Scale and intensity of intertidal habitat use by knots Calidris canutus in the Western Wadden Sea in relation to food,friends and foes

In August–October 1988–1992 we studied the distribution and abundance of knots Calidris canutus around Griend in the western Wadden Sea, and the extent to which these can be explained by benthic prey availability and presence of avian predators. Numbers in the nonbreeding season showed monthly averages of 10 000 to 25 000 birds. Over 100 000 knots were recorded on three occassions. Knots feed in large flocks, individual birds usually experiencing 4 000 to 15 000 flock-mates. The Siberian-breeding/west-African wintering canutus subspecies passed through in late July and early August. Otherwise the Greenlandic/Canadian breeding islandica subspecies was present. Over the period 1964–1992 there were no clear trends in the number of knots, but canutus-knots were particularly abundant in July–August 1991, whereas in 1992 both subspecies were absent.Macoma balthica was the preferred prey of both subspecies. Hydrobia ulvae, Mytilus edulis and Cerastoderma edule were eaten when Macoma was absent close to the surface of the sediment. As Macoma buried deeper from July onwards, canutus faced better average feeding conditions than islandica later in the year. The spatial distributon of knots feeding on the intertidal flats around Griend was best explained by the harvestable biomass of the prevalent prey species in a particular year and season, i.e. Macoma (main prey when their harvestable biomass densities were greater than ca 0.8 g AFDM per m²) and Cerastoderma, and by the avoidance of situations where they run the risk of attack by bird-eating birds. Flocks of knots covered most of the intertidal flats in the Western Dutch Wadden Sea in a couple of tidal cycles. This is about 800 km², much larger than the equivalent area used by knots on their wintering grounds in Mauritania (10–15 km²), a difference that is correlated with prey spectrum, prey availability and predictability.     

Physical and biological aspects of shell accumulation on a modern macrotidal flat,Inchon, Korea

Shell beds are comparatively rare on large tidal flats near Inchon, Korea, where barrier islands, well-developed intertidal drainage channels, and landward salt marshes also are absent. Even though landward transport of non-indigenous shells is discernible, most shell accumulations evidently originate through comparatively rapid deposition of sediments coupled with gradual mortality within local populations; individual valves typically experience only minor lateral displacement. Apparent cohort size classes remain distinguishable within some assemblages. Old shells predominate among gastropod assemblages whereas new shells predominate among bivalve assemblages, implying greater rates of productivity among bivalves than among gastropods.     

The macrozoobenthos of the subtidal western dutch wadden sea. I. Biomass and species richness

During a one-year period in 1981–1982, a survey was conducted on the macrozoobenthos of the subtidal areas of the western half of the Dutch Wadden Sea. In total 80 species were found, half of them polychaetes. In terms of biomass, Mytilus edulis dominated the macrozoobenthos, with Hydrobia ulvae, Heteromastus filiformis, Carcinus maenas and Macoma balthica as other important species. Numerically important were also the polychaetes Pygospio elegans and Scoloplos armiger. Average macrozoobenthic biomass amounted to 43.7 g·m⁻² ash-free dryweight. This value is in the same range as values from intertidal areas in the Wadden Sea. The relatively high value in comparison with data from similar subtidal areas is attributed to the important mussel culture in the area.     

How the food supply harvestable by waders in the Wadden Sea depends on the variation in energy density,body weight,biomass, burying depth and behaviour of tidal-flat invertebrates

For several reasons, waders in the Wadden Sea face a large seasonal and annual variation in their food supply. Observations on a tidal flat in the Dutch Wadden Sea have shown that:

