A histological study of reproduction in the serpulids<Emphasis Type="Italic"> Pomatoceros triqueter</Emphasis> and<Emphasis Type="Italic"> Pomatoceros lamarckii</Emphasis> (Annelida: Polychaeta)

The reproductive cycles of the serpulid polychaetes Pomatoceros lamarckii (Quatrefages, 1865, as Vermilia) and P. triqueter (Linnaeus, 1767, as Serpula triquetra) were studied by histological examination during 1999 and 2000 at Bantry Bay, south-west Ireland. Gametogenesis, sex ratios and hermaphroditism were also investigated. The male/female ratio in P. lamarckii was approximately equal, but in P. triqueter it deviated significantly in favour of females. There was no significant variation in the sex ratios throughout the year in either species. Results confirm that the species are protandric hermaphrodites. In P. lamarckii, but not in P. triqueter, sexual dimorphism was exhibited in body size, the females being larger than the males of the same species. In both species, the proportion of females increased with increasing body size. Simultaneous hermaphroditism was recorded in P. lamarckii, but not in P. triqueter. There was no clearly defined annual gametogenic cycle in either species. Both species appear to have an extended reproductive season, with numerous small-scale peaks in reproductive maturity that can vary annually. Spawning was broadly synchronous between sexes. Visual observation alone (i.e. without histology) was insufficient to accurately assess reproductive condition in individuals not in, or close to, a ripe state.     

Ecology, management and monitoring of grey dunes in Flanders

Grey dunes are a priority habitat type of the European Union Habitats Directive and demand special attention for conservation and management. Knowledge of the ecology of coastal grey dunes can contribute to this policy. Dune grassland succession is initiated by fixation and driven by the complex of soil formation (humus accumulation) and vegetation development. Leaching and mobilization of CaCO₃. which are important in nutrient dynamics, complicate the picture. At present, grass- and scrub encroachment greatly overrules these fine scaled soil processes and causes substantial loss of regional biodiversity. Belgium has an international responsibility in grey dune conservation because of the limited range of its characteristic vegetation, flora and fauna. As biomass removal seems essential in grassland preservation, grazing is an important management tool. Evaluation of management measures focuses on biodiversity measurements on the levels of landscape, community and species.     

Tube-worm-sediment relationships of Diopatra cuprea (Polychaeta: Onuphidae)

Diopatra cuprea (Bosc) builds a long, nearly vertical parchment tube in sediments, which is reinforced with bits of shell, sediment or debris. The tube can be divided on the basis of structure into reinforced sections built at or above the sediment surface, and unreinforced sections built below the sediment surface. If sediment accumulates faster than the worm can build reinforced tube, an unreinforced section results. When this occurs, D. cuprea builds reinforced tube at the new sediment surface, and then pulls it down into the substratum until it joins the next lower reinforced section, or until the worm can no longer overcome sediment resistance. In the latter case, the unreinforced section occurs between two reinforced sections. The tube cap is trimmed as sediment is eroded from around it. Selection for reinforcing materials occurs only in the transitional zone from unreinforced to reinforced tube. The exposed portion of the tube (the tube cap) extends from 1 to 6 cm above the sediment surface as an inverted J. The tube mouth is oriented perpendicularly to the direction of current flow. Tube maintenance continues at temperatures below feeding-response blockage (5° to 10°C), but ceases below about 1.8°C.     

Migratory and reproductive movements of male leatherback turtles (<Emphasis Type="Italic">Dermochelys coriacea</Emphasis>)

The biology of the endangered leatherback turtle (Dermochelys coriacea) at sea is poorly understood. As research has been almost exclusively limited to studies of nesting females, the movements of male turtles and the timing and location of mating activity have remained unknown. We report on the first deployments of satellite tags on male leatherbacks. Male migration to and residency in waters adjacent low-latitude nesting beaches in the western Atlantic suggest that this is where mating occurs, and return migration to these areas reveals male fidelity for breeding sites. Rate of travel decreased markedly after arriving in coastal breeding areas, where males remained for up to 96 days before assuming northward migrations. The initiation of these northward migrations coincided with peak nesting activity in adjacent nesting colonies. Data from satellite-linked time-depth recorders attached to two males revealed diel dive patterns in breeding areas and marked differences in diving behaviour between migratory and breeding periods in one turtle. When male turtles were in waters adjacent nesting colonies, their movements differed from those reported for nesting females, with females ranging farther from shore. Our results suggest that male leatherbacks may be vulnerable to entanglement in coastal fishing gear in waters adjacent nesting beaches.Communicated by R.J. Thompson, St. Johns     

