Embiotoca Lateralis Research Articles

Embiotoca lateralis

This datasheet on Embiotoca lateralis covers Identity.

Bifunctional Role of the Sternohyoideus Muscle During Suction Feeding in Striped Surfperch, Embiotoca lateralis.

SynopsisIn ray-finned fishes, the sternohyoideus (SH) is among the largest muscles in the head region and, based on its size, can potentially contribute to the overall power required for suction feeding. However, the function of the SH varies interspecifically. In largemouth bass (Micropterus salmoides) and several clariid catfishes, the SH functions similarly to a stiff ligament. In these species, the SH remains isometric and transmitts power from the hypaxial musculature to the hyoid apparatus during suction feeding. Alternatively, the SH can shorten and contribute muscle power during suction feeding, a condition observed in the bluegill sunfish (Lepomis macrochirus) and one clariid catfish. An emerging hypothesis centers on SH muscle size as a predictor of function: in fishes with a large SH, the SH shortens during suction feeding, whereas in fish with a smaller SH, the muscle may remain isometric. Here, we studied striped surfperch (Embiotoca lateralis), a species in which the SH is relatively large at 8.8% of axial muscle mass compared with 4.0% for L. macrochirus and 1.7% for M. salmoides, to determine whether the SH shortens during suction feeding and is, therefore, bifunctional—both transmitting and generating power—or remains isometric and only transmits power. We measured skeletal kinematics of the neurocranium, urohyal, and cleithrum with Video Reconstruction of Moving Morphology, along with muscle strain and shortening velocity in the SH and epaxial muscles, using a new method of 3D external marker tracking. We found mean SH shortening during suction feeding strikes (n = 22 strikes from four individual E. lateralis) was 7.2 ± 0.55% (±SEM) of initial muscle length. Mean peak speed of shortening was 4.9 ± 0.65 lengths s−1, and maximum shortening speed occurred right around peak gape when peak power is generated in suction feeding. The cleithrum of E. lateralis retracts and depresses but the urohyal retracts and depresses even more, a strong indicator of a bifunctional SH capable of not only generating its own power but also transmitting hypaxial power to the hyoid. While power production in E. lateralis is still likely dominated by the axial musculature, since even the relatively large SH of E. lateralis is only 8.8% of axial muscle mass, the SH may contribute a meaningful amount of power given its continual shortening just prior to peak gape across all strikes. These results support the finding from other groups of fishes that a large SH muscle, relative to axial muscle mass, is likely to both generate and transmit power during suction feeding.

Excess postexercise oxygen consumption decreases with swimming duration in a labriform fish: Integrating aerobic and anaerobic metabolism across time.

Many vertebrate animals employ anaerobic pathways during high-speed exercise, even if it imposes an energetic cost during postexercise recovery, expressed as excess postexercise oxygen consumption (EPOC). In ectotherms such a fish, the initial anaerobic contribution to exercise is often substantial. Even so, fish may recover from anaerobic pathways as swimming exercise ensues and aerobic metabolism stabilizes, thus total energetic costs of exercise could depend on swimming duration and subsequent physiological recovery. To test this hypothesis, we examined EPOC in striped surfperch (Embiotoca lateralis) that swam at high speeds (3.25 L s-1 ) during randomly ordered 2-, 5-, 10-, and 20-min exercise periods. We found that EPOC was highest after the 2-min period (20.9 mg O2 kg-1 ) and lowest after the 20-min period (13.6 mg O2 kg-1 ), indicating that recovery from anaerobic pathways improved with exercise duration. Remarkably, EPOC for the 2-min period accounted for 72% of the total O2 consumption, whereas EPOC for the 20-min period only accounted for 14%. Thus, the data revealed a striking decline in the total cost of transport from 0.772 to 0.226 mg O2 ·kg-1 ·m-1 during 2- and 20-min periods, respectively. Our study is the first to combine anaerobic and aerobic swimming costs to demonstrate an effect of swimming duration on EPOC in fish. Clarifying the dynamic nature of exercise-related costs is relevant to extrapolating laboratory findings to animals in the wild.

Axial morphology and 3D neurocranial kinematics in suction-feeding fishes.

