COMMENTS ON THE WATER QUALITY OF THE MHLATHUZE ESTUARY IN RELATION TO DETERMINING THE ECOLOGICAL INTEGRITY CLASS

Summary

Water quality forms an integral component of the determination of the Ecological Reserve of a water resource. This paper presents the available historical and current information on the water quality of the Mhlathuze estuary, The data were assessed in order to determine the forcing factors that characterise the water quality of Mhlathuze estuary. These factors were used in conjunction with a previously-developed water quality indexing system to assign a water quality integrity class to the Mhlathuze estuary. Three reaches of the estuary were classified as being largely natural with few modifications. Major issues relating to water quality data gaps were identified. By addressing these issues an integrity class could in future be assigned with greater confidence.     

ZOOPLANKTON OF THE MHLATHUZE (RICHARDS BAY) ESTUARY: AN OVERVIEW,WITH COMMENTS ON FRESHWATER REQUIREMENTS

Summary

The Mhlathuze estuary in its present form was established during construction of the Richards Bay harbour during the early 1970s. This paper summarises available data on the zooplankton community as part of a study on the freshwater requirements of the estuary. The zooplankton community indicates a strong marine influence. The large tidal exchange prevents the establishment of a stable estuarine zooplankton community. The possible influences of changes in freshwater input are discussed.     

INFLUENCE OF FRESHWATER FLOW REGIME ON FISH ASSEMBLAGES IN THE GREAT FISH RIVER AND ESTUARY

Summary

Two and a half years of data were collected from the lower Great Fish River, head region and estuary to determine the fish species composition within these areas. Gilchristella aestuaria, Liza dumerilii, Rhabdosargus holubi and Pomadasys commersonnii were the four most abundant species captured, with riverine flow rate having an important effect on both species composition and numbers of fishes in the different regions. Most marine species displayed a strong inverse relationship between catch per unit effort and elevated freshwater inputs. Euryhaline marine species dominated the catches at all sampling sites during low flows but were less common during high flow periods when catadromous species were most abundant. Based on the available evidence it is suggested that for most marine species in the river this decline in abundance is related to low conductivity levels following floods rather than avoidance of elevated flows. The impact of elevated suspensoid concentrations and lowered dissolved oxygen concentrations on freshwater and estuarine fish populations during major river flooding is also discussed.     

A COMMENT ON THE STATUS AND DISTRIBUTION OF THE GENUS PARATYLODIPLAX SERENE (BRACHYURA: OCYPODIDAE) IN SOUTHERN AFRICA

Summary

The ocypodid genus Paratylodiplax was described in 1974 and contains four species, three of which are endemic to southern Africa where they form an important component of the estuarine benthic fauna. However, very little is known about the biology and ecology of the genus, with discrepancies existing between the commonly quoted distributions and actual records of the species. This comment outlines the current taxonomic status of the genus and attempts to resolve the discrepancies in the distributions of the southern African species Paratylodiplax blephariskios has been recorded from the Morrumbene estuary in Mozambique to the Mngazana estuary in the eastern Cape, while the distributions of P. algoensis and P. edwardsii are given as being from the Mngazana to the Eerste estuary and Langebaan Lagoon in the western Cape respectively.     

THE STATE OF KNOWLEDGE OF WATER QUALITY AND MAJOR BIOTIC COMPONENTS OF THE MHLATHUZE ESTUARY

Summary

This note briefly introduces the concept of the Environmental Reserve of the New Water Act as well as the set of papers hereafter which deal with specific components of the ecology of the Mhlathuze Estuary. These were prepared for an Estuarine Flow Requirements study of the system. Each forms an up-to-date review of the specific topic it deals with.     

