Estuary Types Research Articles

Estuarine geomorphology and low salinity requirement for fertilisation influence spawning site location in the diadromous fish, Galaxias maculatus

In habitats such as estuaries, which are characterised by large and fluctuating gradients in abiotic variables, finding appropriate habitat for successful spawning and egg development can be critical to a species’ survival. We explored how salinity requirements for successful fertilisation may govern the distribution of estuarine spawning habitat for the diadromous fish, Galaxias maculatus, which spawns in inundated vegetation on estuary banks during spring tides. Artificial fertilisation experiments confirmed that successful fertilisation only occurs at low salinities (<20). Thus, we predicted that egg distributions would depend upon the extent of low-salinity surface waters in an estuary. Using estuary geomorphology classification schemes, which classify estuaries by physical and chemical characteristics such as their salinity dynamics, we hypothesised that stratified estuaries would provide a greater extent of low salinity surface water than well-mixed estuaries. This prediction was supported by surveys of egg distributions in five estuaries in Victoria, Australia. Eggs were distributed over a greater proportion of ‘stratified’ v. ‘mixed’ estuary types. We suggest that combining knowledge of the spawning requirements of a species and physical properties of the habitat, such as those encapsulated in estuary geomorphic classification schemes, can greatly facilitate efforts to identify critical habitats and thus aid in species management and conservation.

Tidal Circulation and Salinity Distribution in the Mandovi and Zuari Estuaries: Case Study

The Mandovi and Zuari are two tropical estuaries along the west coast of India, characterized by mixed tides with semi-diurnal dominance and heavy fresh water influx during the southwest monsoon (June to September). Previous observations of tides in these estuaries show that the tidal effects in the upstream regions are subject to decay due to freshwater influx during the southwest monsoon. The longitudinal distribution of salinity in these estuaries undergoes large variations between the southwest monsoon and the dry season (February to May). The main objectives of the present study were to simulate the tidal circulation, the longitudinal distribution of salinity and the freshwater influence on tides and the salinity distribution. Another objective was to study the intra-seasonal variations of salinity during the breaks in the southwest monsoon. A hybrid network numerical model was used for the present study to simulate the tidal circulation and the salinity distribution in these estuaries. The model reproduced observed tides accurately during the dry and wet seasons. The model could reproduce the longitudinal distribution of salinity well during the dry season and the simulation of salinity distribution was reasonably well during the wet season. The simulated tidally-averaged salinities over the M2 tidal period for varying river discharges show that even a small freshwater influx can affect the longitudinal distribution of salinity to a great extent in this type of estuaries.

On the prediction of long-term morphodynamic response of estuarine systems to sea level rise and human interference

The long-term morphodynamic response of estuarine systems to sea level rise and human interference has been studied using a Boolean network approach. The method uses Boolean variables to represent the different elements of the estuarine system, their inter-relationships and the external forcing. The response of a variable to a given change can be deduced from the corresponding Boolean function, which describes the feedbacks between that particular variable and the others in the network. This approach provides qualitative insights into the behaviour of estuary systems without the need for a detailed and quantitative specification of linkages between the various components of the system. Three types of estuaries: glacial valley, drowned river valley and drowned coastal plain are analysed and the results are compared. These estuary types are different in their origin and also have different characteristics due to the geomorphological elements present in each. Human interference, in the form of construction and dredging, has also been considered. An analysis of estuary systems shows that the nature of long-term morphodynamical response to sea level rise depends on the type of estuary and the availability of external sediment to meet the increasing sediment demand within the system. If the estuary has an abundant influx of external sediment on a continuous basis, then the estuary is able to maintain its geomorphology and reach a stable state. In the absence of adequate supply of external sediment, some of the prominent features such as salt marshes and spits are likely to recede or disappear altogether during the process of morphological evolution against sea level rise. Our analysis also suggests that the moderate human interference in the form of dredging and structural construction does not have a significant impact on the overall geomorphology of estuaries in the long-term. However, changes in intermediate evolutionary states can occur in response to such intervention, thereby showing short-to-medium term impacts on estuary systems.

