Use of glacier river-fed estuary channels by juvenile Coho Salmon: transitional or rearing habitats?

Estuaries are among the most productive ecosystems in the world and provide important rearing environments for a variety of fish species. Though generally considered important transitional habitats for smolting salmon, little is known about the role that estuaries serve for rearing and the environmental conditions important for salmon. We illustrate how juvenile coho salmon Oncorhynchus kisutch use a glacial river-fed estuary based on examination of spatial and seasonal variability in patterns of abundance, fish size, age structure, condition, and local habitat use. Fish abundance was greater in deeper channels with cooler and less variable temperatures, and these habitats were consistently occupied throughout the season. Variability in channel depth and water temperature was negatively associated with fish abundance. Fish size was negatively related to site distance from the upper extent of the tidal influence, while fish condition did not relate to channel location within the estuary ecotone. Our work demonstrates the potential this glacially-fed estuary serves as both transitional and rearing habitat for juvenile coho salmon during smolt emigration to the ocean, and patterns of fish distribution within the estuary correspond to environmental conditions.     

Sea to sky: impacts of residual salmon-derived nutrients on estuarine breeding bird communities

Pacific salmon (Oncorhynchus spp.) returning to streams around the North Pacific Rim provide a nutrient subsidy to these ecosystems. While many species of animals feed directly on salmon carcasses each autumn, salmon-derived nutrients can also be stored in coastal habitats throughout the year. The effects of this storage legacy on vertebrates in other seasons are not well understood, especially in estuaries, which can receive a large portion of post-spawning salmon nutrients. We examine the effects of residual salmon-derived nutrients, forest habitats and landscape features on summer breeding birds in estuary forests. We compared models containing environmental variables and combined chum (Oncorhynchus keta) and pink (Oncorhynchus gorbuscha) salmon biomass to test predictions concerning bird density and diversity. We discovered that total bird, insectivore, golden-crowned kinglet and Pacific wren densities and Shannon's diversity in the summer were strongly predicted by salmon biomass in the autumn. For most metrics, this relationship approaches an asymptote beyond 40 000 kg of salmon biomass. Foliage height diversity, watershed catchment area and estuary area were also important predictors of avian communities. Our study suggests that the legacy of salmon nutrients influences breeding bird density and diversity in estuaries that vary across a wide gradient of spawning salmon biomass.     

Growth and condition of 0-group European flounder, Platichthys flesus as indicator of estuarine habitat quality

The purpose of this present study was to use the growth rates, RNA–DNA ratio and morphometric (Fulton’s K) condition indices measured on 0-group juveniles European flounder, as a means of comparing the quality of estuarine nursery habitats. The Seine estuary, heavily impacted by manmade modifications and one of the most contaminated in Europe, was compared to two smaller estuaries considered as clean (low domestic, agricultural and industrial effluents). Indicators of human disturbance (sediment chemical contaminants) as well as biotic data (macrobenthos abundances) were used to establish between-site differences in environmental quality. The abundance of macrobenthos (potential preys for juvenile) was high and not significantly different among the three estuaries confirming the important role played by estuaries as feeding grounds. Sediment metal concentrations (Cd, Cr, Cu, Pb, Zn) were significantly higher in the Seine than in the Canche and Authie estuaries. Otolith growth was closely related to somatic fish growth, and we used daily otolith increments from the previous 10 days before capture as an indicator of 0-group flounder recent growth (RG). RG did not vary significantly among flounders from the Canche and Authie estuaries and individuals from the Seine had slower RG. RNA–DNA ratio and K values were also significantly lower in individuals from the Seine compared to those of the Authie or the Canche. Pollution (e.g. metal contaminants) is the most likely cause of growth and condition differences among estuaries. The results of this study suggest that habitat-specific fish growth and condition are useful proxies for habitat quality since they integrate the effect of multiple environmental factors. Handling editor: P. Viaroli     

Foraging trip decisions by the streaked shearwater Calonectris leucomelas depend on both parental and chick state

