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.     

Changes in rocky reef fish assemblages throughout an estuary with a restricted inlet

Rocky reef habitat is common in many estuaries, yet its role as a habitat for fishes is poorly understood. There is also limited understanding of how access of coastal species into estuaries and habitat quality can affect the distribution of rocky reef fishes within estuaries. This study used baited remote underwater video stations to determine spatial patterns in fish assemblages associated with rocky reef habitat throughout a barrier estuary with a permanently open but restricted inlet. Estuarine rocky reefs provided habitat for a diverse assemblage of fishes, many of which were large juveniles and subadults. In the absence of a pronounced salinity or temperature gradient, a clear transition in fish assemblages occurred from coastal waters, through the inlet channel, to the central estuary, and into the inner estuary. The inlet channel, notably its narrowness and length, limits tidal input into this estuary, which acts as a significant impediment to the dispersal of many coastal fishes, and insufficient habitat excludes many coastal rocky reef species from the inner estuary. This study highlights the need to recognise estuarine rocky reefs as providing habitat for diverse fish assemblages and the role inlets play in restricting access of coastal species.     

Do fish larvae have advantages over adults and other components for assessing estuarine ecological quality?

Using a novel approach to the assessment of ecological quality status of estuarine ecosystems, this study hypothesizes that compared to adult fishes and other components, the younger fish stages will be more sensitive and act as an early warning and will reflect more effectively the ecological status of estuaries. Larval stages of fishes were used to assess the ecological quality status (EQS) of four NW Portuguese estuaries, with different types and magnitudes of human pressures. The larval fish assemblages, together with water column characteristics and pollution indicators (faecal contamination and nutrient load) were sampled in the Lima, Cávado, Ave and Douro estuaries, during spring and autumn 2009. The four estuaries were classified in terms of human pressures by a global pressure index that identified the Cávado estuary as the least impacted estuary, followed by the Ave and Lima, both classified as moderately impacted system, while the Douro was classified as a highly impacted system. The Ave emerged as the most polluted system, carrying the highest nutrient load and sewage contamination. Larval fish assemblages included estuarine species, marine migrants, marine stragglers and the larger estuaries had higher species richness. Compared to adult fishes, three multimetric fish-based indices classified the Cávado, Ave and Douro estuaries with a lower ecological status when fish larvae were used. Similarly, the EQS assessed by macroinvertebrates were equal or higher when compared with fish larvae results. The EQS assessed by fish larvae was negatively correlated with sewage contamination and nitrogen nutrients, but did not reflect other anthropogenic pressures expressed by the global pressure index, which was only detected by adult fish. Fish larvae assessments were able to detect short-time events of hydrological manipulations observed in the Cávado estuary, as well as a seasonal decrease of water quality especially evident in the Ave estuary. The indices used denoted some limitations to the use of fish larvae data, thus emphasising the need for new indices to test the observed tendency for lower EQS given by fish larvae. The advantages and disadvantages of using fish larvae as more sensitive and accurate bioindicators of ecosystem integrity is also discussed as a means of providing strategically important information for improved estuarine management.     

Fish trophic structure in estuaries,with particular emphasis on estuarine typology and zoogeography

A comparative analysis of the fish trophic structure was undertaken on some 190 South African estuaries spanning three zoogeographic regions and incorporating three broad estuarine types. Fish biomass trophic guild compositions and biomass trophic spectrum profiles were analysed using multivariate statistical techniques and included both inter‐regional (zoogeographic) and intra‐regional (estuarine typology) comparisons. Differences in the fish trophic structure of the various estuary types within each zoogeographic region were observed; these were linked to the relative biomass contribution of the various trophic guilds and also to differences in biomass trophic spectrum profiles of the fishes in each estuary type within each region. In spite of these differences in trophic structure, all estuaries were dominated by detritivores, which suggests that the main food source (detritus) is similar in all biogeographic regions. Preliminary indications are that a similar dependence by estuary‐associated fishes on detritus food sources exists on a global basis but that detailed studies are required in order to confirm this assertion.     

Estuarine Typology and the Structuring of Fish Communities in South Africa

Synopsis 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.     

