by the genome substantially improves our understanding of the genetic and metabolic capabilities of the S. velum symbiont and the breadth of niches the partners may inhabit during their lifecycle.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-924) contains supplementary material, which is available to authorized users.

Biogenic Sedimentary Structures of the Yellow River Delta in China and Their Composition and Distribution Characters

The biogenic sedimentary structures (i.e., the morphology and trace makers of burrows, tracks, trails and traces made by extant organisms) and their composition and distribution characters in different micro environments and sub environments of the Yellow River delta in China are described. Three ichnocoenosis can be recognized: (1) Steinichnus-like ichnocoenosis, includes F, Y-shaped traces, birds' footprints on bedding plane, and Y, U-shaped burrows in intrastratal bedding, produced by Coleoptera (Heteroceridae), Orthoptera (Gryllotalpidae) and birds. It is majorly found at the delta plain point bar deposits, denoting the fresh water-related terrestrial environments. (2) Steinichnus-Psilonichnus-like ichnocoenosis, consitsis of Steinichnus-like traces on the bedding plane and Psilonichnus-like burrow which a vertical, irregularly J-, Y-, or U-shaped burrows, some of them with bulbous basal cells burrows in the intrastratal bedding, created by Coleoptera (Heteroceridae), Orthoptera (Gryllotalpidae) and crabs. It is observed in the delta plain abandoned distributary channels, and the delta front tidal creek and subaquous distributary channels, indicating the brackish water environment. (3) Palaeophycus-like ichnocoenosis, includes the round entrance burrows or with craters-shaped loop-protrusionsand and the parallel forked trails on the bedding plane, and the U, J or vertical shaped feeding burrows are in the intrastratal bedding, majorly produced by the clam (bivalve molluscs), gastropods and Nereis. It is present in the subaqueous interdistributary bay, reflecting the intertidal related environment.

Ultraviolet Radiation-Absorbing “Humic Pigments” of Cyanobacteria in Microbial Mats: Their Presumptive Photoprotective Function and Relevance to Early Precambrian Microbial Ecology and Evolution

Cyanobacteria that form the primary components of microbial mats in freshwater bogs and intertidal marine environments in the Bahamas produce water-soluble brown pigments whose spectral properties imply that they are a type of humic acid. These “humic pigments” are produced by vital processes of living cyanobacteria, not by decomposition of dead ones, as shown by decreases in the concentrations of humic pigments, ultraviolet (UV) radiation-absorbing photoprotective mycosporine-like amino acids (MAAs), and chlorophyll from upper to lower layers of the mats, and by the occurrence of humic pigments in cyanobacterial cultures. Unlike MAAs, which absorb UV radiation only within limited ranges of wavelengths, humic pigments absorb radiation spanning the entire UV spectrum, and absorbance increases with decreasing wavelength. These observations suggest that the biosynthesis of humic pigments originated as a photoprotective adaptation in the early Precambrian, enabling cyanobacteria to colonize shallow-water and terrestrial environments even though the atmosphere was virtually devoid of O2 and O3 and therefore transparent to all solar radiation in the UV region of the spectrum. Moreover, the evolution of this photoprotective mechanism may have been linked to the evolution of photosynthesis.

Physiological and biochemical thermal stress response of the intertidal rock goby Gobius paganellus

The intertidal habitat is characterized by environmental conditions with steep gradients. Thus, inhabiting communities have long served as models in stress research. Moreover, several studies have reported their vulnerability to climate change and consequent distribution shifts (up to 50km per decade) and abundance changes. The aims of this study were to test the effects of temperature on the rock goby Gobius paganellus in order to understand its resistance to environmental fluctuations (e.g. low tide events, heat waves) and gain insights into its vulnerability to climate change. The upper thermal limit for the species was estimated through the critical thermal maximum (CTMax). Individuals were exposed to a temperature increase ramp of 1°Ch−1. Two thermal stress biomarkers (hsp70 and total ubiquitin) were quantified in the gill, muscle and liver via enzyme linked immunosorbent assays. Results showed no increases in hsp70 in neither of the organs in response to temperature but ubiquitin levels were elevated in liver at 30°C. Both biomarker basal levels were higher in gills, followed by liver and finally muscle. The results indicate that the species, although adapted to the intertidal environment, can experience stress at high temperatures of 30°C and above. Therefore, it may be vulnerable to heat waves, especially occurring during low tides that coincide with the hottest hours of the day during summer, with adverse implications in a climate change scenario that predicts temperature rising and increasing (in length and frequency) periods of extreme heat. The present study also shows that different organs possess distinct heat stress thresholds and responses, hence the importance of multi-organ approaches in order to comprehend the full health status of the organisms following acute thermal challenge.

