Description:    The propagation of most aquatic macrophytes occurs vegetatively, via fragments. After dispersal, the fragments may exhibit two survival strategies: colonization (the ability to develop roots) and regeneration (the ability to develop new propagules that can disperse). Invasive species, for example, Hydrilla verticillata , are known to have a high potential for dispersal and growth. We experimentally evaluated the colonization and regeneration abilities and growth rates of this species in the early stage of development and compared these properties to the corresponding characteristics of two native species of Hydrocharitaceae ( Egeria densa and Egeria najas ). The following hypotheses were tested: (1) fragments with apical tips have greater colonization and regeneration abilities and higher growth rates than fragments without apical tips and (2) H. verticillata has greater colonization and regeneration abilities and higher growth rates than other native species of Hydrocharitaceae. Our results showed that both types of fragments had the same ability to colonize, whereas fragments without tips had a higher ability to regenerate. However, fragments with apical tips showed higher growth rates. It is probable that these higher growth rates resulted from apical dominance. H. verticillata had the greatest propagation potential. Its colonization and regeneration abilities and growth rates were greater than those of the native species. These differences can produce competitive advantages for the exotic species in the early stages of development in new habitats and may contribute to understanding the success of the exotic compared to the native species. Content Type Journal Article Pages 1-7 DOI 10.1007/s10452-012-9413-0 Authors Cristiane Akemi Umetsu, Programa de Pós-graduação Em Ecologia de Ambientes Aquáticos Continentais, Universidade Estadual de Maringá, Maringá, Paraná CEP 87020-900, Brazil Heloísa Beatriz Antoniazi Evangelista, Programa de Pós-graduação em Biologia Comparada, Universidade Estadual de Maringá, Maringá, Paraná CEP 87020-900, Brazil Sidinei Magela Thomaz, Programa de Pós-graduação Em Ecologia de Ambientes Aquáticos Continentais, Universidade Estadual de Maringá, Maringá, Paraná CEP 87020-900, Brazil Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Salinization of coastal freshwater environments is a global issue. Increased salinity from sea level rise, storm surges, or other mechanisms is common in coastal freshwater marshes of Louisiana, USA. The effects of salinity increases on aquatic macroinvertebrates in these systems have received little attention, despite the importance of aquatic macroinvertebrates for nutrient cycling, biodiversity, and as a food source for vertebrate species. We used microcosm experiments to evaluate the effects of salinity, duration of exposure, and prey availability on the relative survival of dominant aquatic macroinvertebrates (i.e., Procambarus clarkii Girard, Cambarellus puer Hobbs, Libellulidae, Dytiscidae cybister ) in a freshwater marsh of southwestern Louisiana. We hypothesized that increased salinity, absence of prey, and increased duration of exposure would decrease survival of aquatic macroinvertebrates and that crustaceans would have higher survival than aquatic insect taxon. Our first hypothesis was only partially supported as only salinity increases combined with prolonged exposure duration affected aquatic macroinvertebrate survival. Furthermore, crustaceans had higher survival than aquatic insects. Salinity stress may cause mortality when acting together with other stressful conditions. Content Type Journal Article Pages 1-10 DOI 10.1007/s10452-012-9410-3 Authors Sung-Ryong Kang, School of Renewable Natural Resources, Louisiana State University AgCenter, Rm. 307, RNR Building, Baton Rouge, LA 70803, USA Sammy L. King, U.S. Geological Survey, Louisiana Fish and Wildlife Cooperative Research Unit, School of Renewable Natural Resources, Louisiana State University AgCenter, Baton Rouge, LA 70803, USA Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    The multipurpose Jangheung Dam, which was constructed in 2006 on the upper reaches of the Tamjin River, has a trapping and trucking fishway installed next to the dam outlet to facilitate the upstream migration of fish. In this study, the movement of the fluvial specialist Zacco temminckii that did not show distinct spawning migration was examined in a lentic environment following transportation to the reservoir above the dam. In total, 15 fish were tagged with coded acoustic transmitters ( n  = 11) and acoustic depth transmitters ( n  = 4). Thirteen of these fish moved to adjacent tributaries (2 individuals died following release), 9 of which travelled directly, and 4 of which became disorientated, travelling back and forth before finding a tributary. There was no significant relationship between fish characteristics and the tributaries to which the fish moved (Kruskal–Wallis test, p  〉 0.05). All 4 fish that were tagged with depth transmitters demonstrated vertical migration, stayed to relatively deep water 2 h before and after sunrise and sunset, respectively (Mann–Whitney U test, p  〈 0.05), although there were slight differences in migration time and depth between individuals. Although monitoring conducted small-sized