Strongylocentrotus Franciscanus Research Articles

Natural variation of carotenoids in the eggs and gonads of the echinoid genus, Strongylocentrotus: implications for their role in ultraviolet radiation photoprotection

We examined variability in carotenoid concentration in the gonads and eggs of four sea urchin species ( Strongylocentrotus purpuratus, Strongylocentrotus franciscanus, Strongylocentrotus pallidus and Strongylocentrotus droebachiensis) to explore the possible role of carotenes as photoprotectants. Carotene concentrations were measured in gonads and gametes of each species, while in eggs the ultraviolet radiation (UV-R) sensitivity and self-shading capacity by carotenes were calculated. Mean concentrations of carotenes in gonads ranged from 0.13±0.017 mg g −1 dw ( S. purpuratus), 0.14±0.019 mg g −1 dw ( S. franciscanus), 0.29±0.079 mg g −1 dw ( S. pallidus) to 0.36±0.06 mg g −1 dw ( S. droebachiensis). In eggs, concentrations ranged from 0.026±0.003 to 0.09±0.034 mg g −1 dw. UV-R sensitivity in eggs was quantified by measuring UV-R induced first-cleavage delay. Intra-specifically, cleavage delay varied significantly between individuals, and could be correlated with carotene concentration. Interspecific differences in cleavage delay and carotene concentrations were not correlated. Using the observed concentration of β, β-echinenone (which makes up between 82.4% and 94.9% of the total carotene concentration in the eggs) and a molar extinction coefficient of ε=13.7×10 3 mol −1 cm −1 at 334 nm, we calculated self-shading efficiency in the eggs. Self-shading capacity ( J 334) indicated that the eggs could only screen from 4.6% ( J 334=0.046) down to 1.5% ( J 334=0.015) of UV-R at 334 nm. While not sunscreens, we suggest that carotenes can photoprotective in echinoid eggs, probably by mitigating the effects of reactive oxygen species.

Patterns in Early Embryonic Motility: Effects of Size and Environmental Temperature on Vertical Velocities of Sinking and Swimming Echinoid Blastulae

Early embryonic swimming is widespread among marine invertebrates, but quantitative information about swimming behaviors is scarce. Swimming may affect encounters with predators, positioning in the water column, and nutrient absorption. Measured rates and patterns of swimming and sinking for blastulae of four eastern Pacific echinoid species show that sinking speeds equal or exceed swimming speeds. Swimming speed scaled negatively with embryo size, though sinking speed did not scale with size. Analysis of swimming paths of Strongylocentrotus franciscanus revealed a temperature dependency in swimming pattern that affected speed of upward movement. Sinking speeds were significantly greater at 10 degrees C than at 14 degrees C for blastulae of all four species examined. In Dendraster excentricus, killing the blastulae annulled this temperature effect, indicating an active density regulation by these embryos. Finally, measurements of particle velocities around sinking and swimming D. excentricus blastulae show that swimming creates a more localized disturbance than sinking. Embryonic swimming may therefore decrease rather than increase encounters with pelagic predators. Results from subsequent experiments in which embryos were reared in low-oxygen environments suggest that any oxygen-absorption advantages of swimming have little, if any, effect on the development of D. excentricus embryos.

Microsatellite loci from red sea urchins (Strongylocentrotus franciscanus)

Abstract Strongylocentrotus franciscanus is a keystone marine herbivore in the Pacific North West of North America, that is commercially harvested for its roe in wild fisheries and is under development as an aquaculture species. We report the development of 11 novel, highly polymorphic di‐ and trinucleotide loci for use in population studies of this species. In a survey of over 200 individuals from three coastal sites in British Columbia, observed heterozygosities of the loci ranged from 0.39 to 0.85 and an average of 26 alleles per locus were resolved. Seven of the 11 microsatellite loci were in Hardy–Weinburg equiulibruim (HWE).

