Intertidal Distribution Research Articles

The intertidal distribution of the grey mangrove (Avicennia marina) in southeastern Australia: The effects of physical conditions, interspecific competition, and predation on propagule establishment and survival

Abstract The upper and lower limits of the distribution of mature Avicennia marina lie between mean high water and mean sea level in open estuaries in southeastern Australia. Newly established seedlings are highly variable in abundance, but are rarely found in the saltmarsh or on mudflats. Their distribution is unlikely to be limited by dispersal because propagules disperse into the saltmarsh and to intertidal mudflats, but their establishment may be limited by physicochemical conditions, interspecific competition and predation.The model that physicochemical conditions control the intertidal limits of establishment of seedlings was accepted for propagules stranding in the saltmarsh but rejected for those stranding on mudflats. No seedlings established on saltmarsh sediments but similar numbers of seedlings established within light gaps in adult mangrove stands and on intertidal mudflats. The model that interspecific interaction with freeliving macroalgae (Hormosira banksii) reduces the establishment of seedlings on mudflats covered with macroalgae or in stands with a ground cover of macroalgae was accepted. Under controlled conditions five times as many propagules established on cleared ground compared with ground covered with macroalgae. Predators also reduce seedling establishment, but the model that they preferentially act on propagules stranding on the mudflat was rejected. The low number of seedlings found on mudflats without macroalgae appears to relate to wave and current effects on establishment and the effects of waterlogging or fouling on survival.

Intertidal zonation patterns of macroinfauna over a range of exposed sandy beaches in south-central Chile

Ten sandy beaches, covering a range from reflective to dissipative conditions, were sampled in south-central Chile to determine whether different beach morphodynamic states support different macroinfaunal zonation patterns. Three patterns were distinguished through examination of kite diagrams and analysis using multivariate techniques: (1) in reflective beaches with coarse sand, a single zone of air-breathing crustaceans was located above the drift line; (2) a reflective beach with finer sands exhibited 2 faunal zones due to the addition of a second zone of cirolan~d isopods below the dnft line; and (3) in intermediate and dissipative beaches 3 faunal zones were delineated, the above 2 plus a broad zone covering the lower shore. Species representative of these zones are Orchestoidea tuberculata and Excirolana braziliensis in the upper shore, E. hirsuticauda and E. monodi in the middle shore and Ernerita analoga and Bathyporeiapus magellanicus in the lower shore. This study also showed that zones were ordinated along an intertidal gradient of sediment water content. The 3 zone pattern agrees with the worldwide scheme proposed by Dahl (1952; Oikos 4: 1-27). Body-size comparisons showed that individual sizes in some species differed across their intertidal distribution.

The Introduction and Spread of Smooth Cordgrass (Spartina alterniflora) in South San Francisco Bay

Spartina alterniflora was first introduced into south San Francisco Bay in the 1970’s. Since that time it has spread to new areas within the south bay and is especially well established at four sites. The spread of this introduced species was evaluated by comparing its vegetative and reproductive characteristics to the native cordgrass, Spartina foliosa. The characters studied were intertidal distribution, phenology, aboveground and belowground biomass, growth rates, seed production, and germination rates. Spartina alterniflora has a wider intertidal distribution than S. foliosa and outproduced the native cordgrass in all aspects that were studied. These results indicate that the introduced species has a much better chance of becoming established in new areas than the native species, and once established, it spreads more rapidly vegetatively than the native species. Spartina alterniflora is likely to continue to spread to new areas in the bay and displace the native plant. In addition, this introduced species may effect sedimentation dynamics, available detritus, benthic algal production, wrack deposition and disturbance, habitat structure for native wetland animals, benthic invertebrate populations, and shorebird and wading bird foraging areas. *** DIRECT SUPPORT *** A01BY058 00013

Preservational constraints and ecological opportunities: the role of shell-inhabiting organisms in the fossil record

