Dynamics Of Fish Assemblages Research Articles

Structure and dynamics of distinct fish assemblages in three reaches (upper, middle and lower) of an open tropical estuary in Brazil

AbstractWe collected fishes and environmental variables in three zones (upper, middle and lower) of a small open tropical estuary during flood tide. The aim was to test for differences in fish assemblages along a gradient from freshwater to marine waters and to detect any seasonal variation in fishes and environmental variables across these zones. A total of 111 species (18 in the upper, 50 in the middle and 66 in the lower estuary) were recorded, forming three distinct fish assemblages, with the family Eleotridae dominating in the upper, Gerreidae in the middle, and Sciaenidae in the lower estuary. Only two species (Geophagus brasiliensis in the upper and the middle zones, and Eucinostomus argenteus in the middle and the lower zones) composed more than 1% of the total number of individuals in more than a single zone. Short‐term (tidal) changes in salinity in the middle estuary were associated with different assemblages in the three estuarine zones, even in winter, when the differences in salinity are lowest between the middle and the lower zones. Seasonal variation in salinity was irrelevant, except in a protected sidewater lagoon in the middle estuary. Low salinity seasonal change may be related to the lack of seasonal variation in the structure of fish assemblages in all estuarine zones.

Fish Assemblage Dynamics and Community Analysis in the Han River

A study of Han River fish assemblage dynamics for 4 years was conducted. From April 2005 to August, 2008, fishes inhabiting two sites of Han River were sampled for identification. For further analysis, 40 individuals of the dominant species were sampled monthly from March 2006 to November 2008. The fish assemblage at site 1 was dominated by Zacco platypus (32.69%), while the subdominant species were Acheilognathus yamatsutae (14.4%), Acanthorhodeus gracilis (9.43%), Squalidus japonicus coreanus (6.84%), and Tridentiger brevispinis (5.18%). The most abundant species at site 2 was Korean Chub (Zacco koreanus) with relative abundance of 62.45% and followed by Pungtungia herzi (10.29%), Coreoperca herzi (8.67%), and Coreoleuciscus splendidus (6.82%) as the subdominant species. At both sites, the endemics populations show an increasing pattern during the whole survey period, while the natives were declining in the last two years.

Temporal dynamics of fish assemblages of natural and artificial tropical estuaries

We sampled the fish fauna of 9 small natural estuaries and 2 constructed estuarine lakes in Australia’s dry tropics over 15 mo to detail the dynamics of fish assembly structures over time. The estuaries chosen were small enough that the cast net sampling method which we used could cover the full extent of the estuary, obviating the problem that within-estuary migration might lead to the false appearance of assemblage change over time. Temporal patterns in assemblage structure were consistent across the natural estuaries, overprinting complex spatial differences. Nursery ground utilisation and assemblage composition were intimately interlinked. In natural estuaries, assemblage change was a function of changes in both probability of encounter of individual species and in species compositions, and the recruitment, growth and subsequent emigration from the estuaries of juveniles was the main contributor to overall assemblage change. In contrast, in artificial lakes where connectivity with offshore sources of recruits was restricted, species compositions were attenuated and temporal change was not driven by the recruitment of offshore species.

Spatial structure and temporal patterns in a large marine ecosystem: Exploited reef fishes of the southeast United States

The continental shelf of the southeast United States forms one of North America's Large Marine Ecosystems (LME). Despite increased attention on ecosystem management, fisheries within this LME continue to be managed on a single stock basis, in part because interactions among species and environmental effects are poorly understood. Using fishery data from two different sources (recreational and commercial), we applied multivariate statistical techniques to elucidate spatial and temporal dynamics of reef fish assemblages. Spatial analyses of species composition revealed a zoogeographic boundary near Cape Canaveral, Florida, suggesting that management of reef fishes could be applied to the northern and southern regions with discrimination. Temporal analyses revealed, in general, gradual changes in species composition of landings, but with primary shifts in 1992 and again in 1999–2000. Chronological patterns, evident in these two independent data sets, bear the signature of one or more trending factors, which in this LME could include increased exploitation, spread of invasive species, habitat degradation, or climate change.