Catalogue and historical overview of juvenile instars of oribatid mites (Acari: Oribatida).

Oribatid mites (Acari: Oribatida) comprise a taxonomically and morphologically diverse suborder of about 10,000 described species, not including the hyporder Astigmata, with collectively a global distribution. They are primarily soil and litter inhabitants, feeding on fungi and decaying plant remains with various levels of specificity. Though all five active instars are important for reasons that relate to both ecology and systematics, most species are known only as adults. Our purpose was to gather the existing world literature on the active juvenile instars (i.e., excluding prelarva) of oribatid mites, to put classifications and nomenclature in a current context, and to identify the nature of the information in each paper. A selected historical overview identifies the contributions of 19th century authors C.L. Koch, H. Nicolet and A.D. Michael, and summarizes errors that resulted in various oribatid mite juveniles being classified in genera, families and even suborders that were different from those of their adult instars. The catalogue includes all species known to us for which juveniles have been described: 805 species in 310 genera, representing only about 8% of the known oribatid mite species and 30% of genera. These represent 118 families, about 70% of those known. At the superfamily level, representation is weakest among the diverse Oppioidea and Oribatuloidea, and those superfamilies with juveniles that are endophagous in organic substrates, such as Phthiracaroidea, Euphthiracaroidea and Carabodoidea. Representation is strongest in the middle-derivative hyporder Nothrina, in which adults and juveniles are more easily associated, and in brachypyline superfamilies that are mostly affiliated with aquatic, semiaquatic or intertidal environments, such as Limnozetoidea and Ameronothroidea. Juvenile instars remain unknown for 45 families of Brachypylina. Four new nomenclatural actions were proposed: Ojaithrus nymphoides Habeeb, 1982 is a junior synonym of Hydrozetes californiensis Habeeb, 1974, Cepheus feideri Suciu & Panu, 1972 is a junior synonym of Conoppia palmicincta (Michael, 1880). Two species are recombined: Ceratozetes kirgisicus (Shaldybina, 1970) comb. nov. (from Ceratozetella); Scheloribates (Hemileius) nicki (Denmark & Woodring, 1965) comb. nov. (from Hemileius).

The excavation and cultivation in containers of mature grey mangroves, Avicennia marina

The grey mangrove, Avicennia marina, grows in intertidal habitat that is under pressure from expanding human settlement and industry along coastlines in the tropics and subtropics. Inappropriate clearing, and also the dieback of large stands of A. marina associated with pollution, have created an interest in methods for revegetation and also the need for a better understanding of the species physiological tolerances including to herbicide residue. Eco-toxicological studies have so far been exclusively on seedlings because of perceived difficulties cultivating mature plants in controlled environments. Reforestation projects are often associated with low rates of establishment, because of the susceptibility of propagules, seedlings and saplings to wind and wave erosion, as well as flooding and desiccation associated with the natural inter-tidal environment. We report on the successful excavation, and cultivation in containers with an automated irrigation system of eight mature A. marina plants. It is possible to transplant mature mangroves and achieve significant vegetative growth and also flowering and fruiting within the first year. It is difficult to compare the likely costs of transplanting a more limited number of mature plants to many propagules. However, we suggest that in situations where reforestation with young propagules, seedlings or saplings has failed because of excessive wash, drowning or smothering, the transplanting of mature mangroves could be a better option.

Two new fossil woods from the early Miocene of Kutch, Gujarat, India and their significance

The Kutch region of western India (Gujarat State) is today arid to semiarid and characterised by mostly ephemeral streams which carry water during the monsoon. The uneven distribution of rainfall and disturbed topography are the result of climate change during the Cenozoic period. Two fossil woods, namely Bauhinium palaeomalabaricum Prakash and Prasad (Fabaceae) and Ebenoxylon indicum Ghosh and Kazmi (Ebenaceae), are described from Kutch in order to provide insights into the palaeovegetation and palaeoclimate. Because the modern representatives of the present and previously described taxa from the same horizon are thermophilic in nature and grow in evergreen to deciduous forests, a warm and humid climate is interpreted. Furthermore, the finding of some mangrove taxa in the assemblage indicates the lagoonal to intertidal environment at the time of deposition.

