Stable Isotope Analysis of Amphidromous Hawaiian Gobies Suggests Their Larvae Spend a Substantial Period of Time in Freshwater River Plumes

Synopsis We employed stable isotope analysis (δ¹³C, δ¹⁵N) to evaluate the sources of nutrients used by amphidromous gobiid fishes (Lentipes concolor, Sicyopterus stimpsoni, Awaous guamensis) caught migrating into and living in Hakalau Stream, Hawaii. Although considerable variation amongst the stable isotope values of stream items was noted across all 4 years of our study, the relationships between the fishes were relatively constant. Stable isotope values of recruiting gobies were consistently closer to those of both inshore plankton and freshwater adults than those of offshore plankton, suggesting that the larvae of these species derive much of their nutrition from inshore environments influenced by fresh water. Small differences between the stable values of these species further suggested that their larvae come from different inshore locations. After entering fresh water all species appear to swim rapidly upstream without feeding. Finally, once well upstream, adult L. concolor and A. guamensis appear to assume an omnivorous diet while adult S. stimpsoni rely upon autochthonous production within streams. We propose that freshwater food webs play an integral yet complex role in the lives of both larval and adult amphidromous Hawaiian fishes.     

Diet and food selection in the endemic Hawaiian amphidromous goby, Sicyopterus stimpsoni (Pisces: Gobiidae)

Synopsis The ecological role of Sicyopterus stimpsoni as a nearly exclusive algal grazer in Hawaiian streams is established through gut content analysis of 192 fish from Wainiha River on the northern island of Kaua'i. Algae in three phyla (Chlorophyta, Cyanophyta, and Chrysophyta) were found to be the primary components of the fish's diet (94.62% of dry biomass). Aquatic insect immatures (primarily Chironomidae) accounted for most of the remaining food biomass (5.37%). Poorly developed gill rakers and high gut-to-length ratios provide evidence for adaptation to herbivory and morphological separation of S. stimpsoni from sympatric gobiods. Interspecific competition for the green alga, Cladophora sp., is suggested as an important feature of biotic interactions among native stream fishes but is mitigated by interspecific differences in food preference and utilization. A Category V hurricane which devastated the island in September 1992 provided a fortuitous opportunity to study disturbance influences on benthic food resources in the stream. Disturbance regimes influenced food selection of S. stimpsoni by altering the abundance and composition of stream algae. Rapid adjustment of S. stimpsoni to changes occurring in algal resource abundance illustrates its superb adaptation to life in a swift-water environment subjected to periodic flood-induced disturbance.     

Hawaiian biogeography and the islands' freshwater fish fauna

Aim This paper describes known patterns in the distributions and relationships of Hawaiian freshwater fishes, and compares these patterns with those exhibited by Hawaii's terrestrial biota. Location The study is based in Hawaii, and seeks patterns across the tropical and subtropical Indo‐west Pacific. Methods The study is based primarily on literature analysis. Results The Hawaiian freshwater fish fauna comprises five species of goby in five different genera (Gobiidae). Four species are Hawaiian endemics, the fifth shared with islands in the western tropical Pacific Ocean. All genera are represented widely across the Indo‐west Pacific. All five species are present on all of the major Hawaiian islands. All five species are amphidromous – their larval and early juvenile life being spent in the sea. Although there has been some local phyletic evolution to produce Hawaiian endemics, there has been no local radiation to produce single‐island endemics across the archipelago. Nor is there evidence for genetic structuring among populations in the various islands. Main conclusions In this regard, the freshwater fish fauna of Hawaii differs from the well‐known patterns of local evolution and radiation in Hawaiian Island terrestrial taxa. Amphidromy probably explains the biogeographical idiosyncrasies of the fish fauna – dispersal through the sea initially brought the fish species to Hawaii, and gene flow among populations, across the archipelago, has hitherto inhibited the evolution of local island endemics, apparently even retarding genetic structuring on individual islands.     

