Explore the vast range of titles available.

We describe and apply a point model of the joint evolution of tidal landforms and biota which incorporates the dynamics of intertidal vegetation; benthic microbial assemblages; erosional, depositional, and sediment exchange processes; wind‐wave dynamics, and relative sea level change. Alternative stable states and punctuated equilibria emerge, characterized by possible sudden transitions of the system state, governed by vegetation type, disturbances of the benthic biofilm, sediment availability, and marine transgressions or regressions. Multiple stable states are suggested to result from the interplay of erosion, deposition, and biostabilization, providing a simple explanation for the ubiquitous presence of the typical landforms observed in tidal environments worldwide. The main properties of accessible equilibrium states prove robust with respect to specific modeling assumptions and are thus identified as characteristic dynamical features of tidal systems. Halophytic vegetation emerges as a key stabilizing factor through wave dissipation, rather than a major trapping agent, because the total inorganic deposition flux is found to be largely independent of standing biomass under common supply‐limited conditions. The organic sediment production associated with halophytic vegetation represents a major contributor to the overall deposition flux, thus critically affecting the ability of salt marshes to keep up with high rates of relative sea level rise. The type and number of available equilibria and the possible shifts among them are jointly driven and controlled by the available suspended sediment, the rate of relative sea level change, and vegetation and microphytobenthos colonization. The explicit description of biotic and abiotic processes thus emerges as a key requirement for realistic and predictive models of the evolution of a tidal system as a whole. The analysis of such coupled processes finally indicates that hysteretic switches between stable states arise because of differences in the threshold values of relative sea level rise inducing transitions from vegetated to unvegetated equilibria and vice versa.

Vegetation recovery in disturbance‐driven ecosystems is difficult to predict. We demonstrate a concept to analyse time series for short‐term variability in external forcing that can identify potential events for sudden vegetation recovery in biogeomorphic ecosystems such as saltmarshes, mangroves, dunes or floodplains. Time series of external forcing (i.e. water level and wind speed) were analysed for ‘Windows of Opportunity’ (WoO), defined as disturbance‐free periods of a critical minimal duration directly following potential diaspore dispersal, which allow seedling establishment and can induce a sudden shift to a new persistent vegetation cover. Across different ecosystems, the minimal required WoO duration determines how many WoO events are available for seedling establishment. The distribution of WoO along an elevation gradient on riverbanks and in tidal systems, for example, is defined by the combination of the overall disturbance regime (e.g. seasonal vs. tidal flooding cycles) and the stochastic deviations from that regime (e.g. changes in weather conditions). Standardizing the WoO for the frequency of the regular disturbance regime shows that tidal and river systems have a similar relation between the required WoO length and the elevation suitable for establishment. WoO analysis correctly predicted a sudden vegetation recovery event in a saltmarsh case study. Synthesis. Time‐series analysis for ‘WoO’ offers an important tool towards predicting the establishment of vegetation cover in disturbance‐driven ecosystems and may have broader implications for understanding critical transitions in general. Quantifying the effects of stochastic external forcing on critical transitions in ecosystems is crucial for restoration efforts and to assess the effects of anthropogenic and global change.

Marshes display impressive biogeomorphic features, such as zonation, a mosaic of extensive vegetation patches of rather uniform composition, exhibiting sharp transitions in the presence of extremely small topographic gradients. Although generally associated with the accretion processes necessary for marshes to keep up with relative sea level rise, competing environmental constraints, and ecologic controls, zonation is still poorly understood in terms of the underlying biogeomorphic mechanisms. Here we find, through observations and modeling interpretation, that zonation is the result of coupled geomorphological–biological dynamics and that it stems from the ability of vegetation to actively engineer the landscape by tuning soil elevation within preferential ranges of optimal adaptation. We find multiple peaks in the frequency distribution of observed topographic elevation and identify them as the signature of biologic controls on geomorphodynamics through competing stable states modulated by the interplay of inorganic and organic deposition. Interestingly, the stable biogeomorphic equilibria correspond to suboptimal rates of biomass production, a result coherent with recent observations. The emerging biogeomorphic structures may display varying degrees of robustness to changes in the rate of sea level rise and sediment availability, with implications for the overall resilience of marsh ecosystems to climatic changes.