ABSTRACTMany suction-feeding fish use neurocranial elevation to expand the buccal cavity for suction feeding, a motion necessarily accompanied by the dorsal flexion of joints in the axial skeleton. How much dorsal flexion the axial skeleton accommodates and where that dorsal flexion occurs may vary with axial skeletal morphology, body shape and the kinematics of neurocranial elevation. We measured three-dimensional neurocranial kinematics in three species with distinct body forms: laterally compressed Embiotoca lateralis, fusiform Micropterus salmoides, and dorsoventrally compressed Leptocottus armatus. The area just caudal to the neurocranium occupied by bone was 42±1.5%, 36±1.8% and 22±5.5% (mean±s.e.m.; N=3, 6, 4) in the three species, respectively, and the epaxial depth also decreased from E. lateralis to L. armatus. Maximum neurocranial elevation for each species was 11, 24 and 37°, respectively, consistent with a hypothesis that aspects of axial morphology and body shape may constrain neurocranial elevation. Mean axis of rotation position for neurocranial elevation in E. lateralis, M. salmoides and L. armatus was near the first, third and fifth intervertebral joints, respectively, leading to the hypothesis of a similar relationship with the number of intervertebral joints that flex. Although future work must test these hypotheses, our results suggest the relationships merit further inquiry.

Intraspecific variation in aerobic and anaerobic locomotion: gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata) do not exhibit a trade-off between maximum sustained swimming speed and minimum cost of transport.

Intraspecific variation and trade-off in aerobic and anaerobic traits remain poorly understood in aquatic locomotion. Using gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata), both axial swimmers, this study tested four hypotheses: (1) gait transition from steady to unsteady (i.e., burst-assisted) swimming is associated with anaerobic metabolism evidenced as excess post exercise oxygen consumption (EPOC); (2) variation in swimming performance (critical swimming speed; Ucrit) correlates with metabolic scope (MS) or anaerobic capacity (i.e., maximum EPOC); (3) there is a trade-off between maximum sustained swimming speed (Usus) and minimum cost of transport (COTmin); and (4) variation in Usus correlates positively with optimum swimming speed (Uopt; i.e., the speed that minimizes energy expenditure per unit of distance traveled). Data collection involved swimming respirometry and video analysis. Results showed that anaerobic swimming costs (i.e., EPOC) increase linearly with the number of bursts in S. aurata, with each burst corresponding to 0.53 mg O2 kg−1. Data are consistent with a previous study on striped surfperch (Embiotoca lateralis), a labriform swimmer, suggesting that the metabolic cost of burst swimming is similar across various types of locomotion. There was no correlation between Ucrit and MS or anaerobic capacity in S. aurata indicating that other factors, including morphological or biomechanical traits, influenced Ucrit. We found no evidence of a trade-off between Usus and COTmin. In fact, data revealed significant negative correlations between Usus and COTmin, suggesting that individuals with high Usus also exhibit low COTmin. Finally, there were positive correlations between Usus and Uopt. Our study demonstrates the energetic importance of anaerobic metabolism during unsteady swimming, and provides intraspecific evidence that superior maximum sustained swimming speed is associated with superior swimming economy and optimum speed.

The response of striped surfperch Embiotoca lateralis to progressive hypoxia: Swimming activity, shoal structure, and estimated metabolic expenditure

When exposed to moderately low O2 conditions (75–30% O2 saturation), shoaling striped surfperch Embiotoca lateralis show no changes in swimming activity, uniform levels of metabolic expenditure and an unchanging shoal structure. As O2 levels become more hypoxic surfperch reduce their locomotor activity, initially with a decrease in turning rate at 20% O2 saturation, followed by a reduction in swimming speed at 15% O2 saturation. Reductions in activity occur in combination with individuals adopting more uniform turning behaviors, which translate into an increase in the distance traveled per unit time (i.e. net displacement). This increase in net displacement may enhance the ability of surfperch to distance themselves from discrete zones of hypoxia. Measures of shoal structure, including nearest neighbor distances and shoal polarity, were constant throughout low O2 exposure despite changes in swimming activity. Estimation of the energetic costs of these behaviors reveals that metabolic expenditure (routine metabolic rate) remained steady at ~120mgO2kg−1h−1 between 100 and 30% O2 saturation, dropping to ~108mgO2kg−1h−1 at 20 and 15% O2 saturation. Given that surfperch possess a critical oxygen saturation (Scrit) of 15.2%, reductions in swimming activity and metabolic energy expenditure clearly occur as individuals reach their aerobic metabolic limits. These results identify that surfperch demonstrate a multi-faceted coping strategy when exposed to low oxygen conditions, which may prove advantageous when the species experience hypoxic episodes in their natural habitat.