Predictability of littoral-zone fish communities through ontogeny in Lake Texoma,Oklahoma-Texas,USA

Synopsis We sampled larval, juvenile and adult fishes from littoral-zone areas of a large reservoir (Lake Texoma, Oklahoma-Texas) (1) to characterize environmental factors that influenced fish community structure, (2) to examine how consistent fish–environment relationships were through ontogeny (i.e., larval vs. juvenile and adult), and (3) to measure the concordance of larval communities sampled during spring to juvenile and adult communities sampled at the same sites later in the year. Larval, juvenile and adult fish communities were dominated by Atherinidae (mainly inland silverside, Menidia beryllina) and Moronidae (mainly juvenile striped bass, Morone saxatilis) and were consistently structured along a gradient of site exposure to prevailing winds and waves. Larval, juvenile and adult communities along this gradient varied from atherinids and moronids at highly exposed sites to mostly centrarchids (primarily Lepomis and Micropterus spp.) at protected sites. Secondarily, zooplankton densities, water clarity, and land-use characteristics were related to fish community structure. Rank correlation analyses and Mantel tests indicated that the spatial consistency and predictability of fish communities was high as larval fishes sampled during spring were concordant with juvenile and adult fishes sampled at the same sites during summer and fall in terms of abundance, richness, and community structure. We propose that the high predictability and spatial consistency of littoral-zone fishes in Lake Texoma was a function of relatively simple communities (dominated by 1–2 species) that were structured by factors, such as site exposure to winds and waves, that varied little through time.     

Local adaptation despite high gene flow in the waterfall‐climbing Hawaiian goby,Sicyopterus stimpsoni

Environmental heterogeneity can promote the emergence of locally adapted phenotypes among subpopulations of a species, whereas gene flow can result in phenotypic and genotypic homogenization. For organisms like amphidromous fishes that change habitats during their life history, the balance between selection and migration can shift through ontogeny, making the likelihood of local adaptation difficult to predict. In Hawaiian waterfall‐climbing gobies, it has been hypothesized that larval mixing during oceanic dispersal counters local adaptation to contrasting topographic features of streams, like slope gradient, that can select for predator avoidance or climbing ability in juvenile recruits. To test this hypothesis, we used morphological traits and neutral genetic markers to compare phenotypic and genotypic distributions in recruiting juveniles and adult subpopulations of the waterfall‐climbing amphidromous goby, Sicyopterus stimpsoni, from the islands of Hawai'i and Kaua'i. We found that body shape is significantly different between adult subpopulations from streams with contrasting slopes and that trait divergence in recruiting juveniles tracked stream topography more so than morphological measures of adult subpopulation differentiation. Although no evidence of population genetic differentiation was observed among adult subpopulations, we observed low but significant levels of spatially and temporally variable genetic differentiation among juvenile cohorts, which correlated with morphological divergence. Such a pattern of genetic differentiation is consistent with chaotic genetic patchiness arising from variable sources of recruits to different streams. Thus, at least in S. stimpsoni, the combination of variation in settlement cohorts in space and time coupled with strong postsettlement selection on juveniles as they migrate upstream to adult habitats provides the opportunity for morphological adaptation to local stream environments despite high gene flow.     

Life History of the Hawaiian Fish Kuhlia sandvicensis as Inferred from Daily Growth Rings of Otoliths

Kuhlia sandvicensis, the aholehole, is a native Hawaiian fish found in both marine and freshwater habitats. In the lower reaches of streams, they are predators on stream fishes, invertebrates, and insects. Aholehole are an important food fish in the Hawaiian Islands and were often used by ancient Hawaiians in traditional ceremonies. Although aholehole are an important part of stream ecosystems and Hawaiian culture, little is known about their life history, specifically, whether a freshwater phase is obligatory. In this study, light microscopy and electron microprobe techniques were used to analyze otolith daily increments. The analysis estimated age of juveniles and provided information regarding salinity of a fish's habitat at specific points in its life. Sr/Ca profiles from otoliths of juvenile and adult fish from fresh and salt water indicated that this species' use of stream habitats is facultative. Unlike Hawaiian freshwater gobies and at least one other member of the Kuhliidae from the Western Pacific, there is no physiological requirement of fresh water at a specific point in the life cycle of K. sandvicensis. Future research will provide a greater understanding as to the importance of streams as nursery habitats for this species. The research is expected to bolster the argument for maintaining the stream-ocean corridor for access by amphidromous gobies and perhaps also for the aholehole.     