The composition and community structure of the ichthyofauna of the upper Scheldt estuary: synthesis of a 10-year data collection (1991–2001)

Fish collections on the cooling water filter screens of the Doel power plant were used to analyse temporal trends in estuarine fish populations of the upper Scheldt estuary, Belgium. Between 1991 and 2001, 62 species shared the estuary, with 15 species present at any one time. Identified were 23 marine stragglers, 16 freshwater species and four diadromous species, but their contribution to the total catch was insignificant. In terms of numbers, marine estuarine opportunists (17 species) mainly occurring as juveniles and estuarine residents (two species) were the dominant life cycle categories. Six fish species contributed to >97% of the total catch: three Pomatoschistus species [P. minutus (32%), P. microps (30%) and P. lozanoi (6%)], two Clupeidae [Clupea harengus (16%) and Sprattus sprattus (8%)] and Syngnathus rostellatus (5%). Abundance of almost all species in the estuary was highly seasonal and characterized by pronounced abundance peaks. Ordination of the data showed that variability in the temporal structure of estuarine fish community was first determined by differences in annual recruitment and then by predictable, cyclical patterns of species abundance.     

The icthyofauna of the Mhlathuze coastal lakes: some preliminary results

The fish faunas of the four Mhlathuze coastal lakes and the lower river comprise a diverse assortment of over fifty marine, estuarine and freshwater species. Three freshwater species are endemic to KwaZulu-Natal and nine estuarine species are endemic to southern Africa. Five species are of conservation significance. Species numbers in Lakes Mzingazi and Cubhu are similar historically and both lakes served as secondary nursery habitats for estuarine associated fishes. This role has been impacted by the construction of weirs at their outlets which prevent successful recruitment of estuarine species, especially during drought years when lake water levels are low. The fish faunas of Lakes Nsezi and Mangeza are depauperate and lack marine or estuarine components. In order that these systems fulfil their potential function as secondary nursery habitats to many estuarine fish species, minimum lake water levels must be set to ensure sufficient outflows at proposed fish ladders during critical spawning and migration times.     

Molluscan diversity in tidal marshes along the Scheldt estuary (The Netherlands, Belgium)

The mollusc fauna of 64 sites in 31 tidal marshes was surveyed along a salinity gradient from freshwater to marine conditions in the river Scheldt (Belgium–The Netherlands). A total of 10649 specimens involving 31 taxa were identified. Salinity turned out to be a major factor in mollusc assemblages in the Scheldt estuary, but other factors can not be excluded. In the marine part five species were common, compared to the brackish part where only Assiminea grayana was abundant. In the freshwater zone species richness was highest (24). There was a significant correlation between flooding frequency and species richness in the tidal freshwater marsh `Durmemonding'. Finally, the survey confirmed the distribution of the amphibious hygromiid snail Pseudotrichia rubiginosa, a species which in Belgium only occurs in the marshes of the tidal freshwater part of the Scheldt and its tributaries.     

The structure and components of European estuarine fish assemblages

This paper discusses the structure of fish assemblages using information from 17 European estuarine areas (in the British Isles, Portugal, Belgium, France, the Netherlands, Germany, Norway and Spain). Binary (presence/absence) and quantitative data for each assemblage have been used to assess the assemblage structure according to taxonomy (i.e. species identity). Following this, a total of 29 functional guilds were created in order to describe the use made of an estuarine area for each taxon encountered: feeding preferences, reproduction type, substratum preferences (for bottom dwelling fish) and position within the water column (vertical preference guild). The paper focuses on the designation and determination of the proportions of the guild members of the fish assemblage within each estuary. Ecological guilds within the assemblage include estuarine residents, marine juvenile migrants, catadromous and anadromous migrants, marine seasonal users, and freshwater and marine adventitious species. Feeding guilds include detritivores, planktonic feeders, infaunal croppers and sediment ingesters, piscivores, and active predators of mobile crustaceans. Reproduction guilds include planktonic and demersal spawners and those using brood-protection. The substratum preference indicates the proportions of sand, mud, rock and vegetation dwellers, and the vertical preference denotes benthic, demersal or pelagic species. The analysis has allowed both the estuaries to be grouped according to taxonomic and guild similarity and the characterisation of a typical European estuarine fish assemblage. Within the limits posed by differing sampling methods, times of sampling and survey rationale, there is a high similarity between estuaries. The data indicate common patterns of estuarine usage irrespective of the differences between the estuaries although such patterns cannot be interpreted fully given the incomplete knowledge of their physical and anthropogenic characteristics.     