Kinematics and energetic benefits of schooling in the labriform fish, striped surfperch Embiotoca lateralis

Schooling can provide fish with a number of behavioural and ecological advantages, including increased food supply and reduced predator risk. Previous work suggests that fish swimming using body and caudal fin locomotion may also experience energetic advantages when trailing behind neighbours. However, little is known about the potential energetic advantages associated with schooling in fish that swim using their pectoral fins. Using the striped surfperch Embiotoca lateralis, a labriform fish that swims routinely with its pectoral fins, we found that pectoral fin beat frequencies were significantly higher for schooling individuals swimming in the front of a school relative to those swimming in the back, with trailing individuals benefiting from a 14.9 ± 3.2% reduction in fin beat frequency (mean ± SE). Trailing fish were estimated to benefit from a 25.6% reduction in oxygen consumption, based on correlations between swimming speeds and pectoral fin beat frequency and between swimming speeds and oxygen consumption of solitary fish. In addition, leading individuals in a school were estimated to have higher oxygen consumption than solitary individuals swimming at the same speed, based on their higher pectoral fin frequency. We suggest that this may be explained by differences in swimming behaviour, with schooling individuals continuously correcting their position relative to their neighbours whilst solitary individuals maintained a more rigid swimming pattern. Taking into account the increased oxygen consumption in leaders vs. solitary fish, we estimated that for an energetic advantage to occur in a school of striped surfperch as a whole, more than 78% of the individuals need to be in trailing positions, which is likely to be a common occurrence based on previous observations of other schooling species.

Partition of aerobic and anaerobic swimming costs related to gait transitions in a labriform swimmer

Members of the family Embiotocidae exhibit a distinct gait transition from exclusively pectoral fin oscillation to combined pectoral and caudal fin propulsion with increasing swimming speed. The pectoral-caudal gait transition occurs at a threshold speed termed U(p-c). The objective of this study was to partition aerobic and anaerobic swimming costs at speeds below and above the U(p-c) in the striped surfperch Embiotoca lateralis using swimming respirometry and video analysis to test the hypothesis that the gait transition marks the switch from aerobic to anaerobic power output. Exercise oxygen consumption rate was measured at 1.4, 1.9 and 2.3 L s(-1). The presence and magnitude of excess post-exercise oxygen consumption (EPOC) were evaluated after each swimming speed. The data demonstrated that 1.4 L s(-1) was below the U(p-c), whereas 1.9 and 2.3 L s(-1) were above the U(p-c). These last two swimming speeds included caudal fin propulsion in a mostly steady and unsteady (burst-assisted) mode, respectively. There was no evidence of EPOC after swimming at 1.4 and 1.9 L s(-1), indicating that the pectoral-caudal gait transition was not a threshold for anaerobic metabolism. At 2.3 L s(-1), E. lateralis switched to an unsteady burst and flap gait. This swimming speed resulted in EPOC, suggesting that anaerobic metabolism constituted 25% of the total costs. Burst activity correlated positively with the magnitude of the EPOC. Collectively, these data indicate that steady axial propulsion does not lead to EPOC whereas transition to burst-assisted swimming above U(p-c) is associated with anaerobic metabolism in this labriform swimmer.