Zooplankton in different types of estuaries (using Curonian and Vistula estuaries as an example)

Based upon the results of long-term monitoring of zooplankton in the Curonian and Vistula estuaries carried out by the author, specific features of the structure and functioning of the zooplankton communities are studied. It is shown that the zooplankton communities in the open (Vistula Bay) and closed (Curonina Bay) types of estuaries differ in the species structures, numbers, biomasses, and functioning. The similarity of the zooplankton communities of these estuaries has to do with the commonness of their trophic structure. The zooplankton community in the Vistula estuary is more affected by the gradient of abiotic factors than the Curonian bay community. The mechanism providing the stability of the zooplankton communities in the open-type estuaries is the energy flow through the omnivorous species and the increase in the number of facultative predators at the terminal links of the trophic chain. It is shown that the Vistula estuary zooplankton community has a higher specific productivity rate and a higher rate of its circulation and use.

Comparison of material fluxes based on observations in different types of estuaries including mangrove area

Comparison of material fluxes based on observations in different types of estuaries including mangrove area

Using multiple ecosystem components, in assessing ecological status in Spanish (Basque Country) Atlantic marine waters

The European Water Framework and Marine Strategy Directives relate to the assessment of ecological quality, within estuarine and coastal systems. This legislation requires quality to be defined in an integrative way, using several biological elements (phytoplankton, benthos, algae, phanerogams, and fishes), together with physico-chemical elements (including pollutants). This contribution describes a methodology that integrates all of this information into a unique quality assessment for 51 stations from 18 water bodies, within the Basque Country. These water bodies are distributed into four typologies, including soft-bottom coastal areas and three types of estuaries. For each station, decision trees were used to integrate (i) water, sediment and biomonitor chemical data to achieve an integrated physico-chemical assessment and (ii) multiple biological ecosystem elements into an integrated biological assessment. Depending on the availability of ecological quality ratios or global quality values, different integration schemes were used to combine station assessments into water body assessments on a single scale. Several examples from each element have been selected, to illustrate their responses to different pressures; likewise, to establish how the assessed integrated quality has changed, over time. The results made biological and ecological sense and physico-chemical improvements were often correlated with improvements in the quality of benthos and fishes. These tools permit policy makers and managers to take decisions, based upon scientific knowledge, in water management, regarding the mitigation of human pressures and associated recovery processes.

Geographical and typological changes in fish guilds of South African estuaries

A comparative analysis of fish estuary association guilds was undertaken on some 190 South African estuaries. This pioneering study spanned three zoogeographic regions and included three broad estuarine types. The guild compositions of the estuaries were compared based on an importance value, incorporating taxonomic composition, numerical abundance and relative biomass. Multivariate analyses included both inter‐regional (zoogeographic) and intra‐regional (estuarine typology) comparisons. The major estuary‐associated guilds (estuarine species and marine migrant species) were important in all estuary types within all biogeographic regions. Significant differences both between regions and between estuary types within regions, however, were recorded. Cool–temperate estuaries were generally dominated by migratory species (estuarine migrants and marine migrant opportunists) while the importance of species dependent on estuaries (estuarine residents and estuarine‐dependent marine migrants) was higher in warm–temperate and subtropical regions. The significance of estuarine nursery areas, particularly in regions where estuaries are few in number, is highlighted. In terms of typology, migratory species assumed a greater importance in predominantly open systems, while freshwater and estuarine‐resident species were more important in predominantly closed systems. Predominantly closed estuaries, however, were also important for marine migrant species, which further highlights the significance of these systems as nursery areas for fishes.