FISHING YIELD, CURVATURE AND SPATIAL BEHAVIOR: IMPLICATIONS FOR MODELING MARINE RESERVES

ABSTRACT. Given a paucity of empirical data, policymakers are forced to rely on modeling to assess potential impacts of creating marine reserves to manage fisheries. Many modeling studies of reserves conclude that fishing yield will increase (or decrease only modestly) after creating a reserve in a heavily exploited fishery. However, much of the marine reserves modeling ignores the spatial heterogeneity of fishing behavior. Contrary to empirical findings in fisheries science and economics, most models assume explicitly or implicitly that fishing effort is distributed uniformly over space. This paper demonstrates that by ignoring this heterogeneity, yield‐per‐recruit models systematically overstate the yield gains (or understate the losses) from creating a reserve in a heavily exploited fishery. Conversely, at very low levels of exploitation, models that ignore heterogeneous fishing effort overstate the fishing yield losses from creating a reserve. Starting with a standard yield‐per‐recruit model, the paper derives a yield surface that maps spatially differentiated fishing effort into total long‐run fishing yield. It is the curvature of this surface that accounts for why the spatial distribution of fishing effort so greatly affects predicted changes from forming a reserve. The results apply generally to any model in which the long‐run fishing yield has similar curvature to a two‐patch Beverton‐Holt model. A simulation of marine reserve formation in the California red sea urchin fishery with Beverton‐Holt recruitment, eleven patches, and common larval pool dispersal dynamics reinforces these results.

Limited‐Entry Licensing: Insights from a Duration Model

Limited entry is used to manage many fisheries. Effectiveness depends on a program's ability to control aggregate fishing power, which fleet size and composition both affect. This article analyzes fleet composition and attrition in a limited‐entry fishery, the California red sea urchin fishery. It explores the dynamics of heterogeneity in catch and revenue and applies duration analysis to study individual fisherman attrition using both individual‐level and time‐varying covariates. The results show that the fleet is becoming more homogenous but also more potent and spatially mobile. Regulations such as size limits and season restrictions tend to increase attrition.

Density-dependent sexual selection in external fertilizers: variances in male and female fertilization success along the continuum from sperm limitation to sexual conflict in the sea urchin Strongylocentrotus franciscanus.

Sperm competition and female choice are fundamentally driven by gender differences in investment per offspring and are often manifested as differences in variance in reproductive success: males compete and have high variance; most females are mated and have low variance. In marine organisms that broadcast spawn, however, females may encounter either sperm limitation or sperm competition. I measured the fertilization success of male and female Strongylocentrotus franciscanus over a range of population densities using microsatellite markers. Female fertilization success first increased and then decreased with mate density, limited at low density by sperm limitation and at high density by polyspermy. Mate density affected variance in fertilization success in both males and females. In males, the variance in fertilization success increased with mate density. In females, the pattern was more complex. The variance in female success increased similarly to males with increased mate density but then decreased to low levels at intermediate densities, where almost all eggs were fertilized. As density increased further, the female variances again increased as polyspermy lowered average fertilization success. Male and female variances differed only at intermediate densities. At low densities, both sexes may be under selection to increase fertilization success; at intermediate densities, males may compete; and at high densities, both sexes may be under selection to increase success by increasing (males) or decreasing (females) likelihood of fertilization during sexual conflict. Only within a narrow range of densities do patterns of sexual selection mirror those typically noted in internally fertilizing taxa.

Critical thermal maximum and osmotic pressure of the red sea urchin Strongylocentrotus franciscanus acclimated at different temperatures

1. The sea urchin Strongylocentrotus franciscanus acclimated at 15°C, 18°C and 21°C exposed to a rising thermal stress showed a series of well-defined responses. 2. All responses were significantly different and stage E4, characterized when the sea urchins ceased moving, relaxed the large spines but the smaller spines continued to make small movements. This was considered to be the critical thermal maximum (CTMax). 3. The resistance of S. franciscanus is independent of the acclimation interval used in this work. 4. The effect of the CTMax on the osmotic pressure of the sea urchin body fluid acclimated at 18°C was significantly different ( P<0.05) when compare to the 15°C and 21°C conditions.

Modelling the use of two fishery access rights, concessions and licences, in the red sea urchin, Strongylocentrotus franciscanus (Agassiz), fishery at Santo Tomás, Baja California, Mexico

Various stages of the red sea urchin, Strongylocentrotus franciscanus (Agassiz), fishery were simulated to evaluate the effect of two types of access rights under Mexican law: concessions and licences. The resource biomass was evaluated using the critical depensation and Schaefer models. Each model was evaluated as a static or dynamic system. The parameters required for each model were determined from government data and by generating stochastic numbers using the Monte Carlo method to adjust to a dynamic model. In general, both models predicted catches smaller than those observed. The five-year-period simulation for both models showed a drop in biomass when licences are issued, whereas a similar simulation for concessions resulted in increased biomass, except when high temperatures occurred. Our results suggest that issuing concessions rather than licences is the best option to conserve the fishery.

