Intraspecific Interactions and Risk of Predation for Dyspanopeus sayi (Decapoda: Xanthidae) Living on Polychaete (Filograna implexa,Serpulidae) Colonies*

Abstract. Along the Atlantic coast of the United States, the mud crab Dyspanopeus sayi frequently occurs in crevices and depressions within aggregated calcareous tubes (termed “heads”) of the serpulid polychaete Filograna implexa. In New Jersey, U.S.A., waters, crab number was significantly correlated with the logarithm of worm tube colony volume. Laboratory experiments suggested that crabs compete for shelter within worm colonies. Additional laboratory experiments indicated that colony occupancy greatly decreased the risk of predation by blue crabs (Callinectes sapidus), and field tethering experiments also demonstrated that colony occupancy significantly decreased predation risk. Thus, the consequence of holding space on worm tube heads is a greatly increased probability of survival.     

Diel variation in immigration of fishes and decapod crustaceans to artificial seagrass habitat

Fish and decapod entry into small (1.5 m²) artificial seagrass habitats positioned on an open sand area in a New Jersey estuary was examined to determine if immigration varied between day and night. To encounter the structured habitats, colonizers had to cross an expanse of bare sand, with its presumably higher predation risk. Contrasts in abundance in the artificial seagrass plots between dawn and dusk indicated higher nighttime immigration for four species, including the fishesFundulus heteroclitus andMyoxocephalus aenaeus, and the caridean shrimpsPalaemonetes vulgaris andHippolyte pleuracanthus. Size-frequency distributions of colonizers varied between day and night for two fish species,Menidia menidia andSyngnathus fuscus, with a greater proportion of smaller individuals immigrating to the artificial seagrass at night.Callinectes sapidus also displayed a diel contrast in size distribution but, for this species, proportionately more small individuals colonized the plots during the day. We suggest that diel variability in predation risk and/or diel patterns in motor activity may be responsible for these patterns in immigration.     

Extreme ultraviolet spectra of solar active regions and their analysis

Extreme ultraviolet spectra of several active regions are presented and analyzed. Spectral intensities of 3 active regions observed with the NRL Skylab XUV spectroheliograph (170–630 Å) are derived. From this data density sensitive line ratios of Mg viii, Si x, S xii, Fe ix, Fe x, Fe xi, Fe xii, Fe xiii, Fe xiv, and Fe xv are examined and typically yield, to within a factor of 2, electron pressures of 1 dyne cm^–2 (n _e T = 6 × 10¹⁵ cm^–3 K). The differential emission measure of the brightest 35 × 35 portion of an active region is obtained between 1.4 × 10⁴ K and 5 × 10⁶ K from HCO OSO-VI XUV (280–1370 Å) spectra published by Dupree et al. (1973). Stigmatic EUV spectra (1170–1710 Å) obtained by the NRL High Resolution Telescope and Spectrograph (HRTS) are also presented. Doppler velocities as a function of position along the slit are derived in an active region plage and sunspot. The velocities are based on an absolute wavelength scale derived from neutral chromospheric lines and are accurate to ±2 km s^–1. Downflows at 10⁵ K are found throughout the plage with typical velocities of 10 km s^–1. In the sunspot, downflows are typically 5 to 20 km s^–1 over the umbra and zero over the penumbra. In addition localized 90 and 150 km s^–1 downflows are found in the umbra in the same 1 × 1 resolution elements which contain the lower velocity downflows. Spectral intensities and velocities in a typical plage 1 resolution element are derived. The velocities are greatest ( 10 km s^–1) at 10⁵ K with lower velocities at higher and lower temperatures. The differential emission measure between 1.3 × 10⁴ K and 2 × 10⁶ K is derived and is found to be comparable to that derived from the OSO-VI data. An electron pressure of 1.4 dynes cm^–2 (n _e T = 1.0 × 10¹⁶ cm^–3 K) is determined from pressure sensitive line ratios of Si iii, O iv, and N iv. From the data presented it is shown that convection plays a major role in determining the structure and dynamics of the active region transition zone and corona.     

