Sicyopterus Stimpsoni Research Articles

Jaw muscle fiber type distribution in Hawaiian gobioid stream fishes: histochemical correlations with feeding ecology and behavior

Differences in fiber type distribution in the axial muscles of Hawaiian gobioid stream fishes have previously been linked to differences in locomotor performance, behavior, and diet across species. Using ATPase assays, we examined fiber types of the jaw opening sternohyoideus muscle across five species, as well as fiber types of three jaw closing muscles (adductor mandibulae A1, A2, and A3). The jaw muscles of some species of Hawaiian stream gobies contained substantial red fiber components. Some jaw muscles always had greater proportions of white muscle fibers than other jaw muscles, independent of species. In addition, comparing across species, the dietary generalists ( Awaous guamensis and Stenogobius hawaiiensis) had a lower proportion of white muscle fibers in all jaw muscles than the dietary specialists ( Lentipes concolor, Sicyopterus stimpsoni, and Eleotris sandwicensis). Among Hawaiian stream gobies, generalist diets may favor a wider range of muscle performance, provided by a mix of white and red muscle fibers, than is typical of dietary specialists, which may have a higher proportion of fast-twitch white fibers in jaw muscles to help meet the demands of rapid predatory strikes or feeding in fast-flowing habitats.

Morphological Selection and the Evaluation of Potential Tradeoffs Between Escape from Predators and the Climbing of Waterfalls in the Hawaiian Stream Goby Sicyopterus stimpsoni

Environmental pressures may vary over the geographic range of a species, exposing subpopulations to divergent functional demands. How does exposure to competing demands shape the morphology of species and influence the divergence of populations? We explored these questions by performing selection experiments on juveniles of the Hawaiian goby Sicyopterus stimpsoni, an amphidromous fish that exhibits morphological differences across portions of its geographic range where different environmental pressures predominate. Juvenile S. stimpsoni face two primary and potentially opposing selective pressures on body shape as they return from the ocean to freshwater streams on islands: (1) avoiding predators in the lower reaches of a stream; and (2) climbing waterfalls to reach the habitats occupied by adults. These pressures differ in importance across the Hawaiian Islands. On the youngest island, Hawai'i, waterfalls are close to shore, thereby minimizing exposure to predators and placing a premium on climbing performance. In contrast, on the oldest major island, Kaua'i, waterfalls have eroded further inland, lengthening the exposure of juveniles to predators before migrating juveniles begin climbing. Both juvenile and adult fish show differences in body shape between these islands that would be predicted to improve evasion of predators by fish from Kaua'i (e.g., taller bodies that improve thrust) and climbing performance for fish from Hawai'i (e.g., narrower bodies that reduce drag), matching the prevailing environmental demand on each island. To evaluate how competing selection pressures and functional tradeoffs contribute to the divergence in body shape observed in S. stimpsoni, we compared selection imposed on juvenile body shape by (1) predation by the native fish Eleotris sandwicensis versus (2) climbing an artificial waterfall (∼100 body lengths). Some variables showed opposing patterns of selection that matched predictions: for example, survivors of predation had lower fineness ratios than did control fish (i.e., greater body depth for a given length), whereas successful climbers had higher fineness ratios (reducing drag) than did fish that failed. However, most morphological variables showed significant selection in only one treatment rather than opposing selection across both. Thus, functional tradeoffs between evasion of predators and minimizing drag during climbing might influence divergence in body shape across subpopulations, but even when selection is an important contributing mechanism, directly opposite patterns of selection across environmental demands are not required to generate morphological divergence.

Morphological selection in an extreme flow environment: body shape and waterfall-climbing success in the Hawaiian stream fish Sicyopterus stimpsoni

Morphological selection in an extreme flow environment: body shape and waterfall-climbing success in the Hawaiian stream fish Sicyopterus stimpsoni

Jaw lever analysis of Hawaiian gobioid stream fishes: A simulation study of morphological diversity and functional performance