Abstract The present study is a systematic review of the main ecological aspects of nest foundation and the subterranean architecture of established and mature of leaf-cutting ants of the genus Atta. The foundation of nests by queens, burrowing behavior, and abiotic factors affecting the success of colonies and nest distribution of these ants are discussed. The excavation of a vertical tunnel and the first chamber made by a single mated queen begin the nest foundation. Internal network of galleries and chambers in a highly complex architecture compose a mature nest of the Atta genus. The size, number, shape and position of the chambers vary with ant species, substrate, nest age and number of workers. The size of chambers is enlarged over time to allow fungus growth. A tunnel system connects chambers and underground part of the nest to the soil surface. The section of the tunnels is, in general, elliptical or circular, allowing workers and soldiers to move during nest excavation, maintenance, and foraging activities. The present review provides a detailed description of one the most complex and specialized subterranean nests of social insects. Resumo O presente estudo é uma revisão sistemática dos principais aspectos ecológicos da fundação de ninhos e da arquitetura subterrânea de ninhos estabelecidos e maduros de formigas cortadeiras do gênero Atta. São discutidos a fundação dos ninhos pelas rainhas, o comportamento de escavação e os fatores abióticos que afetam o sucesso das colônias e a distribuição dos ninhos dessas formigas. A fundação do ninho tem início com a escavação de um túnel vertical e da primeira câmara, realizada por uma única rainha fecundada. Uma rede interna de galerias e câmaras, em uma arquitetura altamente complexa, compõe o ninho maduro do gênero Atta. O tamanho, número, formato e posição das câmaras variam de acordo com a espécie, o substrato, a idade do ninho e o número de operárias. O tamanho das câmaras é ampliado ao longo do tempo para permitir o crescimento do fungo. Um sistema de túneis conecta as câmaras e a parte subterrânea do ninho à superfície do solo. A seção dos túneis é, em geral, elíptica ou circular, permitindo o deslocamento de operárias e soldados durante as atividades de escavação, manutenção e forrageamento. A presente revisão fornece uma descrição detalhada de um dos ninhos subterrâneos mais complexos e especializados entre os insetos sociais.

Biogenic structures such as oyster reefs and mussel beds can enhance sedimentation and promote the expansion of intertidal flats in the German Wadden Sea. This study presents large-scale measurements of sedimentation at biogenic structures that depend on biological activities, the hydrodynamic environment and surface roughness. As the surface roughness of intertidal flats has changed with the bioinvasion of the Pacific oyster and the resulting transformation of mussel beds into oyster reefs, we hypothesised that sedimentation rates vary between these structures. To quantify the extent of sedimentation over time, we surveyed bivalve-covered intertidal flats in 2020 and 2022 and generated digital models of the structures and surrounding terrain. The sediment accumulation rates for the mussel bed and oyster reefs reached 3.9 cm³/(cm²*y), with higher rates observed within the mussel bed than within the oyster reefs. Generally, biogenic structures at lower elevations experienced higher sediment accumulation rates. All accumulation rates exceeded previously reported rates for intertidal flats and the current rate of sea level rise in the Wadden Sea. Our findings suggest that oyster reefs and mussel beds have comparable effects on sediment accumulation, supporting the persistence of intertidal flats and thus helping to stabilise the Wadden Sea.

Fishing-down-marine-food-webs has resulted in alarming declines of various species worldwide. Benthic rays are one examples of such overexploited species. On tidal flats, these rays are highly abundant and play an ecologically important role. They use tidal flats as refuge, feeding and resting grounds, during which they bury into the sediment, which results in sediment bioturbation. Changes in bioturbation intensity, following ray removal, may affect the biogeomorphology of tidal flats with possible cascading effects on the macrozoobenthic community. However, it is poorly understood how these indirect effects could influence ecosystem function. We therefore studied the geomorphic impact of benthic rays (specifically the pearl whipray/stingray Fontitrygon margaritella) on the tropical tidal flats of the Bijagós Archipelago, Guinea-Bissau, on a landscape scale. We investigated 1) bioturbation rates by rays using drone and ground surveys, 2) the spatial distribution of ray pits on multiple tidal flats, 3) the impact of rays on sediment properties and macrozoobenthos by experimental exclusion (15 months). Benthic rays bioturbated 3.7 ± 0.35% of the tidal flat’s sediment surface per day over one single 24-h period, which equals a complete top-sediment-surface turnover every 27 days. The spatial distribution of ray pits was affected by tidal flat geomorphology since pits decayed faster at areas exposed to strong hydrodynamic forces. Predator exclusion altered sediment properties, leading to changes in sedimentation (− 17%) and erosion (− 43%) rates. In addition, macrozoobenthic species composition changed, marked by an increase in Capitellidae worms and a greater biomass of Malacostraca over time. These changes indicated substantial effects of ray bioturbation on the biotic and geomorphic landscape of tidal flats. Overall, we conclude that changing abundances of benthic rays can have clear landscape-wide geomorphological effects on intertidal ecosystems. These indirect consequences of fisheries should be incorporated in integrative management plans to preserve tidal flats and connected ecosystems.