Specific photosynthetic and morphological characteristics allow macroalgae Gloiopeltis furcata (Rhodophyta) to survive in unfavorable conditions

Gloiopeltis furcata (Postels & Ruprecht) J. Agardh, a macroalga, which grows in an upper, intertidal zone, can withstand drastic environmental changes caused by the periodic tides. In this study, the photosynthetic and morphological characteristics of G. furcata were investigated. The photosynthetic performance and electron flows of the thalli showed significant variations in response to desiccation and salinity compared with the control group. Both PSII and PSI activities declined gradually when the thalli were under stress. However, the electron transport rate of PSI showed still a low value during severe conditions, while the rate of PSII approached zero. Furthermore, PSI activity of the treated thalli recovered faster than PSII after being submerged in seawater. Even though the linear electron flow was inhibited by DCMU [3-(3, 4-dichlorophenyl)-1,1-dimethylurea], the cyclic electron flow could still be restored. The rate of cyclic electron flow recovery declined with the increasing time of dark treatment, which suggested that stromal reductants from starch degradation played an important role in the donation of electrons to PSI. This study demonstrated that PSII was more sensitive than PSI to desiccation and salinity in G. furcata and that the cyclic electron flow around PSI played a significant physiological role. In addition, G. furcata had branches, which were hollow inside and contained considerable quantities of funoran. These might be the most important factors in allowing G. furcata to adapt to adverse intertidal environments.

The geology of the northern tip of the Arabian–Nubian Shield

Recently, a detailed (1:50,000) geological map of the Elat area, southern Israel was published. Attached to this map is a stratigraphic table of the Neoproterozoic metamorphic–magmatic complex of the study area. The Neoproterozoic basement in the Elat area encapsulates the Arabian Nubian Shield (ANS) geologic evolution. Uranium–Lead and Lead–Lead zircon ages, included in previous studies and referred to in this paper, reveal that these rocks were formed during more than 300 million years of Neoproterozoic time. The major process controlling the formation of the ANS as part of the East African Orogen is the closure of the Mozambique Ocean. The first orogenic phase in the Elat area, represented by the metamorphic rocks, includes the development of an island arc, erosion of the islands and deposition, and metamorphism. This event took place between ∼950Ma and 780–790Ma. Elat Schist, the oldest metamorphic rock in the area, was deformed and then intruded by quartz dioritic and granitic plutons that were later deformed and metamorphosed. The amphibolite metamorphic rock facies indicate metamorphic conditions of up to 650°C and between 4 and 5kbar. The peak of the metamorphic event was most probably before 750Ma. A gradual change from compressional to extensional stress regime is evidenced by emplacement andesitic magnesium-rich dykes dated to 705Ma that were later metamorphosed to schistose dykes at a greenschist metamorphic facies. The second orogenic phase (terrane amalgamation, main shaping of crust) was associated with the emplacement of large volumes (>50% of area) of calc-alkaline intrusions in a post-collision setting. These very last stages of metamorphism and deformation are characterized by intrusion of ∼630Ma granitoids exhibiting some foliation. Pluton emplacement continued also after the end of deformation. Exhumation and transition to an extensional regime is recorded by the intrusion of shallow alkaline granites in ∼608Ma which were accompanied in ∼609Ma by rhyolite, andesite and composite dykes. The last magmatic event in the Elat area is represented by the volcano-conglomeratic series comprising rhyolites, basalts, andesites, hypabyssal intrusions of monzonite and syenite and conglomerates. The conglomerates, dated to about 590Ma, are the products of a major erosion phase in which about 12,000m of the section were removed. These conglomerates were intruded by 585Ma rhyolite, andesite and composite dykes. The Neoproterozoic basement is truncated by a peneplain whose age, post 532Ma, is constrained by the age of the youngest eroded dolerite dykes. This Early Cambrian peneplain was associated with erosion of 2000m of the section and by chemical weathering. Three major breaks in Neoproterozoic magmatic activity are recognized: the first, occurred in Cryogenian time, lasted ∼60 million years after the amphibolite facies metamorphism and before emplacement of the calc alkaline plutons, separating the first and the second orogenic phases; the second break between the orogenic and the extensional phases occurred in early Ediacaran time, encompassed ∼20 million years between the emplacement of the calc-alkaline and alkaline plutonic rocks and rhyolite, andesite and the composite dykes; and the third, ∼50Ma break, occurred between the emplacement of the last felsic intrusions at ∼585Ma and intrusion of the dolerite dykes in 532Ma, before the Early Cambrian peneplain developed.The great lateral extension of the Cambrian to Eocene sedimentary rocks and their slow facies and thickness changes suggest a stable flat platform area at the northern tip of the ANS. Early Cambrian sedimentation began with fluviatile subarkoses of the Amudei Shlomo Formation. It was overlain by an Early to Middle Cambrian transgressive–regressive lagoonal cycle of dolostones, sandstones, and siltstones of the Timna Formation. Then Middle Cambrian subarkoses and siltstones of the Shehoret Formation and the quartz arenite of the Netafim Formation were deposited in a coastal, intertidal environment representing the southern transgression of a Cambrian ocean.