reservoir, all of tagged fish (except 2 individuals) were randomly and successfully moved to tributaries under lentic environment. Consequently, it is expected that other fluvial fish species may exhibit similar movement patterns to Z. temminckii , although further research is required. Additionally, a wider range of release sites should be useful for trapping and trucking operations to reduce the amount of energy being expended whilst searching for tributaries and to allow stocks that have previously become fragmented by the dam to remix more effectively. Content Type Journal Article Pages 1-10 DOI 10.1007/s10452-012-9411-2 Authors Ju-Duk Yoon, Biological Resource Center, Kongju National University, Gongju, 314-701 South Korea Jeong-Hui Kim, Department of Biology Education, Kongju National University, Gongju, 314-701 South Korea Gea-Jae Joo, Department of Biological Sciences, Pusan National University, Busan, 609-735 South Korea Min-Ho Jang, Department of Biology Education, Kongju National University, Gongju, 314-701 South Korea Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Stoichiometry theory states that the elemental composition of individual organisms is a taxon-dependent trait, and that organisms maintain relatively constant body nutrient composition, independent of food nutrient content or ingestion rate. Some recent studies have pointed out that assuming a strict homeostasis in fish is an over-simplification, so that nutrient ratios in fish bodies may not be as constant as previously thought. In this study, our aims were (a) to assess the overall nutrient composition of roach, (b) to reveal any significant differences in elemental composition of roach between populations from different lakes and (c) to relate these potential differences to environmental parameters and fish condition. The mean elemental composition of roach (whole fish) was 45.0 ± 5.3 % carbon (C), 10.2 ± 0.8 % nitrogen (N), and 2.4 ± 0.5 % phosphorus (P), while their molar C/N/P ratio was approximately 50:10:1. The elemental composition of roach was not as constant as homeostatic stoichiometry models would predict. Significant differences were found in the carbon, nitrogen, and phosphorus contents of fish sampled from different lakes. Productivity of lakes (expressed as chlorophyll- a ) was positively correlated with  %C, C/N, C/P, and N/P ratios, and negatively correlated with  %N and  %P. In turn, mean lake temperature was negatively correlated with  %C and C/N ratio, but not with other nutrients or nutrient ratios. Condition factor was negatively related to the  %C of fish, but it did not correlate significantly with  %N,  %P, or nutrient ratios. Our results on intraspecific nutrient variation illustrate the potential differences between populations and emphasize the importance of lake-specific approaches. Content Type Journal Article Pages 1-10 DOI 10.1007/s10452-012-9402-3 Authors Gergely Boros, Balaton Limnological Institute, Centre for Ecological Research, Hungarian Academy of Sciences, P.O. Box 35, Tihany, Hungary Jussi Jyväsjärvi, Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, Jyväskylä, Finland Péter Takács, Balaton Limnological Institute, Centre for Ecological Research, Hungarian Academy of Sciences, P.O. Box 35, Tihany, Hungary Attila Mozsár, Department of Hydrobiology, University of Debrecen, P. O. Box 57, Debrecen, Hungary István Tátrai, Balaton Limnological Institute, Centre for Ecological Research, Hungarian Academy of Sciences, P.O. Box 35, Tihany, Hungary Martin Søndergaard, Department of Bioscience, Aarhus University, P. O. Box 314, Silkeborg, Denmark Roger I. Jones, Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, Jyväskylä, Finland Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Periphyton is an important component within the littoral zones of lakes, but it is known to vary dramatically on small (cm–m) and large (km) spatial scales, showing differences in composition and abundance. Until relatively recently, changes in periphyton composition along depth gradients have not been studied sufficiently and the response of small meiobenthic invertebrates inhabiting the periphyton to vertically changing environmental conditions such as light are poorly understood. To investigate the changing community composition of epilithic (on stones) nematodes along a depth gradient, we conducted a field study at Lake Erken, Sweden, with the specific objective to investigate whether changes in periphyton composition (algae, bacteria) are reflected in changing nematode feeding types and what the consequences are for nematodes and their resource consumption. We analysed the abundance, species composition and feeding type distribution of epilithic nematodes along 11 depth levels, from 5 to 300 cm water depth. Our study resulted in the first measurements of carbon ( 13 C) and nitrogen ( 15 N) stable isotopes in free living nematodes in lakes. Nematode community composition and feeding type distribution exhibited dramatic changes along the depth gradient. Nematode feeding types changed from a dominance of algae-feeding species in the shallow littoral zone to one of bacteria-feeding species in the deep littoral zone. The 13 C stable isotope signatures of nematodes and the small (〈20 μm) periphyton fraction changed with increasing depth, with nematodes shown