Differences in feeding behavior and performance among the five native Hawaiian gobioid stream fishes (Sicyopterus stimpsoni, Lentipes concolor, Awaous guamensis, Stenogobius hawaiiensis, and Eleotris sandwicensis) have been proposed based on the skeletal anatomy of their jaws and dietary specialization. However, performance of the feeding apparatus likely depends on the proportions and configurations of the jaw muscles and the arrangement of the jaw skeleton. We used a published mathematical model of muscle function to evaluate potential differences in jaw closing performance and their correlations with morphology among these species. For example, high output force calculated for the adductor mandibulae muscles (A2 and A3) of both A. guamensis and E. sandwicensis matched expectations based on the morphology of these species because these muscles are larger than in the other species. In contrast, Stenogobius hawaiiensis exhibited an alternative morphological strategy for achieving high relative output forces of both A2 and A3, in which the placement and configuration of the muscles conveyed high mechanical advantage despite only moderate cross-sectional areas. These differing anatomical pathways to similar functional performance suggest a pattern of many-to-one mapping of morphology to performance. In addition, a functional differentiation between A2 and A3 was evident for all species, in which A2 was better suited for producing forceful jaw closing and A3 for rapid jaw closing. Thus, the diversity of feeding performance of Hawaiian stream gobies seems to reflect a maintenance of functional breadth through the retention of some primitive traits in combination with novel functional capacities in several species.

Morphological selection in an extreme flow environment: body shape and waterfall-climbing success in the Hawaiian stream fish Sicyopterus stimpsoni

Flow characteristics are a prominent factor determining body shapes in aquatic organisms, and correlations between body shape and ambient flow regimes have been established for many fish species. In this study, we investigated the potential for a brief period of extreme flow to exert selection on the body shape of juvenile climbing Hawaiian gobiid fishes. Because of an amphidromous life history, juvenile gobies that complete an oceanic larval phase return to freshwater habitats, where they become adults. Returning juveniles often must scale waterfalls (typically with the use of a ventral sucker) in order to reach the habitats they will use as adults, thereby exposing these animals to brief periods of extreme velocities of flow. Hydrodynamic theory predicts that bodies with larger suckers and with lower heights that reduce drag would have improved climbing success and, thus, be well suited to meet the demands of the flows in waterfalls. To test the potential for the flow environment of waterfalls to impose selection that could contribute to differences in body shape between islands, we subjected juvenile Sicyopterus stimpsoni to climbing trials up artificial waterfalls (∼100 body lengths) and measured differences in body shape between successful and unsuccessful climbers. Waterfalls appear to represent a significant selective barrier to these fishes, as nearly 30% failed our climbing test. However, the effects of selection on morphology were not straightforward, as significant differences in shape between successful and unsuccessful climbers did not always match hydrodynamic predictions. In both selection experiments and in adult fish collected from habitats with different prevailing conditions of flow (the islands of Hawai'i versus Kaua'i), lower head heights were associated with exposure to high-flow regimes, as predicted by hydrodynamic theory. Thus, a premium appears to be placed on the reduction of drag via head morphology throughout the ontogeny of this species. The congruence of phenotypic selection patterns observed in our experiments, with morphological character divergence documented among adult fish from Hawai'i and Kaua'i, suggests that differences in morphology between subpopulations of adult climbing gobies may result, at least in part, from the selective pressures of high-velocity flows encountered by migrating juveniles.

Muscle fiber type distribution in climbing Hawaiian gobioid fishes: Ontogeny and correlations with locomotor performance

Three species of Hawaiian amphidromous gobioid fishes are remarkable in their ability to climb waterfalls up to several hundred meters tall. Juvenile Lentipes concolor and Awaous guamensis climb using rapid bursts of axial undulation, whereas juvenile Sicyopterus stimpsoni climb using much slower movements, alternately attaching oral and pelvic sucking disks to the substrate during prolonged bouts of several cycles. Based on these differing climbing styles, we hypothesized that propulsive musculature in juvenile L. concolor and A. guamensis would be dominated by white muscle fibers, whereas S. stimpsoni would exhibit a greater proportion of red muscle fibers than other climbing species. We further predicted that, because adults of these species shift from climbing to burst swimming as their main locomotor behavior, muscle from adult fish of all three species would be dominated by white fibers. To test these hypotheses, we used ATPase assays to evaluate muscle fiber type distribution in Hawaiian climbing gobies for three anatomical regions (midbody, anal, and tail). Axial musculature was dominated by white muscle fibers in juveniles of all three species, but juvenile S. stimpsoni had a significantly greater proportion of red fibers than the other two species. Fiber type proportions of adult fishes did not differ significantly from those of juveniles. Thus, muscle fiber type proportions in juveniles appear to help accommodate differences in locomotor demands among these species, indicating that they overcome the common challenge of waterfall climbing through both diverse behaviors and physiological specializations.