Zehnfußkrebse – Pioniere der Evolution

Decapod Crustaceans Decapod Crustaceans, which are by origin a marine group that still occurs mainly in the sea, invaded during their evolution also firm land and freshwater habitats. Stress factors associated with those non‐marine environments have successfully been countervailed by long‐lived benthic juvenile and adult life‐history stages, which were able to evolve structural and physiological adaptations. By contrast, the adaptability of the short‐lived planktonic larval stages has been much weaker, remaining physiologically fragile and mostly dependant on planktonic food sources. Terrestrial as well as limnic decapods have evolved various ”export strategies" based on extended migrations. These are performed by the adult females and/or the first larval stage, being aimed at an avoidance of stress conditions during the larval phase. In order to successfully complete the larval phase in freshwater, already the earliest developmental stages must express special structures and physiological functions aiding to the maintenance of osmotic homeostasis and to an independance from planktonic food sources.     

Feeding performance of the Hawaiian sleeper,Eleotris sandwicensis (Gobioidei: Eleotridae): correlations between predatory functional modulation and selection pressures on prey

The eleotrid fish Eleotris sandwicensis inhabits lower reaches of streams in the Hawaiian Archipelago, where it feeds on juveniles of native amphidromous gobiid fishes migrating upstream from the ocean. Using high‐speed video and geometric modelling, we evaluated the feeding kinematics and performance of E. sandwicensis on free swimming prey, including two species with juveniles of different characteristic sizes, and compared successful and unsuccessful strikes. With fast jaw movements and a highly expansive buccal cavity, E. sandwicensis achieves high suction performance that enables the capture of elusive prey. Our analyses indicated that the species with larger juveniles (Sicyopterus stimpsoni) could be captured from a distance of up to 18.6% of the predator's body length (BL), but capture of the smaller species (Awaous guamensis) required a closer distance (12.2% BL). Predator–prey distance appears to be the predominant factor determining strike outcome during feeding on juvenile A. guamensis. However, during feeding on juvenile S. stimpsoni, E. sandwicensis shows modulations of strike behaviour that correlate with capture success. Moreover, the ability of E. sandwicensis to capture larger prey fish from longer distances suggests a potential biomechanical basis underlying observations that predation by eleotrids imposes significant selection against large body size in juvenile gobies. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 359–374.     

Functional morphogenesis from embryos to adults: Late development shapes trophic niche in coral reef damselfishes

The damselfishes are one of the dominant coral reef fish lineages. Their ecological diversification has involved repeated transitions between pelagic feeding using fast bites and benthic feeding using forceful bites. A highly‐integrative approach that combined gene expression assays, shape analyses, and high‐speed video analyses was used to examine the development of trophic morphology in embryonic, larval, juvenile, and adult damselfishes. The anatomical characters that distinguish pelagic‐feeding and benthic‐feeding species do not appear until after larval development. Neither patterns of embryonic jaw morphogenesis, larval skull shapes nor larval bite mechanics significantly distinguished damselfishes from different adult trophic guilds. Analyses of skull shape and feeding performance identified two important transitions in the trophic development of a single species (the orange clownfish; Amphiprion percula): (a) a pronounced transformation in feeding mechanics during metamorphosis; and (b) more protracted cranial remodeling over the course of juvenile development. The results of this study indicate that changes in postlarval morphogenesis have played an important role in damselfish evolution. This is likely to be true for other fish lineages, particularly if they consist of marine species, the majority of which have planktonic larvae with different functional requirements for feeding in comparison to their adult forms.     

