Spatio‐temporal patterns of fish assemblage structure in a coastal plain stream: appropriate scales reveal historic tales

Quantifying assemblage structure across spatio‐temporal scales is ecologically important and further aids in the understanding of community organisation processes. Currently, few studies have assessed assemblage structure across generous magnitudes of scale, and influences of processes (biotic and abiotic) responsible for structuring assemblages are still questioned. Using community and hydrologic data collected over a 22‐year period from a stretch of river nearing 150 km, we examined spatio‐temporal fish assemblage structural patterns in a temperate coastal plain stream. Results indicated that significant changes in assemblage structure across time were influenced by environmental disturbances, including drought and hurricane events. Assemblages were restructured in a punctuated manner directly following these events, and complete recovery of initial assemblage structure did not occur across the study period. Additionally, we found spatial differentiations between upstream and downstream assemblages, which were driven by greater abundances of several species in downstream sites. Our results suggest that assemblage structure is influenced by environmental variation, specifically, extreme disturbance events and spatial habitat heterogeneity.     

Fish assemblages in the Southern California Current: relationships with climate, 1951–2008

We examined the dominant patterns of variability in the fish fauna of the southern California Current based on a principal component (PC) analysis of the California Cooperative Oceanic Fisheries Investigations ichthyoplankton data set, 1951–2008. Eighty‐six taxa were analyzed, including all ecologically dominant fish species, both exploited and unexploited. The first three PCs accounted for 20.5, 12.4 and 6.8% of the variance of the data, respectively (total: 39.7%). Each was dominated by taxa from particular adult or larval habitats. PC 1 predominantly represented the coherent response of 24 mesopelagic taxa from 10 families and was most highly correlated with long‐term trends in midwater oxygen levels. PC 2 was dominated by six of the seven most abundant ichthyoplankton taxa in the region, predominantly California Current endemics including key pelagic species (northern anchovy, Pacific sardine and Pacific hake), rockfishes (genus Sebastes) and two midwater taxa. It was correlated primarily with sea surface temperature and exhibited a significant declining trend. PC 3 was dominated by coastal and reef‐associated fishes with predominantly southerly affinities. It was positively correlated with sea surface temperature and sea level height, a proxy for diminished flow of the California Current. The taxa dominating PCs 2 and 3 mostly spatially co‐occur as ichthyoplankton. These results suggest that fish assemblages in the California Current are predominantly influenced by environmental forcing of their ocean habitats as adults or larvae, or both.     

A 20‐year census of a rocky littoral fish community in Lake Tanganyika

Takeuchi Y, Ochi H, Kohda M, Sinyinza D, Hori M. A 20‐year census of a rocky littoral fish community in Lake Tanganyika. Ecology of Freshwater Fish 2010: 19: 239–248. © 2010 John Wiley & Sons A/S Abstract – Tropical fish communities are highly diverse with large numbers of allied species coexisting. Concerns have been raised about changes in such communities caused by anthropogenic disturbances, but little is known about long‐term changes. We investigated changes in the littoral fish community of Lake Tanganyika. A 10 × 40‐m quadrat was placed on a rocky shore in the southern part of the lake, and fish censuses were conducted once a year during most years in 1988–2008. In total, 54 cichlid and 6 non‐cichlid species were recorded. Aufwuch feeders were most abundant, followed by plankton feeders, detritus feeders, piscivores, shrimp eaters, zoo‐benthos eaters, and scale eaters. Species richness and abundance were sustained over the study period, with biodiversity, as evaluated by the Shannon–Wiener index, remaining high. However, Mantel tests between the Bray–Curtis index and the difference in years between compared censuses revealed that the species composition of the community gradually changed with time. The fish community gradually underwent a change that may be due to low anthropogenic impacts on food condition. Our results promote awareness about the conservation of diversity in Lake Tanganyika.     