Parents of albatross and shearwater species employ a dual foraging strategy, feeding their chicks quickly in repeated short trips and then restoring their own fuel reserves during longer trips. A decline in parental body condition is believed to trigger longer trips, but chick body condition and age may also play a role. To investigate these factors in the little-studied streaked shearwater Calonectris leucomelas, we monitored the nest attendance of 17 pairs on Mikura Island in 2005 using an automated identification system. We also monitored body mass changes and meal masses of 5 of the 17 pairs using an automated weighing system. Although the birds did not show a clear dual foraging pattern, trip duration varied widely from 1 to 15 days. On average, the birds fed chicks 67.6 g during nighttime meals at 2.74-day intervals. Since meal mass did not depend on trip duration, feeding efficiency (meal mass delivered per unit trip duration) decreased as trip duration increased. Parents accumulated more energy reserves when they took longer trips. Parents appeared likely to initiate longer trips when their body condition declined or chick body condition recovered.     

Building regional threat-based networks for estuaries in the Western United States

Estuaries are ecologically and economically valuable and have been highly degraded from both land and sea. Estuarine habitats in the coastal zone are under pressure from a range of human activities. In the United States and elsewhere, very few conservation plans focused on estuaries are regional in scope; fewer still address threats to estuary long term viability.We have compiled basic information about the spatial extent of threats to identify commonalities. To do this we classify estuaries into hierarchical networks that share similar threat characteristics using a spatial database (geodatabase) of threats to estuaries from land and sea in the western U.S. Our results show that very few estuaries in this region (16%) have no or minimal stresses from anthropogenic activity. Additionally, one quarter (25%) of all estuaries in this study have moderate levels of all threats. The small number of un-threatened estuaries is likely not representative of the ecological variability in the region and will require working to abate threats at others. We think the identification of these estuary groups can foster sharing best practices and coordination of conservation activities amongst estuaries in any geography.     

Using new electrofishing technology to amp‐up fish sampling in estuarine habitats

A prototype, boat‐mounted electrofisher capable of operation in estuarine waters (where electrical conductivities often exceed 20 000 µS cm^?1) was assessed. Electrofishing was compared to fyke and mesh netting in four riverine estuaries and to seining in a lagoonal estuary (consisting of a series of brackish coastal lakes separated from the sea by a barrier system of sand dunes). Fish assemblage composition, length distributions and the probability of detecting ecological fish guilds (relating to estuary use, position in the water column and body size) were compared among gears. The assemblage composition of electrofishing samples differed from those of fyke nets in all riverine estuaries and from mesh netting in two. The assemblage composition of electrofishing samples differed from those of seining in structured seagrass habitats of the lagoonal estuary. When all species were pooled, the electrofisher sampled a broader range of lengths than either fyke or mesh netting in riverine estuaries or seining in lagoonal estuaries. The bias of electrofishing and netting towards particular species and size classes affected the probability of detecting some ecological guilds, highlighting the potential implications of gear choice on understanding estuarine ecological function. The detection of guilds varied with gear type and environmental conditions, including stratification, water depth and surface electrical conductivity. Assessments with the aim to characterize the structure of fish assemblages will benefit from the use of multiple gears. Electrofishing shows immense promise for discretely sampling highly structured habitats to test hypotheses about their use.     

Does the foraging strategy of adult Short‐tailed Shearwaters cause obesity in their chicks?

The chick provisioning behaviour of Short-tailed Shearwaters Puffinus tenuirostris breeding at the northern edge of their distribution on Montague Island, New South Wales, was examined in February and March 1997. The duration of individual foraging trips of parents, weight changes of adults and chicks, and meal sizes delivered to chicks were determined. It was found that individual parents mixed a long foraging trip to Antarctic waters (14.4±2.0 days) with one to three short foraging trips (1.36±0.7 days, mode=1 day). Adults gained body mass on long trips and lost weight on short trips. The size of meals fed to the chicks was significantly greater after a long trip (161±21 g) than after a short trip (135±28 g), although short trips increased the overall chick feeding frequency. The variable number of short trips made by adult Short-tailed Shearwaters and the relationship between short trips and adult body condition were consistent with current life-history theory: adults do not sacrifice their own body condition to increase food delivered to their chicks.
Modelling revealed that this dual foraging strategy inevitable leads to chicks enduring long intervals between meals. These long intervals may have led to the evolution of an over-feeding strategy by parents and the nestling obesity reported in this shearwater. The durations of the long trips from Montague Island were significantly greater than those for Short-tailed Shearwaters breeding at the centre of their distribution in Tasmania, although there was no significant difference in the length of short trips. A commitment to feed regularly in Antarctic waters may explain why the breeding distribution of this species does not extend much further north.     