Ontogenetic Scaling of Body Proportions In Waterfall-climbing Gobiid Fishes from Hawai'i and Dominica: Implications for Locomotor Function

Potential effects of body size changes on locomotor performance in gobiid fishes (family Gobiidae) were studied in two sicydiine species, Sicyopterus stimpsoni from the Hawaiian Islands and Sicydium punctatum from Dominica, West Indies. These taxa both possess a pelvic sucking disc that can be used to adhere to rock surfaces during bouts of waterfall climbing. If this disc scaled isometrically as body size increased, climbing might be impaired in larger fish because body mass increases faster during growth than the area of the sucker that supports body weight. To test whether the pelvic sucker grows in a way that could help maintain climbing performance in large gobies (and that is distinctive compared to other fins), we evaluated the scaling of sucker area, caudal-fin height, and pectoral-fin length with respect to total body length in Sicyopterus and Sicydium across a range of body sizes. Sucker area scaled isometrically with body length for both species, suggesting that climbing performance might decline as these fishes grow. Although the pectoral fin scaled differently in the two species, caudal-fin height showed strong positive allometry relative to body length in both species. The differing scaling patterns of sucker area and caudal-fin height relative to body length may reflect an increase in the importance of swimming over climbing in sicydiine gobies as they grow larger. Moreover, similarities in the scaling patterns of gobies from geographically distant islands suggest that species in this lineage may be subject to common ontogenetic constraints on performance.

Ontogenetic change in novel functions: waterfall climbing in adult Hawaiian gobiid fishes

AbstractJuveniles from three species of Hawaiian gobiid fishes climb waterfalls as part of an amphidromous life cycle, allowing them to re‐penetrate adult upstream habitats after being swept out to the ocean upon hatching. The importance of climbing for juvenile stream gobies is well established, but adult fish in upstream island habitats also face potential downstream displacement by periodic disturbances. Thus, retention of climbing ability could be advantageous for adult stream gobies. Climbing performance might be expected to decline among adults, however, due to the tendency for mass‐specific muscular power production to decrease with body size, and a lack of positively allometric growth among structures like the pelvic sucker that support body weight against gravity. To evaluate changes in waterfall‐climbing ability with body size in Hawaiian stream gobies, we compared climbing performance and kinematics between adults and juveniles from three species: Awaous guamensis, Sicyopterus stimpsoni and Lentipes concolor. For species in which juveniles climbed using ‘powerbursts’ of axial undulation, adult performance and kinematics showed marked changes: adult A. guamensis failed to climb, and adult L. concolor used multiple pectoral fin adductions to crutch up surfaces at slow speeds, rather than rapid powerbursts. Adult S. stimpsoni, like juveniles, still used oral and pelvic suckers to ‘inch’ up surfaces and climbed at speeds comparable to those of juveniles. However, unlike juveniles, adult S. stimpsoni also add pectoral fin crutching to every climbing cycle. Thus, although powerburst species appear to be particularly susceptible to size‐related declines in waterfall‐climbing performance, the addition of compensatory mechanisms prevents the loss of this novel function in some species.

Functional diversity in extreme environments: effects of locomotor style and substrate texture on the waterfall‐climbing performance of Hawaiian gobiid fishes

AbstractJuveniles of three species of Hawaiian gobiid fishes climb waterfalls during migration to adult habitats using two kinematically distinct patterns: Awaous guamensis and Lentipes concolor use rapid, intermittent bouts of axial undulation (‘powerbursts’), whereas Sicyopterus stimpsoni inches up waterfalls by alternately attaching oral and pelvic suckers to the substrate. Despite the differing kinematics and speed of these behaviors, the extreme demands of locomotion up waterfalls might require similar levels of performance from all climbing goby species. However, the roughness of climbing surfaces might affect performance differently between climbing styles, with rough surfaces decreasing inching performance by impairing the grip of sucking discs on the substrate, but improving powerburst performance by allowing the pectoral fins better purchase as they push against the substrate to start climbing bouts. To test whether species of Hawaiian climbing gobies differ in climbing performance, we filmed multiple individuals of each species as they ascended distances of several body lengths over substrates with three different degrees of roughness. Substantial differences in climbing performance among species were independent of climbing style. For example, the powerburst climber L. concolor always had a faster net climbing speed (speed over 20 cm, including rests between climbing bouts) than the inching climber S. stimpsoni; however, the powerburst climber A. guamensis was similar in net speed to S. stimpsoni, or, on smooth substrates, climbed more slowly. Yet, some differences in performance did emerge between the climbing styles. Substrate roughness did not affect climbing speed in S. stimpsoni, but, as predicted, both powerburst climbers climbed faster on rougher surfaces. In addition, the intermittent motion and rest periods for both powerburst climbers seem of appropriate durations to facilitate an increase in the distance that these species travel before fatigue, but the inching climber S. stimpsoni spent more time in motion than either powerburst climber, and the relative durations of its motion and rest periods seem less likely to convey any performance advantages. These results indicate considerable functional diversity among Hawaiian climbing gobies beyond the two varieties of climbing styles, and show that a wide range of performance capabilities can persist among members of a fauna even under extreme environmental conditions.

