Influence of biotic and abiotic factors on the morphology and reproduction of Suaeda maritima on a salt marsh

The aim of this study was to estimate the influence of biotic and abiotic factors on Suaeda maritima reproduction on a salt marsh. Individuals of Suaeda maritima were submitted in natural conditions to four series of densities (100, 1,000, 4,000 and 8,000 plants/m2). When density increases, individuals tend to be less or non-branched, while individual biomass decreases. Consequently, individual seed production decreases as density increases. Despite morphological modifications, Suaeda maritima present density-dependent mortality. For a unit area, total biomass and seed production are higher at intermediate density (1,000 plants/m2). Environmental factors could interfere with self-thinning. They seem to limit the effect of competition on mortality and to have an influence on individual and total seed production. This experiment stressed the importance of a biotic factor such as intra-specific competition, which occurs at the same time as abiotic factors, in Suaeda maritima dynamics in the field.     

Patterns in the utilization of the intertidal salt marsh by larvae and juveniles of Fundulus heteroclitus (Linnaeus) and Fundulus luciae (Baird)

Larval and juvenile fishes were collected at low tide from the surface of an intertidal salt marsh on Sapelo Island, Georgia every 6 days from 25 May through 20 December 1982. Larval fishes were present in shallow puddles of tidal water on the marsh from the beginning of the sampling period until the end of October. Juveniles were present throughout the year. Fundulus heteroclitus (Linnaeus) and F. luciae (Baird) accounted for 96.3% (67.0% and 29.3%, respectively) of the 4355 fishes collected. These fishes exhibited synchronous, temporal pulses in larval abundance, suggesting that reproduction was discontinuous and controlled by the same factor(s) in both species. Larval F. heteroclitus inhabited aquatic micro-habitats near the upland edge of the intertidal marsh, but as the larvae grew to juvenile size (≈ 10 mm standard length) they moved to lower elevations near a tidal creek. Large juveniles and adults of F. heteroclitus infrequently occurred in the samples, presumably because they leave the intertidal marsh as the tide ebbs. F. luciae were rarely found in low marsh areas, but all age classes (including adults) occurred at higher elevations, supporting previous suggestions that this species prefers high marsh habitats. The vegetated, intertidal salt marsh appears to be the principal nursery habitat for both of these cyprinodontid species.     

Decomposition in salt marsh ecosystems of the S.W. Netherlands: the effects of biotic and abiotic factors

Decomposition rates, determined with the litterbag technique in salt marshes of the S.W. Netherlands during the past decade are compared; the biotic and abiotic factors influencing these rates are identified and discussed.Tissue composition is the main variable affecting decay rates of halophytes, particularly variations in lignin content between plant parts and between species.Experiments in which the loss of the tensile strength of cotton strips was used as an index of cellulolytic decay, show that there is a conspicuous variation in decay rates on different sites in a salt marsh. Nonetheless, the locally varying environmental conditions within salt marshes of the S.W. Netherlands have less impact on the variation in decomposition rates of halophyte litter than the chemical make-up of the plant material.Larger fauna elements (> 300 m) may increase decomposition rates, but this effect is only limited and depends on location and litter type. The role of small fauna elements such as nematodes, which occur abundantly in association with halophyte litter, remains largely unknown.     

Effects of historic tidal restrictions on salt marsh sediment chemistry

The effects of tidalrestrictions by diking on salt marshbiogeochemistry were interpreted by comparingthe hydrology, porewater chemistry and solidphase composition of both seasonally floodedand drained diked marshes with adjacentnatural salt marshes on Cape Cod,Massachusetts. Flooding periods weregreatest in natural and least in drainedmarshes.Differences between the chemistry of thenatural and diked marshes depended upon thedepth of the water table and the supply ofsulfate for anaerobic metabolism. Drainedmarsh sediments were highly acidic (pH <4)with porewaters rich in dissolved Fe; thenatural and diked flooded marshes had pH 6–7.5and Fe orders of magnitude lower. Porewater nutrients, sulfides and alkalinitywere much lower in both flooded and draineddiked marshes than in the natural marsh.Sediments of the drained marsh had subsided90 cm relative to the natural site due toorganic matter decomposition and compaction. However, despite the loss of organic matter,much of the P and N was retained, withNH₄ likely protected from nitrificationby low pH and PO₄ adsorbed on Fe and Aloxides. Iron, and to a lesser degree sulfur,had also been well retained by the sediment. Despite eight decades of diking, substantialamounts of reduced S, representing potentialacidity, persisted near the top of the watertable.In contrast, the surface of the seasonallyflooded marsh was only 15 cm below thenatural marsh. Accretion since dikingamounted to 25 cm and involved proportionallyless mineral matter.The restoration of seawater flow to bothseasonally flooded and drained diked marsheswill likely extend flooding depth andduration, lower redox, increase cationexchange, and thereby increase NH₄,Fe(II), and PO₄ mobilization. Increasedporewater nutrients could benefitrecolonizing halophytes but may also degradesurface water quality.     