Addition of structural complexity – contrasting effect on juvenile brown trout in a natural stream

In a field experiment, we examined the effects of structural complexity in the form of added artificial plastic plants and shredded plastic bags on growth and abundance of juvenile brown trout (Salmo trutta). Just after emergence, the added complexity had a positive effect on the density, biomass and condition factor of young‐of‐the‐year (0+) brown trout. This difference in density was not present six weeks later. In contrast, both young‐of‐the‐year and older brown trout generally tended to be larger in the simple habitat. Hence, our data suggest that increased complexity initially is beneficial for young‐of‐the‐year individuals probably due to lower risk of predation and increased densities of prey. However, as density increases in the complex environment, it may induce negative density‐dependent effects, here reflected in smaller sized fish in the complex environment. This might force fish to redistribute to habitats with lower densities of conspecifics as they grow larger. We propose that habitat complexity can increase survival of yearlings in early phases and thereby also affect the overall population structure of brown trout in natural streams.     

Prioritizing aquatic conservation areas using spatial patterns and partitioning of fish community diversity in a near‐natural temperate basin

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Long-term patterns of microhabitat use by fish in a southern Appalachian stream from 1983 to 1992: effects of hydrologic period, season and fish length

Abstract— We quantified microhabitat use by members of a southern Appalachian stream fish assemblage over a ten-year period that included both floods and droughts. Our study site (37 m in length) encompassed riffle, run and pool habitats. Previous research indicated that species belonged to either benthic or water-column microhabitat guilds. Most species exhibited non-random microhabitat use in all seasons, and benthic and water column species generally were over-represented in the deeper portions of the site. In addition, water column species generally were over-represented in microhabitats with lower average velocities. The majority of seasonal shifts in microhabitat use were passive (i. e. correlated with changes in microhabitat availability), whereas, most shifts associated with hydrological periods appeared to be active responses to changing environmental conditions. Most species exhibited length-related shifts in microhabitat use, which were strongly affected by hydrologic period for four of ten species. Microhabitat use patterns of assemblage members appeared to be a consequence of species-specific responses to changing environmental conditions. The highly flexible patterns of microhabitat use exhibited by these species necessitate that decisions regarding their management be based on data covering a range of environmental conditions.     

Structures,dynamics and stability of reef fish assemblages in non‐reefal coral communities in Hong Kong,China

• 1. A detailed study on the spatial and temporal patterns of reef fish assemblages associated with non‐reefal coral communities at A Ma Wan (AMW) and A Ye Wan (AYW) in Tung Ping Chau, Hong Kong, China, was carried out using an underwater visual census method from January 1998 to December 1999.
• 2. The study identified a total of 106 species (76 genera in 39 families) of fish in the study sites, in which 88 species were recorded in AMW and 78 species in AYW. Seasonal patterns in the abundance and species richness of all reef fishes and most of the frequently encountered families/trophic groups in both study sites were observed. Seasonal fluctuation of macroalgae, the influence of recruitment of larvae, and the possible seasonal variation in the behaviour of fish may all contribute to these observed seasonal patterns.
• 3. Multidimensional scaling (MDS) ordinations demonstrated that there were spatial variations in the fish community structures within and between sites. Such spatial patterns were possibly related to the spatial variation of the coral community structures in the study sites. The ordinations also showed that the fish community structures in the study sites were not seasonally stable. Such temporal instability of the fish community structures may be partly due to habitat isolation among the fish communities around the island.
• 4. These results imply that preservation and enhancement of habitat connectivity of the coral communities should be one of the main conservation strategies for the reef fish communities of Tung Ping Chau, and those of Hong Kong in general. This strategy may be equally applicable to other non‐reefal coral communities elsewhere around the world.

Copyright © 2008 John Wiley & Sons, Ltd.     