to feed on this small periphytic component. Nematodes were identified as primary consumers by means of trophic level calculations based on 15 N stable isotopes. Content Type Journal Article Pages 1-14 DOI 10.1007/s10452-012-9408-x Authors Lars Peters, Animal Ecology, University Bielefeld, Morgenbreede 45, 33615 Bielefeld, Germany Carsten Faust, Animal Ecology, University Bielefeld, Morgenbreede 45, 33615 Bielefeld, Germany Walter Traunspurger, Animal Ecology, University Bielefeld, Morgenbreede 45, 33615 Bielefeld, Germany Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Sampling collection for stable isotope analysis has traditionally involved the sacrifice of the animal. Seahorses ( Hippocampus spp.) are listed as threatened by the Convention on International Trade in Endangered Species ( http://www.cites.org ) and consequently lethal sampling is undesirable. We evaluated the adequacy of dorsal fin tissue of adult seahorses Hippocampus guttulatus for stable isotope analysis as an alternative to lethal tissue sampling. Three seahorse tissues (dorsal fin, muscle, and liver) were analyzed for comparisons of δ 15 N and δ 13 C values. Similarities found between δ 15 N and δ 13 C values in dorsal fin and muscle tissue of H. guttulatus suggest that both tissues are adequate for stable isotope analysis to understand feeding ecology of seahorses. However, considering the threatened status of the species, dorsal fin tissue would be recommended in adult seahorses as a non-lethal sampling. The effect of lipid extraction on carbon and nitrogen stable isotope values was also evaluated in each seahorse tissues. Significant effects of lipids extraction did only occur for δ 13 C values in muscle and liver. It was found that lipid removal was not necessary to perform SIA in dorsal fin tissues. Due to the limited availability of fin tissue obtained from fin-clipping in seahorses, the relationship between the mass/surface of dorsal fin clip and stable isotope values was analyzed. δ 15 N and δ 13 C values in fin samples were found to be independent of the size of fin analyzed. According to our study, the use of fin-clipping sampling, with a minimum surface analyzed of 12.74 mm 2 , was found to be an adequate method for SIA in seahorses. Content Type Journal Article Pages 1-8 DOI 10.1007/s10452-012-9407-y Authors Sonia Valladares, Instituto de Investigaciones Marinas (CSIC), Eduardo Cabello 6, 36208 Vigo, Spain Miquel Planas, Instituto de Investigaciones Marinas (CSIC), Eduardo Cabello 6, 36208 Vigo, Spain Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Bluegill ( Lepomis macrochirus ) and yellow perch ( Perca flavescens ) populations are often sympatric in the Great Plains region of the U.S.A. and portions of Canada; however, very little attention has been given to potential interactions between these species for available resources, especially during the early life stages. Relationships between age-0 bluegill and yellow perch growth and relative abundance were explored across multiple lakes and years within the Nebraska Sandhill region, USA. In addition, four habitat patch types (open water, Phragmites spp., Typha spp., Scirpus spp.) were sampled for age-0 bluegill and yellow perch, and food habits were examined for each species during August, September, and October of 2009 in one of these lakes. Age-0 yellow perch growth was negatively related to age-0 bluegill relative abundance across a spatiotemporal scale. Age-0 bluegill and yellow perch exhibited similar habitat use (moderate–high overlap), but generally consumed different important and dominant prey taxa (bluegill consumed both macroinvertebrates—56 % and zooplankton—44 %, while yellow perch consumed more zooplankton—66 %), which resulted in low overall diet overlap between species. Previous research indicates that age-0 yellow perch diet ontogeny often results in feeding predominately on macroinvertebrates and positively selecting them (and avoiding zooplankton prey) at sizes observed in our study. Therefore, yellow perch growth rates may be compromised by the presence of bluegill because of the need to consume less energetically profitable prey items such as zooplankton. Content Type Journal Article Pages 1-10 DOI 10.1007/s10452-012-9406-z Authors Mark A. Kaemingk, Department of Natural Resource Management, South Dakota State University, Brookings, SD 57007, USA David W. Willis, Department of Natural Resource Management, South Dakota State University, Brookings, SD 57007, USA Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Tuna purse seine fisheries target fish aggregated in schools, including free schools that are formed naturally based on fish biology and aggregations associated with natural and/or artificial drifting objects. Using data collected from skipjack tuna ( Katsuwonus pelamis ) fisheries, we evaluated differences in size structures between drifting-floating-object-associated schools and unassociated schools. We developed a generalized linear model to remove impacts of environmental variables on skipjack size composition. This study indicates that the drifting-floating-object-associated schools tended to have significantly wider size ranges than the unassociated schools. This suggests that unassociated schools were likely formed based on similarity in sizes among individuals within