Effects of the river discharge management on the nursery function of the Guadalquivir river estuary (SW Spain)

Within the Guadalquivir estuary, young recruits of marine species seem to respond to changes in freshwater flow by moving with the mass of estuarine water that is most “suitable” for them. The control of the river flow, from a dam 110 km upstream from the river mouth, has an immediate effect on the estuarine salinity gradient, displacing it either seaward or upstream. Consequently, there is a reduction or enlargement of the estuarine area that is used as nursery grounds. The analysis of the temporal estuarine recruitment and spatial distribution of young stages of marine species, during six annual cycles, provides evidence that the estuarine zone used as nursery grounds is mainly that part situated seaward from an isohaline value of 5. The relationship between the position of that isohaline (D₅) and the freshwater discharges from the dam was also examined during high and low tides. It was found that a high percentage of the isohaline position variation (75% and 73% at high and low tides, respectively) can be explained by the freshwater volume discharged from the dam during the previous week. These preliminary results suggest that an accurate model of the relationship between these two variables may be a useful tool for future management strategies of freshwater discharges to the estuary.     

Spatiotemporal Variation in Shallow-Water Freshwater Fish Distribution and Abundance in a Large Subtropical Coastal Lagoon

Patos Lagoon is located off the southern Brazilian coast and represents one of the largest coastal lagoons in the world. We estimated hydrological and physicochemical conditions associated with spatial variation in the abundance and diversity of freshwater fishes along the lagoon, and inter-annual variability in abundances of freshwater fishes occurring in its estuarine zone. During our study, the region experienced two periods of average rainfall and two periods with above-average rainfall. The characids Astyanax eigenmaniorum and Oligosarcus jenynsii and the siluriform Parapimelodus nigribarbis were the most abundant freshwater fishes in the estuary during wet periods when water levels were higher and salinity was lower. Increases in abundance of these species in the estuarine area, all of which members of primary-division freshwater families, apparently were associated with pulses of reproduction and passive transport from freshwater habitats located near middle and upper lagoon reaches. Abundance of species from secondary freshwater families, such as poeciliids and cichlids, were less correlated with hydrological conditions, and their patterns of occurrence in the estuary suggest active migration from nearby freshwater habitats draining into this area. Findings indicate that freshwater discharge in the basin and expansion/retraction of freshwaters in the middle-upper lagoon determined patterns of freshwater fish abundance and species richness in the estuarine zone.     

长江口中华鲟自然保护区潮间带鱼类群落结构

为深入了解鱼类对潮间带水域的利用,2010年5月、8月、11月在长江口中华鲟自然保护区潮间带水域进行了插网调查。结果表明:调查期间共出现28种鱼类,隶属于10目16科,鲤形目种类最多,其次为鲈形目;群落优势种为中国花鲈(Lateolabrax maculates)、鮻(Liza haematocheila)和窄体舌鳎(Cynoglossus gracilis);长江口中华鲟自然保护区潮间带鱼类群落可以分为河口定居鱼类、海洋偶见鱼类、降海洄游鱼类、溯河洄游鱼类、海洋洄游鱼类和淡水鱼类6种生态类群,其中河口定居鱼类和海洋洄游鱼类占据明显优势。对调查水域鱼类群落进行聚类分析,结果表明秋季和春夏季差异显著,鮻、中国花鲈、斑尾刺虾虎鱼(Acanthogobius ommaturus)是对季节差异贡献最大的3种鱼类。主成分分析结果表明,夏季鱼类群落主要受到海洋洄游鱼类的影响,而秋季主要受到河口定居鱼类的影响,这2种鱼类的幼鱼在不同季节利用潮间带水域索饵肥育可能是造成季节差异的主要原因。     

Distribution patterns of the fish assemblage in the Mamanguape River Estuary,North-eastern Brazil