The name of the father: conflict between Louis and Alexander Agassiz and theEmbiotocasurfperch radiation

The surfperch genus Embiotoca currently comprises two species, Embiotoca jacksoni, the black surfperch, and Embiotoca lateralis, the striped surfperch. Originally, however, Louis Agassiz described a third species in the genus Embiotoca, the rainbow surfperch, Embiotoca caryi. This latter name was changed by Louis' son, Alexander, to Hypsurus caryi, a name that remains valid. In this study, new molecular data (3545 bp of DNA from four mitochondrial and two nuclear DNA regions) indicated that the rainbow surfperch should be retained within the genus Embiotoca, a result consistent with recent morphological data. Adaptive radiation combined with sexual selection resulting in rapid morphological changes in the rainbow surfperch may have contributed to the conflicting position of this species.

Isolation and characterization of 12 microsatellites from the black surfperch, Embiotoca jacksoni, a reef fish that lacks a pelagic larval phase

A set of 12 microsatellite markers was developed from Embiotoca jacksoni genomic DNA and tested for polymorphism using 64 individuals from two populations. All loci were polymorphic with a number of alleles ranging from two to 19 with expected heterozygosities ranging from 0.17 to 0.89. There was no evidence of linkage disequilibrium and all loci were in Hardy-Weinberg equilibrium, except for four loci in one population. High numbers of private alleles were consistent with strong population structure, and very limited dispersal. Six microsatellite markers successfully cross amplified and were polymorphic in closely related species, Embiotoca lateralis and Hyspurus caryi.

Pectoral fin beat frequency predicts oxygen consumption during spontaneous activity in a labriform swimming fish (Embiotoca lateralis)

The objective of this study was to identify kinematic variables correlated with oxygen consump- tion during spontaneous labriform swimming. Kine- matic variables (swimming speed, change of speed, turning angle, turning rate, turning radius and pectoral fin beat frequency) and oxygen consumption (MO2) of spontaneous swimming in Embiotoca lateralis were measured in a circular arena using video tracking and respirometry, respectively. The main variable influencing MO2 was pectoral fin beat frequency (r 2 =0.71). No significant relationship was found between swimming speed and pectoral fin beat frequency. Complementary to other methods within biotelemetry such as EMG it is suggested that such correlations of pectoral fin beat frequency may be used to measure the energy requirements of labriform swimming fish such as E. lateralis in the field, but need to be taken with great caution since movement and oxygen consumption patterns are likely to be quite different in field situation compared to a small lab tank. In addition, our methods could be useful to measure metabolic costs of growth and development, or bioassays for possible toxicological effects on fish.

Errata

Journal of Fish BiologyVolume 70, Issue 2 p. 659-659 Free Access Errata This article corrects the following: Exploring the structure of genetic variation and the influences of demography on effective population size in the gag grouper Mycteroperca microlepi (Goode & Bean) N. K. Jue, Volume 69Issue scJournal of Fish Biology pages: 217-224 First Published online: December 1, 2006 Gait transition and oxygen consumption in swimming striped surfperch Embiotoca lateralis Agassiz M. Cannas, J. Schaefer, P. Domenici, J. F. Steffensen, Volume 69Issue 6Journal of Fish Biology pages: 1612-1625 First Published online: December 8, 2006 First published: 02 February 2007 https://doi.org/10.1111/j.1095-8649.2007.01405.xAboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat In Cannas et al. (2006), the final sentence of the abstract was published incorrectly: When speeds ≥Up-c are considered, CT is higher than the theoretical curve extrapolated for PF swimming, suggesting that PF swimming appears to be higher energetically less costly than undulatory swimming using the tail. This sentence should have read: When speeds ≥Up-c are considered, CT is higher than the theoretical curve extrapolated for PF swimming, suggesting that PF swimming appears to be energetically less costly than undulatory swimming using the tail. In Jue (2006), the species name Mycteroperca microlepis appeared incorrectly as Mycteroperca microlepi in the article title. We apologise for these errors. References Cannas, M., Schaefer, J., Domenici, P. & Steffensen, J. F. (2006). Gait transition and oxygen consumption in swimming striped perch Embiotoca lateralis Agassiz. Journal of Fish Biology 69, 1612– 1625. Wiley Online LibraryWeb of Science®Google Scholar Jue, N. K. (2006). Exploring the structure of genetic variation and the influences of demography on effective population size in the gag grouper Mycteroperca microlepi (Goode & Bean). Journal of Fish Biology 69 (Supplement C), 217– 224. Wiley Online LibraryWeb of Science®Google Scholar Volume70, Issue2February 2007Pages 659-659 ReferencesRelatedInformation

