Short term dynamics of the dominant annelids in a polyhaline temperate estuary

Weekly sampling over a two year period from a muddy sand bottom in the polyhaline York River, Virginia, U.S.A., clearly identified the pattern of recruitment and survival of the dominant annelid species. Three intermingled recruitment strategies and two survival patterns were observed, ranging from the classic opportunistic life style of mass recruitment over short time periods followed by mass mortality to prolonged recruitment with lower mortality. Qualitatively the annelid assemblage was very similar from year to year with most of the changes being quantitative. Oligochaetes, Tubificoides spp., were the most stable and characteristic members of the annelid assemblage.Contribution No. 1118 of the Virginia Institute of Marine Science     

Genetic diversity of reintroduced tree populations in restoration plantations of the Brazilian Atlantic Forest

Long‐term ecological success of large‐scale restoration programs planned for the next decades will rely on genetic diversity (GD) of reintroduced or colonizing species, a limiting factor in highly fragmented landscapes. In small and isolated natural remnants or restoration areas, substantial reduction in population's size or connectivity may lead to local extinctions due to the accumulation of deleterious recessive alleles and ongoing reduction of fecundity, plant vigor, recruitment success, and adaptive potential. Despite the paramount role of GD for species persistence, its levels in restoration programs are poorly known. We assessed the GD of four model tree species (different succession stages, dispersal, and pollination syndromes) from the Brazilian Atlantic Forest, comparing two high‐diversity restoration plantations, one forest fragment and one conserved remnant. Contrary to the expectation that the plantation strategies adopted in the restoration programs could result in genetic composition homogenization, we found that restoration areas established heterogeneous genetic groups with similar levels of neutral GD and inbreeding to those observed in natural forest remnants. This pattern was consistent across the four functionally different tree species, despite some species idiosyncrasies. For instance, we observed lower allelic richness in early successional species in restoration sites, suggesting that some species may be more prone to reintroduction with lower GD. Thus, we advocate the use of high GD levels in restoration to support biodiversity conservation in human‐modified landscapes, thus reinforcing the role of ecological restoration for recovering the diversity of genes—the basic constituent of biodiversity.     

The concomitant existence of a typical coastal and a detritus food chain in the Westerschelde estuary

Until now studies of the aquatic ecology of the Westerschelde estuary have been erratic. Yet, from the results of a literature research some structural aspects of the ecosystems in the Westerschelde could be derived.Clear gradients could be found from the river to the sea for the abiotic as well as for the biotic features of the estuary. On the basis of the available quantitative data 2 tentative food chains were distinguished; a mainly detritus-based food chain in the upstream brackish part and a coastal food chain in the downstream seaward part. The centre of the area of the detritus food chain coincided with the zone of a turbidity maximum at the interface of salt and fresh water. This food chain is characterized by a low primary production but a year-round high concentration of suspended organic matter. The suspended organic matter consists of aggregates of detritus and bacteria. The zooplankton as well as the zoobenthos can reach high biomasses. The coastal food chain is mainly based on a seasonally chainging high primary production. The diversity of flora and fauna in this system is much higher than in the detritus food chain, although the biomass can be lower.Communication no. 404 of the Delta Institute, Yerseke.     

Long-term changes in amphipod population dynamics in a temperate estuary following ecosystem restoration

The Mondego estuary (Portugal) has suffered severe ecological stress over the last two decades, as manifested in the replacement of seagrasses by opportunistic macroalgae, degradation of water quality and increased turbidity. A restoration plan was implemented in 1998, which aimed to reverse the eutrophication effects, and especially to restore the original natural seagrass (Zostera noltii) community. This article explores the long-term changes in Ampithoe valida and Melita palmata (Amphipoda) populations in response to eutrophication (with consequent seagrass loss and macroalgal proliferation) and to the subsequent restoration plan (with progressive seagrass recovery and macroalgal biomass decline). Until the early 1990s, high densities of A. valida and M. palmata were recorded in the Mondego estuary, especially during the occurrence of the macroalgal bloom and during all the periods in which green macroalgae were available. After the implementation of the restoration plan, species abundance, biomass and production levels decreased considerably due to the progressive decline of green macroalgae. This implied the virtual disappearance of the amphipod population, mainly A. valida. Distinct behaviours displayed by the two species could be related to different food strategies and habitat preferences. Ampithoe valida showed feeding preferences for ephemeral softer, filamentous or bladed algae (e.g. Ulva sp.) due to its high caloric content, using the Z. noltii bed only as a habitat for protection against predators or shelter from wave action. On the other hand, M. palmata did not suffer a strong decline in its population density, biomass and production, which may indicate that this species is probably not a primary consumer of green macroalgae and may readily shift to alternative ecological niches. Handling editor: P. Viaroli     