The impacts of land-use changes on the recovery of saltmarshes in Portugal

Human-induced land-use changes have resulted in loss and degradation of intertidal environments worldwide. Saltmarsh ecosystem dynamics in Portugal are greatly influenced by historic uses and consequent habitat degradation. This study uses an original approach combining vegetation surveys and spatial analysis of historic maps and aerial photographs to assess the effects of land use changes on saltmarshes in two areas in the Algarve, southern Portugal. Historical maps from c. 1800 and aerial photographs from 1958 to 2010 were analyzed to map saltmarsh ecosystems and quantify land-use changes in the Alvor estuary and Arade River. Between c. 1800 and 2010 more than half of saltmarshes were lost due to dyke building and saltmarsh reclamation for agriculture. In mid-1960s, the abandonment of reclaimed agricultural areas resulted in the recolonization of saltmarsh vegetation, which developed physically separated from natural marshes. In the study area, these saltmarshes naturally evolved into two distinct typologies: (1) enclosed mixed marshes, formed by patches of brackish, freshwater and some invasive species developing due to saline intrusion in areas where dykes have not been breached; and (2) tidally-restored saltmarshes, formed in areas where dyke breaching allows incursion of tides and development of a vegetation structure similar to natural saltmarshes. In Europe, passive (without human intervention) and active (artificially planned) saltmarsh restoration are important mechanisms for voluntary or statutory re-creation of intertidal habitats. Improved understanding of the factors influencing the development of distinct saltmarsh typologies through passive ecosystem recovery can provide new insights to support decision-making concerning intertidal habitat restoration.

Total arsenic concentrations and arsenic species present in naturally decomposing Ecklonia radiata tissues collected from various marine habitats

To investigate the release and degradation of arsenoribosides associated with the brown alga Ecklonia radiata, tissues were collected in various marine micro-habitats (water column, sand intertidal, and rock platform intertidal) to establish the importance of decomposition stage and the micro-habitat in which decomposition occurs on arsenoriboside degradation. Total arsenic concentrations in E. radiata tissues varied in a similar pattern across all three sampling locations (Lake Tabourie, Burrill Lake, and Ulladulla Harbour) with concentrations in live tissues (53–124 μg As g−1 (dry mass)) greater than concentrations in tissues decomposing in the water column (28–90 μg As g−1 (dry mass)), which were in turn higher than concentrations in tissues decomposing in intertidal environments (16–21 μg As g−1 (dry mass)). Arsenoribosides, specifically sulfonate (SO3-), phosphate (PO4-), and glycerol (Gly-) accounted for all of the arsenic extracted from live E. radiata tissues. Arsenoribosides also accounted for 100 % of the extractable arsenic species in E. radiata tissues decomposing in the water column. The proportions of arsenic species in decomposing E. radiata tissue from intertidal environments varied with sampling location and therefore micro-habitat. In rock platform-based intertidal zones (Burrill Lake and Ulladulla harbour), considerable concentrations of unextractable arsenic (10–60 %) were present plus known arsenoriboside degradation products such as dimethylarsinoylethanol (DMAE), dimethylarsenate (DMA), and arsenate (As(V)). In sand/beach-based intertidal zones, however, the vast majority of arsenic (≈95 %) was unextractable with only small concentrations of arsenoribosides and As(V) present.