Gait transition and oxygen consumption in swimming striped surfperch Embiotoca lateralis Agassiz

A flow‐through respirometer and swim tunnel was used to estimate the gait transition speed (Up‐c) of striped surfperch Embiotoca lateralis, a labriform swimmer, and to investigate metabolic costs associated with gait transition. The Up‐c was defined as the lowest speed at which fish decrease the use of pectoral fins significantly. While the tail was first recruited for manoeuvring at relatively low swimming speeds, the use of the tail at these low speeds [as low as 0·75 body (fork) lengths s−1, LF s−1) was rare (<10% of the total time). Tail movements at these low speeds appeared to be associated with occasional slow manoeuvres rather than providing power. As speed was increased beyond Up‐c, pectoral fin (PF) frequencies kept increasing when the tail was not used, while they did not when PF locomotion was aided by the tail. At these high speeds, the tail was employed for 40–50% of the time, either in addition to pectoral fins or during burst‐and‐coast mode. Oxygen consumption increased exponentially with swimming speeds up to gait transition, and then levelled off. Similarly, cost of transport (CT) decreased with increasing speed, and then levelled off near Up‐c. When speeds ≥Up‐c are considered, CT is higher than the theoretical curve extrapolated for PF swimming, suggesting that PF swimming appears to be higher energetically less costly than undulatory swimming using the tail.

Gait transition speed, pectoral fin‐beat frequency and amplitude in Cymatogaster aggregata, Embiotoca lateralis and Damalichthys vacca

Surfperches are labriform swimmers and swim primarily with their pectoral fins, using the tail to assist only at higher speeds. The transition, from pectoral to pectoral and caudal fins, occurs at a threshold speed that has been termed physiologically and biomechanically ‘equivalent’ for fishes of different size. The gait transition (UP‐C) of Cymatogaster aggregata occurred at a higher speed (measured in bodylengths s−1) for smaller fish than larger fish. At UP‐C, pectoral fin‐beat frequency was size‐dependent: smaller fish have a higher pectoral fin‐beat frequency than larger fish. In contrast, at low speeds (i.e. <60% of UP‐C) the pectoral fin‐beat frequency was independent of the size of the fish. Inter‐specific comparisons of UP‐C, pectoral fin‐beat frequency and amplitude among C. aggregata, Embiotoca lateralis and Damalichthys vacca showed that C. aggregata had a higher UP‐C than E. lateralis and D. vacca. The pectoral fin‐beat frequency at UP‐C showed no significant differences among species. Cymatogaster aggregata achieved higher UP‐C, in part, through increased fin beat amplitude rather than frequency. These differences in performance may be related to the different habitats in which these species live.

Kinematic and electromyographic analysis of steady pectoral fin swimming in the surfperches

The musculoskeletal mechanism of pectoral fin propulsion was investigated in representatives of the two subfamilies of the Embiotocidae (surfperches). Kinematic and electromyographic records of steady swimming by the open-water cruiser Amphistichus rhodoterus and the benthic maneuverer Embiotoca lateralis were compared at 80 % of the species' respective pectoral­caudal gait transition speeds. Synchronized records of fin movement and the intensity of pectoral muscle activity allowed previous hypotheses of muscle function, based on anatomical lines of action, to be tested. Divisions of the pectoral musculature inserting on the central and trailing- edge fin rays serve simple functions of abduction and adduction. Muscles controlling the fin's leading edge, by contrast, play more complex roles during the fin stroke, including deceleration of the fin at the downstroke­upstroke transition and rotation of the adducted fin during the non-propulsive period between fin beats. In spite of their phylogenetic and ecological divergence, the surfperches exhibit a number of mechanistic similarities which probably characterize the family. The timings of kinematic events and the maximal excursions of the fin tip, as well as the temporal order of muscle activation and the time to peak activity, are largely conserved. The predominant dorsoventral component of fin movement during the stride is consistent with a lift-based mechanism of propulsion. E. lateralis exhibits a greater anteroposterior range of motion and a more continuous period of fine motor control of the fin than A. rhodoterus, differences which may correspond to the species' respective capacities for maneuvering. Mechanistic variation in the family is associated with rather minor structural differences (in fin shape and fin base orientation). Owing to the similar functional demands placed on the pectoral fins of many fishes, it is probable that the mechanistic details of embiotociform swimming are widely distributed within the Perciformes.

