Subtidal Predators Research Articles

Disease epidemic and a marine heat wave are associated with the continental-scale collapse of a pivotal predator (Pycnopodia helianthoides).

Multihost infectious disease outbreaks have endangered wildlife, causing extinction of frogs and endemic birds, and widespread declines of bats, corals, and abalone. Since 2013, a sea star wasting disease has affected >20 sea star species from Mexico to Alaska. The common, predatory sunflower star (Pycnopodia helianthoides), shown to be highly susceptible to sea star wasting disease, has been extirpated across most of its range. Diver surveys conducted in shallow nearshore waters (n = 10,956; 2006-2017) from California to Alaska and deep offshore (55 to 1280 m) trawl surveys from California to Washington (n = 8968; 2004-2016) reveal 80 to 100% declines across a ~3000-km range. Furthermore, timing of peak declines in nearshore waters coincided with anomalously warm sea surface temperatures. The rapid, widespread decline of this pivotal subtidal predator threatens its persistence and may have large ecosystem-level consequences.

Quantifying Tidal Movements of the Shore Crab Carcinus maenas on to Complex Epibenthic Bivalve Habitats

Many subtidal predators undertake regular tidal migrations into intertidal areas in order to access abundant prey. One of the most productive habitats in soft bottom intertidal systems is formed by beds of epibenthic bivalves such as blue mussels (Mytilus edulis) and Pacific oysters (Crassostrea gigas). In the Dutch Wadden Sea, these bivalves might face substantial predation pressure by the shore crab (Carcinus maenas), which increased considerably in numbers during the last 20 years. However, the quantification of this species on bivalve beds is challenging, since most methods common for quantifying animal abundance in marine habitats cannot be used. This study investigated the potential of two methods to quantify the abundance of C. maenas on 14 epibenthic bivalve beds across the Dutch Wadden Sea. The use of the number of crabs migrating from subtidal towards intertidal areas as a proxy of abundance on bivalve beds yielded unreliable results. In contrast, crabs caught with traps on the beds were correlated with the abundance assessed on the surrounding bare flats by beam trawl and therefore provided usable results. The estimates, however, were only reliable for crabs exceeding 35 mm in carapace width (CW). The application of these estimates indicated that crab abundances on bivalve beds were influenced by the biogenic structure. Beds dominated by oysters attracted many large crabs (> 50-mm CW), whereas abundances of medium-sized crabs (35–50-mm CW) showed no relationship to the oyster occurrence. The combination of traps and trawls is capable of quantifying crab abundance on bivalve beds, which offers the possibility to study biotic processes such as predator-prey interactions in these complex structures in more detail.

Devastating Transboundary Impacts of Sea Star Wasting Disease on Subtidal Asteroids.

Sea star wasting disease devastated intertidal sea star populations from Mexico to Alaska between 2013–15, but little detail is known about its impacts to subtidal species. We assessed the impacts of sea star wasting disease in the Salish Sea, a Canadian / United States transboundary marine ecosystem, and world-wide hotspot for temperate asteroid species diversity with a high degree of endemism. We analyzed roving diver survey data for the three most common subtidal sea star species collected by trained volunteer scuba divers between 2006–15 in 5 basins and on the outer coast of Washington, as well as scientific strip transect data for 11 common subtidal asteroid taxa collected by scientific divers in the San Juan Islands during the spring/summer of 2014 and 2015. Our findings highlight differential susceptibility and impact of sea star wasting disease among asteroid species populations and lack of differences between basins or on Washington’s outer coast. Specifically, severe depletion of sunflower sea stars (Pycnopodia helianthoides) in the Salish Sea support reports of major declines in this species from California to Alaska, raising concern for the conservation of this ecologically important subtidal predator.