The survival of Sicyopterus stimpsoni, an endemic amphidromous Hawaiian gobiid fish, relies on the hydrological cycles of streams: evidence from changes in algal composition of diet through growth stages fish

Gut contents of larval, juvenile, and adult specimens of the Hawaiian gobiid fish Sicyopterus stimpsoni were examined to catalog the algal flora ingested by this species. The developmental stages of S. stimpsoni examined represented hallmark points in the fish’s life cycle corresponding with major migratory and metamorphic transitions. The algal flora was dominated by diatom species and shifted from taxa representative of a marine, planktonic community in larval fish to a freshwater, benthic community in juvenile and adult fish. This change in diet corresponds with the migration of larval fish to freshwater streams just prior to juvenile development in which rapid modification in mouth anatomy makes ingestion of planktonic algal species difficult. Benthic diatoms from juvenile and adult fish assemblages represented multiple genera that live in a narrow set of environmental conditions. These algae grow during a specific period in the development of the benthic algal community in Hawaiian streams. This suggests a highly specialized dietary behavior that depends heavily on continually restarting the benthic algal successional pattern, which appears to be regulated by the hydrological cycles of streams on the island.

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

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.

Kinematics of waterfall climbing in Hawaiian freshwater fishes (Gobiidae): vertical propulsion at the aquatic–terrestrial interface

AbstractTo reach adult habitats, juveniles of three species of Hawaiian gobies (fishes under 3 cm long) climb waterfalls up to 350 m high, over 10 000 times their body length. The demands of moving through such an extreme environment could constrain the range of viable locomotor mechanisms that these fishes use. Previous qualitative observations indicated that Lentipes concolor and Awaous guamensis use ‘powerbursts’ of axial undulation to climb, whereas Sicyopterus stimpsoni‘inches up’ vertical surfaces by alternately attaching oral and pelvic suckers to the substrate. To compare these propulsive mechanisms and their physiological requirements, high‐speed video footage of climbing by juveniles from these three species on an artificial waterfall were collected, and climbing kinematics and performance for the two climbing styles were quantified. Bouts of powerburst climbing by L. concolor and A. guamensis typically begin in or near direct water flow and are initiated by a single, rapid adduction of the pectoral fins. Powerburst climbing bouts are rapid (12.4±1.0 body lengths (BL) s−1), but short in duration (0.07±0.02 s) with few continuous locomotor cycles (3.8±1.3 cycles bout−1). Powerburst climbers use high amplitude undulations along the entire body, but minimum resultant velocities of these undulations are high (>6 BL s−1). This suggests that these species may hybridize terrestrial propulsive mechanisms with aquatic mechanisms. In contrast, climbing by inching in S. stimpsoni involves little axial undulation or fin movement. Sicyopterus stimpsoni typically exit the water outside of direct flow and seem to use terrestrial propulsive mechanisms. As the oral disc attaches to the substrate, it expands to almost twice its resting area, after which the posterior body is pulled upwards; once the pelvic disc attaches, the oral disc releases and the anterior body advances. Climbing bouts include several continuous cycles of disc attachment (11.0±1.4 cycles bout−1) and last several seconds at velocities of 0.21±0.01 BL s−1. Before climbing waterfalls during migration to adult habitats, S. stimpsoni undergo a non‐feeding metamorphosis that leads to the development of the mouth as a secondary locomotor organ. The unusual behaviour and ontogenetic strategy of S. stimpsoni seem to be evolutionary novelties, rather than ancestral retentions, suggesting that the evolution of these features may have been closely correlated. The substantial performance and kinematic distinctions between powerburst and inching climbing indicate that considerable locomotor diversity can evolve even in the context of extreme environmental demands.