Many vegetated coastal ecosystems are formed through ecosystem engineering by clonal vegetation. Recent work highlights that the spatial shoot organization of the vegetation determines local sediment accretion and subsequently emerging landscape morphology. While this key engineering trait has been found to differ between species and prevailing environmental conditions, it remains unknown how the interplay of both factors drive shoot organization and therefore landscape morphology. Here, we compared the spatial shoot organization of young, clonally expanding plants of the two dominant European dune grass species: sand couch (Elytrigia juncea) and marram grass (Ammophila arenaria) across a range of coastal dune environments (from Denmark to France). Our results reveal that, on average, sand couch deployed a more dispersed shoot organization than marram grass, which has a patchy (Lévy-like) organization. Whereas sand couch exhibited the same expansion strategy independent of environmental conditions, marram grass demonstrated a large intraspecific variation which correlated to soil organic matter, temperature and grain size. Shoot patterns ranged from a clumped organization correlating to relatively high soil organic matter contents, temperature and small grain sizes, to a patchy configuration with intermediate conditions, and a dispersed organization with low soil organic matter, temperature and large grain size. We conclude that marram grass is flexible in adjusting its engineering capacity in response to environmental conditions, while sand couch instead follows a fixed expansion strategy, illustrating that shoot organization results from the interaction of both species-specific and environmental-specific trait expression.

Coralligenous (C) includes calcareous build-ups of biogenic origin, formed since the Holocene transgression. Peculiar columnar-shaped C outcrops were documented offshore Marzamemi village (SE Sicily, Ionian Sea), although the actual extension and distribution were not assessed. Project 'CRESCIBLUREEF' produced a new, 17 km 2 high-resolution bathymetric map, leading to good knowledge about their extent in this area. C bioconstructions are largely distributed along two depth ranges 36-42 m and 86-102 m water depth. By coupling the documented uplift rate in this region and the Holocene sea-level curve, we were able to interpret the distribution of C outcrops over terraces. However, additional investigation is required to understand: (1) the role of the inherited continental shelf landscape, in creating a favorable substrate for the settlement and growth of C habitats during the Holocene, and (2) the extent to which C bioconstructions can impact the evolution of present-day continental shelf landforms and landscapes.

Large, low-lying rivers have a variety of societal uses and show a wide range of disturbances. One such example, the Apalachicola River in the Florida Panhandle, experienced anthropogenic activities that altered its hydrologic, geomorphic, and ecologic condition. The river’s sand bars enlarged more than threefold in area because of dredge disposal and localized incision from anthropogenic activities during a navigation project. Once dredging ended, the river experienced passive recovery through the slow regrowth of riparian vegetation, with sand bars reducing in area ~18% from 2005 to 2015. The outcomes of tree-line change analyses from 1999 to 2019 indicate a higher recovery rate in the fir t decade (1999-2010), migrating fastest in locations where vegetation islands stabilize sediments. To help accelerate vegetation regrowth, during the growing seasons of 2018 and 2019, we planted willow stakes at various positions and microhabitats covering ~3.6 ha of three enlarged sand bars near Blountstown, FL. Our mapping shows some synergies between passive recovery and active restoration as tree-line expansion had the fastest rates between 2019 and 2021. Our study gives insights and guidance into passive recovery and restoration projects involving plantings on large, low-lying rivers.