Heliaster Helianthus Research Articles

Determining ecosystem properties and short-term dynamical simulations in Eisenia cokeri kelp forest (north-center of Peru): Implications for conservation and monitoring

A mass-balanced and dynamical multispecies trophic model was constructed for the kelp forest ecosystem dominated by Eisenia cokeri in the central-northern Peruvian coast. Information of biomass, productivity, food spectrum, consumption, catches, and dynamics of the commercial and non-commercial local populations was needed and examined using Ecopath with Ecosim (EwE) software. The brown macroalgae E. cokeri accounted for ∼60% of total system biomass, ∼30% of total system throughput (TST), and ∼26% of ascendency (A), indicating its relevance in the aggregation and transference of energy/matter in the network, as well as in the development and growth status of this coastal ecological system. Based on the values of TST, A, A/C and Ov/C ratios, and path redundancy, this kelp forest would be more developed but less resistant to disturbances than other kelp forests along the SE Pacific and Antarctic coast. Likewise, Luidia magellanica, Heliaster helianthus and Labrisomus phillipi were the components that accounted for the complexity (lowest % of AMI) of the benthic-pelagic network system. The outcomes of mixed trophic impacts (MTI) indicate that the asteroids L. magellanica, H. helianthus, and other sea stars (OSS) propagate the highest magnitudes of direct and indirect effects on the other model compartments. Meanwhile, the dynamical responses using Ecosim short-term simulations (increasing 10%, 30%, and 50% the total mortality by fishing), the brown macroalgae E. cokeri, small epifauna (SE), and Tegula spp. exhibited the highest impacts on the remaining compartments in the model-system. The system recovery time (SRT) (as a measure of system resilience) indicated that E. cokeri, H. helianthus, and Tegula spp. would take the longest time to return (after disturbance) to their initial condition. The macroscopic properties estimated in the present work could be considered as baseline ecosystem conditions before performing an intensive exploitation on E. cokeri.

Effects of artificial light at night and predator cues on foraging and predator avoidance in the keystone inshore mollusc Concholepas concholepas.

The growth of Artificial Light At Night (ALAN) is potentially having widespread effects on terrestrial and coastal habitats. In this study we addressed both the individual effects of ALAN, as well as its combined effect with predation risk on the behaviour of Concholepas concholepas, a fishery resource and a keystone species in the southeastern Pacific coast. We measured the influence of ALAN and predation risk on this mollusc's feeding rate, use of refuge for light and crawling out of water behaviour. These behavioural responses were studied using light intensities that mimicked levels that had been recorded in coastal habitat exposed to ALAN. Cues were from two species known to prey on C.concholepas during its early ontogeny: the crab Acanthocyclus hassleri and the seastar Heliaster helianthus. The feeding rates of C.concholepas were 3-4 times higher in darkness and in the absence of predator cues. In contrast, ALAN-exposed C.concholepas showed lower feeding activity and were more likely to be in a refuge than those exposed to control conditions. In the presence of olfactory predator cues, and regardless of light treatment, C.concholepas tended to crawl-out of the waterline. We provide evidence to support the hypothesis that exposure to either ALAN or predation risk can alter the feeding behaviour of C.concholepas. However, predator cue recognition in C.concholepas was not affected by ALAN in situations where ALAN and predator cues were both present: C.concholepas continued to forage when predation risk was low, i.e., in darkness and away from predator cues. Whilst this response means that ALAN may not lead to increased predation mortality in C.concholepas, it will reduce feeding activity in this naturally nocturnal species in the absence of dark refugia. Such results may have implications for the long-term health, productivity and sustainability of this keystone species.