Biogeography of dinoflagellate cysts in northwest Atlantic estuaries

Few biogeographic studies of dinoflagellate cysts include the near‐shore estuarine environment. We determine the effect of estuary type, biogeography, and water quality on the spatial distribution of organic‐walled dinoflagellate cysts from the Northeast USA (Maine to Delaware) and Canada (Prince Edward Island). A total of 69 surface sediment samples were collected from 27 estuaries, from sites with surface salinities >20. Dinoflagellate cysts were examined microscopically and compared to environmental parameters using multivariate ordination techniques. The spatial distribution of cyst taxa reflects biogeographic provinces established by other marine organisms, with Cape Cod separating the northern Acadian Province from the southern Virginian Province. Species such as Lingulodinium machaerophorum and Polysphaeridinium zoharyi were found almost exclusively in the Virginian Province, while others such as Dubridinium spp. and Islandinium? cezare were more abundant in the Acadian Province. Tidal range, sea surface temperature (SST), and sea surface salinity (SSS) are statistically significant parameters influencing cyst assemblages. Samples from the same type of estuary cluster together in canonical correspondence analysis when the estuaries are within the same biogeographic province. The large geographic extent of this study, encompassing four main estuary types (riverine, lagoon, coastal embayment, and fjord), allowed us to determine that the type of estuary has an important influence on cyst assemblages. Due to greater seasonal variations in SSTs and SSSs in estuaries compared to the open ocean, cyst assemblages show distinct latitudinal trends. The estuarine context is important for understanding present‐day species distribution, the factors controlling them, and to better predict how they may change in the future.     

Comparison of inshore and offshore fish larval assemblages within the wider Yangtze River estuary (China)

It is hypothesized that fish larvae undertake vertical movements in estuarine waters. To test this hypothesis, a sampling period was selected during times when many spring‐spawning fish reach maximum abundance in coastal waters so that spring and summer variations in larval fish assemblages could be determined in the Yangtze River estuary. Six oceanographic surveys were conducted across the salinity gradient of an inshore (freshwater) and offshore area (brackish intersection) during spring (May) and summer (August) between 2010 and 2012. The fish larval community was dominated by species of Engraulidae, Gobiidae, Champsodontidae and Mugilidae. The pre‐flexion and flexion larval stages of euryhaline marine species, which are dependent on estuaries as nursery areas, were common. The brackish and marine larval assemblage was the most abundant with taxa such as Coilia mystus and Engraulis japonicus accounting for more than 57.3% of the total catch. Spatial differences in the taxonomic composition of larval fish assemblages were evident between the inshore and offshore areas. Additionally, the Yangtze River runoff regulatory functions as affected by the Three Gorges Reservoir operational mode (hydrological alternating operations) showed weak influences on fish and habitat environments. Low salinities from high freshwater inflow limited bay anchovy production in the inshore area.     

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.     

Composition, temporal changes and ecological guild classification of the ichthyofaunas of large European estuaries – a comparison between the Tagus (Portugal) and the Elbe (Germany)

