Embiotoca Jacksoni Research Articles

Composition, importance and movement of fishes from San Quintín Bay, Baja California, Mexico

Monthly samplings were conducted at San Quintín Bay (Baja California, Mexico) in 1994 to determine the fish species assemblage, their abundance, frequency of occurrence, and movement. The sampling gear used included the otter trawl and beam trawl (5 and 10 m depth), beach seine net (<3 m depth), gillnet, and hook and line. The 5 and 3 m depths were characterized by seagrasses. A total of 64 fish species were identified. The most important species according to the index of community importance (abundance and occurrence) were the bay pipefish (Syngnathus leptorhynchus), the California halibut (Paralichthys californicus), the shiner surfperch (Cymatogaster aggregata), the diamond turbot (Hypsopsetta guttulata), and the black surfperch (Embiotoca jacksoni). Other abundant species were the topsmelt (Atherinops affinis), which inhabits the zone close to the beach, and the slough anchovy (Anchoa delicatissima), a temporal visitor to the lagoon. Low temperatures were recorded during April and May, coinciding with a movement of fishes towards the inner part of the bay.

Population structure in Banggai cardinalfish, Pterapogon kauderni , a coral reef species lacking a pelagic larval phase

Previous studies on two reef fish lacking a pelagic larval phase (Acanthochromis polyacanthus and Embiotoca jacksoni) revealed features that may be characteristic of their lifestyle: (1) low levels of gene flow, (2) frequent population bottlenecks, and (3) strong phylogeographic breaks, all within their over 1,000 km coastal geographic ranges. The present study tested the predictive nature of these three characteristics in another species lacking a pelagic larval stage, but with a very restricted distribution (<10,000 km2). The Banggai cardinalfish, Pterapogon kauderni Koumans, 1933, is a mouthbrooding species occurring in the Banggai Archipelago (eastern Indonesia). Fish were captured in January and February (2001, 2002). The mitochondrial control region of 122 individuals from 22 locations was sequenced. P. kauderni individuals clustered in two reciprocally monophyletic clades corresponding to a southwestern population (restricted to the southwest of Bangkulu Island) and all northern and eastern populations, which included all the remaining samples. Data were compatible with reduced gene flow and the presence of severe bottlenecks; however, small sample sizes and limited genetic variability in P. kauderni prevented a definitive conclusion. Further studies using larger samples and more rapidly evolving molecular markers may provide enough power to conclusively test our hypotheses.

Fish production of a temperate artificial reef based on the density of embiotocids (Teleostei: Perciformes)

The abundance of two embiotocids (Embiotoca jacksoni and Rhacochilus vacca) was surveyed continually from 1974 to 1998 on the breakwaters comprising King Harbor in Redondo Beach, California, and a nearby natural rocky-reef as a reference. Embiotocids provide an interesting model for reef-fish production because they are viviparous and their entire ontogeny can be observed on the reefs. We deduce that the two reef populations of both species were stable at their carrying capacity. This carrying capacity was greater in King Harbor throughout the study. We also report a linear decline in survival of juveniles of both species over the 25-year period. Overall regional processes were similar on the two reefs, yet temporal differences suggested that they were acting independently. The King Harbor reefs produced greater biomass for both species, which represents one factor explaining the higher density of kelp bass (Paralabrax clathratus), an important predator.Copyright 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.

No Behavioral Control over Mating Frequency in Queen Honey Bees (Apis melliferaL.): Implications for the Evolution of Extreme Polyandry

Ever since the seminal papers of Hamilton (1964), a common focus of sociobiology has been the genetic relationships among individuals of insect societies. At issue are agents that reduce the average relatedness among colony members since they are difficult to interpret in light of the evolution of sociality by kin selection. One such factor is polyandry or female multiple mating. Low levels of polyandry are common among the social Hymenoptera, occurring across a broad range of taxa and social systems (Page and Metcalf 1982; Page 1986; Crozier and Pamilo 1996). In spite of that, high mating frequencies (‚2 mates/ female) are relatively rare among the highly eusocial Hymenoptera, limited to only one or a few genera in each of the ants, bees, and wasps (Boomsma and Ratnieks 1996). These extraordinary levels of polyandry have been of particular interest among students of social insect research since their adaptive significance is still in question and highly debated (Kraus and Page 1998; Sherman et al. 1998). The genus Apis has been studied in depth for both queen reproductive behavior and mating frequency, facts that allow insight into the evolution of extreme polyandry in these species. The reproductive behavior of honey bee queens (Apis mellifera) occurs early in their lifetimes. Virgin queens initiate mating behavior when they are about 1 wk old by briefly exiting the colony and orienting to local landmarks (Ruttner 1956). After such orientation * To whom correspondence should be addressed; e-mail: drtarpy@