Community Regulation: The Relative Importance of Recruitment and Predation Intensity of an Intertidal Community Dominant in a Seascape Context

Predicting the strength and context-dependency of species interactions across multiple scales is a core area in ecology. This is especially challenging in the marine environment, where populations of most predators and prey are generally open, because of their pelagic larval phase, and recruitment of both is highly variable. In this study we use a comparative-experimental approach on small and large spatial scales to test the relationship between predation intensity and prey recruitment and their relative importance in shaping populations of a dominant rocky intertidal space occupier, mussels, in the context of seascape (availability of nearby subtidal reef habitat). Predation intensity on transplanted mussels was tested inside and outside cages and recruitment was measured with standard larval settlement collectors. We found that on intertidal rocky benches with contiguous subtidal reefs in New Zealand, mussel larval recruitment is usually low but predation on recruits by subtidal consumers (fish, crabs) is intense during high tide. On nearby intertidal rocky benches with adjacent sandy subtidal habitats, larval recruitment is usually greater but subtidal predators are typically rare and predation is weaker. Multiple regression analysis showed that predation intensity accounts for most of the variability in the abundance of adult mussels compared to recruitment. This seascape-dependent, predation-recruitment relationship could scale up to explain regional community variability. We argue that community ecology models should include seascape context-dependency and its effects on recruitment and species interactions for better predictions of coastal community dynamics and structure.

Intensive use of an intertidal mudflat by foraging adult American horseshoe crabs Limulus polyphemus in the Great Bay estuary, New Hampshire

Abstract Although concerns about harvesting levels of the American Horseshoe Crab, Limulus polyphemus have prompted increased research into its ecology, current understanding of the species’ foraging ecology is mostly limited to mid-Atlantic populations. This study elucidates the spatial and temporal pattern of Limulus foraging on an intertidal mudflat of a northern New England estuary. A novel survey method was used to monitor Limulus foraging activity without disturbing the sediment. A fixed 50 m×2 m transect was monitored with monthly surveys of the number of Limulus feeding pits from June to October 2009, May and June 2010. Snorkelling surveys were also carried out to observe individual behavior and examine the spatial scale of activity of individual animals. Results showed frequent and intensive use of the mudflat by foraging Limulus. Limulus were actively foraging within the survey area during all months surveyed. Foraging patterns exhibited a seasonal pattern with activity levels peaking in August 2009 and increased significantly towards the end of the study in June 2010. It was also shown that Limulus intertidal foraging persisted and peaked after the spring breeding season. Observations of foraging Limulus revealed that individual predators dig multiple pits within a single high tide, with little disturbance to the sediment in between. In addition to altering the perception of Limulus as a subtidal predator outside of the breeding season, findings from this study suggests a segregation of spawning and feeding habitats, thus underscoring the need to consider a wider range of critical habitats in the management of Limulus populations.

Growth-mortality trade-offs along a depth gradient in Cancer borealis

Intertidal and shallow subtidal ecosystems experience steep environmental gradients over short distances. Individual foraging rate, predation risk, and physiologic stress vary along these gradients, resulting in growth-mortality trade-offs with depth. In the summer, Cancer borealis commonly forage in the shallow subtidal in the Gulf of Maine. C. borealis are the favored invertebrate prey of the Herring Gull and the Great Black-backed Gull, which consume 25%–50% of available C. borealis (those in < 1 m water) during each daytime low tide. We investigated three possible explanations for the presence of C. borealis in the risky gull-predation zone. First, we tested whether predation risk in the gull-predation zone was matched at deeper depths by subtidal predators; we found predation risk decreases with depth. Second, we tested whether water temperatures were warmer in the gull-predation zone and whether these warmer temperatures resulted in increased growth rates. We found that, while waters were warmer in the gull-predation zone, crabs grew at similar rates above and below the thermocline when fed similar diets. Finally, we tested for differences in food availability with depth and whether these differences influenced C. borealis growth rates. Our results suggest a growth-mortality trade-off, where increased food availability provides sufficient growth benefit to outweigh the risk of foraging at shallower depths.