Evaluating the macroscopic system properties of kelp species planted on two artificial reefs: Implications for the restoration of perturbed subtidal areas

Macroscopic ecosystem properties based on an Ascendency theoretical framework were assessed for mass-balance trophic models representing ecological systems constructed by the kelp species Macrocystis pyrifera planted on artificial reefs installed on subtidal barren rocky and sandy bottoms (Antofagasta Peninsula, Chile). Information on biomass, production, diet and consumption was needed. The magnitudes of relative Ascendency, relative Overhead and Redundancy values indicated that kelp planted on artificial reefs allocated on soft bottoms would be more highly developed and less resistant to perturbations than ecological systems on artificial reefs disposed on barren and natural systems inhabiting soft bottoms and kelp habitats. The relative Ascendency corresponding to each component of the ecological systems constructed on artificial reefs on both habitats was represented principally by detritus (~37%), M. pyrifera (between 22 and 26%) and phytoplankton (between 10 and 13%). The compartments of Rhodophyta, Chlorophyta Mesophyllum sp. and the sea star Heliaster helianthus accounted for the system complexity in terms of flow, exhibiting the lowest Average Mutual Information. The Finn cycling index – considered as a ecosystem maturity index – showed contradictory outcomes compared to Ascendency. However, the values of System omnivory index and Average path length quantified for the ecological systems constructed on both artificial reefs showed similar network topologies compared to natural kelp beds. Based on our findings, artificial reefs seeded with M. pyrifera could be used to restore perturbed local marine benthic ecological systems along the Chilean coast. Likewise, this work shows that the trajectory of local ecological systems can be modified, enhancing their global-system health.

Predation on competing mussel species: Patterns of prey consumption and its potential role in species coexistence

Theoretical and empirical studies have demonstrated that predators can modulate coexistence between prey species and can modify broad patterns of community structure. Although the keystone predator effect (i.e., local coexistence and species diversity mediated by predator consumption) is commonly reported, negative effects of predators on species coexistence are also common. The balance depends critically on the asymmetry of competition, predator preferences for different prey, and the effective mortality rates exerted by predator populations on prey per capita growth rates. Here we studied the role of predation on two competing mussels, the dominant competitor Perumytilus purpuratus that dominates in abundance at most shores, and the subordinate Semimytilus algosus, which is common, but persistently abundant only at a smaller set of shores. We examined the potential for keystone effects by quantifying and evaluating the patterns of mussel consumption rates of sea star (Heliaster helianthus) and crab (Acanthocyclus gayi) predators in laboratory experiments, and under natural field conditions. Field sites with contrasting mussel abundance and recruitment (i.e., different local prey population growth rates) were chosen. Laboratory experiments showed that crabs would first consume Semimytilus over Perumytilus in mixed mussel clumps, while the larger sea star predators made no distinction between mussel species. Regardless of the order in which mussel species were first ingested, consumption rates of the two mussel species through the experiment were not different for either predator species. A similar temporal pattern was partly observable in the field through specific differences in the order of mussel consumption; however, experimental mussels of both species where consumed after the first two months of exposure to predators at both sites. Thus, in this system predation could not foster coexistence between mussel species and it may instead favor the occurrence of local extinction of the subordinate competitor, especially at sites where the smaller and more selective crab predators are relatively more abundant and recruitment of the subordinate species is low. Existing patterns of locally abundant Semimytilus beds are probably related to high site-specific recruitment rates of this species and should be further explored.

From Chile to the South African west coast: first reports of the Chilean stone crab Homalaspis plana (H. Milne Edwards, 1834) and the South American sunstar Heliaster helianthus (Lamarck, 1816) outside their natural ranges

CITATION: Peters, K. & Robinson, T. B. 2018. From Chile to the South African west coast : first reports of the Chilean stone crab Homalaspis plana (H. Milne Edwards, 1834) and the South American sunstar Heliaster helianthus (Lamarck, 1816) outside their natural ranges. BioInvasions Records, 7(4):421-426, doi:10.3391/bir.2018.7.4.11.

Behavioural and physiological responses of limpet prey to a seastar predator and their transmission to basal trophic levels