• 1.- (1) The average energy density of ten invertebrate prey species varies between 21 and 23 kJ·g⁻¹ AFDW. In Scrobicularia plana and Mya arenaria, but not in Macoma balthica, the energy density is 10% lower in winter than in summer.
• 2.- (2) Depending on the species, body weights of prey of similar size are 30 to 60% lower in winter than in summer.
• 3.- (3) The year-to-year fluctuation in standing-crop biomass is larger in some species than in others, the difference depending mainly on the frequency of successful recruitment. The overall biomass of the macrobenthos in winter is half of that in summer, but the timing of the peak biomass differs per species.
• 4.- (4) The burying depth varies per species: Cerastoderma edule live just beneath the surface, while M. balthica, S. plana, M. arenaria, Arenicola marina and Nereis diversicolor bury more deeply and the majority of these prey live out of reach of the bird's bill. In all six species, burying depth increases with size. There is no seasonal variation in depth of C. edule and M. arenaria, but the four other species live at most shallow depth in early summer and most deeply in midwinter. Burying depths in winter vary from year to year, but are unrelated to temperature. Neither has temperature any effect on depth within months. For knot Calidris canutus feeding on M. balthica, the fluctuation in the accessible fraction was the main source of variation in the biomass of prey that is actually harvestable, i.e. the biomass of prey of suitable size that is accessible.Accordingly, the paper reviews the available data on the temporal variations in accessibility, detectability, ingestibility, digestibility and profitability of prey for waders. Only a small part of the prey is harvestable since many accessible prey are ignored because of their low profitability, while many profitable prey are inaccessible. The profitability of prey depends on their size and weight but also on their depth in the mud, since handling time increases with burying depth. A simple biomechanical rule explains why the handling time of small prey increases with bill length and why large, long-billed waders ignore a disproportionately larger part of the small prey. The fraction detectable for visually feeding waders is usually very low, especially when the temperature of the substrate is below 3–6°C. Waders vary their prey choice over the year in response to the changes in the availability and profitability of their different prey species. The food supply harvestable by waders is much lower in winter than in summer. For waders wintering in the Wadden Sea, the food supply may be characterized as unpredictable and usually meagre. Waders wintering in NW Europe are concentrated in coastal sites where the average surface temperature is above 3°C. This probably cannot be explained by a greater burying depth, and only partly by a lower body condition, of prey in colder areas. Yet the harvestable fraction is lower in colder sites, especially for sight-feeding waders, as invertebrates are less active at low temperatures. However, the lower energetic cost of living and reduced chances of the prey being covered by ice may also contribute to the waders' preference for warmer sites.

     

Life history and reproductive biology of Corophium volutator (crustacea: amphipoda) and the influence of shorebird predation on population structure in chignecto bay,bay of fundy,Canada

Intertidal populations of Corophium volutator were sampled over a 17-month period at 5 locations in Chignecto Bay, Bay of Fundy, Canada. This is a macrotidal environment with extensive mudflats. Two generations were produced annually. The lengths of gravid females and brood sized were larger than those previously reported in most European studies. Production was highest during May-September. During late summer (July-September) the larger animals were selectively removed from the population by predatory shorebirds (Charadriiformes) thus modifying the population structure from a bimodal to a unimodal distribution composed of numerous but small animals. Although shorebird predation was extensive, the associated reductions in Corophium densities were temporary-Densities increased following the birds' departure from the study sites in early fall. Frequency distribution histograms of size classes remained unimodal and growth was low, until the next breeding season. Annual net production over 2 one-year periods was 6250 and 3277 mg·m⁻² (dry weight).     

Year-to-year variability in the biomass of macrobenthic animals on tidal flats of the Wadden Sea: How predictable is this food source for birds?

The Wadden Sea is important as a stop-over and wintering area for several species of waders, foraging for shorter or longer times on its tidal flats. The size of the food stocks these birds encounter varies from place to place and from year to year. We studied characteristics of the variability in time of such prey stocks, using long-term data series of annual estimates of biomass of macrobenthic animals collected on tidal flats in various parts of the Dutch and German Wadden Sea. Year-to-year fluctuations were stronger in nearly all individual benhos species than in total macrozoobenthic biomass. The various species differed significantly in their year-to-year variability. Everywhere the tellinid bivalve Macoma balthica was relatively stable, whereas species such as the cockle Cerastoderma edule and the polychaetes Lanice conchilega, Nephtys hombergii and Anaitides mucosa fluctuated heavily and rapidly in all parts of the Wadden Sea where they were found. Within species, fluctuations in biomass of individual age or size classes were stronger than those in total biomass of the species.Several species showed minimal biomass values in the same years over vast areas. This synchronization of scarcity was caused particularly by similar responses to winter character, which was each year similar over the entire Wadden Sea. Such similar responses included low over-winter survival during severe winters and recruitment failure after exceptionally mild winters. Immediately after severe winters, such cold-sensitivee species as C. edule, L. conchilega and N. hombegii were scarce all over the Waden Sea, thus liimiting the possibilities for birds to switch to other parts of the Wadden Sea to find their preferred prey in sufficient quantitu. Simultaneous recruitment failure in several important bivalve species (C. edule, Mytilus edulis, and Mya arenaria limited the possibility for specialized bivalve consumers to switch to alternative prey types in certain years.     