Which forcing factors fit? Using ecosystem models to investigate the relative influence of fishing and changes in primary productivity on the dynamics of marine ecosystems

Fishing mortality and primary production (or proxy for) were used to drive the dynamics of fish assemblages in 9 trophodynamic models of contrasting marine ecosystems. Historical trends in abundance were reconstructed by fitting model predictions to observations from stock assessments and fisheries independent survey data. The model fitting exercise derives values for otherwise unknown parameters that specify the relative strength of trophic interactions and, in some instances, a time series anomaly for changes in primary production. We measured how much better or worse were model predictions when bottom-up forcing by primary production were added to top-down forcing by fishing. Searching for cross system patterns, the relative contribution of fishing and changes in primary production, mediated through trophic interactions, are evaluated for the ecosystems as a whole and for selected similar species in different ecosystems. The analysis provides a simple qualitative way to explain which forcing factors have most influence on modeled dynamics. Both fishing and primary production forcing were required to obtain the best model fits to data. Fishing effects more strongly influenced 6 of 9 of the ecosystems, but primary production was more often found to be the main factor influencing the selected pelagic and demersal fish stock trends. Examination of sensitivity to ecological and model parameters suggests that the results are the product of complex food-web interactions rather than simple deterministic responses of the models.

Dynamics of fish assemblages on coral reefs subjected to different management regimes in the Abrolhos Bank, eastern Brazil

Abstract Marine protected areas (MPAs) range from multiple‐use areas (MUA) to absolute no‐take reserves (NTR). Despite their importance for fisheries management, there are few long‐term studies comparing benefits from different types of MPAs within the same region. Fish assemblages were monitored for five years (2001–2005) in the largest coral reefs in the South Atlantic (Abrolhos Bank, Brazil). Monitoring included one community‐based MUA, two NTRs (one established in 1983 and another in 2001), and one unprotected area. Benthic assemblages at these areas, as well as fish assemblages on unprotected deeper reefs (25–35 m), were monitored from 2003 onwards. Habitat characteristics strongly influenced fish assemblages' structure. This, together with the lack of data from before establishment of the MPAs, did not allow an unequivocal analysis of the effects of the MPAs. Biomass of commercially important fish, particularly small carnivores, was higher in the older NTR. Biomass of black grouper Mycteroperca bonaci increased by 30‐fold inside NTRs during the study period, while remaining consistently low elsewhere. A single herbivore species, the parrotfish Scarus trispinosus, dominated fish assemblages (28.3% of total biomass). Biomass of this species increased in 2002 on the younger NTR and on the MUA, soon after establishment of the former and banning of the parrotfish fishery in the latter. This increase was followed by a decline from 2003 onwards, after increased poaching and reopening of the parrotfish fishery. Fish biomass increased in 2002 across the entire region. This increase was stronger in sites closer to deeper reefs, where fish biomass was up to 30‐times higher than shallow reefs: movement of fish from deeper to shallower areas may have played a role. The effective use of MPAs in the Abrolhos Bank is still dependent on adequate enforcement and the protection of critical habitats such as deep reefs and mangroves. Copyright © 2008 John Wiley & Sons, Ltd.

Distribuição espacial de peixes em ambientes lênticos: interação de fatores

To understand the structure and dynamics of fish assemblages in lentic environments, it is fundamental to identify and analyze the main factors linked with physical space occupation strategies of the species, and characterize the patterns of spatial distribution of fish in different habitats. Factors as biogeographical history, physical and chemical parameters, productivity, structure and complexity of habitats, biotic interactions have been suggested as regulators of ichthyofauna distribution. These factors interrelated with the geological history of the drainage basin determine the patterns of spatial distribution in different lentic environments

Temporal dynamics of fish assemblages in small seasonal streams in the Queensland tropics

The structure and dynamics of fish assemblages were studied in two small coastal streams in the seasonal tropics of northern Queensland. The study encompassed two consecutive wet seasons of contrasting flood magnitudes. Flooding had substantial effects on physical habitats by shifting sediments and removing aquatic macrophytes, and short-term changes in the fish assemblages reflected these habitat changes. Changes were of higher magnitude following a one-in-eighteen-year flood than a one-in-one-year flood; however, in both cases return to prior assemblage structure occurred as the dry season progressed, but with more rapid recovery after the smaller event. The stream fish assemblages showed high resilience to the flood disturbance at magnitudes seen in this study.

