Shell Hash Research Articles

Cold front induced changes on the Florida panhandle shelf during October 2008

A significant step transition between seasonally stratified and destratified hydrographic conditions occurred during an October 2008 cruise to the Florida Panhandle Shelf along a cross-shelf transect that was sampled before and after a cold front passed through the area. Meteorological measurements from nearby ocean and land-based stations characterized the event. Cross-shelf continuous Acrobat profiles and discrete CTD stations characterized water column hydrographic patterns, while mid-shelf multicorer and box corer samples characterized sediment texture and nutrients. Water samples collected from selected depths biased toward the sediment interface were analyzed for nutrient content and phytoplankton community composition. Pre-front, the cross-shelf water column exhibited vertical stratification with complex temperature and salinity patterns. A prominent near-bottom chlorophyll a maximum of ∼1.5μgL−1 between the 25–35m isobaths occurred with the 1% light level at ∼18m depth and a near-bottom nitrate+nitrite (NO3−+NO2−) maximum >3μM between the 30–40m isobaths. HPLC-determined phytoplankton community composition in the near-bottom chlorophyll a maximum consisted of gyroxanthin-containing dinoflagellates (Karenia brevis) and less abundant diatoms, both verified by FlowCAM analysis, mixed with detectable cryptophytes and chlorophytes. Sediment trends based on limited core replicates suggested the sediments were a potential source of nutrients to near-bottom populations of K. brevis and that shell hash could provide abundant pore space for K. brevis incursions. Between the 40–50m isobaths, diatoms, cryptophytes and chlorophytes dominated near-bottom, gyroxanthin-containing dinoflagellates and prasinophytes occurred throughout the water column, and cyanophytes dominated near-surface. Post-front, the cross-shelf water column exhibited destratification with temperature and salinity increasing offshore. A chlorophyll a maximum of ∼0.75μg Chl aL−1 left the sediment between 25–35m isobaths and extended offshore especially in the lower water column with the 1% light level at ∼15m depth and NO3−+NO2− concentrations ∼2μM to the 60m isobath. HPLC-determined phytoplankton community composition of the offshore plume retained the signature of gyroxanthin-containing dinoflagellates and chlorophytes. Between the 30–50m isobaths, prasinophytes increased in the lower water column, while cyanophytes increased at all depths across the shelf. The observed step transition from stratification to destratification on the Florida Panhandle Shelf contributed to altered phytoplankton community patterns in response to predominant downwelling favorable winds. Pre-front, K. brevis cells were broadly distributed cross-shelf, but concentrated near-bottom between the 25–35m isobaths and staged for prolific bloom seeding in response to the upwelling favorable west winds more typical of spring-summer. Post-front, K. brevis cells were mixed throughout the mid-shelf water column and were staged for diffuse bloom seeding in response to either the downwelling or upwelling favorable winds occurring fall-winter. Cyanophytes located predominantly near-surface offshore pre-front, were ubiquitous cross-shelf and more closely associated with K. brevis post-front.

Surficial geology and geophysical investigations of the Capers Inlet, South Carolina (USA) 7.5-Minute Quadrangle

Surficial geology and geophysical investigations of the Capers Inlet, South Carolina (USA) 7.5-Minute Quadrangle is a compilation of geological and geophysical data collected in the Caper's Inlet Quadrangle, situated along the central coastline of South Carolina, USA. The 1:24,000 scale map area encompasses marine environments in the shallow nearshore and offshore (constituting approximately 80% of the study area) and terrestrial barrier island and Pleistocene upland environments (20% of the study area). The geologic map was compiled by overlaying existing topographic maps with data from high-resolution sidescan sonar, subbottom profiler, and GPR surveys supplemented with surficial sediment grabs and vibracore samples. These data were collected in 2009 and early 2010 for an MSc thesis project conducted through the Department of Geology and Environmental Geosciences at the College of Charleston, South Carolina. The resulting maps illustrate the spatial variability of surficial seafloor geology in the area, with sediment distribution ranging from a coarse shell hash to fine-grained mud. The shallow stratigraphy is characterized by a thin layer of modern sediment overlying the boundary between the Quaternary and Tertiary as well as the presence of several paleochannels in the backbarrier and shallow offshore. By portraying both seafloor geology and shallow stratigraphy, maps and accompanying information provide scientists and coastal managers with a better understanding of the relationship that exists between stratigraphy, sediment distribution, and geomorphology in the area.