Physiological tolerance predicts species composition at different scales in a barnacle guild

This study examined how the species composition of an intertidal barnacle guild varied according to physical gradients in the environment at small scales governed by microclimates, medium scales of wave exposure and large scales of latitude. Barnacle distributions at small and medium scales were sampled in Ireland between 51°29′ and 52°44′N and 6°50′ and 10°08′W. Sampling on European shores spanned ~18° latitude from 37°05′ to 55°16′N. Barnacle surveys mainly took place in 2003–2004. An index of wave fetch was calculated along the wave exposure gradient using a digital coastline-based model that was supported by a biological exposure scale. A ‘dryness’ index was defined according to mean monthly wind speed, fetch along the average wind direction and mean monthly air or sea surface temperatures for 2 years (January 2001–December 2002) which is the period when the most recent adults in the barnacle community would have settled and grown to adulthood. The proportion of the dry-loving barnacle Chthamalus montagui Southward increased within the barnacle guild at all scales as the habitat became warmer and drier. Barnacle densities were high in all habitats, mean densities ranged from a minimum of 4.16 cm⁻² on moderately exposed shores to a maximum of 6.27 cm⁻² in sunlit or south-facing microclimates. Percentage cover of barnacles across the gradient of latitudes was usually >70%. The results suggest that the distribution and abundance of interacting barnacle species on European coasts is strongly controlled by abiotic factors, most likely temperature and desiccation.     

Seed arrival and ecological filters interact to assemble high-diversity plant communities

Two prominent mechanisms proposed to structure biodiversity are niche-based ecological filtering and chance arrival of propagules from the species pool. Seed arrival is hypothesized to play a particularly strong role in high-diversity plant communities with large potential species pools and many rare species, but few studies have explored how seed arrival and local ecological filters interactively assemble species-rich communities in space and time. We experimentally manipulated seed arrival and multiple ecological filters in high-diversity, herbaceous-dominated groundcover communities in longleaf pine savannas, which contain the highest small-scale species richness in North America (up to > 40 species/m2). We tested three hypotheses: (1) local communities constitute relatively open-membership assemblages, in which increased seed arrival from the species pool strongly increases species richness; (2) ecological filters imposed by local fire intensity and soil moisture influence recruitment and richness of immigrating species; and (3) ecological filters increase similarity in the composition of immigrating species. In a two-year factorial field experiment, we manipulated local fire intensity by increasing pre-fire fuel loads, soil moisture using rain shelters and irrigation, and seed arrival by adding seeds from the local species pool. Seed arrival increased species richness regardless of fire intensity and soil moisture but interacted with both ecological filters to influence community assembly. High-intensity fire decreased richness of resident species, suggesting an important abiotic filter. In contrast, high-intensity fire increased recruitment and richness of immigrating species, presumably by decreasing effects of other ecological filters (competition and resource limitation) in postfire environments. Drought decreased recruitment and richness of immigrating species, whereas wet soil conditions increased recruitment but decreased or had little effect on richness. Moreover, some ecological filters (wet soil conditions and, to a lesser extent, high-intensity fire) increased similarity in the composition of immigrating species, illustrating conditions that influence deterministic community assembly in species-rich communities. Our experiment provides insights into how dispersal-assembly mechanisms may interact with niche-assembly mechanisms in space (spatial variation in disturbance) and time (temporal variation in resource availability) to structure high-diversity communities and can help guide conservation of threatened longleaf pine ecosystems in the face of habitat fragmentation and environmental change.     

Estimates of critical acid loads and exceedances for forest soils across the conterminous United States

Concern regarding the impacts of continued nitrogen and sulfur deposition on ecosystem health has prompted the development of critical acid load assessments for forest soils. A critical acid load is a quantitative estimate of exposure to one or more pollutants at or above which harmful acidification-related effects on sensitive elements of the environment occur. A pollutant load in excess of a critical acid load is termed exceedance. This study combined a simple mass balance equation with national-scale databases to estimate critical acid load and exceedance for forest soils at a 1-km(2) spatial resolution across the conterminous US. This study estimated that about 15% of US forest soils are in exceedance of their critical acid load by more than 250eqha(-1)yr(-1), including much of New England and West Virginia. Very few areas of exceedance were predicted in the western US.