Besides the well-documented behavioural changes induced by predators on prey, predator-induced stress can also include a suite of biochemical, neurological and metabolic changes that may represent important energetic costs and have long-lasting effects on individuals and on the demography of prey populations. The rapid transmission of prey behavioural changes to lower trophic levels, usually associated with alteration of feeding rates, can substantially change and even reverse direction over the long term as prey cope with the energetic costs associated with predation-induced stress. It is therefore critical to evaluate different aspects and assess the costs of non-consumptive predator effects on prey. We investigated the behavioural and physiological responses of an herbivorous limpet, Fissurella limbata, to the presence of chemical cues and direct non-lethal contact by the common seastar predator, Heliaster helianthus. We also evaluated whether the limpets feeding behaviour was modified by the predator and whether this translated into positive or negative effects on biomass of the green alga, Ulva sp. Our experimental results show the presence of Heliaster led to increased movement activity, increased distances travelled, changes in time budget over different environmental conditions and increased feeding rate in the keyhole limpets. Moreover, additional experiments showed that, beyond the increased metabolic rate associated with limpet increased activity, predator chemical cues heighten metabolic rate as part of the induced stress response. Changes in individual movement and displacement distances observed through the 9-day experiment can be interpreted as part of the escape response exhibited by limpets to reduce the risk of being captured by the predator. Increased limpet feeding rate on algae can be visualized as a way individuals compensate for the elevated energetic costs of movement and heightened metabolic rates produced by the predator-induced stress, which can lead to negative effects on abundance of the lower trophic level. We suggest that in order to understand the total non-consumptive effect of predators in natural communities, it is necessary to evaluate not only short-term behavioural responses, but also the costs associated with the multiple interdependent pathways triggered by predator-induced stress, and determine how individuals cope with these costs in the long term.

Network properties and keystoneness assessment in different intertidal communities dominated by two ecosystem engineer species (SE Pacific coast): A comparative analysis

Multispecies quantitative and qualitative models of the kelp Lessonia nigrescens and the tunicate Pyura praeputialis were constructed for intertidal areas of northern Chile (SE Pacific). Information on biomass, P/B ratios, catches, food spectrum, consumption and dynamics of commercial and non-commercial species was obtained and examined using Ecopath with Ecosim and Loop Analysis theoretical frameworks. The biomass of L. nigrescens and P. praeputialis constituted the most important compartments, exceeding 97% of the total biomass in each model system. Based on Pp/R, the system of P. praeputialis appeared to be the most developed. However, according to Pp/B, A/C, Ai/Ci, and redundancy, the L. nigrescens system was the most developed and, in turn, the least resistant to disturbances. The results obtained using mixed trophic impacts (MTI), Ecosim simulations, and system recovery time (SRT) showed different response patterns. The tunicate species propagated higher effects on the remaining species, whereas the kelp species presented the longest SRT (as a resilience measure). The model keystone species indices suggested that each model system contained a core of ecologically related species. In the L. nigrescens system, core was made up of the filter feeders Semimytilus algosus, barnacles, and small epifauna herbivores (SEH) and the predators Concholepas concholepas and Heliaster helianthus. In the P. praeputialis system, the core consisted of phyoplankton, zooplankton, other filter feeders and the predators C. concholepas, H. helianthus, other starfish, and large epifauna. The outcomes obtained in the current work did not indicate that the alien tunicate P. praeputialis was a better or superior bio-engineer when compared to the system constructed by the kelp L. nigrescens. Rather, each species was relevant and relied on different ecological mechanisms.

<strong>Autotomy of rays of Heliaster helianthus (Asteroidea: Echinodermata)*</strong>

In species of the family Heliasteridae, the ossicles of the proximal parts of the sides of each ray are joined by connective tissue to those of the adjacent rays to form interradial septa. These provide support to the extensive disc. Only a relatively small part of the ray is free. Autotomy of rays occurs in Heliaster helianthus in response to predatory attack by the asteroid Meyenaster gelatinosus. Autotomy of the ray does not occur at the base of the free part of the ray (arm) but near the base of the ray. In addition to the plane of autotomy at this location, a longitudinal plane of autotomy occurs in the connec­tive tissue between the ossicles of the interradial septa. This indicates a plane of mutable collagenous tissue is present. Autotomy of the ray involves all these planes of autotomy and results in loss of most of the ray.