Seasonal dynamics of fish assemblage in a pond canal

The annual dynamics of fish assemblage in a pond-connecting canal of a South Moravian pond aquaculture facility was studied to reveal potential assemblage effects on pond stocks and vice versa. The species richness of fish assemblage and seasonal dynamics of its development were predominantly dependent upon the fish stock of the interconnected ponds (particularly due to escapees during the period of pond harvesting), which contributed to a considerable increase of commercial fish species occurrence. Using a seasonal parameter, the season proved to have a major impact on fish assemblage dynamics (r = −0.71, P < 0.001). Spring samples were dominated by commercial fishes of aquaculture origin (mainly Cyprinus carpio). Occurrence of several fish species originating from the wild (bleak, Alburnus alburnus, chub, Leuciscus cephalus and roach, Rutilus rutilus) was also reported.

Effects of floods on fish assemblages in an intermittent prairie stream

Summary1. Floods are major disturbances to stream ecosystems that can kill or displace organisms and modify habitats. Many studies have reported changes in fish assemblages after a single flood, but few studies have evaluated the importance of timing and intensity of floods on long‐term fish assemblage dynamics.2. We used a 10‐year dataset to evaluate the effects of floods on fishes in Kings Creek, an intermittent prairie stream in north‐eastern, Kansas, U.S.A. Samples were collected seasonally at two perennial headwater sites (1995–2005) and one perennial downstream flowing site (1997–2005) allowing us to evaluate the effects of floods at different locations within a watershed. In addition, four surveys during 2003 and 2004 sampled 3–5 km of stream between the long‐term study sites to evaluate the use of intermittent reaches of this stream.3. Because of higher discharge and bed scouring at the downstream site, we predicted that the fish assemblage would have lowered species richness and abundance following floods. In contrast, we expected increased species richness and abundance at headwater sites because floods increase stream connectivity and create the potential for colonisation from downstream reaches.4. Akaike Information Criteria (AIC) was used to select among candidate regression models that predicted species richness and abundance based on Julian date, time since floods, season and physical habitat at each site. At the downstream site, AIC weightings suggested Julian date was the best predictor of fish assemblage structure, but no model explained &gt;16% of the variation in species richness or community structure. Variation explained by Julian date was primarily attributed to a long‐term pattern of declining abundance of common species. At the headwater sites, there was not a single candidate model selected to predict total species abundance and assemblage structure. AIC weightings suggested variation in assemblage structure was associated with either Julian date or local habitat characteristics.5. Fishes rapidly colonised isolated or dry habitats following floods. This was evidenced by the occurrence of fishes in intermittent reaches and the positive association between maximum daily discharge and colonisation events at both headwater sites.6. Our study suggests floods allow dispersal into intermittent habitats with little or no downstream displacement of fishes. Movement of fishes among habitats during flooding highlights the importance of maintaining connectivity of stream networks of low to medium order prairie streams.

Environmental forcing and larval fish assemblage dynamics in the Lima River estuary (northwest Portugal)

This study investigated the potential control of selected abiotic parameters on an estuarine larval fish assemblage from the Lima River. Surveys were done fortnightly during spring tides, from April 2002 until April 2004, at 11 stations distributed along the estuary from the mouth to 7 km upstream. The surveys consisted of subsurface plankton tows of 5-min duration using a 1-m diameter, 500-μm mesh net and coupled with vertical profile measurements of temperature, salinity, dissolved oxygen, pH and turbidity. The Lima River estuary exhibited seasonal vertical stratification of salinity during the winter period, when salinity sharply increased with depth and a layer of fresh water was sometimes present at the surface. Temperature was always vertically stratified. Cooler water was typically found near the bottom of the water column, except during winter, when a thermal inversion occurred. A seasonal decrease in abundance and diversity of the larval assemblage was observed during winter, when fish larvae were almost absent from the plankton collections. Canonical correspondence analysis (CCA) results showed that the first axis represented a temporal gradient and the second axis represented a spatial gradient. Seasonal variations on temperature and precipitation were responsible for the temporal differences on the fish larval assemblages. This study reinforced the concept that interannual climate and hydrodynamic variations have a strong influence on estuarine ichthyoplankton and, consequently, on the recruitment of marine coastal fish populations.