Palaeoecology and Geoarchaeology of Varna Lake, Northeastern Bulgaria

Palaeoenvironmental data from the high-resolution spore-pollen analysis of laminated sediments from newly-taken Core 3 ‐ Varna Lake were combined with analyses of dinoflagellate cysts, acritarchs and other non-pollen palynomorphs (NPP), including fossil algal and fungal remains. The location of the core is close to submerged prehistorical sites and permits the palaeoenvironmental correlations of obtained results with available archaeological and geochronological data. The established Age Model shows that the accumulation of lake sediments started after 7870 cal. BP and is connected with a rise of the Black Sea level. One-hundred-ninety-cm-long molluskan shell hash layer of Mytilus galloprovincialis covers the interval from 7776 to 6183 cal. BP. The mixed oak and hornbeam forests dominated the vegetation cover during the Atlantic, Subboreal and Subatlantic chronozones of the Holocene. An important change in the forest composition occurred at ca 5598 cal. BP, when Carpinus betulus increased its spreading due to climatic changes. The high-resolution reconstruction of palaeovegetation also reveals the extent of anthropogenic influence in Varna Lake area. Two periods of significant presence of pollen from cultivated cereals, weeds and ruderals were identified. According to the available AMS-radiocarbon data, these periods are attributed to the Late Eneolithic and Early Bronze Age. The anthropogenic impact on the natural vegetation has been identified by deforestation and agricultural practice. The Transitional period without human activities between these two periods lasted ca 319 years

High-frequency acoustic backscattering from a sand sediment: Experiments and data/model comparisons

In the Spring of 2012, high-frequency backscattering from a sandy sediment was measured in the Gulf of Mexico at the site of the upcoming, ONR-sponsored reverberation experiment. The measurements were made using an array of sources and receivers that collected data from 200 to 500 kHz and that could be rotated such that the incident grazing angles varied from 10 to 50 degrees. This array was used previously to measure scattering from a sand/mud sediment during the Sediment Acoustics Experiment 2004 (SAX04). To support data/model comparisons, the seabed roughness, sediment shell content, sediment sound speed, and sediment attenuation were also measured. For scattering below the critical grazing angle, sediment roughness is found to be the dominant scattering mechanism while above the critical angle, roughness scattering underpredicts the measured scattering strength. To understand the scattering strength at high grazing angles, scattering from shells and shell hash is considered. The measured scattering strengths and environmental properties at the experiment site are also compared to those made during SAX04. (Work supported by the US Office of Naval Research)

Seasonal transfer and net accumulation of fine sediment on a muddy tidal flat: Willapa Bay, Washington

Tidal flats act as natural laboratories in which fundamental sediment-transport processes can be directly related to resulting seabed deposits. These environments represent important repositories for terrestrial particles (including organic carbon) entering marine dispersal systems. Along the coast of the US Pacific Northwest, tides, waves, currents, and storms create year-round energetic environments that evolve on myriad time scales, from semi-diurnal to interannual. In southern Willapa Bay, WA, an extensive tidal flat is accreting at a distance away from local fluvial sources. During winter, freshwater input and the peak suspended-sediment concentration (SSC) are one-to-two orders of magnitude greater than in summer, and wind- and wave-generated shear stresses prevent sediment from accumulating on the tidal flat. Temporary deposits form as a drape across secondary channels off the Bear River Channel. Sedimentary structures from these deposits reveal 15–30cm of physically stratified sediment underlain by a discrete shell-hash layer 2–8cm thick. The presence of relatively uniform excess 210Pb activities in the sediment above the shell hash, and only supported activities below indicate rapid deposition of the surficial sediment. During summer, the distribution of bed shear stresses is not significantly weaker than in winter due to the effect of local basin geometry on fetch, yet the SSC is much less, likely due to reduced fluvial sediment supply and enhanced benthic biological factors. Progressively through the summer, tidal currents and wind waves remove the temporary channel deposits and expose the buried shell-hash layer, and concurrent seabed changes allow the tidal flats to trap this remobilized sediment. Accumulation rates determined by 210Pb analysis for cores collected on the tidal flats show mean accretion at 1.4mm/yr, which can be accounted for by local river sources. The mass of sediment stored in the temporary channel drapes during winter is approximately the same as the annual tidal-flat accumulation in the vicinity of these channels. This agreement suggests a mechanism by which sediment temporarily stored in winter channel deposits is subsequently reworked during summer, and transferred onto the tidal flats. The accumulation rate on the flats approximately matches local sea-level rise, which implies this system accretes over longer time scales in equilibrium with the space provided. The preservation of layered deposits (65–90cm thick) buried 155–230cm beneath the modern surface suggests that the past accommodation space was greater than at present. Coseismic subsidence during Cascadia earthquakes represents a possible mechanism by which vertical space can be created.

