Oligocottus Maculosus Research Articles

Osmo-respiratory compromise in the mosshead sculpin (Clinocottus globiceps): effects of temperature, hypoxia, and re-oxygenation on rates of diffusive water flux and oxygen uptake.

In nature, mosshead sculpins (Clinocottus globiceps) are challenged by fluctuations in temperature and oxygen levels in their environment. However, it is unclear how mosshead sculpins modulate the permeability of their branchial epithelia to water and O2 in response to temperature or hypoxia stress. Acute decrease in temperature from 13 to 6 oC reduced diffusive water flux rate by 22% and ṀO2 by 51%, whereas acute increase in temperature from 13 to 25 oC increased diffusive water flux rate by 217% and ṀO2 by 140%, yielding overall Q10 values of 2.08 and 2.47 respectively. Acute reductions in oxygen tension from >95% to 20% or 10% air saturation did not impact diffusive water flux rates, however, ṀO2 was reduced significantly by 36% and 65% respectively. During 1-h or 3-h recovery periods diffusive water flux rates were depressed while ṀO2 exhibited overshoots beyond the normoxic control level. Many responses differed from those seen in our parallel earlier study on the tidepool sculpin, a cottid with similar hypoxia tolerance but much smaller gill area that occupies a similar environment. Overall, our data suggest that during temperature stress, diffusive water flux rates and ṀO2 follow the traditional osmo-respiratory compromise pattern, but during hypoxia and re-oxygenation stress, diffusive water flux rates are decoupled from ṀO2.

Gill surface area allometry does not constrain the body mass scaling of maximum oxygen uptake rate in the tidepool sculpin, Oligocottus maculosus.

The gill oxygen limitation hypothesis (GOLH) suggests that hypometric scaling of metabolic rate in fishes is a consequence of oxygen supply constraints imposed by the mismatched growth rates of gill surface area (a two-dimensional surface) and body mass (a three-dimensional volume). GOLH may, therefore, explain the size-dependent spatial distribution of fish in temperature- and oxygen-variable environments through size-dependent respiratory capacity, but this question is unstudied. We tested GOLH in the tidepool sculpin, Oligocottus maculosus, a species in which body mass decreases with increasing temperature- and oxygen-variability in the intertidal, a pattern consistent with GOLH. We statistically evaluated support for GOLH versus distributed control of [Formula: see text] allometry by comparing scaling coefficients for gill surface area, standard and maximum [Formula: see text] ([Formula: see text],Standard and [Formula: see text],Max, respectively), ventricle mass, hematocrit, and metabolic enzyme activities in white muscle. To empirically evaluate whether there is a proximate constraint on oxygen supply capacity with increasing body mass, we measured [Formula: see text],Max across a range of Po2s from normoxia to Pcrit, calculated the regulation value (R), a measure of oxyregulatory capacity, and analyzed the R-body mass relationship. In contrast with GOLH, gill surface area scaling either matched or was more than sufficient to meet [Formula: see text] demands with increasing body mass and R did not change with body mass. Ventricle mass (b = 1.22) scaled similarly to [Formula: see text],Max (b = 1.18) suggesting a possible role for the heart in the scaling of [Formula: see text],Max. Together our results do not support GOLH as a mechanism structuring the distribution of O. maculosus and suggest distributed control of oxyregulatory capacity.

Aerobic scope falls to nil at Pcrit and anaerobic ATP production increases below Pcrit in the tidepool sculpin, Oligocottus maculosus.