REGULATION OF INTERTIDAL FOOD WEBS BY AVIAN PREDATORS ON NEW ENGLAND ROCKY SHORES

Although there is a large body of research on food webs in rocky intertidal communities, most of the emphasis has been on the marine benthic components. Effects of avian predation on highly mobile predators such as crabs, remains practically unstudied in rocky shore ecosystems. The crab, Cancer borealis, is an important component of the diet of gulls (Larus marinus, L. argentatus) at the Isles of Shoals, Maine, USA. C. borealis prey include the predatory gastropod Nucella lapillus L., the herbivore Littorina littorea, and mussels Mytilus edulis L. We hypothesized that gulls reduce abundance of C. borealis in the low intertidal and shallow subtidal, thereby allowing C. borealis prey to persist in high numbers. A study of crab tidal migration showed that C. borealis density nearly doubled at high tide compared to low tide; thus, crabs from a large subtidal source population migrate into the intertidal zone during high tides and either emigrate or are removed by gulls during low tides. Results from a small-scale (1 m2) predator caging experiment in the low intertidal zone indicated that enclosed crabs significantly reduced L. littorea abundance when protected from gull predation. In a much larger-scale gull exclusion experiment, densities of C. borealis increased significantly during low and high tides in exclosures relative to the controls. C. borealis density was inversely correlated with changes in the abundance of two mesopredators Carcinus maenas and Nucella lapillus, and with the space-occupier M. edulis. There was a similar negative correlation between abundance of C. borealis and the change in abundance of the herbivore L. littorea, but the trend was not significant. Mortality of tethered L. littorea was associated with C. borealis density across sites. However, preferred algae did not change in response to L. littorea density during the experiment. Thus, we found suggestive, but not conclusive, evidence for a three-level cascade involving gulls, crabs, and L. littorea. Our studies strongly suggest that gulls, as apex predators, generate three-level trophic cascades in rocky intertidal food webs by preventing the highly mobile subtidal predator, C. borealis, from establishing substantial populations in the low-mid intertidal zone thereby indirectly enhancing densities of two key mesopredators (N. lapillus, Carcinus) and blue mussels (M. edulis).

Trophic linkages across seascapes: subtidal predators limit effective mussel recruitment in rocky intertidal communities

Food-web linkages between habitats across a landscape are known to be important in terrestrial systems. Linkages through the lower (nutrients) and higher (predators) trophic levels are also starting to be recognized across seascapes. Here, we test the potential importance of a subtidal- intertidal trophic linkage through predation on mussel recruits by fish in mussel-dominated commu- nities at 2 tidal levels on wave-exposed shores of southern New Zealand. We show that on rocky shores that include both intertidal benches and subtidal reefs, labrid fish move into the intertidal zone during high tide and exert fast and strong predation pressure on small mussels in the low-, and to a lesser extent mid-shore, intertidal levels. Within 1 d, 80 to 95% of small (5 to 15 mm) transplanted mussels were removed from experimental tiles on the low shore when unprotected from fish preda- tion, while 20 to 60% were removed on the mid-shore; in contrast, most fully protected mussels sur- vived for months. Although at a slower pace, predation was also evident in cages that excluded fish but allowed access to large invertebrate predators. This predation occurred mostly at night when large predatory crabs were abundant at the study sites. The combined predation pressure on small mussels by fish and crabs was reflected in the scarcity of larger/older mussel recruits (5 to 15 mm) outside mature beds on the low shore compared to greater abundance on the mid-shore. The number of mussel settlers in artificial collectors and of smaller/younger recruits (<5 mm) within barnacle patches did not significantly differ between shore heights; thus, we attribute the difference in abundance of late recruits to differential predation rates by subtidal predators. This study clearly demonstrates that highly mobile subtidal predators, particularly fish, can have important impacts on temperate intertidal food webs, especially on early life stages of habitat-dominating invertebrates, such as mussels in New Zealand and probably elsewhere.

