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Results for “Journal of Marine Biology”

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98 records · Page 6Linked to original sources
USGS2005

Quaternary geomorphology and modern coastal development in response to an inherent geologic framework: An example from Charleston, South Carolina

Coastal landscapes evolve over wide-ranging spatial and temporal scales in response to physical and biological processes that interact with a wide range of variables. To develop better predictive models for these dynamic areas, we must understand the influence of these variables on coastal morphologies and ultimately how they influence coastal processes. This study defines the influence of geologic framework variability on a classic mixed-energy coastline, and establishes four categorical scales of spatial and temporal influence on the coastal system. The near-surface, geologic framework was delineated using high-resolution seismic profiles, shallow vibracores, detailed geomorphic maps, historical shorelines, aerial photographs, and existing studies, and compared to the long- and short-term development of two coastal compartments near Charleston, South Carolina. Although it is clear that the imprint of a mixed-energy tidal and wave signal (basin-scale) dictates formation of drumstick barriers and that immediate responses to wave climate are dramatic, island size, position, and longer-term dynamics are influenced by a series of inherent, complex near-surface stratigraphic geometries. Major near-surface Tertiary geometries influence inlet placement and drainage development (island-scale) through multiple interglacial cycles and overall channel morphology (local-scale). During the modern marine transgression, the halo of ebb-tidal deltas greatly influence inlet region dynamics, while truncated beach ridges and exposed, differentially erodable Cenozoic deposits in the active system influence historical shoreline dynamics and active shoreface morphologies (block-scale). This study concludes that the mixed-energy imprint of wave and tide theories dominates general coastal morphology, but that underlying stratigraphic influences on the coast provide site-specific, long-standing imprints on coastal evolution.

Journal of Coastal Research↗
USGS2025

Factors influencing daily nest survival rates of Aleutian terns in the Kodiak Archipelago, Alaska

The Aleutian tern ( Onychoprion aleuticus ) is a species of high conservation concern in Alaska, USA, owing to large declines at known breeding locations since the 1960s. The small population size and ephemeral behavior of this species have limited the collection of basic biological information and hindered the identification of potential drivers of this decline. Significant unknowns include the factors, and their relative importance, influencing nest survival. To investigate these questions, we estimated daily nest survival (DNS) for 148 nests from 5 breeding colonies during 2017 to 2020 in the Kodiak Archipelago, Alaska with 105 monitored using remote cameras. We used the nest survival model in program MARK to estimate DNS rates as a function of colony location, year, within-season time trends, vegetation cover and height, and 6 daily weather covariates. Our top model suggested that DNS rates increased with vegetation height, decreased as the season progressed, and included a significant interaction between year and colony. Average nest success (i.e., percent chance that a nest survived to hatch) over the 22-day incubation period varied by colony but was generally very low, averaging 1.2% (95% CI = 0–11%) in 2017–2018 to 14% (95% CI = 0.1–38%) in 2019–2020 across all colonies. The importance of year in the model suggests that a large-scale annual driver, like food availability, may have played an important role in this species' breeding success. A severe marine heatwave was present in the Gulf of Alaska during 2014–2016 and our results suggest that some effects of this anomalous event, such as reduced prey availability, lingered even after temperatures returned to normal. Additionally, the variation in DNS across colony locations indicated that local factors, such as predation pressure, may also drive significant variation in Aleutian tern productivity. These findings suggest that a combination of local factors and climate change may be important drivers of the >90% decline in Alaska's breeding population of Aleutian terns.