A Holocene record of coastal landscape dynamics in the eastern Kimberley region, Australia

A 6-m-long sediment core from the King River region of north-west Australia has been analysed using sedimentological and palynological techniques. The core spans most parts of the Holocene and contains a detailed record of early to mid-Holocene landscape development. In the early Holocene an intertidal environment supported a diverse and probably extensive mangrove forest. Intensified fluvial activity, high mangrove biodiversity and the proximity of freshwater swamp vegetation reflect enhanced summer monsoon rainfall. From 7.4k cal a BP onwards, the mangrove forest starts to contract reaching minimum (and probably present-day) extent by 6.5k cal a BP. Late Holocene aridification led to shifts in mangrove composition, the expansion of hypersaline flats and the transition of freshwater swamps to intermittent wetlands. In addition, fire potentially played an increasing role in controlling ecosystem composition, in particular in the savanna/woodland vegetation. This record is the first of its kind from coastal north-west Australia and demonstrates that sea-level and climatic fluctuations, in addition to local geomorphological settings, are major controllers of landscape development. Although the general pattern of change is similar to other sites in tropical Australia, detailed analysis shows that the timing and character of vegetation shifts are considerably different.

Severe hypoxia impairs lateralization in a marine teleost fish.

In intertidal environments, the recurring hypoxic condition at low tide is one of the main factors affecting fish behaviour, causing broad effects on ecological interactions. We assessed the effects of hypoxia on lateralization (e.g. the tendency to turn left or right), a behaviour related to brain functional asymmetry, which is thought to play a key role in several life history aspects of fish. Using staghorn sculpin (Leptocottus armatus), a benthic fish that typically inhabits the intertidal zone, we found that hypoxia affects behavioural lateralization at the population level. On average, staghorn sculpins showed a distinct preference for right turns under normoxic conditions (>90% oxygen saturation), but an equal probability of turning right or left after exposure to hypoxia for 2 h (20% oxygen saturation). The specific turning preference observed in the staghorn sculpin control population is likely to have an adaptive value, for example in predator-prey interactions by enhancing attack success or survival from predatory attacks. Therefore the alteration of lateralization expressed by staghorn sculpins under hypoxic conditions may have far-reaching implications for species ecology and trophic interactions. Moreover, our work raises the need to study this effect in other species, in which a hypoxia-driven disruption of lateralization could affect a wider range of behaviours, such as social interactions and schooling.

Ecological roles and biotechnological applications of marine and intertidal microbial biofilms.

This review is a retrospective of ecological effects of bioactivities produced by biofilms of surface-dwelling marine/intertidal microbes as well as of the industrial and environmental biotechnologies developed exploiting the knowledge of biofilm formation. Some examples of significant interest pertaining to the ecological aspects of biofilm-forming species belonging to the Roseobacter clade include autochthonous bacteria from turbot larvae-rearing units with potential application as a probiotic as well as production of tropodithietic acid and indigoidine. Species of the Pseudoalteromonas genus are important examples of successful surface colonizers through elaboration of the AlpP protein and antimicrobial agents possessing broad-spectrum antagonistic activity against medical and environmental isolates. Further examples of significance comprise antiprotozoan activity of Pseudoalteromonas tunicata elicited by violacein, inhibition of fungal colonization, antifouling activities, inhibition of algal spore germination, and 2-n-pentyl-4-quinolinol production. Nitrous oxide, an important greenhouse gas, emanates from surface-attached microbial activity of marine animals. Marine and intertidal biofilms have been applied in the biotechnological production of violacein, phenylnannolones, and exopolysaccharides from marine and tropical intertidal environments. More examples of importance encompass production of protease, cellulase, and xylanase, melanin, and riboflavin. Antifouling activity of Bacillus sp. and application of anammox bacterial biofilms in bioremediation are described. Marine biofilms have been used as anodes and cathodes in microbial fuel cells. Some of the reaction vessels for biofilm cultivation reviewed are roller bottle, rotating disc bioreactor, polymethylmethacrylate conico-cylindrical flask, fixed bed reactor, artificial microbial mats, packed-bed bioreactors, and the Tanaka photobioreactor.