SEASCAPE-DEPENDENT SUBTIDAL–INTERTIDAL TROPHIC LINKAGES

In this study, we test in southern New Zealand a conceptual model of food web linkage that is seascape dependent, which can explain some of the variability in rocky shore community structure among sites and coasts. Using a comparative-experimental approach at local and distant sites we demonstrate that mobile subtidal predators (fish and crabs) can exert strong predation pressure on small mussels in the low tidal zone, but only in sites where the seascape includes subtidal reefs. On intertidal benches with adjacent subtidal reefs (+SR), 60-100% of small (5-15 mm) transplanted mussels were removed within a day from experimental tiles on the low shore when unprotected from predation, compared to fully caged controls that had approximately 100% survival over several months. In partial cages that exclude fish but not crabs, survivorship was intermediate. In contrast, on benches without subtidal reefs (-SR) 40-100% of mussels survived for months, even if unprotected. This difference is expressed in lower cover (0-60%) of mussels on rocks at +SR benches compared to -SR benches (70-99%). The central to northern west coast of the South Island is composed mostly of -SR benches, and predation on small mussels there was low and similar to the -SR benches on the east coast, whereas the +SR benches on the east coast had much greater predation. This contrasts to other studies in New Zealand that examined only predation on larger mussels by seastars and concluded that predation is strong on the west coast and weak on the east coast. Excluding large predators from low-shore areas with new recruits for a year in one +SR site showed longer-term predation effects on their abundance and cover. Short-term sampling at the east coast sites showed that mussel settlement was greater in -SR compared to +SR sites, providing some evidence that seascapes may also affect settlement. Overall, predation depended on the local seascape and ultimately affected community structure via suppression of effective recruitment rates. This study emphasizes the importance of predation on early life stages of basal species and the influence of seascapes on top-down interactions between subtidal predators and their intertidal prey.

Feeding habits and phenotypic changes in proboscis length in the southern oyster drill, Stramonita haemastoma (Gastropoda: Muricidae), on Florida sabellariid worm reefs

The southern oyster drill, Stramonita (= Thais, Kool 1987) haemastoma, is a common intertidal and subtidal predator in the southeastern United States. It uses specialized feeding structures and foraging strategies to bore holes through the shell of its bivalve prey. However, on the east coast of Florida, S. haemastoma, is common on sabellariid worm reefs constructed by the polychaete Phragmatopoma lapidosa (Walton Rocks Beach, Florida, 27°17′N, 80°12′W), a habitat where the snail’s typical prey are scarce. From 1999 to 2001, we examined the feeding habits of S. haemastoma on sabellariid reefs and the behavioral and morphological responses of S. haemastoma that accompanied switching from a diet of bivalves to sabellariids. On worm reefs S. haemastoma feeds on P. lapidosa by inserting the proboscis deep into a worm’s tube. Worm-feeding snails had longer proboscises (~3.7 times shell height) than bivalve-feeding conspecifics (~2.0 times shell height). Snails raised on different diets showed significant differences in proboscis length suggesting that the proboscis length is phenotypically plastic. Whereas typical oyster drills must bore holes for days before ingesting prey, S. haemastoma on worm reefs avoids boring and attacks and consumes worms in 15–50 min. In the laboratory, oyster drills consumed 1.7 worms per day, spending <1 h each day feeding. On sabellariid reefs, differences in feeding, handling costs, and prey value, are likely to have a significant effect on the ecology and life history of S. haemastoma in this habitat.