The critical oxygen tension of whole-animal oxygen uptake rate, or Pcrit, has historically been defined as the oxygen partial pressure (PO2) at which aerobic scope falls to zero and further declines in PO2 require substrate-level phosphorylation to meet shortfalls in aerobic ATP production, thereby time-limiting survival. Despite the inclusion of aerobic scope and anaerobic ATP production in the definition, little effort has been made to verify that Pcrit measurements, the vast majority of which are obtained using respirometry in resting animals, actually reflect the predictions of zero aerobic scope and a transition to increasing reliance on anaerobic ATP production. To test these predictions, we compared aerobic scope and levels of whole-body lactate at oxygen partial pressures (PO2s) bracketing Pcrit obtained in resting fish during progressive hypoxia in the tidepool sculpin, Oligocottus maculosus. We found that aerobic scope falls to zero at Pcrit and, in resting fish exposed to PO2s < Pcrit, whole-body lactate accumulated pointing to an increased reliance on anaerobic ATP production. These results support the interpretation of Pcrit as a key oxygen threshold at which aerobic scope falls to nil and, below Pcrit, survival is time-limited based on anaerobic metabolic capacity.

A phylogeny based on cytochrome-c oxidase gene sequences identifies sympatric Ichthyophonus genotypes in the NE Pacific Ocean.

In recent decades, evidence has accumulated to suggest that the widespread and highly variable parasite Ichthyophonus hoferi is actually a species complex. Highly plastic morphology and a general lack of defining structures has contributed to the likely underestimate of biodiversity within this group. Molecular methods are a logical next step in the description of these parasites, but markers used to date have been too conserved to resolve species boundaries. Here we use mitochondrial encoded cytochrome-c oxidase (MTCO1) gene sequences and phylogenic analysis to compare Ichthyophonus spp. isolates from several marine and anadromous fish hosts. The resulting phylogeny displays lineage separation among isolates and possible host/niche segregation not previously described. The parasite type that infects Pacific herring Clupea pallasii, Atlantic herring C. harengus, Atlantic salmon Salmo salar, and Pacific staghorn sculpin Oligocottus maculosus (Clade A) is different from that which infects Chinook salmon Oncorhynchus tshawytscha, walleye pollock Gadus chalcogrammus, Greenland halibut Reinhardtius hippoglossoides, and Pacific halibut Hippoglossus stenolepsis (Clade B). MTCO1 sequences confirmed the presence of a more divergent Ichthyophonus sp. isolated from American shad Alosa sapidissima in rivers of eastern North America (Clade C), while American shad introduced to the Pacific Ocean are infected with the same parasite that infects Pacific herring (Clade A). Currently there are no consensus criteria for delimiting species within Ichthyophonidae, but MTCO1 sequences hold promise as a potential species identifying marker and useful epizootiological tool.

Interactive effects of temperature and hypoxia on diffusive water flux and oxygen uptake rate in the tidepool sculpin, Oligocottus maculosus

The osmorespiratory compromise hypothesis posits that respiratory epithelial characteristics and physiological regulatory mechanisms which promote gas permeability also increase permeability to ions and water. The hypothesis therefore predicts that physiological responses which increase effective gas permeability will result in increased effective ion and water permeabilities. Though analyses of water and gas effective permeabilities using high temperature have generally supported the hypothesis, water permeability responses to hypoxia remain equivocal and the combination of high temperature and hypoxia untested. We measured diffusive water flux (DWF) and oxygen uptake rate (Ṁo2) in response to acute temperature change, hypoxia, and the combination of high temperature and hypoxia in a hypoxia-tolerant intertidal fish, the tidepool sculpin (Oligocottus maculosus). In support of the osmorespiratory compromise hypothesis, Ṁo2 and DWF increased with temperature. In contrast, DWF decreased with hypoxia at a constant temperature, a result consistent with previously observed decoupling of water and gas effective permeabilities during hypoxia exposure in some hypoxia tolerant fishes. However, DWF levels during simultaneous high temperature and hypoxia exposure were not different from fish exposed to high temperature in normoxia, possibly suggesting a failure of the mechanism responsible for down-regulating DWF in hypoxia. These results, together with time-course analysis of hypoxia exposure and normoxic recovery, suggest that tidepool sculpins actively downregulate effective water permeability in hypoxia but the mechanism fails with multi-stressor exposure. Future investigations of the mechanistic basis of the regulation of gill permeability will be key to understanding the role of this regulatory ability in the persistence of this species in the dynamic intertidal environment.