Biological parameters, in addition to physical parameters, are important in determining past ecology, taphonomy and the effects of human intervention. Research conducted on a Recent community of gastropods and two late Pleistocene fossil assemblages from Puerto Penasco, Mexico, reveal a complex pattern of interrelationships among gastropod shell users. First, shell representation is biased in the intertidal of Puerto Penasco, Mexico, because of a complex mosaic of secondary shell occupants. Hermit crabs (five species) represent almost half (47%) of the intertidal gastropod shell resource available throughout the year. Living snails are represented by 17 out of the 32 gastropod taxa. Additionally, hermit amphipods (three species) occupy ten gastropod taxa. Hermit crabs and hermit amphipods retain the shells in anomalous habitats (that differ from the living snail). Second, physical factors act as a temporal component which affects shell use and availability during the seasons at Puerto Penasco. Late winter storms mix-up the intertidal distribution of living gastropods and hermit crabs. Subtidal to low intertidal shells appear in the high intertidal; living snails are buried under a thick bed of sand. Most importantly, empty shells become available, and the hermit amphipod population peaks. Thus, physical factors contribute to the demise of living snails (i.e, burial by sand) and the mixing of shells. However, the organisms (hermit crabs and amphipods) maintain this motif by retaining the shells in the anomalous habitats.Third, all hermit crab species (Paguristes anahuacus, Pagurus lepidus, Paguristes roseus), except for one (the high intertidal, Clibanarius digueti), have epi-and endobionts associated with the gastropod shell. More than 20 species of invertebrates bore into or encrust the hermitted shells at Penasco. Of these, the encrusting bryozoans Hippothoa, Hippopodinella adpressa, ?Floridia antiqua, Lichenopora, Antropora tincta and the boring spionid polychaetes (Polydora commensalis, Polydora, Boccardia) and spirorbid polychaetes (Spirorbis; Serpula) are important bionts to use in recognizing hermit crab shell use in the fossil record of the northern Gulf of California. The encrusting bryozoans (H. adpressa and A. tincta) are present on Pleistocene gastropods at the unusual Pelican Point terrace deposit (large gastropod shells preserved among large bryozoan encrusted cobbles) indicating hermit crab inhabitation. These bryozoans appear to protect the gastropods from taphonomic alteration.Finally, reworked fossil shells occur within the hermit crab guild and the beach drift assemblage. Hermit crabs retain fossil shells of the moon snail, Polinices, (n=two occurrences) and Turritella (n=3 occurrences). These species are common in the coquina beach rock which makes up the intertidal substrate of Puerto Penasco. However, reworking of fossil coquina is quite substantial in the beach drift assemblage. Three sampling periods (=150 samples) indicate the following: three species of fossil bivalves (Chione, Trachvcardium and Glycimeris) and five species of fossil gastropods (Oliva, Polinices, Muricanthus, Nassarius, and Turritella) dominated the beach drift assemblage (over 16, 600 fossil whole shells/fragments). Fossil Chione represented the most shells (958 valves;>15,557 fragments). Recent bivalves were represented by 1115 shells/fragments (representing 12 species) and Recent gastropods contained mostly fragments (1069 pieces; 30 species). Additionally, the fossil gastropods were large, unlike the species that occur today, which have been picked over by humans. Thus, a large part of active beach deposition at Puerto Penasco contains late Pleistocene shells, taphonomically altered by secondary occupants and beachcombers.

Intertidal microalgal production and molluscan herbivory in relation to season and elevation on two rocky shores on the east coast of southern Africa

Microalgal production (ungrazed rock) and standing stock (grazed) were measured over a period of 15 months in the lower, middle and upper balanoid zones of two rocky snores in the Transkei region of southern Africa. The mean monthly production of chlorophyll a, which ranged from 0,3 to 2,0 μg·cm−2. was inversely correlated with tidal elevation. Highest rates of production (3,5–6,0 μg·cm−2) were recorded in winter at all tidal levels. The amplitude of seasonal fluctuations decreased with tidal height. At the middle and upper levels standing stock usually exceeded monthly production, whereas the opposite often occurred in the lower balanoid. No temporal or spatial trends in standing stock were evident. The intertidal distribution of grazing gastropods (excluding littorinids) correlated positively with primary production but showed no relationship with standing stock. No clear seasonal trends in grazer abundance were evident. The fact that standing stock exceeds monthly production suggests that grazing press...