New insights into the life-history of the isopod Edotia dahli (Valvifera: Idoteidae): report of host-use and distribution records in the central Chilean coast

Unreported aspects of the life-history of the isopod Edotia dahli are described based on intertidal collections carried out during 2002, 2005 and 2011 in 5 locations in central Chile (29-33°S; Pacific coast). Isopods were recorded for the first time living on 2 species of echinoderms, the sea-star Heliaster helianthus and the sea-urchin Arbacia sp. The observation of sea-urchins hosting isopods was casual (i.e., no formal samplings); however, nearly 20% of the sampled sea-stars hosted isopods (from 2 to > 100 individuals per host). This association was similar through years. Surveys also revealed that E. dahli was present at higher latitudes than those previously recorded in the central Chilean coast, extending the northern distribution range 3° to 29°S.

Sea urchin Tetrapygus niger distribution on elevated surfaces represents a strategy for avoiding predatory sea stars

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 444:85-95 (2012) - DOI: https://doi.org/10.3354/meps09396 Sea urchin Tetrapygus niger distribution on elevated surfaces represents a strategy for avoiding predatory sea stars Juan Diego Urriago1,2,3, John H. Himmelman1, Carlos F. Gaymer2,* 1Département de Biologie, Université Laval, Québec City, Québec, Canada G1V 0A6 2Departamento de Biología Marina and Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Universidad Católica del Norte, Casilla 117, Coquimbo, Chile 3Present address: Department of Biology, Hong Kong Baptist University, Swire Institute of Marine Science, Cape d'Aguilar Road, Shek O, Hong Kong SAR *Email: cgaymer@ucn.cl ABSTRACT: We ran field experiments to examine whether the micro-distribution of the sea urchin Tetrapygus niger on elevated surfaces represents a strategy for limiting predation by the sea stars Heliaster helianthus and Meyenaster gelatinosus. Several lines of evidence supported this hypothesis. (1) A survey of the distribution of the urchin and the 2 sea stars showed that urchins occur mainly on elevated surfaces, and sea stars on low surfaces. (2) In trials involving simulated attacks, the time needed by the urchin to sever contact with the sea stars was 48% less on elevated surfaces than on the bottom. (3) In trials involving sustained simulated attacks (high predatory risk) the urchins could detach themselves from the elevated surfaces to avoid being eaten. Finally, tethering experiments indicated that the urchin had a higher survival rate on elevated than low ­surfaces. Our observations indicate that M. gelatinosus represents a stronger predatory threat to T. niger than H. helianthus. KEY WORDS: Tetrapygus niger · Heliaster helianthus · Meyenaster gelatinosus · Predator−prey interactions · Aggregation · Distribution · Tethering Full text in pdf format PreviousNextCite this article as: Urriago JD, Himmelman JH, Gaymer CF (2012) Sea urchin Tetrapygus niger distribution on elevated surfaces represents a strategy for avoiding predatory sea stars. Mar Ecol Prog Ser 444:85-95. https://doi.org/10.3354/meps09396 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 444. Online publication date: January 10, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Scales of detection and escape of the sea urchin Tetrapygus niger in interactions with the predatory sun star Heliaster helianthus

Predators can simultaneously have lethal (consumption) and non-lethal (modification of traits) effects on their prey. Prey escape or fleeing from potential predators is a common form of a non-lethal predator effect. The efficiency of this response depends on the prey's ability to detect and correctly identify its predator far enough to increase the probability of successful escape, yet short enough to allow it to allocate time to other activities (e.g. foraging). In this study, we characterized the non-lethal effect of the sun star Heliaster helianthus on the black sea urchin Tetrapygus niger by assessing the nature of predator detection and the spatial scale involved both in predator detection and in the escape response. Through field and laboratory experiments we demonstrate that T. niger detects chemical cues released by H. helianthus. In the laboratory, these chemical signals can be detected at distances of up to about 50cm. In the field, the distance traveled by urchins when escaping, after recognition of the predation risk, was also restricted to about 40cm. Thus, considering the sizes of the predator and prey, the spatial scale of both detection and escape is comparatively small suggesting that non-lethal effects of H. helianthus (e.g. how it modifies the behavior of T. niger) should be important at local spatial scales and highly variable at the landscape scale.