BARRIERS TO GENE FLOW IN EMBIOTOCA JACKSONI, A MARINE FISH LACKING A PELAGIC LARVAL STAGE

Marine species generally show high dispersal capabilities, which should be accompanied by high levels of gene flow and low speciation rates. However, studies that focused on the relationship between dispersal and gene flow in marine fishes have been inconclusive. This study focuses on the black surfperch, Embiotoca jacksoni, a temperate reef fish that lacks a pelagic larval stage and lives on almost continuous reefs along the California and Baja California coasts. Mitochondrial control-region sequences from 240 individuals were obtained, and phylogeographic patterns were analyzed. A major phylogeographic break was found at Santa Monica Bay, a sandy expanse that prevents adult dispersal. Deep water separating the southern California Channel Islands was also found to be a major barrier to gene flow. Minor phylogeographic breaks were also detected in the Big Sur/Morro Bay and in the Punta Eugenia/Guerrero Negro regions, but none in the Point Conception region. Gene flow levels in E. jacksoni were found to be almost identical to those of another species with limited dispersal, Acanthochromis polyacanthus, thus indicating that the lack of a pelagic larval stage combined with barriers to adult dispersal may have had similar effects on these two species.

Trophic Ecology of the Dominant Fishes in Elkhorn Slough, California, 1974-1980

Food habits of the dominant fishes collected from 1974 to 1980 at eight locations in Elkhorn Slough, California, and the adjacent ocean were investigated. Epifaunal crustacea was the major prey group identified from stomach contents of more than 2,000 fishes, followed by epifaunal and infaunal worms, and molluscs. Overall, 18 fish species consumed 263 different prey taxa, ranging from 10 taxa to 125 taxa per fish species and including 99 crustacean, 56 polychaete, and 39 molluscan taxa. Mean prey richness was greatest at stations near the ocean and lowest at inshore stations. Detailed dietary data for all prey taxa were summarized as trophic spectra for each fish species. Trophic spectra represented functional groups of prey and were used for comparisons of dietary similarity. Cluster analyses, based on trophic spectra, resulted in four feeding guilds of fishes. Of 18 fish species, seven (Amphistichus argenteus, Leptocottus armatus, Embiotoca jacksoni, Clevelandia ios, Gillichthys mirabilis, Cymatogaster aggregata, andCitharichthys stimaeus) fed principally on epifaunal crustacea. Four species (Pleuronectes vetulus, Platichthys stellatus, Phanerodon furcatus, andMyliobatus californica) consumed mostly molluscs and infaunal worms. Two species (Psettichthys melanostictus andTriakis semifasciata) fed on mobile crustacea, and five species (Hyperprosopon anale, Engraulis mordax, Clupea pallasi, Atherinopsis californiensis, andAtherinops affinis) fed largely on zooplankton and plant material. Our results suggest that high food availability enhances the nursery function of imshore habitats, and emphasize the importance of invertebrate prey populations and the indirect linkage of plant production to the ichthyofaunal assemblarly marine immigrant species that are likely ‘estuarine dependent’.

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).

Functional analysis of a specialized prey processing behavior: Winnowing by surfperches (Teleostei: Embiotocidae)

Several surfperches (Embiotocidae), including the black surfperch, Embiotoca jacksoni, exhibit a specialized prey handling behavior known as winnowing, in which ingested food and non-nutritive debris are separated within the oropharyngeal cavity. Prey items are swallowed, and unpalatable material is ejected from the mouth. Winnowing is believed to play an important role in the partitioning of food resources among sympatric embiotocids. We present a mechanistic model for this separative prey processing based on high-speed video analysis, cineradiography, electromyography, and buccal and opercular cavity pressure transducer recording. Winnowing by embiotocids is characterized by premaxillary protrusions repeated cyclically with reduced oral gape. Protrusion is accompanied by depression of the hyoid apparatus and adduction of the opercula. Alternating expansion and contraction of the buccal and opercular cavities generate regular pressure waveforms that indicate bidirectional water flow during processing. Separation of food from debris by Embiotoca jacksoni occurs in three phases. The prey-debris bolus is transported anteriorly and posteriorly within the oropharyngeal cavity and is then sheared by the pharyngeal jaws. Mechanical processing is complemented by the rinsing action of water currents during hydraulic prey transport. The feeding apparatus of Embiotoca jacksoni is functionally versatile, although not obviously specialized relative to that of nonwinnowing surfperches. Protrusion of the premaxillae and depression of the hyoid apparatus are critical to both prey capture and subsequent prey processing. The pharyngeal jaws exhibit kinematic patterns during separation of food from debris distinct from those observed during mastication of uncontaminated prey. This behavioral flexibility facilitates resource partitioning and the coexistence of E. jacksoni in sympatric embiotocid assemblages.