Vegetation changes in the freshwater tidal marsh of the Delaware estuary

We examined the areal extent and changes in thefreshwater tidal wetlands along a 56.4 km and a80.6 km reach of the Delaware River between Chester,Pa. and Trenton, N.J. Most of the remainingfreshwater tidal wetlands of the Delaware River arefound along tributaries which drain the coastal plainof New Jersey. We identified polygons of marsh, mud,and open water using color infrared aerial photographyobtained at low tide in 1977 and 1978. Marsh polygonswere classified into either high marsh or low marshaccording to the dominant visual signature of thevegetation of each polygon, and placed in a geographicinformation system for subsequent analysis. The totalarea of marsh within the two reaches totaled 1416 ha,of which 71% was high marsh and 29% low marsh. Asite re-examination in 1997 and 1998 of marsh arearepresenting 32% of the total marsh area revealedthat, while the total area of wetland appears to haveremained constant, high marsh vegetation along thelower reaches of the tributaries has been replaced bylow marsh vegetation. The fraction of the sample thatwas low marsh increased from 9% in 1977–78 to 34% in1997/8.     

Effects of winter conditions on Daphnia dynamics and genetic diversity in a dimictic temperate reservoir

1. Winter conditions shape plankton dynamics and community composition in temperate regions, but their effect on dynamics and genetic composition of cyclical parthenogens like Daphnia is largely unclear. 2. For 5 years, we studied the dynamics, hatching from resting eggs and genetic structure of a D. galeata × longispina hybrid complex in a dimictic, temperate reservoir. Our main hypothesis was that higher spring densities and an earlier population peak will be observed after warmer winters, with a lower genetic diversity because of a lower contribution of resting eggs to population growth. 3. The study period could clearly be categorised into cold‐winter years (n = 3) and warm‐winter years (n = 2). Daphnia densities at the end of spring overturn were ～10‐fold lower after cold winters than after warm ones, but no pattern emerged concerning the timing and the height of the population peak in early summer. 4. Hatching intensity from resting eggs was higher and contributed up to 8.5% to Daphnia abundance in a cold‐winter year compared to a negligible contribution in a warm‐winter year. Consistent with this finding, new multilocus genotypes (MLGs) adding to the overwintering stock after the end of spring overturn and presumably originating from resting eggs increased genetic diversity and attained high frequencies within the population only after a cold winter. New MLGs were recorded also after warm winters, but they never gained dominance and no shift in genetic diversity was observed. However, genetic diversity was not generally reduced after warm winters. 5. Our results confirm earlier findings that winter conditions have only a limited effect on the main growth phase and the peak of Daphnia during late spring and early summer. However, winter conditions determine the contribution of resting eggs to the population development, which may profoundly alter the genetic composition of the population compared to the previous season.     

Parasitism and predation as agents of mortality of winter moth populations in neglected apple orchards in Nova Scotia

Abstract.

• 1 This study compared the roles of pupal mortality and parasitism in winter moth (Operophtera brumata) population dynamics in Nova Scotian apple orchards and assessed the importance of beetles as pupal predators.
• 2 The component of pupal mortality termed predation accounted for greater stage-specific mortality of winter moth than parasitism by Cyzenis albicans in four neglected orchards.
• 3 Parasitism by Cyzenis albicans was not spatially density-dependent in any orchard, whereas the predation component of pupal mortality was spatially density-dependent in the two orchards most densely populated by winter moth.
• 4 Field experiments indicated that over 60% of pupal predation may be attributed to beetles, and that about 46% of pupal predation occurred within 4 weeks after pupal drop.
• 5 Mortality of introduced populations of winter moth in Nova Scotia resembles that of native populations in England where density-dependent predation regulates the winter moth population and reduces the parasitoid population to minimal levels. The situation in Nova Scotia appears to have changed appreciably since the establishment of parasitoids into the system in the 1950s.