A comparison of fish assemblages associated with different riparian vegetation types in the Hawkesbury–Nepean River system

Fish assemblages in six reaches of the Hawkesbury–Nepean River were studied to identify the effects of two types of riparian vegetation; well‐vegetated banks supporting complex flora dominated by trees and shrubs, and grassed banks, that have been colonised only by grasses after historical deforestation. The fish assemblages showed both spatial and temporal differences and habitats adjacent to grassed banks supported more individuals and more fish species than well‐vegetated banks. Three small species of fish, firetail gudgeon, Hypseleotris galii (Ogilby), flathead gudgeon, Philypnodon grandiceps (Krefft), and empire gudgeon, Hypseleotris compressa (Krefft), occurred in greater abundances adjacent to grassed banks, but freshwater mullet, Myxus petardi (Castelnau), were less abundant near grassed banks than beside well‐vegetated banks. Differences were also shown in the size frequencies of the four larger fish species between riparian vegetation types. The observed differences in the distributions of fish species appeared to be related to the greater abundance aquatic macrophytes near grassed banks, probably an effect of shading of macrophytes near well‐vegetated banks.     

Parasitism of a native Hawaiian stream fish by an introduced nematode increases with declining precipitation across a natural rainfall gradient

Climate change can promote disease emergence if shifting conditions favour infection of native fauna by introduced parasites and pathogens. In Hawai'i, climate warming is predicted to reduce net precipitation and surface flow in streams, which in turn could increase parasitism of native stream fishes by non‐native parasites. In this study, we utilised a natural precipitation gradient across the Hamakua coast on the island of Hawai'i to assess the relationship between precipitation and infection of Awaous stamineus, a native amphidromous goby, by the introduced nematode Camallanus cotti. We found that the abundance, intensity and prevalence of C. cotti in A. stamineus increased with declining rainfall. Our results also show that parasitism tracks precipitation patterns across the archipelago and that parasitism increases even with moderate decreases in rainfall. As the Hamakua coast precipitation gradient represents a proxy for predicted climate‐driven reductions in precipitation, these findings suggest that infection of native Hawaiian fishes by introduced parasites will increase if climate conditions change as expected. Our findings also suggest that parasitism may be exacerbated by other factors that reduce surface flow, including water extraction for agricultural and urban uses. If so, then adaptive management of minimum flow standards in Hawai'i and elsewhere could improve the well‐being of at‐risk native fishes by alleviating parasitism under current and future climate conditions.     

Effects of anthropogenic disturbances on α and β diversity of fish assemblages and their longitudinal patterns in subtropical streams,China

Identifying the spatial patterns of α and β diversity of biotics is an important yet little‐understood area of basic and applied ecological research. Although the upstream–downstream patterns of α diversity of stream fishes are numerously reported, β diversity has received less attention. In this study, we surveyed fishes along the upstream–downstream gradients in three headwater streams of the Qingyi River, China, which were affected by different extents of human activities. We aimed to assess how anthropogenic disturbances affect α and β diversity of stream fishes and their upstream–downstream patterns. We found that, compared with that in the Shuxi Stream disturbed less, endemic species decreased and cosmopolitan species increased in the Maxi and Puxi Stream disturbed heavily. The streams disturbed heavily showed lower α diversity and higher β diversity than that in the stream disturbed less. This among‐stream variations in fish diversity only occurred at the mid‐downstream, not upstream segments. α diversity increased downstream and β diversity decreased downstream from headwaters to mouth in the stream disturbed less, whereas this upstream–downstream pattern in fish diversity shifted in the streams disturbed heavily, in which both α and β diversity showed the quadratic distributions with the hump‐shape for α diversity and the U‐shape for β diversity respectively. Our results suggest that anthropogenic disturbances cause some cosmopolitan fishes replacing many endemic fishes in upland streams. This replacement processes result in α diversity decreasing and β diversity increasing, and shift the spatial patterns in fish diversity along the upstream–downstream gradient.     

Environmental assessment of boreal rivers using fish data – a contribution to the Water Framework Directive

Abstract A fish‐based assessment method was developed to estimate the ecological status of boreal rivers. Electric fishing data were collected from 902 rapids, together with information on the land use, channel modification and water chemistry. Discriminant function analysis was used to select fish variables that most correctly classified the undisturbed reference sites and human impacted sites into exact classes. The relationship between the level of human alteration and fish metrics was examined. Five metrics were selected for the index: the number of fish species, proportion of sensitive species, proportion of tolerant species, density of cyprinid individuals and the density of age‐0+ salmonids. The value for each metric (between 0 and 1) was calculated according to a point estimate for classical probability. The index is used to estimate the ecological classification of rivers according to the EU Water Framework Directive.     