Biogenic habitat structure and characteristics of temperate reef fish assemblages

AbstractAssemblages of non‐cryptic, substrate‐oriented species of fish were compared on a series of reefs in Southern California, USA. Reefs were grouped according to algal cover: dense beds of giant kelp (Macrocystis pyrifera) with turf understorey; sparse beds of giant kelp with foliose algae understorey: foliose algae &lt; 1 m in height; and open barrens. Despite affinities to particular algal substrates by many individual species, we detected no differences in fish species richness and only weak differences in species composition among reefs of different habitat types. Planktivores and species that consume macro‐invertebrates were less likely to occur on reefs that supported giant kelp; the frequencies of occurrence of three other trophic groups (piscivores, herbivores and micro‐carnivores) were unaffected by giant kelp.Algal composition on reefs in Southern California is temporally highly dynamic. Changes in macro‐algal composition of reefs influenced population dynamics of two fish species (black surfperch and striped surfperch) examined. Overall, the weak spatial variation in fish assemblages on reefs in Southern California appears to result from relatively unspecialized ecological requirements of many species combined with temporal changes in algal structure on reefs that are rapid relative to generation times of the fish. We hypothesize that the degree of spatial differentiation in assemblages of substrate‐associated species of fish may be inversely related to the temporal constancy of biogenic reef structure.

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.

Population Responses of Surfperch Released from Competition

Previous short—term (behavioral) field experiments revealed that two temperate marine reef fish, black surfperch (Embiotoca jacksoni) and striped surfperch (E. lateralis), compete with one another along a depth gradient. Here we report abundance responses of these viviparous species following 4 yr of sustained release from competition with each other. We tested predictions derived from the short—term experiments concerning the symmetry of interspecific competitive effects on abundance. We also explored among—habitat variation in the occurrence and magnitude of density compensation. Populations of both surfperch species increased on the order of 40% at experimental (competitor—removal) sites; no change in density was detected for either species at unmanipulated control sites. These strong, reciprocal effects on density conformed with our expectations based on behavioral shifts in microhabitat use immediately following competitive release and on correlation analyses between population densities and feeding—associated resources, but not with predictions from habitat shifts (e.g., changes in depth distribution) that occurred shortly after manipulation. Density compensation was detected only in habitats (depths) where behavioral responses to competitive release had occurred (i.e., in shallow reef habitats). The correlation analyses accurately predicted variation in the relative magnitude of density compensation among habitats and among populations; predictions of the absolute changes in density based on the analyses were less accurate. Take together, these results suggest that behavioral experiments may be useful in identifying potential spatial variability in competitive effects on density. “Scaling—up” the results of behavioral experiments to project relative interspecific effects on density will be more problematic, in part because the relative demographic costs of the interaction may not be accurately portrayed.

Resource Overlap, Prey Dynamics, and The Strength of Competition

Patterns of resource use and the strength of interspecific competition were explored for two temperate marine reef fishes, black surfperch (Embiotoca jacksoni) and striped surfperch (E. lateralis). These species occupy a depth—related gradient in abundance of food (crustaceans) and preferred foraging microhabitats (species of foliose algae that contain food items). Field experiments revealed that the intensity of competition varied greatly along the resource gradient. At the shallow end of the gradient, which contains seasonally high food levels and large amounts of the most preferred foraging microhabitat (the red alga Gelidium), interspecific competition was intense during seasons when food was scarce. This was accompanied by low overlap in use of feeding microhabitats. We detected no competition in deep areas that lacked Gelidium. In this portion of the resource gradient, low overlap occurred because there was no preferred microhabitat that both fishes could share. Low overlap in the deep habitat was not a consequence of competition but rather of the slightly different foraging adaptations of each species. In the surfperch system, static, among—habitat patterns of resource overlap provided little insight into the existence or strength of competition. High overlap occurred when competition was dampened by abundant food (in the shallow zone during food—rich seasons). Low overlap was either associated with strong competition (during periods of relative scarcity of food in the shallow zone) or its absence (deep areas which lacked the shared, preferred microhabitat). Spatial and temporal variation in the strength of interspecific competition was better predicted by dynamic (seasonal) patterns of microhabitat overlap, but only when coupled with knowledge of food dynamics, foraging adaptations of the competitors, and availability of preferred shared microhabitat.