Factors influencing the characteristics of the fish faunas in offshore, deeper waters of permanently-open, seasonally-open and normally-closed estuaries

This study explored the ways in which various factors influence the species compositions, species richness and catch rates of fishes in offshore, deeper waters of the basin and river regions of five estuaries, which are located along ca 400 km of the southern coastline of Western Australia and differ markedly in their physico-chemical characteristics. Gill netting seasonally for two years at sites in the basin and saline lower reaches of the main tributary of the seasonally-open Broke, Irwin and Wilson inlets, the permanently-open Oyster Harbour and the normally-closed Wellstead Estuary yielded 22,329 fishes representing 58 species. Overall, and irrespective of estuary type, the species compositions of the basins and rivers differed markedly. This was attributable to consistently greater abundances of Mugil cephalus, and usually also of Acanthopagrus butcheri, in the rivers of each estuary and to the restriction of a range of species largely to the basins. However, the compositions in the basins of the five estuaries varied markedly, reflecting differences in the extent and duration of the opening of the estuary mouth and/or whether extensive growths of macrophytes were present. Changes in the ichthyofaunal composition of the normally-closed Wellstead Estuary between the first and second years of the study were attributable, in particular, to the movement of two mugilid species into offshore waters as they increased in size. Cyclical changes in ichthyofaunal composition were conspicuous in both regions of the estuary that underwent the most pronounced seasonal variations in environmental conditions. In each estuary, species richness was greater in the basin than river, where salinities were more variable and fell to lower levels and were thus less conducive to the immigration of most marine species. Catch rates were least in Broke Inlet, which had the lowest primary productivity, and were particularly high in Wellstead Estuary, which is highly eutrophic. The results of this study emphasise that ichthyofaunal composition can vary greatly with region (basin vs river) in microtidal estuaries, a finding that is of direct relevance to managers as these systems are becoming increasingly degraded and yet still constitute important nursery areas for certain fish species and often support recreational and commercial fisheries.

Sedimentary facies of the Silurian tide-dominated paleo-estuary of the Tazhong area in the Tarim Basin

As the relative sea-level rose, a paleo-estuary was formed by the marine inundation of the braided river incised valley during the period of the lower sub-member of the upper member of the Kalpingtage. formation of the Silurian in the Tarim Basin, west China. Sandstone-mudstone rhythmite, tidal structures and bimodal cross-bedding are common in these deposits, indicating that tides played a significant role in generating the sedimentary structures and the estuary type was tide-dominated. Five depositional facies were grouped: tidal river, sandy and muddy subtidal flat, tidal flat, tidal bar, tidal channel on the basis of lithology, electric properties, rhythmicity, sedimentary structure, fossil and the contact relationship. The sediment distribution showing first fining seaward and subsequent coarsening seaward from head to mouth, implies the two sediment sources in the paleo-estuary. The paleo-estuary of the Tarim Basin is very different from other representative estuaries. The most important distinction is that there are two adjacent estuaries joined by tidal flat onshore and by sandy and muddy subtidal fl at in the sea at the same time, while the others only have one. So the Tazhong paleo-estuary shows a good architecture model for the tide-dominated estuary.

A Boolean Approach to Prediction of Long-Term Evolution of Estuary Morphology

Abstract A systems method based on a Boolean approach is used to predict medium- to long-term behaviour of estuary morphology. Boolean networks are formed for various types of generic estuaries by taking into account the feedback involved between various estuary elements and external forcing which drive morphological evolution. A logical framework is then developed, and the Boolean matrix is derived. Various different potential morphological evolutionary pathways are then selected from the Boolean matrix, analysed, and discussed. The Boolean method provides a complementary approach for qualitative modelling of complex estuary systems. The method was applied to the Ribble Estuary in northwest England, and the predictions from the Boolean approach were in very good qualitative agreement with the observed morphological evolution of the Ribble Estuary during the last 150 years.

Heterogeneity in intertidal fish fauna assemblages along the world’s longest mangrove area in northern Brazil

The first comparison of the intertidal fish fauna from three estuaries within the longest contiguous mangrove area of the world, in north Brazil, revealed a significant heterogeneity in the species composition and functional and ecological guilds with an increase of Tetraodontidae and Engraulidae and a decrease of Sciaenidae and Mugilidae towards the Amazon mouth. A classification of the mangrove estuaries to identify types of estuaries and coastal sectors is urgently required to provide a tool for regional management systems in order to improve research, monitoring and conservation of this unique mangrove ecosystem.