Variation Among Four Health Indices in Natural Populations of the Estuarine Fish, Fundulus heteroclitus (Pisces, Cyprinodontidae), from Five Geographically Proximate Estuaries

Variation among four commonly used health indices was examined in the mummichog, Fundulus heteroclitus. The four indices were liver glycogen content (LGC), liver-somatic index (LSI), condition index (K) and RNA–DNA ratio. Fish were collected from five coastal locations in southeastern Connecticut. Fish health, as determined by these four indices, varied considerably among estuaries and between sexes. The relationship between each index and specimen length was significantly different among estuaries for either sex. When regressed against length, the slopes for the indices ranged from positive to negative. For each index, significant differences existed among some of the length-centered means at each estuary for either sex. Estuary rank for one index did not necessarily correlate with the estuary rank for another index. The significance of this variability and its impact on the use of the indices as bioindicators of environmental perturbation is discussed.     

Insect community organisation in estuaries: the role of the physical environment

Insects are reportedly uncommon in marine habitats and, from a spatial/temporal intercomparison perspective, estuaries are among the least studied. We examined the natural variability seen among insect community organisation in estuaries on both sides of the North Atlantic, and evaluated the role of their physical environments. Community composition was found to be strongly influenced by three physical factors: estuary size, the degree of inundation by incoming tides, and substrate size/stability. Insects formed a significant proportion (17–54%, by numbers) of the benthic community of coarse-grained-substratum estuaries, and species richness increased with estuary size. Nymphs/larvae of mayflies, stoneflies, caddisflies, elmid beetles and chironomids dominated channel sites inundated by up to 25% of all incoming tides, but a gradual loss in species richness occurred downstream. However, even the most seaward sites supported high insect densities (up to 25 016 and 5433 m⁻², supporting 26 and 4 species, at sites inundated by 75 and 100% of all incoming tides, respectively). Sites covered by tides for between 3 and 5 h twice daily were dominated by orthocladine chironomids, especially of the genus Orthocladius . Chironomid larvae contribute significantly to the diets of some coastal fish species, particularly juvenile flounder and sticklebacks. We present a schematic model summarising the relationships between estuary size, degree of inundation by salt water and insect community structure.     

Assessing the likely responses by fishes to stream bank rehabilitation in a large,urban estuary

Urban streams are under increasing threat from anthropogenic disturbances that alter their biological, chemical and physical characteristics. To attempt to repair the negative consequences of urbanization, management activities are commonly implemented with the aim of rehabilitating or restoring habitats. However, subsequent monitoring of these efforts is often done poorly or not at all. The setting of goals for these projects is also hindered by a lack of knowledge about the likely size of any potential response, and also the scope for undertaking activities at sufficient scales to override the likely larger‐scale effects of urbanization. In this study, we completed a series of surveys in a large, urban estuary to generate information that can be used to assess the likely responses of fish to management activities aimed at rehabilitating estuary bank habitats. Initially, we mapped the banks of the estuary to describe the distribution of different potential habitat types for fishes. Surveys were then carried out to assess associations between fish and these habitats, with a view to providing an indication of the likely effect size that management works might produce. We then initiated a BACI (Before‐After Control‐Impact)‐style monitoring design around management works aimed at stabilizing the banks of the estuary and increasing habitat complexity for fishes (the installation of coir logs and planting of native rushes). Power analyses based on the effect sizes and estimates of variability from our initial survey and subsequent monitoring respectively indicate that only large magnitude responses will be detectable. However, these are likely to be constrained by the influence of the larger‐scale effects of urbanization. Even if localized responses occur, wider‐scale manipulations to fish habitat in large urban estuaries are likely to be limited by a range of logistical, social and financial constraints that govern the scale and location of management activities.     