Functional design and prey capture dynamics in an ecologically generalized surfperch (Embiotocidae)

Kinematic and electromyographic analyses of prey capture in two species of surfperch (Embiotocidae) reveal differing abilities to modulate strike activity in response to different prey types. Both the black perch, Embiotoca jacksoni, and the shiner perch, Cymatogaster aggregata, demonstrate stereotyped and conserved neuromuscular and kinematic activity in suction feeding. A distinguishing anatomical trait in this family, the interopercular shelf, enhances the coupling of hyoid movement with mandibular depression. Analyses of variance suggest a preprogrammed motor output that is ballistically launched for suction generation, with the possibility of more plasticity in latter phases of the strike. While the trophically limited shiner perch displays a stereotyped repertoire of this one strike pattern, very small prey, larger conglomerates of these, and large distinct prey elicit three modulated patterns in the black perch. Functional characteristics that enable the ecologically generalized black perch to exploit a variety of prey types include energy–conserving modulatory ability, behavioural flexibility in utilizing a conserved suction–generating programme, and the addition of specialized winnowing and spitting activity.

Effects of predation risk on foraging behavior: mechanisms altering patch choice

Responses of foraging young-of-year black surfperch Embiotoca jacksoni Agassiz to benthic predators, kelp bass Paralabrax clathratus (Girard) and grass rockfish Sebastes rastrelliger (Jordan and Gilbert), were investigated in laboratory and field experiments. Young-of-year black surfperch fed on crustacean prey from a variety of benthic algal substrata. In laboratory experiments using uniform patches of a favored alga, black surfperch avoided kelp bass or grass rockfish by reducing time spent feeding in a patch containing a predator, although no effect on the feeding rate of the surfperch was observed. Surfperch showed no difference in their response to kelp bass or grass rockfish. Field experiments indicated that, under conditions of safety, the low-growing alga Zonaria farlowii Setchell and Gardner was the most highly favored substratum. As risk of predation increased, preference for Zonaria declined sharply and the tall, bushy alga Sargassum palmeri Grun became the most highly favored feeding substratum. The mechanisms producing the shift in preference involved an increased number of visits to Sargassum and a longer duration foraging bout per visit. The responses of young-of-year black surfperch to piscivorous fishes appear to enable the surfperch to reduce mortality risk while still continuing to feed actively.

The Combined Effects of Predation Risk and Food Reward on Patch Selection

Experiments were performed to examine the effects of predation risk on selection of food patches by a mobile forager, young black surfperch (Embiotoca jacksoni). The goals were to investigate (1) how predation risk affected relative selectivity among patches that differed in density of food, and (2) whether the forager's response depended on how variations in food level and predation risk were encountered. In the experiments, density of food (crustaceans on algae) was manipulated among spatially uniform patches of a foliose alga. Safety of the forager was varied by manipulating the presence in patches of kelp bass (Paralabrax clathratus), a principal predator of young surfperch. Patch choice was determined for an array of situations where food and risk were varied separately and together in space and time. The response of foragers to variations in food level and risk depended upon the specific manner in which the factors were encountered. When patches with a high food level contained a predator, foragers shunned the risky food—rich areas for safe food—poor patches. When food was equal between safe and risky patches, the degree to which patches with a predator were avoided remained constant over a range of absolute food densities. By constrast, selectivity between patches of differet food densities was dampened when all available patches contained a predator. Finally, predators enhanced relative selectivity for food—rich areas when foragers had simultaneous access to the complete combination of variation in rish and food level. Heightened selectivity in the presence of predators resulted from two hierarchical responses: foragers always took less risk to feed in the food—poor patch, and, when the difference in comparable value of available food patches was sufficiently great, they took more risk to eat where the density of food was higher. Overall, these results indicate that juvenile black surfperch possess an array of responses to food and predators, which together may act to minimize the sublethal effect of predators on feeding at a minimal increase in probability of death. Such plasticity may be a general characteristic of foragers that experience variation in food and risk at several spatial scales and temporal combinations.

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%.

Seasonally fluctuating resources and temporal variability of interspecific competition.