Cascading effects of predatory fish on the composition of benthic algae in high‐altitude streams

Cascading effects of predators can affect ecosystem properties by changing plant biomass, distribution and assemblage composition. Using data from field surveys and whole‐stream experiments we tested the hypothesis that predatory trout change assemblage composition of benthic algae in high‐elevation streams mediated by grazer behavior. Field surveys revealed that the taxonomic composition of algal assemblages differed significantly between streams that contained trout and those that were fishless; but comparisons of palatable versus unpalatable algal taxa between fish and fishless streams were equivocal because of high natural variability. Therefore, we tested for a behavioral (non‐consumptive) trophic cascade experimentally by adding brook trout chemical cues to six naturally fishless streams for 25 days and compared responses of grazers and algae to six reference streams without fish cues added. Algal response variables included rates of change in the abundance of three physiognomic categories, from most palatable (attached erect and prostrate diatoms) to least palatable (non‐diatoms), as determined from food selectivity analyses of the most common grazers (mayflies and caddisflies). Fish cues did not affect the mean densities or changes in densities of total grazers or any individual grazer species. However, in streams where fish cues were added, rates of accrual of attached erect diatoms, which was the preferred algal type for the grazer most vulnerable to trout predation (Baetis), were higher and their densities increased significantly faster with increasing densities of this grazer species than in reference streams. Results of his experiment support the hypothesis that predator induced suppression of grazer foraging behavior, rather than cascading effects of top predators on grazer density, may contribute to variation in the composition of algal assemblages among streams by allowing proliferation of most palatable algal species.     

Cookeolus spinolacrymatus sp. nov., a Late Pliocene priacanthid fish from Okinawa, Japan

A new fossil priacanthid fish,Cookeolus spinolacrymatus, is described on the basis of a single specimen from the Late Pliocene Shinzato Formation, Shimajiri Group, Miyagi-shima, Okinawa, Japan. This species is distinguished from the Recent speciesC. japonicus (Cuvier, 1828) by having a strong spine on the anterior portion of the lacrymal. The specimen was identified as a small benthic adult, or large juvenile, based on comparison with pelvic fin length development in the Recent species.     

Nutrient status,algal and cyanobacterial flora of six fresh water streams of Schirmacher Oasis,Antarctica

The algal and cyanobacterial flora and the chemical environment of six freshwater streams of Schirmacher Oasis, Antarctica were investigated. Over 30 species of algae, predominantly cyanobacteria (Cyanophyceae), were recorded. N₂-fixing species, both heterocystous and unicellular diazotrophs, contributed more than 50% to the counts and their dominance was greatest in the middle of the stream where nitrogen and other nutrients were low. Green algae and diatoms also contributed to the flora. The species composition varied between streams. Glacial and snow drift meltwater streams contained a distinctive community. Based on diversity indices, these streams could be classified into two clusters.     

Dunaliella salina from saline environments of the central coast of Peru

An evaluation of the algal flora of the Salinas de Huacho on the coast of Peru between 1984 and 1990 was carried out by collection of algal mats and natural waters from a variety of habitats and by microscopic examination. D. salina occurred in lagoons and pools with a salinity range of 165\% to 350\% and formed planktonic and benthic communities. The benthic palmelloid stage of D. salina was found at higher salinities. Aplanospore formation was also observed. Associated halophilic species included D. viridis, Oscillatoria tenuis and Pleurocapsa entophysaloides. D. salina was also found at two other salinas on the central Peruvian coast (Chilca and Otuma).     