Intertidal distribution of infauna in a central California lagoon: the role of seasonal blooms of macroalgae

This study examined the roles of seasonal blooms of green algae, Ulva expansa (Setchell) Setchell et Gardner, and biotic disturbance by burrowing ghost shrimp, Callianassa gigas Dana, and foraging rays, on the intertidal distributions of a phoronid, Phoronopsis viridis Hilton, and a tellinid bivalve, Macoma nasuta (Conrad). Algal removal experiments in 1984 and 1986 demonstrated that heavy seasonal algal cover in the lower zone significantly reduced the abundances of both Phoronopsis and Macoma. Growth of Macoma transplanted into the algal zone was significantly lower in plots with algal cover than in plots regularly cleared of algae. Algal cover did not significantly affect early recruitment of either Phoronopsis or Macoma. Neither ghost shrimp nor rays appeared to reduce the abundances of phoronids or clams, although ray disturbance did result in a significant increase in the proportion of phoronids regenerating dorsal body parts. These results indicate that seasonal algal blooms are capable of producing discrete patterns of infaunal distribution in intertidal sedimentary habitats.

Effect of freezing on photosynthesis of intertidal macroalgae: relative tolerance of Chondrus crispus and Mastocarpus stellatus (Rhodophyta)

The effect of freezing on photosynthetic metabolism was studied in the red algae, Chondrus crispus and Mastocarpus stellatus. Plants of both species were collected from the intertidal at Chamberlain or Kresge Point, Maine, USA (43°56′N, 69°54′W) between February and March 1987. Photosynthetic rates were measured immediately after freezing at-20°C and following recovery periods in seawater. Photosynthesis in C. crispus declined rapidly following freezing, falling to 70% of control values within 1 h and 30% after 3 h exposure. Minimum photosynthetic rates (7 to 9% of controls) occurred following freezing exposures of 12 h or more. Full photosynthetic recovery in C. crispus after 3 h at-20°C required 48 h. Photosynthesis in C. crispus did not fully recover in plants frozen for 6 h or more. In contrast, photosynthesis in M. stellatus was relatively unaffected by freezing exposures of <12 h. Twelve hours or more at-20°C reduced photosynthesis to 55% of controls. Photosynthesis in M. stellatus fully recovered from 24 h at-20°C within 24 h. In both species the reduction of photosynthesis by freezing was associated with damage to the plasma membrane and reduced efficiency of energy transfer from phycobilisomes to chlorophyll a, but did not appear to involve ribulose-1,5-bisphosphate carboxylase oxygenase activity. The freezing tolerance of C. crispus and M. stellatus positively correlates with their respective intertidal distributions, suggesting that freezing may be involved in controlling the distributions of these species on the shore.

Morphological variation along intertidal gradients in a population of black abalone Haliotis cracherodii Leach 1814

Temporal patterns of morphological variation in multivariate size and shape in a population of black abalone Haliotis cracherodii Leach 1814 in an intertidal boulder field in southern California was examined. From July 1983 to May 1985, 707 individuals were tagged and measured for six shell traits. The extent and pattern of morphological variation in allometric size, tremata (= respiratory pore) number, and relative tremata size was similar among surveys. Shore-level gradients in morphology varied temporally and involved independent variation in both shell size and shape. In the summer and fall, individuals with relatively fewer smaller tremata occurred higher on the shore than individuals with relatively more larger tremata. Seasonal variation in intertidal distribution and the incidence of Octopus-drilled abalone shells indicated that declines in abalone abundance were due to predation by Octopus in the summer and fall. Shore-level gradients were thus associated with opposing selective regimes, predation in the low intertidal and desiccation in the high intertidal. These results support the hypothesis that shore-level gradients in morphology result from movement and differential growth and are a dynamic response of individuals to temporal changes in physical stresses and predation which vary along intertidal gradients.

Seasonal abundance, distribution and growth of postlarval and juvenile grass shrimp (Palaemonetes pugio) in a Georgia, USA, salt marsh

Postlarval and juvenile grass shrimp (Palaemonetes pugio Holthuis) ≦15 mm total length (TL) were abundant at low tide in shallow aquatic microhabitats (i.e. puddles and films of residual tidal water) in the intertidal zone of a salt marsh on Sapelo Island, Georgia, USA from 1982 to 1984. The highest concentrations of young P. pugio occurred at 190 to 200 cm above mean low water, ∼10 to 20 cm below mean high water. The intertidal distributions of young grass shrimp expanded and contracted with changes in tidal amplitude. Postlarval grass shrimp (6 to 8 mm TL) continuously recruited into the intertidal marsh population from May until October, but densities varied in a regular pattern with peaks in abundance occurring at ∼2-week intervals, corresponding to spring tide periods in the lunartidal cycle. Although present nearly year-round in the intertidal marsh, juveniles (9 to 15 mm TL) were most abundant from August to October. Apparent growth rates of individuals up to 15 mm TL averaged 0.268±0.026 (mean±95% C.I.) mm d-1 from May to October and 0.070±0.032 mm d-1 in November and December. Unlike larger aquatic organisms, which can forage in the emergent marsh only when it is flooded by the tide, juvenile grass shrimp have constant access to intertidal resources. Although potentially important predators in this system, the role of young P. pugio in the trophic organization of salt marsh benthic invertebrate assemblages has yet to be examined.