Predation Resistance and Nematocyst Scaling forMetridium senileandM. farcimen

Previous studies suggest that large body size reduces the risk of predation for acontiate sea anemones. For two species of Metridium, we found significant increases in the length of the acontial threads and in the mean lengths of the unfired acontial nematocyst capsules, with increasing body size. This supports the hypothesis that more damaging acontial defenses protect larger acontiate anemones from their predators. Metridium is planktivorous, and food size does not increase substantially with body size; so we expected smaller increases in nematocyst size for the feeding tentacles. In fact, scaling exponents were significantly smaller for the tentacle nematocysts than for acontial nematocysts of the same types in 3 out of 4 cases. This suggests that nematocyst scaling responds predictably to selection pressure. When specimens of the same size were compared, the non-clonal, subtidal species, M. farcimen, had significantly larger acontial nematocysts than did its clonal congener, M. senile, which lives at the upper tidal limits for major subtidal predators in the northeastern Pacific. Therefore, larger acontial nematocysts may be particularly advantageous where predation levels are high. These data demonstrate that closely related anemone species can be distinguished on the basis of ecologically and functionally relevant differences in nematocyst scaling.

Role of current and prey odour in the displacement behaviour of the sea starAsterias vulgaris

We performed a factorial experiment to investigate the effects of current and prey odours (mussels) on the displacement behaviour of the sea star Asterias vulgaris (Verrill, 1866). This sea star is a common subtidal predator of sessile and slow-moving animals in the western North Atlantic Ocean. In the presence of current and prey odours in a flume, sea stars oriented themselves upstream and 70% succeeded in finding the prey. Also, the degree of orientation toward the prey increased as the sea star approached the prey. In contrast, only 5% of individuals tested in still water found the prey. Thus, for A. vulgaris the presence of macroscale flow is an essential condition for locating distant prey. Sea stars tested in current alone showed rheotactic behaviour, moving diagonally upstream. This behaviour should enhance the probability of encountering prey odour plumes in the field. Sea stars moved faster and straighter in flowing water than in still water. The slow movement of A. vulgaris in still water probably minimizes costs of foraging when there is a low chance of finding prey and the straight diagonal movement in current should ensure that the sea star continuously samples new areas, rather than resampling the same odour-free area.

Distribution and feeding ecology of the seastars Leptasterias polaris and Asterias vulgaris in the northern Gulf of St Lawrence, Canada

Extensive field observations were made in the Mingan Islands, northern Gulf of St Lawrence, to evaluate spatial and temporal variations in the use of habitat and prey resources by two major subtidal predators, the seastars Leptasterias polaris and Asterias vulgaris. Although both seastars have similar size structures and generally overlapped in their spatial and temporal distribution, the degree of overlap varied in different sites and appeared to be related to prey abundance, substratum type and slope. Three general patterns were observed: (1) both species aggregating in shallow water and decreasing in numbers with depth; (2) the two species showing inverse depth distributions; and (3) both seastars occurring in low numbers across the subtidal zone. Temporal changes in availability of the preferred prey of the two seastars, the mussel Mytilus edulis, appeared to be a major factor affecting their abundance and distribution. The two seastars occurred together in dense aggregations on mussel beds in shallow water. They consume similar-sized mussels until the number of mussels becomes reduced when A. vulgaris, but not L. polaris, begins to select larger mussels. Once a mussel bed is decimated, the seastars appear to move away, possibly in search of other beds. Intensive seastar foraging limits the distribution of mussels to a few metres in depth. Below the mussel zone, the two seastars are spatially segregated at a small spatial scale (1 m2 quadrat) and select different alternative prey, L. polaris feeding mainly on the crevice-dwelling clam Hiatella arctica and A. vulgaris on the ophiuroid Ophiopholis aculeata. The size partitioning of the preferred prey in shallow water, and spatial segregation and selection of different alternative prey at greater depths may reflect mechanisms permitting the two seastars to coexist.