附植小型底栖动物生物量测定方法的初步研究

为探讨小型底栖动物生物量的测定,于2004年10～12月对青岛太平角潮间带2种海藻上附生的小型底栖动物进行了连续3个月的采样调查,对小型底栖动物各类群的生物量进行了估算,同时测定了附植海洋线虫优势种类的个体干重和ATP含量。结果表明2种海藻上共采得12个小型底栖动物类群,平均丰度和生物量分别为518.95 inds./g algae和1270.05 μg/g algae,海洋线虫和桡足类为优势类群。不同粒级海洋线虫的个体干重为0.14～32.65 μg/ind.,ATP含量为1.18～297.64 ng/ind.,碳/ATP比值为43:1～99:1。     

Screening global <Emphasis Type="Italic">Medicago</Emphasis> germplasm for weevil (<Emphasis Type="Italic">Hypera postica</Emphasis> Gyll.) tolerance and estimation of genetic variability using molecular markers

The genus Medicago encompasses many important forage species for both temperate and tropical regions. M. sativa L., commonly known as lucerne, is one of the most important forage species grown worldwide, but its production suffers seriously from weevil (Hypera postica Gyll.) infestation. The aim of this work was to identify species/accessions with tolerance to weevil and their molecular analysis using simple sequence repeat (SSR) markers. After screening 197 global germplasm encompassing 50 Medicago species for weevil tolerance, 22 lines representing 13 species were identified where leaf damage was ≤15% (P ≤ 0.05). In total, 37 accessions of the 22 lines, five Indian lucerne cultivars with leaf damage ≥75% and 10 accessions of the 13 Medicago species with low to high infestation (>25%) were molecularly assessed using 11 SSR markers (5 newly developed) to delineate closest to lucerne lines for breeding. In total, 33 bands were scored. The SAHN clustering using UPGM algorithm resulted into two main clusters supported with high boot strap values and with genetic similarity ranging from 0.33 to 0.96. Two accessions of M. tenoreana were observed closest to Indian lucerne cultivars. The rich variability revealed can be used as potential resource for transferring genes across species. Although the inter-specific hybridization is difficult preposition in genus Medicago largely due to post fertilization barrier, the identified species/accessions can be utilized on priority in breeding programs especially employing biotechnological tools like culturing of fertilized pods, ovule-embryo culture and electroporation.     

Community structure and biomass distribution of seagrasses and macrofauna in the flores sea,Indonesia

In several locations in the Flores Sea region the community structure and the biomass distribution of seagrasses were studied along transects perpendicular to the shoreline. The share of each species within a sample plot was estimated, divided in above- and below-ground biomass. Statistics regarding substrate coverage, shoot density and leaf-area index were sampled. A standard relation was calculated between seagrass dry weight, ash-free dry weight and organic carbon content.The biotic data were related to environmental factors: DOC and nutrients in the water, salinity, tidal amplitude, sediment composition. A relation was estimated between bottom coverage of seagrasses and standing stock. Further calculations of biomass-production ratios allow a quick and rough estimate of seagrass productivity. Maximum above-ground biomass values (500–700 g AFDW·m⁻²) together with qualitative data indicate resource (= space) partitioning among the component seagrasses within a community, and suggest a carrying capacity of the reefflat habitat for seagrass density and biomass.A tentative model was constructed, starting from a constant, non-distributed multispecies vegetation in the lower intertidal and subtidal zone on sand and coral rubble, and moving into several suboptimal situations. The upper shore carries an impoverished, constrained vegetation (irregular tides, desiccation, harvesting). Sediment reworking by animals and physical displacement of sand disturbs the vegetation and favours pioneer species. Muddy habitats bordering mangroves carry monospecific stands showing extremely high biomass (e.g. below-ground Enhalus acoroides 3500 g AFDW·m⁻²). Thalassia hemprichii and Enhalus acoroides are the most constant species in all habitats mentioned.Macrofauna biomass within the seagrass beds fluctuated widely (maximum values 50–70 g AFDW·m⁻² in mixed seagrass vegetations) and only a weak relation between benthic macrofauna biomass and seagrass community structure and biomass was found.     

