The influence of legacy effects and recovery from perturbations in a tritrophic salt marsh complex

Abstract. 1. Much has been learned in recent years regarding the influence of environmental conditions on top‐down and bottom‐up effects acting on insect herbivores. Temporal variation in environmental conditions, however, has gone largely unstudied in spite of undoubtedly strong influences in most systems. 2. A 2‐year study was conducted to examine the legacy effects of previous manipulations of host plant quality and parasitism pressure on the top‐down and bottom‐up effects influencing population densities of the salt marsh planthopper Pissonotus quadripustulatus. 3. For 10 months in 1998, a 2 × 2 factorial experiment was carried out, in which host plant quality was increased by the addition of nitrogen fertiliser, and parasitism pressure was decreased through the use of yellow sticky traps. This was followed by 2 months in the winter with no treatment applications. Treatments were then reversed in 1999 for a further 10 months. 4. In 1998, fertilisation treatments increased plant quality significantly, which resulted in strong effects on P. quadripustulatus density. Parasitism reduction treatments had weaker and time‐dependent effects on the herbivore, increasing planthopper density in late summer and autumn. 5. After 2 months without treatments, previous fertilisation treatments were still influencing all response variables measured significantly. The legacy effects of fertilisation persisted for at least 7 months for the host plant, and at least 5 months for the herbivore and parasitoid. 6. Fertilisation treatments in 1999 increased P. quadripustulatus density by approximately the same percentage as in 1998, suggesting that previous reductions in parasitism had no influence on herbivore responses to increased nutrients. Parasitism reduction treatments in 1999, however, resulted in greater increases in herbivore density than in 1998, suggesting that previous increases in nutrients enabled greater responses to reductions in top‐down pressure. 7. The results show that the top‐down effects of parasitism attenuated more quickly than did the bottom‐up effects of increased plant quality through greater nutrient availability. They also suggest that the recent history of nutrient status in an ecosystem may be important in determining the relative strengths of top‐down and bottom‐up forces.     

Species zonation in Corroios salt marsh in the Tagus estuary (Portugal) and its dynamics in the past fifty years

The objective of this study was to understand the main factors controlling salt marsh plant species structure and dynamics. So, we determined plant cover and composition across a permanent transect, 450 m long and 1 m wide, defined in 1951 in Corroios salt marsh, in the Tagus estuary (Portugal) and we characterized the physicochemical variables every 50 m along this transect. Based on those results we discuss the dynamic and evolution of salt marsh vegetation during the last 50 years comparing former and recent data. The results showed that differences in salinity and flooding were determinant factors in plant species composition and distribution along the studied transect. In addition, long-term variations of these factors as a consequence of vertical accretion and sea level rise seem to be responsible for the evolution in plant structure and vegetation zonation patterns, during the last 50 years in the Tagus estuary salt marshes.     

The effects of predation by the mummichog, Fundulus heteroclitus (L.), on the abundance and distribution of the salt marsh snail, Melampus bidentatus (Say)

Enclosure and exclosure experiments were conducted in Canary Creek marsh to examine how predation by a killifish, Fundulus heteroclitus (L.), affects the abundance and size distribution of the salt marsh snail, Melampus bidentatus (Say). Enclosures (7.6 × 19.7 m) were stocked with Fundulus heteroclitus at densities of one-half normal, normal, twice normal, and four times normal density. Fish exclusion pens were also built. In both years of study, the mean density of snails increased significantly in pens where fish were excluded or their density reduced. During the same period in each year, the density of snails in pens containing higher than normal fish density fell by ≈50%.

Fish density also affected the size distribution of snails within pens. In both years, mean shell length of snails in the pen with the highest density of fish was significantly greater, and mean shell length of snails within fish exclusion pens was significantly lower than in all other treatments. Gape size limitation of F. heteroclitus causes selective predation on small snails and apparently is responsible for the difference in mean shell length among treatments.