Water quality in South African temporarily open/closed estuaries: a conceptual model

Of the five types of estuaries found in South Africa, temporarily open/closed estuaries comprise approximately 70% of the total. This paper provides an overview and a simple conceptual model of the water quality features and characteristics of temporarily open/closed estuaries in South Africa. Available literature on estuaries in the warm- and cool-temperate biogeographic regions of South Africa was reviewed and assessed against this model. The structure and water quality characteristics of the estuaries considered supported the conceptual model under the three dominant mouth states: open, semi-open and closed. However, the scale and extent to which biogeochemical processes within estuaries influence water quality is still poorly understood and further research is required to improve understanding of these processes in temporarily open/closed estuaries.

Potential Natural Environments Based on Pedological Properties in the Coastal Conurbation of Subtropical Southeast Florida

Much of the coastal southeast Florida Peninsula is heavily urbanized, and many native environments have been destroyed or severely affected by urbanization. In an attempt to reconstruct potential natural environments, soil properties were used as a basis for recognizing prior landscapes. Pedological associations were adopted because they provided landscape features that were least modified by urbanization and they could be used as a unifying basis for categorization of native coastal environments. A geographic information system analysis ring was used for querying coverages for soil distribution patterns, vegetation, hydrology (drainage), topography, and geology. By simultaneously generalizing and recombining soil survey data, land use cover types, topography, and hydrology, it was possible to identify recurring patterns of soils, landforms, and vegetation. Results of this analysis produced 13 land systems with 25 subunits that included various types of lakebeds, tree islands, marshes, prairies, sloughs, sandplains, glades, marshlands, lagoons, estuaries, and beaches. The resulting map for potential natural environments in Palm Beach and Broward Counties complements conceptual ecological models for the Greater Florida Everglades Ecosystem, developed for the Comprehensive Everglades Restoration Plan. The Australian land systems approach, as applied in this study, provides insight into coastal environments that lie outside of ecological models for mostly protected areas inland.

Application of a multimetric fish index to assess the environmental condition of South African estuaries

A multimetric fish index, the Estuarine Fish Community Index (EFCI) of Harrison and Whitfield (2004), was applied to data collected for 190 South African estuaries. Estuaries spanned three biogeographic regions and included three distinct estuarine typologies. The EFCI is based on 14 metrics or measures that represent four broad fish community attributes: species diversity and composition, species abundance, nursery function, and trophic integrity. Metric reference conditions and scoring criteria were developed separately for each estuary type within each zoogeographic region. The final EFCI was applied to each estuary by comparing its fish community with the appropriate reference. Index values ranged between 18 (very poor) and 66 (very good). A comparison of the EFCI with independent measures of estuarine condition revealed that the index was able to effectively differentiate between poor and good quality sites. Applying the EFCI to estuaries in which multiple samples were taken also showed that the index is reproducible. The EFCI is both a robust and sensitive method for assessing the ecological condition of estuarine systems; it is also an effective communication tool for converting ecological information into an easily understood format for managers, policy makers, and the general public.

Using attached macroalgae to assess ecological status of British estuaries for the European Water Framework Directive

The EC Water Framework Directive requires that ecological quality be assessed in transitional waters using the abundance and species composition of macroalgae. In estuaries, which form the majority of transitional waters, species composition is not a suitable measure. This arises from two features: (i) there is a continuous, natural change in species composition along the gradient of estuarine conditions which makes it difficult to know where within an estuary the species composition should be assessed, (ii) the inner estuarine macroalgal community of mat-forming species is very tolerant to both natural and anthropogenic stress and species poor which makes it insensitive to environmental variations in terms of species composition. An alternative feature is proposed based on the extent of upstream penetration of perennial fucoid algae. This proposal is founded on a series of case studies of the changes in fucoid limits, within a number of estuaries in the British Isles, consequent upon changes in pollution status over the last three decades. This also has to take into account variations of fucoid penetration owing to natural factors such as range of salinity variation and turbidity. The abundance criterion is taken to mean the absence of macroalgal blooms or “green tides”, because general abundance of species is hard to quantify meaningfully in the upper estuarine mat-forming species and in the lower estuary is subject to great variation owing to the physical variability of estuary types.

