Hindcasting Ecosystem Functioning Change in an Anthropogenized Estuary: Implications for an Era of Global Change

Understanding how altered hydrodynamics related to climate change and anthropogenic modifications affect ecosystem integrity of shallow coastal soft-sediment environments requires a sound integration of how species populations influence ecosystem functioning across heterogeneous spatial scales. Here, we hindcasted how intertidal habitat loss and altered hydrodynamic regimes between 1955 and 2010 associated with geomorphological change to accommodate expansion in anthropogenic activities in the Western Scheldt altered spatial patterns and basin-wide estimates of ecosystem functioning. To this end we combined an empirically derived metabolic model for the effect of the common ragworm Hediste diversicolor on sediment biogeochemistry (measured as sediment oxygen uptake) with a hydrodynamic and population biomass distribution model. Our integrative modeling approach predicted an overall decrease by 304 tons in ragworm biomass between 1955 and 2010, accounting for a reduction by 28% in stimulated sediment oxygen uptake at the landscape scale. Local gains or losses in habitat suitability and ecosystem functioning were primarily driven by changes in maximal current velocities and inundation regimes resulting from deepening, dredging and disposal practices. By looking into the past, we have demonstrated how hydro- and morphodynamic changes affect soft-sediment ecology and highlight the applicability of the integrative framework to upscale anticipated population effects on ecosystem functioning.

Rus detachment in Dammam Dome, Eastern Saudi Arabia: a new soft-sediment structure as a ‘sensitive stress sensor’ for the Zagros collision

This paper describes in detail hydroplastic structures, which are ‘odd’ kinematic indicators in the basal part of the Eocene Middle Rus Formation. Such structures were previously ignored or falsely interpreted. These hydroplastic structures are found in the massive limestone exposures on the King Fahd University of Petroleum and Minerals (KFUPM) campus. They occur in relation to a principal displacement zone along the boundary/interface between the Lower/Middle Rus, which is referred to as the Rus soft-sediment detachment. The structures are fist-sized vugs associated with carrot- or comet-trail imprints (VCT structures) which were previously translated calcite geodes that have been weathered out. VCT structures show transport/slip towards the NNW (345°) and are found on flat to low-dipping surfaces classified as Y, R and P shears with respect to the orientation of the Rus detachment. Palaeostress analysis indicates an Andersonian transtension stress regime, though it does not facilitate the activation of the Rus soft-sediment detachment. Detachment activity occurred due to the negative effective principal stress σ3′ and the abnormally low frictional coefficient caused by fluid pressure. The soft-sediment Rus detachment can be considered a ‘sensitive stress sensor’ for the Zagros collision since it indicates the Arabian platform’s instability in the wider area of the Dammam Dome during the Late Eocene. This instability is attributed to the inception of the Zagros collision, which was previously considered to occur during the Oligocene based on the well-established pre-Neogene unconformity.

Habitat formed by the invasive macroalga Caulerpa filiformis (Suhr) Hering (Caulerpales, Chlorophyta) alters benthic macroinvertebrate assemblages in Peru

The green macroalga Caulerpa filiformis has been spreading on shallow soft sediment habitats along the Peruvian coast, colonizing previously unvegetated sediments to create monospecific meadows. We examined the nature of the impact of C. filiformis meadows on the density, taxonomic richness and assemblage structure of epifaunal and infaunal benthic macroinvertebrates. Specifically, we tested whether the spread of C. filiformis has resulted in different macroinvertebrate assemblages than those formed by the dominant native macroalgae (i.e., Rhodymenia spp.) and unvegetated sediments. Surveys were undertaken in two bays in each of two locations, in central and southern Peru, during winter 2017 and summer 2018. In general, our results show that macroinvertebrate assemblages were similar across all three habitats, although there were some differences, related to location and season, but with no clear patterns observed. Taxonomic richness and density was generally higher in the vegetated habitats than the unvegetated habitat, and where there were differences between the two vegetated habitats there was no consistent pattern of which habitat supported the highest richness or density. Given invading C. filiformis is primarily colonizing unvegetated habitats it would appear that this species is creating a new niche which supports similar assemblages, but higher taxonomic richness and density than unvegetated habitats. While our study suggests that C. filiformis is having a limited ecological impact we recommend that actions be put in place to limit the spread of this invasive species at the same time as increasing monitoring of the ecological impacts of this species as lags in the ecological impacts of invasive species are common.

Small-Scale Soft-Sediment Deformation Structures in the Cross-Bedded Coconino Sandstone (Permian; Arizona, United States); Possible Evidence for Seismic Influence

The Permian Coconino Sandstone of northern Arizona contains numerous small-scale, soft-sediment deformation structures (SSDSs). These novel structures may be indicators of paleoenvironment or sedimentary processes. These SSD are generally shallow and occur on the surfaces of cross-beds, in contrast to convoluted bedding up to tens of meters thick commonly observed in some other eolian sandstones. These differences in structures imply differences in the processes that formed the Coconino Sandstone, or differences in the underlying depositional conditions. These SSDSs occur in outcrops at the Grand Canyon, and farther south in quarries near the towns of Seligman and Ash Fork. Size, orientation, structure, sedimentary context, clay content, and porosity of the structures are described. The SSDSs occur as small folds and ridges on the paleo lee side of otherwise undisturbed cross-beds. Some are associated with small rotated sandstone blocks within the cross-beds. The structures are exposed on bedding plane surfaces and in cross-section on vertical quarry walls. A few SSDSs up to a meter thick also occur in the Coconino Sandstone, but the others are only up to a few cm thick, 2–10 cm wide, and 20 cm to 10 m long. Evidence is presented that liquidization (as fluidization or liquefaction) may have been involved in producing these features, implying a high water content in scattered locations at time of deformation, but this process also requires some stressor to trigger the deformation. Seismic events may provide a triggering mechanism. The Coconino Sandstone SSDSs represent unusual or previously overlooked small-scale features related to individual foreset surfaces.