Increased mortality in alternative bivalve prey during a period when the tidal flats of the Dutch Wadden Sea were devoid of mussels

In the course of 1990, stocks of mussels (Mytilus edulis) declined to unprecedentedly low levels in the Dutch Wadden Sea. Hardly a wild mussel bed was left on the tidal flats as a consequence of three years (1988, 1989, and 1990) with failing recruitment and intensive fishing for seed mussels. During these three years, recruitment of cockles (Cerastoderma edule) also failed, whereas fishing was continued. Bird species taking these bivalves as staple food, the oystercatcher (Haematopus ostralegus) and the eider (Somateria mollissima), experienced food shortage. Significant numbers of eiders left the Dutch Wadden Sea area or died, whereas oystercatchers remained abundant trhoughout the winter in most of the Dutch Wadden Sea.Alternative prey species of oystercatchers experienced unsually high mortality rates in the appropriate size classes. This was so in all other common species of bivalves, viz. first-year and older cockles, adult Macoma balthica, and juvenile Mya arenaria. This led to minimal stocks of food for oystercatchers in the late winter of 1991. In March 1991, cockles were depleted and the combined stocks Mya and Macoma would soon have run out of food supply to the overwintering oystercatcher population. Apparently, oystercatchers are able to reduce the stocks of their various bivalve prey species to very low levels.     

Animal traces on a tidal flat in Hangzhou Bay,China

Despite prevailing low salinity (S ranging from 1 to 10) of the Hangzhou Bay, its extensive (up to 2 km wide) flats along the northern coast have a species-rich macrobenthic fauna of crustaceans, bivalves, gastropods and polychaetes. These produce a variety of crawling, feeding, dwelling and resting traces, some comparable to those observed on the flats of Korea and Taiwan. The characteristic starlike feeding traces of the bivalve Tellina (Moerella) iridescens are described here for the first time. Sediment reworking appears to be largely confined to the surface layer. The burrow-inhabiting crabs are also mainly surface sediment feeders. These Chinese flats lack organisms reworking deeper sediment layers such as lugworms or callianassid crustaceans. As compared to the Wadden Sea, sedimentation rate is higher and subsurface sediment reworking less intense, resulting in relatively few bioturbation structures in vertical sections of the Hangzhou tidal flat sediments.     

Long-term soft-bottom faunal changes in three shallow fjords,West Sweden

Three West Swedish fjords were investigated at the same 14 stations in 1976 and 1986, and 8 of these had been investigated in the 1920's. The stations are situated at 7 to 27 m water depths in protected areas without any significant local pollution input, but now with organically enriched sediments. Comparisons of benthic fauna between 1976 and 1986 showed the following significant reductions: in total mean abundance and biomass (excluding some large and rare species); in abundance and biomass of molluscs; in abundance of suspension feeders and carnivores. Similarity indices gave significant differences between 1976 and 1986, and between the 1920's and both 1976 and 1986. The greatest changes had occurred in the two fjords with the most restricted water circulation. Although these faunal changes may be attributed to several factors, recently increased periods of hypoxia in the bottom water, which could be a result of large-scale eutrophication, are suggested as the main impact on the benthos.     

Comparison of the fish communities of the reef flat,the reef edge and the pelagic system in Flores sea reef environments

During the Snellius-II Expedition beach seines and gill nets were used to sample the fish fauna of reef flats and reef edges of Flores Sea reefs. Beach seining r sulted in the largest samples: in total about 14 700 specimens representing 104 species. These catches from sand flats and seagrass beds show a remarkable diversity. Slightly over 1000 specimens were collcted with gill nets along the reef edges. These much smaller catches show a still wider variety: 143 species. Only six out of the 107 dominant species occur in both habitats. Of the total number of 204 species 43 species were sampled in both habitats. Fishes occurring in both habitats are mainly sand-dwelling species and active predatory species. Pelagic species mainly occur along the reef edge; only epipelagic species are commonly sampled over the reef flat.     