Description and ecology of larvae of Glossogobius callidus and Redigobius dewaali (Gobiidae) from temperate South African estuaries

This paper describes the morphology and ecology of the larvae and early juveniles of two common gobiids in warm temperate South African estuaries. The early developmental stages of Glossogobius callidus and Redigobius dewaali were collected during plankton surveys in seven permanently open and five intermittently open estuaries along southeastern South Africa. Larval G. callidus have a characteristic ventral row of pigment that extends from the cleithral symphysis along the ventral midline of the tail to the end of the caudal peduncle; notochord flexion takes place at the yolk-sac stage, between 3 and 4 mm BL. Larval R. dewaali are characterized by having two very large stellate melanophores on the ventral surface of the trunk and tail, and internal pigment between the snout and hindgut; notochord flexion takes place between 4 and 6 mm. Body lengths at settlement for G. callidus and R. dewaali are 13 mm and 16 mm, respectively. G. callidus and R. dewaali dominate the larval gobiid catch in warm temperate estuaries. Estuary type and freshwater input played a defining role in the occurrence of larvae of these, often sympatric, species in temperate estuaries. Larval G. callidus occurred in both permanently open and intermittently open estuaries, and were most abundant in mesohaline regions over the spring/summer period. By contrast, larval R. dewaali occurred exclusively in permanently open estuaries and were more prevalent in the fresh and oligohaline regions in autumn. Larvae of both species were more prevalent in freshwater-rich estuaries. Densities of G. callidus and R. dewaali peaked at 101 and 3829 larvae per 100 m3respectively. The usefulness of using the early stages of these gobiids as indicators of estuarine health based on their specific and often prolific estuarine occurrence is discussed.

Predicting macrofaunal species distributions in estuarine gradients using logistic regression and classification systems

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 316:69-83 (2006) - doi:10.3354/meps316069 Predicting macrofaunal species distributions in estuarine gradients using logistic regression and classification systems J. Ellis1,*, T. Ysebaert2, T. Hume3, A. Norkko3, T. Bult4, P. Herman2, S. Thrush3, J. Oldman3 1Crydium Group Ltd, 10 Linden Place, St John’s, Newfoundland A1B 2S8, Canada 2Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, PO Box 140, 4400 AC Yerseke, The Netherlands 3National Institute of Water and Atmospheric Research, PO Box 11-115, Hamilton, New Zealand 4Netherlands Institute for Fisheries Research, PO Box 68 1970 AB, IJmuiden, The Netherlands *Email: jellis.ca@gmail.com ABSTRACT: There is a growing need to predict ecological responses to long-term habitat change. However, statistical models for marine soft-substratum ecosystems are limited, and consequently there is a need for the development of such models. In order to assess the utility of statistical modelling approaches for predicting likely changes in species distributions under varying environmental conditions, we tested the utility of logistic modelling and classification approaches. We successfully developed models relating the presence/absence of common intertidal macrofauna to changing environmental variables such as sediment characteristics, depth/elevation, tidal currents and wind-wave (i.e. wind-generated wave activity) disturbance. The final model for each species contained between 1 and 6 variables, where the percentage correctly predicted was moderate to high, ranging from 59 to 97%. We were also able to identify relationships between higher level variables such as estuary type, basin morphometry and catchment-draining processes in driving macrobenthic community composition; however, we were unable to fully test the utility of the classification approach due to differences in the scale at which the macrobenthic data was collected and the scale of the higher level physical variables. These models were developed and tested using data that covered a range of environmental conditions in 5 estuaries in New Zealand. Such broad-scale statistical models play a critical role in our understanding of the likely effects of large-scale habitat change. However, a greater understanding of the fine-scale mechanistic controls on species distributions such as life-history characteristics, density information and biotic interactions would potentially lead to the development of more sensitive models. KEY WORDS: Logistic regression · Statistical modelling · Classification systems · Benthic macrofauna · Sedimentation · Estuary · Macroecology · New Zealand Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 316. Online publication date: July 03, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Estuarine Typology and the Structuring of Fish Communities in South Africa