Cannibalism in red king crab, Paralithodes camtschaticus (Tilesius, 1815): Effects of habitat type and predator density on predator functional response

Red king crab, Paralithodes camtschaticus, an important fishery species in Alaska, exhibits cannibalism both within and among age classes. Cannibalism in crab species can be an important determinant of recruitment success, and this might be especially important in king crab because year-0 and year-1 crab occupy the same habitat types in the wild. In this study we used laboratory experiments to determine the predator functional response, or the effect of prey density on predation rates of year-1 crab preying on year-0 crab in three different habitat types: Sand, which was unstructured soft sediment, Whole Shell, which was whole clam valves, and Shell Hash, which was smaller pieces of crushed shell. We also examined how predator density (one or two predators) affects the functional response. The data was fit to Type I, or density independent, Type II, or inversely density dependent, and Type III, or density dependent, functional response models and the best fit model was chosen using Akaike's information criterion. The functional response was a Type II in all habitat types; however, the predation rate was lower at all prey densities in the Whole Shell habitat than in Shell Hash and Sand. The functional response was a Type II at both predator densities as well. The presence of a second predator decreased both the attack rate and the handling time, resulting in slightly lower predation rates at low prey densities, and slightly higher predation rates at high prey densities when compared to the single predator treatment. This indicates a low level of predator interference. This work has implications for potential stock enhancement activities, as year-1 crab could inhibit enhancement success though cannibalism of introduced year-0 crab, especially given the destabilizing nature of the Type II functional response. A potential solution would be to enhance a given area only every other year to give previous cohorts a chance to start podding in less complex habitats. Future work should examine whether the presence of alternative prey changes the functional response to a Type III, as this would give year-0 crabs a low‐density refuge from predation.

Ontogenetic diet shifts in snapper (Pagrus auratus: Sparidae) within a New Zealand estuary

The diet of the sparid fish Pagrus auratus (snapper) was examined within the Mahurangi Harbour in north-eastern New Zealand. Ontogenetic shifts occurred in diet. Individuals <20 mm (fork length) consumed planktonic copepods, with a shift at 20 mm to benthic copepods, mysid and caridean shrimps and polychaetes. Snapper >100 mm consumed brachyuran crabs, caridean shrimps, bivalves, polychaetes and hermit crabs, with individuals >300 mm also able to consume harder shelled molluscs and bivalves. The stomach contents of juvenile snapper (10–100 mm) sampled across habitats of sand, shell hash, horse mussels and subtidal mud showed differences in major prey taxa; however, these differences were small. This may be advantageous for juveniles, which can then select a habitat for other qualities. A comparison with eight other studies on the diet of snapper from coastal areas showed crustaceans were consistently the most highly ranked major taxon; however, differences among other major taxa were relatively minor.

Dispersal of Oyster (Ostrea chilensis) Larvae in Tasman Bay Inferred using a Verified Particle Tracking Model that Incorporates Larval Behavior

ABSTRACT We present a particle tracking model that simulates the dispersal of the oyster Ostrea chilensis Philippi in Tasman Bay, New Zealand. The model was calibrated to reproduce observed vertical distributions of larvae, and was verified against an independent data set of such distributions. The seabed in Tasman Bay contains little hard substrate other than shell hash. By comparing simulated and observed settlement, we infer that larvae must either be able to sense shell hash at a distance and orient onto it, such that settlement success is higher than indicated by the 1-km2 resolution relative density (square meter of exposed shell per square meter of seabed), or be settling on material other than shell hash. The modeling indicates that only a very small proportion of those larvae that do settle travel more than 1 km from their natal location. There are plans to endeavor to restore the oyster fishery by provision of new shell hash to the bed. Our simulations suggest that these new beds will be coloniz...

