Source: Photo by author, April, Share link DOI :. Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website. Include Metadata Specify width in pixels leave blank for auto-width :. Our image viewer uses the IIIF 2. Ecology of salmonids in estuaries around the world : adaptations, habitats, and conservation [Book Supplement].
Levings, Colin D. UBC Press. For centuries, biologists have marvelled at how anadromous salmonids — fish that pass from rivers into oceans and back again — survive as they migrate between these two very different environments. Yet, relatively little is understood about what happens to salmonid species including salmon, steelhead, char, and trout in the estuaries where they make this transition from fresh to salt water. This book explains the critical role estuaries play in salmonid survival. Ecology of Salmonids in Estuaries around the World synthesizes information from a vast array of literature, to: describe the specific adaptation of eighteen anadromous salmonids in four genera Hucho, Oncorhynchus, Salmo, and Salvelinus ; explain the ecological relationships between anadromous salmonids, the fish they coexist with, and their estuarine habitat; discuss key fitness elements salmonids need for survival in estuaries including those relating to osmoregulation, growth and feeding mechanisms, and biotic interactions ; provide guidance on how to conduct estuarine sampling and scientific aspects of conservation, management, and recovery plans; offer directions for future research.
This critical reference is further enhanced by extensive supplementary appendices that are available to readers online, including data tables, additional references on estuarine salmonids, and a primer on estuaries and salmonids for citizen scientists. Vancouver : University of British Columbia Library. The lack of tides in the Baltic allows the stable salinity gradient to be mapped e.
A site may be classified into vastly different salinity bands depending on which criteria are used for salinity assessment e. A secondary aspect of the Remane model that has received some discussion is the position and cause of the species minimum, termed artenminimum e. In the original diagram this minimum falls between salinities of 5—8, which led to suggestions that hydrochemical characteristics at these salinities cause an ecophysiological barrier Khlebovich and thus are characterized by a minimum number of species Kinne , who termed this boundary the horohalinicum.
A further inconsistency apparent when attempting to apply the Remane diagram to estuaries is the location of sample site, i. Due to the minimal tidal movement in the Baltic, the original model was naturally constructed using all subtidal sites, whereas traditionally most work in estuaries has concentrated on intertidal mudflats.
Diversity trends plotted for estuaries therefore can have a combination of intertidal e.
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Application of the Remane model to estuaries assumes that sites in the same salinity regime will have similar levels of diversity, but this is not necessarily the case Fig. Consistency in sample location is therefore an important factor if trends are to be compared between estuaries. Comparison of mean subtidal solid bars and intertidal clear bars diversity for sites in the Thames estuary over the full salinity range, where sites have both subtidal and adjacent intertidal components. While the Remane diagram has many limitations in terms of its quantitative use in estuaries, it has persisted because, despite some criticism, no suitable alternative has been suggested.
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The aim of this paper therefore is to present an alternative model for diversity trends in estuaries that can be consistently applied. This will allow quantitative comparisons between estuaries and the testing of a priori hypotheses affecting estuarine diversity. Sites were located in both intertidal 12 sites and subtidal 16 sites regions, with a set of sites having both components.
Three to four replicates were obtained from each site, the sampling methodology being detailed by Attrill All macroinvertebrates in samples were identified to species and enumerated. Additionally, meiofauna samples were only obtained for the first year of the survey.
Linear regression methods were used to examine the significance of relationships between invertebrate diversity and selected environmental variables. Statistical assumptions of the technique include normally distributed residuals and homoscedastistic variances. Brackish water organisms exist at far lower salinities in the Baltic than in estuaries. The bivalve Macoma balthica L.
This is due to the contrasting environmental stresses affecting the organisms. Due to the stable salinity regime, the distribution of organisms in the Baltic tends to correspond closely to their lower lethal salinity limit McLusky ; in estuaries the fluctuating salinities and other associated parameters add a level of stress that prevents organisms maximizing their potential distribution Carriker The distribution of organisms within estuaries and thus diversity patterns are therefore influenced more highly by variation than by absolute salinity regimes Wolff A measure of environmental variability, particularly associated with the prime stressor of salinity, would therefore seem a more valid parameter to utilize in models of estuarine diversity.