Effects of structural marsh management on fishery species and other nekton before and during a spring drawdown

We sampled experimental research areas in the Barataria Basin of Louisiana, USA to examine the effects of structural marsh management on habitat use by small nekton (>100 mm Total Length or Carapace Width). The research areas consisted of two control (unmanaged) marshes and two impounded (managed) marshes; managed areas were surrounded by levees with water-control structures constructed by the U.S. Department of Interior, National Biological Survey. We sampled nekton with 1-m² enclosure samplers in 1995 just as a drawdown was initiated (March) and after two months of drawdown (May); a drawdown is an active management technique in which water is allowed to flow out of, but not back into, the impoundment. Samples were collected randomly from all available habitat types (shallow open water, submerged aquatic vegetation (SAV), and intertidal marsh) in the managed and unmanaged areas. In March, the densities of resident taxa (e.g., Lucania parvac rainwater killifish and Palaemonetes paludosus riverine grass shrimp), which complete their life cycles within the estuary, were significantly greater in the managed areas compared to the unmanaged areas. The densities of most resident species were either similar in managed and control areas, or significantly greater in control areas during the drawdown (May). In contrast to residents species, the transient fishery species (e.g., Callinectes sapidus blue crab and Farfantepenaeus aztecus brown shrimp) reproduce outside of the marsh system and recruit to these areas as young. The densities of these transient species were significantly higher in unmanaged areas compared to managed areas during both sampling periods. We estimated standing crop (number or biomass of nekton per hectare of marsh area) by combining habitat densities with the area of different habitat types. The standing crops of transient species also were substantially greater in unmanaged than managed areas. We conclude that the restricted water exchange in marshes under structural marsh management diminishes recruitment and standing stocks of species that must migrate from coastal spawning sites to marsh nurseries. Even when water-control structures were open, the densities of these transient species were low inside managed areas. In contrast to the negative effect of management on transient species, the resident fish and crustacean populations seemed to flourish in the managed areas when a drawdown was not in effect. Following two months of a drawdown, however, the populations of residents appeared similar inside and outside managed areas. Increases in submerged aquatic vegetation (SAV) within ponds occurred outside the managed areas during the study period, but not inside managed areas. Because many resident species were closely associated with the SAV, the effect of management on SAV may have been responsible for the distribution patterns of resident species.     

Disturbance of salt marsh vegetation by wrack mats in Great Sippewissett Marsh

To quantify disturbance to salt marsh vegetation, and to test the notion that disturbance and species richness are related, we studied disturbance of vegetation by 195 wrack mats that had become stranded over Great Sippewissett Marsh. The mats varied in area, thickness, residence time, and elevation of stranding. Mats that were large, that had residence times of 3–4 months, and were stranded at higher elevations produced the most damage, ranging from total eradication to a decrease in shoot density of underlying vegatation. Thickness had no effect. About 70% of mats caused no damage, and of those that did, damage was usually 50% or less of the area beneath the mat. Plant species were differentially distributed along the tidal excursion within the marsh, and there were more species (8–9) high in the intertidal range than lower (4–6 species). Vertical distribution of species, species richness, and rate of annual disturbance were not well correlated, although highest and lowest disturbance rates corresponded to highest and lowest species richness. Most of the increases in species richness, however, occurred over a very small range of disturbance, so narrow that it seemed unlikely that disturbance affected richness. It seems more likely that factors other than disturbance rate control vertical position of species in salt marshes. It also appears that the effect of disturbance by wrack is less important than has been claimed.     