Density and size distribution measurements of the natural Melampus bidentatus population in Canary Creek marsh were also taken. Larger snails were found to occur in the low marsh zone, whereas smaller snails occurred in the high marsh zone. Since the high marsh area is flooded less often than the low marsh, and the grass types found in the high marsh zone are known to afford protection from fish predation, the distribution of snails in the marsh is consistent with the idea that fish predation is an important factor influencing the distribution of snails in Canary Creek marsh.     

Intertidal zonation of benthic macrofauna in a subtropical salt marsh and nearby unvegetated flat (SE, Brazil)

Intertidal zonation and seasonal variability of benthic macrofaunawere analysed along a Spartina alterniflora (Loisel) marshand nearby unvegetated flat in a subtropical bay. Fivereplicate samples were taken along six tidal levels from the uppermarsh, limited by mangroves, to the lower unvegetated flat.Sediment composition, live and dead above- and below-ground biomassof S. alterniflora and detritus biomass from the vegetatedand unvegetated areas were determined to evaluate whethervariations on plant structure and detritus along the 25 m transectaffect the dynamics of benthic invertebrates. Composition andabundance of invertebrates varied with the elevation and plantcover clearly plays a key role on the distribution patterns of themacrofauna. Below-ground and dead above-ground biomass presentedthe highest correlation with the densities of the invertebrates.Vertical distribution of benthic fauna, however, appears not to beaffected by bellow-ground fraction. Higher detritus biomass in theupper unvegetated flat coincided with higher densities ofdetritivorous or omnivorous species in this level. An eruptivealgal growth during summer affected positively most of the dominantspecies.     

The effects of elevated CO2 and eutrophication on surface elevation gain in a European salt marsh

Salt marshes can play a vital role in mitigating the effects of global environmental change by dissipating incident storm wave energy and, through accretion, tracking increasing water depths consequent upon sea level rise. Atmospheric CO₂ concentrations and nutrient availability are two key variables that can affect the biological processes that contribute to marsh surface elevation gain. We measured the effects of CO₂ concentrations and nutrient availability on surface elevation change in intact mixed‐species blocks of UK salt marsh using six open‐top chambers receiving CO₂‐enriched (800 ppm) or ambient (400 ppm) air. We found more rapid surface elevation gain in elevated CO₂ conditions: an average increase of 3.4 mm over the growing season relative to ambient CO₂. Boosted regression analysis to determine the relative influence of different parameters on elevation change identified that a 10% reduction in microbial activity in elevated CO₂‐grown blocks had a positive influence on elevation. The biomass of Puccinellia maritima also had a positive influence on elevation, while other salt marsh species (e.g. Suaeda maritima) had no influence or a negative impact on elevation. Reduced rates of water use by the vegetation in the high CO₂ treatment could be contributing to elevation gain, either directly through reduced soil shrinkage or indirectly by decreasing microbial respiration rates due to lower redox levels in the soil. Eutrophication did not influence elevation change in either CO₂ treatment despite doubling aboveground biomass. The role of belowground processes (transpiration, root growth and decomposition) in the vertical adjustment of European salt marshes, which are primarily minerogenic in composition, could increase as atmospheric CO₂ concentrations rise and should be considered in future wetland models for the region. Elevated CO₂ conditions could enhance resilience in vulnerable systems such as those with low mineral sediment supply or where migration upwards within the tidal frame is constrained.     

Influence of salt marsh on bacterial activity in two estuaries with different hydrodynamic characteristics (Ria de Aveiro and Tagus Estuary)

The influence of salt marsh on estuarine bacterioplankton was investigated in two estuaries with different hydrodynamic characteristics (Ria de Aveiro and Tagus Estuary). In the Ria de Aveiro, bacteria in the flood water overlying the marsh were two times more abundant and five to six times more active than in the main channel. In the Tagus Estuary, bacterial abundance was similar in flooding and channel water, but bacterial activity was up to two times higher in the main channel. The two salt marshes have distinct influences on estuarine bacterioplankton abundance and activity. In the Ria de Aveiro, salt marsh enhanced estuarine bacterial communities, increasing their size and stimulating their activity. By contrast, the salt marsh in the Tagus Estuary does not seem to increase the bacterial abundance and production in the channel water. These distinct influences may be explained by the hydrodynamic characteristics of the salt marshes, which were confirmed by the hydrodynamic model implemented for both systems.     