Juvenile-adult associations in sea urchins Strongylocentrotus franciscanus and S. droebachiensis: Is nutrition involved?

Juvenile-adult associations (i.e. juvenile sheltering) in sea urchins of the genus Strongylocentrotus provide an example of an important post-settlement behaviour in benthic invertebrates. It has been suggested that these associations provide a nutritional advantage to juveniles by facilitating access to kelp. We examined this hypothesis in a series of growth experiments involving 2 sea urchin species, Strongylocentrotus franciscanus and S. droebachiensis, which show high and low levels of juvenile sheltering, respectively. Juvenile sea urchins (7.73 ± 0.09 mm [mean ± SE] test diameter) of both species had lower growth rates in the presence versus absence of adults, regardless of food type, though the effect was more pronounced in S. franciscanus (0.2 ± 0.1 vs 1.2 ± 0.3 mm mo -1 ) than in S. droebachiensis (0.8 ± 0.5 vs 1.2 ± 0.7 mm mo -1 ). This relationship was not evident in the absence of food, which leads us to conclude that the reduction in growth is due to intercohort competition. Hence, other post-settlement factors (e.g. predation and hydrodynamic disturbance) are likely responsible for maintaining the juvenile-adult associations observed in S. franciscanus. Species-specific strategies in juvenile sheltering indicate that behavioural processes are important for the recruitment of benthic invertebrates with mobile juvenile stages.

Density-Dependent Sexual Selection in External Fertilizers: Variances in Male and Female Fertilization Success along the Continuum from Sperm Limitation to Sexual Conflict in the Sea Urchin Strongylocentrotus franciscanus

Density-Dependent Sexual Selection in External Fertilizers: Variances in Male and Female Fertilization Success along the Continuum from Sperm Limitation to Sexual Conflict in the Sea Urchin Strongylocentrotus franciscanus

Comparison of gonad quality factors: color, hardness and resilience, of Strongylocentrotus franciscanus between sea urchins fed prepared feed or algal diets and sea urchins harvested from the Northern California fishery

Quality factors important in sea urchin roe marketing are color and texture. In two laboratory experiments, spring and fall, Strongylocentrotus franciscanus, were starved or fed a low carotenoid pigment diet (13.86 μg/g), a high carotenoid pigment diet (146.83 μg/g) or kelp, Nereocystis luetkeana (73.60 μg/g). Gonads from laboratory groups and three grades of commercially processed roe (Fort Bragg A, B, and C) were examined for color and texture. Grade A roe is the most commercially valuable. S. franciscanus weighed 329.1±43.0 g and had a test diameter of 91.4±5.3 mm. Feed consumption was greater in fall than spring for prepared diets and lower in fall for N. luetkeana. The lightness ( L*) of S. franciscanus gonads was significantly greater in spring than fall. Gonads from laboratory treatments showed lower values for red and yellow resulting in overall lighter color than commercially processed roe. Red color ( a*) remained similar in both season while yellow color ( b*) decreased significantly in fall. Hardness and resilience were greater in fall than spring, reflecting greater dry matter content and gonad reproductive condition. Spring gonads were large, soft and mature. Fall gonads were large, firm and in the recovering and growing stages of the reproductive cycle. Seasonal differences in color, hardness, and resilience indicate reproductive state and must be considered in aquaculture strategies of sea urchins.

The species-specific egg receptor for sea urchin sperm adhesion is EBR1,a novel ADAMTS protein.

Species-specific adhesion of sperm to the egg during sea urchin fertilization involves the interaction of the sperm adhesive protein,bindin, and a complementary receptor on the egg surface,and serves to restrict the gene pool to individuals of the same species. We used PCR representation difference analysis to clone the species-specific egg receptor for bindin, EBR1, from Strongylocentrotus franciscanus (Sf) and S. purpuratus (Sp). Sf-EBR1 contains a novel ADAMTS-like N-terminal domain followed by approximately 19 tandem EBR repeats consisting of alternating CUB and thrombospondin type 1 (TSP-1) domains where the last 10 EBR repeats are species-specific and highly conserved. Recombinant protein corresponding to the species-specific EBR repeat displays species-specific sperm adhesion and bindin-binding activity. The Sp-EBR1 ortholog has the same ADAMTS (a disintegrin and metalloprotease with thrombospondin type-1 modules) core region followed by eight and one-half tandem egg bindin receptor (EBR) repeats that share 88% identity with the Sf-EBR1 repeats,but has an entirely different species-specific domain consisting of hyalin-like (HYR) repeats. Thus,the species-specific domains of egg bindin receptor 1 (EBR1) from both species function as the egg surface receptor to mediate species-specific sperm adhesion.