Seed Predation in Relation to Tree Dominance and Distribution in Mangrove Forests

The ecology of seed predation was studied in mangrove forests. Controlled field experiments were used to assess the magnitude of predation on mangrove propagules, to test for differences in predation among five species of mangroves, and to examine how differential amounts of predation on seeds are correlated with conspecific dominance and may contribute to observed patterns of tree distribution across the intertidal region. Averaged over all species and forests, 75.7 ± 28.7% (° ± 1 sd) of the seeds used in the experiments were consumed by predators (small crabs belonging to the family Grapsidae). Significant differences existed in the amounts of predation among mangrove species. Avicennia marina was most heavily preyed upon, followed in decreasing order by Bruguiera exaristata, Ceriops tagal, Bruguiera gymnorrhiza, and Rhizophora stylosa. Differences in chemical composition of the propagules accounted fro ≥97% of the differences in amounts of predation among the five species. Nutritive quality of the propagules, expressed as a function of protein, simple sugar, fiber, and tannin content, was more important in explaining the differences than was propagule size. Significant differences also existed among three forest types, which differed in species dominance. Lowest amounts of predation for C. tagal were in the forest where adults of this species were absent, and highest in the forest where the species was most dominant. For A. marina, the two Bruguieras, and R. stylosa, however, amounts of predation were significantly higher in forests where conspecifics were rare or absent and lowest where conspecifics were dominant. For these latter four species, conspecific dominance in the canopy explained ≥63% of the variation in predation among forest types. The pattern of differences in seed predation among forests across the intertidal region indicates that seed predators may play a significant role in determining the intertidal distribution of the mangrove species studied.

Predation on a burrowing shrimp: Distribution and community consequences

Predation has been shown to be an important factor determining the species composition of certain communities. However, its effect in marine soft-sediment habitats is not well understood. This study examines the role of predation in limiting the intertidal distribution of a burrowing ghost shrimp, Callianassa californiensis Dana, on an Oregon tideflat. The ghost shrimp displays a distinctive zonation pattern in many Pacific northwest embayments, with dense beds of this deep burrower restricted primarily to the midintertidal zone. Direct effects of surface predators in maintaining this zonation were examined by excluding predators immediately seaward of the lower edge of a dense bed and by transplanting ghost shrimp to the low intertidal in cages. Diets and distributions of potential predators were also observed. With the exclusion of surface predators, ghost shrimp migrated downward in the intertidal zone and showed high survival in transplanted areas. Examination of predator diets indicates that at least one common fish, the stagorn sculpin Leptocottus armatus Girard, consumes large numbers of Callianassa californiensis. Because burrowing by the ghost shrimp can affect the numbers of many other tideflat organisms, restriction of this animal to higher tidal zones allows a different assemblage of species to exist in the low intertidal than otherwise would be present. Predation on the ghost shrimp is thus an important factor determining the relative species composition of many tideflats along the Pacific coast of North America.

Littoral Distributions and Evidence For Differential Post-Settlement Selection of the Morphs of Actinia Equina

Examination of the intertidal distributions of isozyme and pedal colour phenotypes of Actinia equina L. has shown that anemones displaying column coloration ranging from red to brown, are divisible into three, ecologically distinct forms in Britain, which we currently interpret as being morphs of a single species. These are termed the upper (U), mid (M) and lower (L) shore morphs, which are relatively most abundant on the upper mid, lower mid and low shores, respectively; not all morphs are represented on some shores. The U, M and L morphs may be separated on the basis of their hexokinase and malate dehydrogenase phenotypes. The U morph is homozygous slow and fast respectively, the L morph is slow and fast respectively whilst the M morph is heterozygous at both loci. Data on linkage of pedal disc colour and alleles at a tetrazolium oxidase locus, and of an association between alleles at the hexokinase locus and those at an esterase locus, are given.