Relationships between seed germinability of Spergularia marina (Caryophyllaceae) and the formation of zonal communities in an inland salt marsh

BACKGROUND AND AIMS: The formation of zonal communities may be attributed to differences in germination across the community and to timing of germination of seeds present in the seed bank. Our goals were two-fold: (1) to assess the annual germination pattern of Spergularia marina; and (2) to determine whether germination of S. marina differed across zonal communities. METHODS: Fresh seeds were buried in an experimental garden in polyester bags. Bags were harvested monthly for 1 year and exposed to differing 12 h/12 h temperature regimes (5/15 degrees C, 5/25 degrees C, 15/25 degrees C and 20/35 degrees C) with a 12 h dark/12 h light photoperiod. Replicate seeds were exposed to 24 h dark. Seeds were also placed in different zonal communities to assess germinability in the field. KEY RESULTS: Spergularia marina has a primary physiological dormancy. Conditional dormancy occurs from December to May and non-dormancy from June to November. Field germination initiates in the spring when temperatures are cool and salinity is low due to flooding, and ceases in the summer when temperatures exceed germination requirements. Spergularia marina has a light requirement for germination. CONCLUSIONS: If seeds become buried in the field or are light inhibited by Phragmites australis, they will remain dormant until they receive an adequate amount of light for germination. Since S. marina can germinate across all zones in a salt-marsh community, the formation of zonal communities is not determined at the germination stage, but at some later stage of development.     

潮汐作用下干湿交替对黄河三角洲盐沼湿地净生态系统CO2交换的影响

潮汐作用作为盐沼湿地独特的水文特征能在短时间内强烈影响盐沼湿地的碳平衡.利用涡度相关和微气象监测技术,对黄河三角洲盐沼湿地净生态系统CO₂交换(NEE)和环境因子进行监测,并同步监测潮汐变化,探究潮汐过程及潮汐作用下干湿交替对NEE的影响.结果表明: 潮汐过程促进了白天生态系统CO₂的吸收但未对夜晚CO₂的释放产生显著影响,潮汐淹水成为影响白天NEE的主要因子.干旱阶段和湿润阶段NEE的日平均动态均呈“U”型曲线,但干旱阶段NEE的变幅较小.干湿交替增强了白天生态系统CO₂的吸收,干旱阶段最大光合速率(A_max)、表观量子产量(α)和生态系统呼吸(R_eco)的均值均高于湿润阶段.此外,干湿交替减少了盐沼湿地夜晚NEE释放的同时增强了其温度敏感性.     

潮汐作用下干湿交替对黄河三角洲盐沼湿地净生态系统CO2交换的影响

潮汐作用作为盐沼湿地独特的水文特征能在短时间内强烈影响盐沼湿地的碳平衡.利用涡度相关和微气象监测技术,对黄河三角洲盐沼湿地净生态系统CO₂交换(NEE)和环境因子进行监测,并同步监测潮汐变化,探究潮汐过程及潮汐作用下干湿交替对NEE的影响.结果表明: 潮汐过程促进了白天生态系统CO₂的吸收但未对夜晚CO₂的释放产生显著影响,潮汐淹水成为影响白天NEE的主要因子.干旱阶段和湿润阶段NEE的日平均动态均呈“U”型曲线,但干旱阶段NEE的变幅较小.干湿交替增强了白天生态系统CO₂的吸收,干旱阶段最大光合速率(A_max)、表观量子产量(α)和生态系统呼吸(R_eco)的均值均高于湿润阶段.此外,干湿交替减少了盐沼湿地夜晚NEE释放的同时增强了其温度敏感性.     