Use of prey resources by the seastars Leptasterias polaris and Asterias vulgaris: a comparison between field observations and laboratory experiments

The subtidal predators Leptasterias polaris and Asterias vulgaris strongly overlap in their size, distribution and use of prey resources. We evaluate the factors determining their use of prey (feeding rate and prey selection) by comparing prey use in the laboratory and in the field. Both seastars have the same preferred prey, the mussel Mytilus edulis, select medium-sized mussels (1.5–3.0 cm), and show similar responses to increasing mussel density (functional response). Differences between the two seastars in their feeding abilities appear to affect both their size selection of mussels and use of alternative prey when mussels become rare or absent. A. vulgaris selects larger mussels than L. polaris when mussel abundance is low, and this may optimize its energetic intake. L. polaris is be better able to prey on the crevice-dwelling clam Hiatella arctica and A. vulgaris on the ophiuroid Ophiopholis aculeata. These differences in prey selection may reduce potential competitive interactions between the two seastars, as they cause prey partitioning when the preferred prey is rare or absent. The greater feeding rate of A. vulgaris on larger mussels likely provides it with a competitive advantage when the abundance of preferred prey is limited.

Mortality, behavior and the effects of predators on the intertidal distribution of littorinid gastropods.

Predators can affect the vertical distribution of mobile intertidal invertebrates in two ways: they can (1) cause greater mortality of prey at certain intertidal levels, and (2) induce prey to seek safer intertidal areas. In this study, we investigate whether low-intertidal and subtidal predators affect the intertidal distribution of two congeneric species of small herbivorous gastropods of northeastern Pacific shores, Littorina sitkana Philippi 1846, and L. scutulata Gould 1849. In particular, we tested the hypothesis that predators affect the distribution of these snails by inducing them to seek higher and safer intertidal areas. On a wave-sheltered shore in Barkley Sound, British Columbia, L. sitkana and L. scutulata were both killed by predatory crabs (e.g., Cancer productus) more frequently when tethered near the lower limit of their intertidal distribution ( approximately 1 m) than when tethered where they were most common ( approximately 2.5 m), suggesting that high mortality rates are partly responsible for the lower-limit of these snails' intertidal distribution. However, two field mark-recapture experiments indicated that the snails' behavioral response to predation risk also influences their distribution. In the first experiment, snails from the 2.5-m level (low risk) transplanted to the 1.0-m level (high risk) displayed a strong and consistent tendency to move shoreward, especially L. sitkana, some traveling 10-15 m in 2-3 days to regain their original level. These shoreward movements were especially precise in the northern part of the study area, where predation rates on tethered snails were greatest. Furthermore, larger more vulnerable snails were more strongly oriented shoreward than smaller individuals, indicating that antipredator behavior might also contribute to intertidal size gradients in these species. In the second mark-recapture experiment, we manipulated predation risk using small cages and found that snails exposed to the odors of C. productus crabs foraging on conspecific and heterospecific snails displayed more precise (L. sitkana and L. scutulata) and longer (L. sitkana) shoreward movements than snails held in control conditions. These results provide the first experimental evidence that antipredator behavior may contribute to the intertidal distribution patterns of littorinids.

The climbing behaviour of Cerithidea anticipata (Mollusca: Gastropoda): The roles of physical and biological factors

Abstract Many molluscs in tidal wetlands climb trees as the tide rises, a behaviour usually assumed to be a means of avoiding subtidal predators. Some species are more active during neap tides, when the access of subtidal predators to the forest is limited, but rest on trees during spring tides. Cerithidea anticipata, which inhabits the mangrove forests around Darwin Harbour (Northern Territory, Australia), displayed almost exactly the opposite pattern. This species climbed higher, and was less active, during neap tides that did not flood the forest than during spring tides. In experiments with tethered snails, individuals prevented from climbing died during neap tides, apparently from physiological stress. Further, individuals resting on trees around clearings, usually selected shaded sites. These results suggest that the major reason C. anticipata climbed was to avoid physiological stress during neap tides, not subtidal predators during spring tides. There was some evidence of predation under the canopy, but the rate was relatively low and the species responsible appeared to be resident in the forest.