Physical tidepool characteristics affect age- and size-class distributions and site fidelity in tidepool sculpin (Oligocottus maculosus)

Rapidly changing environments pose unique challenges to the resident organisms. Tidepools in coastal environments vary in biophysical characteristics spatially and temporally, and how they vary determines their short- and long-term suitability as habitats and therefore influence on the distributions of tidepool organisms. Biophysical effects on distribution could differ between age classes, depending on their intrinsic ontogenetic requirements and dominance relations. In this study, we investigate the influence of physical pool characteristics on the site fidelity and population distribution of tidepool sculpin (Oligocottus maculosus Girard, 1856). We assessed short-term recapture of marked individuals and size-class distribution among four pool sets. The proportion of adults varied between pools primarily in association with water temperature and pool volume. Smaller adult and larger juvenile fish occupied warmer, small-volume pools, whereas larger adults occupied larger, cooler pools. Between 24% and 56% of marked fish were recaptured, with a higher probability of recapture in pools with “smooth” basins than in those with more rugose basins. Few fish moved among study pools, but the proportion of adults declined with repeated sampling, suggesting greater pool fidelity of juveniles. These results illustrate that intrinsic habitat features influence age- and size-class distributions in a resident tidepool sculpin species, with corresponding consequences for site fidelity.

A walking behavior generates functional overland movements in the tidepool sculpin, Oligocottus maculosus

Tidepool sculpins (Oligocottus maculosus) have been observed moving overland in the rocky intertidal, and we documented the terrestrial walking behavior that they use to accomplish this. We quantified the terrestrial movements of O. maculosus and compared them to (1) their aquatic locomotion, (2) terrestrial locomotion of closely-related subtidal species (Leptocottus armatus and Icelinus borealis), and (3) terrestrial movements of walking catfishes (Clarias spp.). We recorded sculpin movements (210 fps) on a terrestrial platform and in a water tank and tracked body landmarks for kinematic analysis. The axial-appendage-based terrestrial locomotion of O. maculosus is driven by cyclic lateral oscillations of the tail, synchronized with alternating rotations about the base of the pectoral fins, a behavior that appears similar to a military “army crawl.” The pectoral fins do not provide propulsion, but act as stable points for the body to rotate around. In contrast, individuals of O. maculosus use primarily axial undulation during slow-speed swimming. The army crawl is a more effective terrestrial behavior (greater distance ratio) than the movements produced by L. armatus and I. borealis, which use rapid, cyclic oscillations of the tail, without coordinated pectoral fin movements. Relative to Clarias spp., O. maculosus rotated the body about the base of the pectoral fin, rather than the tip of the fin, which may cause O. maculosus to have a lower distance ratio. Since O. maculosus lack major morphological adaptations for terrestrial locomotion, instead relying on behavioral adaptations, we propose behavioral adaptations may evolutionarily predate morphological adaptations for terrestrial locomotion in vertebrates.

Site fidelity and homing behaviour of intertidal sculpins revisited.

To assess the repeatability of an ecological study, this study both partially replicates and extends a previous study on the site fidelity and homing ability of two abundant and ecologically important species of rocky intertidal sculpin fishes, Oligocottus maculosus and Oligocottus snyderi. A traditional mark and recapture approach was utilized and found that both of these species display high site fidelity to a home range of tidepools and homing ability to these pools, confirming the findings of previous work. Unlike the previous study, however, there was no effect of body size on homing ability and a modelling approach that incorporates encounter probability provided evidence for a sex effect on homing ability. In addition, this study extends the maximum homing ability of O. snyderi to 179 m and O. maculosus to 218 m, which were the maximum displacement distances for each species in this study, suggesting they may be capable of even greater homing distances. This work, however, finds that homing success was negatively related to displacement distance. These findings suggest adult sculpin populations are likely to be highly sub-structured geographically, possibly contributing to the exceptionally high species richness of the group.