The quadratic nature of the relationship is the inverse of the putative estuarine diversity trend Fig. Additionally, salinity range provides a good predictor of other stressors in the estuarine system, particularly particle size of the sediment Fig. Therefore, salinity range can be used as an analogue for a set of variable conditions within the estuary that may be influencing organisms at any particular point; it is not intended that salinity range alone is to be considered causative of any pattern observed.
Relationship between mean annual salinity range and percentage mud in the Thames estuary. A criticism of the Remane diagram was the poor definition of axes and sample location, so the construction of any model based on salinity range therefore requires a priori definition of terms. Only subtidal samples will be included to give consistency along the estuary, and allow comparison with river samples. The use of subtidal samples is also important in order to allow comparative consistency between sampled estuary water and interstitial water in contact with infauna.
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However, there is no evidence that this is the case for subtidal areas, Wolff , p. Robust models were also evident when the data were divided into individual seasons Fig. Similar significant trends were also apparent when the estuary was split into two, investigating the relationship from the point of maximum salinity range to both freshwater and fully marine conditions Fig. The model was also consistent for meiofaunal diversity Fig. Fitted regression lines and CIs as for Fig. Circles highlight points that fall below the lower CI, i.
Scattergram of data in Fig. Fitted regression lines as Fig. Additionally, a significant relationship was also evident for meiofaunal diversity, highlighting that the salinity range model is applicable to other components of the biota. The existence of a linear model will therefore allow diversity trends in estuaries to be compared statistically e. For example, Fig.
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The comparative responses of two different components of the biota can also be compared by assessing differences in the models for macroinvertebrates and meiofauna. The linear model also provides information on the possible causes of the estuarine species minimum artenminimum stated to be in salinities between 5 and 8 e. Kinne Certainly, the linear model provides a framework for future experimental work in estuaries, concentrating on salinity range, and that perhaps it is time to separate estuaries and other brackish water systems in terms of searching for general mechanisms controlling species diversity.
The linear model will also allow testing of a priori hypotheses about estuarine diversity and direct comparisons between systems. For example, it has been suggested that tropical estuaries are more diverse than temperate estuaries e. The significance of diversity differences can be tested using the linear model, allowing the development of scenarios on how differences in diversity could be expressed Fig. In scenario Fig. Similarly, scenarios for the putative impact of pollution on estuarine systems compared with unimpacted controls can be developed and tested.
The model could also provide a useful management tool for application within an estuarine system, enabling sites of concern to be highlighted.
In Fig. Further investigation reveals these to be sites in the southern, outer Thames estuary where a combination of sediment mobility due to circulation patterns and the deposition of decaying seagrass material decreases macroinvertebrate diversity Attrill It is interesting to note that the equivalent sites do not show the same pattern for meiofauna, suggesting a specific impact on the larger fauna consistent with such mechanical disturbance e.
Examples of an a priori scenario suitable for testing. A comparison of a tropical vs.
Analysis of data from the Thames estuary has highlighted the existence of a linear trend between species diversity and salinity range in this system, creating a testable model for use in other estuaries. However, it is clear that this suggested model now requires extensive testing and validating in order to determine whether this is a macroecological phenomenon or restricted in this form to the Thames. In particular, it will be interesting to test the model in estuaries with different levels of salinity range.
Due to the length of the Thames estuary, anthropogenic narrowing Tinsley and a comparatively large freshwater input the highest mean salinity range at any one point was rarely above 10; other estuaries with different morphological characteristics could exhibit much higher salinity ranges. The patterns for similar sets of species in estuaries with higher salinity ranges would be interesting and allow information to be generated on comparative responses of estuarine taxa to salinity variation.