Environmental effects of the growth rate of intertidal invertebrates and some implications for foraging waders

The paper describes effects of intertidal height and sediment type on growth rate of the bivalves Cerastoderma edule, Macoma balthica, Mya arenaria, Mytilus edulis and Scrobicularia plana, and of the worms Arenicola marina, Nephtys hombergii and Nereis diversicolor in the eastern part of the Dutch Wadden Sea. In most species, exposure time was negatively correlated with length growth, although interfering effects of sediment type could not be ruled out. When controlled for the effects of exposure time, clay content of the sediment appeared to affect the growth of all species, but in different ways. The variation was related to the foraging methods of the invertebrates. Foraging waders may use the spatial variation in growth rate of the invertebrates to optimize the exploitation of individual cohorts.     

Effect of the brown shrimp Crangon crangon L. on endobenthic macrofauna,meiofauna and meiofaunal grazing rates

The effect of natural densities (50 and 100 ind·m⁻²) of juvenile (<20 mm) Crangon crangon on abundance of endobenthic macrofauna and meiofauna and on meiofaunal grazing rates was investigated in two experiments using an outdoor flow-through system with sandy sediment. The experiments differed in duration (3 wk and 7.5 wk), and in time of the year (August – September and July – August). Macrofaunal biomass differed by a factor of 10 between the experiments, and was depressed by shrimp in both experiments. Neither total meiofaunal biomass, nor the biomass of the dominant taxon (nematodes), was significantly affected by the presence of Crangon in the shorter experiment. However, harpacticoid copepods and other meiofauna taxa (mainly ostracods, foraminiferans and juvenile bivalves) decreased in the presence of Crangon. In the longer experiment, no significant effect of Crangon on meiofauna was seen, and the biomass of most meiofaunal groups increased in all treatments. Meiofaunal grazing rates in microalgae and bacteria, measured with a dual-labelling method, using ¹⁴C-bicarbonate and [methyl-³]]-thymidine as tracers, were 0.7 to 4.7% of algal biomass per day, and 0.8 to 7.9% of bacterial biomass per day. Generally, grazing rates were lower in the presence than in the absence of Crangon. In terms of carbon ingested, microalgae constituted a more important food source than bacteria for all three meiofaunal groups (nematodes, harpacticoids and other meiofauna). No individual growth of Crangon was found in the high-density treatment in the longer experiment, suggesting that intraspecific competition occurred. The difference between the two experiments in the effect of Crangon on meiofauna is thought to be caused by the large difference in macrofaunal biomass between the experiments; the shrimp ate mainly juvenile macrofauna in the longer experiment. Overall, the effect of Crangon on the sediment system was weak, suggesting that other factors (physical and chemical) are more important than epibenthic predation in setting the overall limits for production in this sediment.     

Intercropping fenugreek (Trigonella foenum‐graecum L.) and barley (Hordeum vulgare L.) with and without biochar: Tests along a competition gradient