Alaska↗
USGS2021

Mapping biological soil crusts in a Hawaiian dryland

Historical and ongoing land use patterns in the Hawaiian Islands have degraded the Islands’ drylands, causing erosion and detrimentally affecting adjacent coastal marine ecosystems. Biological soil crust (biocrust) communities have been shown to increase soil stability in drylands worldwide, but their efficacy in mitigating soil erosion in Hawaiian drylands is largely unknown. Using a combination of field data and imagery collected by small unmanned aerial systems (sUAS), we mapped biocrusts and examined their influence on soil stability in the Kawaihae watershed, an erosion-prone dryland on leeward Hawai`i Island. We created classified maps of biocrust cover from imagery collected at three spatial resolutions (1.2, 2.1 and 2.8 cm/pixel) using the pixel-based Support Vector Machine (SVM) classifier and investigated the impacts of spatial resolution and biocrust level of development on classification accuracy. Our medium (2.1 cm) resolution image produced the highest overall classification accuracy when biocrust was treated as a single class (82.1%). We explored the spatial impacts of biocrusts on soil loss via sUAS-derived measurements of elevation change over a four-year time span. We found differences in soil loss among land cover types, but robustly quantifying these was a challenge, as much of the change fell below statistically significant limits of detection. We investigated the relationship between biocrust development and soil stability by conducting soil aggregate stability testing at the three biocrust levels of development (LODs) present at the study site. We found a significant increase in soil stability from soils without surface biocrusts (LOD score of 0) to those with biocrusts at any development level (LOD 1–3). Our research adds to the body of biocrust knowledge by presenting new information about biocrust distribution and soil stabilization capabilities in Hawaiian drylands. We also provide insights into the trade-offs between spatial resolution and classification accuracy for biocrust classification and land cover analysis.

Hawaii↗
USGS1999

The diving physiology of bottlenose dolphins (Tursiops truncatus). III. Thermoregulation at depth

During diving, marine mammals initiate a series of cardiovascular changes that include bradycardia and decreased peripheral circulation. Because heat transfer from thermal windows located in peripheral sites of these mammals depends on blood flow, such adjustments may limit their thermoregulatory capabilities during submergence. Here, we demonstrate how the thermoregulatory responses of bottlenose dolphins ( Tursiops truncatus ) are coordinated with the diving response. Heart rate, skin temperature and heat transfer from the dorsal fin and flank were measured while dolphins rested on the water surface, stationed 5–50 m under water and floated at the surface immediately following a dive. The results showed that heat flow ranged from 42.9±7.3 to 126.2±23.1 W m −2 and varied with anatomical site and diving activity. Upon submergence, heat flow declined by 35 % from the dorsal fin and by 24 % from the flank. An immediate increase in heat flow to levels exceeding pre-dive values occurred at both sites upon resurfacing. Changes in heart rate during diving paralleled the thermoregulatory responses. Mean pre-dive heart rate (102.0±2.6 beats min −1 , N =26) decreased by 63.4 % during dives to 50 m and immediately returned to near resting levels upon resurfacing. These studies indicate that heat dissipation by dolphins is attenuated during diving. Rather than challenge the diving response, heat transfer is delayed until post-dive periods when the need for oxygen conservation is reduced.

Journal of Experimental Biology↗
USGS2008

Trace fossils and sedimentary facies from a Late Cambrian‐Early Ordovician tide‐dominated shelf (Santa Rosita Formation, northwest Argentina): Implications for ichnofacies models of shallow marine successions