Role of burrows as refuges from sub-tidal predators of temperate mangrove crabs

Role of burrows as refuges from sub-tidal predators of temperate mangrove crabs

Reproductive risk: high mortality associated with spawning by horseshoe crabs (Limulus polyphemus) in Delaware Bay, USA

It has been presumed that intertidal spawning by Limulus polyphemus minimizes the loss of egges to subtidal predators; however, this strategy involves considerable risks. Massive beach strandings of adults accompany seasonal spawning migrations of crabs along Cape May in Delaware Bay, (USA). At least 190000 horseshoe crabs, approximating 10% of the adult population, died from beach stranding along the New Jersey shore of Delaware Bay during the 1986 (May to June) spawning season. Abnormalities of the telson (which is used in righting behavior) were significantly more common among stranded crabs than among individuals actively spawning on the intertidal beach. The number of stranded crabs per day was not correlated with tidal height or environmental variables (wind speed, wave height) which characterized the conditions at spawning. A complex suite of factors, including the size of the available spawning population, tidal and weather conditions, and beach slope, influence the number stranded during the breeding season. Horseshoe crab stranding results in a large loss of gravid females from the population, and may represent a major input of organic matter to intertidal sandy beaches in certain regions of Delaware Bay.

Size‐Dependent Growth in Two Zoanthid Species: A Constrast in Clonal Strategies

The widespread occurrence of genet fragmentation among modular, clonal organisms results in size—dependent life history patterns that are often independent of clonal age. In this study the size dependence of clonal growth rates was experimentally evaluated using two common coral reef cnidarians that inhabit shallow reef environments at Discovery Bay, Jamaica. As a result of the turbulent conditions associated with storms, these organisms commonly undergo fragmentation. The growth of aggregations of these clonal fragments in three small size classes (ranging over three orders of magnitude) was statistically evaluated against a null, exponential model that predicts that relative growth rates of small aggregations are size independent. Growth rates for Zoanthus solanderi were consistent with this model. Z. sociatus, on the other hand, exhibited size—dependent relative growth rates. The smallest aggregations of this species had the higher relative growth rates, which were sufficiently high to more than compensate for losses due to mortality. These results are consistent with other life history and distributional differences between these two species. Zoanthus sociatus has a higher rate of mortality, does not undergo sexual reproduction until reaching a larger aggregation size, and commonly has a higher vertical distribution (which may represent a spatial refuge from subtidal predators) than does Z. solanderi. The comparatively rapid relative growth rates of small aggregations of Z. sociatus may be the result of spatial constraints on growth in large aggregations and/or of higher relative energy allocations to growth in small aggregations. The incorporation of fragmentation into the life history strategy of clonal organisms has a range of predicted consequences. Among some organisms, fragmentation and associated adaptations may be rare and of little consequence. Among organisms that frequently fragment as a result of physical disturbances, natural selection should favor repair and regenerative processes as well as resistance to this source of mortality. At the extreme, fragmentation need not be associated with death and injury. Adaptations at the developmental and physiological level may involve genetically programmed production of asexual fragments and size—dependent shifts in energy allocations to growth, sexual reproduction, and energy reserves. The degree of interdependence of the processes controlling the dynamics of genets and fragmented modules may well depend on the relative importance of such adaptations.

Prey capture by Pisaster brevispinus (Asteroidea: Echinodermata) on soft substrate

Observations on the subtidal seastar Pisaster brevispinus (Stimpson) indicate that this predator can extend the central tube feet into sand-mud substrate for a distance roughly equal to the radius of the seastar. Field and laboratory evidence demonstrates the use of the elongated tube feet by the asteroid for the capture of burrowed prey items. A relationship between predator size and the size of juveniles of the deep-burrowing clam Tresus nuttallii taken as prey is a product of the ability of larger seastars to extend the tube feet further into the substrate and capture deeper prey. The role of P. brevispinus as an important subtidal predator along the Pacific Coast of North America is discussed.