Mapping Benthic Habitats in Delaware Bay and the Coastal Atlantic: Acoustic Techniques Provide Greater Coverage and High Resolution in Complex, Shallow-Water Environments

Accurate benthic habitat maps are critical for resource management in coastal waters with competing uses. We used a 500 kHz phase-measuring bathymetric sonar (PMBS) and 900 kHz side-scan sonar to acquire seafloor data in estuarine and shelf environments. Grab samples and remotely operated vehicle video created geological and biological classifications for segmented maps produced by a backscatter clustering program. PMBS improves regional map resolution (<1 m), reduces the need for direct sampling, extends information on sediment–biological relationships to larger areas, and allows measurements of bedforms. Auto-segmentation was successful in environments with highly contrasting acoustic signatures and meters-scale homogeneity. Patchier communities are identifiable in PMBS data. Species preferences for sediment (i.e., tubeworm preference for sediment without shell hash) allowed us to determine potential habitat without identifying individual organisms in acoustic data. PMBS with sufficient ground-truthing offers an efficient way to map seafloor characteristics, which is critical in marine spatial planning efforts.

Implications of the presence of shell hash on the speed and attenuation of sound in water-saturated granular sediments

The propagation of sound through water-saturated granular sediments has been widely studied, yet there is no consensus on an expected wave speed and attenuation in these materials owing to variation in both physical properties and test methods used for their interrogation. One aspect confounding model predictions is the presence of inhomogeneities such as rocks, bubbles, and biological organisms in an otherwise homogeneous sediment. In a laboratory setting, it is possible to control both manufacture of artificial sediments with specific inclusions and the measurement method used to observe their properties. To study the effect of inclusions on the speed of sound and attenuation in an otherwise homogeneous sediment, shells were systematically added to a sand sediment. The volume fraction of shells relative to sand grains was varied and the speed of sound and attenuation was measured using a time of flight technique from 200 to 800 kHz. Results will be compared to both sediment acoustic models and scatterin...

Sea level controls sedimentation and environments in coastal caves and sinkholes

Quaternary climate and sea-level research in coastal karst basins (caves, cenotes, sinkholes, blueholes, etc.) generally focuses on analyzing isotopes in speleothems, or associating cave elevations prior sea-level highstands. The sediments in coastal karst basins represent an overlooked source of climate and sea-level information in the coastal zone, but to accurately interpret these sediments first requires an understanding of the forcing mechanisms that emplace them. In this study, we hypothesize that coastal karst basins transition through vadose, littoral, anchialine, and finally into submarine environments during sea-level rise because groundwater and sea level oscillate in near synchrony in the coastal zone, causing each environment to deposit a unique sedimentary facies. To test this hypothesis, the stratigraphy in twelve sediment cores from a Bermudian underwater cave (Green Bay Cave) was investigated and temporally constrained with twenty radiocarbon dates. The results indicate that we recovered the first succession spanning the entire Holocene from an underwater cave (~ 13 ka to present). The sediments were characterized with X-radiography, fossil remains, bulk organic matter, organic geochemistry (δ 13C org, C:N), and grain size analysis. Four distinct facies represent the four depositional environments: (i) vadose facies (> 7.7 ka, calcite rafts lithofacies), (ii) littoral facies (7.7 to 7.3 ka: calcite rafts and mud lithofacies), (iii) anchialine facies (7.3 to 1.6 ka: slackwater and diamict lithofacies), and (iv) submarine facies (< 1.6 ka: carbonate mud and shell hash lithofacies). The onset and duration of these sedimentary depositional environments are closely linked to Holocene sea-level rise in Bermuda, indicating that sea level controls environmental development in coastal karst basins. Finally, we present a conceptual model for interpreting the sediments and environments in coastal karst basins as a result of sea-level change.