丛枝菌根真菌对盐胁迫下黄瓜植株生长、果实产量和品质的影响

采用有机基质栽培,选用盐敏感黄瓜品种‘津春2号’为试验材料,研究了丛枝菌根真菌(AMF)对盐胁迫下黄瓜植株生长、矿质营养吸收、果实品质和产量的影响.结果表明：接种AMF可以有效促进黄瓜植株生长和对矿质营养的吸收,提高果实产量和改善蔬菜营养品质;盐胁迫下,黄瓜生长受到抑制,植株体内N、P、K、Cu、Zn含量减少和K⁺/Na⁺降低,果实产量和可溶性蛋白、总糖、Vc、硝酸盐含量下降;接种AMF可缓解盐胁迫对黄瓜生长的抑制作用,使植株体内N、P、K、Cu和Zn含量分别比对照提高7.3%、11.7%、28.2%、13.5%和9.9%,K⁺/Na⁺、果实产量、可溶性蛋白、总糖、Vc含量明显提高,果实硝酸盐含量显著降低.表明AMF可通过促进盐胁迫下黄瓜植株对矿质营养的吸收,促进植株生长,增强植株对盐胁迫的耐性,进而提高其产量和改善营养品质.     

The influence of the host plant of diamond-back moth (Plutella xylostella) on the plant preferences of its parasitoid Cotesia plufellae in Sri Lanka

Abstract. In Y-tube olfactometer tests, female Cotesia plutellae Kurdjmov (Hymenoptera: Braconidae), a major parasitoid of Plutella xylostella (L.) in southeast Asia, preferred the odour of the brassica type (Blue Lake cabbage) on which they had developed.Such plants were even preferred to the odour of caterpillar-infested and damaged leaves of another brassica (Early Phenomenal cauliflower).However, within one brassica type, the odour of caterpillar-infested leaves was preferred to that of uninfested and undamaged leaves.Odours of both Blue Lake and Early Phenomenal were preferred to the control odour (water).However, following the transfer of the parasitoid from Blue Lake to another cabbage (Brunswick) for one generation, females no longer distinguished between Blue Lake and Early Phenomenal.     

The biology of the phonotactic parasitoid, Homotrixa sp. (Diptera: Tachinidae), and its impact on the survival of male Sciarasaga quadrata (Orthoptera: Tettigoniidae) in the field

Abstract.

• 1 Unlike most parasitoids, tachinid flies of the tribe Ormiini use sound to locate their hosts. Although thought to exert selection pressure on their host's calling behaviour, little is known about the biology of ormiines. Accordingly, this study reports the biology and impact of the ormiine Hornotrixa sp. upon calling males of the univoltine bushcricket Sciarasaga quadrata Rentz in south-western Australia.
• 2 Populations of adult S.quadrata were monitored in the field over two successive calling seasons. Females, which do not call, were not parasitized by Hornotrixa sp., but the risk of parasitism for males increased as the 3-month calling season progressed. Parasitism did not commence until c. 2 weeks into the calling season, but by the end of the season up to 87% of surviving males were parasitized.
• 3 Parasitized males lived for 14 days and were found singing until their penultimate evening before death in the field. Unparasitized males lived on average 69 days and a maximum of 119 days.
• 4 Multiparasitism of hosts was common, with up to sixteen fly larvae found within parasitized males. The number of fly larvae within hosts significantly increased at the end of the season. However, successful emergence of fly larvae from hosts, as well as pupal size, significantly decreased as more than one fly larva developed within the host.
• 5 Hornotrixa sp. has a long pupal duration of 30–31 days at 20°C. As a consequence, only one complete fly generation, which overwinters in the pupal stage, is likely within each host generation.
• 6 No evidence for differential (size-bias) mortality by Hornotrixa sp. on male S.quadrata was found. The size of parasitized and unparasitized males collected in the field was not significantly different.
• 7 It is concluded that Hornotrixa sp. is a significant mortality factor acting on the survival of adult male S.quadrata.