Fish species densities from 1025 hauls obtained with beam trawl and stow net catches from the southern Tagus and northern Elbe estuaries were analysed for two different periods of time between 1978 and 1997. The data were related with environmental factors to compare species composition and densities, contributions of different ecological guilds, structuring environmental key factors, intra‐annual cyclicity and interperiodical stability of ichthyofaunas in large European estuaries at different latitudes. Although the total number of species in both the Tagus and Elbe estuaries (Tagus: 57 species, Elbe: 58 species) was very similar, significant differences were estimated in species compositions, species densities and number of species, and individuals of the different ecological guilds between both estuaries. A total of 15 species occurred in both estuaries but only two of these species, the catadromous Anguilla anguilla and the marine estuarine opportunist Pleuronectes flesus, contributed substantially to the total abundance. Marine species together contributed more than 5% of the total number of species in the Tagus and Elbe estuaries, whereas their contribution in number of individuals amounted to 22% in the Tagus and only 9% in the Elbe. In terms of number of individuals, the ichthyofauna of the Tagus estuary was dominated by estuarine species (especially Pomatoschistus spp.) contributing 68% of the total abundance. In contrast, the fish fauna of the Elbe estuary was dominated by high numbers of anadromous species (88%) individuals, especially Osmerus eperlanus. Canonical corresponding analyses (CCA) indicated that, besides intra‐annual variables, salinity and mouth distance were two of the most important environmental factors structuring the fish communities in both estuaries. Moreover, water depth was found to be an important environmental factor in the Tagus estuary, whereas the water temperature substantially affected the ichthyofaunal composition in the Elbe estuary. In both estuaries, contributions by number of species and number of individuals of the different ecological guilds were not statistically different between the two periods considered, 1978–80 and 1995–97 for the Tagus, and 1981–86 and 1989–95 for the Elbe. Nevertheless, from 1981–86 until 1989–95 a remarkable increase of about 4.5 times in the densities of O. eperlanus was observed in the Elbe estuary, probably related to improved water quality, especially of oxygen conditions in the nurseries since 1990. This was also supported by the results of CCA, suggesting important influences of the years 1989 and 1990 on the Elbe estuary fish assemblage. Climate change as a result of global warming may be evident for the observed changes of the densities of P. flesus which decreased in the southern Tagus estuary and, in contrast, increased in the northern Elbe estuary during comparable periods of time. It is recommended to use the ecological guild classification scheme which was applied for the Tagus and Elbe estuaries for further studies of European estuarine fish assemblages.     

Parasitological diversity of the common goby, Pomatoschistus microps (Krøyer, 1838), in estuarine systems along the Portuguese coast

Parasitological diversity of the common goby Pomatoschistus microps along the Portuguese coast was studied based on samples collected using beam trawls in five coastal estuaries (Ria de Aveiro, Tagus, Sado, Mira and Guadiana estuaries) between May and July 2006. The classes Digenea, Cestoda, Nematoda and phylum Mastigophora were found, with Digenea Cryptocotyle sp. and Lecithochirium musculus being the most abundant taxa. Prevalence and mean abundance of Cryptocotyle sp. were highest in Ria de Aveiro (74%) and Mira estuary (28.05), respectively, whereas L. musculus values of both indices were highest in Sado estuary (prevalence = 64%; mean abundance = 11.77). Values varied along the Portuguese coast; the discriminant analysis based on the number of parasites showed some overlap between estuaries, although successfully separating the Sado and Mira estuaries. Overall, variations in estuaries were explained by different environmental pressures, leading to differences on host abundance and life-history of the parasites. Feeding behaviour and habitat selection therefore play a crucial role in shaping the biology, ecology and parasite assemblages of the common goby along the Portuguese coast.     

Importance of the upper estuary as a nursery ground for fishes in Ariake Bay,Japan

To examine the importance of the upper estuarine areas of Ariake Bay as a nursery ground for fish, assemblages of larvae and juveniles were compared among various aquatic habitats. The upper estuaries of the bay (the Rokkaku and Hayatsue estuaries) are brackish, highly turbid waters with high tidal velocities, and differ substantially from the Isahaya area, which has been separated from the bay by a man-made dike, to the middle estuary (the Kikuchi estuary). Abundances of larvae and juveniles were higher in the estuaries than in the open bay and Isahaya areas. Abundant species in the upper estuaries were similar to each other, but differed from those of the middle estuary. This was primarily due to larvae and juveniles of fishes that occurred almost entirely in the upper estuaries, such as Acanthogobius hasta, Boleophthalmus pectinirostris, Coilia nasus, Cynoglossus abbreviatus, Nibea albiflora, Odontamblyopus lacepedii, Trachidermus fasciatus and Tridentiger barbatus. These results suggest that the upper estuaries play an important role as nursery grounds for fishes.     