Divergent transcriptional patterns are related to differences in hypoxia tolerance between the intertidal and the subtidal sculpins.

Transcriptionally mediated phenotypic plasticity as a mechanism of modifying traits in response to an environmental challenge remains an important area of study. We compared the transcriptional responses to low oxygen (hypoxia) of the hypoxia-tolerant intertidal fish, the tidepool sculpin (Oligocottus maculosus) with the closely related hypoxia-intolerant subtidal fish, the silverspotted sculpin (Blepsias cirrhosus) to determine whether these species use different mechanisms to cope with hypoxia. Individuals from each species were exposed to environmental O(2) tensions chosen to yield a similar level of tissue hypoxia, and gene transcription was assessed in the liver over time. There was an effect of time in hypoxia, where the greatest transcriptional change in the silverspotted sculpin occurred between 3 and 24 h in contrast to the tidepool sculpin where the largest transcriptional change occurred between 24 and 72 h of hypoxia. A number of genes showed similar hypoxia-induced transcription patterns in both species (e.g. genes associated with glycolysis and apoptosis) suggesting they are involved in a conserved hypoxia response. A large set of genes showed divergent transcriptional patterns in the two species, including fatty acid oxidation and oxidative phosphorylation, suggesting that these biological processes may contribute to explaining variation in hypoxia tolerance in these species. When both species were exposed to a single environmental O(2) tension, large transcriptional responses were seen in the hypoxia-intolerant silverspotted sculpin while almost no response was observed in the hypoxia-tolerant tidepool sculpin. Overall, divergent transcription patterns in response to both magnitude and duration of hypoxia provide insights into the processes that may determine an animal's capacity to tolerate frequent bouts of hypoxia in the wild.

Critical oxygen tensions as predictors of hypoxia tolerance and tissue metabolic responses during hypoxia exposure in fishes

An organism's critical oxygen tension (Pcrit) reflects its ability to extract environmental O2. Consequently, Pcrit has been used as an indicator of hypoxia tolerance in aquatic animals. The relationship between Pcrit and hypoxia tolerance and hypoxic metabolic responses, however, remains incompletely understood. Among several species of sculpin fishes (superfamily Cottoidea), we previously demonstrated a correlation between Pcrit and hypoxia tolerance, as measured as the time required for 50% of a group of fish to lose equilibrium (LOE50) at a water PO2 of 6.4Torr. In the present study, we further investigated the relationship between Pcrit, hypoxia tolerance, and hypoxic metabolic responses by examining the effects of hypoxia exposure at a fixed percentage of Pcrit (30%; termed relative hypoxia exposure) on LOE50 and metabolic responses in brain, liver, and white muscle in three sculpin species that differ in Pcrit and hypoxia tolerance at 6.4Torr. We also assessed the tissue metabolic responses underlying hypoxic loss of equilibrium (LOE). The species, from most to least hypoxia-tolerant at 6.4Torr and from lowest to highest Pcrit values, were the tidepool sculpin (Oligocottus maculosus), staghorn sculpin (Leptocottus armatus), and silverspotted sculpin (Blepsias cirrhosus). If Pcrit predicts hypoxia tolerance, then we expected similar LOE50 values and similar tissue metabolic responses across all species during relative hypoxia exposure. LOE50 values were similar in staghorn sculpins and tidepool sculpins, but not in silverspotted sculpins, which had a comparatively lower relative hypoxia LOE50 value. Thus, Pcrit, and consequently the ability to extract environmental O2, cannot predict hypoxia tolerance in all species, at least at a water PO2 of 30% of Pcrit. During relative hypoxia exposure, tissue lactate accumulation and ATP levels were similar between species, suggesting that the ability to extract environmental O2 is an important determinant of cellular energy status and reliance on anaerobic glycolysis in hypoxic sculpins. However, whereas tissue glycogen content and utilization were similar between tidepool sculpins and staghorn sculpins, there were lower normoxic levels and greater hypoxic depletion in silverspotted sculpins, potentially explaining their poorer relative hypoxia tolerance. In all species, LOE was associated with depletion of brain [ATP]. Overall, caution is warranted when Pcrit is used as an indicator of hypoxia tolerance, especially when considering temporal aspects of hypoxia tolerance and related metabolic characteristics (e.g. glycogen availability). Ideally, comparative studies of hypoxia tolerance should feature multiple measures (e.g. Pcrit and LOE50) in order to assess the overall responses of fishes to hypoxia.