     

Impact of sampling methods on sulfate reduction rates and dissolved organic carbon (DOC) concentrations in vegetated salt marsh sediments

The impact of sediment coring on measured rates of sulfate reduction(SRR) by the whole core ³⁵S-injection technique was assessed inmarshsediment vegetated by Spartina anglica. Simultaneously,therole of extraction method (centrifugation vs. sippers) for determination ofporewater DOC in vegetated sediment was evaluated. SRR was measuredinsitu with radiotracer injected directly into the sediment and in atime series from 1 to 24 h after coring. SRR incubations carriedout within 6 h (June) or 12 h (August) of coringyielded up to an order of magnitude higher rates than measured insitu. The enhancement of SRR was instantaneous but temporary andcorrelated with measured porewater DOC concentrations. Cores sampled fromrootedsediments should therefore not be used for sulfate reduction incubations withinthe first 12 h due to the effect of DOC leaching from roots cutduring the coring procedure. The labile fraction of leached DOC appears to beexhausted after a pre-incubation period of at least 12 h.Measurement of porewater DOC is also problematic in vegetated sediment.Porewater extraction by centrifugation of sediment may result in up to oneorderof magnitude higher DOC concentrations than in porewater obtained by anondestructive sipper technique. DOC is probably forced out of roots duringcentrifugation resulting in erroneously high porewater DOC concentrations.     

江苏沿江和江淮区褐飞虱前期迁入量与太平洋海温场的遥相关及其可能机制

为筛选出有效的长期预测因子,对江苏通州和江苏淮安褐飞虱前期迁入量与太平洋海温场遥相关时空分布分别进行了相关分析及其稳定性检验。结果表明： 与褐飞虱前期迁入量连续稳定显著相关的海温区,在空间上主要分布在中太平洋和南太平洋（72.4%）,在时间上主要分布在前两年和前一年（82.7%）。分别分析褐飞虱前期迁入量与当年4-8月上旬各旬降水量、平均温度、当年1-8月500 hPa西太平洋副高月平均指数之间的两两相关关系,并比较这三者与前期太平洋海温场遥相关时空分布的异同。根据对两地的个例分析表明：前一冬春季赤道中东太平洋海温的变化引起当年6月副高面积指数的变化,影响江苏通州当年6月下旬降水,从而影响江苏通州褐飞虱的前期迁入量;前两年春夏季赤道中东太平洋海温的变化引起当年5月副高北界位置的变化,影响江苏淮安当年7月上旬降水,从而影响江苏淮安褐飞虱的前期迁入量。在此基础上,对褐飞虱前期迁入量与太平洋海温场遥相关的可能机制提出“海温→大气环流（副高）→气候→褐飞虱前期迁入"的一般假想模式。     

The effects of developmental stage and source leaf position on integration and sectorial patterns of carbohydrate movement in an annual plant, Perilla frutescens (Lamiaceae)

A well-integrated plant shows extensive carbohydrate translocation through the plant body. Even in highly integrated plants, however, translocation patterns will be sectorial if vascular tissue restricts carbon movement to sectors along stems. Both integration and sectorial translocation patterns are sensitive to plant architecture and thus may change as a plant develops. These patterns should vary also with the position of the source leaf because leaves at each node are unique in age and vascular relationship to the rest of the plant. I measured the effects of developmental stage and location of the source leaf on integration and sectoriality in an annual plant, Perilla frutescens, by labeling plants with C at one of three leaves and four developmental stages. Stage and source leaf affected both integration and sectoriality. Most notably, integration declined and sectoriality increased during seed fill, when resource demand at each node was high. Furthermore, translocation was least extensive from the leaf supporting the largest number of seeds on its axillary branch. These results suggest that plants are not homogeneous collections of subunits; rather, the role of each leaf in a plant's carbon budget is a function of its age and location on the plant.     