Functional morphology of intertidal seaweeds; adaptive significance of aggregate vs. solitary forms

Many intertidal seaweeds show a tremendous gradient of morphological form ranging from spatially separated thalli, to thalli that are aggregated into dense turfs. Aggregation of seaweeds into turfs decreases productivity per g organic weight due to crowding of thalli but increases resistance to desiccation. The intertidal distribution of the turf growth form is correlated with the intensity of desiccation stress. Also turfs transplanted into tide pools developed the non-turf morphology, while non-turfs transplanted to emergent substrate either developed the turf form or died. The turf growth form is energetically expensive; apparent productivity of turfs was 23 to 48 % less than that of individuals. Increasing light and nutrients available to turfs by separating the thalli increased apparent productivity by 36 to 113 %. We tested the hypothesis that these turfs minimize energetic costs of this aggregated growth form through the spatial partitioning of photosynthetic and respirative activity. The lower portions of turfs showed less apparent photosynthesis than the upper portions (reductions of 37 to 85 %); however, this spatial partitioning was also found in the individual forms (37 to 63 % reductions) of these relatively simple seaweeds. Spatial differentiation of respiration was similar in turfs and non- turfs. The seaweeds, examined are able to alter the extent of thalli compaction in accordance with varying levels of environmental stress. This phenotypic plasticity allows seaweeds to adopt morpholo- gical features that maximize fitness in a wide variety of habitats without being developmentally committed.

Habitat preference, predation, and the intertidal distribution of gammaridean amphipods in a north carolina salt marsh

Habitat islands designed to simulate small patches of Spartina wrack were used to sample intertidal amphipods in Tar Landing Marsh, North Carolina, U.S.A. Orchestia grillus Bosc, Orchestia sp. (an as yet undescribed saline salt marsh endemic), and Gammarus palustris Bousfield were the common species at the study site. In transect samples along a tidal gradient, Orchestia grillus occurred only at extreme high marsh sites, while Gammarus palustris colonized islands that were more frequently inundated by the tide. Orchestia sp. was intermediate in distribution with a tendency toward the high marsh habitat. Other investigators have suggested that predation by the killifish, Fundulus heteroclitus ( L.), maintains the high marsh distribution of Orchestia grillus. Transplantation experiments with sets of habitat islands placed at different vertical positions within a tidal gradient were used in the present investigation to determine whether the natural distribution of O. grillus could occur in the absence of predation. Results suggested that physical conditions associated with relatively frequent and prolonged tidal inundation make the low marsh an unsuitable habitat for O. grillus. The intertidal distribution of this amphipod appears to be independent of killifish predation in Tar Landing Marsh. Collections from naturally colonized habitat islands at different levels in the tidal gradient are consistent with the hypothesis that intertidal distributions of Orchestia sp. and Gammarus palustris are also determined primarily by preferences for specific physical conditions.

Comparative distribution and habitat preferences of two species of stichaeoid fishes in yaquina bay, oregon

The intertidal distribution of two species of estuarine stichaeoid fishes, Anoplarchus purpurescens purpurescens (Gill) and Pholis ornata (Girard), was assessed in order to determine the extent of partitioning of microhabitat. Pholis ornata was abundant both in rocky intertidal areas and in seasonal plant cover of mudflats while Anoplarchus purpurescens was restricted to rocky substrata. Differences in relative abundance were observed at different sites in the estuary. While Anoplarchus purpurescens predominated at the mouth of the estuary closest to oceanic influence, Pholis ornata was the only species found at upper bay sites closest to freshwater influence. Two seasonal patterns in the distribution and abundance of P. ornata were also recorded: (1) intertidal vertical range decreased in the summer months, (2) density increased in late winter-early spring with the onset of post larval settling in rocky intertidal areas.

Predation, Physical Stress, and the Organization of a Tropical Rocky Intertidal Hermit Crab Community

Predation pressure and physical stress are shown to be important selective pressures on hermit crabs in the Bay of Panama, influencing their intertidal distributions, shell preferences, and behaviors. Predation on hermit crabs by shell—crushing teleost fish and crabs is greatest in the low intertidal habitat and decreases in the high intertidal environment where physical stresses are the most intense. Pagurus sp. (undescribed) lives in the low intertidal habitat exclusively and prefers relatively heavy shells with narrow apertures which reduce vulnerability to predation while decreasing resistance to thermal stress. Calcinus obscurus is found in the middle to low intertidal environment, and Clibanarius albidigitus has a middle to high intertidal distribution, partly as a result of active competitive displacement by C. obscurus from the low intertidal habitat. These two speices prefer shells that minimize thermal stress and give relatively little defense against predators. Predation in these crabs is avoided by a behavioral escape response most acutely developed in C. obscurus, while C. albidigitus is superior to C. obscurus in withstanding thermal stress. Habitat and shell resource utilization pattern sin this tropical hermit crab community can be interpreted to represent the result of a complex interaction between predation, physical stress, and competitive pressures.