Towards sustainable exhibits – application of an inorganic fertilization method in coral reef fish larviculture in an aquarium

Coral reef fish are collected from the wild and exhibited in aquaria worldwide. Some of the fish spawn in captivity; however, the eggs are usually neglected. In this study, we collected the eggs spawned naturally in the exhibit tanks, hatched and cultured them indoor in 2000‐L fibreglass tanks (initial density = 18 000 egg tank^?1). We applied an inorganic fertilization method commonly used in freshwater fish culture in raising these coral reef fish larvae. We maintained inorganic phosphorus concentration at 100 μg P L^?1 and inorganic nitrogen at 700 μg N L^?1 daily in the fertilized group (n = 4), while the control tanks (n = 4) were fed with rotifers (10 ind mL^?1). Chlorophyll a at particle sizes of both 0.45–20 μm and >20 μm, as well as NH₃‐N, NO₃‐N, and PO₄‐P concentrations were significantly higher in the fertilized group than the control. Zooplankton in the size groups of 10–50 μm (mainly flagellates) and 50–100 μm (mainly ciliates) were abundant (about 10~60 ind mL^?1) during 3–7 days in fertilized tanks. The average larval fish survival rate at 21 day after hatch in fertilized group was consistently higher than the control in two trials. The experiments demonstrated that the inorganic fertilization approach can be successfully adapted for coral reef fish culture in an aquarium to achieve sustainable exhibits.     

The relative influence of spatial context and catchment‐ and site‐scale environmental factors on stream fish assemblages in a human‐modified landscape

Abstract – Environmental factors act in a hierarchical manner at multiple spatial scales to influence the organisation of ecological assemblages; however, the relative influence of the different scale‐related factor groups is poorly known. We evaluated the importance of catchment‐scale and site‐scale environmental variables, as well as the spatial context of the sampling sites, in shaping stream fish assemblages in an agriculture‐dominated landscape in Hungary. Beside the variables describing spatial context (principal coordinates of a truncated distance matrix among sites), altogether 60 environmental variables were used to predict variability using a variance‐partitioning procedure in redundancy analysis. Presence–absence‐ and relative abundance‐based data were examined at two assemblage levels (entire assemblage and native assemblage) at 54 stream sites. Incorporation of spatial variables increased largely the total explained variability in case of relative abundance, but not for presence–absence data. Of the environmentally explained variance, catchment‐scale variables (e.g., land cover types, patch density) were relatively more influential for the native assemblage‐level analyses, than for analyses at the entire assemblage level, where site‐scale variables (e.g., altitude, depth) proved to be more influential. In addition, pure catchment‐ and pure site‐scale variables have the primary role in determining fish assemblage patterns, whereas the influence of shared variance and that of site‐scale riparian variables proved to be less important. Our findings demonstrate the importance of incorporating the spatial context of the sampling sites in predicting fish assemblage patterns and the effects of channelisation (dikes) in shaping assemblage–environment relationships in this human‐influenced landscape.     

Mesopelagic fish larval assemblages during El Niño‐southern oscillation (1997–2001) in the southern part of the California Current

Mesopelagic species are the principal constituents of larval fish assemblages inhabiting the southerly California Current region. Seasonal larval abundance is influenced by circulation of the California Current and subtropical Countercurrent, including regional changes of the physical, chemical, and biological characteristics during the El Niño‐Southern Oscillation. This study examines the mesopelagic fish larvae distribution and abundance patterns between seasons and years, with the aim of describing the mesopelagic larval assemblages during dynamic environmental changes induced by El Niño (1997–1998) and the rapid transition to La Niña (1998–2000) along the west coast of the Baja California Peninsula (25–31°N). Despite large oceanographic variability, larval assemblages varied principally on a seasonal basis, related to reproductive periods and the north–south gradient influenced by the seasonal pattern of the California Current. An increased diversity, number of species, and abundance of tropical species was noticeable during the northward expansion of warm‐water taxa during El Niño, principally in the northern areas (Ensenada and Punta Baja). After El Niño, population adjustments and rapid recovery occurred during La Niña conditions, which reflected seasonal differences in the mesopelagic community structure that are closely related to the seasonal pattern of oceanic currents.     