Effects of a predatory starfish on substrate colonization by a dominant mussel

The pressure exerted by consumers has generally been considered to be among the main factors affecting the structure and processes in marine communities. Here, we assessed the effects of the predatory starfish Heliaster helianthus on substrate colonization by the dominant mussel Semimytilus algosus in a rocky intertidal area of the central Peruvian coast. We conducted 3 experiments: exclusions of starfish (1) from the edge of mussel beds, (2) from areas on bare substrate and (3) from areas surrounding recruitment mediators (i.e. branched macroalgae). The exclusion of H. helianthus resulted in increased cover of S. algosus in the 3 experiments. However, the colonization of the available space by S. algosus in the absence of starfish was more evident when facilitated by recruitment mediators or by migration from the edge of mussel beds than when colonization occurred during succession starting from bare substrate. By the end of the study period, however, increased S. algosus abundance, which coincided with the end of the cold phase (La Nina) of the El Nino-Southern Oscillation, overwhelmed the effects of starfish. We suggest that periodic oceanographic fluctuations are also important in controlling community dynamics in Peruvian rocky intertidal zones, highlighting the variation in the relative importance of top-down versus bottom-up control when different temporal scales are considered. © Inter-Research 2011.

Responses of the black sea urchin Tetrapygus niger to its sea-star predators Heliaster helianthus and Meyenaster gelatinosus under field conditions

We ran field experiments to examine the responses of the black sea urchin Tetrapygus niger to predatory sea stars. Trials involving simulated attacks (one or several arms of a sea star being placed on top of half the urchin) showed that the urchin differentiated between the predatory sea stars, Heliaster helianthus and Meyenaster gelatinosus, and a non-predatory sea star, Stichaster striatus, and showed almost no response to a sea star mimic. We further compared the responses of the urchin to different threat levels presented by the two predatory sea stars. The highest threat level was a simulated attack, then mere contact, and subsequently sea stars being placed at different distances from the urchin. All urchins responded to simulated attacks and contact with both sea stars. The proportion responding decreased with distance and more rapidly in trials with H. helianthus (0% at a distance of 30 cm) than with M. gelatinosus (33% at a distance of 50 cm). At each of the threat levels where there was a response to both sea stars, the urchins responded more rapidly to M. gelatinosus than to H. helianthus. In a third experiment where a predatory sea star was added to a circular area (1-m diameter) in which either 4–8 or 11–19 undisturbed urchins were present, the urchins fled the area more rapidly when the added sea star was M. gelatinosus, but the rate of fleeing did not vary with density, as might occur if there was communication among urchins using alarm signals. Our observations suggest that M. gelatinosus presents a stronger predatory threat than H. helianthus. This corresponds to field observations showing that the urchins are more frequently consumed by M. gelatinosus. These are the first field experiments demonstrating distance chemodetection by a marine invertebrate under back-and-forth water flow from wave activity.

Risk recognition and variability in escape responses among intertidal molluskan grazers to the sun star Heliaster helianthus

Escape responses are a common form of inducible defense in the presence of a predator, which can be species-specific and adaptive. While conditions for their evolution have been amply investigated, little is known about variability in prey responses over the range of variation in predation risks typical of most systems. We characterized escape responses of 4 intertidal grazers (2 chitons, 2 fissurellid limpets) to the sunstar Heliaster helianthus. Comparisons were made among sites of apparently distinct predation risks: high risk, where the grazers constitute a significant portion of H. helianthus diet; moderate risk, where H. helianthus primarily consume preferred mussel prey; no risk of predation, where prey exist beyond the southern geographic limit of H. helianthus. Prey responses were highly specific to the H. helianthus stimulus. Escape responses differed among grazer species, but these differences did not correspond to taxonomic relatedness, nor to their intertidal vertical distribution. No differences in escape responses were observed between sites where H. helianthus exhibit different diets, suggesting that these grazer species cannot ‘perceive’ and/or respond to this apparent change in predation risk. In contrast, a greater proportion of individuals of all 4 species responded to the H. helianthus cue, predator recognition was significantly faster, and distance traveled after stimulation was greater at sites of predator-prey coexistence than at the site beyond the predator’s geographic range. Thus, longer contact history with the predator appears to favor greater capacity to display escape responses in all species examined. We highlight the importance of evaluating phenotypic responses to predators under natural conditions and across natural gradients of predation risks.