Evaporative water loss and intertidal vertical distribution in relation to body size and morphology of stichaeoid fishes from California

Five species of amphibious stichaeoid fishes (four stichaeids, one pholidid) with distinct but overlapping distribution patterns in the rocky intertidal zone of central California were studied in the laboratory with respect to body size and shape, survival out of water, evaporative water loss and water resorption upon re-immersion. Members of all species survived periods of emersion of at least 6 h, but maximum survival times varied with species and body size. Surface area to weight ratios in relation to body length were highest in Xiphister atropurpureus (Kittlitz) and X. mucosus (Girard), lowest in Cebidichthys violaceus (Girard) and Anoplarchus purpurescens Gill and most variable in Xererpes fucorum (Jordan & Gilbert) (the pholidid). Weight-specific water loss (mg · g −1 · h −1) was highest in the two species of Xiphister followed in order by Xererpes fucorum, Cebidichthys violaceus and Anoplarchus purpurescens. In general, adaptive relationships were found between body size, surface area, tolerance of water loss and intertidal distribution patterns. Among juvenile stichaeoids, for which problems of emersion are most critical, those of Cebidichthys violaceus possess the combination of attributes, including small surface area to weight ratio, high water content and long tolerance of emersion, that should give them an adaptive edge in occupying the upper levels of the shore. In accordance with these characteristics, C. violaceus has the highest, most exposed vertical distribution of the five study species.

Reproductive, genetic and ecological evidence thatActinia equinavar.mesembryanthemumand var.fragaceaare not conspecific

The intertidal distributions of the two varieties ofActinia equinaL. defined by Stephenson (1935), varmesembryanthemumand vai.fragacea, have been studied on several shores of the English Channel. The reproductive physiology and iso-enzyme genetics of sympatric populations of the two taxa have been investigated in greater detail on one shore. The genetic results show that the two taxa are reproductively isolated and, overall, the evidence indicates that they are separate species.

The ecology of sandy beaches in southern Africa

The physical features, macrofauna and meiofauna of four exposed sandy beaches along the southern coast of South Africa were quantitatively investigated. All beaches had medium to fine sands with relatively poor to moderate macrofauna and very rich meiofauna. The results are compared with the present knowledge of the southern African coastline. Sandy beaches types around the southern African coastline are summarized according to geomorphology and wave action and three Zoogeographie provinces are recognized. The macrofauna is dominated by crustaceans, mostly scavengers, on the warmer east coast and by molluscs, mostly filterfeeders, on the temperate south coast. Relationships between diversity and abundance of macrofauna, beach slope and particle size are analysed in detail. Intertidal zonation of macrofauna is described and a zonation scheme based on crustaceans proposed. Relationships between meiofauna composition and particle size are described as well as intertidal distribution patterns of the meiofauna...

Food Habits of Three Species of Rocky Intertidal Sculpins (Cottidae) in Central California

C. analis had the most diverse diet. 0. snyderi and A. lateralis had roughly similar levels of diversity in their diets, although they concentrated on different food items (0. snyderi on amphipods and polychaetes, and A. lateralis on shrimp and fishes). There were no statistical differences in diet composition between large and small fish within species. Size classes of C. analis had the greatest average diversity of food while size classes ofA. lateralis had the lowest average diversity. 0. snyderi, the smallest species, generally took the smallest prey while A. lateralis, the species with the largest gape, took the largest prey. Variation in prey size was smallest for 0. snyderi and largest for A. lateralis. Much of the variation in prey sizes eaten by each species was due to the large average variation in prey sizes eaten by individual size classes. Information on food habits is combined with earlier data on intertidal distributions of the fishes. Differences among species in the use of food and space resources are viewed as a way for species to minimize, and as a possible result of, competition. Some degree of complementarity in use of resource dimensions (tidepool category, food category, prey size) also indicates that competition may have influenced patterns of resource use shown by these fishes.