Self-Organizing Maps in Revealing Variation in Non-obligatory Riverine Fish in Long-term Data

Sensitiveness to the overall influence of the river channel regulation, impoundment and pollution was studied for 12 non-obligatory riverine (NOR) fish species in the Warta River, Poland, over the period of 1963–1998. Their total abundance has not considerably changed unlike the structure of their aggregation, which was revealed by a self-organizing map (SOM, Kohonen unsupervised artificial neural network) almost perfectly separating 1960s samples from 1990s ones. The greatest changes in proportion were recorded for the dominant roach Rutilus rutilus (from 28.6 to 60.0%), perch Perca fluviatilis (1.9 to 9.5%), pike Esox lucius (2.9 to 4.9%), and the former codominant bleak Alburbus alburnus (22.9 to 1.8%). They resulted from highly significant (p < 0.001), reaching even one order of magnitude, differences in the abundance of these species. Such remarkable alternations in dominant NOR ichthyofauna obviously influenced the whole fish assemblage structure, which was best illustrated by a clear vertical gradient over SOM in Simpson and Shannon indices. Thus, NOR species, both studied together and separately, can supply valuable information on the fish assemblage dynamics and should not be neglected in temporal analyses, often focused only on vulnerable obligatory riverine, migratory and/or endemic species.

Reef fish assemblage structure affected by small-scale spacing and size variations of artificial patch reefs

To examine how varying the distance between patch reefs affects reef fish assemblage structure, replicate concrete reef modules (∼ 1 m 3 each) were deployed on sand bottom at 8 m depth off Ft. Lauderdale, Florida, USA (26°07N, 80°05W). Modules were positioned at the apices of one of four differently sized equilateral triangles. Triangular configurations had side lengths of: 25 m, 15 m, 5 m, and 0.33 m; each treatment with two replicates. Two additional configurations: (1) a solitary module (Single) and (2) two modules side by side (Double), also with two replicates, were deployed in order to examine the interaction of reef size with fish assemblages. SCUBA divers censused fishes monthly, for 2 years, recording the species present, their abundance and sizes (TL). Fishes were assigned to one of five length categories: < 2 cm, > 2–5 cm, > 5–10 cm, > 10–20 cm, and > 20 cm. In general and excluding the smallest three-module spacing treatment (0.33 m treatment), which may have provided unique treatment-specific refuge, total fish abundance and richness were shown to increase when isolation distance increased. However, there were also species-specific and size class differences in response to isolation distance. The second part of this study indicated varying reef size, by doubling and tripling the number of reef modules, increased total fish abundance and species richness. Nevertheless, fish abundance and species richness did not change by an identical multiplier (e.g., doubling modules ≠ double abundance). These results suggest that scientists and marine managers alike should consider reef size and isolation as habitat attributes capable of altering the structure and dynamics of reef fish assemblages.

Long-Term Fish Assemblage Dynamics of the Alvarado Lagoon Estuary, Veracruz, Mexico