The feeding ecology and relative abundance of mullet (Mugilidae) in Natal and Pondoland estuaries

An investigation of the feeding ecology of Mugilidae in Natal and Pondoland estuaries showed that although the diet of the eleven species is similar it varies from one estuary to another and is determined largely by the occurrence of particular food items on substrates of the preferred particle size of each species. The findings of this study support the conclusions reached by Blaber (1976) with regard to the partitioning of the food resource according to inorganic particle size. Particle sizes consumed by each species do not remain the same but vary according to locality. Within any one estuary the mullet species avoid interspecific competition by selecting particles of different sizes. The fish are always graded in the same order with regard to particle size. The relative abundance of the various species of mullet in Natal and Pondoland estuaries is probably not controlled by food or substrate requirements because most species are sufficiently flexible in their feeding ecology to cope with a wide variety of estuarine substrates.     

Spatial and temporal variation in the provisioning behaviour of female rockhopper penguins Eudyptes chrysocome filholi

As seabirds are central place foragers during breeding, their provisioning behaviour and their ability to face variable energy demand from the chicks is expected to vary with environmental conditions. The provisioning behaviour of female rockhopper penguins Eudyptes chrysocome filholi was recorded over the chick‐rearing period at Kerguelen (KER) and Crozet (CRO) archipelagoes (two very distinct marine environments), using time‐depth recorders, or VHF transmitters coupled with an automatic recording station. No influences of the method have been found on the average foraging trip durations. Some previously undescribed short and multiple trips within a day were recorded using the automatic recording system. These multiple trips (6.8 h) were mostly performed with <5 days old chicks, a period during which feeding rates were the highest (1.1 meals per day), at both sites. During the brooding period, both KER and CRO females mainly performed daily trips of increasing duration (2 h longer at CRO) and at decreasing frequency. During the crèche compared to the brooding period, females from KER performed slightly fewer daily trips (0.6 per day) and more (<3 days) overnight trips, while females from CRO performed very few daily trips (0.1 per day) and more overnight trips, some of them being long trips lasting 5 to 29 days, mostly initiated during the transition between the brooding and the crèche periods. The result fit the hypothesis that long trips permit females to restore and/or maintain their body condition at more distant foraging places. It seemed that chick developement during the brooding period and environmental factors during the crèche period conditioned trip duration of females. Due to more long trips at CRO, the female feeding frequency was twice as high at KER than at CRO during the crèche period, while males participated in the feeding duties. Based on differences in female behaviour, we hypothesize that the male's contribution is likely to differ strongly from one site to another, and may buffer the possible decrease in female feeding frequency by feeding the chicks if food is less abundant.     

Characteristics of the ichthyofaunas of southwestern Australian estuaries,including comparisons with holarctic estuaries and estuaries elsewhere in temperate Australia: A review

Data on the species compositions and the ages, sizes, reproductive biology, habitats and diets of the main species in the ichthyofaunas of seven estuaries in temperate southwestern Australia have been collated. Twenty-two species spawn in these estuaries, of which 21 complete their lifecycles in the estuary. The latter group, which includes several species of atherinids and gobies with short lifecycles, make far greater contributions to the total numbers of fish in the shallows of these estuaries than in those of holarctic estuaries, such as the Severn Estuary in the United Kingdom. This is presumably related in part to far less extreme tidal water movements and the maintenance of relatively high salinities during the dry summers, and thus to more favourable conditions for spawning and larval development. However, since estuaries in southwestern Australia have tended to become closed for periods, there would presumably also have been selection pressures in favour of any members of marine species that were able to spawn in an estuary when that estuary became landlocked. Furthermore, the deep saline waters, under the marked haloclines that form in certain regions during heavy freshwater discharge in winter, act as refugia for certain estuarine species. The contributions of estuarine-spawning species to total fish numbers in the shallows varied markedly from 33 or 34% in two permanently open estuaries to ≥ 95% in an intermittently open estuary, a seasonally closed estuary and a permanently open estuary on the south coast, in which recruitment of the 0 + age class of marine species was poor. The larger estuarine species can live for several years and reach total lengths of ~ 700 mm and some estuarine species move out into deeper waters as they increase in size. Several marine species use southwestern Australian estuaries as nursery areas for protracted periods. However, sudden, marked increases in freshwater discharge in winter and resultant precipitous declines in salinity in the shallows, and in other regions where haloclines are not formed, are frequently accompanied by rapid and pronounced changes in ichthyofaunal composition, partly due to the emigration of certain marine species. In contrast, the ichthyofaunal compositions of macrotidal holarctic estuaries undergo annual, cyclical changes, due largely to the sequential entry of the juveniles of different marine species for short periods. The ichthyofaunal compositions of the narrow entrance channels, wide basins and saline riverine reaches of large, permanently open southwestern Australian estuaries vary, reflecting the marked tendency for some species to be restricted mainly to one or two of these regions. Comparative data indicate that the characteristics determined for ichthyofaunas in southwestern Australian estuaries apply in general to estuaries elsewhere in temperate Australia.     