Effect of fish predation on intertidal benthic fauna is modified by crab bioturbation

The burrowing crab Chasmagnathus granulatus is an important bioturbator in SW Atlantic estuaries where they generate dense and extended intertidal beds. Its bioturbation leads to profound changes in the structure, quality and dynamics of sediments with concomitant impacts on the entire benthic community. In this study, we evaluate whether the presence of this crab affects the predator-prey interaction between juvenile fishes and their benthic prey. Gut content and benthic prey selection by juvenile fishes inside and outside crab beds were evaluated, and predation effect was experimentally contrasted between areas using fish exclosures. The results show that in crab beds the percentage of fish with empty guts was lower and the number of polychaetes consumed by fish higher than outside crab beds. The silverside Odontesthes argentinensis and the catfish Pimelodella laticeps fed on larger polychaetes outside than inside crab bed areas, while the white mouth croaker Micropogonias furnieri preyed upon larger polychaetes inside crab beds. In addition, field experiments shows that fish predation decreases polychaete abundances only in crab beds. These results suggest that crab bioturbation facilitate fish predation on benthic prey.     

Differential effects of four abiotic factors on the germination of salt marsh annuals

Interspecific differences in responsiveness to temperature, photoperiod, soil salinity, and soil moisture confirm the hypothesis that abiotic factors differentially affect the germination of salt marsh plants. In growth chamber experiments, four of eight annual species responded to small differences in temperature or photoperiod. Increasing soil salinity decreased the final proportion of seeds germinating and slowed germination for each of the seven species tested. Higher soil moisture increased the proportion germinating of five species and germination speed of all seven species. Salinity and moisture interacted to affect the proportion germinating of five species and germination speed of all seven species. Although the abiotic factor with the largest effect on germination varied among species, more species responded to, and the magnitudes of the responses were larger for, soil salinity than for the other abiotic factors. These germination tests partially explained interspecific differences in the timing of germination in the field. Patterns of Hutchinsia procumbens, Lythrum hyssopifolium, Parapholis incurva, and possibly Lasthenia glabrata ssp. coulteri germination in response to a nonseasonal rainfall could be explained by their response to salinity, temperature, or photoperiod. Fine-scale differences in the timing of establishment within the typical germination window and spatial distributions along salinity and moisture gradients were not explained.     

Effects of biotic and abiotic factors on the distribution of trout and salmon along a longitudinal stream gradient

Synopsis We examined the influence of biotic and abiotic factors on the distribution, abundance, and condition of salmonid fishes along a stream gradient. We observed a longitudinal change in fish distribution with native cutthroat trout, Oncorhynchus clarki utah, and introduced brown trout, Salmo trutta, demonstrating a distinct pattern of allopatry. Cutthroat trout dominated high elevation reaches, while reaches at lower elevations were dominated by brown trout. A transition zone between these populations was associated with lower total trout abundance, consistent changes in temperature and discharge, and differences in dietary preference. Variation in cutthroat trout abundance was best explained by a model including the abundance of brown trout and diel temperature, whereas variation in brown trout abundance was best explained by a model including the abundance of cutthroat trout and discharge. These results suggest the potential for condition-mediated competition between the two species. The results from our study can aid biologists in prioritizing conservation activities and in developing robust management strategies for cutthroat trout.     

Effects of salt marsh invasion by Spartina alterniflora on sulfate-reducing bacteria in the Yangtze River estuary,China

To investigate how plant invasion affects sulfate-reducing bacteria (SRB) responsible for sulfate reduction, we conducted a comparative study of diversity and composition of SRB in rhizosphere soils of invasive exotic species (Spartina alterniflora) and two native species (Phragmites australis and Scirpus mariqueter) on Jiuduansha Island located in the Yangtze River estuary, China. Throughout the growing season, profiles of DGGE fingerprints of SRB had distinct variations in relation to phenological stages of these three plant species. The higher richness and abundance of SRB in the rhizospheres of native plants mainly occurred when the plants were in vegetative growth and reproductive stages. However, the higher richness and abundance of SRB also occurred in the late growing season (senescent stage) of S. alterniflora rhizosphere, during which Desulfobulbus, Desulfuromonas, Desulfovibrio, and Firmicutes were dominant. Our results adding to our previous studies suggested that abundant SRB in late stage might have close relationships with decomposition of soil organic matters produced by S. alterniflora.     