Molecular Species Identification of Newly Hatched Hawaiian Amphidromous Gobioid Larvae.

: This report describes a method for the determination of species identity of newly hatched larvae of five sympatric Hawaiian amphidromous gobioids (Lentipes concolor, Sicyopterus stimpsoni, Awaous guamensis, Stenogobius hawaiiensis, and Eleotris sandwichensis). Polymerase chain reaction (PCR) was used to amplify a homologous section of the cytochrome b (Cyt b) region of the mitochondrial genome (mtDNA) from adults of all five species. The resulting PCR-amplified DNA was subjected to restriction fragment length polymorphism (RFLP) analysis producing species-specific restriction patterns. PCR products from the five species were sequenced to substantiate correct amplification, restriction site locations, and fragment sizes. The sequence data were also used to construct a phylogenetic tree. Individual, newly hatched, wild-caught larvae of amphidromous gobioids of unknown species affinity were sorted into six morphotypes based on physical characteristics. These typed larvae and those from two species that spawned in captivity were subjected to the same molecular analysis as the adults. The RFLP results from adults and larvae were compared, allowing larval morphotypes to be assigned to the appropriate species. These comparisons permitted construction of an identification key to the newly hatched larvae of these species based solely on physical characteristics for use in future field studies.Key Words: fish larvae, species identification, Hawaii, gobioidea, PCR, RFLP.http://link.springer-ny.com/link/service/journals/10126/bibs/1n2p167.html

Rapid acquisition of directional preferences by migratory juveniles of two amphidromous Hawaiian gobies, Awaous guamensis and Sicyopterus stimpsoni

The native freshwater fish fauna of the Hawaiian Islands is composed of four gobiid species and one eleotrid. All five species are amphidromous. They spawn in freshwater, go to sea as free embryos and, as juveniles (sometimes referred to as post-larvae), enter fresh water again. Juveniles of two of these species, Awaous guamensis and Sicyopterus stimpsoni, had been observed maintaining directed migratory activity in the absence of water flow during the early freshwater phase of their upstream migration. Our experiments demonstrate that these juveniles are strongly attracted to flowing water. But, when water flow stops the fish persist in migratory behaviour in the same compass direction even when the tank is rotated, controlling for local landmarks and chemical cues, or when the trap that was the original water source is moved. This indicates a rapid (10 min or less) learning of directional cues. Preliminary data indicates a similar ability in a third species, Lentipes concolor. Rapid acquisition of directional preferences may be critical during upstream migration, when these tiny fish traverse water falls and other barriers by climbing in intermittent water flows. We suggest that rapid directional learning may have evolved in gobies as part of their predator avoidance repertoire and been subsequently applied to migration in streams.

Patterns of mtDNA variation in Hawaiian freshwater fishes: the phylogeographic consequences of amphidromy.

MtDNA sequencing was used to assess the phylogeographic structure of four species of Hawaiian freshwater fishes: Lentipes concolor, Stenogobius hawaiiensis, Sicyopterus stimpsoni, and Awaous guamensis. Samples of each species were collected from streams on the northeast side of Kauai, Maui, Molokai, Oahu, and Hawaii. We sequenced segments from both coding and noncoding regions (638-1391 bp) in each species. Sequence analysis uncovered genetic variability in these fishes but no evidence of strong geographic structure among island populations. This result is most readily explained by the fishes' larval marine life stage (amphidromy), which likely facilitates gene flow among island populations. By constraining genetic differentiation among populations, amphidromy may impede speciation in these fishes, possibly explaining why the Hawaiian freshwater fish fauna is depauperate compared to other species-rich Hawaiian faunas. It may also provide them with a kind of evolutionary flexibility atypical of other, more isolated island faunas and allow natural restocking to occur in streams that have been restored to suitable conditions. Comparisons of restriction site and sequence data suggested similar population genetic conclusions for all species except S. stimpsoni, for which the restriction site data is questioned.