Frontiers in large igneous province research

Earth history is punctuated by events during which large volumes of mafic magmas were generated and emplaced by processes distinct from “normal” seafloor spreading and subduction-related magmatism. Large Igneous Provinces (LIPs) of Mesozoic and Cenozoic age are the best preserved, and comprise continental flood basalts, volcanic rifted margins, oceanic plateaus, ocean basin flood basalts, submarine ridges, ocean islands and seamount chains. Paleozoic and Proterozoic LIPs are typically more deeply eroded and are recognized by their exposed plumbing system of giant dyke swarms, sill provinces and layered intrusions. The most promising Archean LIP candidates (apart from the Fortescue and Ventersdorp platformal flood basalts) are those greenstone belts containing tholeiites with minor komatiites. Some LIPs have a substantial component of felsic rocks. Many LIPs can be linked to regional-scale uplift, continental rifting and breakup, climatic shifts that may result in extinction events, and Ni–Cu–PGE (platinum group element) ore deposits.

Some current frontiers in LIP research include:

(1) Testing various mantle plume and alternative hypotheses for the origin for LIPs.

(2) Characterizing individual LIPs in terms of (a) original volume and areal extent of their combined extrusive and intrusive components, (b) melt production rates, (c) plumbing system geometry, (d) nature of the mantle source region, and (e) links with ore deposits.

(3) Determining the distribution of LIPs in time (from Archean to Present) and in space (after continental reconstruction). This will allow assessment of proposed links between LIPs and supercontinent breakup, juvenile crust production, climatic excursions, and mass extinctions. It will also allow an evaluation of periodicity in the LIP record, the identification of clusters of LIPs, and postulated links with the reversal frequency of the Earth's magnetic field.

(4) Comparing the characteristics, origin and distribution of LIPs on Earth with planets lacking plate tectonics, such as Venus and Mars. Interplanetary comparison may also provide a better understanding of convective processes in the mantles of the inner planets.

In order to achieve rapid progress in these frontier areas, a global campaign is proposed, which would focus on high-precision geochronology, integrated with paleomagnetism and geochemistry. Most fundamentally, such a campaign could help hasten the determination of continental configurations in the Precambrian back to 2.5 Ga or greater. Such reconstructions are vital for the proper assessment of the LIP record, as well as providing first-order information related to all geodynamic processes.     

Experimental abiotic synthesis of methanol in seafloor hydrothermal systems during diking events

The abiotic synthesis of organic compounds in seafloor hydrothermal systems is one mechanism through which the subsurface environment could be supplied with reduced carbon. A flow-through, fixed-bed laboratory reactor vessel, the Catalytic Reactor Vessel (CRV) system, has been developed to investigate mineral–surface promoted organic synthesis at temperatures up to 400°C and pressures up to 30 MPa, conditions relevant to seafloor hydrothermal systems. Here we present evidence that metastable methanol can be directly synthesized from a gas-rich CO₂–H₂–H₂O mixture in the presence of a mineral substrate. Experiments have been performed without a substrate, with quartz, and with a mixture of quartz and magnetite. Temperatures and pressures in the experiments ranged from 200°C to 350°C and from 15 to 18 MPa, respectively. Maximum conversion of 5.8×10⁻⁴% CO₂ to CH₃OH per hour was measured using a mixture of magnetite and quartz in the reactor. After passivation of the stainless steel reactor vessel, experiments demonstrate that methanol is formed at temperatures up to 350°C in the presence of magnetite, and that the formation rate decreases over time. The experiments also show a loss of surface reactivity at 310°C and a regeneration of surface reactivity with increased temperature up to 350°C. Concentrations of CO₂ and H₂ used in the experiments simulate periodic, localized and dynamic conditions occurring within the seafloor during and immediately following magmatic diking events. High concentrations of CO₂ and H₂ may be generated by dike injection accompanied by exsolution of CO₂ and reaction of dissolved H₂O with FeO in the magma to form H₂. The experiments described here examine how the ephemeral formation of an H₂–CO₂-rich vapor phase within seafloor hydrothermal systems may supply reactants for abiotic organic synthesis reactions. These experiments show that the presence of specific minerals can promote the abiotic synthesis of simple organic molecules from common inorganic reactants such H₂O, CO₂ and H₂ under geologically realistic conditions.     