The Santa Rosita Formation is one the most widely distributed lower Paleozoic units of northwest Argentina. At the Quebrada del Salto Alto section, east of Purmamarca, Jujuy Province, it is represented by four sedimentary facies: thick‐bedded planar cross‐stratified quartzose sandstones (A), thin‐bedded planar cross‐stratified quartzose sandstones and mudstones (B), wave‐rippled sandstones and bioturbated mudstones (C), and black and greenish gray shales (D). Paleocurrent data, sandstone architecture, and sedimentary structures from faciès A and B indicate bipolar/bimodal paleoflows, suggesting the action of tidal currents. The succession is interpreted as that of a tide‐dominated shelf, with only secondary influence of wave processes. Trace fossils are restricted to facies B and C. The Cruziana ichnocoenosis is preserved on the soles of thin‐bedded planar cross‐stratified quartzose sandstones (faciès B). This ichnocoenosis consists of Conostichus isp., Cruziana omanica, C. semiplicata, C. cf. tortworthi, Cruziana isp. Helminthopsis abeli, Monomorphichnus bilinearis, M. multilineatus, Palaeophycus tubularis, Rusophycus carbonarias, R. latus , and R. isp. The occurrence of Cruziana semiplicata , C. omanica, C. cf. tortworthi , and Rusophycus latus supports a Late Cambrian‐Tremadoc age. Slabbing of Cruziana shows complex interactions between biologic and sedimentologic processes, and suggests a predominance of exhumed traces, washed out and recast by tractive sand deposition. Sandstone soles are densely packed with biogenic structures and exhibit distinctive clusters of Rusophycus isp. that most likely represent trilobite nesting burrows. The Cruziana ichnocoenosis records the resident fauna of a protected, lower intertidal to subtidal interbar setting. The Skolithos ichnocoenosis is represented by high to low density vertical burrows of Skolithos linearis , which extend downwards to the quartzose sandstone soles of faciès B and cross the Cruziana ichnocoenosis. The Skolithos ichnocoenosis represents colonization by suspension‐feeding organisms following a major change in environmental conditions, related to the migration of lower intertidal to subtidal sandwaves. The Planolites ichnocoenosis consists exclusively of Planolites montanus within mudstones overlying wave‐rippled sandstones (facies C). The Planolites ichnocoenosis records opportunistic colonization by inf aunal deposit feeders that mined the organic‐rich fine‐grained sediment during the waning phase of storms that scoured organic detritus from the sea bottom. The section records, from base to top, a Cruziana‐Skolithos ichnofacies zone, a Skolithos ichnofacies zone and an unbioturbated zone typified by the thick‐bedded cross‐stratified quartzose sandstone (fades A). This trend reflects progressively higher energy conditions linked to the establishment of a large sand wave complex. The presence of a mixed Cruziana‐Skolithos ichnofacies in the lower interval reflects changes in substrate and energy levels, rather than water depth. Accordingly, contrasting ichnocoenoses from interbars (Cruziana) and sandwaves (Skolithos) must be considered an example of ichnofacies controlled by local parameters instead of general bathymétrie trends. Conversely, the vertical replacement of the Cruziana ichnofacies by the Skolithos ichnofacies towards the middle interval of the section reflects the environmental changes associated with the transition between the intertidal and subtidal zones. As overall tidal energy increases from supratidal to subtidal settings, the Skolithos ichnofacies tends to occur seaward of the Cruziana ichnofacies in tide‐dominated shallow marine environments. Therefore, onshore‐offshore ichnofacies replacement in tide‐dominated shallow seas is opposite to that in wave‐dominated marine settings.

Ichnos: An International Journal for Plant and Ani↗
USGS2021

Migration patterns and wintering distribution of common loons breeding in the Upper Midwest

Identification of geographic linkages among breeding, migratory and wintering common loon Gavia immer populations is needed to inform regional and national conservation planning efforts and compensation of loons lost during marine oil spill events. Satellite telemetry and archival geolocator tags were used to determine the migration patterns and wintering locations of breeding adult and young of the year juvenile common loons captured and marked on lakes in Minnesota, Wisconsin and Michigan. Adult loons typically traveled from breeding lakes, often via larger staging lakes, to the Great Lakes (primarily Lake Michigan) and then on to wintering areas. Most radiomarked juvenile common loons utilized natal lakes or local lakes through mid-November. Subsequently, the first fall migration of juvenile loons was generally initiated later, and more direct and quicker to wintering areas relative to adults. Among adult (n = 103) and juvenile (n = 23) loons that completed fall migration, most wintered in the Gulf of Mexico (GOM), with smaller proportions wintering off the southern Atlantic Coast or impoundments in the southeastern United States. Spring migration of adults to breeding lakes was less prolonged than fall migration, with adult male loons tending to depart wintering areas earlier than adult females. Juvenile common loons migrated during their first spring from wintering sites in the GOM to summer in the Gulf of St Lawrence/Nova Scotia Coastal region. Juvenile mortality was largely linked to parasitic infection and emaciation; spring appeared to be a survival bottleneck among juvenile loons monitored in our study. Our results identify several areas where common loon conservation efforts could be directed to protect key habitats and minimize stressors during the non-breeding period.