Intertidal Zone Management in the Western Indian Ocean: Assessing Current Status and Future Possibilities Using Expert Opinions

This expert opinion study examined the current status of the intertidal zone in the Western Indian Ocean (WIO) and ranked and discussed future management approaches. Information was gathered from scientists, practitioners, and managers active in the WIO region through a questionnaire and a workshop. The experts stated that the productive intertidal environment is highly valuable for reasons such as recreation, erosion protection, and provision of edible invertebrates and fish. Several anthropogenic pressures were identified, including pollution, harbor activities, overexploitation, and climate change. The experts considered the WIO intertidal zone as generally understudied, undermanaged, and with poor or no monitoring. The most important management strategies according to the expert opinions are to develop and involve local people in integrated coastal zone management (ICZM), to increase knowledge on species-environment relationships, and to develop awareness campaigns and education programs. To improve coastal environmental management and conservation, we argue that the intertidal zone should be treated as one organizational management unit within the larger framework of ICZM.

Assessment of sediment quality in Avicennia marina-dominated embayments of Sydney Estuary: The potential use of pneumatophores (aerial roots) as a bio-indicator of trace metal contamination

Currently, coastal intertidal environments are under stress from increased contaminant loads due to urbanization and other anthropogenic disturbances. Mangrove habitats are abundant in tropical and sub-topical intertidal zones and frequently act as a metal bio-filter in estuarine systems. Mangrove reforestation is often considered as one of the management options to protect estuarine–marine habitats. The main objective of the present investigation was to assess the bio-indicator potential of Avicennia marina by determining heavy metal concentrations in pneumatophore (aerial root) tissues and ambient sediments from Sydney Estuary (Australia). We collected mangrove sediments and pneumatophores in fifteen locations covering five major embayments of the estuary for a detailed biogeochemical investigation. Metal concentrations in sediment were mostly above Australian interim sediment quality guidelines (ISQG)-Low and in few instances above ISQG-High values. Enrichment factors (EFs >6, especially of Cu, Pb and Zn) suggest “very severe” modification of sediment in Sydney Estuary in all but one embayment which was mainly due to rapid changes in land use in connection with urbanization. High bio-concentration factors (BCFs) were observed for Cu and Ni in comparison with other metals (i.e., As, Cd, Co, Cr, Pb and Zn). A strong, positive relationship between metals in sediments and pneumatophores suggests potential use of these tissues as a bio-indicator of estuarine contamination and that metals are entering the biotic environment. The study further highlights a positive role of mangroves in sequestering metals from sediments and the water column and thus protecting estuarine environments from pollution.

Bioclaustration trace fossils in epeiric shallow marine stromatolites: the Cretaceous-Palaeogene Yacoraite Formation, Northwestern Argentina

The shallow carbonate facies at the top of the Yacoraite Formation (Late Cretaceous–Early Palaeocene) in the Metan sub-basin, Salta Basin (Cretaceous-Eocene), northern Argentina, have domal stromatolitic boundstones with peculiar cavities, interpreted here as bioclaustrations. The cavities appear to have been produced by organisms that lived within the microbial mat contemporarily with its growth, producing a distinctive ichnofabric. This is the oldest reported record of bioclaustrations in stromatolites, and the first in shallow marine environments. The interpretation of the facies suggests a stressed shallow, restricted setting with variations in salinity, represented by an intertidal environment with an extensive tidal flat. Bioclaustrations, stromatolites, endobiont Yacoraite Formation (Cretaceous-Palaeogene), Northwestern Argentina.