The Onset Temperature of the Heat-Shock Response and Whole-Organism Thermal Tolerance Are Tightly Correlated in both Laboratory-Acclimated and Field-Acclimatized Tidepool Sculpins (Oligocottus maculosus)

We examined the relationship between thermal tolerance, measured as critical thermal maximum (CT(max)), and aspects of the heat-shock response in tidepool sculpins (Oligocottus maculosus) acclimated to constant laboratory temperatures or acclimatized to field conditions. The CT(max) of fish laboratory acclimated to 6°, 13°, and 20°C were 27.6° ± 0.1°C, 29.5° ± 0.1°C, and 30.8° ± 0.1°C, respectively, increasing linearly by 0.2°C for each 1°C increase in acclimation temperature. The CT(max) of field-acclimatized fish from the low intertidal (29.9° ± 0.1°C) was significantly lower than that of fish from the mid- (30.5° ± 0.1°C) and high (30.4° ± 0.1°C) intertidal. CT(max) and the onset temperature of hsp70 induction in gill (T(on)) were highly correlated in both laboratory-acclimated and field-acclimatized sculpins, with T(on) occurring at 2°C below CT(max) in all cases. However, there was no consistent relationship between CT(max) and the maximum levels of gill hsp70 mRNA. Predicted "acclimation" temperature (15.9° ± 0.3°C) and mean habitat temperature (15.9° ± 1.6°C) were similar for sculpins from low intertidal pools, but this relationship was not apparent in mid- and high intertidal fish. Mark-recapture experiments indicated that approximately 80% of fish from low intertidal pools were residents of that pool, but residency rates were less than 50% in mid- and high intertidal pools, which may explain the lack of correlation between CT(max) and habitat variables in these groups. These data indicate that gill hsp70 T(on) and CT(max) are highly correlated indicators of the thermal performance of tidepool sculpins in both laboratory and field settings.

The integration of locomotion and prey capture in divergent cottid fishes: functional disparity despite morphological similarity

Many mobile animals rely on the integration of locomotion and feeding to capture prey. Fishes commonly swim up to a prey item and utilize a combination of ram and suction feeding for prey capture. Marine cottids represent a diverse and abundant lineage of fishes that exhibit variation in feeding mode that is related to their mouth morphology. However, little is known regarding the integration of the locomotor and feeding systems during prey capture. We quantified the feeding kinematics, feeding performance and integration of locomotion and feeding in two species of divergent cottids: Blepsias cirrhosus (silver-spotted sculpin) and Oligocottus maculosus (tidepool sculpin). Individuals were caught from sympatric habitats near the Bamfield Marine Sciences Centre on Vancouver Island and filmed with a high-speed video camera (500 Hz) while feeding on amphipod prey. Two principal component axes summarize differences in integration and feeding mode despite similarity in attack velocity and feeding morphology (peak gape, peak cranial elevation and peak jaw protrusion). A greater number of correlations between locomotor and feeding variables in B. cirrhosus, compared with O. maculosus, indicate greater integration. We conclude that traditional measures of attack kinematics do not capture functionally and ecologically relevant differences between species. The mechanisms underlying differences in locomotor strategy likely result from unexplored morphological or ecological differences between species. In cottids, integration is apparent in more basal, subtidal species such as B. cirrhosus, and the need for integration may be superceded by demands from the habitat in more derived, shallow-water species such as O. maculosus.