Movement patterns of the seastar Heliaster helianthus in central Chile: relationship with environmental conditions and prey availability

The rates and patterns of feeding and displacement of predators constitute two of the most important plastic behavioral responses that allow individuals to respond quickly to changes in abundance of their prey, predation risks and to rapid alterations in environmental conditions. In this study, we quantified seasonal and spatial variation in displacement (net changes in location in 12 or 24 h periods) and prey consumed of marked individuals of the keystone seastar Heliaster helianthus at six sites spanning 600 km along the coast of north-central Chile. We evaluated the hypotheses that: (1) at sites with low availability (cover) of the main prey, the mussel Perumytilus purpuratus, Heliaster displays larger displacements and consumes a greater proportion of other prey (e.g. mobile species) than at sites with high mussel cover, (2) daily displacements will be correlated with sea surface temperature (SST) and (3) increased wave action will reduce seastar daily displacement. Our results show that Heliaster displacement is higher at sites with lower availability of P. purpuratus; and at these sites, a larger proportion of Heliaster individuals are observed feeding, mostly on other prey (e.g. limpets), which could offset the higher costs associated with increased movement. In addition, wave forces affected the activity of Heliaster negatively. Contrary to our expectations, the daily displacements did not show any relationship with SST measured on the day or the previous days of the surveys, despite the fact that average displacement was generally higher in summer than in winter months. Future studies should examine Heliaster movement during single foraging excursions and determine whether these responses affect the growth and reproductive output of individuals. Such information is vital to understand how changes in prey abundance and environmental conditions alter the behavior and energy budget of this predator and its ability to control prey populations.

Ontogenetic changes in habitat use and diet of the sea-starHeliaster helianthuson the coast of central Chile

Ontogenetic shifts in habitat use and diet are ubiquitous in nature and usually have profound consequences for the ecology and evolution of the species. In the case of species with strong interactions within their communities, such as keystone predators, understanding this kind of size-related change is critical to understand variation and connectivity among spatially distinct habitats of coastal communities. Yet the ecology of early life stages of marine benthic invertebrates, particularly asteroids, is poorly understood. Here we describe the results of surveys to characterize the habitat and quantify the abundance and diet of recruits of the sun starHeliaster helianthus, a keystone predator at rocky intertidal sites in central Chile. Our results support the existence of size-related, ontogenetic changes in habitat use and diet of this species. Recruits occupy boulders and crevices in the high or mid-high intertidal zones of wave-protected habitats and as they grow they move down towards lower tidal levels. Adults are characteristically found in the low intertidal zone of wave exposed and semi-exposed habitats. These changes in habitat use are accompanied by changes in diet composition and particularly by a broadening of the prey species incorporated in the diet. Since early stages ofHeliasterappear to be most sensitive to predation and abiotic stress and since adults are such important predators in wave exposed rocky shores, knowledge of the basic ecology of early stages of this species is critical to fully understand the dynamics of intertidal communities.

Mantle defensive response of marine pulmonate Trimusculusperuvianus

The marine pulmonate Trimusculus peruvianus (Sowerby, 1835) which is found in caves or narrow crevices along the Chilean coast was studied to determine a possible chemical defense against the intertidal key predator Heliaster helianthus. T. peruvianus releases a white secretion through the extended mantle animal covers, to contact with the tube feet of starfish. This behaviour significantly decreases predation of gastropod and it has not been described previously for members of the Trimusculidae family.

Phenotypic variability in byssus thread production of intertidal mussels induced by predators with different feeding strategies