Effects of grazing and inundation on pasture quality and seed production in a salt marsh

During a six-year period, changes in the composition of dominant plant species of importance to foraging birds in a salt marsh on the Swedish west coast were followed inside and outside exclosures to document effects of grazing on herbage quality and seed production. Since marshes provide an important habitat for foraging geese and ducks, it was of interest to determine how cattle grazing would affect herbage production inAgrostis stolonifera andPuccinellia maritima and seed and root-tuber production inScirpus maritimus. Measurements of cover and height in permanent plots revealed that a wetter weather type favouredAgrostis, probably through reduced salinity, at the expense ofPuccinellia, which was the most favoured food of both cattle and birds.Agrostis out-competedPuccinellia when grazing pressure was low. Seed production inScirpus maritimus was reduced by cattle grazing, particularly whenPhragmites australis formed part of the vegetation. In the absence of cattle grazing, both herbage- and seed producing plants were gradually reduced, andPhragmites increased. Since high herbage consumption and high seed production are mutually exclusive, grazing rotation in combination with mowing is suggested as a management strategy.     

Effects of biotic and abiotic factors on the temporal dynamic of bat-fruit interactions

Mutualistic interactions between animals and plants vary over time and space based on the abundance of fruits or animals and seasonality. Little is known about this temporal dynamic and the influence of biotic and abiotic factors on the structure of interaction networks. We evaluated changes in the structure of network interactions between bats and fruits in relation to variations in rainfall. Our results suggest that fruit abundance is the main variable responsible for temporal changes in network attributes, such as network size, connectance, and number of interactions. In the same way, temperature positively affected the abundance of fruits and bats. An increase in temperature and alterations in rainfall patterns, due to human induced climate change, can cause changes in phenological patterns and fruit production, with negative consequences to biodiversity maintenance, ecological interactions, and ecosystem functioning.     

Effects of predation-risk on habitat use by Himalayan Snowcocks

Summary When given a choice, animals often prefer foraging habitats where predation risk is low, even if such habitats provide reduced foraging opportunities. We evaluated foraging rates of tame but free-ranging Himalayan Snowcocks (Tetraogallus himalayensis) in 16 types of alpine habitats. Foraging rate was highest on level or slightly-sloping terrain and where grasses were relatively abundant. We also observed 102 wild snowcocks and found they were most nervous about raptorial predators when on level or slightly-sloping terrain and in small coveys. Snowcocks face a dilemma: they are most vulnerable to raptors in areas where they can forage most efficiently. During summer snowcocks trade off higher foraging efficiency on level terrain for lower predation risk on steeper terrain. During winter, when raptor numbers are lower, snowcocks apparently revert to using level or slightly-sloping, high-efficiency foraging habitats. Risk of predation plays an important role in habitat selection and resource utilization by snowcocks.     

Effects of frequent fish predation on corals in Hawaii

The abundance of lesions from fish bites on corals was quantified at nine shallow reefs in the main Hawaiian Islands. There were on average 117 bite scars m⁻² on Pocillopora meandrina tissue from the barred filefish Cantherhines dumerilii, 69 bites m⁻² on Porites compressa tissue, and 4 bites m⁻² on Porites lobata tissue from the spotted puffer Arothron meleagris. Across sites, the frequency of A. meleagris bites on P. compressa per unit area of living coral cover declined exponentially with increasing coral cover. P. compressa nubbins in two size classes (1–2 cm and 4–5 cm) were transplanted onto six study reefs. Nubbins in the small size class were entirely removed by bites from A. meleagris, while nubbins ≥4 cm were only partially consumed, leaving them able to recover. At sites with abundant P. compressa, predation had little effect on transplanted nubbins; at sites where P. compressa comprised less than 5% of living cover, all nubbins were preyed upon. A. meleagris bite lesions on P. compressa were monitored through time and fully recovered in 42 ± 4 days. A model of the risk of over-predation (a second predation event before the first is healed) decreased exponentially with increasing coral cover and increased linearly with increasing lesion healing time. The increased risk of over-predation at low coral cover could indicate an Allee effect limiting the recovery of coral populations if coral cover is substantially reduced by natural or anthropogenic disturbances.     