Fish assemblages associated with urban structures and natural reefs in Sydney,Australia

Abstract Fish ecology in urban estuaries is poorly understood. As coastal landscapes are transformed, recognizing the impact that urban structures, such as marinas, seawalls and wharfs, have on local fish populations is becoming increasingly important. The extent to which fish are able to maintain natural ecological assemblages can be measured, to a certain extent, by how closely they mimic natural habitats. In Sydney Harbour, assemblages of fish associated with artificial structures were compared with those associated with natural rocky reefs. Sampling was carried out in five locations, each with a marina, swimming enclosure and natural reef. In each location, different habitats supported different assemblages, but differences between habitats were not consistent among locations. Subsequent sampling compared artificial and natural sites in three different areas in each of three different estuaries. Results indicated that differences in fish assemblages between artificial and natural sites were greater than differences between sites within each habitat, but there were no patterns among different positions in an estuary or from estuary to estuary. This study provides initial evidence that, although artificial habitats generally support the same species as found on natural reefs, assemblages usually differed between natural and artificial habitats. In addition, without knowing if these habitats do, in fact, sustain viable populations of fish, it would be premature to label artificial structures as effective habitat for fish.     

河口生态系统氨氧化菌生态学研究进展

由amoA基因编码的氨单加氧酶(AMO)所调控的氨氧化作用,是硝化作用的限速步骤和中心环节,而含有amoA基因的氨氧化细菌(AOB)和氨氧化古菌(AOA)多样性与环境因子关系密切,对缓解河口生态系统因人类活动造成的富营养化等环境问题具有特别重要的意义。水、陆和海交汇形成高度变异的具环境因子梯度的河口生态系统,是研究AOA和AOB生态学的天然实验室。河口AOA与AOB的群落组成、丰富度特征和生物有效性,与河口主要环境因子盐度、富营养化程度、植被、温度、碳、氮、硫、铁等,尤其是对盐度和富营养化有着较为强烈的响应。AOA和AOB多样性变化规律及其与河口特有的环境因子之间的相关性,应当是今后我国河口氨氧化菌研究的方向和重点。包括:(1)建立有效的氨氧化菌活性评价方法;(2)研究AOA的同化作用方式;(3)依据氨氧化菌分类和组成对河口环境变化的适应进化机制,建议可作为指示河口环境质量变化的生物标记;(4)将传统的分离培养方法与现代分子生物学研究方法相结合,筛选我国河口高效的氨氧化菌,并将其应用于生产。     

Post-settlement migratory behaviour and growth-related costs in two diadromous fish species, Galaxias maculatus and Galaxias brevipinnis

The physiological challenges incurred during the transition from sea to fresh water and the constraints they place on the rate at which the common galaxiid Galaxias maculatus and the climbing galaxiid Galaxias brevipinnis can migrate from marine to freshwater habitats were examined. The duration of the marine to freshwater transition, the relationship between post-settlement age (PSA) and standard length ( L _S) as a proxy for energetic costs incurred during settlement and the potential effects of estuary geomorphology on migratory behaviour was investigated. Rate of upstream migration after settlement was not uniform. Upstream migration rate was slowest directly after settlement and increased with increasing PSA and distance from the river mouth, indicating a delay in upstream migration by newly recruited galaxiids. L _s did not increase with age, at least within the first 21 days post settlement. These patterns were consistent for both species, in spite of differences in their life histories, across the recruitment season, despite seasonal variation in recruit size, and among estuaries with different properties. The results suggest that the timing and speed of migratory behaviour primarily reflect physiological constraints. Given the duration of residency of these species in estuaries, this study indicates that estuaries are critical transitional habitats for diadromous fishes during their migration from marine to freshwater habitats.     