Annual recruitment of three species of tide‐pool fishes is driven by variation in springtime coastal hydrodynamics

Using an 18‐yr time series of annual recruitment of three tide‐pool fishes, Clinocottus globiceps, Clinocottus embryum, and Oligocottus maculosus, we investigated the relationship between recruitment and upwelling and downwelling, date of the spring transition, and spring wave climate. There were no significant regressions between springtime upwelling and recruitment in any species. The timing of the spring transition, however, was related to the recruitment of C. globiceps and C. embryum: the later the spring transition the larger their annual recruitment. We found a negative exponential relationship between timing of the spring transition and O. maculosus recruitment, though only after removing one outlying data point (the strong 1997 El Nino year). Significant negative exponential regressions were also found between O. maculosus recruitment and hours in April and May when waves were ≪2 and ≪3 m in amplitude. In these regressions, 1997 was no longer an outlier. O. maculosus recruitment also varied positively with seawater temperature on the shore. The different hydrodynamic correlates of recruitment in this assemblage of species, as well as published observations, suggest that the larvae of these species are occupying different nearshore areas. Clinocottus species likely develop in coastal waters, while O. maculosus develops very close to shore, essentially in the surf zone, where its larvae may be swept offshore by currents generated during large wave events. Abiotic factors driving larval success can explain persistent differences in recruitment among these species over 18 yr.

The response of the tidepool sculpin, Oligocottus maculosus, to hypoxia in laboratory, mesocosm and field environments

Animals living in the intertidal zone experience regular, predictable fluctuations in physical parameters including temperature, oxygen and salinity and rely on behavioural, physiological and biochemical mechanisms to cope with environmental variation. In the present study, behavioural strategies induced by aquatic hypoxia (e.g. emergence) were performed at similar oxygen tensions across laboratory, mesocosm and field environments; the number of individuals performing these behaviours at any one time was similar in mesocosms and the field. The use of aquatic surface respiration (ASR) was more plastic than emergence behaviour, occurring at a lower oxygen tension in juveniles than adults and being influenced by the addition of alarm substance. Oxygen uptake was lower in air than in water in adults but, in contrast, oxygen uptake was not influenced by the respiratory medium in juveniles. In the laboratory, 72 h of forced emergence did not affect whole body concentrations of lactate but when ASR and emergence were prevented within mesocosm environments there was a significant elevation of lactate. The present study highlights the benefits of transcending traditional laboratory/field boundaries allowing the responses of laboratory-held animals to environmental fluctuation to be integrated with how these animals perform in their natural environment.

CONCORDANCE BETWEEN SHORT-TERM EXPERIMENTS AND LONG-TERM CENSUSES IN TIDE POOL FISHES

Sixteen years of annual censuses (1990-2005) of an assemblage of tide pool sculpins at Tatoosh Island, Washington, USA, revealed relative constancy in the numbers of recruits and adults. However, the dominant species as a recruit (Clinocottus globiceps) was always replaced numerically as an adult by another species (Oligocottus maculosus). When mechanisms of coexistence were evaluated, little support was found for either a lottery model, because competitive interactions are hierarchical, or a storage-effect model of coexistence, because the relative ranking of recruitment varied little among years and did not covary among species with environmental variables such as ocean temperature, upwelling indices, or an estimator of ocean productivity (oyster condition index). There was also little evidence of niche partitioning based on habitat affinities. Additionally, predation-mediated coexistence had little support, given that the competitive dominant did not have the greatest rates of mortality. Instead, a competition-colonization trade-off may contribute to the coexistence of these species, where C. globiceps always recruits in the greatest numbers, while O. maculosus dominates the adult assemblage via competitive processes. The importance of post-recruitment processes in this assemblage is further suggested by some negative associations among species, the presence of density dependence, some habitat affinities, and previously published experimental work that demonstrated the competitive dominance of O. maculosus over C globiceps.