Does the presence of a seawater gill morphology induced by dietary salt loading affect Cl(-) uptake and acid-base regulation in freshwater rainbow trout Oncorhynchus mykiss

The goal of this study was to determine the effect of the changes in gill morphology induced by dietary salt feeding on several aspects of gill function in rainbow trout Oncorhynchus mykiss maintained in fresh water with specific emphasis on Cl(-) uptake (J(IN)Cl(-)) and acid-base regulation. The addition of 11% NaCl to the diet caused J(IN)Cl(-) to be reduced by c. 45% from 214·4 ± 26·7 to 117·3 ± 17·4 μmol kg(-1) h(-1) (mean ± s.e.). Rates of Cl(-) efflux (J(OUT)Cl(-)), net Cl(-) flux (J(NET)Cl(-)), J(NET) Na(+) and plasma levels of Na(+) or Cl(-) were unaffected by salt feeding. On the basis of significant effect of the salt diet on decreasing the maximal uptake rate of Cl(-)(J(MAX)Cl(-)), it would appear that internal salt loading caused a decrease in the number of functional ion transport proteins involved in Cl(-) uptake (e.g. Cl(-) -HCO(3)(-) exchangers) and decreased the transporting capacity of existing proteins. The acid-base regulating capacity of control fish and salt-loaded fish was assessed by monitoring arterial blood acid-base status [partial pressure of CO(2) (PCO(2)), pH and HCO(3)(-)] during exposure to external hypercapnia (nominally 7·5 mm Hg). Both groups of fish exhibited typical compensatory responses to sustained hypercapnia consisting of the gradual accumulation of plasma HCO(3) (-) and thus metabolic restoration within 24 h of the initial respiratory acidosis elicited by hypercapnia. Overall, the results demonstrate that while Cl(-) uptake capacity is reduced in salt-fed fish, there is no associated alteration in acid-base regulating capability.     

Establishment,spread, and impact of an invasive planthopper on its invasive host plant: Prokelisia marginata (Homoptera: Delphacidae) exploiting Spartina anglica (Poales: Poaceae) in Britain

1. Since its recent arrival in Britain, the planthopper Prokelisia marginata has spread widely around saltmarshes on the east and south coast of England and south Wales, feeding on Common Cordgrass, Spartina anglica, itself an invasive non-native species. 2. Results suggest that P. marginata populations in Britain benefit from a degree of natural enemy release. No evidence of parasitism was found in over 71 000 eggs, nymphs, and adults inspected. The only potential natural enemy control was suggested by a positive correlation between the densities of planthoppers and generalist spiders. 3. Experimental exposure under both glasshouse and field conditions to typical field densities of planthoppers resulted in significant negative effects on a number of host plant performance metrics. 4. Spartina anglica is important for stabilising estuarine sediments and has been deliberately planted for this purpose in the past. Its weakening as a result of heavy planthopper herbivory could have serious consequences for the long-term stability of Britain's vulnerable saltmarsh habitats.     

Effect of host deprivation on egg quality,egg load,and oviposition in a solitary parasitoid,Chetogena edwardsii (Diptera: Tachinidae)

Solitary parasitoids are limited to laying one egg per host because larvae compete within hosts. If host encounter rate is low, females should not increase the number of eggs/host in response. The tachinid fly, Chetogena edwardsii,was used to evaluate the effect of host deprivation on egg accumulation, oviposition behavior, and egg quality in a solitary parasitoid. Females deprived of hosts for 2– 7 days accumulate about 1 day's supply of eggs. Egg output of deprived females once hosts are restored does not differ from that of control females. Deprived females retain one egg in the uterus where it undergoes embryogenesis. Maggots emerging from retained eggs are more likely to survive in hosts molting in 40 h or less after receipt of an egg than are maggots emerging from eggs fertilized shortly before oviposition. Egg retention is a consequence of host deprivation that permits females to broaden the range of hosts they can exploit to include soon-to-molt hosts and possibly multiply parasitized hosts.     

The army ant Aenictus silvestrii and its related species in Southeast Asia,with a description of a new species (Hymenoptera: Formicidae: Aenictinae)

Three species of Aenictus with reduced numbers of antennal segments (8–9) occur in Southeast Asia: A. jarujini sp. nov., A. latifemoratus and A. silvestrii. Aenictus latifemoratus is new to Java and Borneo, while A. silvestrii is recorded for the first time from Borneo.