Molecular Phylogenies and Divergence Times of Sea Urchin Species of Strongylocentrotidae, Echinoida

Sea urchins of the family Strongylocentrotidae have been important model systems in many fields of basic biology, yet knowledge of their evolutionary identities such as the phylogenetic relationships and divergence times remains limited. Here, I inferred molecular phylogenies of seven Strongylocentrotid species (Strongylocentrotus franciscanus, S. nudus, S. purpuratus, S. intermedius, S. droebachiensis, S. pallidus, and Hemicentrotus pulcherrimus) from the analyses of mitochondrial DNA sequences of 12SrDNA (349 nt), 12SrDNA-tRNA(gln) region (862 nt), and a combined sequence of cytochrome oxidase subunit I (COI, 1080 nt) and NADH dehydrogenase subunit I (NDI, 742 nt). The rate of sequence evolution and divergence times for each species were then estimated from the trees with reference to the time of separation between Strongylocentrotidae and Parechinidae, 35 to 50 MYA. The three trees agree well with each other, and the phylogeny is summarized by ((S. franciscanus, S. nudus), (H. pulcherrimus (S. purpuratus, S. intermedius (S. droebachiensis, S. pallidus)))). It is notable that the genus Strongylocentrotus consists of two distinct clades and that H. pulcherrimus branches off within Strongylocentrotus, implying assignment of a separate, monospecific genus to this species inappropriate. The rate of sequence evolution is calibrated to be 0.24%-0.34%/Myr in 12SrDNA, 0.25%-0.36%/Myr in 12SrDNA-tRNA(gln), and 0.65%-0.93%/Myr in COI-NDI combined sequences. S. purpuratus, in particular, shows the significantly higher rate of evolution in the 12SrDNA and 12SrDNA-tRNA(gln) regions compared to other species, suggesting careful use of its sequences in comparative studies. The two clades of Strongylocentrotidae seem to have split 13-19 MYA, and H. pulcherrimus branched off 7.2-14 MYA. In the former clade, S. franciscanus and S. nudus separated 5.7-8.1 MYA. In the latter clade, S. purpuratus, S. intermedius, and the clade of S. droebachiensis and S. pallidus diverged approximately 4.6-12 MYA, and the last two closest species separated 2.1-3.1 MYA.

Bioerosion in coral reef communities in southwest Puerto Rico by the sea urchin Echinometra viridis

Bioerosion is one of the most important structuring forces in coral reef communities. The bioerosion impact of several species of fish, sponges and sea urchins have been estimated in the Caribbean; however, there is no information for one important species, the red sea urchin Echinometra viridis. This species can be found in high densities in many localities. In this study, bioerosion rates for E. viridis were estimated in two patch reefs off La Parguera, southwest Puerto Rico, using the population size-class distribution, average densities, and the CaCO3 content in fecal pellets produced over 24 h. Average densities of urchins along four depth intervals were estimated using 40-m transect lines and 1-m2 quadrats. Average size and size-structure distribution were estimated by measuring the diameter of 180–220 urchins haphazardly collected at each of the four depth intervals. The ignition–loss method was used to estimate the daily rate of bioerosion. Fecal pellets produced by the urchins over a 24 h period were collected in buckets, rinsed in fresh water, dried for 24 h at 70°C, and then burned in a furnace at 550°C, first to eliminate organics, and then at 1000°C until constant weight to determine the amount of calcium carbonate (CaCO3) in the fecal pellets. HCl (10%) was then added to the remainder of the sample to test for presence of CaCO3. Average individual CaCO3 bioerosion rates were estimated at 0.181±0.104 g day−1. Average densities (0.77–62.0 ind. m−2), size (2.01–2.44 cm) and average bioerosion rates (0.114–4.14 kg m−2 year−1) were significantly higher in shallow areas (1–3 m) in both reefs. Bioerosion rates were low compared to those reported for parrotfish, endolithic sponges and the black sea urchin D. antillarum, but they were higher than those reported for other small-sized sea urchins in the Caribbean and the Indo-Pacific.