Predator-induced defenses have a significant influence on the expression of morpholog- ical and behavioral traits of marine species. In mussels, common responses to predators include thick- ening of the shell, enlargement of the adductor muscle and increases in byssus production. We hypothesize that predators with different feeding strategies have different effects on byssus produc- tion of the common intertidal mussels Perumytilus purpuratus and Semimytilus algosus in central Chile. Predators that dislodge prey mussels before killing them, such as crabs and seastars, should elicit increased byssus production in their prey compared to other predators such as whelks, which use different feeding mechanisms. Laboratory experiments with the seastar Heliaster helianthus, the crab Acanthocylus gayi, and the muricid gastropods Concholepas concholepas and Acanthina mon- odon showed that only A. gayi induced significant increases in byssus production, causing remark- ably similar responses in both mussel species. Further experiments in which individual mussels with different attachment strengths were offered to A. gayi showed that the crabs first tried different mus- sels and then selected those with the weakest attachment, leading to consumption rates of weakly attached mussels that were 5 to 6 times higher than those of mussels with strong attachment to the substratum. Measurements of mussel attachment strengths in the field showed that, where A. gayi is abundant, both mussel species are more strongly attached than in habitats where this predator is scarce. While responses of mussels to crabs seem to be adaptive, the lack of a response to H. helianthus is intriguing, because it is one of the most important mussel predators in the system which can dislodge entire clumps of mussels at a time. It is possible that increased byssus production is inef- fective in reducing predation by this large predator; however, this adaptive explanation requires fur- ther studies. These results highlight the predator-specific nature of many prey phenotypic responses and the importance of considering the multiplicity of predators typically present in most habitats.

A keystone predatory sea star in the intertidal zone is controlled by a higher-order predatory sea star in the subtidal zone

The impact of keystone predators may be affected by physical conditions and interactions with other predators. We evaluated the impact of the sea star Meyenaster gelatinosus on another sea star, Heliaster helianthus, which was previously described as a keystone predator along the coast of central Chile. Field surveys showed that H. helianthus is a common prey of M. gelatinosus. H. helianthus occurred across the subtidal zone at locations with few M. gelatinosus, but was largely restricted to the intertidal and upper-subtidal zones at locations where M. gelatinosus was abundant. The proportion of H. helianthus feeding decreased with increasing M. gelatinosus abundance, and H. helianthus with autotomized arms, mainly the result of sublethal attacks by M. gelatinosus, increased with increasing M. gelatinosus abundance. Additions of M. gelatinosus to a sediment bottom area where H. helianthus was actively feeding on the gastropod Turritella cingulata provoked (1) reduced feeding and (2) a strong escape response in which H. helianthus took the ‘crown’ position (arm tips raised) in about 40 s and then fled. T. cingulata is an abundant prey resource that is likely only available to H. helianthus when M. gelatinosus is rare. The predatory role of H. helianthus is greatly reduced when M. gelatinosus is common. Our observations suggest that M. gelatinosus, rather than H. helianthus or the whelk Concholepas concholepas, is the keystone predator in subtidal communities. Our study demonstrates that the role of a keystone predator (in our case H. helianthus in the intertidal zone) can change in an adjacent habitat (the subtidal zone) due to interactions with other predators.

INDIVIDUAL- AND POPULATION-LEVEL RESPONSES OF A KEYSTONE PREDATOR TO GEOGRAPHIC VARIATION IN PREY

Investigating how food supply regulates the behavior and population structure of predators remains a central focus of population and community ecology. These responses will determine the strength of bottom-up processes through the food web, which can potentially lead to coupled top-down regulation of local communities. However, characterizing the bottom-up effects of prey is difficult in the case of generalist predators and particularly with predators that have large dispersal scales, attributes that characterize most marine top predators. Here we use long-term data on mussel, barnacle, limpet, and other adult prey abundance and recruitment at sites spread over 970 km to investigate individual- and population-level responses of the keystone intertidal sunstar Heliaster helianthus on the coast of Chile. Our results show that this generalist predator responds to changes in the supply of an apparently preferred prey, the competitively dominant mussel Perumytilus purpuratus. Individual-level parameters (diet composition, per capita prey consumption, predator size) positively responded to increased mussel abundance and recruitment, whereas population-level parameters (density, biomass, size structure) did not respond to bottom-up prey variation among sites separated by a few kilometers. No other intertidal prey elicited positive individual predator responses in this species, even though a large number of other prey species was always included in the diet. Moreover, examining predator-prey correlations at approximately 80, 160, and 200 km did not change this pattern, suggesting that positive prey feedback could occur over even larger spatial scales or as a geographically unstructured process. Thus individual-level responses were not transferred to population changes over the range of spatial scales examined here, highlighting the need to examine community regulation processes over multiple spatial scales.