Influence of Transport over a Mountain Ridge on the Chemical Composition of Marine Aerosols during the ACE-2 Hillcloud Experiment

Aerosol chemical composition and trace gas measurements were made at twolocations on the northeastern peninsula of Tenerife during the ACE-2HILLCLOUD experiment, between 28 June and 23 July 1997. Measurementswere made of coarse (#gt;2.5 m aerodynamic diameter) and fine (#lt; 2.5m) aerosol Cl^–, NO₃ ^–,SO₄ ^2–, non-sea saltSO₄ ^2– (NSSS),CH₃SO₃ ^– (MSA) andNH₄ ⁺, and gas phase dimethylsulphide (DMS), HCl,HNO₃, SO₂, CH₃COOH, HCOOH andNH₃. Size distributions were measured using a cascadeimpactor. Results show that in marine air masses NSSS and MSA wereformed via DMS oxidation, with additional NSSS present in air massescontaining a continental component. Using a Eulerian box model approachfor aerosols transported between upwind and downwind sites, a mean NSSSproduction rate of 4.36 × 10^–4 gm^–3 s^–1 was calculated for daytimeclear sky periods (highest insolation), with values for cloudy periodsduring daytime and nighttime of 3.55 × 10^–4 and2.40 × 10^–4 g m^–3s^–1, respectively. The corresponding rates for MSA were6.23 × 10^–6, 8.49 × 10^–6and 6.95 × 10^–6 g m^–3s^–1, respectively. Molar concentration ratios forMSA/NSSS were 8.7% (1.8–18.2%) and 1.9%(1.3–3.5%) in clean and polluted air masses, respectively.Reactions occurring within clouds appeared to have a greater influenceon rates of MSA production, than of NSSS, while conversely daytime gasphase reactions were more important for NSSS. For MSA, nighttimein-cloud oxidation rates exceeded rates of daytime gas phase productionvia OH oxidation of DMS. NSSS, MSA and ammonium had trimodal sizedistributions, with modes at 0.3, 4.0 and >10.0 m (NSSS andNH₄ ⁺), and 0.3, 1.5 and 4.0 m (MSA). Nosignificant production of other aerosol species was observed, with theexception of ammonium, which was formed at variable rates dependent onneutralisation of the aerosol with ammonia released from spatiallynon-uniform surface sources. Seasalt components were mainly present incoarse particles, although sub-micrometre chloride was also measured.Losses by deposition exceeded calculated expectations for all species,and were highest for the seasalt fraction and nitrate.     

Subsidence hazards due to evaporite dissolution in the United States

Evaporites, including gypsum (or anhydrite) and salt, are the most soluble of common rocks; they are dissolved readily to form the same type of karst features that typically are found in limestones and dolomites, and their dissolution can locally result in major subsidence structures. The four basic requirements for evaporite dissolution to occur are: (1) a deposit of gypsum or salt; (2) water, unsaturated with CaSO₄ or NaCl; (3) an outlet for escape of dissolving water; and (4) energy to cause water to flow through the system. Evaporites are present in 32 of the 48 contiguous states of the United States, and they underlie about 35–40% of the land area. Karst is known at least locally (and sometimes quite extensively) in almost all areas underlain by evaporites, and some of these karst features involve significant subsidence. The most widespread and pronounced examples of both gypsum and salt karst and subsidence are in the Permian basin of the southwestern United States, but many other areas also are significant. Human activities have caused some evaporite–subsidence development, primarily in salt deposits. Boreholes may enable (either intentionally or inadvertently) unsaturated water to flow through or against salt deposits, thus allowing development of small to large dissolution cavities. If the dissolution cavity is large enough and shallow enough, successive roof failures above the cavity can cause land subsidence or catastrophic collapse.     