a school while drifting-floating-object-associated schools were probably composed of individuals of large size ranges and their formation was not based on the “size selection” rule. We concluded that the unassociated schools and the drifting-floating-object-associated schools were formed through different mechanisms, and drifting floating objects could aggregate unassociated schools of different size structures. Thus, a large scale of deployment of man-made floating objects might disrupt the spatial aggregation pattern of fish that otherwise tended to school based on their sizes in the absence of floating objects. Content Type Journal Article Pages 1-10 DOI 10.1007/s10452-012-9405-0 Authors Xuefang Wang, College of Marine Sciences, Shanghai Ocean University, 999 Hucheng Huan Road, Shanghai, 201306 China Liuxiong Xu, College of Marine Sciences, Shanghai Ocean University, 999 Hucheng Huan Road, Shanghai, 201306 China Yong Chen, School of Marine Sciences, University of Maine, Orono, ME 04469, USA Guoping Zhu, College of Marine Sciences, Shanghai Ocean University, 999 Hucheng Huan Road, Shanghai, 201306 China Siquan Tian, College of Marine Sciences, Shanghai Ocean University, 999 Hucheng Huan Road, Shanghai, 201306 China Jiangfeng Zhu, College of Marine Sciences, Shanghai Ocean University, 999 Hucheng Huan Road, Shanghai, 201306 China Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    Organic matter release by scleractinian corals fulfils an important ecological role as energy carrier and particle trap in reef ecosystems, but the hypothetically stimulating impact of water currents, an essential and ubiquitous environmental factor in coral reefs, on this process has not been investigated yet. This study therefore quantifies organic matter release by two species of scleractinian corals subjected to ambient water current velocities ranging from 4 to 16 cm s −1 using closed-system flow-through chambers. Findings revealed that particulate organic matter (POM) concentration was significantly increased in the flow-through chambers in all investigated coral species compared to still water conditions, while no effect on dissolved organic carbon (DOC) concentration could be observed. These results suggest that POM release by corals may be controlled by hydro-mechanical impacts, while DOC fluxes are rather influenced by the physiological condition of the corals. Hence, this study indicates that previous POM release quantification results are conservative estimates and may have underestimated in situ POM release through corals in reef environments. The contribution of coral-derived POM to biogeochemical cycles in reef ecosystems, therefore, may be more pronounced than already assumed. Content Type Journal Article Pages 1-7 DOI 10.1007/s10452-012-9404-1 Authors Christian Wild, Coral Reef Ecology Group (CORE), Faculty of Biology and Chemistry (FB2), University of Bremen, Fahrenheitstr. 6, 28359 Bremen, Germany Christian Laforsch, Department Biology II and GeoBio-Center, Ludwig-Maximilians-University Munich, Großhadenerstraße 2, 82152 Martinsried, Germany Christoph Mayr, Institute of Geography, Friedrich-Alexander-Universität Erlangen-Nürnberg, Kochstr. 4/4, 91054 Erlangen, Germany Roland Fuß, Institute of Soil Ecology, Helmholtz Zentrum München, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany Wolfgang Niggl, Coral Reef Ecology Group (CORE), Faculty of Biology and Chemistry (FB2), University of Bremen, Fahrenheitstr. 6, 28359 Bremen, Germany Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588

Description:    In the Koitajoki River, Eastern Finland, there exists a self-sustaining population of river-spawning densely rakered whitefish ( Coregonus lavaretus pallasi ). The population has been classified as near-threatened due to overexploitation and possible hybridization with the lake-spawning sparsely rakered whitefish form. Thus, knowledge of habitat use, movements, and migrations is important for threat assessment and management decisions. We employed conventional tagging and acoustic telemetry to provide information on movements and home range of the Koitajoki River whitefish. We tagged mature individuals at their spawning areas and followed fish movements by tag recoveries and continuously recording fixed receiving stations. The maximum movement distances were 40–50 km both upstream and downstream from the releasing site. There were indications of a clear seasonal migration pattern and spawning-site fidelity; riverine habitats were mainly occupied for spawning and overwintering, while feeding and growth mainly took place in lacustrine environments within several lakes of the river system. Due to their migratory nature, whitefish is vulnerable to environmental disturbances and overfishing in a large geographic area. Content Type Journal Article Pages 1-10 DOI 10.1007/s10452-012-9403-2 Authors Hannu Huuskonen, Department of Biology, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland Helena Haakana, Department of Biology, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland Ari Leskelä, Finnish Game and Fisheries Research Institute, Yliopistokatu 6, 80100 Joensuu, Finland Jorma Piironen, Finnish Game and Fisheries Research Institute, Yliopistokatu 6, 80100 Joensuu, Finland Journal Aquatic Ecology Online ISSN 1573-5125 Print ISSN 1386-2588