Pectoral fin locomotion in the striped surfperch. I. Kinematic effects of swimming speed and body size

Swimming trials at increasing velocity were used to determine the effects of steady swimming speed on pectoral fin kinematics for an ontogenetic series of striped surfperch Embiotoca lateralis, ranging from 6 to 23 cm in standard length (SL). The fin stroke cycle consisted of a propulsive period, the duration of fin abduction and adduction, and a 'refractory' period, during which the fin remained adducted against the body. Pectoral fin-beat frequency (fp) measured as the inverse of the entire stride period, as in past studies, increased curvilinearly with speed. Frequency, calculated as the reciprocal of the propulsive period alone, increased linearly with speed, as shown previously for tail-beat frequency of fishes employing axial undulation. Fin-beat amplitude, measured as the vertical excursion of the pectoral fin tip during abduction, increased over a limited range of low speeds before reaching a plateau at 0.35­0.40 SL. Pectoral fin locomotion was supplemented by intermittent caudal fin undulation as swimming speed increased. At the pectoral­caudal gait transition speed (Up-c), frequency and amplitude attained maxima, suggesting that the fin musculature reached a physiological limit. The effects of body size on swimming kinematics differed according to the method used for expressing speed. At a given absolute speed, small fish used higher stride frequencies and increased frequency at a faster rate than large fish. In contrast, the relationship between fp and length-specific speed (SL s-1) had a greater slope for large fish and crossed that for small fish at high speeds. We recommend that comparisons across size be made using speeds expressed as a percentage of Up-c, at which kinematic variables influencing thrust are size-independent.

Compensation in resource use by foragers released from interspecific competition

On shallow reefs where their populations co-occur, black surfperch ( Embiotoca jacksoni Agazzi) and striped surfperch ( Embiotoca lateralis Agazzi) compete strongly for a single preferred resource, dense patches of crustacean food located on the alga Gelidium robustum. Four-ear-long competition experiments revealed a substantial degree of density compensation by each competitor; densities of each species increased on the order of 40% in the absence of the competitor. However, overall densities of surfperch on experimental reefs remained much lower at the end of the experiment than initial (combined) densities. Studies of behavioral compensation, following a reduction in competitor density, revealed that both black surfperch and striped surfperch were able to immediately utilize foraging opportunity on Gelidium, but the two species differed greatly in their ability to garner the freed resources. Striped surfperch compensated behaviorally for all of the new foraging opportunity, whereas black surfperch made use of only a small fraction of it. Although newly-available resources were not shared equitably among members of local populations of either species of surfperch, the unevenness in resource distribution during competitive release appeared to be more pronounced for black surfperch. An understanding of patterns of behavioral compensation sheds light on the determinants of the magnitude of density compensation by each competitor. The degree of density compensation realized by each species was influenced by different factors: the quantity of freed foraging opportunity for striped surfperch, and the ability of the forager to fully exploit the freed resource (black surfperch).

Causes and Consequences of Dietary Specialization in Surfperches: Patch Choice and Intraspecific Competition