Sea surface wind stress and drag coefficients: The hexos results

Turbulent fluxes have been measured in the atmospheric surface layer from a boom extending upwind from the Dutch offshore research platform Meetpost Noordwijk (MPN) during HEXMAX (Humidity Exchange over the Sea Main Experiment) in October–November, 1986. We started out to study eddy flux of water vapour, but discrepancies among simultaneous measurements made with three different anemometers led us to develop methods to correct eddy correlation measurements of wind stress for flow distortion by nearby objects. We then found excellent agreement among the corrected wind stress data sets from the three anemometers on the MPN boom and with eddy correlation measurements from a mast on a tripod. Inertial-dissipation techniques gave reliable estimates of wind stress from turbulence spectra, both at MPN and at a nearby ship. The data cover a range of wave ages and the results yield new insights into the variation of sea surface wind stress with sea state; two alternative formulas are given for the nondimensional surface roughness as a function of wave age.     

Patterns, rates and possible causes of saltmarsh erosion in the Greater Thames area (UK)

The estuary-dominated coast of the Greater Thames in England has experienced rapid lateral erosion and internal dissection of saltmarshes. This paper provides an overview of saltmarsh development in this area, and re-examines the role of environmental and human forcing factors. It draws on documentary evidence, including historical maps, survey data and time-series data of forcing factors. Lateral marsh retreat began in the 19th century in the Medway and Blackwater Estuaries, followed by other estuaries in the Greater Thames region at the beginning of the 20th century. The outer estuaries and the wider parts of the inner estuaries especially have experienced erosion. Erosion has been modest in wave-sheltered areas, e.g., the Colne and the inner Crouch. In the 1960s and, more widely, the 1970s, a phase of rapid erosion took place, with erosion rates of up to ca. 16 ha year⁻¹ per site, notably along the open coast of Dengie and Foulness, and in the Blackwater and Thames Estuaries. At all sites, vertical sediment accretion was well able to keep up with sea level rise over the past century. Evidence indicates that there may have been several causes for the erosion of saltmarshes. These are notably land claim and embankment construction (increasing the tidal range and current velocities) and a continuous rise of, especially, high and extreme water levels. The latest episode of rapid erosion in the 1970s is largely attributed to changes in the wind/wave climate. For example, erosion at wave-exposed sites coincided with a peak in high magnitude waves combined with a high incidence of southeasterly waves. The study shows that many factors, including natural forcing factors and human activities, have to be taken into account when explaining saltmarsh development.     

Long-term Trends of Benthic Habitats Related to Reduction in Wastewater Discharge to Boston Harbor

A combination of methods (infaunal grabs and sediment profile cameras) were used to monitor the response of Boston Harbor benthic habitats to reductions in wastewater associated with movement of the outfalls to the mouth of the harbor and then offshore. From 1992 to 2006, there was strong evidence that benthic habitats within Boston Harbor have shifted from a more anaerobic state to a more aerobic state and that these changes are directly related to changes in carbon loading associated with outfall placement and improvements in wastewater treatment. Over the period of 1992 to 2000, when the ocean outfall started to operate, there was >90% reduction in organic loadings to Boston Harbor from 11,400 to 1,200 t C per year. There were also corresponding decreases in primary production due to reduced nutrient loadings. The most apparent change in harbor benthos was the widespread increase in 1992 and subsequent decline by 2005 in Ampelisca spp. tube mats. The long-term increase in thickness of the apparent color redox potential discontinuity layer was consistent with reductions in organic loading and increases in bioturbation. The optimal organic loading for maintaining large areas of amphipod tube mats and high bioturbation rates was around 500 g C per square meter per year. Above and below this level, the area of tube mats in Boston Harbor declined.