Effects of the Natural Tidal Cycle and Artificial Temperature Cycling on Hsp Levels in the Tidepool SculpinOligocottus maculosus

The rocky intertidal zone is characterized by a predictable cycle of environmental change cued by the ebb and flow of the tides. Tidepools are thus an excellent environment in which to determine whether predictability of environmental change can entrain an endogenous rhythmicity in heat shock protein (Hsp) levels. In this study, we monitored changes in Hsp mRNA and protein levels that occurred over the tidal cycle in tidepool sculpins and investigated whether there was an endogenous tidal rhythm in Hsp expression that persisted once the sculpins were transferred to a stable environment. Fluctuations in the tidepool environment increased hsc70, hsp70, and hsp90 mRNA levels, which translated into increased Hsc/Hsp70 and Hsp90 protein levels; however, this was not due to an endogenous tidal rhythm in Hsp levels because sculpins held under constant conditions did not show any rhythmicity in the expression of these genes. By exposing sculpins to an artificial temperature cycling regime that mimicked the temperature changes of a mid-intertidal pool, we were able to account for the direct role of temperature in regulating Hsp expression. However, there are additional extrinsic factors that likely integrate with temperature and result in differences between the hsp induction profiles that were observed in sculpins inhabiting their natural environment and those in cycling conditions in the laboratory.

A NEW SPECIES OF MALMIANA (OLIGOCHAETA: HIRUDINIDA: PISCICOLIDAE) FROM TIDEPOOL FISHES IN NORTHERN CALIFORNIA

Malmiana buthi n. sp. is described from the body and fins of the fluffy sculpin, Oligocottus snyderi, the tidepool sculpin, Oligocottus maculosus, and the woolly sculpin, Clinocottus analis, collected from tidepools at Horseshoe Cove on the Bodega Marine Reserve in Sonoma County, California. Prevalence of the leech was 32.6% on live-caught O. snyderi; mean intensity on O. snyderi was 3.3 leeches per fish, with a range from 1 to 7. The leech is not known to exceed 8 mm total length. The body is smooth, lacking papillae, tubercles, or pulsatile vesicles. Two pairs of crescentiform eyes are present on the oral sucker, and 1 pair of punctiform eyes occurs on the second annulus of the trachelosome. The caudal sucker has 14 small punctiform ocelli spaced evenly around the margin. The last 9 segments of the urosome have pairs of large punctiform ocelli both dorsally and ventrally. Body and caudal sucker pigmentation is uniformly reddish brown dorsally and ventrally with segental, lateral, unpigmented areas on both the urosome and trachelosome; pigmentation on the oral sucker is in the form of a cross. There are 5 pairs of testisacs; accessory gland cells on the atrial cornua and vector tissue are absent.

Relationships between fish and supralittoral vegetation in nearshore marine habitats