Integrating soil amendment biochar to legume‐based intercropping systems may amplify the intercropping benefits and lead to more sustainable production due to its positive effects on the soil physicochemical and biological environment. Fenugreek (Trigonella foenum‐graecum) is a legume used in an intercropping system in several countries in Southern Europe, the Middle East, and Asia. A barley cultivar and an Iranian fenugreek ecotype were studied in two replacement series experiments to find the best combination of the two species as well as the effect of adding biochar to the soil. Fenugreek and barley were grown in 4‐L pots in five density combinations (20:0, 15:5, 10:10, 5:15, 0:20) with and without application of biochar in sandy loam soil. The biomass, nitrogen (N) and carbon (C) amount of the two crops were measured fifty days after sowing, and the Relative Yield Total (RYT) was estimated. Our results showed that biochar application resulted in a higher total biomass, N and C amount in all combinations of fenugreek and barley. Total biomass was increased by biochar 19.2% when fenugreek was grown alone and 8.1 and 12.9% in series with 25 and 50% barley when biochar was added, respectively. Biochar increased dry matter, N and C accumulation in both crop species in the mixtures. An exception was the C amount of barley which was not influenced by biochar in intercropping. RYT values were largest for biomass, C and N amount in mixtures with 15 fenugreek plants per pot and 5 barley plants per pot corresponding to approximately 400 fenugreek plants per m mixed with 130 barley plants per m². Biochar application increased RYT of the total dry weight by 2.7 and 5.5% in mixtures of 25 and 50% barley plants, RYT of the total nitrogen by 0.8% in mixtures with 25% barley plants, and RYT of the total carbon by 2.7 and 6.6% in mixtures with 25 and 50% barley plants. The RYT values declined with increasing number of barley plants as a result of a less competitive ability of fenugreek when growing in high barley densities. The yield was highest with intercropping but monoculture of barley also resulted in high yields. The total highest yield was found when approximately 130 fenugreek plants per m² were mixed with 400 barley plants per m². Mixtures with 75% fenugreek and 25% barley obtained RYT values larger than 1 for biomass, carbon and nitrogen percentages.     

Quantitative models of hydrolysis conversion efficiency and biomass crystallinity index for plant breeding

In conjunction with improvements to processing technology, selective breeding can be used to increase bioenergy yield potential either through an increase in total harvestable biomass or by modifying biomass conversion efficiency. In this study, the measurement of biomass composition (lignin, cellulose and hemicellulose) and proximate (fixed carbon, volatile matter, ash and moisture contents) components was conducted on leaf and tissue samples from diverse Sorghum bicolor genotypes across two environments. Multiple regression analysis was used to create models that predict two biomass conversion traits: hydrolysis yield potential (HYP) and crystallinity index (CI). CI model variables included tissue type, ash and lignin. HYP model variables included tissue type, ash, cellulose and volatile matter. The presence of ash content in all models was a salient finding of our study. Given that several models were able to predict HYP and CI in alternate grow‐out years, these models may be useful in selective breeding programmes aimed at sorghum bioenergy feedstock improvement through increased conversion efficiency.     

Effects on the benthic fauna of embanking an intertidal flat area (the Markiezaat,Eastern Scheldt estuary,The Netherlands)

Effects of embanking an intertidal-flat area in the south-western part of the Netherlands, the Markiezaat, on abundance and condition of benthic animals were followed at 3 stations during spring, 1983. Part of the former intertidal flats became permanently submerged with stagnant salt water, whereas another part became permanently emerged.At the submerged sampling station, no clear changes were found during the first 3 months of submersion. However, within 6 months, most species died off.At the drained stations, all individuals of most species died off within 2 months. During some preliminary experiments with drained sediment cores, a high mortality of the animals was reached within much shorter periods. During these experiments the animals showed a retarded mortality after they had been returned to a normal tidal cycle. Species living in the lower part of the intertidal zone were found to be less tolerant to drainage than those living in the higher part. The observed mortality rates in the Markiezaat probably represent minimal values, because of the heavy rainfall and the absence of extreme temperatures during drainage. At high (summer) and low (winter) temperature and low precipitation, benthic animals may be less tolerant to drainage.Neither permanent submersion nor emersion affected the condition determined as dry weight per unit of volume. Therefore, the suitability of this condition-index as an indicator of stress for intertidal benthic animals may be questioned.     

云南楚雄州双子叶植物区系特征分析

云南省楚雄州自然分布(少数几种为栽培)的双子叶植物有2939种(含种以下单位)，隶属170科914属。本文对其区系成分进行了统计分析，结果表明双子叶植物科的分布类型主要是以热带——亚热带分布型(41科，占24．18％)和热带——温带分布型(31科，占18．24％)为主。属的分布类型主要以泛热带分布型(243属，占26．59％)、东亚分布型(112属，占12．25％)和北温带分布型(94属，占10．28％)为主。楚雄州双子叶植物区系特征有以下显著特点：①植物种类丰富；②区系成分复杂、起源广泛；③热带、亚热带成分突出。