     

Dynamics of biogenic Si in freshwater tidal marshes: Si regeneration and retention in marsh sediments (Scheldt estuary)

The sequestration and recycling of biogenic silica (BSi) in freshwater tidal marshes was modelled through the combination of short-term year round sediment trap data with a long-term sedimentation model, MARSED. The modelling was implemented through the complete evolution from a young rapidly rising marsh to a marsh with an elevation close to mean high water. BSi in imported suspended matter was higher in summer (10.9 mg BSi g⁻¹ sediment) than winter (7.6 mg BSi g⁻¹ sediment). However, the deposition of BSi on the marsh surface was higher in winter compared to summer, due to the higher sedimentation rates. Deposition of BSi was correlated to the suspended matter deposition. In the old marsh, yearly about 40 g BSi m⁻² was deposited, while in the young marsh deposition could rise up to 300 g m⁻². Young marshes retained up to 85% of the imported biogenic silica. Recycling efficiency (60%) increased drastically for older marshes. The study shows that marshes act as important sinks for BSi along estuaries. The recycling of the imported BSi to DSi in summer and spring is most likely an essential factor in the buffering role of tidal marshes for estuarine DSi concentrations.     

Post‐storm sediment burial and herbivory of Vallisneria americana in the Hudson River estuary: mechanisms of loss and implications for restoration

This article investigates the mechanics of loss of Hudson River Vallisneria americana after the high volume storms at the end of the 2011 growing season, when two severe weather events—Tropical Storm Irene and the remnants of Tropical Storm Lee—struck the Hudson River watershed. In 2012, the distribution of the most common species of submerged aquatic vegetation (SAV), Vallisneria americana (wild celery, water celery, or tape grass), in the Hudson River estuary declined by more than 90%, with no appreciable recovery in 2013 and 2014. Because of its important habitat value for aquatic life and for increasing dissolved oxygen, managers and scientists have begun discussing the reasons for the loss, as well as how to assist its recovery through assisted restoration efforts in the estuary. Supported by in situ and in vitro experiments, the article posits the hypothesis that sediment, washed into the river by the storm, buried overwintering tubers of the plant, thus reducing sprouting success. Sprouting was as low as 50% with sediment depth between 2 and 5 cm; sprouting did not occur with sediment depth greater than 10 cm. Field experiments found no support for the hypothesis that herbivory inhibited regrowth of the plant after the storm events. These results suggest that future assisted restoration of Vallisneria americana and SAV in general may require attention to system‐specific factors.     

碱化草地群落恢复演替空间格局动态分析

对松嫩平原碱化草地1989年开始围栏封育的1hm^2样地9a间的空间格局进行了分析,结果表明：（1）不同物种斑块空间格局动态不同,在恢复演替各个阶段中的地位与作用也不同。（2）结论基本上支持了斑块化－稳定性假说。     

Effect of sedimentological and hydrodynamical changes in the intertidal areas of the Oosterschelde estuary (SW Netherlands) on distribution,density and biomass of five common macrobenthic species: Spio martinensis (Mesnil), Hydrobia ulvae (Pennant), Arenicola marina (L.), Scoloplos armiger (Muller) and Bathyporeia sp.

In order to evaluate the impact of the construction of the storm-surge barrier and secondary dams on macrobenthos of the tidal flats in the Oosterschelde (SW Netherlands), changes in distribution, density and biomass of five common species (Spio martinensis, Hydrobia ulvae, Arenicola marina, Scoloplos armiger and Bathyporeia sp) were analysed.Data on macrobenthos were collected from 1979 to 1989 on five different tidal flats. Changes in sediment texture and hydrodynamic factors during the construction and after the completion of the coastal engineering project were taken into account.Three severe winters in a row caused more disturbance in the population of the main predator of S. armiger than did the hydrodynamical changes. A temporary prolongation of the emersion time (in 1986 and 1987) caused a temporary decrease in juvenile A. marina. But afterwards they still occupy the same nursery grounds. Increased wave action on the edges of the flats probably created new niches for Bathyporeia sp. and Spio martinensis, replacing other benthic species.It is not yet clear what has caused the decline of H. ulvae in many places in the Oosterschelde estuary. Parasitic infestation is one of the possibilities.     

Exploring stable pattern formation in models of tussock moth populations

1. The western tussock moth ( Orgyia vetusta ) at the University of California Bodega Marine Reserve (Sonoma County, California, USA) exhibits dense, localized populations in the midst of extensive habitats where variation in host plant quality or predator abundance is unable to explain the restricted extent of the outbreaks.
2. Two primary features suggest that the host patterning is intrinsically generated: (i) female tussock moths are wingless, producing a low effective dispersal distance for the hosts; and (ii) the tussock moth population is attacked by several species of widely dispersing wasp and fly parasitoids.
3. We consider a set of spatially explicit host–parasitoid models to examine whether intrinsically generated patterns are possible within this system. These models include a spatially extended Nicholson–Bailey model to examine general features of pattern formation in host–parasitoid systems, and two system-specific models, an individual-based simulation and a population-level analytic model, to examine the details of this empirical system.
4. Both stable patterning and rapid extinction of the host population are initial-condition dependent outcomes of the general and specific models, implying that an intrinsically generated stable host pattern is feasible within the tussock moth system.
5. Stable patterning is enhanced by a large parasitoid-to-host dispersal ratio, local host resource limitation, and increased parasitism at the host patch's edge.     