Some 190 South African estuaries, covering all biogeographic provinces within the region, were classified into three types based on a combination of mouth condition and estuary size (surface area). The fish communities of the estuary types within each zoogeographic region were described and compared. Multivariate analyses revealed that each estuary type contained somewhat distinct fish communities. In addition, the study identified common patterns in species richness and ichthyofaunal composition. Open estuaries have relatively high species richness; this is a reflection of a permanent or near-permanent connection with the sea which allows access into these estuaries by all marine migrant species within the region. Intermittent connection with the sea limits the recruitment and utilisation of closed estuaries by marine migrant species; this results in reduced species richness in moderate to large closed estuaries. Small closed estuaries exhibit the lowest species richness and this is probably a result of their limited habitat and increased isolation from the sea. The key fishes that utilise estuaries could also be categorised into a number of groups based on their relative importance within each estuary type. Some species are largely restricted to predominantly open systems. Other taxa, while important in predominantly open estuaries, also occur in moderate to large closed systems. Some estuarine-associated species are well represented in all estuary types but exhibit a greater importance in closed estuaries. This study has shown that South African fish communities not only reflect estuarine typology but also respond to these differences in a consistent manner that spans all zoogeographic regions. The prevalence of similar patterns in other parts of the world suggests that estuarine typology is a major driver in the structuring of global estuarine fish communities.

Benthic macrofaunal communities in intermittent estuaries during a drought: Comparisons with permanently open estuaries

Drought conditions have prevailed in many areas of NSW since 2002. On the mid-north coast, below-average rainfall resulted in reduced riverine flows and the extended closure of intermittent estuaries within the Solitary Islands Marine Park. Patterns of structure of benthic infaunal communities were evaluated at the height of the drought to determine if they differed between closed, intermittent estuaries and permanently open estuaries within the region. Replicate van Veen grab samples were taken in the upper, mid- and lower reaches of six intermittent and three permanently open estuaries and sieved to retain the macrofauna. A range of physico-chemical measures was also taken at each sampling time. Multivariate analyses of assemblage data revealed a significant difference between the structure of the two estuary types and also among estuaries within each type. Differences between estuary types were attributable to small differences in the abundance of a number of taxa but also to the absence of the amphipod Urohaustorius metungi from most of the intermittent estuaries. In contrast, these small amphipods dominated communities in the lower reaches of the permanently open estuaries. Physico-chemical variables were highly variable among estuaries and were not strongly correlated with assemblage patterns. Correlations with catchment size were the strongest and, as most of the intermittent estuaries in the region are smaller than the permanently open estuaries, this confounds the interpretation of assemblage patterns in this preliminary study. In order to differentiate between the effects of catchment size and entrance status, the same estuaries need to be resurveyed during periods when at least some of the intermittent estuaries are open.

An Examination of Empirical Stability Relationships for UK Estuaries

The international data on tidal prism and cross-sectional area of tidal inlets and estuaries are examined as a basis for exploring the variability in the comparable UK data. The data are then used to evaluate the existing classification of estuary types; to present a number of relationships between the key bulk parameters of estuary volume, plan area, and cross-sectional area; and to test some theoretically derived relationships. The results suggest that the degree of Holocene sedimentation, and hence Holocene development, may explain much of the variability seen in the data, and this is not, as yet, fully accounted for in the theoretical relationships.