下挖深度对节能日光温室环境因子日变化及空间分布的影响

对山东省泰安市下挖0、0.5、1.0、1.5m节能日光温室(不同下挖深度温室的结构参数完全一致)太阳直射辐射能截获量进行分析,研究了2009年12月20日—24日(冬至日前后)和2010年6月19日—23日(夏至日前后)温室环境因子日变化规律及其空间分布特点.结果表明:随着下挖深度的增加,下挖壁面在温室内的阴影面积逐渐增加,进入室内的太阳直射辐射逐渐由南向北迁移,地面辐射/后墙辐射值逐渐减小;日光温室下挖深度在0～1.0m时,下挖越深,温室气温和地温增温效果越显著、保温效果越好,下挖深度达1.5m时增温效果则显著下降、最低地温偏离度增大;下挖越深,温室内光照度越低、相对湿度越大.兼顾温室的采光与保温性能,泰安地区10m跨度的下挖式日光温室的适宜下挖深度应不超过1.0m.     

Effects of morphological changes on metal accumulation in a salt marsh sediment of the Skallingen peninsula,Denmark

In 1931 a red-colored, sandy marker horizon was placed on the emergingSkallingen salt marsh. Sedimentation on top of the marker horizon sincethen shows two opposing tendencies. Coincident with salt marshdevelopment the sediments display up to 1964 a fining upward sequencewith an increasing content of organic matter. Since 1964 a nearby creekhas meandered towards the sampling plot. Consequently, the sedimentsbecome coarser with a decreasing organic matter content. Themorphological induced changes in sedimentary conditions strongly influencemetal content in the sediments and thereby hide anthropogenic inducedconcentration variations. Thus, an apparently diminishing Zn content (perkg dry weight) since 1964 could indicate lesser load to the area. However,corrected for grain size effects there is an increasing content of Zn. Othermetal concentrations (e.g. Cu) show a diminishing trend when corrected forgrain size effects and therefore indicate a reduced anthropogenic inducedload of these metals to the salt marsh.     

Importance of predation by white shrimp Litopenaeus setiferus on estuarine subtidal macrobenthos

Macrobenthic invertebrates are an important food source for higher trophic levels in freshwater and marine habitats, yet the importance of predation impacting regular seasonal changes in macrobenthos abundance remains unclear. Benthic invertebrates and transient marine species in temperate estuaries display inverse patterns of seasonal abundance, suggesting a link between predation and summer macrobenthos abundance minima. We conducted manipulative caging experiments to test the importance of predation by white shrimp (Litopenaeus setiferus) in regulating estuarine subtidal macrobenthos densities. We predicted greater declines in macrobenthos densities with increased shrimp densities due to predation rather than disturbance and macrobenthos emigration. Using these field and laboratory data, we estimate whether white shrimp predation can significantly contribute to the macrobenthos seasonal abundance minima observed in long-term monitoring data.White shrimp predation was measured in the field using 7-d predator enclosure/exclusion experiments. Within the uppermost 0-2 cm of sediment, total macrobenthos densities decreased within shrimp enclosure cages using 12 or 36 shrimp m^− 2. Laboratory experiments distinguished between the effects of shrimp predation versus shrimp disturbance and macrobenthos emigration. Shrimp predation significantly reduced macrobenthos densities, while effects of shrimp disturbance and macrobenthos emigration were not significant in these experiments. Despite the impacts from other ambient predators and other abiotic factors, white shrimp were clearly capable of driving subtidal macrobenthos from their annual maximum density in winter/spring to their summertime minimum density.     

Effects of growing conditions on the growth of and interactions between salt marsh plants: implications for invasibility of habitats

A common but often less tested explanation for the successful invasion of alien species is that invasive alien species outcompete their co-occurring natives, which may not always be the case. In this study, we established artificial environmental gradients in a series of pot experiments with controlled environments to investigate the effects of salinity, sediment type and waterlogging on the performance of and interactions between Phragmites australis (native) and Spartina alterniflora (alien), which generally co-exist in the saline intertidal zones of Chinese and American coasts. Significant effects of salinity and waterlogging were detected on biomass production and morphological characteristics of S. alterniflora and P. australis, and the competitive interactions between the two species were found to vary with all three environmental factors in our experiments. Relative Neighbor Effect (RNE) analyses indicate that competitive dominance of S. alterniflora occurred under the conditions of high salinity, sandy sediment and full immersion, whereas P. australis showed competitive dominance under the conditions of low salinity and non-immersion. Our results suggest that S. alterniflora might outcompete P. australis under conditions present in early salt marsh succession, which support the viewpoint that the outcomes of competition between co-occurring native and invasive alien plants depend on the growing conditions. The implication of this study is that in response to the environmental changes expected from seawater intrusion and sea-level rise, the range of S. alterniflora is expected to expand further in the Yangtze River estuary in the future.