N2 fluxes in sediments of the Elbe Estuary and adjacent coastal zones

ABSTRACT: The conversion of reactive nitrogen species to N 2 during denitrification in sedimentsmay be one of the most valuable ecosystem services provided by estuarine and intertidal environ-ments near river discharge areas. To quantify the rates and limiting factors of denitrification in theestuary of the Elbe River and adjacent Wadden Sea (SE North Sea), we measured sediment N 2 fluxes across subtidal and intertidal sediments, and along gradients in nitrate and organic matterconcentrations. We conducted 2 sampling campaigns, in March and September 2009, duringwhich N 2 fluxes were quantified by N 2 /Ar measurements in sediment core incubations, and com-pared to isotope pairing results in September 2009. At ambient nitrate concentrations, sediments inthe inner Elbe Estuary produced N 2 fluxes of up to 156 µmol N m −2 h −1 . In September, nitrate con-centration in bottom water and organic matter content in sediments limited N 2 production; suchlimitations were not observed in March. We extrapolated the estuarine sediment nitrogen removalof March and September to the present-day area of intertidal and subtidal sediments in the ElbeEstuary between the port of Hamburg and the transition to the North Sea. Our estimate suggeststhat 3.3 ± 1.2 kt nitrate-N are removed in sediments in this region in spring and summer. This im-plies that reactive nitrogen removal in the inner Elbe Estuary reduces the spring/summer load ofthe Elbe River (47 kt N) by around 7%, a reduction that is much lower than commonly assumed forestuaries, and significantly lower than nitrate removal in the Elbe was in historical times.KEY WORDS: Denitrification · Nitrogen cycle · Eutrophication · Elbe Estuary

Comparative study of methodologies to measure in situ the intertidal benthic community metabolism during immersion

Methods used to estimate community primary production and respiration in intertidal environment are still subject of controversy. Underwater community respiration (CR), net production (NCP) were calculated from simultaneous in situ measures of change in oxygen (O2), dissolved inorganic carbon (DIC) and carbon dioxide (CO2) concentration in benthic chambers performed in February, April, July and November on a Zostera noltii bed. The CRQ (CRDIC/CRO2) and CPQ (NCPo2/NCPDIC) varied between 0.15 and 3.07 and between 0.03 and 6.83, respectively. Carbon fluxes calculated from CO2 measurement were greatly underestimated, representing only 0.4–5.9% of fluxes estimated from DIC measurement. Indeed, CO2 or HCO3− input or uptake by seagrass community affect the proportions of all the chemical components of dissolved inorganic carbon (DIC, the sum of free dissolved CO2, carbonic acid H2CO3, bicarbonate and carbonate ions, HCO3− and CO32−). Thus, CO2 method is not reliable. O2 measurement does not take into account anaerobic respiration through chemical oxidation and simultaneous O2 and DIC measurements should be favored to calculate CRQ and CPQ which need to be discussed in marine environment at community scale.

Ecological tradeoffs of stabilized salt marshes as a shoreline protection strategy: Effects of artificial structures on macrobenthic assemblages

Armoring shorelines to prevent erosion is a long-standing global practice that has well-documented adverse effects on coastal habitats and organisms. A relatively new form of shoreline protection, referred to as hybrid stabilization, incorporates created marsh in combination with a stabilizing structure such as a low-profile stone sill and is being implemented in many US coastal states as a means to not only control erosion but also to restore coastal habitat. However, there has been limited scientific investigation of ecological benefits and impacts associated with implementation of hybrid stabilization. We evaluated relative habitat capacity of marsh-sills by comparing plant, sediment, and benthic macroinvertebrate attributes in intertidal and subtidal zones of existing marsh-sills, natural marshes, tidal flats, and riprap revetment within two subestuaries of Chesapeake Bay, USA. Low and high marsh plant characteristics (stem count and height) of marsh-sills were similar to or greater than natural marshes. However, sediment was coarser, total organic carbon and total nitrogen concentrations were lower, and benthic macrofaunal community structure differed in marsh-sills compared to natural marshes. Marsh-sills supported lower deposit-feeding infaunal biomass than marshes in the intertidal. Epifaunal suspension-feeders were most prevalent at sites with artificial structure (riprap and marsh-sill), but highly variable among subestuaries. Infaunal abundance, biomass, diversity, and proportion of suspension/interface and deposit feeding animals were greater in shallow subtidal than in intertidal environments. Conversion of existing habitat to marsh-sills may cause localized loss of benthic productivity and sediment bioturbation and nutrient-cycling functions, with the opportunity to enhance filtration capacity by epifaunal recruitment to structures. When creating marshes that require structural support, there should be a balance of minimizing loss of existing habitats while encouraging use of suitable structural habitat for suspension-feeders. If properly implemented, the addition of structural habitat could subsidize secondary productivity particularly in areas where loss of complex biogenic habitat (e.g., oyster reefs) has occurred.