Spatial and temporal variation of community composition and species cover following dune restoration in the Devesa de Albufera (Valencia,Spain).

Plant populations were reintroduced to the coastal dune bar of the Devesa de Albufera from 1988 to 2004; different coastline sections received different species composition and cover. With the aim to detect spatial and temporal variation of floristic diversity, we compared current species composition and cover across the length of the Devesa and across the dune bar with those imposed at the time of restoration. Non-metric multidimensional scaling (NMDS) detected significant differences both across the dune faces and across the coast sections. Differences across the dune faces reflect the sea-inland ecological gradient and resulted from a spatial rearrangement of plant populations: Calystegia soldanella, Achillea maritima and Polygonum maritimum prefer the windward face; Malcolmia littorea and Lagurus ovatus the leeward. Differences across coast sections are related to those at restoration time, with a slow trend towards the homogenization of plant communities. At the current level of anthropic pressure, the plant cover is likely to evolve following the trends pointed out in this research.     

温带落叶阔叶林地表鞘翅目成虫小尺度空间格局动态分析

土壤动物空间格局是格局—过程以及生物多样性维持机制研究的重要基础,目前小尺度空间土壤动物空间格局动态特征仍不清楚。基于地统计空间分析方法,以鞘翅目成虫为研究对象,研究帽儿山温带落叶阔叶林小尺度空间(5m)地表鞘翅目成虫群落及类群的空间格局动态特征。结果表明:4次调查共捕获鞘翅目成虫11科、29类、1021只个体,调查月份鞘翅目成虫群落具有较强的时空变异性;Moran'sⅠ系数表明鞘翅目成虫群落和类群具有复杂的正的空间自相关性,其空间异质性可用球状、指数、高斯和线性模型进行拟合。这种空间异质性具有一定的时间变化特征,且这种空间分异是由随机性因素单一调控或结构性因素和随机性因素共同调控的结果;类群之间在多种尺度上表现为复杂的以负相关居多的空间关联性,这种空间关联性的形成主要是结构性因素或随机性因素单一调控的结果。本实验表明地表鞘翅目成虫群落在小尺度空间具有明显的空间异质性特征,这种空间异质性时间变异性较明显。     

Estimation des paramètres fondamentaux de la dynamique d'un estuaire à marées. On the Dynamics of a Tidal Estuary: Estimation of the Principal Factors

In order to obtain a better understanding on the relationship between salt and fresh-water masses in an estuary on the Northern Brittany coast, a study on the tidal dynamics has been carried out. A simple model for the calculation of the mean current velocities is proposed taking into account the estuarine topography, tidal parameters and river discharge. The model also estimates the Richardson, Froude and Reynolds estuarine numbers. These can be used in further studies on the particle transport in this estuary.     

Spatially patterned guild structure in larval parasitoids of cyclically outbreaking winter moth populations

1. Wide temporal fluctuations in host abundance are a potential source of instability and stochasticity in the spatiotemporal population dynamics of associated parasitoid species. Within parasitoid guilds (i.e. parasitoids with similar modes of host utilisation), a conceivable outcome is guild organisation according to a lottery model, in which guild members attain local dominance by colonising previously emptied habitats during increasing host density, before other guild members. In the spatial dimension, an expected manifestation of such dynamics is variable guild structure even across homogeneous habitats. 2. We examined the extent of large‐scale spatial patterning of guild characteristics in larval parasitoid wasps associated with cyclically outbreaking populations of the geometrid moth Operophtera brumata in northern Fennoscandia. The study was performed at the onset of the crash‐phase of the geometrid's outbreak cycle, along a 70‐km transect in costal northern Norway, characterised by largely homogeneous environmental conditions, except for a small climatic gradient. 3. There was a distinct large‐scale spatial turnover in dominance among the major parasitoid groups (i.e. guild structure) in O. brumata along the transect, whereas the total prevalence rate of the guild and its diversity showed no consistent variation. Guild structure was unrelated to host density. 4. Although group‐specific responses to a slight spatial climatic gradient cannot be rejected as a causal mechanism, we conclude that our results are consistent with the expectation from large‐scale stochastic extinction‐recolonisation dynamics among functionally equivalent parasitoids relying on a host with strongly cyclic population fluctuations.