The Mamanguape River Estuary was studied along a continuum ranging from shallow sandstone reefs adjacent to the river mouth up to the limit of influence of seawater, the upper portions of the estuary. Fish samples were gathered using three types of nets along 17 sample sites, grouped in four regions according to salinity range (reefs and low, middle and upper estuaries), to seasonality (dry and rainy seasons) and to habitat usage (marine visitor, marine estuarine-opportunist, marine estuarine-dependent, estuarine resident and estuarine &; marine). Differences were found in the fish assemblages along the estuarine-reef gradient, with most species (n?=?30) being considered marine, estuarine-opportunists or estuarine-dependent, according to its abundance and distribution. A low number of species (n?=?11) were considered estuarine residents. Some species exhibited significant differences in spatial distribution pattern, in which juveniles and adults predominated in different portions of the estuary, suggesting an ontogenetic migration both in relation to the adjacent reef area and across estuarine regions. Several species were newly recorded in the Mamanguape Estuary: Anchoa spinifer, Halichoeres poeyi, Hyporhamphus roberti, Scomberomorus cavalla, Sphyraena barracuda and Ocgocephalus vesperilio.     

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.     

福建敖江口表层沉积硅藻空间分布特征

为探讨福建敖江口表层沉积硅藻空间分布特征,2019年7月对敖江口进行表层沉积硅藻的采样调查,并研究了硅藻与环境因子的关系。结果表明,从13个站点共检出硅藻114种,隶属于39属。硅藻丰度具有从河口向外海先减少后增加的变化特征。聚类分析表明,主要硅藻属种可划分为淡水种组合带和半咸水-咸水种组合带。典型对应分析（CCA）表明,表层海水温度和盐度是影响硅藻分布的主要环境变量。河口区盐度相对较低,主要分布淡水种双面曲壳藻、优美曲壳藻和颗粒沟链藻;外海区北部盐度相对较高,主要分布咸水种流水双菱藻;外海区南部盐度相对较低,主要分布淡水种优美曲壳藻和颗粒沟链藻;滩涂的沉积物较粗,主要分布优美曲壳藻。此外,河口区和外海区南部可能存在一定的水体污染。     

Reappearance of Eumarcia fumigata (G.B. Sowerby II, 1853) (Bivalvia: Veneridae) into the Swan River,Western Australia

ABSTRACT

The venerid bivalve Eumarcia fumigata was a common species in Western Australia (WA) during the Pleistocene, where it was distributed as far north as Shark Bay. It became extinct in WA as the climate changed several thousand years ago but remains common in eastern Australia from southern Queensland to South Australia and Tasmania. The species has recently reappeared in the Swan River, probably due to shipping movements. Of the > 60 marine and estuarine species introduced into WA it is only the third confirmed introduction from eastern Australia, and the first that is a reappearance in the Swan River of a species present in the geological past. The present reappearance of E. fumigata, and the introduction of other species, has been made possible by the removal of a rocky bar at the mouth of the estuary and the creation of more marine conditions in the lower Swan estuary.     

Differential growth in estuarine and freshwater habitats indicated by plasma IGF1 concentrations and otolith chemistry in Dolly Varden Salvelinus malma

This study employed a combination of otolith microchemistry to indicate the recent habitat use, and plasma concentrations of the hormone insulin‐like growth factor 1 (IGF1) as an index of recent growth rate, to demonstrate differences in growth and habitat use by Dolly Varden Salvelinus malma occupying both freshwater and estuarine habitats in south‐west Alaska. Extensive sampling in all habitats revealed that fish had higher IGF1 levels in estuarine compared to lake habitats throughout the summer, and that the growth rates in different habitats within the estuary varied seasonally. In addition, otolith microchemistry indicated differentiation in estuarine habitat use among individual S. malma throughout summer months. Although growth in the estuary was higher than in fresh water in nearly all sites and months, the benefits and use of the estuarine habitats varied on finer spatial scales. Therefore, this study further illustrates the diverse life histories of S. malma and indicates an evaluation of the benefits of marine waters needs to include sub‐estuary scale habitat use.     