Biological effectiveness of an inexpensive nature‐like fishway for passage of warmwater fish in a small Ontario stream

Few studies have been conducted to evaluate the effectiveness of nature‐like fishways, particularly in low gradient warmwater streams with diverse fish communities. We evaluated a nature‐like fishway that was installed to facilitate upstream passage at a low head dam on Indian Creek near Spencerville, Ontario, Canada. A passive integrated transponder (PIT) array was used to quantify attraction and passage efficiency for 391 PIT tagged warmwater fish, represented by seven species. Attraction efficiency for the three most common species, common shiner (Luxilus cornutus), creek chub (Semotilus atromaculatus) and white sucker (Catostomus commersonii), was 63.3%, 83.7% and 65.6%, respectively, and passage efficiencies were 5.1%, 38.4% and 25%, respectively. Creek chub were able to locate the fishway in less time than white sucker and common shiner; however, took longer to successfully pass. Manipulation of creek chub release locations was used to separate issues of attraction and passage and revealed that passage efficiency was highest (76.2%) for those released within the fishway and intermediate for those released at the entrance (42.1%). This multispecies fishway improved stream connectivity, but additional work is needed to fine tune its configuration. Similar projects that engage stakeholders in nature‐like fishway construction are a promising approach for the thousands of small dams that occur on low gradient streams around the globe, but those studies should incorporate a biological evaluation to ensure that attraction and passage efficiency are optimised.     

A simple approach for assigning the conservation status of freshwater fish based on their natural variability – a case study from the Iberian Ecoregion

A simple, non‐lethal method for assigning conservation status is proposed based on three conservation classes (favourable, unfavourable/inadequate and unfavourable/bad) to fish species based on their natural population variability. To demonstrate this approach, conservation classes were allocated to three native fish species (brown trout Salmo trutta L., northern Iberian chub Squalius carolitertii (Doadrio), and northern straight‐mouth nase, Pseudochondrostoma duriense (Coelho) based on basic population variables (density and biomass) using a 9‐year dataset (2004–2012) from 15 different sampling sites in Spain. The classification of the population variables into conservation classes was made using previously described nonparametric methods and percentiles categorisation, and the current conservation status of the studied species was established. Temporal trend analyses showed that S. carolitertii experienced a progressive significant decrease during the study period, whereas both S. trutta and P. duriense exhibited weak increases in density. The study exemplifies the need to quantify the natural variability of fish resources to reveal their current conservation status and to determine whether short‐term and long‐term management actions are needed to rehabilitate native fish assemblages. The proposed approach could easily be employed by fisheries managers to monitor the conservational status of other native species.     

Changes in the fish and fisheries ecology of a large man-made lake in Tanzania, 1965–94

Abstract Nyumba ya Mungu Reservoir in northern Tanzania has a maximum surface area of 180 km², an average depth of 6 m, and contains moderately saline, fertile water. The postimpoundment decade, 1965–74, was characterised by a spectacular rise and fall of a tilapiabased fishery. Since then a gill-net fishery catching large numbers of large, periphyton-grazing tilapias has given way to a mainly beach-seine fishery producing large numbers of small, phytoplankton-feeding Oreochromis esculentus (Graham). Yields remain higher than preimpoundment predictions but the size at maturity of all tilapia species has fallen and few larger than 15 cm TL are caught. These changes, and others in the fish community trophic structure, are chiefly explained by changes in the littoral environment and fishing pressures. Nyumba ya Mungu provides a case history of developments in the tilapia fishery of a man-made river lake conducted on an essentially laissez-faire basis.     

Fattv acid content of some freshwater fish in lakes of different trophic levels – a bottom-up effect?