The distribution of macroinvertebrates and fishes in Tasmanian estuaries

The distributions of 390 taxa of benthic macroinvertebrates collected in forty-eight estuaries and 101 fish species collected in seventy-five Tasmanian estuaries were related to geographical and environmental variables. Distribution patterns for the two taxonomic groups were largely congruent at both between and within-estuary scales. Faunal composition and the number of species collected at a site were primarily related to site salinity, the biomass of seagrass and tidal range. At the broader estuary scale, the distributions of macroinvertebrate and fish assemblages were primarily correlated with the presence of an entrance bar. Species richness varied with geographical location for both macrofauna and fishes, with highest numbers of species occurring in the Furneaux Group, north-eastern Tasmania and south-eastern Tasmania. These patterns primarily reflected differences in estuary type between regions rather than concentrations of locally endemic species. Although the majority of species collected during the study were marine vagrants, they constituted a very low proportion of total animal densities within estuaries. Only four species considered exotic to Tasmania were identifed. Nearly all species recorded from Tasmanian estuaries occurred widely within the state and have also been recorded in south-eastern Australia. Only 1% of estuarine fish species and < 5% of invertebrate species were considered endemic to the state. The generally wide ranges of species around Tasmania were complicated by (i) the absence of most species from the west coast (ii) a small (< 10%) component of species that occurred only in the north-east and Furneaux Group (eastern Bass Strait), and (iii) a few species (< 5%) restricted to other regions. The low number of species recorded from estuaries along the western Tasmanian coast reflected extremely low faunal biomass in that area. This depression in biomass on the west coast was attributed to unusually low concentrations of dissolved nutrients in rivers and dark tannin-stained waters which greatly restricted algal photosynthesis and primary production.     

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.     

Factors affecting the distribution of juvenile estuarine and inshore fish

The differential distributions of juveniles and adults of 25 species of teleost were investigated and compared from four habitat types in sub-tropical Moreton Bay, Queensland. The aim of the study was to identify factors influencing the distribution of juveniles, particularly the species which enter estuaries. The following habitats were sampled: a shallow, sheltered tidal estuary (Caboolture); a shallow, exposed bay with muddy substrates (Deception Bay); an exposed area of sandy substrates and seagrass (Toorbol Point) and a sheltered oceanic site with sandy substrates and seagrass (Kooringal). Data on diet, spawning seasons and recruitment periods of fry are presented together with measurements of salinity, temperature and turbidity. Species entering estuaries recruited mainly in summer (rainy season). The possible preference of juveniles for calm water, the roles of food and predation pressure, the effects of salinity, temperature and turbidity are discussed in relation to the biology and distribution of the fish. Salinity and temperature were probably not important to most juvenile fish. The effects of calm water, suitable food and predators vary according to species. Although all juveniles studied preferred shallow water, in the case of those entering estuaries, turbidity was the single most important factor. Juveniles of the same species occurred in both the estuary and Deception Bay where abiotic and biotic factors other than turbidity were different. During summer, turbidity gradients extended from east to west in Moreton Bay with highest turbidities in Caboolture estuary and Deception Bay. In winter, turbidities throughout Moreton Bay were low and relatively uniform. At this time many of the ‘clear water’ species occurred in Deception Bay. The influence of high turbidity on fish may be linked to reduced predation pressure and perhaps food supply in shallow water. Turbidity gradients in summer may aid fry in locating estuarine nursery grounds. It is apparent however, that juveniles of many species are probably not attracted to estuaries per se but to shallow turbid areas.     

High levels of sediment contamination have little influence on estuarine beach fish communities

While contaminants are predicted to have measurable impacts on fish assemblages, studies have rarely assessed this potential in the context of natural variability in physico-chemical conditions within and between estuaries. We investigated links between the distribution of sediment contamination (metals and PAHs), physico-chemical variables (pH, salinity, temperature, turbidity) and beach fish assemblages in estuarine environments. Fish communities were sampled using a beach seine within the inner and outer zones of six estuaries that were either heavily modified or relatively unmodified by urbanization and industrial activity. All sampling was replicated over two years with two periods sampled each year. Shannon diversity, biomass and abundance were all significantly higher in the inner zone of estuaries while fish were larger on average in the outer zone. Strong differences in community composition were also detected between the inner and outer zones. Few differences were detected between fish assemblages in heavily modified versus relatively unmodified estuaries despite high concentrations of sediment contaminants in the inner zones of modified estuaries that exceeded recognized sediment quality guidelines. Trends in species distributions, community composition, abundance, Shannon diversity, and average fish weight were strongly correlated to physico-chemical variables and showed a weaker relationship to sediment metal contamination. Sediment PAH concentrations were not significantly related to the fish assemblage. These findings suggest that variation in some physico-chemical factors (salinity, temperature, pH) or variables that co-vary with these factors (e.g., wave activity or grain size) have a much greater influence on this fish assemblage than anthropogenic stressors such as contamination.     