The existence, causes, and consequences of dietary specialization were explored for a temperate reef fish, striped surfperch (Embiotoca lateralis). Analyses of diets of adults from Santa Cruz Island, California, revealed three dietary regimes within the same population: specialization on caprellid amphipods, specialization on gammarid amphipods, or a mixed (generalized) diet composed of both caprellids and gammarids. Individuals that had specialized on caprellids at the time of capture had obtained a greater intake of prey than did generalists or specialists on gammarids. Different diets were associated with marked differences on body size within most adult year classes; specialists on caprellids were the largest and specialists on gammarids were the smallest for a given age. Generalists were intermediate in size. Females in the different dietary categories were projected to experience different expected lifetime reproductive outputs. Fitness was calculated to be °10% lower for generalists and °20% lower for specialists on gammarids compared with caprellid specialists. The different diets did not arise from active choice of prey taxa, but from selective use of available foraging patches (i.e., types of benthic algae from which prey are harvested). The degree to which an individual fed from the red alga Gelidium robustum was an excellent indicator of the taxonomic composition of its diet. Gelidium was the only alga harboring substantial members of caprellid amphipods; more importantly, it was the most profitable foraging microhabitat. Access to Gelidium was unequal among striped surfperch due to strong interference, and only competitively dominant individuals appeared able to consistently harvest crustaceans from this microhabitat. The least aggressive individual fed from other, less profitable patches that contained mostly gammarid amphipods. "Dietary" specialization was a passive consequence of patch selection dictated by a strong competitive hierarchy, and was not the result of active choice among available types of prey items.

Contrasting effects of giant kelp on dynamics of surfperch populations.

The effect of giant kelp, Macrocystis pyrifera, on the population dynamics of two temperate reef fishes, striped surfperch (Embiotoca lateralis) and black surfperch (E. jacksoni), was examined. Based on an understanding of how particular reef resources influence abundances of the surfperch and of the effect of giant kelp on those resources, we anticipated that Macrocystis would adversely affect populations of striped surfperch but would enhance those of black surfperch. The natural establishment of giant kelp at sites at Santa Cruz Island, California, resulted in the predicted dynamical responses of surfperch. Abundances of striped surfperch declined rapidly when and where dense forests of giant kelp appeared, but showed little change where Macrocystis was continuously absent over the 8 y period of study. Abundances of adult black surperch, which increased following the appearance of giant kelp, were lagged by >1 y because the dynamical response involved enhanced local recruitment. No change in abundance of black surfperch populations was evident at areas without giant kelp.The mechanism by which giant kelp altered the dynamics of the surfperch involved modification of the assemblage of understory algae used by surfperch as foraging microhabitat. Foliose algae (including Gelidium robustum) were much reduced and turf was greatly enhanced following the appearance of Macrocystis; these two benthic substrata are the favored foraging microhabitat for striped surfperch and black surfperch respectively. Populations of both surfperch species tracked temporal changes in the local availability of their favored foraging microhabitat. Thus, while neither species used Macrocystis directly, temporal and spatial variation in giant kelp indirectly influenced the dynamics of these fishes by altering their foraging base. These results indicate that the dynamics of striped surfperch and black surfperch were governed to a large degree by density-dependent consumer-resource interactions. The present work underscores the predictive value that arises from a knowledge of the mechanisms by which processes operate.

Food acquisition by competing surfperch on a patchy environmental gradient

Black surfperch, Embiotoca jacksoni, and striped surfperch, Embiotoca lateralis, coexisted along steep sloping rocky habitats at Santa Cruz Island, California. The range of depths occupied (to 15 m) was characterized by a strong gradient in abundance of prey and a changing mosaic of substrate types from which surfperch harvested food. Availability of prey and diversity of benthic substrates were greatest in shallowest areas and both declined with increasing depth. Individuals of both surfperch species were residential within a narrow range of depths, with the result that different segments of their populations were consistently exposed to different foraging environments. These two phenomena (residential behavior combined with a gradient in availability of resources) resulted in variation in foraging behaviors and diets among individuals that resided at different depths. The pattern of within-population variation differed between the surfperch species. Black surfperch individuals achieved similar taxonomic diets and expended similar foraging effort at all depths, but deep-water foragers captured much less prey biomass per unit effort. The taxonomic composition of striped surfperch diets differed among depths, and although similar amounts of prey biomass were captured everywhere, individuals in deep areas expended much greater effort to obtain that level of food return. For both species, habitat profitability (food return to foraging effort) declined with depth. The difference in habitat profitability appeared to influence fitness components of both surfperches. Individuals occupying deep habitats were about 5% shorter in standard length than conspecifics of the same chronological age living in shallow areas; the disparity in body size resulted in an estimated difference in clutch size of 10–18%.