Abstract– Various sizes of roach, perch, pike, zander (pike-perch) and crucian carp were collected from lakes of different trophic levels in order to study the variation of lipids and fatty acids (FA) within and between species. Freeze-dried samples of the dorsal muscle were analysed quantitatively for total lipid content and FA content. The results indicate that total lipid and FA contents can vary considerably, both within and between species. In contrast to herbivorous fish, carnivorous-piscivorous fish FA patterns were more constant and independent of size - fry excepted. Lipid and FA contents of roach from two oligotrophic lakes were significantly higher than in roach from a eutrophic lake. Differences in basic food webs may be responsible for these results. In the oligotrophic lakes, the algal flora was dominated by species classified as high quality food for grazers, e. g. flagellates and diatoms. It was shown in earlier papers that these algal groups contain two long-chained FA of φ 3 type (eicosapentaenoic acid and docosahexaenoic acid) which are used as criteria indicating high nutritional value. Conversely, the eutrophic lake was dominated by blue-greens, a group of autotrophs lacking these long-chained φ 3 FA. Blue-greens have generally been classified as poor food for grazers. (The fatty acids are described by three numbers, x:yφz, where x=number of carbon atoms, y=number of double bonds, and z=position of the first double bond counted from the methyl end of the molecule.)     

冬季东海外海鱼类群落特征及其对拉尼娜事件的响应

根据2004年12月和2008年12月东海区渔业资源底拖网调查资料,利用多元分析[非度量多变量排序(nMDS)、SIMPER],对比分析正常年份(2004年)和拉尼娜(La Ni(n)a)年份(2008年)不同生态属性鱼类的变化特征,探究鱼类群落结构对拉尼娜事件的响应模式.结果表明,2008年冬季与2004年冬季相比,调查水域的种类组成由45种增加至61种,其中,暖水性种类比例减少,暖温性种类比例增加.主要优势种年间变化不大,仍为带鱼(Trichiurus japonicus)和小黄鱼(Larimichthys polyactis),两者资源密度之和分别占总资源密度的59.95％和55.16％.不同生态属性种类的资源密度发生了显著变化,以带鱼(Trichiurus japonicus)为代表的暖水性鱼类资源密度下降,而以小黄鱼(Larimichthys polyactis)为代表的暖温性鱼类资源密度增加.研究水域生物丰富度指数(R)、多样性指数(H')和均匀度指数(J))的均值均有所升高,但独立样本t检验表明,年间3指数间无显著性差异(P＞0.05).在捕捞压力保持相对稳定的情况下,群落组成的变化可能与拉尼娜事件有关,未来需要掌握不同种类对拉尼娜事件的响应模式.     

Luminal uptake of Vibrio (Listonella) anguillarum by shed enterocytes – a novel early defence strategy in larval fish

As adhesion and translocation through fish gut enterocytes of the pathogen Vibrio (Listonella) anguillarum are not well investigated, the effective cause of disease and mortality outbreaks in larval sea bass, Dicentrarchus labrax, suffering from vibriosis is unknown. We detected V. anguillarum within the gut of experimentally infected gnotobiotic sea bass larvae using transmission electron microscopy and immunogold labelling. Intact bacteria were observed in close contact with the apical brush border in the gut lumen. Enterocytes contained lysosomes positive for protein A‐gold particles suggesting intracellular elimination of bacterial fragments. Shed intestinal cells were regularly visualized in the gut lumen in late stages of exposure. Some of the luminal cells showed invagination and putative engulfment of bacterial structures by pseudopod‐like formations. The engulfed structures were positive for protein A‐colloidal gold indicating that these structures were V. anguillarum. Immunogold positive thread‐like structures secreted by V. anguillarum suggested the presence of outer membrane vesicles (MVs) hypothesizing that MVs are potent transporters of active virulence factors to sea bass gut cells suggestive for a substantial role in biofilm formation and pathogenesis. We put forward the hypothesis that MVs are important in the pathogenesis of V. anguillarum in sea bass larvae.