Distribution patterns of fishes in a canyon-shaped reservoir

In August 2004 and 2005, an extensive study of the fish community was carried out in the largest water supply reservoir in the Czech Republic and Central Europe, the canyon‐shaped ?elivka Reservoir, using a fleet of Nordic multimesh gillnets. Fishes were sampled at eight locations along the longitudinal profile of the reservoir and at five benthic depth layers covering depths from the surface down to 18 m (benthic gillnet 1·5 m high), and at three pelagic depth layers down to the depth of 5 m above the bottom (pelagic gillnets 4·5 m high). Catches of both juvenile (age 0+ year) and adult (fishes >1 year) fishes were highest in the upper layers of the water column (i.e. in the epilimnion down to 5 m, and down to 10 m in the benthic habitats). Along the tributary–dam axis in the pelagic habitats, both juvenile and adult fishes preferred the upper part of the reservoir, where the maximum number of species and also the greatest abundance of zooplankton were found. In the benthic habitats, fishes selected location according to factors other than trophic status. More juvenile fishes were recorded in the benthic habitats than in the pelagic habitats. Depth had the largest explanatory power for predicting fish community composition, followed by the affiliation with benthic and pelagic habitats, and location on the longitudinal axis of the reservoir. The fish community was represented mainly by cyprinids and consisted of two distinct groups of species, with bleak Alburnus alburnus, rudd Scardinius erythrophthalmus and asp Aspius aspius dominating the offshore group while perch Perca fluviatilis and ruffe Gymnocephalus cernuus were affiliated with the inshore group of the adult fish community. Roach Rutilus rutilus, bream Abramis brama and pikeperch Sander lucioperca occurred in important proportions in both the inshore and the offshore zones. All species, with the exceptions of adult perch (1+ year and older), 0+ year perch and 0+ year roach, preferred the most eutrophic tributary part of the reservoir. The fish community was relatively stable between the 2 years sampled.     

Spatial variation in density of stream benthic fishes in northern Hokkaido, Japan: does riparian vegetation affect fish density via food availability?

The densities of two benthic fishes, the Siberian stone loach (Noemacheilus barbatulus) and the wrinklehead sculpin (Cottus nozawae), and the biomass of their food resources (i.e., periphyton and benthic invertebrates) were compared between forest and grassland streams in northern Hokkaido, Japan, to examine whether riparian deforestation had positive effects on the benthic fishes via enhancement of food availability. The comparisons indicated that riparian vegetation had little influence on periphyton, invertebrates, or fishes. Regression analysis indicated that spatial variations in loach and sculpin densities were explained more by substrate heterogeneity, competitor abundance, or both, rather than by food abundance. However, when the two species were combined as benthic insectivores, a strong correlation was found between total benthic fish density and invertebrate biomass. Our results suggest that, although total benthic fish abundance was food limited, riparian vegetation had no positive effects via food availability on the benthic fishes in our streams.     

Top-down control of a meiobenthic community by two juvenile freshwater fish species

Top-down control of prey assemblages by fish predation has been clearly demonstrated for zooplankton and macroinvertebrates. However, in the benthic communities of freshwater ecosystems, the impact of fish predation on meiofaunal assemblages is nearly unknown. In this study, the predation effects of juvenile carp (Cyprinus carpio) and gudgeon (Gobio gobio) on meiofaunal abundance, biomass, community structure, and the diversity of nematodes were examined using microcosms that were sampled repeatedly over 64 days. Significant differences in abundance and biomass were found between the two fish treatments (carp and gudgeon) and their respective controls for nematodes, oligochaetes, and crustaceans (copepods, harpacticoids, ostracods, and cladocerans), but not for rotifers. These changes were consistent with top-down control of the freshwater meiofaunal assemblages in the microcosms over time. By contrast, small-bodied meiofauna was more abundant, suggesting indirect facilitation. Neither the species richness nor the diversity of the nematode community was affected by fish predation. The results indicate that predation by juvenile freshwater fish depresses the overall abundance and biomass of meiofaunal assemblages, except for rotifers, and alters the size structure of the meiofaunal community. Therefore, the meiofaunal assemblages of freshwater ecosystems may be influenced by bottom-feeding juvenile fish, e.g., carp and gudgeon, through top-down control of meiofaunal populations.     