The fish assemblages of Alvarado Lagoon Estuary (a complex of coastal lagoons in the state of Veracruz, Mexico) have been surveyed intermittently by different researchers over the last 40 years. Assessing longterm trends in fish assemblage composition for this ecosystem is problematic due to differences in sampling efforts among the survey periods (1966–1968, 1987–1988, 1989, 1989–1990, 1990–1991 and 2000–2001) and by the inherent ecological variability of estuaries. To overcome these data limitations and better understand fish assemblage change over time, we used robust, simulation-based analyses to compare collections from the different surveys. The 107 fish species collected from the Alvarado Lagoon Estuary in these surveys represent 4 ecological guilds: marine stenohaline, marine euryhaline, estuarine, and freshwater fishes. The occurrence frequency of fish species representing each guild did not change significantly among the survey periods: the chi-square deviation statistic ( 2 = 8.53) was not significantly larger than the average value for 1000 simulated matrices ( 2 = 138.64; P = 1.00). A non-metric multidimensional scaling (MDS) based on Bray-Curtis similarities of fish species presenceabsence data showed that the 1966–1968 survey period was the least similar to the other survey periods. For the 1966–1968 survey, the range of Bray-Curtis inter-survey similarities was 40.4–58.6 (n = 5). By comparison, the remaining range of inter-survey similarities was 61.5–81.7 (n = 10). Average taxonomic distinctness (Δ+) and variation in taxonomic distinctness (Λ+), two sample size-independent measures of diversity, were calculated for all survey periods. Although Δ+ and Λ+ for all survey periods were within the simulated 95% confidence limits for expected values, these values for the 2000–2001 survey period were less than the average Δ+ and Λ+ values for the entire species pool. This suggests that the fish assemblage collected during the latest survey reflects a loss of both widespread higher taxa (reduced Δ+) and that the higher taxa lost are those with only a few representative species in the assemblage (reduced Λ+). These assemblage data show that fish assemblages of Alvarado Lagoon Estuary have not experienced significant changes over 40 years, but differences among the earliest (1966–1968), the latest (2000–2001), and the remaining survey periods indicate a recent decline in diversity.

Dynamics of larval fish assemblages over a shallow coral reef in the Florida Keys

Few time series collections have been made of the larval ichthyofauna in waters directly above shallow coral reefs. As a result, relatively little is known regarding the composition and temporal dynamics of larval fish assemblages in shallow-reef waters, particularly those near a major western boundary current. We conducted a series of nightly net tows from a small boat over a shallow reef (Pickles Reef) along the upper Florida Keys during four new moon and three third-quarter moon periods in July (two new moons), August, and September 2000. Replicate tows were made after sunset at 0–1 m and at 4–5 m depth to measure the nightly progression in community composition, differences in depth of occurrence, and abundance and diversity with lunar phase. A total of 66 families was collected over the 3-month period, with a mean (±SE) nightly density of 23.7±2.1 larvae per 100 m3 and diversity of 24.2±0.9 taxa per tow. A total of 28.8% of the catch was composed of small, schooling fishes in the families Atherinidae, Clupeidae, and Engraulidae. Of the remaining catch, the top ten most abundant families included reef fishes as well as mangrove and oceanic taxa (in descending order): Scaridae, Blennioidei (suborder), Gobiidae, Paralichthyidae, Lutjanidae, Haemulidae, Labridae, Gerreidae (mangrove), Balistidae, and Scombridae (oceanic). These near-reef larval fish assemblages differed substantially from those collected during previous offshore collections. Taxa such as the Haemulidae were collected at a range of sizes and may remain nearshore throughout their larval period. Overall, the abundance and diversity of taxa did not differ with depth (although within-night vertical migration was evident) or with lunar phase. Temporal patterns of abundance of larval fish families clustered into distinct groups that in several cases paralleled family life-history patterns. In late July, a sharp shift in larval assemblages signaled the replacement of oceanic water with inner shelf/bay water. In general, the suite and relative abundance of taxa collected each night differed from those collected on other nights, and assemblages reflected distinct nightly events as opposed to constant or cyclical patterns. Proximity to the Florida Current likely contributes to the dynamic nature of these near-reef larval assemblages. Our results emphasize the uniqueness of near-reef larval fish assemblages and point to the need for further examination of the biophysical relationships generating event-related temporal patterns in these assemblages.

Discerning vegetation and environmental correlates with subtidal marsh fish assemblage dynamics duringPhragmites eradication efforts: Interannual trend measures