On the genus Raphidrilus Monticelli, 1910 (Polychaeta: Ctenodrilidae) with description of two new species

Raphidrilus harperi sp. nov., is described from the Gulf Intracoastal Waterway (GIWW) in Venice, Florida from sediments consisting of coarse sands and shell hash. Raphidrilus hawaiiensis sp. nov., is described from Oahu’s shallow waters and inhabits a successful invasive alga in Waikiki and sandy sediments adjacent to ocean outfalls in Barbers Point and Sand Island, off Honolulu. The genus Raphidrilus is emended, the distinctness between the genera Raricirrus and Raphidrilus is confirmed and keys to all recognized genera of Ctenodrilidae and species of Raphidrilus are given.

Winter coastal movement of Gulf of Mexico sturgeon throughout northwest Florida and southeast Alabama

Summary In order to characterize distribution of Gulf of Mexico sturgeon in nearshore Gulf of Mexico (GOM) and compare distributions prior to and after hurricane activity, 187 Gulf sturgeon (Acipenser oxyrinchus desotoi) were tagged with acoustic transmitters in Ochlockonee, Apalachicola, Brothers, Choctawhatchee, Yellow, Blackwater and Escambia rivers to monitor marine movement along the GOM coastline from Florida (FL) to Alabama (AL). Nine juveniles (79–86 cm fork length, 3.4–5.2 kg), 22 sub-adults (91–126 cm fork length, 4.5–17.1 kg) and 156 adults (130–210 cm fork length, 14.9–75.2 kg) were tagged between 2003 and 2005 and acoustically monitored each year between January and April, 2004–2008. Of the 187 tagged Gulf sturgeon, 72 adults, one sub-adult and no juveniles were relocated in the GOM throughout the entire duration of monitoring between 2004 and 2008. Fish were relocated on average 1.5 km from shore in two very important foraging and over wintering areas, one of which is not currently protected under the critical habitat designation: Site A located geographically between Pensacola, FL and Gulf Shores, AL and Site B located between Mexico Beach, FL and Panama City Beach, FL. Sediment studies conducted concluded that substrate at Site A consisted of fine sand, shell and areas of silty mud and substrate at Site B consisted of shell hash and fine sand. Macro invertebrates, such as polychaetes: Hobsonia florida and Mediomastus ambiseta and mollusk: Ervillia concentric, all typical to the Gulf sturgeon diet, were present at both sites. Forty-three tagged adult Gulf sturgeon were relocated at Site A and 27 adults and one sub-adult were relocated at Site B, with two additional fish located in other areas. Individual fish movement in one direction ranged from 10 to 315 km each year. Several fish exited one river, over wintered in the GOM, and entered a different river. Identification of new, frequently used Gulf sturgeon habitat (Site A), outside of federally protected critical habitat, provided vital information that will aid in the future protection of coastal areas that support Gulf sturgeon during the winter and help with recovery efforts of the species.

Samarang Field - Redevelopment Evaluation Brings New Life to an Old Oil Field

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper IPTC 13162, ’Samarang Field - Seismic-to-Simulation Redevelopment Evaluation Brings New Life to an Old Oil Field, Offshore Sabah, Malaysia,’ by J.K. Forrest, SPE, Schlumberger; A. Hussain, SPE, and M. Orozco, SPE, Petronas Carigali Shd. Bhd.; and J.P. Bourge, SPE, T. Bui, SPE, R. Henson, SPE, and J. Jalaludin, SPE, Schlumberger, originally prepared for the 2009 International Petroleum Technology Conference, Doha, Qatar, 7-9 December. The paper has not been peer reviewed. The Samarang field is offshore Sabah, East Malaysia, approximately 45 miles northwest of the Labuan gas terminal. The field surrounds a shallow reef with a water depth of 30 ft. Shell was the initial operator and relinquished the concession to Petronas Carigali Sdn. Bhd. (PCSB) in April 1995. Field-Development History Fig. 1 summarizes the production and development history of the field. The field was developed in phases, with the initial phase including the larger A and B drilling platforms; separate producing platforms at A, B, and C; and well jackets at C, D, and E. Subsequent development included well jackets at F and G. An additional well jacket, H, was planned by Shell for the east-flank development but was not implemented in 1986 because of low reserves potential and low oil prices. Formation Evaluation and Characterization A 1984 3D-seismic survey is available and was interpreted, but the best data and control are provided by the openhole logs from 144 wells. Within the field, log correlation is good in general. All of the producing reservoirs in the field are normally pressured, and the field has a normal temperature gradient for the area of approximately 1.05°/100 ft. The cored interval comprises three main facies types (i.e., sandstones, heterolithic sandstones, and shales). These facies types then were subclassified into nine lithofacies to cover the broad spectrum of sand/shale content, primary sedimentary structures, intensity of bioturbation, and unique sedimentologic character that was identified and described from the core. The ninth lithofacies in the cored intervals represents the presence of carbonates in the form of patchy carbonate cement, broken/intact shell hash layers, dolomite patches, and layered or nodular siderites. This last lithofacies, though negligible in occurrence in the whole cored section (0.4% of the total cored interval), was important as a local vertical-flow baffle. Following the identification of these lithofacies, geologists used a neural-network procedure to extend the lithofacies to most of the noncored wells. Some of the wells had wellbore problems including missing logs or cork-screwed boreholes, which did not allow their inclusion in this work. But in all cases, there was sufficient well coverage to allow the estimation of lithofacies throughout the reservoir sequences. The final neural-network model involved used the sand, silt, and clay volumes for each individual well as calculated by petrophysical methods.