Structural requirements for species-specific induction of the sperm acrosome reaction by sea urchin egg sulfated fucan

The sulfated fucan (SF) of egg jelly induces the acrosome reaction (AR) of sea urchin sperm. Strongylocentrotus franciscanus ( Sf) SF is sulfated only at the 2-position. Strongylocentrotus purpuratus ( Sp) has two SF isotypes, each one being female specific. One is rich in sulfate at both the 2- and 4-positionS (SF-1), and the other is rich in sulfate at the 4-position, but not the 2-position (SF-2). Sf SF is poor at inducing the AR of Sp sperm, presumably due to lack of 4-sulfation. Sp SF-1 is better at inducing the AR of Sf sperm than Sp SF-2, hypothetically due to increased 2-sulfation. Chemical oversulfation of Sf SF increases the percentage of AR of Sp sperm, showing that 4-sulfation is important for recognition of SF by Sp sperm. Chemically oversulfated Sp SF-2 is better at inducing the Sf sperm AR, presumably because of increased 2-sulfation. The species, Strongylocentrotus drobachiensis ( Sd), has an SF-2 that is exclusively 2-sulfated (like Sf), except the glycosidic linkage in Sd is α(1→4), whereas in Sf it is α(1→3). Sd SF-2 does not induce the AR of Sf sperm, showing the strict requirement for the α(1→3) linkage in recognition between Sf sperm and SF. Egg jelly from Echinometra lucunter ( El) contains sulfated galactan (SG) which differs from Sf SF only in that the monosaccharide is l-galactose, not l-fucose. This SG and Sf SF are equally potent in inducing the AR of Sf sperm, showing that modification at C6 of l-fucose is not important for proper recognition between SF and Sf sperm receptors. This system permits study of the structural basis for recognition between sulfated polysaccharide and receptors controlling signal transduction pathways in animal cells.

The relationship between conspecific fertilization success and reproductive isolation among three congeneric sea urchins.

Few data are available on the effectiveness of reproductive isolating mechanisms in externally fertilizing taxa. I investigated patterns of conspecific and heterospecific fertilization among three coexisting sea urchin species, Strongylocentrotus droebachiensis, S.franciscanus, and S. purpuratus. In the laboratory, both among and within species, eggs from individual females whose eggs are more easily fertilized by conspecific sperm are also most susceptible to heterospecific fertilization. At one extreme, S. droebachiensis requires an order of magnitude fewer conspecific sperm to fertilize eggs than do the other two species and shows very little distinction between conspecific and heterospecific sperm in no choice experiments. Strongylocentrotus franciscanus has an intermediate susceptibility to fertilization by heterospecific sperm. At the other extreme, S. purpuratus rarely cross-fertilizes. Field observations indicate that S. droebachiensis is often surrounded by heterospecific sea urchins. Genetic analysis of larvae produced during heterospecific spawning events indicate that hybrids are generally produced if male conspecifics are more than 1 m from a spawning female S. droebachiensis. Laboratory cultures indicate that these hybrids suffer high mortality relative to conspecific larvae. Comparisons of reproductive success of S. droebachiensis during single-species and multispecies spawning events indicate that the benefits of producing easily fertilized eggs under conditions of sperm limitation may outweigh the costs of losing some offspring to hybrid fertilization. Patterns of variability in heterospecific fertilization are considered in light of three hypotheses: phylogenetic relatedness, reinforcement selection, and sexual selection.

The effect of sea urchins as biogenic structures on the local abundance of a temperate reef fish.