1. This study was conducted to determine whether there were significant differences in the species richness and community composition of fish assemblages in coastal nearshore habitats with differing compositions of supralittoral vegetation. 2. We sampled fish assemblages and conducted supralittoral vegetation surveys at 27 beaches on the west coast of Vancouver Island, British Columbia. Thirteen of the beaches had supralittoral vegetation characteristic of old-growth coastal forests and 14 had been previously subjected to logging or other disturbances. 3. Physical features (e.g. substrate, salinity, etc.) were recorded at each beach to determine whether there were significant associations between supralittoral vegetation and beach characteristics as well as between beach characteristics and fish assemblages. 4. Across all 27 beaches, 1832 individuals of 31 species of nearshore fish were collected, primarily juvenile cottids and salmonids. Mean species richness did not differ between beaches with old-growth versus secondary-growth supralittoral vegetation; however, a higher cumulative number of species was found at beaches with old-growth supralittoral vegetation. 5. Canonical Correspondence Analysis (CCA) showed that beach characteristics and supralittoral vegetation were not significantly associated. Separate CCA for fish associations with beach characteristics and fish associations with supralittoral vegetation explained ∼55% of the variance in fish assemblage composition, suggesting that fish assemblage composition is significantly affected by substrate, submerged vegetation, and physico-chemical conditions as well as by the community composition of vegetation in adjacent supralittoral habitats. 6. Specifically, we found associations between supralittoral vegetation and penpoint gunnels (Apodichthys flavidus Girard), tidepool sculpins (Oligocottus maculosus Girard), Pacific staghorn sculpins (Leptocottus armatus Girard), arrow gobies (Clevelandia ios Jordan and Gilbert), shiner perch (Cymatogaster aggregata Gibbons) and kelp perch (Brachyistius frenatus Gill). Juvenile chum (Oncorhynchus keta Walbaum) and coho (Oncorhynchus kisutch Walbaum) salmon were strongly associated with supralittoral vegetation characteristic of mature coastal forests such as mosses and western red cedar (Thuja plicata) suggesting that some nearshore fish species may be affected by processes originating in terrestrial ecosystems. 7. Our results suggest that some nearshore fish species may be affected by removal of supralittoral vegetation. Copyright © 2006 John Wiley & Sons, Ltd.

Cross‐Tolerance in the Tidepool Sculpin: The Role of Heat Shock Proteins

Cross-tolerance, or the ability of one stressor to transiently increase tolerance to a second heterologous stressor, is thought to involve the induction of heat shock proteins (Hsp). We thus investigated the boundaries of cross-tolerance in tidepool sculpins (Oligocottus maculosus) and their relationship to Hsp70 levels. Survival of sculpins exposed to severe osmotic (90 ppt, 2 h) and hypoxic (0.33 mg O(2)/L, 2 h) stressors increased from 68% to 96%, and from 47% to 76%, respectively, following a +12 degrees C heat shock. The magnitude of this heat shock was critical for protection. A +10 degrees C heat shock did not confer cross-tolerance, while a +15 degrees C heat shock was deleterious. Sculpins required between 8 and 48 h of recovery following the +12 degrees C heat shock to develop cross-tolerance. There was no association between Hsp70 levels before the onset of the secondary stressor and cross-tolerance. However, branchial Hsp70 levels following osmotic shock were highly correlated with the time frame of cross-tolerance. Thus, Hsp70 induction by the priming stressor may be less important than the ability of the cell to mount an Hsp response to subsequent stressors. The time frame of cross-tolerance is similar to the interval between low tides, suggesting the possible relevance of this response in nature.

A molecular assessment of homing in the tidepool sculpin

Molecular analyses of the mitochondrial genome using restriction fragment length polymorphism (RFLP) were utilized to determine the existence of discrete populations of the tidepool sculpin Oligocottus maculosus from the Barkley Sound region of south‐western Vancouver Island, British Columbia. Fifty‐five haplotypes were found with three haplotypes making up 38, 16 and 8% of the total sample, respectively. Within individual tidepools, haplotype diversity ranged from 0·30 to 0·92, but haplotypes were typically closely related to one another (nucleotide diversity ranged from 0·0004 to 0·005). The majority of haplotype variation (96–97%) was located within tidepools, but a significant amount of variation (c. 3–4%) was detected among tidepools within single islands. By contrast, there was no significant differentiation among islands or between samples from the Barkley Sound area and a single sample from north‐eastern Vancouver Island. The results suggest a low level of population structure within the sample area and that the distribution of haplotypes and haplotype divergences represents a demographic expansion from a single ancestral lineage beginning between 300 000 and 1 000 000 years ago. The low level of population subdivision resolved suggests that despite their ecological specialization in tidepool habitats, tidepool sculpins are influenced by demographic and genetic processes that operate on spatial scales much larger than single tidepools or islands.