Dynamics of the shallow-water fish assemblage of the Patos Lagoon estuary (Brazil) during cold and warm ENSO episodes

In southern Brazil, cold ( La Niña ) and warm ( El Niño ) episodes of the El Niño Southern Oscillation (ENSO) phenomenon cause drought and high rainfall, respectively. The low precipitation and freshwater outflow associated with La Niña during 1995–1996 were associated with an increase in the abundance of marine species in the Patos Lagoon estuary. During the 1997–1998 El Niño , high precipitation and river discharge were associated with low abundance of marine species in the estuary. ANOVA results showed a higher abundance during La Niña than El Niño for estuarine resident (RES) and estuarine dependent (DEP) fishes. During La Niña catch per unit of effort (CPUE) of RES increased from the marine to estuarine area, but during El Niño CPUE increased at the marine area and diminished during summer and autumn in some estuarine sites. DEP fishes had an opposite abundance pattern. During La Niña , these fishes were abundant at the coastal marine area and along some estuarine sites, but during El Niño , CPUE remained almost the same at the marine area but dropped along some estuarine sites. These different abundance patterns for dominant fish groups yielded a positive interaction between stations and climatic events. With higher river discharge and the consequent decline of dominant euryhaline fishes, such as Mugil platanus and Atherinella brasiliensis , freshwater species increased in abundance and richness in the shallow waters of the stuary. The ENSO phenomenon influences precipitation and estuarine salinity in southern Brazil and thereby seems to have a strong influence on recruitment, immigration, and emigration dynamics of fish species living within and adjacent to estuarine habitats.     

The dynamics of the yeast community of the Tagus river estuary: testing the hypothesis of the multiple origins of estuarine yeasts

Yeasts are common inhabitants of different types of aquatic habitats, including marine and estuarine waters and rivers. Although numerous studies have surveyed yeast occurrence in these habitats, the identification of autochthonous populations has been problematic because several yeast species seem to be very versatile and therefore mere presence is not sufficient to establish an ecological association. In the present study we investigated the dynamics of the yeast community in the Tagus river estuary (Portugal) by combining a microbiological study involving isolation, quantification, and molecular identification of dominant yeast populations with the analysis of hydrological and hydrographical data. We set out to test the hypothesis of the multiple origins of estuarine yeast populations in a transect of the Tagus estuary and we postulate four possible sources: open sea, terrestrial, gastrointestinal and the estuary itself in the case of populations that have become resident. Candida parapsilosis and Pichia guilliermondii were correlated with Escherichia coli, which indicated an intestinal origin. Other cream-colored yeasts like Debaryomyces hansenii and Candida zeylanoides had similar dynamics, but no association with E. coli and quite distinct ecological preferences. They might represent a group of resident estuarine populations whose primary origin is diverse and can include marine, terrestrial, and gastrointestinal habitats. Another major yeast population was represented by Rhodotorula mucilaginosa. The cosmopolitan nature of that species and its moderate association with E. coli point to terrestrial sources as primary habitats.     

Fish community response to increased river flow in the Kariega Estuary,a freshwater-deprived,permanently open southern African system

The littoral and demersal ichthyofaunal community structure in the freshwater-deprived, permanently open Kariega Estuary was investigated following heavy rain in November 2006 and was compared to low-flow condition data from 1991 and 1996. All surveys took place during the spring months and allowed for a comparison of a wet and a dry spring period. The 2006 freshwater pulse generated a strong horizontal salinity gradient within the estuary. In the absence of freshwater inflow, the ichthyofaunal community in the littoral zone was numerically dominated by estuarine resident species, whilst after the freshwater pulse an increased contribution of marine migrant species was observed. Within the demersal zone, marine straggler species dominated during the dry spring period and estuarine residents during the wet spring period. Numerical analyses of the littoral and demersal fish assemblages indicated the presence of three distinct groupings — corresponding to the upper and middle reaches during separate wet and dry periods, and a community associated with the lower reaches of the estuary. It is suggested that the shift in community structure between the dry and wet spring periods could be related to altered physico-chemical and trophic conditions within the estuary, as well as the increased presence of freshwater and estuarine olfactory cues within the coastal zone, which would have resulted in the recruitment of 0+ estuary-associated marine species into the Kariega system.