Evidence for sediment recirculation on an ebb-tidal delta of the East Frisian barrier-island system, southern North Sea

The Otzum ebb-tidal delta, located between Langeoog and Spiekeroog islands along the East Frisian barrier-island coast, southern North Sea, was investigated with respect to its morphological evolution, sediment distribution patterns and internal sedimentary structures. Bathymetric charts reveal that, over the last 50 years, the size of the Otzum ebb-tidal delta has slightly shrunk, while sediment has accreted on the ebb-delta lobe to the east of the main inlet channel (west of Spiekeroog). Swash bars superimposed on the eastern ebb-tidal shoal (Robben Plate) have migrated south or south-eastwards, i.e. towards the inlet throat. The main ebb-delta body is composed of fine quartz sand, whereas the superimposed swash bars and the inlet channel bed consist of medium-grained quartz sand containing high proportions of coarser bioclastic material. Internal sedimentary structures in short box-cores (up to 30 cm long) are dominated by flood-oriented cross-beds. Longer vibro-cores (up to 1.5 m long) show that, at depth, the sediment is dominated by storm-generated parallel (upper plane bed) laminations with intercalated shell layers and dune cross-bedding. The cross-bedded sands in both box-cores and vibro-cores from the ebb-delta shoal predominantly dip towards the south or southeast, indicating transport towards the inlet throat by the flood current. The observations demonstrate that, contrary to previous contentions, the sediments of the highly mobile swash bars do not bypass the inlet but are instead being continually recirculated by the combined action of tidal currents and waves. In this model, the cycle begins with both fine and medium sands, including shell hash, being transported seawards in the main ebb channel until they reach the shallow ebb-delta front. From here, the sediment is pushed onto the eastern ebb-delta shoal by the flood current assisted by waves, becoming strongly size-sorted in the process. The medium sands together with the shell hash are formed into swash bars which migrate along arcuate paths over a base of fine sand back to the main ebb channel located south of the ebb delta. By the same token, the fine sand between the swash bars is transported south-eastwards by the flood current in the form of small dunes until it cascades into the large flood channel located to the west of Spiekeroog. From here, the fine sand is fed back into the main ebb channel, thus completing the cycle. No evidence was found on the ebb delta for alongshore sediment bypassing.

Holocene litho- and biostratigraphy of the NW Black Sea (Romanian shelf)