Epibiotic macroalgae on the scallop <Emphasis Type="Italic">Mizuhopecten yessoensis</Emphasis> in Peter the Great Bay,Sea of Japan

The composition and structure of the epibiotic flora of the Japanese scallop Mizuhopecten yessoensis were studied on the basis of data from long-term (1979 to 2007) observations on the scallop beds in Peter the Great Bay (Sea of Japan). In all, 52 species of macroalgae belonging to three phyla were found on the scallop shells; 3 species were new records for the benthic flora of the area studied. Red algae constituted the bulk of the species richness of algal epibionts; brown algae were represented by the lowest number of species. Species of Chlorophyta predominated in terms of biomass; species of Rhodophyta were found in lower numbers. The main form of the thallus of epibiotic algae was bushy or filamentous. The ratio of common to rare species was 30 : 70. As compared to the benthic flora, the epibiotic flora on the scallop shells was characterized by a greater number of warm-water species.     

Observations on development,larval growth and metamorphosis of four species of aplysiidae (gastropoda: Opisthobranchia) in laboratory culture

The development of simple, reliable techniques for the laboratory culture of aplysiid gastropods through their complete life cycle, has enabled us to study the larval biology, metamorphosis, and early juvenile development of these animals. Egg masses, duration of the embryonic phase, veligers, and larval growth and development are described for four species of Hawaiian Aplysiidae, namely, Aplysia dactylomela Rang, Aplysia Juliana Quoy and Gaimard, Dolabella auricularia (Lightfoot) and Stylocheilus longicauda (Quoy and Gaimard). Metamorphosis and early juvenile development of A. Juliana are described in detail with additional comments on these processes in the other three species. Length of the embryonic phase and size of the veliger at hatching are a function of the size of the uncleaved egg. All four species develop planktotrophically and have ≈ 30-day larval phases. In each species the larval phase includes a period of rapid shell growth to a species-specific size followed by a non-growth period during which other morphological developments occur to culminate in metamorphic competence. The larvae of each species metamorphose preferentially on a particular species of benthic algae. The events of metamorphosis require 2 to 4 days for completion and transform the planktonic filter-feeding larva into a benthic, radular-feeding juvenile. Postlarval development includes growth of the shell, parapodia, oral tentacles, rhinophores, anal siphon, and structures of the mantle cavity.     

Indirect effects of the algivorous fish Plecoglossus altivelis altivelis on the growth of two insectivorous benthic fish

1. Animals exploiting different resources may nevertheless interact if one species indirectly alters the abundance and distribution of the food of the other. To analyse this indirect effect, we conducted experiments in artificial pools and in the field to investigate the influence of the algivorous fish Plecoglossus altivelis altivelis (known as the ayu) on two species of insectivorous benthic fish, Pseudogobio esocinus esocinus and the goby Gymnogobius petschiliensis .
2. In the pool experiments, algal biomass was not correlated with the number of ayu, but the percentage of blue-green bacteria rose as the number increased. The number of aquatic macroinvertebrates on the upper surface of ceramic tiles placed in the pool bed decreased as the number of ayu increased.
3. Although ayu and the benthic species did not interact directly, the reduction in invertebrate abundance on the upper surface of tiles in the pool reduced the growth rate of the benthic insectivores.
4. In field experiments, the introduction of ayu into habitats with P. esocinus esocinus or G. petschiliensis reduced the growth rate of these benthic fish. In the field experiment that was carried out over 5 years in the G. petschiliensis habitat, the population density of the goby decreased when ayu were stocked.
5. The ayu is a strong interactor or bioengineer in streams, affecting not only benthic algae but also aquatic invertebrates and fishes. We conclude that to predict the outcome of interspecific interactions amongst fishes in streams with high algal production, possible indirect effects must be considered alongside better known direct effects.     

The influence of pre‐settlement and early post‐settlement processes on the adult distribution and relative dominance of two invasive mussel species

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