Ichthyofaunal assemblages in estuaries: A South African case study

This review places the life-history styles of fishes associated with South African estuaries in a global context and presents a classification system incorporating all the major life-history categories for estuary-associated fish species around the world. In addition, it documents the early life histories of the major fish groups in South African estuaries, with particular emphasis on the differing modes of estuarine utilization by marine, estuarine and freshwater taxa.This review details factors influencing the ichthyofaunal community structure in South African estuaries. The availability of fish for recruitment into an estuary depends primarily upon the distributional range of euryhaline marine and estuarine species, with tropical and temperate taxa showing marked abundance trends. Within a particular biogeographic region, however, estuarine type and prevailing salinity regime have a major influence on the detailed ichthyofaunal structure that develops. There is an increasing preponderance of marine fish taxa when moving from a freshwater-dominated towards a seawater-dominated type of system, and a decline in species diversity between subtropical estuaries in the north-east and cool temperate systems in the south-west. Similar declines in fish species diversity between tropical and temperate estuaries in other parts of the world are highlighted.Fish assemblages in estuaries adjust constantly in response to changing seasons, salinities, turbidities, etc. Despite persistent fluctuations in both the biotic and abiotic environment, the basic ichthyofaunal structure appears to have an underlying stability and to be predictable in terms of the response of individual species to specific conditions. This stability seems to be governed by factors such as the dominance of eurytopic taxa within estuarine assemblages and the robust nature of food webs within these systems. The predictability arises from factors such as the seasonality associated with estuarine spawning cycles and juvenile fish recruitment patterns. These patterns, together with a well-documented resilience to a wide range of physico-chemical and biotic perturbations, appear to be an underlying feature of fish assemblages in estuaries around the world.In contrast to marine fish species, estuary-associated taxa have received little conservation attention. Apart from the designation of protected areas, the main direct means of conserving estuary-associated fish stocks include habitat conservation and controls over fishing methods, effort, efficiency and seasonality. Of these, the conservation of fish habitats, the most important, because healthy aquatic environments invariably support healthy fish populations. The use of estuarine sanctuaries for fish conservation is briefly reviewed, as well as the legislation governing the USA National Estuarine Research Reserve System (NERRS) and the Australian Marine and Estuarine Protected Area (MEPA) system. It is concluded that South Africa requires an expansion of the existing Estuarine Protected Area (EPA) network, as well as the upgrading of selected 'estuarine reserves' where fishing is permitted, into 'estuarine sanctuaries' where no exploitation of biological resources is allowed.     

Landscape transformation alters functional diversity in coastal seascapes

The ecological impacts of landscape modification and urbanisation have transformed the composition of plant and animal assemblages, and altered the condition of ecosystems globally. Landscape transformation influences the spatial distribution of species and ecological functions by selecting for generalist species with wide ecological niches, which can adapt to opportunities in highly-modified environments. These effects of landscape modification can shape functional diversity on land, but it is not clear whether they have similar functional consequences in the sea. We used estuaries as a model system to test how landscape transformation alters functional diversity in coastal seascapes, and measured how variation in level of urbanisation, catchment modification and habitat loss influenced fish diversity across thirty-nine estuaries in eastern Australia. Fish were surveyed with baited remote underwater video stations and functional diversity was indexed with three metrics that describe variation in the functional traits and niche space of assemblages. The extent of landscape transformation in the catchment of each estuary was associated with variation in the functional diversity of estuarine fish assemblages. These effects were, however, not what we expected as functional diversity was highest in modified estuaries that supported a large area of both urban and grazing land in their catchments, were bordered by a small area of natural terrestrial vegetation and that contained a moderate area of mangroves. Zoobenthivores and omnivores dominated assemblages in highly-modified estuaries, and piscivorous fishes were common in natural waterways. Our results demonstrate, that the modification and urbanisation of ecosystems on land can alter functional diversity in the sea. Intense landscape transformation appears to select for abundant generalists with wide trophic niches, and against species with specialised diets, and we suggest that these changes might have fundamental consequences for ecosystem functioning in estuaries, and other highly modified seascapes.     