Detailed lithological and micropaleontological studies were performed on several cores from the Romanian Black Sea shelf, located in front of the Danube Delta, in front of the Razelm–Sinoe lagoonal complex, close to the Eforie beach, as well as on the Romanian inner shelf. All the studied cores are situated at a water depth varying between 12m and 67m. The purpose of the investigations was to reveal Upper Holocene lithological changes and the associated calcareous nannoplankton fluctuations in a very shallow marine setting such as the Romanian Black Sea inner shelf. The youngest Holocene unit or “Shallow Unit” is composed of alternating sequences of mud, silt, clay and coquina layers, containing marine mollusc faunas. The upper part of the Shallow Unit contains blooms of the nannoplankton species Emiliania huxleyi, while its lower part yields, besides common E. huxleyi, rare specimens of Braarudosphaera bigelowii. The Shallow Unit overlies a “shell hash layer”, mainly made by coquinas, containing mixing marine and brackish mollusc faunas. Towards the upper part of this level, monospecific assemblages with B. bigelowii were observed in a layer rich in carbonate acicular crystals. The Shallow Unit partly corresponds to the Unit 1 (finely laminated coccolith ooze) and Unit 2 (sapropelic sediments) of slope and basinal settings of the Black Sea. The layer rich in carbonate acicular crystals could be a shallower equivalent of the oldest layer of aragonite bands placed at the lower part of the Unit 2 in deep parts of the Black Sea. In the analyzed cores, the oldest lithological unit (Unit 3, the muddy clay sediments deposited in a brackish to freshwater environment) is characterized by the deposition of green-yellowish clay devoid of any Holocene calcareous nannoplankton species and containing brackish mollusc faunas. Based on nannofloral fluctuations, an increasing salinity from the base towards the upper part of the Shallow Unit may be supposed, together with the progressive establishment of a stable marine setting, similar to today.

Palaeo-drainage, incised valley fills and transgressive systems tract sedimentation of the northern KwaZulu-Natal continental shelf, South Africa, SW Indian Ocean

Two sequence boundaries are recognised in seismic data collected from the narrow northern KwaZulu-Natal continental shelf. These correspond to late Cretaceous and latest Pleistocene–Last Glacial Maximum (LGM) periods of sea-level fall where fluvial incision into the shelf resulted in several incised valleys having formed. In both examples, the ensuing transgressive valley fills document an evolution from fluvially dominant sedimentation to classic backbarrier estuarine conditions. Central estuary basin sedimentation is most prominent within each fill and is separated from the underlying fluvial sediments by bayline ravinement processes. Tidal-ravinement surfaces separate the upper estuarine sequences from barrier and shoreface deposition, most easily observed in the latest Pleistocene/Holocene valley fills where a Holocene unconsolidated sediment wedge overlies the estuarine fill. The wedge itself is characterised by two packages of sediment separated by a regionally occurring wave/shoreface transgressive ravinement surface which crops out as a semi-indurated shell hash in the mid to outer shelf. Late Cretaceous examples are capped by deposits exhibiting oblique parallel to wavy reflectors interpreted as increasingly energetic deposits analogous to flood-tide deltaic sedimentation. Valley incision and fill are linked to two onshore coastal lake systems, Lake Sibaya and Lake St Lucia and appear to be the product of barrier breaching and fluvial re-adjustment to baseline shifting of these systems during forced regression. Lake St Lucia exhibits a composite palaeo-drainage channel where both sequence boundaries merge within the lake margins. Lake Sibaya has two distinct palaeo-channels for each sequence boundary episode, a late Cretaceous channel which fed a small incised valley within which a modern day submarine canyon is located, the other an LGM channel directed in towards the head of Wright Canyon, the subsequent input of sediment causing this canyon to breach furthest into the shelf than any other canyon in the area. Offshore of Lake St Lucia, the most proximal portions of the associated Leven Canyon occupy the mid shelf and are underlain by Lake St Lucia palaeo-drainage channels of LGM age where erosion along the initial LGM palaeo-channel has occurred. Freshwater exchange between the shelf and the fringing lake system has resulted in the development of sinuous features of Leven Canyon which have eroded in a downslope-fluvial like manner, thus occupying palaeo-drainage lows as erosive flows were entrained. Models proposed here indicate that 1) the limited accommodation space offered by a narrow continental shelf may allow for a greater preservation potential of wave-dominated estuarine facies; 2) the seismic expression of these fills may vary, yet still satisfy similar sedimentological conditions and 3) antecedent valley topography increases the preservation potential of these valley fills by providing a preferred space in which to re-incise and then fill during sea-level rise.