Although widely distributed on rocky reefs at Santa Catalina Island (southern California, USA), the small, substrate-oriented fish, Lythrypnus dalli, often reaches its highest densities in areas of extreme vertical relief where the sea urchin, Centrostephanus coronatus, is common. Through surveys and manipulative field experiments, we examined the extent to which the availability of C. coronatus influenced the distribution and abundance of L. dalli. Adult L. dalli were strongly associated with C. coronatus, but not with two shorter-spined urchins, Strongylocentrotus franciscanus and S. purpuratus. Variation in fish abundance among C. coronatus was affected by three features: the amount of space between the body of the urchin and its rocky shelter, the location of occupied shelters, and urchin size. Field manipulations of C. coronatus density indicated that spatial patterns of L. dalli abundance are causally linked to the presence of urchins. Urchins also had a significant effect on recruitment, migration, and survival of L. dalli. These processes were greatly enhanced where urchins were present. Structural substitutions (models) produced about half the effect of live urchins indicating that biological, as well as structural, attributes of urchins may be important to fish. Our results suggest that habitat selection at the time of settlement, small-scale migration of fish after settlement, and differential survival relative to the presence of sea urchins contribute to the formation and maintenance of the association between L. dalli and C. coronatus. By altering the availability of refuges, sea urchins appear to have a direct and positive effect on the local abundance of this temperate reef fish.

Induction of metamorphosis with KCl in three species of sea urchins and its implications in the production of juveniles

A common practice for inducing metamorphosis in larvae of marine invertebrates is the use of a wide variety of artificial inducers. Excess K+ and Cs+ in seawater have proved to be very effective for this purpose, but not universally effective to induce metamorphosis in different phyla of marine invertebrates. In the present study we tested the response of three species of sea urchins to excess K+ in seawater as an artificial inducer. Excess K+ in seawater was presented to the larvae as continuous (24 h) or pulse exposure in concentrations ranging from 0.01 to 100 mM. Results showed that excess K+ in the form of KCl added to seawater was an effective metamorphic inducer of the three species of sea urchins tested; the purple sea urchin Strongylocentrotus purpuratus, the red sea urchin S. franciscanus and the white sea urchin Lytechinus pictus. The response was dependent on concentration and time of exposure. Continuous exposure (24 h or more) to excess K+ (100 mM) resulted lethal to the larvae of the three species. Excess K+ (100 mM) for 15 min resulted the most effective pulse-period to induce metamorphosis in the three species. This method of induction allows us to produce synchronous metamorphosed postlarvae useful for aquaculture and studies of signal transduction mechanisms during metamorphosis of sea urchins.

Sutural loosening and skeletal flexibility during growth: determination of drop-like shapes in sea urchins.

The shape of sea urchins may be determined mechanically by patterns of force analogous to those that determine the shape of a water droplet. This mechanical analogy implies skeletal flexibility at the time of growth. Although comprised of many rigid calcite plates, sutural collagenous ligaments could confer such flexibility if the sutures between plates loosened and acted as joints at the time of growth. We present experimental evidence of such flexibility associated with weight gain and growth. Over 13-, 4-, and 2-week periods, fed urchins (Strongylocentrotus droebachiensis) gained weight and developed looser sutures than unfed urchins that maintained or lost weight. Further, skeletons of fed urchins force-relaxed more than did those of unfed urchins and urchins with loose sutures force-relaxed more than those with tight sutures. Urchins (Strongylocentrotus franciscanus) fed for two and a half weeks, gained weight, also had looser skeletons and deposited calcite at sutural margins, whereas unfed ones did not. In field populations of S. droebachiensis the percentage having loose sutures varied with urchin diameter and reflected their size-specific growth rate. The association between feeding, weight gain, calcite deposition, force relaxation and sutural looseness supports the hypothesis that urchins deform flexibly while growing, thus determining their drop-like shapes.

Abundance and associations of two commercially important gastropods (Astraea and Haliotis) in Isla San Jeronimo, Baja California, Mexico

We present the status of Astraea (Lithopoma) undosa, A. (L.) turbanica, and Haliotis spp. in Isla San Jerónimo, Baja California, Mexico and describe the associations between the dominant flora and fauna in their habitat. Forty years ago this area was one of the main fishing areas for Astraea and Haliotis along the peninsula, but now it is overexploited. The mean density of A. undosa was 0.1 m–2 and that of A. turbanica was 0.006 m–2. Both species have a low proportion of organisms with the minimum legal size of capture. No abalones were found around the island, but few were found in the intertidal. There is a good proportion of suitable rocky habitat and food for Astraea and Haliotis. Positive associations between dominant macroinvertebrates and flora were detected. Rocky areas with vegetation are the common habitat of Kelletia sp. and Pisaster sp. (predators); and of Strongylocentrotus franciscanus, Tegula spp., and Megathura crenulata (prey); and they were positively associated. Our results suggest a negative covariation and spatial segregation between A. undosa and A. turbanica.