The potential for mitten crab Eriocheir sinensis H. Milne Edwards, 1853 (Crustacea: Brachyura) invasion of Pacific Northwest and Alaskan Estuaries

Eriocheir sinensis H. Milne Edwards, 1853 is on the list of top 100 invaders compiled by the International Union for Conservation of Nature and Natural Resources. The recent establishment of a large Chinese mitten crab population in San Francisco Bay and the potential for introductions from California, Asia and Europe pose a significant invasion potential for estuaries and rivers from California to Alaska. This alien species would place at risk the catchment areas of the Pacific Northwest including the economic and social activities that depend upon intact aquatic systems. An analysis of ecological conditions that define the mitten crab’s native and introduced range suggests that large stable estuaries with long flushing times are necessary to sustain significant populations. Most Pacific Northwest estuaries have limited salinity intrusion, estuarine habitat and short flushing times and face a reduced risk of population establishment. Large, stable estuaries, such as the Puget Sound, may support significant populations. River-dominated estuaries, such as the Columbia River, have flushing times less than the duration of larval development and wouldn’t support populations. An application of a temperature based larval development rate to near-shore and estuary sea surface temperatures suggests that estuaries in Oregon and Washington have sufficient thermal regimes to support larval development. Most estuary systems in Alaska have limited periods where water temperatures are above the mortality threshold for the larval stages and are at a low risk for the establishment of populations. A potential sea temperature rise of two degrees Celsius would permit larval development in Alaskan estuaries, where sufficient estuarine and freshwater habitats exist.     

Zonation of intertidal macrobenthos in the estuaries of Schelde and Ems

Based on data, collected in 1980–1990, the intertidal benthic macrofauna of the Schelde and Ems estuaries was compared. The spatial occurrence of the benthic macrofauna along the salinity gradient, including the freshwater tidal area was emphasized. Both estuaries appeared to have a very similar species composition, especially at genus level. The higher number of species observed in the Schelde estuary was probably due to a greater habitat diversity. In both estuaries species diversity decreased with distance upstream. The total density did not vary along the estuarine gradient, whereas biomass is highest in the polyhaline zone.In both estuaries distinct intertidal benthic communities were observed along the salinity gradient: a marine community in the polyhaline zone, a brackish community in the mesohaline zone, and a third community in the oligohaline and freshwater tidal zones of the estuary. These three communities were very similar between both estuaries. Their main characteristics were discussed together with the occurrence and distribution of the dominant species.For the Schelde estuary and to a lesser extent also for the Ems estuary, there was evidence that anthropogenic stress had a negative effect on the intertidal macrobenthic communities of the oligohaline/freshwater tidal zone. Only Oligochaeta were dominating, whereas the very euryhaline and/or true limnetic species were missing. In the mesohaline zone, the Schelde estuary was dominated by large numbers of short-living, opportunistic species, whereas in the Ems estuary relatively more stable macrobenthic communities were observed. A comparison with some other European estuaries showed in general similar trends as those observed for the Schelde and Ems estuaries.     

Fish species diversity in southern African estuarine systems: an evolutionary perspective

Synopsis The ichthyofauna of southern African estuaries consists primarily of juvenile marine species that use these habitats as nursery areas. The abundance and biomass of fishes in estuarine systems are typically high but species diversity is generally low, with only a few taxa dominating the community. This relatively low species diversity is attributed to the fact that estuaries in the region are unpredictable environments which lack any degree of permanence and are dominated by mobile marine eurytopes. Although stenotopes, represented mainly by small resident species from the families Gobiidae, Clinidae and Syngnathidae, are present in southern African estuaries, little speciation appears to have occurred. A possible reason for this lack of speciation, apart from the seasonal and annual variability of the abiotic environment, is that the lifetime of individual systems is usually limited to a few thousand years. In addition, fishes utilising southern African estuaries need to remain flexible (eurytopic) in their responses to an external environment which is unlikely to become more stable in the future. Thus the lack of permanence and fluctuating nature of southern African estuaries on both a spatial and temporal scale, together with the dominance of eurytopes in these systems, does not favour the evolution of new species. A preliminary examination of the available literature indicates that a detailed review of estuarine ichthyofaunal communities on a global basis will probably mirror the trends outlined above, and reveal a domination of these dynamic ecosystems by eurytopic taxa with low speciation potential.