Food relations between coexisting native Hawaiian stream fishes

In this study, an ecomorphological perspective is used to examine the role of feeding morphology in shaping patterns of food resource use and coexistence for Awaous guamensis and Sicyopterus stimpsoni, two native gobies (Gobiidae) which inhabit mountainous streams of the high Hawaiian Islands. Using data from underwater census, gut content analysis, and benthic sampling, I determined that A. guamensis, the generalist, had nearly unchallenged use of invertebrate foods. Overlap in fitness for algal use, however, resulted in a partitioning of benthic algae, with A. guamensis having domain over most green algae (43.0% of diet), whereas S. stimpsoni the algal specialist, fed predominantly on blue-green algae (22.6% of diet) and diatoms (54.2% of diet). Cladophora sp. (Chlorophyta) and pennate diatoms (Chrysophyta) were determined to be the ‘primary algal foods’ of A. guamensis and S. stimpsoni, respectively, and were utilized in a mutually exclusive manner with other ‘secondary algal foods’ depending upon availability. Heterogeneity, found in the abundance and composition of algal and invertebrate foods in the benthic landscape both spatially and seasonally, may be regulated by stream flow and periodic disturbance. This changing mosaic of foods is suggested as having provided opportunities for minimizing competitive conflicts and enhancing the potential for stream species to coexist. Competition for preferred foods, created by inter-specific overlap in ecomorphology and spurred by constraints placed on food diversity by the extreme geographic isolation of the Hawaiian Islands, is hypothesized as having played an evolutionary role in shaping resource use patterns which facilitate coexistence.

Evolutionary Genetics of Hawaiian Freshwater Fish

We surveyed mitochondrial (mt)DNA restriction site variation within each of the five native species of Hawaiian freshwater fishes: Lentipes concolor, Stenogobius hawaiiensis, Sicyopterus stimpsoni, Awaous guamensis, and Eleotris sandwicensis. MtDNA haplotypes did not vary geographically except among samples of S. hawaiiensis, where haplotypes from Maui clustered together. One haplotype in this cluster also was found on Kauai and on Oahu, and one haplotype was found only on Kauai. MtDNA data suggest gene flow among islands, consistent with interisland dispersal through amphidromous larvae. We hypothesize that dispersal has prevented further speciation in these fishes and that colonization of island freshwater habitats by larvae could be independent of natal island.

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

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.

Use of fish behavior in assessing the effects of Hurricane Iniki on the Hawaiian island of Kaua'i

Declared the most compact and powerful storm known to have reached the Hawaiian Archipelago, Hurricane Iniki destroyed terrestrial and freshwater habitats island-wide when it struck Kaua'i late on the afternoon of Friday, 11 September 1992. Five weeks after the storm, a research group began underwater studies on the north shore of Kaua'i to assess the physical and biological effects of the hurricane and to track at four-month intervals the recovery of three high quality streams that are home to Hawaii's native and mostly endemic freshwater fishes, mollusks, and crustaceans. Early in the investigation, information on the social behavior of resident fishes showed particular promise for assessing the impact of the hurricane and for tracing the recovery of stream ecosystems. In Hanakapi'ai Stream, the stream damaged most by the hurricane and a subsequent flash flood, two downstream species,Eleotris sandwicensis andStenogobius hawaiiensis, were missing, and members of a third one,Sicyopterus stimpsoni, were sufficiently crowded into the lower section of the stream that aggressive behavior, occasionally resulting in injury, sharply curtailed feeding and prevented all but the earliest phases of courtship. Although the study began in the middle of the spawning season forAwaous guamensis, the few males found were in poor condition and showed neither territorial behavior in response to other males nor courtship when gravid females were encountered. Farther upstream, males ofLentipes concolor directed an inordinate amount of effort toward maintaining territories. Similar, but less dramatic alterations in distribution and behavior were seen in fishes from the less damaged Wainiha River. In Nu'alolo Stream, protected from hurricane winds by nearly vertical valley walls, the behavior was typical for fishes throughout its length except forE. sandwicensis in the damaged section at the stream mouth. Most progress in the return to social behaviors characteristic of pre-hurricane conditions for fishes in Hanakapi'ai Stream and Wainiha River occurred during the first four months of the study, but it was not until October 1993, more than a year after Iniki, that the behavior of the fishes signaled a return to conditions that existed before the storm. The study demonstrated that Hawaii's stream fishes are remarkably capable of rebounding from the effects of hurricanes because of the hardiness of adults and the recruitment of young animals from the ocean as a natural part of each species' amphidromous life cycle.