Connectivity between estuaries and marine environment: Integrating metrics to assess estuarine nursery function

Natural or anthropogenic induced variations in estuaries and the dynamics of marine fish populations potentially promote differences in connectivity between estuaries and marine areas, i.e. in their importance as nursery grounds. Within this context, an integrated assessment of the differential nursery function of the main estuaries along the Portuguese coast for commercial fish species common sole Solea solea, Senegalese sole Solea senegalensis, flounder Platichthys flesus and sea bass Dicentrarchus labrax was performed through several indicators based on available data. Contribution of individual estuaries to marine subpopulations was measured with potential metrics (juvenile density, habitat quantity, juvenile number and habitat quality within estuaries) and effective metrics (estuarine source of young adults in marine environment measured via otolith elemental fingerprints). The relationship between the two types of metrics was also assessed. Estuaries identified as important nursery and/or effective juvenile habitat (EJH) differed with species and no single estuary was best for all, highlighting species-specific regulation of nursery function. Multiple species assessment of nursery and EJH function differed among estuaries. Management and conservation of estuaries should focus on sites with higher contributions to adult subpopulations of multiple species. The importance of defining precise scientific and management objectives was emphasized by the different rankings of estuaries obtained with nursery or EJH criteria. Potential and effective contribution of estuaries were not significantly correlated, but in a quantitative analysis juvenile densities and number of juveniles seem related with effective contribution in some species. An agreement between potential and effective contributions of estuaries is concurrent with the acknowledged minor role of juvenile stage processes in regulation of recruitment to adult subpopulations.     

广东沿岸海域鱼类群落排序

根据广东沿岸海域春秋两季底拖网鱼类采样数据,运用多维尺度转换分别对两季的鱼类样品进行排序。排序揭示出的鱼类群落格局及其季度差异与环境变异性密切相关。同处混合水区域的站位鱼类组成较为相似;分布在珠江冲淡水和外海高盐水区域的站位,鱼类组成则与多数沿岸站位有明显差异。春季沿岸海域鱼类组成有一东北－西南向的变化趋势,这一群落格局是由于该海域东北部受低温东海沿岸流影响所致;秋季珠江河口区受冲淡水的影响,而调     

The primary carbon sources utilised by fishes in the Mngazi and Mngazana estuaries,South Africa: a preliminary assessment

A number of studies have used stable carbon isotopes to analyse aspects of the food web structure in South African estuaries but none has compared mangrove and non-mangrove estuarine food webs. This study compares the primary carbon sources utilised by the ichthyofauna in the Mngazana (with extensive mangroves) and Mngazi (without mangroves) estuaries. In contrast to the Kariega Estuary, where past research identified two basic carbon pathways, there were no clear carbon pathways within the Mngazi and Mngazana fish assemblages. Instead, the carbon isotopic values of fishes in both estuaries displayed a continuum rather than a tight clustering around particular energy sources. Most detritus feeders of the family Mugilidae from both estuaries were relatively more enriched (with carbon isotopic values ranging from ?16.9% to ?12.3%) than other fish taxa. The isotopic values of the mullet species suggest a diet derived from relatively enriched carbon sources such as benthic microalgae, the eelgrass Zostera and associated epiphytes. Based on the isotopic values, piscivorous fishes from both estuaries could not be linked to specific prey fish taxa, but clearly the mullet species were not their main food source. The invertebrate feeders that were common to both estuaries showed greater isotopic variations in the Mngazana Estuary (?24.7% to ?19.3%) than in the Mngazi Estuary (?21.9% to ?18.4%), probably reflecting the higher diversity of habitats and invertebrate prey items in the Mngazana system. Generally, the isotopic signatures of fishes from the Mngazi Estuary were more enriched than those from the Mngazana Estuary, thus indicating the possible effect of δ¹³C-depleted mangrove-derived carbon in the latter system.