We examined the 5-yr (1996–2000) response of subtidal marsh creek fishes (2,793 trawls, 47 species, 30,719 fish) to a large marsh restoration project in the upper Delaware Bay, and found that the salinity gradient covaried along with marsh surface vegetation type among two treated and one untreated reference sites, confounding direct comparison of fish utilization. Examination of environmental correlates with monthly yearly trends highlighted differences between potential mechanism driving assemblage dynamics either intrinsic or extrinsic to the marshes. Within-site and among-site differences in fish assemblage, as described by principal components analysis, correlated poorly with marsh vegetation on both seasonal and interannual scales and appeared to driven by larval supply. Assemblage dynamics could be expalined in part by the occurrence of juveniles of transient marine fishes along a salinity gradient (0–15.2%) range in monthly site mean), but were largely determined by fluctuations in the distribution of two transient species: young-of-the-year bay anchovyAnchoa mitchilli and Atlantic croakerMicropogonias undulatus. A minor mode in variance, driven by locally spawned species, was moderately correlated with environmental parameters. Analysis of marshes on an individual basis did not discern additional important gradients. Our findings are in contrast to those in systems dominated by resident species, probably because transient fishes, which often dominante the system, are more plastic to the nature of ecological services or are affected as much by environment outside of the marsh as by that in the marsh.

Structure of patch-reef fish assemblages at St. Croix, US Virgin Islands, and One Tree Reef, Australia

The structure and dynamics of reef fish assemblages on small patch reefs in the Caribbean (St. Croix, US Virgin Islands) were compared with those studied previously (Sale et al. 1994) on the Great Barrier Reef (One Tree Reef), Australia, in order to test whether assemblage struc- ture and function are consistent despite overall taxonomic differences. St. Croix reefs were monitored over 5 yr (1991 to 1996), while those at One Tree Reef had been monitored for 10 yr (1977 to 1986). Analyses of species richness and abundances for individual patch reef assemblages revealed con- siderable change in assemblage structure between censuses. Specifically, number of individuals and species varied among summer and winter censuses, with summer censuses generally showing greater numbers. Among years but within a season, there was significant variation in the number of indi- viduals (summer and winter) and species richness (summer only) at St. Croix, while only species richness varied yearly (summer and winter) at One Tree Reef. In addition, when the proportional abundances of species observed on each patch reef were compared among censuses on the same patch reefs but at different times (measured as Czekanowski similarity values), results indicated that faunal similarity declined with increasing length of interval between censuses. The mean, between- census Czekanowski similarity values for individual assemblages were 0.56 and 0.59 for St. Croix and One Tree Reef, respectively. These results suggest that there is substantial temporal change in assem- blage structure at both locations. Species in each location were classified into 12 trophic guilds in order to determine whether the assemblages at St. Croix and One Tree Reef showed similar trophic structure despite different species present. Results indicated that guild structure varied among censuses in both locations and that average guild structure differed substantially between these locations. At St. Croix, diurnal and nocturnal planktivores were proportionately more important, while site-attached herbi- vores, wide-ranging grazing herbivores, wide-ranging browsing herbivores, sedentary carnivores, and demersal planktivores were proportionately more important on the Australian patch reefs. Results confirm that comparable assemblage dynamics occur for patch reef assemblages at St. Croix and One Tree Reef. However, there are also clear differences in structure and dynamics in these 2 locations, despite the very similar physical and hydrographic habitats occupied.

Structure and Dynamics of Fish Assemblages in a Tidal Creek Environment

Studies were carried out on structure and dynamics of fish assemblages in the Baguaçu tidal creek, Paranaguá Bay, Brazil. A total of 30,104 fish were captured, comprising 21 families and 47 species. Both in weight and in number, the species Anchoa parva prevailed. Monthly captures in number and weight were largest in the autumn and part of the winter. No seasonal tendency was observed in the indexes of community structure. The dendrogram produced by the classification of the samples separated the 12 months of collection into three groups, reflecting differences in the qualitative and quantitative occurrences of the most important taxa. Some ecological likeness, not only seasonal patterns of abundance, seemed evident in the seasonality of the groupings of species revealed through the cluster analysis. The principal component analysis reflected mainly the periods of rain and drought

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

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

On the dynamics of demersal fish assemblages off Namibia in the 1990s

Demersal fish surveys carried out off Namibia from 1990 to 2000 were used to study the dynamics of demersal fish assemblages on the shelf and upper slope. The study was performed on each major assemblage, i.e. over the shelf (100–300 m deep) and the slope (300–600 m). Changes in size spectrum, diversity, species composition and trends in abundance of the dominating species were analysed. The most evident changes were those related to overall abundance and diversity of the slope assemblage.