The influence of seasonal availability of two critical resources (food and substrates from which food was harvested) on interspecific competition between striped surfperch (Embiotoca lateralis) and black surfperch (Embiotoca jacksoni) was examined. There was a strong depth-related gradient in density of prey and in cover of foliose algae; both declined with increasing bottom depth. Density of prey was reduced 5-10 fold during the winter season, but cover of substrates remained constant throughout the year. Although both fishes co-occurred throughout the same depth range, striped surfperch were more common in shallow habitats and black surfperch were more abundant deeper. Local abundance and distribution patterns of both surfperch species did not change seasonally. Stepwise regression analyses suggested that availability of favored substrates was a proximate influence on local patterns of surfperch distribution and abundance, and that interspecific competition depressed abundance of the two species to the same degree. Removal experiments conducted during the cold-water season revealed that interspecific competition influenced depth distribution of black surfperch but not striped surfperch. Seasonal change in density of prey was accompanied by marked changes in overlap in use of foraging substrates by the surfperches. The pattern of change in interspecific overlap suggested that surfperch competed for food only when prey were seasonally scarce. There was no difference in the agonistic tendencies of the two fishes, and the absolute and relative frequency of interspecific chases was independent of food level. These results have important implications regarding the impact of temporal variability of interspecific competition in natural communities. In the surfperch system, competition was characterized by constant and time-varying elements that had symmetrical and asymmetrical effects and involved both interference and exploitation mechanisms.

Age-Related Dietary Patterns of Sympatric Adult Surfperch

Dietary separation between age-classes of adult black and striped surfperch (Embiotoca jacksoni and E. lateralis) was explored. Despite the fact that the sampled fish were locally sympatric and were capable of consuming the entire range of available invertebrate prey sizes and taxa, there were significant differences between diets of older (Age III-V) and younger (Age I-II) fish within each species. Intraspecific differences were of the same magnitude as interspecific dietary differences. Divergence in both sizes and taxa of prey contributed to the dietary separation. egions of three lizard species. J. Morph. 139:377ENVIRONMENTAL STUDIES BOARD, UNIVERSITY

The influence of plant cover on surfperch abundance at an offshore temperate reef

At an offshore reef near Santa Barbara, southern California, young-of-year (‘young’) of five surfperch species (Embiotocidae: Embiotoca jacksoni, E. lateralis, Hypsurus caryi, Rhacochilus toxotes, Damalichthys vacca) once thrived in a dense kelp understory of Pterygophora californica and Laminaria farlowii, but disappeared after a severe storm in February, 1980 deforested their habitat. Measurements of fish density and kelp cover made before deforestation indicated that the young surfperch appeared in the spring and disappeared in the fall as cover increased and declined. Adult surfperch and large kelp bass (Paralabrax clathratus), which can eat young but not adult surfperch, remained all year. We tested to see if kelp cover was an essential refuge for the young by pruning back (‘thinning’) kelp blades from one of two transects. The thinning caused a significant redistribution of young which clearly avoided open spaces, but not of adults which are less vulnerable to predation. Measurements of fish density made after the storm-induced deforestation showed that adult surfperch and kelp bass still remained abundant even after the young surfperch were gone. Only after an abrupt reforestation in 1983, more than a year after the present study was terminated, were young once again seen on the reef. Although young surfperch may seek tiny prey living on kelp blades, most lines of evidence indicated that the distribution of the young is more a response to risk of predation. Hence the extent of kelp understory was probably the main determinant of the survival of young surfperch on the reef.

Patch selection by juvenile black surfperch (Embiotocidae) under variable risk: Interactive influence of food quality and structural complexity

The influence of risk on the selection of foraging patches by young-of-year black surfperch, Embiotoca jacksoni Agassiz, was investigated by laboratory and field experiments. These foragers harvest crustacean prey from a variety of benthic algal substrata. In field environments, patch types vary in two ways. First, substrata differ in structural complexity and probably afford different degrees of protection from predators. Second, substratum types vary in prey richness. There was no correlation between structural complexity and prey richness, and either or both factors could be a component of foraging patch value. Each patch is small and individual foragers are simultaneously confronted with arrays of patches encompassing the full range of variation in structure and prey richness. Furthermore, a major predator of young-of-year black surfperch, the kelp bass, Paralabrax clathratus (Girard), is patchily distributed in space and time. Thus similar arrays of patch types can be characterized by different levels of overall risk. Risk to foragers is dependent on light level as well as the presence and density of predators. The interplay between food quality and shelter potential in influencing patch choice was examined under different regimes of risk. Both laboratory and field experiments indicated patch preference was based primarily on food quality. However, the physical structure of a patch did become a component of patch choice as risk increased. The relative value of physical structure under high risk was dependent on the prey richness of a patch; food-poor substrata with high shelter potential remained unfavored even in situations of high risk.