Analysis of Sediment and Gut Contents of the Sand Dollars Mellita tenuis, Encope michelini, and Encope aberrans off the Central Florida Gulf Coast

Sand dollars are conspicuous macroinvertebrates on particulate substrates in intertidal and shallow water environments. Their locomotion and feeding can have major effects on the sediment and infauna. We investigated the sediment and gut contents of three species of sand dollars off the central Florida gulf coast. Sediment comprised quartz particles at two sites and mixed quartz particles and carbonate shell hash at the third site. At all sites, gut particles were smaller than those of the sediment. This could have been the result of the teeth of the Aristotle’s lantern crushing the particles. However, particles in the food grooves of two species (Mellita tenuis and Encope michelini) were similar to those in the gut contents, smaller than in the sediment. This indicates that selection for small particles from the sediment occurred and that crushing of particles was not necessary to account for the small size of particles in the gut for those collections. The concentration of organic matter in the gut contents was much greater than that of the sediment, indicating that selection of organic matter not associated with the inorganic sediment particles occurred. It is possible that the contribution of organic matter not associated with the inorganic sediment particles is of considerable importance to the nutrient requirements of the sand dollars.

Species diversity in the soft-bottom intertidal zone: Biogenic structure, sediment, and macrofauna across mussel bed spatial scales

Mussels are important ecosystem engineers that have significant impacts on the ecology of the seafloor. In this study, we attempt to characterize and explain infaunal and epifaunal abundance patterns across scales in a spatially complex, intertidal, soft-bottom habitat: beds of the semi-infaunal mussel, Mytilus edulis. We used univariate and multivariate analyses in a nested sampling design at three locations in eastern Maine to show the relationships between environmental and macrofaunal assemblage variables. The results support the hypotheses that: 1) environmental and macrofaunal assemblage variables vary widely across spatial scales and exhibit maximum variance at different spatial scales; 2) abundance and diversity patterns of macrofauna are linked to spatial variation in environmental variables in the form of biogenic structure (live mussels and mussel shell hash), terrestrially-derived gravel, and, to a lesser degree, the proportion of silt-clay in the sediment; and 3) epifauna are generally positively correlated with hard-substrate features such as live mussels and gravel, and negatively correlated with the silt-clay content of the sediment, although the latter relationships were not strong. On the other hand, the results did not support the hypotheses that: 4) most infauna, specifically those with free-swimming larvae, are negatively correlated with live mussels and silt-clay proportion; instead, they were often positively correlated with live mussels and had weak, insignificant correlations with silt-clay; and 5) infauna without free-swimming larvae are positively correlated with live mussels and silt-clay proportion; instead, they showed some positive correlations with live mussels, but a mix of weak, insignificant correlations with silt-clay. Thus, mussel beds had a variety of scale-dependent relationships, both positive and negative, with each of the macrofaunal groups. The results show that biogenic structure in the form of live mussels and mussel shell hash is important in this system, as is terrestrial gravel, and that these variables are more important than silt-clay content for the macrofaunal assemblage. Mussel beds play an important role in regulating macrofaunal diversity in soft-bottom habitats, and their effects vary across spatial scales.

Ontogenetic pattern of resource use by the tiny hermit crab Pagurus villosus (PAGURIDAE) from the temperate Chilean coast

The biology of hermit crabs in the temperate zone is understudied in comparison with hermit crabs in the tropics and subtropics. Here we provide the first observations of population traits of the smallest South Pacific hermit crab, Pagurus villosus, using descriptive and experimental approaches. The principal emphasis is on ontogenetic and spatio-temporal variation in the breeding season, recruitment, sex ratio, microhabitat use, and shell occupancy pattern. We also experimentally evaluated colonization rates, in order to assess the pattern of habitat use. P. villosus showed continuous reproduction and recruitment, and an unbiased sex ratio. Algae turf was the microhabitat with highest record of individuals, regardless of their ontogenetic stage. Females were smaller and showed less movement activity on experimental trays than did males, for three microhabitat analyses. Early stages colonized higher proportions of artificial algae and shell hash (only juveniles). Diversity of gastropod shells used by hermit crabs (12 in total) decreased during development, but for all stages Tegula tridentata and Nassarius gayi were the most used. Females in different reproductive conditions (ovigerous and non-ovigerous) showed a shift of shell occupancy pattern likely related to the tradeoff between fitness and shape, weight, thickness and internal volume of shells. Population and life-history traits, i.e., continuous breeding and high resource use during all ontogenetic phases (microhabitats and shells), of P. villosus on the temperate Chilean coast seem more similar to pagurid species from low latitudes. These traits may reflect a tropical origin of this species and/or an adaptive strategy of these tiny crabs in a temperate region.