Michigan, Minnesota, Wisconsin↗
USGS2015

Hydro-bio-geomechanical properties of hydrate-bearing sediments from Nankai Trough

Natural hydrate-bearing sediments from the Nankai Trough, offshore Japan, were studied using the Pressure Core Characterization Tools (PCCTs) to obtain geomechanical, hydrological, electrical, and biological properties under in situ pressure, temperature, and restored effective stress conditions. Measurement results, combined with index-property data and analytical physics-based models, provide unique insight into hydrate-bearing sediments in situ. Tested cores contain some silty-sands, but are predominantly sandy- and clayey-silts. Hydrate saturations S h range from 0.15 to 0.74, with significant concentrations in the silty-sands. Wave velocity and flexible-wall permeameter measurements on never-depressurized pressure-core sediments suggest hydrates in the coarser-grained zones, the silty-sands where S h exceeds 0.4, contribute to soil-skeletal stability and are load-bearing. In the sandy- and clayey-silts, where S h < 0.4, the state of effective stress and stress history are significant factors determining sediment stiffness. Controlled depressurization tests show that hydrate dissociation occurs too quickly to maintain thermodynamic equilibrium, and pressure–temperature conditions track the hydrate stability boundary in pure-water, rather than that in seawater, in spite of both the in situ pore water and the water used to maintain specimen pore pressure prior to dissociation being saline. Hydrate dissociation accompanied with fines migration caused up to 2.4% vertical strain contraction. The first-ever direct shear measurements on never-depressurized pressure-core specimens show hydrate-bearing sediments have higher sediment strength and peak friction angle than post-dissociation sediments, but the residual friction angle remains the same in both cases. Permeability measurements made before and after hydrate dissociation demonstrate that water permeability increases after dissociation, but the gain is limited by the transition from hydrate saturation before dissociation to gas saturation after dissociation. In a proof-of-concept study, sediment microbial communities were successfully extracted and stored under high-pressure, anoxic conditions. Depressurized samples of these extractions were incubated in air, where microbes exhibited temperature-dependent growth rates.

Journal of Marine and Petroleum Geology↗
USGS1998

Does the Sverdrup critical depth model explain bloom dynamics in estuaries?

In this paper we use numerical models of coupled biological-hydrodynamic processes to search for general principles of bloom regulation in estuarine waters. We address three questions: what are the dynamics of stratification in coastal systems as influenced by variable freshwater input and tidal stirring? How does phytoplankton growth respond to these dynamics? Can the classical Sverdrup Critical Depth Model (SCDM) be used to predict the timing of bloom events in shallow coastal domains such as estuaries? We present results of simulation experiments which assume that vertical transport and net phytoplankton growth rates are horizontally homogeneous. In the present approach the temporally and spatially varying turbulent diffusivities for various stratification scenarios are calculated using a hydrodynamic code that includes the Mellor-Yamada 2.5 turbulence closure model. These diffusivities are then used in a time- and depth-dependent advection-diffusion equation, incorporating sources and sinks, for the phytoplankton biomass. Our modeling results show that, whereas persistent stratification greatly increases the probability of a bloom, semidiurnal periodic stratification does not increase the likelihood of a phytoplankton bloom over that of a constantly unstratified water column. Thus, for phytoplankton blooms, the physical regime of periodic stratification is closer to complete mixing than to persistent stratification. Furthermore, the details of persistent stratification are important: surface layer depth, thickness of the pycnocline, vertical density difference, and tidal current speed all weigh heavily in producing conditions which promote the onset of phytoplankton blooms. Our model results for shallow tidal systems do not conform to the classical concepts of stratification and blooms in deep pelagic systems. First, earlier studies (Riley, 1942, for example) suggest a monotonic increase in surface layer production as the surface layer shallows. Our model results suggest, however, a nonmonotonic relationship between phytoplankton population growth and surface layer depth, which results from a balance between several 'competing' processes, including the interaction of sinking with turbulent mixing and average net growth occurring within the surface layer. Second, we show that the traditional SCDM must be refined for application to energetic shallow systems or for systems in which surface layer mixing is not strong enough to counteract the sinking loss of phytoplankton. This need for refinement arises because of the leakage of phytoplankton from the surface layer by turbulent diffusion and sinking, processes not considered in the classical SCDM. Our model shows that, even for low sinking rates and small turbulent diffusivities, a significant % of the phytoplankton biomass produced in the surface layer can be lost by these processes.

Journal of Marine Research↗